Pressure sensor for being introduced into the circulatory system of a human being

Abstract

The invention relates to a passive pressure sensor (501) for being introduced into the circulatory system of a human and for being wirelessly read out by an external reading system. The pressure sensor comprises a housing (502) having a diffusion barrier for maintaining a predetermined pressure within the housing and a magneto-mechanical oscillator having a magnetic object (508) providing a permanent magnetic moment. The magneto-mechanical oscillator converts an external magnetic or electromagnetic excitation field into a mechanical oscillation of the magnetic object, wherein at least a portion of the housing is flexible for allowing conversion of external pressure changes into changes of the mechanical oscillation of the magnetic object. The pressure sensor can be very small and still provide high quality pressure sensing.

Description

TECHNICAL FIELD

[0001] The present invention relates to a pressure sensor for being introduced into the circulatory system of a human being. The present invention further relates to a stent, a liver shunt device, a wire for treating a brain aneurysm and a heart valve, respectively comprising a pressure sensor. Furthermore, the present invention relates to a reading system, a method and a computer program for wirelessly reading out a pressure sensor. BACKGROUND

[0002] US 2007 / 0236213 Al describes a pressure sensing essentially based on a mechanical resonator with attached magnetized material. A magnetic field can interact with the magnetized material and initiate mechanical oscillations. The mechanical oscillations are then detected by recording the time-varying field by a coil or other suitable magnetometer. An external pressure on the device can change the effective spring constant and thus cause a change in the resonance frequency which can be detected. Thus a pressure sensor is formed.

[0003] While this works in principle, it has several drawbacks and is not suitable for measuring the pressure deep in a patient with sufficient accuracy and with a small enough device. The main problem is the use of a mechanical resonator. Typically, the maximum possible quality factor that can be reached in a mechanical resonance is too low for efficient operation. There are some materials like fused silica that will provide a high quality factor in oscillation. These materials are typically quite hard and do not allow a high enough oscillation amplitude (high enough angle) for efficient, i.e. for generating a large enough field change. The next problem is that the sensitivity of the resonance frequency to external pressure is low because only the elastic parameters are modified. This, combined with the low quality factor, leads to a need for a rather high signal-to-noise ratio, which in turn leads to a need for a large amount of magnetic material, which makes the sensor large.

[0004] Furthermore, there are already implantable pressure sensors, for example those developed by CardioMems and disclosed in US 7,147,604 Bl. The working principle of these sensors is to use a resonant LC (inductor-capacitor) device. The resonance frequency is shifted by mechanical movements induced by the pressure, which in turn changes the L or C value (or both). When this system works, it cannot be scaled down to the size required for being introduced into the circulatory system of a human being. The main reason is that in US 7,147,604 Bl, the detectable signal is proportional to the high power of the radius of the coil of the pressure sensor. This puts a strict limit on scaling down the pressure sensor. SUMMARY

[0005] It is therefore an object of the present application to provide a pressure sensor for being introduced into the circulatory system of a human being which is very small and still allows a high quality pressure measurement. The present application also relates to a stent, a liver shunt device, a wire for treating a brain aneurysm and a heart valve, respectively comprising a pressure sensor. Furthermore, the present application relates to a reading system, a method and a computer program for wirelessly reading out a pressure sensor.

[0006] In a first aspect of the present application, a pressure sensor for being introduced into the circulatory system of a human being is presented, wherein the pressure sensor is a passive sensor configured to be wirelessly read out by a reading system placed outside the human being, wherein the pressure sensor comprises a housing having a diffusion barrier layer covering at least a portion of the housing and configured to maintain a predetermined pressure inside the housing, wherein the pressure sensor comprises a magneto-mechanical oscillator inside the housing, the magneto-mechanical oscillator having a magnetic object providing a permanent magnetic moment, wherein the magneto-mechanical oscillator is configured to convert an external magnetic or electromagnetic excitation field into a mechanical oscillation of the magnetic object, wherein at least a portion of the housing is flexible for allowing conversion of external pressure changes into changes of the mechanical oscillation of the magnetic object, wherein the magnetic object is arranged inside the housing such that it can rotate away from an equilibrium orientation if the external magnetic or electromagnetic excitation field is acting on the magnetic object, wherein the pressure sensor further comprises a restoring torque unit adapted to provide a restoring torque to force the magnetic object back into the equilibrium orientation in case the external magnetic or electromagnetic excitation field has rotated the magnetic object away from the equilibrium orientation, thereby allowing the magnetic object to mechanically oscillate at a resonance frequency, wherein the restoring torque unit comprises a further magnetic object being a permanent magnet for generating a magnetic field at the position of the magnetic object such that it provides the restoring torque, wherein the pressure sensor is configured such that external pressure changes are converted into changes of the resonance frequency.

[0007] Since the pressure sensor uses a magneto-mechanical oscillator which mainly uses magnetism to store oscillation energy, a very small pressure sensor suitable for being introduced into the circulatory system of a human being can be used which allows a high quality factor, a high oscillation amplitude and a high sensitivity to external influences at the same time.

[0008] The dimensions of the pressure sensor are preferably such that they can be introduced into the circulatory system outside the main pulmonary artery. Preferably, the pressure sensor has an elongated shape with a maximum dimension of less than or equal to 5 mm, further preferably less than or equal to 4 mm, and a minimum dimension of less than or equal to 1 mm. These dimensions preferably refer to the longitudinal direction and the transversal direction of the pressure sensor. Thus, preferably, in the longitudinal direction, the dimensions of the pressure sensor are less than or equal to 5 mm, further preferably less than or equal to 4 mm, and in the transversal direction, the dimensions of the pressure sensor are less than or equal to 1 mm.

[0009] In a preferred embodiment, the pressure sensor comprises an outer biocompatible coating. Furthermore, preferably, the flexible part of the housing comprises a bellows for allowing the conversion of external pressure variations into variations of the mechanical oscillations of the magnetic object. Bellows are particularly suitable for allowing the conversion of external pressure variations into variations of the mechanical oscillations of the magnetic object, as they provide sufficient flexibility for pressure measurements, even if coated with, for example, a diffusion barrier and / or a biocompatible coating. The bellows can be made of a rather flexible material like silicone rubber.

[0010] The pressure sensor can further comprise an outer cover over the bellows. The outer cover can be used to avoid blood clot formation. The outer cover is preferably soft enough to allow the bellows to change in response to external pressure.

[0011] The diffusion barrier preferably comprises a metal. For example, it can be provided as a metal coating on the housing of the pressure sensor.

[0012] In one embodiment, the pressure sensor further comprises an outer wire cage attached to the outside of the housing for allowing the outside of the housing to stay at a distance from the vessel wall. The wire cage can advantageously be delivered directly into the vessel, where the cage can fix the pressure sensor without obstructing the vessel lumen. The cage can comprise a ring- or disc-shaped central part from which curved legs protrude. It can be made of a wire material, for example Nitinol, as it has a high flexibility and good biocompatibility. Other materials like stainless steel or polymers can also be used. An alternative to wire is a structure cut out of a sheet material, which can be made into a curved shape using a mold tool and heat treatment. For polymers, injection molding is also feasible. In order to connect to the sensor housing, the ring- or disc-shaped structure can be used as an interface between the cage and the sensor housing. The ring-shaped structure can be slitted on a cylindrical housing and can be fixed by spring force and / or by gluing or welding. The disc-shaped structure can be glued or welded to the pressure sensor.

[0013] The magnetic object is arranged within the housing such that it can rotate away from an equilibrium orientation if an external magnetic or electromagnetic excitation field is acting on the magnetic object, wherein the pressure sensor further comprises a restoring torque unit adapted to provide a restoring torque to force the magnetic object back into the equilibrium orientation if the external magnetic or electromagnetic excitation field has rotated the magnetic object away from the equilibrium orientation, thereby allowing the magnetic object to mechanically oscillate at a resonance frequency, wherein the pressure sensor is configured such that an external pressure change is converted into a change of the resonance frequency.

[0014] The restoring torque unit comprises a further magnetic object for generating a magnetic field at the position of the magnetic object such that it provides the restoring torque. Further, the further magnetic object is a permanent magnet in addition to the magnetic object. Further, the magnetic object is preferably a magnetic sphere. The further magnetic object can also be a magnetic sphere. However, the magnetic object as well as the further magnetic object can also have another shape. For example, they can be cylindrical. The magnetic object is preferably attached to one end of a filament, wherein the other end of the filament is attached to the housing. The further magnetic object can also be attached to one end of a filament, wherein the other end of the filament can be attached to the housing. However, the further magnetic object can also be stationary.

[0015] In one embodiment, the magnetic object and / or the interior of the housing is coated with a smooth non-stick material. Preferably, the smooth non-stick material is graphite. The further magnetic object can also be coated with a smooth non-stick material. Preferably, a non-stick material is considered to be "smooth" if the coefficient of friction under dry conditions (i.e. without lubrication) is below 0.2 and further preferably below 0.1.

[0016] Generally, if a pressure sensor has been introduced into the human body, it can be problematic to scan the body in a magnetic resonance imaging (MRI) scanner. Because the pressure sensor is relatively small and thus only causes a small force and torque, the problem is not dangerous to the body, i.e. to the patient, which is not a threat to the patient. Likewise, due to the relatively small size of the pressure sensor, the MR image generated by the MRI scanner is also not impaired. However, in many clinical MRI scanners high field strengths of more than 1.5 T are used and the strong magnetic field can destroy the pressure sensor either by changing the magnetization of the magnetic object or by damaging the mechanical arrangement within the device. For this reason, in one embodiment the pressure sensor is constructed such that the magnetic object is alignable with an external magnetic field regardless of the position and orientation of the pressure sensor in the external magnetic field. For example, the pressure sensor can comprise an outer shell surrounding the housing, wherein the housing is rotatable within the surrounding outer shell, wherein the pressure sensor is configured such that external pressure changes outside the surrounding outer shell are transmitted to the housing outside and the external pressure changes inside the surrounding outer shell. The outer shell can be spherical or ellipsoidal. Furthermore, the outer shell can also be filled with a fluid, wherein the fluid is preferably a highly viscous fluid. The term "highly viscous" preferably means a viscosity at which the maximum rotational speed of the device is limited to below 10000 degrees / second or the angular velocity is not higher than 160 l / s at a magnetic flux density of 0.1 T. For a typical device configuration, this translates to a minimum viscosity of between 1 and 100 Pas. The main determining factor is the volume fraction of the hard magnetic material. There is also a maximum available viscosity, which is about 100 to 1000 times the minimum available viscosity.

[0017] The outer shell can be, for example, a very soft outer shell filled with a fluid or an outer shell with openings in order to effectively convert external pressure changes into changes in the mechanical oscillations of the magnetic object. Preferably, the outer shell is considered "very soft" if the pressure change inside the outer shell deviates from the external pressure by no more than 0.2 mbar (20 Pa) on the timescale of the expected pressure changes, which is typically between 0.01 s and 1 s. The hardest known material in the right shape formed with a sufficiently low thickness can form a "very soft" outer shell. The outer shell then preferably incorporates a structure that acts as a bellows.

[0018] The magnetic object is preferably a magnetic sphere attached to one end of a filament, wherein the other end of the filament is attached to the inside of the housing, wherein in one embodiment the filament has a length of at least π / 4 of the diameter of the magnetic sphere. If the other magnetic object is also a magnetic sphere, it can be attached to one end of another filament, wherein the other end of the other filament is attached to the housing. In this case, preferably the other filament also has a length of at least π / 4 of the diameter of the other magnetic sphere. These lengths of the filaments allow the magnetic object to freely align with an external magnetic field. The magnetic sphere and the other magnetic sphere preferably have the same diameter.

[0019] Furthermore, in one embodiment, the magnetic object is a magnetic sphere attached to one end of a filament, wherein the other end of the filament is attached to a length-changing unit configured to allow for changing the length of the filament and its attachment to the interior of the housing. The length-changing unit can be, for example, a winding unit. The winding unit can include a winding mechanism. Preferably, the pressure sensor is adapted such that the filament length from the magnetic sphere to the length-changing unit is adjustable such that it equals a predefined length. For example, the filament and / or the length-changing unit can include a stop arranged and configured to stop further shortening of the filament while the length-changing unit shortens the filament if the filament length from the magnetic sphere to the length-changing unit has reached the predefined length. In one embodiment, the stop is arranged and configured to stop winding of the filament if the filament length from the magnetic sphere to the winding unit has reached the predefined length.

[0020] In one embodiment, the length-changing unit includes a spring with a spring force, wherein the spring is configured such that the filament is attached to the spring, such that the spring force forces the filament away from the housing of the pressure sensor and into the length-changing unit to shorten the length of the filament within the housing of the pressure sensor, and the length of the filament within the housing of the pressure sensor can be increased if a force acting on a magnetic object resists the spring force and pulls the filament out of the length-changing unit. The length-changing unit may include a stop configured and arranged to limit the relaxation of the spring such that if no force acts against the spring force, the filament within the housing of the pressure sensor has a predefined length.

[0021] In a preferred embodiment, the pressure sensor is configured to compensate for the temperature dependence of its resonant frequency. Specifically, the pressure sensor includes a compensation element adapted to modify the resonant frequency in a first frequency direction, opposite to a second frequency direction, depending on temperature changes. If the compensation element were not part of the pressure sensor, the resonant frequency of the pressure sensor would be modified in the second frequency direction depending on temperature changes. Because the measuring device includes a compensation element adapted to modify the resonant frequency in a first frequency direction, opposite to the second frequency direction, and if the compensation element were not part of the pressure sensor, the resonant frequency of the pressure sensor would be modified in the second frequency direction depending on temperature changes, this can reduce or even eliminate temperature-induced shifts in the resonant frequency. The first frequency direction is towards a higher or lower frequency, while the opposite second frequency direction is towards a lower or higher frequency, respectively.

[0022] Preferably, the compensation element comprises a magnetic material whose magnetization is altered, and thus its resonant frequency changes with temperature. The magnetic material is selected and arranged within the pressure sensor, particularly within the housing, such that the direction of resonant frequency modification is in the direction of a first frequency. The compensating magnetic material is preferably arranged adjacent to a magnetic object and / or adjacent to another magnetic object (if present). This allows for the design of the pressure sensor to significantly reduce or even eliminate undesirable temperature dependence in a technically relatively simple manner, and without requiring a large space within the housing.

[0023] In one embodiment, the magnetic object is a magnetic sphere attached to one end of a filament, wherein the other end of the filament is attached directly or indirectly to a housing, and wherein the magnetic sphere includes a through-hole passing through the center of gravity of the magnetic object, with one end of the filament arranged and secured in the through-hole. This attachment reduces the magnetic dipole moment by only a small fraction and thus maintains a good signal. The shape of the magnetic object is not significantly altered, which can be important in the case of a sphere.

[0024] Furthermore, in one embodiment, the magnetic object is a magnetic sphere attached to one end of a filament, wherein the other end of the filament is attached directly or indirectly to a housing, and one end of the filament is sandwiched between two magnetic components (forming the magnetic object). This attachment method produces results almost as good as through-hole attachment methods, but does not require specialized equipment for manufacturing.

[0025] In one embodiment, the magnetic object is a magnetic sphere glued to one end of a filament, wherein the other end of the filament is attached directly or indirectly to a housing. This method is technically very simple and makes full use of magnetic objects.

[0026] Furthermore, in one embodiment, the magnetic object is a magnetic sphere attached to a non-magnetic object, and the non-magnetic object is attached to one end of a filament, wherein the other end of the filament is attached directly or indirectly to the housing. This also allows for the relatively simple attachment of the filament to the magnetic object.

[0027] In another aspect of the invention, a stent including a pressure sensor is provided. For example, the pressure sensor may be positioned distally on the stent to indicate in-stent restenosis. In one embodiment, the stent includes several pressure sensors to monitor, for example, the pressure drop across the entire stent or a portion of the stent as a parameter of in-stent restenosis. Early detection allows for adjustments to pharmacological therapy or timely stent reinsertion, thereby avoiding unplanned hospitalizations.

[0028] In another aspect of the invention, a liver shunt device including pressure sensors is provided. For example, the pressure sensors can be positioned proximally to the shunt device to monitor whether decompression is effective, i.e., whether the shunt device is open. The liver shunt device may also include several pressure sensors, specifically for monitoring pressure drop. Furthermore, early detection here allows for adjustments to medication or timely stent reimplantation, thereby avoiding unplanned hospitalizations.

[0029] In another aspect of the invention, a filament for treating cerebral aneurysms is provided, comprising a pressure sensor. The filament can be used for coiling, which causes blood to clot to fill the aneurysm space. The pressure sensor can be used to indicate whether clotting has actually occurred, i.e., a decrease in pulsatile blood pressure changes.

[0030] In another aspect of the invention, a heart valve including pressure sensors is provided. For example, a first pressure sensor may be placed proximally to the heart valve, and a second pressure sensor may be placed distally to the heart valve to monitor pressure drops during cardiac activity. Information about valve function can be extracted based on the monitored dynamic pressure changes. Positioning sensors may also be placed directly on a movable portion of the valve to deliver not only pressure information but also motion information via the determination of sensor orientation and spatial positioning.

[0031] In another aspect of the invention, a reading system for wirelessly reading out a pressure sensor as defined in any one of claims 1 to 11 is provided, wherein the reading system comprises:

[0032] A field generator is used to generate a magnetic or electromagnetic excitation field, which is used to sense the mechanical oscillations of a magnetic object in a pressure sensor.

[0033] - A transducer used to convert the magnetic or electromagnetic field generated by the mechanical oscillation induced by the magnetic object of a pressure sensor into an electrical response signal.

[0034] - A processor for determining a pressure value based on an electrical response signal, wherein the processor is configured to apply a compensation algorithm to correct the determination of the pressure value for dependence of the electrical response signal on at least one of the following:

[0035] a) The distance between the pressure sensor and the field generator;

[0036] b) The phase of the mechanical oscillation of a magnetic object;

[0037] c) The orientation of the housing relative to the reading system; and

[0038] c) The amplitude of mechanical oscillations of a magnetic object.

[0039] The field generator and the transducer can be two separate units, or they can be integrated. If the field generator and the transducer are integrated, the same coil can be used to generate a magnetic or electromagnetic excitation field and to convert the magnetic or electromagnetic field generated by the mechanical oscillation induced by the magnetic object of the pressure sensor into an electrical response signal.

[0040] In a preferred embodiment, the processor is configured to apply a compensation algorithm to correct the pressure value determination for the dependence of the resonant frequency on at least one of the following: a) the distance between the pressure sensor and the field generator; and b) the excitation of the in-phase coil.

