Location and orientation identification system in an electromagnetic field

Abstract

A navigation system for navigating within a magnetic field, including a catheter with a head that is moved through the magnetic field by moving a handle of the catheter; the head includes one or more pairs of magnetic sensors; wherein the magnetic sensors are solid-state sensors that measure an electrical signal indicating a three dimensional intensity of the magnetic field at the location of the magnetic sensor; wherein each pair of magnetic sensors are rigidly connected together with a fixed displacement; and wherein the measurements of the magnetic sensors of each pair are processed together with details of the fixed displacement between the magnetic sensors of the pair to determine the location and the angular orientation of the pair of magnetic sensors.

Description

[0001] LOCATION AND ORIENTATION IDENTIFICATION SYSTEM IN AN

[0002] ELECTROMAGNETIC FIELD

[0003] RELATED APPLICATIONS

[0004] This application claims priority from US provisional application No: 63 / 524,930 dated July 5, 2023, the disclosure of which is incorporated herein by reference.

[0005] FIELD OF THE DISCLOSURE

[0006] The present disclosure relates to a system and method of location and orientation identification in an electromagnetic field and more specifically to identifying the location and orientation of a catheter head while navigating through the electromagnetic field.

[0007] BACKGROUND OF THE DISCLOSURE

[0008] A borescope is an optical instrument designed to assist visual inspection of narrow, difficult-to-reach cavities. Borescopes are used for visual inspection work where the target area is inaccessible by other means, or where accessibility may require destructive, time consuming and / or expensive dismounting activities. Borescopes are commonly used in the visual inspection of aircraft engines, aeroderivative industrial gas turbines, steam turbines, diesel engines, and automotive and truck engines. The navigation of the borescope may be largely based on visual and optical means; hence, the use of the borescope may be limited in cases where the optical means cannot be relied upon such as navigation in a thick liquid environment. For medical use, similar instruments are called endoscopes.

[0009] In order to perform a variety of medical interventions, a catheter is inserted into the patient's body while monitoring its location. Furthermore, in many medical procedures such as heart ablation or biopsy, the catheter is guided through narrow internal body organs and is directed towards a target location. Monitoring the catheter location imprecisely may lead to carrying out the medical intervention in the wrong place, rendering it to be useless or even harmful.

[0010] A known method of locating the catheter is utilizing sensors located on the catheter which measure magnetic fields generated by one or more generators placed outside the body of the patient. In order to identify the location of the catheter tip with sufficient accuracy a number of generators and / or a number of magnetic sensors must be used due to the effect of the angles and distances of each of the sensors relative to the generators. Adding to this complexity is the need for a separate array of sensors and generators for detecting a contact, (touch), of the catheter with the target organ, in addition to the above-mentioned sensors and generators used for the navigation of the catheter.

[0011] Accurate and rapid identification of the location and orientation of the catheter in real time is beneficial to medical procedures and other fields, therefore improvement in the speed and accuracy of the current available systems is desirable.

[0012] SUMMARY OF THE DISCLOSURE

[0013] An aspect of an embodiment of the disclosure, relates to a system and method for navigating within a magnetic field with a catheter. The catheter includes one or more pairs of magnetic sensors, which are solid state sensors that are rigidly connected together with a fixed displacement. The measurements of the magnetic sensors of each pair are processed together with details of the displacement between the magnetic sensors to determine the location and angular orientation of the pair of magnetic sensors.

[0014] There is thus provided according to an embodiment of the disclosure, A navigation system for navigating within a magnetic field, comprising:

[0015] A catheter with a head that is moved through the magnetic field by moving a handle of the catheter;

[0016] The head comprises one or more pairs of magnetic sensors; wherein the magnetic sensors are solid-state sensors that measure an electrical signal indicating a three dimensional intensity of the magnetic field at the location of the magnetic sensor;

[0017] Wherein each pair of magnetic sensors are rigidly connected together with a fixed displacement; and

[0018] Wherein the measurements of the magnetic sensors of each pair are processed together with details of the fixed displacement between the magnetic sensors of the pair to determine the location and the angular orientation of the pair of magnetic sensors.

[0019] In an embodiment of the disclosure, the navigation system functions with a DC and / or time constant magnetic field. Optionally, the system forms images of the path followed by the head of the catheter based on data from a CT of a user, information of a form of the magnetic field, and the measurements of the magnetic sensors. In an embodiment of the disclosure, the head comprises multiple pairs identifying curvature of the cavity while the catheter is held stationary. Optionally, a rotation sensor that comprises an accelerometer or gyroscope is connected to one of the pairs of magnetic sensors. In an embodiment of the disclosure, a touch sensor that comprises a single magnetic sensor or a pair of magnetic sensors is connected by a spring or flexible member to a last pair of magnetic sensors along an elongated axis of the head; wherein the touch sensor tilts when coming into contact with an obstacle in the path of the catheter head. Optionally, the head comprises multiple pairs and the measurements of each pair are given a different weight for being considered in determining the location or curve of the catheter head. In an embodiment of the disclosure, the weights are location dependent or time dependent. In an embodiment of the disclosure, the pairs are connected in parallel over a common cable. Optionally, each pair has a unique address to be addressed for transferring measurements. In an embodiment of the disclosure, specific pairs deliver measurements more frequently than other pairs.