[0041] A large magnetic moment in a magnetic object is desirable because it produces a stronger response that can be picked up by a transducer, which may include a corresponding pickup coil. However, a large magnetic moment implies a large restoring force, meaning the resulting oscillating motion will have a large amplitude. When large oscillations occur, the restoring force decreases at large angular displacements. Therefore, for such oscillations, the response frequency will depend on the restoring force, which in turn depends on the distance between the field generator coil and the pressure sensor. To address this issue, the processor can be adapted to correct the pressure value determination based on the dependence of the resonant frequency on the distance between the pressure sensor and the field generator.

[0042] During a cardiac cycle, the pressure within the catheter changes. A typical human heart rate is approximately 50 to 90 beats per minute, with a possible maximum of up to 200 beats per minute. To determine the minimum and maximum pressure during a cardiac cycle, the measurement frequency should not be less than approximately 5 Hz. Preferably, the measurement frequency is higher than 10 to 20 Hz, and most preferably higher than 40 Hz. On the other hand, for a good signal-to-noise ratio, a very high Q factor of the oscillator is preferred, where a high Q factor implies slow decay. Therefore, when the next measurement pulse is sent to the sensor, oscillations from the previous measurement pulse may not be completely eliminated, and they will affect the measurement. Therefore, by compensating for this in-phase coil excitation, a high Q factor can be better combined with a measurement frequency large enough to allow for the measurement of the minimum and maximum heart rate.

[0043] In another aspect of the invention, a pressure measurement method is provided for performing measurements using a pressure sensor as defined in any one of claims 1 to 11, wherein the pressure measurement method comprises:

[0044] – Generate a magnetic or electromagnetic excitation field that is used to sense the mechanical oscillations of a magnetic object in a pressure sensor.

[0045] - Convert the magnetic or electromagnetic field generated by the mechanical oscillation induced by the magnetic object of the pressure sensor into an electrical response signal.

[0046] - The pressure value is determined based on the electrical response signal, wherein in the determination step, the pressure value is corrected for the dependence of the electrical response signal on at least one of the following:

[0047] a) The distance between the pressure sensor and the field generator;

[0048] b) The phase of the mechanical oscillation of a magnetic object;

[0049] c) The orientation of the housing relative to the reading system; and

[0050] c) The amplitude of mechanical oscillations of a magnetic object.

[0051] Furthermore, in another aspect of the invention, a computer program is proposed that includes program code components, which, when run on a computer controlling the reading system, cause the reading system as defined in claim 13 to perform the steps of the pressure measurement method.

[0052] It should be understood that the pressure sensor of claim 1, the implantable device of claim 12, particularly stents, liver shunt devices, sutures for treating cerebral aneurysms, and heart valves, the reading system of claim 13, the pressure measurement method of claim 14, and the non-transient medium including a computer program of claim 15 have similar and / or identical preferred embodiments, particularly as defined in the dependent claims.

[0053] It should be understood that the preferred embodiments of the present invention may also be any combination of the dependent claims or the above embodiments with the corresponding independent claims.

[0054] These and other aspects of the invention will become apparent from the embodiments described below. Attached Figure Description

[0055] In the following figures:

[0056] Figure 1 An embodiment of a pressure sensor in the presence of a first external pressure is illustrated schematically and exemplary.

[0057] Figure 2 The following is schematically and exemplary: In the case where the second pressure is greater than the first pressure... Figure 1 Implementation examples,

[0058] Figure 3 Different embodiments of a pressure sensor with a bellows are illustrated schematically and exemplary.

[0059] Figure 4 Another embodiment of the pressure sensor is illustrated schematically and exemplary.

[0060] Figure 5 Another embodiment of a pressure sensor with a bellows is illustrated schematically and exemplary.

[0061] Figure 6 and Figure 7 An embodiment of a guidewire with a pressure sensor is illustrated schematically and exemplary.

[0062] Figure 8 An embodiment of a bracket with a pressure sensor is illustrated schematically and exemplary.

[0063] Figure 9 An embodiment of a heart valve with a pressure sensor is illustrated schematically and exemplary.

[0064] Figure 10 An embodiment of a filament for treating cerebral aneurysms using a pressure sensor is illustrated schematically and exemplary.

[0065] Figure 11 An embodiment of a liver shunt with a pressure sensor is illustrated schematically and exemplary.

[0066] Figure 12 An embodiment of a pressure sensor is illustrated schematically and exemplary.

[0067] Figure 13 The following is schematically and exemplary illustrating the situation with a high external magnetic field. Figure 1 Implementation examples,

[0068] Figure 14 An embodiment of a pressure sensor with a spherical outer housing is shown.

[0069] Figure 15 An embodiment of a pressure sensor having an elliptical outer housing is illustrated schematically and exemplary.

[0070] Figure 16 Another embodiment of a pressure sensor with a relatively long filament is illustrated schematically and exemplary.

[0071] Figure 17 An embodiment of a sensing device having a winding unit and a stop is illustrated schematically and exemplary.

[0072] Figure 18 An embodiment of the winding unit is illustrated schematically and exemplary.

[0073] Figure 19 An embodiment of a pressure sensor with temperature compensation is illustrated schematically and exemplary.

[0074] Figure 20 andFigure 21 A detection system for reading out the resonant frequency of a sensor is illustrated schematically and exemplary.

[0075] Figure 22 The excitation pulse and the resulting induced voltage are illustrated schematically and exemplary.

[0076] Figure 23 A multi-coil array integrated into the mattress of a patient bed for an imaging system is illustrated schematically and exemplary.

[0077] Figure 24 The coil of the detection system is shown schematically and exemplary.

[0078] Figure 25 The spectrum used to determine the resonant frequency is shown.

[0079] Figure 26 An analog receiving filter is illustrated schematically and exemplary.

[0080] Figure 27 An exemplary example is shown: the Chebyshev Type II bandpass frequency response.

[0081] Figure 28 The calibration settings for calibrating a pressure sensor are illustrated schematically and exemplary.

[0082] Figure 29 An illustrative example shows the relationship between the detected sensor response frequency and the measured reference pressure.

[0083] Figure 30 Exemplary examples illustrate i) the alignment of the detected sensor response frequency with the measured reference pressure, and ii) the calibration curve.

[0084] Figure 31 An example of simulation results for sensor sensitivity is shown.

[0085] Figure 32 An example map shows the noise level of the pressure measurement.

[0086] Figure 33 The correlation of measured signal amplitudes in different harmonics relative to the sensor orientation of a single transmit-receive coil is shown, and

[0087] Figure 34 Another embodiment of the pressure sensor is illustrated schematically and exemplary. Detailed Implementation

[0088] Figure 1An embodiment of a pressure sensor 501 for use in the human circulatory system is illustrated schematically and exemplary. The pressure sensor 501 includes a magnetomechanical resonator having two magnetic elements 507, 508.

[0089] Magnetic element 508 is suspended on filament 506 and thus freely rotates about the resonator's main axis. In this embodiment, another magnetic object 507 is fixed. However, in another embodiment, another magnetic element may also be suspended on filament and thus freely rotate about the resonator's main axis.

[0090] In equilibrium, magnets 507 and 508 are aligned with their antiparallel magnetization orientations. An external magnetic field pulse can be used to initiate resonant rotational oscillations. The attractive force determines the resonant frequency of the oscillation; for a spherically suspended magnet, this resonant frequency is given by the following equation:

[0091] , (1)

[0092] in It is the saturation magnetization of magnetic materials. It is its density, It is the diameter of the sphere, and It is a field generated by a fixed magnet. It can be approximated as a dipole field.

[0093] , (2)

[0094] in It is the magnetic moment of the magnet.

[0095] The field change generated by the oscillating magnetic element can be detected via the induced voltage in one or more detection coils of a transducer configured to convert the magnetic or electromagnetic field generated by the mechanical oscillation of the magnetic object of the pressure sensor into an electrical response signal. (See the time trajectory of the detection signal). Figure 22 The spectrum can be obtained by Fourier transform (see...). Figure 25 This allows us to determine the resonant frequency.

[0096] Due to the low resonant frequency of a few kHz, the magnetic field is not shielded by the metal, and therefore all non-ferromagnetic metals can be used as structural or coating materials. Similarly, as long as the metal thickness does not significantly exceed the skin depth, the sensor can be placed within a non-ferromagnetic metal object without affecting its operation. At these frequencies, the skin depth is on the order of 1 mm for very good conductors, such as copper, and around 10 mm for nitinol.

[0097] A basic magnetomechanical oscillator comprises two magnetic elements, which, in equilibrium, are aligned with antiparallel magnetization. An external field pulse can be used to initiate rotational oscillation of a suspended sphere about the principal axis of the resonator, wherein the other sphere (i.e., another magnetic object) is fixed. In another embodiment, if the other sphere is also suspended in free space and can perform rotational oscillation, then both spheres can perform resonance counter-oscillation.

[0098] US2007 / 0236213A1 essentially describes a mechanical resonator with an attached magnetized material. A magnetic field can interact with the magnetized material and initiate mechanical oscillations. The mechanical oscillations are then detected by an oscillating mechanical structure by recording a time-varying field. The recording device can be a coil or other suitable magnetometer. External pressure on such a device can change the effective spring constant, and thus cause a change in the detectable resonant frequency. This forms a pressure sensor.

[0099] While this works in principle, as mentioned above, it has several drawbacks and is unsuitable for sufficiently precise measurement of pressure deep within a patient's body, and for use with sufficiently small devices. The main problem is the use of mechanical resonators. Typically, the maximum possible quality factor achievable in mechanical resonance is too low for effective operation. Some materials, like fused silica, provide a high quality factor in oscillations. These materials are generally quite hard and do not allow sufficiently high oscillation amplitudes (sufficiently high angles) to be effective, i.e., they do not allow for sufficiently large field changes. Another problem is that because only the elastic parameters are modified, the resonant frequency is insensitive to external pressure. This, combined with the low quality factor, leads to the need for a fairly high signal-to-noise ratio, which in turn leads to the need for a large amount of magnetic material, making the sensor large. Another problem with the device disclosed in US2007 / 0236213 A1 is the integration of high-strength permanent magnets into the device. The best permanent magnets are sintered types. These are incompatible with MEMS manufacturing processes. Therefore, either manufacturing is complex, or inferior magnetic materials must be used. The positive factor is the relatively high operating frequency of the sensor disclosed in US2007 / 0236213 A1. On the downside, the noise in the body also increases with frequency and above several hundred kHz, with no further gain. Therefore, the claimed GHz resonant frequency does not help. High-frequency operation also requires rapid switching from transmit to receive mode, which is technically challenging. Another issue with US2007 / 0236213 A1 is durability. At sufficiently high amplitude-time-frequency products, the spring material is subjected to considerable stress, which can lead to breakage.

[0100] Through, for example Figure 1The proposed design avoids these problems. Since energy is primarily stored in the magnetic field, a high quality factor is relatively easy to achieve. High oscillation amplitudes are also readily possible. Thin filaments are not subject to severe wear. The resonance can be easily altered by changing the magnetic field through the mechanical movement of the magnets relative to each other. This also makes it easy to match with pressure variations (using the correct compliance and the correct shape of the material, discussed below), thus enabling very high frequency variations. The sensor can be made from the best available magnetic materials, and the volume fraction of the magnetic material is high.

[0101] As explained above, implantable pressure sensors already exist, such as those developed by CardioMems and disclosed in US7,147,604B1. These sensors operate using a resonant LC (inductor-capacitor) device. The resonant frequency is shifted by the mechanical movement induced by pressure, which in turn changes the value of L or C (or both). When the system is in operation, it cannot be scaled down to the size required for the intended application. This is an inherent problem with LC oscillators. By reducing the size, the power level generated at the oscillator and the dynamic dipole moment generated by the power decrease. This can be seen in the following equation. The quality factor of the resonator cannot be higher than the quality factor of the coil. An approximation of the coil quality factor can be written as:

[0102] , (3)

[0103] in It's frequency. It is the vacuum permeability. It is resistivity. It is a fraction of the radius of the conductor, and This is the radius of the coil. It is assumed that the coil is cylindrical, with its diameter matching its height. For a 1mm diameter copper coil at 100kHz, a quality factor of approximately 1 is obtained. This is clearly not feasible. For a 1cm (or larger) coil used by CardioMems, the quality factor is above 100 at 100kHz and above 1000 at 1MHz. The above formula overestimates the practically achievable Q value because it assumes that all volume is filled with conductive material and neglects proximity and skin effects, as well as losses in the capacitor. However, these values ​​result in a working system. US7,147,604B1 states a quality factor of 48 measured between 1MHz and 100MHz. Since the dynamic dipole moment of an LC oscillator is Q times the external magnetic field multiplied by the volume, the signal and... Proportional, whereas in the case of a mechanical oscillator (with elastically stored energy), the signal and Proportional, and in, for example, reference Figure 1In the described embodiment (magnetomechanical oscillator, with energy stored in a magnetic field), the signal and This is proportional, because frequency is inversely proportional to linear size. Therefore, the recommendations presented in this paper are well-suited for sensor miniaturization.

[0104] In embodiments with a fixed sphere, the fixed sphere may have a diameter of 620 μm, while the oscillating sphere 108 may have a diameter of 500 μm. The magnetic moment of the oscillating sphere 108 may be... µAm 2 The base frequency can be kHz, and the quality factor can be roughly expressed as The SNR depends on a) the distance between the coil used to read the resonant frequency and b) the sensing device, as well as the coil parameters. For a handheld coil with a diameter of 10 cm, 200 windings, and a resistance of 10 ohms, the theoretically achievable SNR at a distance of approximately 30 cm and a sampling duration of 0.1 s is about 4000. However, if measurements for background signal suppression are hardly implemented, the typical SNR value for a demonstrator with a fixed sphere can be between 10 and 100. Therefore, noise is primarily determined by fluctuations in the main power supply harmonics. For a hemisphere diameter, i.e., 250 μm for an oscillating sphere, the magnetic moment can be... µAm 2 The base frequency can be At kHz, the quality factor can remain constant, and the theoretical SNR can drop to approximately 1000.

[0105] There are several ways to attach a wire to a movable magnetic object.

[0106] For example, through-hole attachment can be used. In this case, the wire is drilled through the center of gravity and approximately perpendicular to the magnetization. Although the magnetic material is hard and brittle, there are several drilling methods, such as pulsed laser or electrical discharge machining (EDM). The wire is threaded through the hole and bonded in place. It is best to use a vacuum suction process to complete the threading. Several types of adhesives can be used. The most economical is light-curing adhesive. They should have low viscosity so that the wire can easily fill the hole by capillary force. Alternatively or additionally, the wire can be attached to the magnetic object by mechanical means. For example, by having knots in the wire or by having some other thicker sections in the wire, such as glue droplets or thermally generated (molten) beads. The latter is particularly easy to make from UHMWPE fibers. This attachment method reduces the magnetic dipole moment by only a small fraction and therefore maintains a good signal. The shape of the magnetic object is not changed much, which may be important in the case of spheres.

[0107] Clamping can also be used for attachment. In this case, the magnetic object is divided into at least two components. Preferably, a dividing plane is created perpendicular to the magnetization and parallel to the wire attachment direction. The wire, i.e., the filament, is placed on this plane. Precise alignment is not required. The second magnetic part is placed on top. The magnetic parts are typically held together by magnetic force. Finally, glue is applied to secure all the items in place. The preferred type of glue is the same as that used in the through-hole attachment process. Furthermore, grooves can be ground into one or two magnetic objects to reduce the overall gap between them. This method produces results almost as good as the through-hole method, but does not require specialized manufacturing equipment. Typically, magnetic sub-objects are not made by dividing a single complete magnetic object, but by grinding two (identical) magnetic objects. The downside is that this process is more wasteful when using two initial objects, and it can also be slightly more labor-intensive.

[0108] The cheapest method is to attach the top of the wire directly to the top of a magnetic object using suitable glue. The magnetic object is held and aligned in some kind of tool. Both functions can be achieved using a suitable magnetic field. The tool can be funnel-shaped with the wire passing through it, and the magnetic object is attached to the funnel opening by magnetic force. Glue is applied to the funnel and cured. The assembly is then removed from the tool, and any unwanted parts of the wire are cut off. This method can be very inexpensive and makes full use of the magnetic object. The disadvantages are that it adds a considerable amount of material, reduces the oscillation frequency, and requires space in the finished device.

[0109] In another embodiment, a structure for attachment and additional adhesive can be used. The wire can be attached to the magnetic object by first attaching the wire to a non-magnetic object and then adhesiveing ​​the non-magnetic object to the magnetic object. The non-magnetic object can be manufactured by injection molding or an equivalent inexpensive process. The shape of the non-magnetic object should allow for simple wire attachment; that is, it can have holes or clamping mechanisms, or even simply notches. The non-magnetic object is then adhesiveed to the magnetic object. Alternatively, it can be clamped or screwed onto the magnetic object. This method is simple and inexpensive, but may require excessive additional space for some applications.

[0110] In principle, all the methods discussed for attaching wire-magnetic objects are applied in the same way to wire-shell attachment. However, since shell materials are generally easier to use, through-hole methods may be a good option. Clamping is also a good option. This may be cheaper but may be more difficult to achieve a final seal.

[0111] At least a portion of the housing is flexible to allow changes in external pressure to be converted into changes in the mechanical oscillations of the magnetic object. Preferably, the housing comprises, for example... Figure 1 and Figure 2The diagram schematically and exemplary illustrates a deflectable diaphragm. Deflection depends on the pressure applied to the sensor and changes the distance between the spheres. A decrease in distance leads to an increase in the resonant frequency, and vice versa. Figure 1 and Figure 2 The basic working principle of a pressure sensor can be seen in the diagram. The increase in pressure causes the diaphragm 515 to deflect and reduce the distance between the spheres 507 and 508, resulting in an increase in the resonant frequency. Figure 1 and Figure 2 The housing 502 and filament 506 are also shown, through which the magnetic sphere 508 is attached to the diaphragm 515. Figure 1 In the middle, the pressure acting on the diaphragm and the resonant frequency are less than Figure 2 The pressure and resonant frequency within.

[0112] Figure 3 This illustrates another embodiment of a bellows design, specifically a pressure sensor with a bellows. The bellows yields to the force generated by the pressure acting on the sensor; that is, increased pressure compresses the bellows and reduces the distance between the bulbs. Figure 3 A illustrates the first bellows design. The bellows 703 is designed to utilize the available space around the filament 706 without increasing the sensor diameter, wherein an increase in pressure compresses the bellows 703 and reduces the distance between the magnetic spheres 707 and 708, resulting in an increase in the resonant frequency. Figure 3 Figure A also shows the housing 702 of the pressure sensor 701 and the fixed magnetic sphere 707. The pressure sensor 701 also includes a thin metallic coating 717, i.e., a diffusion barrier layer, which serves as a diffusion barrier. It should be noted that all embodiments of the invention include a diffusion barrier layer, even if not explicitly shown in all figures for clear reasons.

[0113] Figure 3 B shows a coated sensor 801, which is similar to... Figure 3 The pressure sensor shown in A has an additional smooth and flexible cover above the bellows 803 to prevent blood clot formation. Sensor 801 also includes the bellows 803, which is designed to utilize the available space around the filament without increasing the sensor diameter. An increase in pressure compresses the bellows 803 and reduces the distance between the magnetic spheres 807 and 808, resulting in an increase in the resonant frequency. Figure 3 B also shows the housing 802 of the pressure sensor 801 and the fixed magnetic sphere 807. The pressure sensor 801 also includes a thin metal coating 817, i.e., a diffusion barrier layer, which serves as a diffusion barrier.

[0114] Figure 3 C shows a pressure sensor 901, which is similar to Figure 3The pressure sensor shown in B, additionally, has a 3-element wire cage 920 for direct delivery into the blood vessel. The cage secures the sensor without obstructing the blood vessel lumen. Therefore, also in this embodiment, a smooth and flexible cover 918 exists above the bellows 903 to prevent blood clot formation. The bellows 903 is designed to utilize the available space around the filament without increasing the sensor diameter, wherein an increase in pressure compresses the bellows 903 and reduces the distance between the magnetic spheres 907, 908, thereby causing an increase in the resonant frequency. Figure 3 C also shows the housing 902 of the pressure sensor 901 and the fixed magnetic sphere 907. The pressure sensor 901 also includes a thin metal coating 917, i.e., a diffusion barrier layer, which serves as a diffusion barrier.

[0115] Corrugated pipes can be made in different ways. First, they can be made from fairly flexible materials like silicone rubber (see...). Figure 4 In fact, it can simply be a piece of silicone rubber. Figure 4 In this design, the pressure sensor 1001 includes a cylindrical housing 1002 having an open end closed by means of rubber elements 1009 and 1003. The first rubber element 1009 holds a fixed magnetic sphere 1007, and the second rubber element 1003 holds a rotatable oscillating magnetic sphere 1008 via a filament 1006. The cylindrical rubber element 1003 serves as an expansion joint instead of a bellows.

[0116] However, when at least one diffused dense layer is incorporated into the bellows, i.e., as shown in the reference above... Figure 3 A to Figure 3As described in C, when a bellows is coated with a diffusion barrier layer, a simple tube is often too rigid. Therefore, a practical bellows structure is preferred. Bellows are well known, and bellows of different shapes are possible. In particular, the "origami" type structure is well-suited for pressure sensor applications. Several methods exist for manufacturing bellows. It can be simply manufactured in an injection molding process. This has the advantage that the bellows can be manufactured together with the housing in a single step. However, the manufacturing process is challenging because the diaphragm needs to be very thin. An alternative is to produce only the internal free space of the bellows in a production process such as injection molding or even turning or milling. The material should be readily soluble, such as polyvinyl alcohol or polystyrene. Some metals are also suitable, such as aluminum, iron, or copper. The bellows structure is deposited on this material, and the internal structure is removed by a suitable solvent and / or by applying heat. Many deposition processes are suitable for producing bellows. For example, noble metals (gold, palladium, etc.) can be deposited electrochemically. Metals, compounds, and polymers can be thermally deposited in a vacuum. Sputtering and chemical vapor deposition are suitable. Many other processes, such as simple spraying, can also work. While pure metal bellows work, it is best to combine the metal with a polymer, as this provides a bellows with less rigidity. Integrating at least two or more very thin metal layers is also effective. Thus, for example, it is best to first deposit (sputter) a gold-palladium layer, then deposit poly(p-phenylene dimethyl)-C using a CVD process, and then sputter a gold alloy again on top. Even with a few cracks in the metal layers, this allows the diffusion barrier to function, as the gas must diffuse a long distance within the poly(p-phenylene dimethyl) layer, which is already very diffusion-resistant. An additional layer may or may not be present on top to enhance biocompatibility; i.e., each of the described embodiments may include one or more external biocompatibility layers. External molds can also be used instead of inner molds. They must be segmented to release the bellows, but can be reused multiple times. Physical deposition methods may not work very well for this production process, but chemical deposition and electrochemical deposition, for example, are suitable. Once the (unfinished) bellows is removed from the mold, other deposition processes as mentioned above can be used.

[0117] As mentioned above, there are many methods for coating sensors. For example, as referenced above... Figure 3 A to Figure 3 As described in C, recoating the final sensor with metal is particularly useful. This ensures a tight diffusion of all possible junctions. Physical or chemical vapor deposition is also useful here. If desired, a biocompatible coating, such as poly(p-phenylene dimethyl)-C, can be deposited on top of this layer (or as an alternative). Additionally, noble metal or titanium coatings already offer good biocompatibility.

[0118] like Figure 3 B and Figure 3As shown in C, a smooth and soft top layer 818, 918 can be added to prevent blood clots from forming at the rather sharp edges of the bellows. The void between the soft layer 818, 918 and the bellows can be filled with a fluid such as water or silicone oil.

[0119] Figure 3 C illustrates a sensor 901 with a 3-element wire cage 920 for direct delivery into a blood vessel. The cage secures the sensor without obstructing the blood vessel lumen. The cage typically consists of an annular or disc-shaped central portion from which curved legs protrude. It can be made of a wire material, such as nitinol, due to its high flexibility and good biocompatibility. Other materials, such as stainless steel or polymers, can also be used. An alternative to wire can be a structure cut from sheet material and then shaped into a curved form using die-cutting tools and heat treatment. Injection molding is also feasible, particularly for polymers. For attachment to the sensor housing, the annular or disc-shaped structure serves as an interface between the cage and the sensor housing. The annular structure can be slotted in the cylindrical housing and can be secured by spring force and / or by gluing or welding. The disc-shaped structure can be glued or welded to the sensor.

[0120] To avoid the forces generated by contact with the blood vessel wall, the cage 920 is only connected to a portion of the sensor 901, protecting the space around the other portion (see [reference]). Figure 3 C). It can be attached to a section containing fixed magnetic elements, or it can be attached to a section with rotatable magnets. The cage design can also include a helical structure (single or multiple filaments) or a mesh structure. These structures can be optimized for compression, for example, during transvenous delivery via a fine needle.

[0121] Figure 5 A to Figure 5 D schematically and exemplary illustrates another embodiment of the pressure sensor. Here, a symmetrical sensor design that minimizes torque coupling with the environment is proposed. Figure 5 A and Figure 5 In B, it is shown that the pressure is low ( Figure 5 A) and high pressure ( Figure 5 B) Symmetrical sensor 1101. Symmetrical sensor 1101 includes a cylindrical housing 1102, wherein bellows 1103, 1104 are located at opposite ends of housing 1102, i.e., the end faces of housing 1102 are held by bellows 1103, 1104. Magnetic spheres 1107, 1108 are attached to the end faces via corresponding filaments 1105, 1106, wherein the magnetic spheres are permanent magnets as in other embodiments. The outer surface of housing 1102 is provided with a thin metallic coating 1117 as a diffusion barrier, i.e., the outer surface of housing 1102 is provided with a diffusion blocking layer 1117. Figure 5C and Figure 5 D illustrates another embodiment 1201, corresponding to embodiment 1101, but additionally featuring a wire cage attachment 1220 to maintain distance from the vessel wall. For the final design, open wire ends should be connected to prevent single wires from becoming stuck in the vascular structure during flow-based delivery. Therefore, a symmetrical sensor design is also present in this embodiment to minimize torque coupling with the environment. Figure 5 C and Figure 5 In D, it is shown that it is under low pressure ( Figure 5 C) and high pressure ( Figure 5 The symmetrical sensor 1201 (D) includes a cylindrical housing 1202, with bellows 1203 and 1204 located at opposite ends of the housing 1202, i.e., the end faces of the housing 1202 are held by the bellows 1203 and 1204. Magnetic spheres 1207 and 1208 are attached to the end faces via corresponding filaments, wherein the magnetic spheres are permanent magnets as in other embodiments. The outer surface of the housing 1202 is provided with a thin metallic coating 1217 as a diffusion barrier, i.e., the outer surface of the housing 1202 is provided with a diffusion blocking layer 1217.

[0122] The aforementioned pressure sensor can be integrated into, for example, guide wire 1310, such as Figure 6 and Figure 7 The diagram is schematic and exemplary. The end of the guide wire 1310 can be welded to the housing 1302 of the pressure sensor 1301, wherein the fixed magnetic ball 1307 and the rotatable magnetic ball 1308 are attached to the diaphragm 1304 via a filament 1306. The housing 1302 includes at least one opening 1303, which can be considered as a vent port for providing fluid connection to the outside of the housing 1302 to allow pressure measurement. Figure 6 and Figure 7 The dimensions shown are merely exemplary. Dimensions may vary. However, the dimensions shown are well-suited for shunt reserve pressure sensor applications. Applying the scaling law to the observed demonstrator SNR indicates that the indicated dimensions will provide sufficient SNR and accuracy for remote operation at distances large enough to fully penetrate the patient. Therefore, the pressure sensor can be integrated into the guidewire to create a pressure wire.

[0123] Connect the pressure sensor to other implantable devices (see...) Figure 8 For example, monitoring the pressure drop above stent 1401 could be useful. This could be useful for characterizing the pressure distribution within and around the stent, for example, to detect blockages or to monitor disease progression. Figure 8A bracket integration of a pressure sensor 1403 with actual dimensions (bracket length = 30 mm, bracket diameter = 4 mm, wire diameter = 0.2 mm, sensor length = 1.2 mm, sensor diameter = 0.5 mm) is shown, wherein... Figure 8 A shows two sensors 1403 at the inlet and outlet of the support 1402, which can be used to monitor the pressure drop above the support 1402 and the potential blockage therefrom. Figure 8 B shows that the fixed portion of sensor 1403 needs to be connected to wire frame 1402. For better integration into the bracket (not shown), a covering material can be added to give the sensor a more streamlined shape. Figure 8 C shows a view inside the stent 1402. The movable sensor portion can be tilted slightly into the blood vessel to avoid or delay excessive tissue growth.

[0124] Applications include coronary stents, aneurysm stents (pressure monitoring can help detect endoleaks), stents used in transjugular intrahepatic portosystemic shunt (TIPS), or stents used in peripheral vascular disease. As mentioned above, circular or disc-shaped structures can be used as the interface between the device and the sensor, with all the accessory options described above. Similar accessories can be applied to other in vivo devices, such as wire loops, shunt grafts, or transmural Amplatzer devices. For larger devices, such as guidewires, FFR pressure wires, catheters, large shunt grafts, or artificial heart valves, holes can be drilled in the device to accommodate the sensor. Inside the hole, only one side of the sensor is attached, for example, by gluing or clamping, while the other side moves freely, for example, in a fluid or directly in the blood. The fluid can be an unmixed type, such as silicone oil or perfluorinated polyethylene ether, or it can be separated from the blood by an attached thin and flexible diaphragm, or both.

[0125] All clinical applications take advantage of the fact that the sensor is passive and small. It can be placed inside the body, and the readout system can detect it wirelessly from a distance without physical contact. For most clinical monitoring applications, the sensor needs to be stable inside the body for months to years. However, for guidewires and catheters, stability only needs to be provided within hours. For intravenously injected sensors, stability for several weeks is also sufficient, as new sensors can be delivered periodically.

[0126] Figure 9 An embodiment of a heart valve 2000 combined with a stent is illustrated schematically and exemplaryly, wherein in Figure 9In the figure, the stent material is indicated by reference numeral 2011. The heart valve 2000 includes a valve structure 2001 having a non-moving portion 2002 and a moving portion 2004. The heart valve 2000 includes pressure sensors according to the embodiment described. A first pressure sensor 2020 is disposed on the low-pressure side of the non-moving portion 2002 of the valve 2000. Furthermore, a second pressure sensor 2008 is disposed on the moving portion 2004 of the valve 2000. Both pressure sensors are attached to the outer wall of the valve 2000. However, pressure sensors can also be integrated into the valve structure, wherein in this case, there exists a space within the valve structure covered by a diaphragm and filled with fluid, in which the corresponding pressure sensor is disposed. External pressure via the diaphragm and the fluid causes a pressure change at the location of the corresponding pressure sensor within the corresponding cavity. Figure 9 In this configuration, a third pressure sensor 2007 is disposed within cavity 2005, which is covered by a diaphragm 2003 on the low-pressure side located within the non-moving portion of valve 2000. A fourth pressure sensor 2010 is disposed in a space within the moving portion 2004 of valve 2000, wherein this space is also filled with fluid and covered by a diaphragm 2021. Another pressure sensor 2009 may be disposed within the non-moving portion of the valve structure in cavity 2006 on the high-pressure side, wherein in this case, this cavity is also filled with fluid and covered by a diaphragm 2014.

[0127] Figure 10 An embodiment of a filament for treating cerebral aneurysms is illustrated schematically and exemplary. The filament 2100 includes a pressure sensor according to the embodiment. Specifically, a first pressure sensor 2104 may be disposed at a first end of the filament 2100, on one side of the first end. Furthermore, another pressure sensor 2101 may be attached to a second end of the filament 2100, and another pressure sensor 2103 may be mounted within a middle portion of the filament 2100, wherein the filament 2100 may include an inner cavity in which the pressure sensor 2103 is disposed, wherein the inner cavity has a fluid connection to the outside of the filament 2100 via an opening 2102.

[0128] Figure 11An embodiment of a liver shunt device 2200 including a filament structure 2203 is illustrated schematically and exemplary. In this embodiment, the filament structure 2203 has a first portion 2201 surrounded by a lining material and an exposed second portion 2202. In this embodiment, the first portion 2201 is lined using PTFE (polytetrafluoroethylene). Furthermore, in this embodiment, the first portion 2201 of the filament structure has separate filaments, while in the second portion 2202 of the filament structure 2203, the filaments are interwoven. The liver shunt device 2200, also referred to as a liver shunt, includes several pressure sensors. For example, a first pressure sensor 2204 is arranged adjacent to a corresponding filament of the first portion 2201 of the filament structure 2203 within the PTFE tube. A second pressure sensor 2205 is arranged within the "filaments" within the PTFE tube, i.e., the pressure sensor 2205 is arranged between the two ends of a corresponding filament of the filament structure 2203. A third pressure sensor 2206 is disposed between two adjacent wires of the wire structure 2203 within the PTFE tube, and is also connected to these wires. The wires of the wire structure 2203 have a waveform shape, wherein another pressure sensor 2207 is disposed between the crests or troughs of the corresponding waveform, wherein, for example, the pressure sensor may be connected to two adjacent crests or troughs of the corresponding waveform.

[0129] Figure 11 Another pressure sensor 2208 is shown adjacent to the filaments of the filament structure 2203 within the PTFE tube. The exposed portion 2202 of the filament structure 2203 may also include a pressure sensor. For example, a pressure sensor 2209 may be positioned between and connected to two adjacent interlaced filaments. Another pressure sensor 2210 may be positioned adjacent to the filaments, and a pressure sensor 2211 may be positioned between and connected to two peaks or troughs of the waveform of a corresponding filament of the filament structure 2203.

[0130] It should be noted that, Figure 8 to Figure 11 The arrangement of pressure sensors in this embodiment is merely exemplary; more or fewer pressure sensors may be arranged at or within the same or other locations on the corresponding device. The corresponding device may also comprise only a single pressure sensor. One or more pressure sensors of the corresponding device are at least one of those described in the embodiments.

[0131] In the following text, it is assumed that the sensor length is always approximately twice the diameter. All sensors with a diameter of 0.3 mm or greater will enable real-time pressure monitoring (more than 10 readings per second) at a distance greater than 30 cm with pressure accuracy below 1 mbar and a pressure range of at least 400 mbar. These parameters enable blood pressure measurement with clinically relevant accuracy.

[0132] The sensor can be integrated into the guidewire, for example, as shown in the reference above. Figure 6 and Figure 7 As explained, typical guidewire diameters range from 0.33 mm to 1.0 mm, meaning that for fine pressure wires, the sensor diameter should be approximately 0.3 mm or less. Therefore, a sphere diameter of 0.25 mm would be feasible, leading to the aforementioned estimates for frequency, SNR, and Q factor. A theoretically achievable SNR of approximately 1000 at a distance of 30 cm would be sufficient for all readout scenarios. For larger wire diameters, larger spheres can be used, thus reducing the need for optimal background suppression. Therefore, sensor diameters between 0.3 mm and 1.0 mm can be used for guidewire integration.

[0133] Sensors can also be integrated into the catheter. Here, when the sensor is placed in the catheter lumen, the same independent variable applies as that applied to the guidewire. It may be desirable to place the sensor within the material of the catheter wall, which would result in stronger size constraints. It is feasible to construct a sensor with a spherical diameter of 0.1 mm, but the effort required for background signal removal will increase and / or the distance at which the sensor can be reliably read will decrease. Alternatively, averaging with the heartbeat can be used to improve SNR, however at the cost of time resolution. Therefore, sensor diameters between 0.1 mm and 1.0 mm are suitable for catheter integration.

[0134] The sensor can also be placed on a stent. To minimize its impact on blood flow through the stent, the sensor diameter should not be much larger than the wire diameter. Typical stent wire diameters are between 0.2 mm and 0.5 mm. Therefore, this is a useful range for the sensor diameter. However, larger sensors can also be integrated, optionally with an additional streamlined cover.

[0135] The sensor can also be injected using a syringe, where it can be lodged in a smaller blood vessel in the lung or liver region without posing a risk to the patient. Typical sensor diameters for injection will be between 0.3 mm and 1.0 mm. The cage size needs to be adjusted according to the diameter of the blood vessel where the sensor should be optimally placed. Preferably, the cage diameter will be greater than 1 mm, because in smaller vessels, the pressure may deviate from the pressure required in larger supply vessels. To simplify delivery into the venous system via needle insertion, the cage should be compressible in the radial direction to the diameter of the sensor housing.

[0136] Because pressure sensors contain magnetic objects such as permanent magnets, scanning the body in an MRI scanner can be problematic. Since the pressure sensors are very small and therefore generate only very small forces and torques, the problem is unlikely to be dangerous to the body (i.e., the patient), and therefore poses no threat. Similarly, because the pressure sensors are so small, the MR images generated by the MRI scanner will not be damaged. However, many clinical MRI scanners use high field strengths greater than 1.5T, and strong magnetic fields can damage the pressure sensor by altering the magnetization of the magnetic object or by disrupting the mechanical arrangement within the sensor. This will be referenced... Figure 12 and Figure 13 To describe in more detail.