[0020] There is further provided according to an embodiment of the disclosure, a method of navigating within a magnetic field with a navigation system, comprising:

[0021] Moving a handle of a catheter that moves a head through the magnetic field; wherein the head comprises one or more pairs of magnetic sensors that are solid state sensors; Wherein each pair of magnetic sensors are rigidly connected together with a fixed displacement;

[0022] Measuring an electrical signal indicating a three dimensional intensity of the magnetic field at the location of the magnetic sensor; and

[0023] Processing the measurements of the magnetic sensors of each pair together with details of the fixed displacement between the magnetic sensors of the pair to determine the location and the angular orientation of the pair of magnetic sensors.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present disclosure will be understood and better appreciated from the following detailed description taken in conjunction with the drawings. Identical structures, elements or parts, which appear in more than one figure, are generally labeled with the same or similar number in all the figures in which they appear, wherein:

[0026] Fig. 1 is a schematic illustration of a system, according to an embodiment of the disclosure;

[0027] Fig. 2 A is a schematic illustration of parts of the system, including a tip sensor, according to an embodiment of the disclosure;

[0028] Fig. 2B is a schematic illustration of parts of the system, including a tip sensor in contact with an object, according to an embodiment of the disclosure;

[0029] Fig. 3 is a schematic illustration of an array for generator calibration, according to an embodiment of the disclosure;

[0030] Fig. 4 is a schematic illustration of final calibration, according to an embodiment of the disclosure;

[0031] Fig. 5 A is a schematic illustration of various components of a system for detecting and mapping objects and navigation of an elongated flexible part through a curved cavity, according to an embodiment of the disclosure;

[0032] FIG. 5B is a schematic illustration of a capsule and a flexible cap, according to an embodiment of the disclosure;

[0033] FIG. 6 is a schematic flowchart showing an overview of stages, according to an embodiment of the disclosure;

[0034] Fig. 7 A is a schematic illustration of a cable for supplying power and communication during production, according to an embodiment of the disclosure; Fig. 7B is a schematic illustration of a cable for supplying power, communications with sensors attached, according to an embodiment of the disclosure;

[0035] Fig. 8 is a schematic illustration of a navigation system using a catheter, according to an embodiment of the disclosure;

[0036] Fig. 9 is a schematic illustration of a catheter head, according to an embodiment of the disclosure;

[0037] Fig. 10 is a schematic illustration of degrees of freedom identified for a pair of sensors, according to an embodiment of the disclosure; and

[0038] Fig. 11 is a schematic illustration of a process of preparing a catheter head, according to an embodiment of the disclosure.

[0039] DETAILED DESCRIPTION

[0040] The specific details of the single embodiment or variety of embodiments described herein are to the described system and methods of use. Any specific details of the embodiments are used for demonstration purposes only, and no unnecessary limitations or inferences are to be understood thereon. Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of components and procedures related to the system. Accordingly, components have been represented, where appropriate in the drawings, showing only those details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

[0041] Fig. 8 is a schematic illustration of a navigation system 800 using a catheter 850, according to an embodiment of the disclosure. In an embodiment of the disclosure, the navigation system 800 includes a treatment surface 805 on which a patient is positioned to be treated by a medical practitioner. Optionally, an electromagnetic field generator 830 is located below the treatment surface 805 to form a predefined electromagnetic field 840 in an examination volume 860 above the treatment surface 805, generally enclosing a part of the patient’s body. In an embodiment of the disclosure, the practitioner inserts a catheter 850 with a head 852 that includes one or more pairs 920 (see Fig. 9) of rigidly connected magnetic sensors 922 to identify the location and orientation of each pair of magnetic sensors on the head 852 within the electromagnetic field 840. Optionally, measurements from the sensors 922 are transferred to a handle 854 of the catheter 850, for example by a cable 960 or wirelessly. The measurements are then transmitted from the handle 854 by a cable or wirelessly to a computer 810 that processes the measurements with a software application 820.