[0137] Figure 12 A pressure sensor 1 without MRI field immunity is schematically and exemplaryly shown. The pressure sensor 1 has two magnetic spheres 7 and 8, both suspended by corresponding filaments 5 and 6, which are attached to a housing 2 at corresponding attachment points 3 and 4. When excited by an oscillating external magnetic field, the spheres 7 and 8 begin to oscillate in opposite directions around the filament axis. This resonant oscillation generates a field that can be recorded from a distance. The housing 2 is partially flexible, so the distance between the two spheres 7 and 8, and therefore the resonant frequency, varies depending on the external pressure. For clarity, the flexible portion of the housing 2 is shown in… Figure 12 It is not highlighted in the text.

[0138] exist Figure 13 middle, Figure 12 The pressure sensor 1 is introduced into a strong magnetic field in the axial direction 9. This forces the spheres 7 and 8 to orient themselves in the direction of the magnetic field. However, in this implementation, the filaments 5 and 6 are too short to be perfectly aligned with the spheres 7 and 8. If the sensor housing 2 cannot move, or the filaments 5 and 6 break, or assuming the very strong magnetic field of the high-intensity field MRI scanner, the spheres 7 and 8 change their magnetization direction, rendering the device 1 inoperable.

[0139] One solution to this problem is to place the pressure sensor housing within an outer housing 10, 110, preferably a spherical or elliptical shell filled with a highly viscous fluid, so that the entire housing with the spheres can be reoriented to align the magnetization of the spheres with the external field, thereby avoiding remagnetization. The spherical outer housing 110 allows for arbitrary reorientation of the sensor and can therefore be used in simpler sensor designs, where one sphere 107 is fixed while another sphere 108 oscillates on a filament 106, such as... Figure 14 As indicated schematically. Figure 14In this embodiment, a pressure sensor 111 is formed using a relatively simple magnetomechanical oscillator 101, which includes a housing 102 comprising a fixed sphere 107 within a spherical outer casing 110 and another sphere 108 capable of oscillating on a filament 106. For Figure 13 The design shown allows for partial reorientation of sensor 1, depending on the lengths of filaments 5 and 6, and the outer casing 10 can be more elliptical, i.e., smaller in one or two directions, such as... Figure 15 The diagram illustrates the pressure sensor, indicated by reference numeral 11.

[0140] The pressure sensor is configured such that changes in external pressure surrounding the exterior of the housing are transmitted to changes in external pressure surrounding both the exterior and interior of the housing. For example, the outer housing may be a very soft housing filled with fluid or a housing with openings to effectively convert changes in external pressure into changes in the mechanical oscillations of a magnetic object.

[0141] The additional outer shells 10 and 110 enable the reorientation of shells 2 and 102 to align the magnetization of the sphere with the external field, wherein... Figure 14 A spherical housing 10 is shown, capable of reorienting a free sensor, and is therefore also suitable for designs with, for example, a fixed magnetic sphere, wherein... Figure 15 In this case, the required tilting is possible within the housing 110, which is flattened in one or both directions, i.e., has a greater tilt than... Figure 14 The sphere 10 has a smaller diameter. The elliptical housing 110 is particularly suitable for sensors where spheres 7 and 8 are suspended on filaments 5 and 6.

[0142] exist Figure 16 In the middle, the pressure sensor 201 with ropes 205 and 206 (i.e., filaments 205 and 206) and Figure 12 and Figure 13 The pressure sensor 1 shown is elongated, while the tube diameter remains constant. Therefore, there is ample space for the spheres 207 and 208 to align with an external magnetic field in any direction. The minimum string length is Pi / 4 of the diameter of the spheres 207 and 208. The only possible problem is that the field changes in the way the filaments 205 and 206 are wound around the spheres (multiple) 207 and 208. To make this impossible, the spheres 207 and 208 and the interior of the housing 202 can be coated with a smooth, non-stick material, such as graphite. The filaments 205 and 206 are attached to the housing 202 at attachment points 203 and 204.

[0143] Another embodiment is illustrated schematically and exemplary. Figure 17In this design, the cords 305 and 306 (i.e., filaments) of the pressure sensor 301 are too short for the device to withstand MRI. However, corresponding winding units 314 and 315 are attached to the corresponding cords 305 and 306 and the housing 302. If the force on the corresponding filaments 305 and 306 becomes too great, the units 314 and 315 release more of the filaments 305 and 306. Therefore, the corresponding spheres 307 and 308 can rotate freely, thus solving the problem. For normal operation outside the MRI machine, the length of the filaments 305 and 306 needs to be precisely limited. This is achieved through stops 311 and 312 that can be attached to the cords 305 and 306 or through some kind of stop in the winding unit.

[0144] exist Figure 18 The diagram shows a possible winding unit 414. It includes a spring material 422 that holds a filament 405 via a pulley 427 and an attachment point 426. When the force on the filament 405 is low, the spring 422 is stopped by some stops 424, 425. The spring 422 presses against the stops 424, 425, and therefore the length of the filament 405 is fixed. If the force becomes greater, the spring material 422 bends and the available length within the housing 420 increases. This configuration preferably allows for filament elongation up to 1.5 ball radius. This means that it is sufficient regardless of the filament length within the housing 420. The filament 405 is guided out of the housing 420 and into the housing of the sensing device through the housing opening 421. The spring is attached to the housing 420 at the spring attachment point 423.

[0145] The described pressure sensor is preferably configured to compensate for the temperature dependence of the resonant frequency. Reference will be made below. Figure 19 This describes the configuration of a pressure sensor used to compensate for temperature-based offsets in the resonant frequency.

[0146] Also in Figure 19In this embodiment, pressure sensor 3001 includes a housing 3002 and a magnetic object 3004 disposed within the housing 3002 such that if an external magnetic torque is applied to the magnetic object 3004, the magnetic object 3004 can rotate away from its equilibrium orientation. Pressure sensor 3001 also includes a recovery torque unit 3003 adapted to provide a recovery torque to force the magnetic object 3004 back to its equilibrium orientation if an external magnetic force has rotated the magnetic object 3004 out of its equilibrium orientation, thereby allowing rotational oscillations of the magnetic object 3004 excited by the external magnetic torque. In this embodiment, housing 3002 is cylindrical, and the magnetic object 3004 is rotatable about a virtual axis of rotation traversing its center, wherein the magnetic object 3004 is rotationally symmetrical with respect to the virtual axis of rotation. Specifically, in this embodiment, the magnetic object 3004 is a magnetic sphere.

[0147] The restoring torque unit 3003 includes another magnetic object 3003 for providing restoring torque. Specifically, a magnetic object 3004 is attached to one end of a filament 3007, the other end of which is attached to the housing 3002. The filament 3007 is adapted to prevent the magnetic object 3004 from contacting the other magnetic object 3003 due to its magnetic attraction, and to allow the magnetic object 3004 to rotate and oscillate. In this embodiment, the other magnetic object 3003 is fixedly attached to the housing 3002 using adhesive 3009.

[0148] Magnetic object 3004 forms a first magnetic dipole, and another magnetic object 3003 forms a second magnetic dipole. The magnetic objects 3004 and 3003 are arranged such that, in a balanced orientation, the first and second dipoles point in opposite directions. The first and second magnetic objects 3004 are permanent magnets, wherein, in a balanced orientation, the north pole of magnetic object 3004 faces the south pole of magnetic object 3003, and vice versa.

[0149] The housing 3002 is cylindrical, and the cylindrical housing 3002 includes two end faces 3030 and 3031, and a magnetic object 3003 is fixedly attached to the first end face 3030, and the end of the filament 3007 opposite to the end attached to the magnetic object 3004 is attached to the second end face 3031 of the cylindrical housing 3002.

[0150] In this embodiment, the second end face 3031 of the housing 3002 is formed by a flexible portion 3008 of the wall of the housing 3002, wherein a magnetic object 3004 is attached to the flexible portion 3008 via a filament 3007, such that external pressure acting on the flexible portion 3008 from outside the housing 3002 causes a change in the distance between the magnetic object 3004 and another magnetic object 3003. Due to this change in distance caused by the external pressure, the strength of the magnetic field generated by the other magnetic object 3003 at the location of the magnetic object 3004, and therefore its resonant frequency, changes. Thus, the resonant frequency varies depending on the external pressure, allowing the pressure sensor 3001 to be used to measure the external pressure as another physical quantity. The flexible portion 3008 of the wall of the housing 3002 can therefore be considered a measuring element adapted to modify the resonant frequency depending on the external pressure.

[0151] The pressure sensor 3001 also includes magnetic materials 3005 and 3006 arranged adjacent to another magnetic object 3003. These magnetic materials 3005 and 3006 influence the magnetic field generated by the other magnetic object 3003, wherein the influence of the magnetic materials 3005 and 3006 depends on temperature, so that a change in temperature alters the magnetic field strength at the location of the magnetic object 3003, and thus changes the resonant frequency. The magnetic materials 3005 and 3006 are adapted such that their magnetization decreases with increasing temperature. Furthermore, the magnetic material 3006 is adapted such that its magnetization direction is opposite to that of the other magnetic object 3003, and the magnetic material 3005 is adapted such that its magnetization direction is the same as that of the other magnetic object 3003. Therefore, the magnetic materials 3005 and 3006, as soft magnetic materials, influence the resonant frequency in opposite frequency directions depending on temperature; that is, one of these magnetic materials changes towards a higher frequency with increasing temperature, while the other changes towards a lower frequency with increasing temperature.

[0152] The pressure sensor is preferably configured such that its resonant frequency is independent of temperature. However, for example, the flexible portion 3008 of the housing wall can be formed of a diaphragm, which can have temperature-dependent flexibility, such that the resonant frequency can also generally be temperature-dependent. Other portions of the pressure sensor can also be temperature-dependent, where such dependence may also affect the resonant frequency. To compensate for this undesirable temperature-dependent frequency shift, magnetic materials 3005, 3006 can be tailored such that they provide the same frequency shift in opposite frequency directions depending on temperature changes. In particular, magnetic materials 3005, 3006 can be selected and arranged to eliminate any temperature dependence of the resonant frequency of the pressure sensor 3001. Alternatively, only one type of magnetic material can be used—either a material whose resonant frequency decreases with increasing temperature, or a material whose resonant frequency increases with increasing temperature—to reduce or even eliminate the temperature dependence of the resonant frequency of the pressure sensor 3001. One or both of magnetic materials 3005, 3006 can be considered compensating elements for compensating for temperature-sensitized shifts in the resonant frequency.

[0153] Figure 20 A detection system 1501 for detecting the resonant frequency of a corresponding sensor for reading out the corresponding sensor is illustrated schematically and exemplaryly, i.e., a reading system for wirelessly reading out a corresponding pressure sensor. Figure 21 A prototype of the detection system 1501 is shown as an example. The detection system 1501 essentially includes at least one magnetic field generator and at least one magnetic field sensor, i.e., a transducer for converting a magnetic or electromagnetic field generated by induced oscillations of a magnetic object from a pressure sensor into an electrical response signal. The operating frequency band is in the low kHz range and must be wide enough to cover the responses of several sensors operating in parallel at different frequencies, and may also cover higher harmonics of the sensor's resonant frequency, for example, to improve the SNR. The amplitude of the transmitted field is at most a few millitesla, while the amplitude of the field to be detected is between 1 / 10 nT and several nT. Many different field generators can function (oscillating permanent magnets, cored / coreless coils, magnetostrictive field modulators, etc.) and many different magnetometers (Hall effect, various magnetoresistive sensors, magnetic resonance sensors, SQUIDS, etc.). The simplest system is a coreless conductor loop for transmitting and receiving magnetic fields. Coils are generally good enough for sensor applications. The coil used to generate the magnetic field can also be used to receive the magnetic field. However, different coils can be used for these tasks, which offers some advantages. Figure 20 and Figure 21 A detection system is shown as a single-channel transmit-receive system, in which multiple channels can be operated in parallel to obtain spatial information.

[0154] exist Figure 20In this system, detection system 1501 includes a transmitting coil 1503 and an audio amplifier 1502. The transmitting coil 1503 is connected to a microcontroller 1507 via a digital-to-analog converter 1506 (DAC). The audio amplifier 1502 is used to generate an external magnetic torque for a pressure sensor 1520, which can be any described pressure sensor. A receiving coil 1504 is also connected to the microcontroller 1507 via a low-noise amplifier 1505 and an analog-to-digital converter 1508 (ADC) for reading out the resonant frequency. The microcontroller 1507 is connected to a display computer 1509. The microcontroller 1507 is configured for, for example, signal generation and reception, frequency evaluation and control, and optional reference pressure measurement. Figure 21 The transmit / receive decoupler is also shown.

[0155] The microcontroller 1507 generates the transmit pulse (see...). Figure 22 The transmitted pulse (upper track 1350) is amplified using an audio amplifier 1502 and then transmitted to a transmitting coil 1503, which can also be referred to as an excitation coil. In this implementation, a separate receiving coil 1504 is used, which utilizes two additional decoupling coils 1510 (for clarity, in...). Figure 20 (Not shown) and decoupled from the transmit coil 1503. The received signal is fed to the low-noise amplifier 1505 and passed to the ADC 1508 of the microcontroller 1507, where a time trajectory typically 1 / 20 of a second is sampled at a rate of approximately 20 kS / s. In addition to the transmit pulse 1350 (also referred to as the excitation pulse), Figure 22 The induced voltage 1351 in the receiving coil 1504 due to spherical oscillations in the sensor and thus due to the sensor response is also shown. The interval of the excitation pulses 1350 can be continuously adjusted by the microcontroller 1507.

[0156] The advantages of multi-coil systems will be discussed below. In a single-coil system, the relative orientation of the sensor and coils prevents the coils from driving the magnetic sphere to oscillate and from reading back the generated field changes. Therefore, multi-element coil systems are desirable to avoid the need for the user to reorient the system relative to the sensor. The coils should have different spatial sensitivity distributions to generate the optimal excitation field vector in all cases. Furthermore, using several coils allows for sensor localization by determining the position and orientation of the oscillating magnetic dipole in space. The different amplitudes of the received signal and the known sensitivities of the coil elements can be matched to a dipole model used to determine the position and orientation parameters. An example of a multi-coil system implemented in a pillow or mattress is provided below. Figure 23The above is shown in the image. In cases where many receiving coils and channels are available, additional information can also be used to improve background signal suppression, as described further below.

[0157] exist Figure 23 In this system, several coils 1652 form a multi-coil array, which is integrated into the mattress 1651 of the patient bed of the imaging system 1650 (such as a C-arm system). The coils 1652 are preferably aluminum coils with X-ray absorption of less than 10%. Therefore, if coils 1652 are used, there is no need to increase the patient dose.

[0158] The following describes, in more detail, an exemplary coil-based transmitting system for the detection system. A coil-based transmitting system includes a transmitting amplifier and a transmitting coil. Optionally, it also includes the matching circuitry and a "mute" circuitry involved. Since the shape of the transmitted signal is not critical in sensor applications, many amplifiers are suitable for this task (Class A, Class B, Class AB, Class D, etc., employing transistors, vacuum tubes, thyristors, and many more components). Since signal quality is not critical, an amplifier topology with the lowest loss can be chosen, which is a half-bridge or full-bridge amplifier employing switches with low on-resistance. Preferred switches are MOSFETs or IGBTs. In the simplest case, the matching circuitry is a simple capacitor connected in series with an inductor. If the amplifier operates at a sufficient supply voltage, this matching capacitor can be omitted, or the capacitance can be chosen so that the resonant frequency of the coil with the capacitor is much lower than the operating frequency. Matching circuitry is of interest for another reason. Medical devices should always be operated in a safe manner, and voltage reduction is a concern. By placing a capacitor in the middle of the coil, allowing current to flow through one coil section, then through the matching capacitor, and finally to the second coil section, the peak voltage difference can be reduced. This is even more true if the coil is divided into more sections, each connected to a suitable capacitor. This makes the coil and matching circuit a combined unit. The field amplitude is conveniently controlled by pulse width modulation, i.e., the amplifier increases / decreases the current through the coil only for a portion of the cycle or rapidly alternates between increasing / decreasing the current. Since the exact signal shape is less relevant to sensor applications, it is best to achieve this by changing the state only twice within half a wave (or once at full power, where the pulse length is the same as half the wavelength). Ideally, the amplifier should not only have the possibility of increasing or decreasing the current, but also the possibility of keeping the current more or less constant or at the level specified by the matching circuit. This is achieved through the appropriate switching sequence of the transistors in the half-bridge or full-bridge. Typically, the amplifier's supply voltage should be fairly low and in the range below 50 V. Furthermore, the matching circuit should be configured in a way that does not exceed this 50 V limit at any two points. In both cases, it is best not to exceed 24 V. This means that the number of windings should be kept low. However, the peak operating current should exceed 10 A, preferably 100 A.

[0159] The following describes the transmit / receive insulation. Importantly, there should not be much noise coupling from the transmitting system (i.e., from the field generator) into the receiving system (i.e., into the transducer used to convert the magnetic or electromagnetic field generated by the mechanical oscillations induced by the magnetic object of the pressure sensor into an electrical response signal), while the transmitting system is not in transmit mode, i.e., not generating an excitation field. Furthermore, the transmitting amplifier should not short-circuit the received signal or even partially reduce the received signal. Several possibilities exist for achieving this. If we have different transmitting and receiving coils, the two coils can be geometrically decoupled (see...). Figure 24 ).

[0160] Figure 24 An implementation of a gradient measurement receiver coil design for suppressing transmitted and background signals in the receive path is shown. A large coil 1452 is selected here, enabling readout of the sensor up to approximately 30 cm above the upper coil. The gradiometer design uses a geometric decoupling method: the transmit coil loop 1451 is connected to generate a parallel field, while the receive coil loop 1450 is connected to receive the field gradient and suppress the uniform field. This transmit and receive system provides inherent geometric decoupling through the use of parallel transmit loops and antiparallel receive loops, which can be referred to as a gradiometer configuration. This results in inherent geometric coupling. This system with air coils is highly linear. Figure 24 Also shown is a DC block 1455 with an audio amplifier 1454 and a low-pass transmit filter 1453. Figure 24 The lower part of the figure shows the outer winding of the receiving coil 1450 and the inner winding of the transmitting coil 1451.

[0161] In particular, Figure 24 The lower left image is a close-up of the middle section of the upper coil assembly. In the lower left image, one can only actually see the one-turn transmitting coil 1451 peeking out from the bottom. The remaining portion is obscured by the receiving coil, wound with a finer wire. The DC blocking circuit 1455 is merely signal conditioning in front of the audio amplifier, as the signal for the audio amplifier can be generated by a simple PWM output. The low-pass filter 1553 is a filter between the output of the audio amplifier 1454 and the transmitting coil 1451. It serves two purposes: first, to avoid introducing high-frequency noise, and second, to combine the two output channels of the audio amplifier into one.

[0162] Geometric decoupling is not always possible, especially when using an array of transmitters and receivers. In such cases, a transformer with terminals connecting to both the transmitting and receiving circuits can be introduced. This transformer provides decoupling between the transmitting and receiving systems. This transformer solution can be used even when using combined transmitting / receiving coils. The transformer can be replaced by a decoupling network of capacitors (or even resistors) with combined and separate transmitting / receiving coils. The disadvantages of compensation methods are that they require considerable space, increase noise, and narrow the frequency operating range of the detection system in the case of capacitive decoupling. A more robust and cheaper solution is to add circuitry that completely silences the transmitting amplifier during the receiving time. For this purpose, a cross diode can be added to the amplifier's output. Diodes with low capacitance at zero voltage, such as PIN diodes, are particularly useful. This provides high impedance when no current flows. To further enhance this, an electronic switch can be placed at the amplifier's output to short-circuit all residual noise signals during reception. The diode still provides the desired high impedance. Special amplifiers that are completely noiseless and provide high impedance when not in operation can also be constructed. This can be achieved by using half-bridge and full-bridge designs, with absolutely no switching operation in any component during reception, low output capacitance transistors, approximately half the supply voltage at the outputs in receive mode, no noise from the input connectors (optical insulation), and a highly filtered supply voltage (heavily filtered or no power switching during receive operation).

[0163] The coil-based receiving system for the detection system will be discussed below. The receiving amplifier should be of low-noise type. However, the requirements are not so high that uncommon receiving transistors are necessary. Standard low-noise bipolar or JFET silicon transistors are usually sufficient. The only special feature is that the amplifier needs to withstand the transmit pulse and start operating immediately after the transmit pulse. There are several ways to achieve this. In the case of decoupled transmit / receive systems (including combined transmit / receive coils with decoupling networks), the receiving amplifier does not require special features to achieve this. If decoupling is not present, the amplifier may be hardened to the transmit pulse. This can be achieved by adding an appropriate capacitor to the input of the amplifier and adding a cross diode to the second terminal. This provides an appropriate high impedance in the transmit case and shorts all high voltages to a harmless level for the amplifier. Naturally, the added capacitor needs to be rated for the maximum transmit voltage. The capacitance value needs to be high enough that the signal at the amplifier does not drop too much in the receive case. For JFET-based amplifiers, this is usually not a critical issue. The cross diode can be enhanced or replaced by an appropriate electronic switch, such as an optocoupler with a MOSFET output. This has the advantage of further reducing the input voltage. If done properly, the receiving amplifier will not saturate and will come into play immediately after the transmitted signal has sufficiently decreased.

[0164] The interface to digital systems will be discussed in more detail below, starting with digital signal output and processing. While analog timer systems can generate output signals, digital systems such as DSPs or FPGAs are typically used. Different outputs can be used depending on the type of output amplifier. For analog amplifiers, some type of ADC can be used. Since output signal quality is not critical, a simple PWM-type analog output may suffice. Digital amplifiers are best interfaced using digital output lines. However, analog outputs can also be used, and a switching mode generator can be implemented on the amplifier. Generating switching modes directly on the digital system using optimally matched amplifiers, half-bridges, or full-bridges is most suitable. Furthermore, switching modes used for receiving amplifier input protection and sending amplifier output denoising can also be generated directly by the digital system. A common characteristic of all output options is that they need to be fast enough to accurately maintain phase on different excitations of a single sensor or between different sensors. Therefore, the output needs to have the capability to switch updates on gratings finer than the 10th of the full cycle time and finer than the 100th of the full cycle time. For a sensor, say 2kHz, this means updating on a grating that is finer than 220kHz, or even better, at 200kHz. This doesn't mean that a state change at every grating point is possible. Therefore, for example, there could be a serial interface and protocol for each amplifier, which transmits the new switching state to the amplifier, and the protocol is used to execute that change at a specific time via the same serial interface. This is particularly useful for amplifier types that are inherently silent during the reception phase. For this purpose, a 1-bit serial interface requiring only a single optocoupler on the amplifier can be implemented. This makes it easy to achieve noise-free operation on the digital transmission side, as the parasitic capacitance in a single optocoupler can be very low.

[0165] The analog-to-digital interface will be discussed below. Analog-to-digital conversion is fairly standard. Since the signal is low-bandwidth, at least if only a single sensor is used, the signal can be down-mixed to near DC and sampled. However, sensor signals have relatively low frequencies, typically below 10kHz. Many suitable ADC chips are available today that sample directly from this. In particular, since digital signal processing is limited compared to analog filters, it is best to use heavy oversampling in the ADC. At least 10 times the sensor frequency should be used, with 100 or 1000 times being viable options. High oversampling makes the design of the ADC input filter easy and inexpensive, as only the sensor signal frequency needs to pass through, and no signal above the Nyquist frequency will pass. However, filtering below the sensor frequency is also useful for avoiding the typically high background signal. High background signals can reduce the potential amplification before the ADC, increasing the ADC noise contribution. The ADC noise (effective number of bits) and sampling should be matched to the desired dynamic range and noise expectation. This means that the ADC should not be saturated when the maximum desired signal and all noise components are present. Simultaneously, the quantization noise of the ADC should be low enough that the total noise does not increase. Here, noise means all unwanted components in the recorded signal originating from real noise sources, such as coil resistance or receiver amplifier behavior. It also includes interfering components that cannot be eliminated through proper filtering and background signal subtraction. Typically, this requirement can be met for modern ADC chips, such as an 18-bit ADC with 2 MS / s. While it may be useful to use an ADC with lower specifications to save cost, gain control should be added to still achieve good overall performance.

[0166] Data processing will be discussed below. The raw ADC data must be processed before data evaluation. Since oversampling is desired, the first processing step can be a decimation step. This has the major advantage of reducing the data size and thus reducing the computational power required for further steps. Optionally, the decimation step can include additional filters, i.e., bandpass filters around the desired signal frequency. This simplifies further processing steps and reduces the dynamic range of the signal, which in turn saves computational power (with fewer bits of variables). Another optional data processing step is to apply an inverse nonlinear filter to reduce the nonlinearity of the receiving system. This means that the nonlinearity of the entire receiving system is measured, and a computational filter is constructed to reverse the effects of the nonlinearity. This is particularly useful if low-cost components are used, as they tend to have more nonlinear behavior. This nonlinear filter can alternatively be used as the first processing step. If more than one received signal is used, additional signal processing steps exist. If at least one receiving channel does not detect a sensor signal and therefore provides a measurement of the background signal, this signal (and all other such signals) is correlated with the received signal, and the correlated component is subtracted from the signal-carrying channel. This subtraction can be performed in the time domain, the frequency domain, or a mixture of both. If no channel exists that does not contain sensor signals, a data processing strategy sometimes referred to as a "virtual gradiometer" can be used. This decomposes multiple channels in a virtual channel into a linear combination of physical channels to minimize interference from signals not generated by sensors. The factors of the linear combination can be found by correlating the signals of channels outside the sensor's signal band.

[0167] Furthermore, the data evaluation will be explained below. The frequency is the primary parameter extracted from the acquired sensor signal, as changes in pressure on the sensor alter the distance between the magnetic spheres and thus the resonant frequency of the magnetomechanical oscillator. Due to the resonator's high mass factor (a time constant of several seconds), subsequent excitation pulses are typically released before the oscillation has fully decayed (see [link to relevant documentation]). Figure 22 Therefore, correct phase and timing are required to amplify the existing oscillations. This necessitates real-time frequency extraction between subsequent excitations. Frequency extraction can be achieved using a comparison algorithm that minimizes the phase difference between the measured signal and a pre-calculated time trajectory across the frequency range, or via Fourier analysis, which is the preferred method. High-resolution frequency information can be obtained by zero-filling in the time domain or interpolating in the frequency domain, followed by locating the resonant peaks in the spectrum using peak finding or curve fitting processes. To further improve the accuracy and reliability of frequency determination, higher harmonics of the detected resonant signal can be incorporated into the evaluation, for example, by using weighted frequency estimation based on several harmonics or by checking the consistency of frequency determination among several harmonics (see...). Figure 25 (Spectrum in the upper right corner).

[0168] exist Figure 25 In the example involved, the second harmonic signal is an order of magnitude smaller than the fundamental frequency signal. Therefore, better filtering is required. Various filter stages can be used to optimize the signal at the resonant frequency and its higher harmonics, such as analog excitation filters (e.g., DC blocks and low-pass filters), analog receive filters (e.g., bandpass filters), and digital receive filters (e.g., IIR response filters) for real-time processing (sixth-order Chebyshev type II). Figure 25 In the filter spectrum, the center position of the f0 resonant peak is determined by the maximum peak. Based on f0, the timing of the next in-phase excitation pulse is calculated. The system repetition frequency is between 5Hz and 30Hz, providing a real-time trajectory of the frequency response (see [link to relevant documentation]). Figure 32 ).

[0169] exist Figure 25 The image shows the signal spectra with and without digital bandpass filtering (1051 vs. 1050). The dashed lines are within the range selected for evaluation. Different dot symbols represent different filter types; they do not actually show significant differences and can therefore be ignored. Figure 26 In this configuration, the bandpass 1054 is attached to a commercial low-noise audio range amplifier 1053, of which the type is the FEMTO Messtechnik GmbH DLPVA-100-BUN-S. Figure 27 The actual 40 dB suppression spectrum of the digital filter is compared to the range of the selected frequency band. No significant difference is shown between the two implementations. The filter shown is applied to... Figure 25 The data shown leads to the difference between 1050 and 1051.

[0170] Based on the determined frequency and the known timestamp of the received signal, the correct timing for the next excitation pulse can be calculated. The number and width of the excitation pulses are adapted to generate oscillations with sufficiently high amplitude to produce a sufficient signal in the receiving coil.

[0171] To calibrate a pressure sensor, it is necessary to obtain the frequency response to many well-defined pressures acting on the sensor. For this purpose, a high-quality pressure sensor can be connected to the pressure chamber containing the sensor (see...). Figure 28 and Figure 29 Based on one or more scans over a relevant pressure range (up to 400 mbar above ambient pressure to safely cover the blood pressure range), a frequency versus pressure calibration curve can be determined, such as... Figure 30As shown in the diagram. Depending on the sensor characteristics, a simple fit to the calibration curve may suffice. However, real sensors may exhibit hysteresis behavior, dynamic response behavior of diaphragms or other mechanical sensor elements, or temperature dependence. Therefore, it may be desirable to fit a model based on physical sensor parameters to the measured calibration data to achieve highly accurate calibration of the sensor.

[0172] Figure 28 A calibration setup for calibrating a pressure sensor is illustrated schematically and exemplary, wherein the calibration setup includes a pressure applicator 1070, a pressure chamber 1071, a reference pressure sensor 1072 (which may be a commercially available pressure sensor), and a data log recording and display unit 1073. When measuring the resonant frequency, the pressure applicator 1070 applies a specific pressure measured by the reference pressure sensor 1072, such that the measured resonant frequency can be assigned to the actual pressure value during the calibration process. Figure 29 The data log recording and display unit 1073 is schematically shown, displaying the measured reference pressure 991 and the measured sensor response frequency 990, i.e. Figure 29 A real-time display showing the relationship between the sensor response frequency and the pressure measurement detected using a commercial reference pressure sensor is shown. Figure 30 The corresponding calibration curve 890 is shown at the bottom, and a comparison between a well-aligned reference pressure 892 and a resonant frequency 891 is shown at the top. This exemplary calibration curve has a sensitivity of 0.17 Hz / mbar, which corresponds to a pressure resolution of approximately 0.1 mmHg if we assume a frequency resolution of approximately 20 mHz.

[0173] The sensitivity of a sensor is determined by the amplitude of the frequency change for each pressure variation. This depends on several parameters, such as sensor design, diaphragm stiffness, the size of the magnetic elements, and the distance between them. For a given design and sensor size, simulation allows us to find the optimal distance between the magnetic elements and the desired diaphragm characteristics for optimal deflection relative to the applied pressure. Figure 31 Simulation examples of sensor sensitivity prediction for frequency ranges of interest for two sensor sizes are shown. In this figure, curve 437 corresponds to the demonstrator, and curve 438 corresponds to the aforementioned target size for fractional flow reserve (FFR) applications.

[0174] In addition to the relative sensor sensitivity determined above, the absolute sensitivity, or pressure resolution, depends on the noise level determined with respect to frequency. Figure 32 In the example shown, the noise level is approximately 0.2 Hz, and the sensor resolution is limited to approximately 1 mbar. Curve 441 shows the sensor frequency response, and curve 442 shows the measured reference pressure. Figure 32This involves limiting the pressure resolution to a noise level of approximately 1 mbar at the initial demonstrator. This is sufficient for most medical applications. Improved strategies for removing background noise can further enhance the resolution.

[0175] The processor of a readout system for wirelessly reading out the corresponding pressure sensor can be configured to apply a compensation algorithm to correct the pressure value determination for the dependence of the resonant frequency on at least one of the following: a) the distance between the pressure sensor and the field generator; and b) the excitation of the in-phase coil. This compensation will be explained in more detail below.

[0176] Here, we introduce methods for compensating for the effects of distance and orientation on the frequency in a magnetomechanical resonator for position and parameter (i.e., pressure) measurements. This compensation is only needed when a physical parameter (such as pressure) is sensed and the information is encoded in the oscillator frequency. For oscillator localization (which will be explained further below), frequency effects are irrelevant (sensitivity encoding discussed further below) or negligible (gradient field encoding also discussed further below). For localization using gradient field methods that also act on the sensor frequency, these compensations are unnecessary because only the frequency variation over sub-second time intervals needs to be evaluated. This variation is less dependent on the oscillation amplitude.

[0177] The signal of the magnetomechanical oscillator is generated by the coil. i The induced voltage u i (t) is detected, and this voltage is the result of the change in magnetic field caused by the oscillating motion of the magnetic moment m(t) of the suspended magnetic sphere at position r0:

[0178] (4)

[0179] in It is a location Detection coil at the location i The coil sensitivity, which remains largely constant over time. In the final step, the magnetic moment has been replaced by the following formula.

[0180]

[0181] in It is a unit vector describing the spatial orientation of magnetization. It is the saturation magnetization of the material used (typically between 1.30 T / µ0 and 1.45 T / µ0 for NdFeB), and It is the volume of the magnetic object.

[0182] As can be seen from (4), a large dynamic magnetic moment is desirable to induce a high voltage in the receiving coil. Since the volume of the sphere must be small in most applications, it can be achieved by using a larger dynamic magnetic moment. The large oscillation amplitude is used to increase the signal. However, the recovery torque does not change with the recovery field provided by the fixed sphere. Magnetization of the oscillating sphere Angle between (That is, the amplitude of the oscillation) increases linearly:

[0183]

[0184] Considering the damping coefficient C friction The resulting torque and having mass and radius The torque required for the angular acceleration of a sphere We can establish equations for motion:

[0185]

[0186] Small angle approximation And replace lead to:

[0187]

[0188] The high quality factor of the system allows for further approximations. And makes it possible to calculate the angular resonant frequency as

[0189]

[0190] Since micro-oscillators are typically driven to amplitudes much greater than 10°, this approximation is invalid in general. For large angles, the restoring torque is small, and therefore the frequency decreases, resulting in an amplitude-dependent frequency. ,in Furthermore, the change in restoring torque during oscillation introduces nonlinearity into the sensor response, as indicated by the presence of higher harmonics of the fundamental frequency in the spectrum.

[0191] In addition to the nonlinear restoring torque, the force between the two magnetic spheres depends on the mutual orientation of their magnetization:

[0192]

[0193] For a given sensor design, the force always points along the connection vector between the two magnetic spheres. However, at an oscillation amplitude of 90°, the magnitude of the force becomes zero, and even at higher angles, it changes from attraction to repulsion. If the filament suspending the spheres elongates due to the applied force, then the decrease in the average force at high oscillation amplitudes increases the distance between the spheres, thus reducing the force. This reduces the oscillation frequency. Not only can the length of the filament be changed, but other structures within the sensor can also change their length.

[0194] If the excitation field generated by the transmitting coil has a constant amplitude, then the oscillation amplitude... The amplitude decreases as the distance between the coil and the sensor increases (reducing the excitation field), and therefore the frequency decreases. The amplitude also depends on the relative orientation between the coil and the sensor, such as... Figure 33 As shown in the image.

[0195] Figure 33 The diagram illustrates the dependence of signal amplitude in different harmonics measured relative to a single transmit / receive coil on sensor orientation. If the excitation field is aligned parallel to the magnetic dipole orientation, no excitation occurs, and the signal is zero. The highest oscillation amplitude is achieved for orthogonal alignment of the field and dipole. Note that the spatial modes of even harmonics are orthogonally aligned with odd harmonics. This can be seen from the zero point of the second harmonic amplitude at the orientation corresponding to the maximum value in the fundamental signal (first harmonic) and third harmonic. The amplitude ratio plot (center plot) highlights this difference in orientation dependence: the second harmonic ratio changes from zero to a maximum value (or singularity) compared to the first harmonic, while the third harmonic ratio is flat compared to the first harmonic. The knowledge of the dynamic response at even harmonics and the orthogonal orientation of odd harmonics can be used to determine the sensor's third orientation angle.

[0196] Therefore, determining the initial frequency will result in readings that depend not only on the physical quantity but also on the sensor's position and orientation. This is generally undesirable, and thus mechanisms to reduce this effect are preferred.

[0197] There are two strategies to mitigate this effect. One is to ensure that the oscillation amplitude remains constant for all valid positions and orientations (i.e., within the field of view). The other is to calculate a virtual frequency based on one or more frequency readings, where the virtual readings are independent of the oscillation amplitude. The chosen virtual frequency can be the resonant frequency at a very low amplitude, i.e., the zero-amplitude frequency given by equation (8). Of course, a combination of the two strategies can be used.

[0198] The control of the oscillation amplitude will be described below, using the position and orientation of the pressure sensor known from the positioning.