[0042] In an embodiment of the disclosure, the computer 810 is provided with data from a computed tomography scan (CT) of the body of the patient that is being examined and details of the form of the generated electromagnetic field 840 within the examination volume 860 (e.g., an electromagnetic field B as a function of position and / or time). The computer 810 combines the processed measurements with the structure of the electromagnetic field 840 and the CT data to construct realtime images 875 of the catheter head 852 within organs of the patient’s body. Optionally, the images 875 are shown on a display 870 that is connected to the computer 810, so that the practitioner can accurately identify the location and orientation of the catheter head 852 in vivo.

[0043] Fig. 9 is a schematic illustration of a catheter head 852, according to an embodiment of the disclosure. Optionally, the catheter head 852 includes one or more pairs 920 of rigidly attached magnetic sensors 922. The head may be enclosed in a protective flexible enclosure 980A (e.g., a bio-compatible flexible sleeve) to protect the sensors 922 located within the catheter head 852 from surrounding fluids or to prevent direct collisions with other objects that may damage the sensors 922. In an embodiment of the disclosure the magnetic sensors 922 are solid-state sensors and not coils. The solid-state sensors provide a digital electronic signal to convey 3 dimensional (3D) measurements of the magnetic field 840 at the locations of the sensors 922. Each pair 920 includes two sensors 922 that are coupled together with a rigid connection 924, so that the displacement (e.g., distance and orientation) relative to each other is constant. Optionally, the distance between the two magnetic sensors 922 in a pair 920 is between 0.05 to 5 mm. A 3D solid-state magnetic sensor 922 is more accurate than a coil since it generally has a smaller signal to noise ratio. Typically, two sets of 3D coils positioned by a rigid connector at a small, fixed distance from each other may not be able to differentiate between their measurements due to the accuracy of the measurements. In contrast solid-state magnetic sensors can differentiate between the measurements of a pair of sensors even at a distance smaller than 1 mm, for example 0.05 mm.

[0044] As explained below the measurements from two rigidly attached magnetic sensors 922 provide 6 degrees of freedom and enable determination of the location (e.g., X, Y, Z coordinates 1010 - Fig. 10) and angular orientation (yaw, roll, pitch or (forward, backward), (left, right), (up, down)) 1020 - Fig. 10) of the sensors 922 of pair 920 relative to the electromagnetic field 840 in the examination volume 860. A single magnetic sensor 922 or two magnetic sensors 922 without rigid displacement information would not provide enough information to calculate both the location and orientation of the magnetic sensors 922. The above determination of the location and orientation is true regardless of the type of electromagnetic field 840 used and number of generators. Optionally, electromagnetic field 840 may be generated by a single magnetic generator 830 or multiple magnetic generators 830 and may be a DC magnetic field, a time constant / steady magnetic field or an AC time varying magnetic field. The location and orientation of the pair 920 can be determined as long as the form of the electromagnetic field 840 in the examination volume 860 is known as a function of location and time. In an embodiment of the disclosure, a DC or time constant / steady electromagnetic field will simplify the calculations since the magnetic field vector at each point is less complex.

[0045] It should be noted that solid state magnetic sensors 922 respond more rapidly and more accurately than coils, which require a lot of time to provide a measurement for a point in space. The measurements provided by the pairs 920 are used by application 820 to identify the location and orientation of one or more points of catheter head 852 within the magnetic field 840 and optionally, within the body of the patient (e.g., by being combined with the information from the CT).

[0046] In an embodiment of the disclosure, each sensor 922 may be a packaged MEMS sensor and / or each pair may serve as a combined MEMS sensor, for example each pair 920 may be provided as a packaged chip 926 with a pair of rigidly attached magnetic sensors 922 and optionally, may include other sensors to enhance accuracy of the measurements. Optionally, the catheter head 852 may include multiple pairs 920 (e.g., 2-20) that are connected together on a flexible cable 960. Thus the multiple pairs 920 of the catheter head 920 move together along axis 950 but can curve / rotate relative to each other within a cavity of the patient and simultaneously or sequentially provide multiple measurement points identifying the shape of the cavity. For example identifying curvature of the cavity while the catheter is held stationary. In contrast when using a single pair 920 the curvature is determined only by moving the catheter 850forward or backward within the cavity.

[0047] In an embodiment of the disclosure, a rotation sensor 910 is connected to a first pair 920 or to one of the pairs to provide an indication or enhance determining rotation or motion of the cable 960 with all of the pairs 920 in head 852. Optionally, the rotation sensor 910 may include an accelerometer, gyroscope, IMU, MEMS or other sensors to enhance the accuracy of the measurements. The rotation sensor may identify the motion or rotation of the entire catheter.

[0048] In an embodiment of the disclosure, a last pair 920 is connected by a spring 930 or flexible member to a touch sensor 940, which comprises a single magnetic sensor 922 or a pair 920. The touch sensor 940 is enclosed by the flexible enclosure protecting the head 852 and is configured to tilt when coming into contact with obstacles. The touch sensor 940 serves as a tip of the catheter head 852 / catheter 850 and may be enclosed by an independent enclosure 980B, which may be more flexible than enclosure 980A, which protects the rest of the head 852, to enable increased flexibility of touch sensor 940.