[0199] The simplest conceptual approach to correcting frequency shift is to use a known position and orientation relative to the transmitting / receiving coil array. This position can be obtained through sensitivity coding or gradient coding, or a combination thereof, all of which will be further described below. When the position and orientation are known, the absolute dynamic dipole moment can be derived. Typically, the dynamic dipole moment is already a fitting parameter during position determination. Otherwise, as given in equation (3), it is derived from the known sensitivity of the coils at the relative sensor position and orientation and the recorded signal strength. The oscillation amplitude can be derived from the sensor's dynamic dipole moment and the known static dipole moment. (If the sensor's static dipole moment was previously unknown, it can be derived from multiple dynamic dipole moments measured at different excitation amplitudes as the maximum possible dynamic dipole moment reached or extrapolated.) The transmit field amplitude can now be adjusted to achieve a predetermined maximum oscillation angle. A slightly simpler, but also slightly less reliable, approach is to simply adjust the transmitted amplitude to a value such that the driving field component at the sensor is always constant. Typically, a directional field component (the amplitude relative to the sensor in one direction) dominates the excitation process. The amplitude depends on various simultaneous excitation currents in several excitation coils. The amplitude and phase of the currents in the coils are adjusted in a way that gives the desired amplitude at the desired location and orientation. How to do this is well known in the field of electromagnetism. Since the solution to this problem and previous methods for adjusting the transmitted amplitude are not explicit, at least one second criterion is used for the current optimization. In this context, "not explicit" means that multiple amplitude-phase combinations in the transmitted coil current have the same desired result. The second criterion is generally to minimize undesirable excitation side effects. Examples of undesirable side effects are total power dissipation, maximum power dissipation in a coil, maximum temperature in a coil (which also depends on the excitation history), heat or force from surrounding objects. Of course, any other relevant criteria or combinations can be used for this optimization. Equally effective is not to use the optimal solution, but simply to use the first efficient solution already found by a specific optimization algorithm (such as gradient descent or simulated annealing).

[0200] The determination of the zero-amplitude frequency will be described below, using the position and orientation of the pressure sensor known from the positioning process.

[0201] For cases where the position relative to the coil array is known, a second method can also be described, where the amplitude is not controlled, but the frequency is converted to, for example, a zero-amplitude frequency. For this method, a model of the sensor is required. This model describes the relationship between frequency and oscillation angle directly or in some equivalent form, such as frequency and dynamic dipole moment strength. The model can take the form of expressing the frequency as a zero-amplitude frequency minus a function dependent on the oscillation amplitude. More complex descriptions can also be used, for example, with correction terms introduced after equation (6) above, such as... Multiplication. Both frequency and amplitude can be interpreted as an average or curve fit over a predetermined integration period or sequence length. Since the position and coil sensitivity are known, the oscillation amplitude can be determined from the recorded signal, as described above. Therefore, since the actual frequency and amplitude are known, the zero-amplitude frequency can be derived by inverting the model function. Inversion can be performed in an analytical manner or through well-known numerical methods. Mathematically, any other relevant quantity can be used instead of the zero-amplitude frequency, such as the frequency at 10° amplitude or quantities that do not reflect frequency at all, such as absolute inter-sphere distance. However, this transformation does not change the fundamental nature of this evaluation process.

[0202] Typically, even when using the zero-amplitude extrapolation method, some form of amplitude control is preferred for most applications. If the sensor is close to the coil array, a lower current can be used through the coils than would be required if the sensor were farther away. The advantage of the zero-amplitude extrapolation method is that it can still function even if the sensor is so far away that the predetermined oscillation amplitude of the constant amplitude method can no longer be maintained due to limitations on the coil current.

[0203] The above description assumes that the oscillation amplitude can be derived from the known position and orientation of the sensor and the induced voltage in the receiving coil. However, any other method that can provide amplitude information can be used to compensate for amplitude-dependent frequencies using constant excitation and interpolation methods. Below, some alternative methods for this amplitude determination will be provided. These methods may be useful when only a small number of coils are available and the exact relative positions cannot be determined. The compensation methods themselves will not be repeated below.

[0204] Below, we will describe how to determine the oscillation amplitude by using the amplitude of the harmonics of the fundamental frequency.

[0205] One method for determining the oscillation amplitude is to evaluate the harmonics of the induced signal in the coil. As a nonlinear oscillator, the magnetomechanical sensor generates harmonics at the resonant frequency in a dynamic dipole moment. These harmonics are picked up in the receiving coil(s). Preferably, care is taken not to suppress these multiples of the fundamental frequency during the sampling and filtering steps. The spectrum of the harmonics depends on the details of the sensor. It is possible that predominantly odd-order harmonics are generated (in...). Sensors at (location) and generators of even and odd harmonics (in) (The sensor is located at the point of origin). However, hybrid types can be constructed. The dynamic dipole moment of odd harmonics tends to align with the dynamic dipole moment of the fundamental frequency, while that of even harmonics tends to align perpendicular to the dynamic dipole moment of the fundamental frequency and perpendicular to the axis of rotation. Therefore, odd harmonics are conceptually the easiest to use because, for example, the ratio of the dynamic dipole moment of the third harmonic to that of the fundamental frequency is reflected as the corresponding ratio in the voltage recorded in a single coil, for example, evaluated as the peak amplitude of the spectrum. However, since the amplification in the receiving system may be frequency-dependent, it is preferable to apply a correction to maintain the true ratio of the dynamic dipole moment of the third harmonic to that of the fundamental frequency. This ratio can be measured over a predetermined integration period. For each sensor, this ratio can be calibrated for the oscillation amplitude or the direct frequency shift, and thus the correction is applied. In the case of even harmonics, the situation is somewhat more complicated because the direction of the dynamic dipole moment is not aligned with the dynamic dipole moment of the fundamental frequency. Therefore, it is usually necessary to use more than one coil here, or to determine the orientation of the coil relative to the sensor by other means. While the sensor position and orientation can be reconstructed for a large set of coils (e.g., >= 6), a smaller set of coils (e.g., 3-5) should at least allow for the reconstruction of the sensor's orientation relative to the coils using a method similar to the positioning determination method described in this document. The coil sensitivity can then be used to determine the true ratio of the dynamic dipole moment for even harmonics. The intermediate steps of orientation determination can be omitted, and a direct mapping of the ratio of the fundamental frequency amplitude to the harmonic amplitude in the coil can be established using linear algebraic methods. It should be understood that the methods described herein in the frequency domain can be mapped to methods in other bases (e.g., the time domain). In the time domain, frequency analysis is mapped to oscillation shape analysis. These mapping methods are well known in the mathematical literature.

[0206] The determination of the oscillation amplitude based on the time-domain envelope function will be described below.

[0207] Another method to determine the oscillation amplitude is to utilize the nonlinear decay behavior of the signal. The damping of a sensor is typically nonlinear. Nonlinear decay means that, with double the stored energy, the average power dissipation of the sensor does not double, but rather increases by a factor slightly greater than 2. This can be due to the stretching of the filament caused by the force modulation described above. Equation (9) shows that at low oscillation amplitudes, the attraction between the magnetic objects is largely constant, but at higher amplitudes, it is no longer constant. This force variation in the first approximation depends on the square of the oscillation amplitude, corresponding to an approximation of the cosine function of the parabola. This square dependence is the cause of the nonlinearity in the dissipation. The varying force between the magnetic objects periodically stretches the filament(s), which contributes to the dissipation. Other effects may also cause nonlinear behavior. In summary, these effects result in the shape of the envelope of the decay curve over a given time depending on the initial amplitude. Therefore, a scaled version of the initial decay envelope is found if the sensor has a constant initial oscillation amplitude and the sensor's distance and / or orientation changes relative to the receiving coil(s). However, if the excitation amplitude of the sensor changes, not only does the total amplitude of the decay curve change, but its shape also changes. This means that amplitude effects and distance / orientation effects can be decoupled, and the initial oscillation amplitude can therefore be reconstructed using, for example, a lookup table of pre-recorded decay curves. This, in turn, leads to the possibility of determining the zero-amplitude frequency or controlled, constant-amplitude excitation, as described above. This method requires only a single coil to function. However, it is somewhat sensitive to sensor movement during recording, as this also alters the shape of the envelope. Therefore, it is beneficial to incorporate models of possible sensor movements into the evaluation. For example, if it is known that the sensor will not perform rapid acceleration, it is useful to use the assumption of continuous motion to correct the decay curve envelope.

[0208] The determination of oscillation amplitude based on the signal amplitude response to changes in the excitation field will be explained below.

[0209] Another method for determining the oscillation amplitude is to analyze the sensor signal's response to different excitation intensities. In this case, the current pulses are systematically varied, and the responses of (multiple) sensors to different excitation pulses are evaluated. The transmitted pulse current, duration, and phase, or combinations thereof, can vary. For example, suppose there are two excitation pulses. If the distance is high and the local field amplitude is low, the two pulses are designed to generate twice the amplitude that a single pulse would produce. However, if the distance is low and the local field at the sensor is high, the amplitude will be less than twice the amplitude. This results in a decrease in the characteristic of the received voltage relative to the expected factor of 2. Therefore, for a given excitation mode, the ratio of (multiple) amplitudes of the received signal (Fourier) amplitude of the sensor is a measure of the excitation amplitude and can again be used for interpolation to the zero-amplitude frequency and / or for having a constant excitation amplitude. In addition, other quantities, such as frequency and decay time, can be evaluated. The ratios of these quantities are also characteristics of the oscillation amplitude and can be used for interpolation to the zero-amplitude frequency.

[0210] The following describes a complete model based on all contribution factors to determine the correct parameters.

[0211] All the methods described above are merely evaluation methods, some of which require changes in the emitted field pulses. No hardware changes to the system are required to perform these evaluations. Therefore, it is logical to implement all of these. This can be done by simply running the evaluations in parallel and combining the results in a way that minimizes noise, i.e., by weighted averaging based on relative noise. While this is relatively straightforward and easy to implement, better results can be expected by using a truly integrated mathematical approach, which will be outlined below. On the other hand, mathematically complex methods are considerably more difficult to implement and may require too many computational resources to run on cost-effective computer hardware. The foundation of a proper mathematical approach is a mathematical model for the sensor. This model predicts the sensor's response to the excitation field, the current sensor state, and the measured parameters (i.e., the sensor environment). The sensor state can be the unique current deflection angle and rotational speed of a suspended sphere. However, specifically, but not exclusively, for pressure sensors, this can also incorporate the elastic state of the structure, which can deform under varying external or internal forces. Therefore, a model for hysteresis, such as that of diaphragms and filaments, needs to be incorporated. This model can have different mathematical forms, but the most common way is to express it as a set of differential equations. Next, models of the transmitting and receiving coils, including filter and amplifier characteristics, must be generated. This can be formulated using differential equations, although Fourier parametric representations are not uncommon here, provided the transmitting and receiving systems are inherently linear enough. Finally, a model for the coil's transmitting and receiving sensitivity needs to be provided. This can simply be a set of spatial points with additional sensitivities and interpolation algorithms between points. It can also be based on a simulation of the coil based on the Biot-Savart law. This model can then predict the sensor's voltage response at any given location and orientation using a given history of excitation pulses and external parameters. Therefore, the process involves varying the sensor location and orientation, as well as the sensor's influence on physical parameters in the simulation, in a way that best matches the recorded signals and the simulation. Many well-known optimization methods can be used, such as gradient descent or random walks. The match can be defined as the root mean square of the sum of the differences between the measured and simulated sampling points. The lowest this value indicates the best match. The best fit can be modified by introducing additional constraints, such as through a model of the expected relative position and orientation, or through constraints on the maximum expected sensor acceleration and / or a model of the measured quantities, which, for example, give constraints on the maximum rate of change of these quantities. Additional sensor inputs, such as accelerometers on a handheld coil system for at least one independent input for changes in distance and orientation, can also be used. Since full model-based evaluation processes are computationally intensive, they can be combined with one or more of the previous methods to provide a good starting point for further optimization.

[0212] The processor can also be configured to compensate for the effects of gravity, as explained below.

[0213] In pressure sensors, the weight of the movable sensor segment affects the pressure reading: if it's on top of the fixed sensor section, it compresses the sensor and thus causes a significant increase in pressure; if it's at the bottom, it causes a significant decrease. The weight on a 0.5 mm diameter NdFeB sphere is approximately 5 μN. For comparison, the change in force on the cylindrical back of the sensor caused by a 1 mbar pressure change (conservatively assuming the same diameter as the sphere) is approximately 20 μN. Therefore, the force difference between the sensor's upper and lower orientations in air limits the accuracy to 0.5 mbar. To mitigate this problem, a correction can be applied based on the sensor's spatial orientation obtained according to one of the methods described herein for restoring (position and) orientation. In liquid environments such as blood, the weight effect can be minimized by matching the density of the sensor segment to the density of the liquid, and then buoyancy compensates for gravity.

[0214] The processor can also be configured to compensate for Earth's magnetic field and other static field effects.

[0215] A static background field is added to the field of a stationary magnetic object, and thus modulates the recovered field seen by the oscillating magnet. This changes the resonant frequency according to equation (8) and is therefore the source of error for sensing via frequency changes of the oscillator. It is independent of oscillator positioning. For a magnetic sphere with a diameter of 0.5 mm made of NdFeB saturated with a magnetization of 1.3 T / μ0, the fields generated by the fixed sphere at the center of the oscillating sphere are 16.1 mT and 6.8 mT for center-to-center distances of 0.75 mm and 1.0 mm, respectively. The Earth's magnetic field is between 25 μT and 65 μT. For the aforementioned distances of 0.75 mm and 1.0 mm, the frequency difference between parallel and antiparallel alignments of the static field component of the Earth's magnetic field with a maximum of 65 μT will create frequency differences of approximately 5 Hz and 9 Hz, respectively. This worst-case calculation results in substantial errors in the sensed values, given the typical frequency resolution between 10 mHz and 100 mHz and the prototype sensitivities of -0.3 K / Hz for the temperature sensor and 20 mbar / Hz for the pressure sensor. Different mitigation strategies for this are described below.

[0216] The sensor-side mitigation is achieved by using a design with two suspended spheres having the same magnetic dipole moment and moment of inertia (or an appropriate ratio of the two quantities) instead of a single sphere. Since the reverse oscillations occur at a single frequency, the first-order effects of static bias fields (such as the Earth's magnetic field) are eliminated.

[0217] Another mitigation strategy is to use an absolute field sensor in the detector system to measure the amplitude and orientation of the static background field. Based on the sensor orientation determined using the methods discussed in this document, frequency or field corrections can be calculated to obtain the correct sensor values ​​for pressure, temperature, or other parameters. To sense the static background field, any magnetic field sensor with sufficient sensitivity and coverage that can be integrated into the detector system can be used. A cost-effective option could be a 3-axis Hall sensor. An alternative is a 3-axis array of temperature-compensated micro-bots with well-defined zero-field frequencies. The amplitude and orientation of the background field can be determined from variations in their corresponding frequencies. Ideally, their resonant frequencies are chosen so that they do not interfere with the frequencies of the sensor of interest. Instead of correcting for frequency shifts in the evaluation, one can also use the coils of a multi-coil detection system to generate small offset fields to counteract geomagnetic and other background fields. If a non-uniform field exists in the field of view due to the presence of ferromagnetic materials, several sets of 3-axis magnetic field sensors can be used to characterize the spatial field variations. Based on the interpolated background field map derived from these measurements, corrections to the sensor at known locations and orientations can be calculated, or a corresponding correction offset field can be applied, or a combination of the two correction methods can be used.

[0218] Pressure sensors and markers should have a high quality factor and require a large frequency sweep to be sensitive to the measured quantity within the range required for a particular application. The high quality factor is particularly important at high oscillation amplitudes where the highest signal is generated. Both characteristics can be degraded because two magnetic objects have a strong attraction, and this force increases dramatically with decreasing distance (up to the fourth power of the distance, see Equation (9)). The strong force results in a relatively strong tension in at least one filament holding at least one magnetic object. This tension itself does not lead to a dissipation path. However, especially at large oscillation amplitudes, the force between the magnetic objects decreases, and therefore the tension on the filament decreases periodically. This results in periodic elongation and shortening of the filament, which typically leads to heat generation. Power is thus extracted from the oscillator. These forces are also strongly dependent on the distance between the magnetic objects and become very large if the objects are close to each other. This behavior is particularly problematic for pressure sensors. The force between the magnetic objects is functionally equivalent to external pressure. Therefore, if the external pressure increases, the magnetic objects become closer, which in turn increases the apparent pressure. This effect is compensated for when using a calibration curve for pressure determination measurements, but when the sensor reaches its tilt point, it can lead to a situation where magnetic objects are rapidly pulled towards each other and eventually make contact. This results in the sensor becoming ineffective. This can be avoided by simply stiffening the diaphragm or bellows structure of the pressure sensor. However, this reduces the sensor's sensitivity, i.e., reduces the frequency shift per applied pressure. To address this issue, a method for reducing force and force variation is described. Figure 34 As shown, it consists of only a portion of a magnetic material that is magnetized in the opposite direction to another adjacent magnetic object.

[0219] exist Figure 34 In this embodiment, the pressure sensor 4001 includes a magnetic object 4008, which is a permanent magnet suspended from a flexible portion 4010 of the housing 4002 via a filament 4006, preferably a high-strength wire. The flexible portion 4010 is preferably a diaphragm, which may be a latex diaphragm. The remainder of the housing 4002 may be made of metal or polymer. The housing 4002 may be filled with gas or it may provide a vacuum space, wherein the internal space has Figure 34 Reference numeral 4009 is used in the accompanying drawings. Another magnetic object 4007 is fixed to the inner end surface of the housing 4002 via adhesive 4011. The two magnetic objects 4007, 4008 are generally magnetized in opposite directions. However, the fixed magnetic object 4007 also includes a portion having a reverse magnetization orientation 4012.

[0220] Therefore, if two magnetic spheres are involved, in this example, at least one sphere acquires a cap magnetized in opposite directions. This cap is located near the other magnetic sphere. If one sphere is stationary and the other is oscillating, it is best to place the cap on the stationary sphere. In this way, the dynamic dipole moment of the sensor is not reduced; only the oscillation frequency is slightly lower. However, it is also possible to reverse the roles of the spheres. The oppositely magnetized portion is small enough that the net force between the magnetic objects remains attractive at all operating distances. If the reverse magnetized portion is small enough, the attraction condition can be satisfied just enough until the magnetic objects come into contact. There are several methods to create the reverse magnetization. One is to add some magnetic material on top of at least one magnetic object. The magnetic material can be a soft magnetic material or a hard magnetic material. It can be a solid continuous magnetic object or a magnetic coating or something between them. The magnetic material tends to align itself in a way that forms opposite magnetization. Furthermore, it tends to adhere to the magnetic object. However, this additional material should be glued to the magnetic object, especially if the two main magnetic objects occasionally come into contact with each other. To maintain the initially desired shape, some material can be removed from the magnetic object to be altered, for example, by grinding. An alternative way to form a reverse magnetization region exists. It can be created simply by reverse magnetizing the desired region of the magnetic object. This can be achieved by a strong pulse of current passing through a conductor near the magnetic object. However, this is not very practical due to overheating. It can be more easily achieved by heating only the affected portion of the magnetic object to near or above the Curie temperature. This will result in a reversal of magnetization. This effect can be enhanced by applying a pulse or constant magnetic field in the opposite direction. These fields can also be combined with a strong gradient by using some hard or soft magnetic material near the region to be affected. Because the heating must be quite localized, the temperature rise needs to be very rapid so that the total energy deposited into the magnetic object is low and does not overall bring it close to the Curie temperature. A suitable heating source could be a laser. Resistance or inductive heating methods can also work.

[0221] The following will explain how to locate the pressure sensor.

[0222] For tracking systems, it is necessary to determine the orientation and 3D position of the marker, which may also include a magnetomechanical oscillator. However, for purely sensing systems, the orientation and position of the oscillator also need to be determined to improve the accuracy of sensor readings as discussed above. Two independent positioning strategies can be used for positioning. In some cases, one strategy may be sufficient; in others, a combination of both methods can be used to improve accuracy or to represent systematic errors that lead to conflicting results between the two methods (e.g., strong ferromagnets in the workspace).

[0223] One strategy will be based on coil sensitivity for positioning. This method utilizes each coil in the coil array.i Different spatial sensitivity distributions based on their location and orientation The fact is that, according to equation (3), a single oscillator then creates a response with a characteristic amplitude for each coil, which is determined by the dynamic dipole moment of the oscillator. Compared to The corresponding orientation is determined. For the reconstruction of sensor position and orientation, a set of forward functions given by equation (4) needs to be determined. Finally, the mapping between the position and orientation coordinates of the six markers of all receiving channels and the voltage amplitude at the fundamental frequency or higher harmonics is expected. The following equation describes how to eliminate the time dependence in equation (4) so ​​that only the amplitude needs to be considered. We do this by including all independent variables, i.e., the position vector and orientation vector Let's begin:

[0224]

[0225] The required coil sensitivity distribution can be calculated based on known coil geometry, measured at defined locations, and then interpolated, or determined by a combination of both (i.e., by fitting a model of the experimental results with appropriate fitting parameters). For magnetized oscillations, the oscillation frequency within the marker frame... and amplitude The explicit description will be

[0226]

[0227] The prime number indicator local marker framework uses a design for low oscillation amplitudes. The extension of trigonometric functions. Therefore, the time variation will be...

[0228]

[0229] The first term characterizes the fundamental frequency response, and the second term characterizes the second harmonic frequency response. A rotation matrix is ​​used. It can calculate the magnetization in a general orientation in space, i.e. Therefore, starting from (11), the voltage amplitudes for the fundamental frequency and the second harmonic frequency can be determined as follows:

[0230]

[0231] as well as

[0232]

[0233] Therefore, coil i The total voltage is

[0234]

[0235] The marker position and orientation can be calculated by solving the system of equations using a set of forward functions (14) and (15) and the measured response amplitude, based on a standard mathematical method. The accuracy of the solution will increase with the number of receiving coils and the orthogonality (i.e., the magnitude of the difference) between their corresponding coil sensitivities. The mismatch between six unknowns and more (or fewer) receiving channels can be considered by solving the system of equations in a least-squares sense.

[0236] Positioning can also be performed based on gradient field encoding. While coil sensitivity positioning is based on the amplitude distribution picked up by the coil array, the frequency of the marker can be manipulated to provide independent position information. This can be done, for example, by applying a low-frequency current to selected coils of the coil array to generate a non-uniform magnetic field with an ideal constant field gradient in the workspace. This additional field alters the recoverable field acting on the oscillating sphere. This alters the frequency (Equation 9). Due to the non-uniform nature of the field, the frequency variation will depend on the position and orientation of the marker. By sequentially applying several coding fields (e.g., field gradients applied on six different orientations), two of the three orientation parameters of the marker, as well as all three positions, can be determined. However, at the cost of higher field strengths required to generate sufficient higher-order contributions, the remaining angles can be deferred from the sensor's higher-order response to an external magnetic field. The basic coding concept involves gradient coding in MRI; therefore, frequency coding and phase coding can be performed.

[0237] For frequency coding, a non-uniform field is applied during signal readout to produce the desired frequency offset. For the desired spatial resolution, the applied coding field strength must be adapted to the frequency sensitivity of the tag and the frequency resolution passed by the system. Assuming the frequency sensitivity of an NdFeB tag with a sphere diameter of 0.5 mm is... Hz / mT, for a spatial resolution of mm and the assumed frequency resolution is The field gradient is approximately mHz.

[0238]

[0239] This will be necessary. The gradient intensity is approximately 100 times lower than that of a typical MRI system. Therefore, a dedicated water-cooled gradient coil is not required, but the coils of the transmit-receive array can be used for field generation.

[0240] For phase coding, a non-uniform coding field is applied before signal readout; that is, a position-dependent frequency offset is applied only within a short window during which a position-dependent signal phase offset is generated. When phase resolution is insufficient for accurate localization, the duration and / or amplitude of the phase coding pulses can be varied in sequential excitation to allow for the discrimination of ambiguities (greater than 2π) in phase accumulation. Thus, complete spatial information is obtained during multiple readouts. Phase coding with one non-uniform field pattern (e.g., coding one spatial axis) can be combined with frequency coding with another non-uniform field pattern (e.g., coding orthogonal spatial axes) for efficient localization. If a coarse marker location is already known from a sensitivity coding method (faster due to its parallel nature), a few phase coding steps that provide the missing high-resolution (high spatial frequency) components without providing complete spatial information are sufficient.

[0241] As described in this specification, the comparison between the localization result obtained using the gradient and the sensitivity encoding can be used to identify, for example, systematic errors caused by the background field. Furthermore, it should be noted that the linear response of sensors employing two suspended spheres to low-frequency external fields can be suppressed; in such cases, higher-order responses at those frequencies can be used for localization or integrity checks. However, the field sensitivity of these oscillators is much lower, necessitating a much larger gradient field for gradient field encoding.

[0242] The following describes the parameter determination and location determination for tightly coupled sensors.

[0243] Determining position (meaning three position and three orientation parameters) and measuring parameters (such as pressure or temperature) is particularly difficult when using only a few coils. However, using only a few coils is cost-effective and preferred in some applications due to space constraints. Therefore, it is desirable to modify the detection process and hardware to operate using only a few coils. One way to do this is by using several markers and / or sensors in a coupled manner. Coupling here means that several sensors / markers (each operating at a different known frequency) are combined in assembly with fixed relative orientations. Typically, the sensors are attached to a rigid frame, but technically, only the relative positions of the sensors / markers need to be known at the evaluation point in time. With enough sensors, position can be determined using only two coils. This is most readily apparent when compared to conventional electromagnetic navigation systems. These typically consist of several (usually more than six) transmitting coils and one receiving coil, which is positioned and its orientation is evaluated. However, due to the rotational symmetry of the coils, rotation of the coils about their axis (the axis of the dynamic dipole moment) cannot be detected. In this comparison, the rigidly coupled sensor array can be viewed as a transmitting array, and the individual transmit-receive coils as markers. Therefore, the sensor / marker array can be positioned somewhere on a loop around the dynamic dipole axis of the transmitting coil. Note that if the coil is not circular, the loop is not a perfect circle in space, but this does not change the independent variable point. Therefore, the position cannot be determined by a single coil, but the symmetry of the two coils (with non-parallel dynamic dipole moments) is broken, and the position and orientation of the sensor / marker array can be determined. Evaluation of different sensor signals is best accomplished using the complete modeling approach described elsewhere in this document. In short, this involves generating a model for each sensor / marker in the array in the form of differential equations. This model predicts the sensor response to a given excitation. Together with the transmit / receive system model (including amplifiers, filters, and coils), the overall response of the array can be predicted. Knowing past excitation pulses (typically only a few pulses with decay times are needed), the expected received signal and parameter values ​​for the sensor position can be calculated. Now, the sensor position / orientation and the physical parameters measured by the sensor are optimized to minimize the difference between the calculated and the actually received signal. Prior knowledge can also be incorporated into this process, namely, allowing only the maximum displacement velocity of the sensor relative to the coil. The only difference here from the previously described method is that the process is not performed for a single sensor, but for a group of coupled sensors in an array, or simultaneously for several arrays. For sensor arrays, there is also a set of prior knowledge available, namely the relative positions and orientations of the sensors / tags in the array. Employing a full-parameter method, or at least a zero-amplitude frequency extrapolation method, is particularly useful because it is difficult to make all the many sensors operate simultaneously at the desired amplitude.However, the full model approach is somewhat computationally intensive. To reduce the required computational power, it can be beneficial to first evaluate individual, already interpreted sensor / tag methods and use their results as starting points for the final full model-based location and value reconstruction.

[0244] Some calibration aspects will be explained below, with calibration first addressed in the presence of conductive and soft ferromagnetic materials.

[0245] The presence of conductive, particularly soft ferromagnetic, materials can interfere with positioning by distorting the field created by the oscillating magnet of the marker or sensor and / or by distorting the field generated by the transmitting coil(s). To a lesser extent, sensor readings can also be altered, especially when compensation for amplitude effects may reduce accuracy. Therefore, a calibration process for the field is desirable. Furthermore, it is preferable to also have measurements that identify potential field interference. Therefore, methods for detecting interference are discussed first. Typically, positioning systems use an array of transmitting / receiving coils. The coils can be separate transmitting-only and receiving-only coils, or the same coil can be used for both functions. In any case, in this configuration, one coil can transmit, while all other coils directly receive the transmitted signal. The received signal is compared to a stored reference value. If the actual received signal deviates too much from the stored value, some action is triggered, such as warning of inaccuracy, triggering a self-calibration process, or suggesting a calibration process involving user interaction, or a combination of these. It is also possible to transmit simultaneously with several coils. The transmitting pulse should contain multiple frequencies. This can be achieved by generating pulses or by using frequency scanning or some intermediate method, which is known in the literature. Frequency analysis is important because eddy currents operating on conductive structures are highly frequency-dependent. Therefore, a significant change could be the ratio of the received signal at two different frequencies exceeding a certain limit. This could also be significant if at least one spectral component changes a defined value. However, uniform variations across the entire spectrum can be attributed, for example, to gain changes in the receiving amplifier. Therefore, if the receiving amplifier is constructed, for example, in a way that the gain might change, this effect can be used to set a new gain value in software to compensate for that gain change. An argument is maintained in a similar manner if a gain change is expected in the transmitting amplifier rather than in the receiving path. Here, as a correction, the transmitting amplitude is changed in the computational model (leading to changes in the oscillation amplitude of the sensor, etc.). Theoretically, the impedance of a single coil can also be measured, and the change in impedance can be used as an indication of changes in the eddy current environment. However, the ability to measure impedance is not naturally inherent in electronic devices and requires specialized equipment. Not only can environmental changes in eddy currents be detected using coil coupling, but also known characteristics of sensors / tags within their operating range can be detected. In particular, sensors can be integrated into the transmitting / receiving coil array itself. Even a single sensor / tag is useful. For example, if a single marker is incorporated into a system at a fixed position relative to (multiple) coils, the change in the marker's response indicates a change in the eddy current environment. Even more advantageous is the incorporation of a sensor / marker sensitive to low-frequency magnetic fields, but insensitive to or barely sensitive to other potentially rapidly changing physical properties. This marker serves not only as an indicator of a static magnetic field but also as an indicator of the presence of ferromagnetic materials.To detect ferromagnetic materials, current is fed not only at the oscillation frequency of the sensor / tag, but also at a much lower frequency. This current feeding can be achieved by a single coil or by using several coils. If the measured sensor response (i.e., the frequency variation due to the applied low-frequency magnetic field) differs from the stored expectation, the ferromagnetic material is likely distorting the field. If sufficient coils are present in the system, it is not even necessary to place the field-dependent sensor / tag at a known location. With enough coils, the tag's location can be determined using the coil's sensitivity at the sensor / tag's oscillation frequency and independently by using the sensor / tag's sensitivity to a near-DC magnetic field (gradient field encoding). If the locations obtained by both methods diverge, the eddy current (or ferromagnetic) environment has changed. However, it is better to incorporate not just one such sensor into the system, but multiple such sensors. Having them in known locations is better than in unknown locations. However, it is also useful to know only some characteristics of the location, not the absence of location information. A practical way to achieve partial knowledge is to place the sensor / tag on a rigid structure that ensures a known and time-stable position and orientation relative to each other. This calibration “frame” with sensors / tags can be permanently or periodically placed within the operating body of the positioning system. If the positioning system finds a deviation from the expected relative position and orientation, the system is affected by eddy currents or ferromagnetic materials. Similarly, if the sensors / tags are also sensitive to near-DC magnetic fields and the coil array has sufficient coils, the relative positions of the sensors / tags can be determined independently at extremely low frequencies where only ferromagnetic materials interfere with the field and at the sensor / tag’s resonant frequency, where both ferromagnetism and eddy currents cause field distortion. Thus, if, for example, ferromagnetic materials contribute to the interference, information about the nature of the interfering object can be generated. Likewise, the best method for detecting interference is a complete mathematical model of the transmitting / receiving amplifier, coils, and (multiple) tags / (multiple) sensors. This model also includes known absolute and relative positions and orientations. In a first step, all positions / orientations and physical parameters are optimized in a manner that minimizes error. This step includes, for example, prior knowledge about the relative positions of fixed-position tags attached to the coil array and possible frames. As a side note, the “frame” does not have to be something introduced solely for calibration; rather, a set of tags consisting of many oscillators can act as a frame itself. In the second step, the total weighted error between the expected signal and the delivered signal is calculated. If the error exceeds a certain threshold, it is determined that some material is interfering with the field. Based on the nature of the error (i.e., whether it occurs on the AC-sensitive component or the DC-sensitive component), the nature of the interfering material can be deduced.

[0246] The last method to determine the existence of field interference is also a good starting point for methods to compensate for its effects. This method is most easily illustrated when it is assumed that there is a conductive material rather than a ferromagnetic material that induces eddy currents. When applying the model described above, we obtain the correct position from the evaluation of the near-DC correlated signal (gradient field encoding), but incorrect position and local field amplitude at the sensor frequency and its harmonics (coil sensitivity encoding). Therefore, we can distort the higher frequency field in a way that matches the expected result. After applying the distortion, all positions and sensor readings will be improved. It is advantageous not only to rely on position estimation based on the near-DC magnetic field, but also because AC sensitivity encoding is much faster. The most critical part of this compensation method is determining the correct model for distorting the AC field. A simple solution is, for example, to parameterize the field offset function using a simple 3D polynomial. This means using the field values ​​at the positions transformed by the 3D polynomial, instead of the actual field values ​​at the positions. This is computationally efficient, but may lack physical insight, and it is not obvious how measurements of coil coupling can be incorporated into this framework. Therefore, it is better to use a model that is closer to physical reality. For example, it is better to use a field model of the conductive plate near the coil system to induce the desired field distortion. Therefore, the position, angular thickness, and dimensions of some virtual plates are essentially changed until the model's expected and measured data match. How to simulate such conductive plates is well known in electromagnetic simulation literature. This type of modeling has the added advantage of easily incorporating the shapes of objects that might appear in a specific environment. Thus, if a particular device is brought close to the field of view, such as an X-ray C-arm, the device is known and can be modeled beforehand, requiring only optimization of the exact orientation and position via system software. Another advantage is that the system can display the hypothetical location of interfering objects or transmit data to a second system performing the display task. In this way, the user can be specifically pointed at the object interfering with the measurement, and the user can move or remove them if desired. During this process, the coupling data of the coils is essentially used as an array of metal detectors. The combination of ferromagnetic materials is conceptually the same as that of conductive materials that generate eddy currents. However, ferromagnetic material simulation is computationally slightly more intensive and may not produce precise locations due to the possible lack of a well-defined reference position defined by a dedicated marker. But again, it is best to model a set of ferromagnetic materials, such as sheets and rods, and place and deform them while simulating around the coil array. Here, providing a database of possible ferromagnetic objects would be highly beneficial for this model. Furthermore, the process of mutual coupling measurements can be enhanced by measuring harmonic generation in the coil environment. The presence of harmonics is a strong indication of soft ferromagnetic materials, and the measured signals provide valuable input regarding the size and location of the object.

[0247] The generation of excitation pulses will be described below.

[0248] The system preferably includes software for generating the timing and excitation pulse shape. The excitation pulse generator is preferably aware of the hardware's capabilities. Different types of amplifiers and possible filters exist. One type of amplifier is capable of generating current waveforms that follow a fairly arbitrary path. These are referred to herein as "analog amplifiers." Another type is only capable of increasing the current at a predetermined rate, decreasing the current at a similar rate, and keeping the current more or less constant. Essentially, these amplifiers apply a voltage with a positive or negative sign at the coil or act as a short circuit. These are referred to herein as "digital amplifiers." Digital amplifiers can have different switching speeds, i.e., the number of state changes allowed per unit time. If the switching speed is much higher than the oscillation speed, the digital amplifier again works like an analog amplifier. Therefore, this type of amplifier can conceptually be considered an analog amplifier. If the switching speed is only about the same as the marker / sensor oscillation frequency, the processing must be slightly different. However, this is a more difficult case, so all discussion will focus on this. This type of amplifier has several advantages over analog amplifiers. The main advantage is that the amplifier's efficiency is typically very high, and 98% efficiency is easily achieved. Another advantage is that it is very easy to interface with computing systems. A matching circuit can exist between the amplifier and the coil. The simplest matching circuit is simply a capacitor connected in series with the coil. Using a matching circuit, the maximum current through the coil increases for a given amplifier supply voltage. However, this matching circuit has the disadvantage of blocking low-frequency current. Some sequences may require low-frequency current. A solution to this problem can be twofold. First, a matching circuit that is transparent at both high and low frequencies can be provided. An example of such a circuit is a coil or coil-capacitor circuit connected in series with a first matching capacitor. Another approach is to have a switch that bypasses the matching circuit, and the switch closes when near-DC current is needed. If the resonant frequency is low enough, a capacitor can also be integrated in the bypass path. In the same way, multiple switches and capacitors can be used to provide a whole series of different matching frequencies. And note that even when the circuit is tuned near DC, some current at the marker / sensor resonant frequency is still available. It should be noted that DC current may not necessarily be used during readout. There are two main components to provide this capability. First, DC current must not interfere with the readout. This is indeed a problem if the transmitting and receiving coils are combined. A DC source can provide a short-circuit path for the signal. This situation must be avoided, and proper matching circuitry is necessary to prevent it. The matching circuit must introduce sufficiently high impedance between the coil and the DC source. This can be achieved by adding an additional coil in series with the inductance at the same level as the transmitting / receiving coil's inductance. If not needed, the inductance can have a parallel switch that shorts it. Many other solutions exist. The second situation is when the DC source does not introduce too much noise, i.e., current source noise does not prevent accurate measurements from the marker / sensor.This can be achieved through appropriate analog filtering in the case of DC transmission. This filtering can be bypassed by appropriate switches (e.g., MOSFET optocouplers) during AC transmission pulses. It may also be feasible to avoid switching in the DC source during signal reception and use only the slowly decaying current in the coil. It may also be feasible to perform only some switching during reception and cancel the received data only if the received data is corrupted. The DC field source can also be a completely isolated coil, or the field generator can be a (moving) permanent magnet. This avoids most problems. Another problem with the presence of DC current during signal reception is that the coil can provide a different environment for the sensor. This means, for example, that some coil can be shortened for AC current, and the AC field no longer penetrates the coil, thus changing the field value in nearby coils. This effect must be considered when calculating position and sensor values. Two main field elements interact with the sensor / tag. One is the approximate DC amplitude of the current, i.e., the averaged current value over a time interval on the order of 0.1 seconds (approximately 0.01 seconds to approximately 1 second). The other is the Fourier amplitude at the resonant frequency of the sensor / tag (as a complex value, since phase is important). Therefore, the first task is to map these two values ​​to the generation of the sequence.

[0249] The mapping of desired Fourier amplitude and current to specific time-domain pulse modes will be described below.

[0250] It is also useful to generate a software subsystem that performs this exact type of mapping; this subsystem is the software part that takes the desired near-DC current and the desired Fourier amplitude (and frequency) as input and generates a time-domain pulse sequence. It is also expected that this software returns information on whether the desired value can be achieved within the constraints imposed by the hardware, such as the maximum current of the coil or maximum heat or regulation limits, such as patient heat or peripheral nerve stimulation. Instead of simple yes / no information, information about the severity of undesirable side effects can be provided. This information can be provided for each individual transmit channel (per transmit coil). Another return value could be the actual best-fit output DC current and (multiple) Fourier amplitudes. The input can be not only a combination of frequency and Fourier amplitude, but also various Fourier amplitudes at different frequencies. The maximum length of the pulse sequence can also be a parameter input to this function. Internally, it works as follows: In the case of an analog amplifier, the first result can be generated simply by performing an inverse Fourier transform of the desired Fourier amplitude (and DC value) with respect to the desired transmit time. If the process results in a waveform that cannot be achieved due to certain limitations, it is reported back and can be scheduled into a scaled version for generation. Appropriate convolutions illustrate possible filter characteristics. If several switching filter states exist, all switching filter states can be tested, and the one with the lowest requirements for the amplifier can be selected. Note that several heuristics exist so that, for most cases, it is not necessary to evaluate all filter states. For example, if a better filter is available, a filter with a farther resonant frequency can be omitted. For digital amplifiers, the inverse Fourier transform (including filtering effects) provides a good starting point for optimization. In this first approximation step, the resulting peak in the time spectrum is approximated by two (or at most a few) ramps and a flat region in between. Thus, for example, a half-cycle of a sine wave starting from zero and ending at zero is approximated as: first a flat (zero) portion, then a ramp rising, then a flat portion, then a ramp falling, and finally a flat (zero) region. The timing of the different portions is arranged in a way that reaches approximately the same region. Following this first approximation is a second step, where the starting positions of the ramp and flat sections are shifted to achieve a best fit with the desired Fourier value. The best fit can be the least squares sum of the differences (complex numbers) between the desired and realized Fourier components. All commonly used optimization algorithms, such as gradient descent, can be used.

[0251] The mapping from the expected Fourier value at the sensor / marker to the current in the coil will be described below.

[0252] The next higher level of abstraction in the pulse generation process is the software part, which takes specific field Fourier values ​​and directions at a specific location as input and translates them into a requirement for the current in the coil. The evaluation algorithm typically provides some measurement of the sensor / tag's position and orientation. The position is not, and does not need to be, a position in 3D space. However, 3D position is the ideal case. For example, if only one coil exists, the field value in the sensitive direction can be determined only at the sensor. However, this also translates to some virtual position and orientation in 3D space. Therefore, these cases do not require special processing in the software. The translation of the requirement for the coil current is a result of the optimization process. There exists a model that calculates the Fourier field components at a specific spatial location from the current in the coil. This is the basis for optimization, where the Fourier components of the coil current are optimized in a way that generates the desired field components. Often, there is no explicit way to form the desired field from the coil current. There may also be cases where the desired current is incompatible with the limitations of the hardware system. The lower-level software returns values ​​describing the negative impact, and the software uses this information to optimize the current. The goal of optimization is to achieve a good trade-off between the Fourier field components obtained at the sensor / tag and the negative impact. This means that the deviation from the desired field and its side effects are combined into a number, and for that number, a standard optimization algorithm is used to find its maximum or minimum value. This combination of numbers can be a weighted sum of squares. Naturally, for this entity, a large number of working mathematical combinations can be found. Finally, this part of the program returns the field and mass values ​​obtained at the location to the calling program (a higher-level program) for its optimization.

[0253] The generation of the desired field Fourier values ​​for the marker / sensor will be described below.

[0254] At this abstraction layer, the software system actually handles the measurements that need to be performed. Therefore, the input to this program is what needs to be measured accurately and quickly. These requirements depend on the specific application using the sensors / tags and are therefore not part of this document. The requirements can vary considerably. For example, if only a single sensor is involved, the requirement might be, say, to measure a single quantity as accurately as possible every 0.1 seconds. If the application is a tracking solution with multiple coupled tags, the desired result might be, say, a position update of the entire tag assembly every 0.1 seconds, regardless of which tag / sensor contributes to the signal (based on coil sensitivity), and an independent position check using a gradient method every 1 second. The program also has access to the current state of the sensors / tags (position / oscillation parameters, etc.) and the simulation model described elsewhere in this document. From this, the optimal excitation field Fourier values, including the orientation of each sensor / tag, can be calculated. These parameters can be passed to the lower software level described earlier (with the desired execution somewhere later) to ultimately generate a current. In the case of a single sensor, this will work immediately, and the plan can be written to a hardware output buffer. However, for example, to track tag assembly, there may not be a pulse shape that perfectly excites all individual sensors / tags. In particular, the phase will not fit all individual sensors / tags. Therefore, the software may have to try to concentrate the optimal excitation on only a subset of the existing sensors / tags and try to find a solution that gives a working pulse sequence. This is the general working principle of the software optimization. It attempts to change the desired excitation of various sensors and concentrate on a few sensors to still obtain the desired result. The conceptually simplest approach is to go through all possible subsets of sensors / tags and check which subset of excitation gives the best information about the desired parameters. Since there may be many subsets, the program needs to add some heuristics to reduce complexity. For example, if a given tag / sensor is excited and these tags / sensors can always be grouped together, it can be observed first that other tags / sensors are also excited. If a suitable solution is found, it can be written to the output buffer. Depending on the hardware implementation, the inclusion of near-DC magnetic fields may require additional logic. If the hardware is capable of applying a DC magnetic field while recording the signal, the software does not need to do anything very special except apply one or a few gradients during readout. However, if the DC gradient and readout are incompatible, additional optimization steps are required to generate the correct DC field or gradient at some point between excitation pulses. The optimized logic remains the same. Parameters are varied until the simulation predicts measurements that are good enough for the application.

[0255] The generation of the startup sequence will be described below.

[0256] Algorithms typically assume considerable knowledge about the sensors available for sequence optimization. This knowledge is usually not fully available at the beginning of the sequence. For example, the number of sensors / tags that should be present in the application and the frequency range are known. However, the exact frequencies and locations are unknown. Therefore, a special start-up sequence is needed that attempts to find all possible sensors at all possible locations. The simplest possible start-up sequence is as follows: The workpiece is divided into a spatial 3D or abstract grid. An abstract grid is used when there are not enough coils for full 3D encoding. Each spatial point is divided into different orientations. The procedure passes through each location and each angle at that location, applying the highest transmission power for a given frequency and preset transmission time. The system then records the potential signals from the sensors / tags. Typically, a single transmission pulse excites not only one tag but also many other tags simultaneously. However, this process ensures that even the sensor / tag with the weakest possible signal will be detected. An optional next step is to excite each sensor individually with different amplitudes. This allows the extraction of nonlinear properties. Another optional step is to excite each sensor / tag in the presence of a DC field, or to measure the signal phase (again in various directions) after the DC field, to determine the sensitivity of the sensor / tag to the DC magnetic field. These basic processes can be greatly accelerated by using some knowledge about the system. For example, it is possible that if distant bodies have already been searched for the sensors / tags, many or all of the closer bodies will receive the highest possible amplitude, at least for some angles. Therefore, only a few remaining parameters need to be applied for the closer bodies. The same logic can be used to evaluate the nonlinear characteristics of the sensors / tags or their response to a DC magnetic field.

[0257] The strategy for high temporal resolution measurements will be explained below.

[0258] For many applications, high time resolution is desirable. One example is the measurement of intracatheter pressure modulated by a heartbeat cycle, which can reach frequencies up to 200 beats per minute in the human body. To determine the minimum and maximum pressure during a heartbeat cycle, a minimum measurement frequency of approximately 5 Hz is required, preferably higher than 10 Hz-20 Hz, and most preferably higher than 40 Hz. On the other hand, for a good signal-to-noise ratio, the oscillator needs a very high Q factor. A high Q factor means slow decay. Therefore, when the next measurement pulse is sent to the sensor, oscillations from the previous measurement pulse are not completely eliminated, and they will affect the measurement.

[0259] Therefore, a strategy for achieving high time resolution using a magnetomechanical oscillator is needed for positioning and parameter determination. The simplest method for high time resolution is to simply reduce the repetition time. The repetition time refers to the period between subsequent excitation pulses. After each excitation pulse, the frequency and amplitude are determined, from which physical values ​​and position can be calculated, as described elsewhere. However, the quality factor of sensors / tags tends to be relatively high, and the oscillation amplitude does not decrease significantly with the next excitation pulse. To always obtain the desired sensor / tag excitation, the phase of the next excitation must be considered. Typically, we want "in-phase excitation," i.e., excitation in the manner in which the sensor / tag receives energy from the beginning of the excitation pulse. How to optimize timing is described elsewhere. In-phase excitation minimizes the transmitted energy and therefore keeps the excitation pulse length to a minimum. This increases the overall signal-to-noise ratio.

[0260] High repetition rates have several drawbacks. First, the system typically cannot receive values ​​during and shortly after the excitation pulse, and therefore the signal-to-noise ratio may not be optimal. Second, each transmitted pulse destroys some knowledge about the phase of the sensor oscillation. Phase information survives to some extent only if the excitation pulse and sensor orientation remain strictly controlled and precisely known, which is a technical challenge. Phase information over longer time intervals can be useful because information about the average frequency (and therefore the average physical quantity) is encoded within it. When evaluating double-length intervals, the measurement of the average physical quantity is much more accurate than evaluating only the first and second halves independently and averaging the two results. Therefore, it may be worthwhile to extract more than one measurement from a single signal pulse, rather than having as many excitation pulses as measurements. This can be easily done by dividing the signal into several sub-parts and evaluating each sub-part individually. This simple approach does not account for the improved measurement quality when using longer datasets. To address this, the dataset can be divided into a hierarchical structure of subsets, and each subset within each hierarchy can be evaluated, with the average value scaled to match the longer dataset. Therefore, a dataset (an undisturbed decaying signal) is first evaluated as a whole. It is then split into two, and each split is evaluated separately. The same number is then added to each result so that their mean matches the mean of the entire dataset. This process can be repeated to have subsets of 4, 8, etc., in the end. This method can be mathematically refined to be an evaluation based on a complete model. To do this, a model of the evolution of physical parameters (and possibly the spatial movement of the sensor) is generated. This model can be a polynomial of some degree or some other suitable mathematical function. This function should describe the physical properties of the measured quantity in a way that requires only a small number of parameters. Thus, for example, when the parameter is blood pressure, the model could be a better Fourier series, as this describes the pressure wave form of the heartbeat better than a polynomial. The parameters are then varied to match the measurement dataset as well as possible. If discrete measurement points are needed at the end, they can be simply stacked using the model's output for some time points.

[0261] It should be noted that even though the diffusion barrier layer is not shown in all the figures for clarity, all described embodiments include a diffusion barrier layer that covers at least a portion of the housing and is configured to maintain a predetermined pressure within the housing. The configuration of the pressure sensor allows temperature compensation for providing the resonant frequency to also be applied in any of the described embodiments.

[0262] By studying the accompanying drawings, this disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments in practicing the claimed invention.

[0263] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0264] A single unit or device can perform the functions of several items recited in the claims. The fact that certain measures are recited in mutually different dependent claims does not indicate that combinations of these measures cannot be used advantageously.

[0265] Functions such as determining the resonant frequency based on the inductive signal, determining the pressure based on the resonant frequency, and determining the calibration curve performed by one or more units or devices can also be performed by any other number of units or devices. The control of the detection system can be implemented as program code components of a computer program and / or dedicated hardware.

[0266] Computer programs can be stored / distributed on suitable media, such as optical storage media or solid-state media, provided with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0267] Any reference numerals in the claims should not be construed as limiting the scope.

[0268] This invention relates to a passive pressure sensor for introduction into the human circulatory system and for wireless reading by an external reading system. The pressure sensor includes a housing and a magnetomechanical oscillator. The housing has a diffusion barrier layer for maintaining a predetermined pressure within the housing, and the magnetomechanical oscillator has a magnetic object providing a permanent magnetic moment. The magnetomechanical oscillator converts an external magnetic or electromagnetic excitation field into mechanical oscillations of the magnetic object, wherein at least a portion of the housing is flexible to allow changes in external pressure to be converted into changes in the mechanical oscillations of the magnetic object. The pressure sensor can be very small while still providing high-quality pressure sensing.

Claims

1. A pressure sensor for introduction into the human circulatory system, The pressure sensor is a passive sensor configured to be read wirelessly by a reading system placed outside the human body. The pressure sensor further includes a housing, the housing including a diffusion barrier layer that covers at least a portion of the housing and is configured to maintain a predetermined pressure within the housing; The pressure sensor further includes a magnetomechanical oscillator comprising a magnetic object that provides a permanent magnetic moment within the housing, wherein the magnetomechanical oscillator is configured to convert an external magnetic or electromagnetic excitation field into mechanical oscillations of the magnetic object. At least a portion of the housing is flexible to allow changes in external pressure to be converted into changes in the mechanical oscillations of the magnetic object. The magnetic object is arranged within the housing such that if the external magnetic or electromagnetic excitation field acts positively on the magnetic object, the magnetic object is rotatable away from its equilibrium orientation. The pressure sensor further includes: A restoring torque unit includes another magnetic object that generates a magnetic field at the location of the magnetic object, such that the restoring torque unit provides a restoring torque, wherein the restoring torque unit is adapted to provide a restoring torque to force the magnetic object back to the equilibrium orientation. The pressure sensor is configured such that changes in external pressure are converted into changes in resonant frequency.

2. The pressure sensor as defined in claim 1, wherein the flexible portion of the housing includes a bellows for allowing the external pressure change to be converted into a change in the amplitude or resonant frequency of the mechanical oscillation of at least the magnetic object.

3. The pressure sensor as defined in claim 2, wherein the pressure sensor further includes an outer cover above the bellows.

4. The pressure sensor as defined in any of the preceding claims, wherein the diffusion barrier layer comprises a metal.

5. The pressure sensor as defined in any one of claims 1-3, wherein the pressure sensor includes an external wire cage attached to the outside of the housing for allowing the outside of the housing to maintain a distance from the blood vessel wall.

6. The pressure sensor as defined in any one of claims 1-3, wherein the inner surface of the magnetic object and / or the housing is coated with a smooth, non-stick material.

7. The pressure sensor as defined in any one of claims 1-3, wherein the pressure sensor is configured such that the magnetic object can be aligned with an external magnetic field, regardless of the position and orientation of the pressure sensor in the external magnetic field.

8. The pressure sensor as defined in claim 7, wherein the pressure sensor includes an outer housing surrounding the housing, wherein the housing is rotatable within the outer housing, and wherein the pressure sensor is configured such that external pressure changes outside the outer housing are transmitted to external pressure changes outside the housing and inside the outer housing.

9. The pressure sensor as defined in any one of claims 7 and 8, wherein the magnetic object is a magnetic sphere attached to one end of a filament, wherein The other end of the filament is attached to the interior of the housing, wherein the filament has a length of at least π / 4 of the diameter of the magnetic sphere, or The other end of the filament is attached to a length-changing unit configured to allow the length of the filament to be changed and attached to the interior of the housing.

10. The pressure sensor as defined in any one of claims 1-3, wherein the pressure sensor is configured to compensate for the temperature dependence of the resonant frequency.

11. The pressure sensor as defined in claim 10, wherein the pressure sensor includes a compensation element adapted to modify the resonant frequency in a first frequency direction depending on a temperature change, the first frequency direction being opposite to a second frequency direction, and if the compensation element is not part of the pressure sensor, then the resonant frequency of the pressure sensor is modified in the second frequency direction depending on the temperature change.

12. An implantable medical device comprising a pressure sensor device as defined in any one of claims 1 to 11, wherein the implantable medical device is selected from one of the following: a liver shunt device, a suture for treating a cerebral aneurysm, an artificial heart valve, or a stent.

13. A reading system for wirelessly reading a pressure sensor as defined in any one of claims 1 to 11, wherein the reading system comprises: A field generator is used to generate a magnetic or electromagnetic excitation field, which is used to sense the mechanical oscillations of the magnetic object of the pressure sensor. - A transducer for converting the magnetic or electromagnetic field generated by the mechanical oscillations induced by the magnetic object of the pressure sensor into an electrical response signal. - A processor for determining a pressure value based on the electrical response signal, wherein the processor is configured to apply a compensation algorithm to correct the determination of the pressure value for dependence of the electrical response signal on at least one of the following: a) The distance between the pressure sensor and the field generator; b) The phase of the mechanical oscillation of the magnetic object; c) The orientation of the housing relative to the reading system; as well as d) The amplitude of the mechanical oscillation of the magnetic object.

14. A pressure measurement method for performing the measurement using a pressure sensor as defined in any one of claims 1 to 11. The pressure measurement method mentioned above includes: - Generate a magnetic or electromagnetic excitation field to sense the mechanical oscillations of the magnetic object of the pressure sensor; - Convert the magnetic or electromagnetic field generated by the mechanical oscillation induced by the magnetic object of the pressure sensor into an electrical response signal; - Determine the pressure value based on the electrical response signal, wherein in the determination step, the pressure value is corrected for the dependence of the electrical response signal on at least one of the following: a) The distance between the pressure sensor and the field generator; b) The phase of the mechanical oscillation of the magnetic object; c) The orientation of the housing relative to the reading system; as well as d) The amplitude of the mechanical oscillation of the magnetic object.

15. A non-transient medium comprising a computer program, the computer program including program code components for causing the reading system (1501) as defined in claim 13 to perform the steps of the pressure measurement method as defined in claim 14 when the computer program is run on a computer controlling the reading system (1501).

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