[0049] Thus when advancing within a cavity of the patient the touch sensor 940 generally leads along an elongated axis 950 of the catheter head 852. When the touch sensor 940 comes in contact with an obstacle, the touch sensor 940 will tilt relative to the last pair 920 that it is coupled to with spring 930. The measurements of the touch sensor 940 relative to the measurements of the last pair 920 provide an indication if the catheter head 852 has encountered an obstacle (e.g., reaching the end of a path and tilting 90 degrees or more) or if the catheter head 852 is merely curving within a cavity (e.g., the natural curvature of an artery). Optionally, a tilt angle 955 relative to elongated axis 950 can be determined from the measurements of touch sensor 940 and the measurements of the pair 920, which the touch sensor 940 is connected to.

[0050] In an embodiment of the disclosure, each pair 920 is wired independently via cable 960 to handle 854. Thus the magnetic sensors 922 and / or pairs 920 may be sampled simultaneously or by a time distribution scheme (e.g., with a time based multiplexor), for example sampling each pair 10-20 times a second. Alternatively, all the pairs 920 may be connected in parallel over a common wire. Optionally, each pair may have a unique address so that the handle 854 can address a specific pair to receive measurements. For example, each pair may deliver measurements 10-20 times a second. Alternatively, specific pairs 920 may deliver measurements more frequently than others, for example the first and last pairs may be sampled more frequently than others to set up boundaries of head 852 in the constructed images 875. In some embodiments of the disclosure, the measurements of some pairs 920 may be given more weight in calculating the locations, interpolating a curve or forming image 875. The weights may be set based on the intensity, signal to noise ratio, time of sampling or stability of the magnetic field in the vicinity of the pair 920. These parameters may be determined by knowledge of the form of the generated magnetic field 840 or empirical measurements. Optionally, the weights may be time dependent or location dependent. For example, points that are closer to the electromagnetic field generator 830 may be given more weight than points that are further away. Likewise points that are more current may be given more weight than points that are less current.

[0051] In some embodiments of the disclosure, different magnetic sensors 922 of a pair 920 are given different weights based on location or time as described above. Alternatively or additionally, magnetic sensor 922 may include additional sensors (e.g., an MEMS sensor that measures a magnetic field and acceleration). Optionally, the different sensors at a given location may be given different weights.

[0052] Fig. 11 is a schematic illustration of a process of preparing a catheter head 852, according to an embodiment of the disclosure. This process produces a flat cable 960 with a miniature catheter head 852.

[0053] Initially a wire, for example with 4 tendons (e.g., 4 independent wires), is flattened (1110) with a press or other means to form flat wires. The wires are combined (1120) to a single reel with a pre-defined space between the 4 flat wires. In an embodiment of the disclosure, the wires are coated (1130) with a plastic or polymer layer or other protective material. The coating is removed (1140) at predefined locations, (e.g., by laser or heating device). A manufacturing robot (e.g., a pick and paste robot) uses soldering paste to prepare locations for coupling between the cable 960 and the components (e.g. chip package 926 for pair 920, magnetic sensor 922, rotation sensor 910 or touch sensor 940). In an embodiment of the disclosure, the manufacturing robot places (1150) the components at the predefined locations and connects them (1160), for example solders them via reflow, laser heating or other means. The components may be coupled to a single tendon or to multiple tendons (e.g., 2, 3 or 4 wires). Optionally, the components may be square or rectangular and are connected in the direction of axis 950 or they may form an angle relative to axis 950 as shown in (1160). In some embodiments a component may be connected to two or more non-adjacent tendons. Optionally, the end of the cable 960 with the components is coated with a flexible enclosure 980A and 980B to form a catheter head 852 that protects the components and connection points from environmental factors and / or for biomedical applications. Optionally, the tip of the head is enclosed by a more flexible enclosure 980B than the rest of the head 852.

[0054] In some embodiments of the disclosure, the catheter 850 includes multiple pairs 920 of magnetic sensors 922 along a large portion of the catheter 850 to enhance the ability to track the entire catheter 850. Optionally, the head 852 as depicted in Fig. 9 is then considered to extend along a large portion of the catheter 850, for example until the handle 854.

[0055] In an embodiment of the disclosure, the electromagnetic field is generally not uniform and each electromagnetic field generator 830 provides a different field, for example represented by a vector B. Therefore, the form of the electromagnetic field represented by vector B is initially calibrated to provide application 820 with a correct function to represent each point in the field represented by vector B, so that the measurements of the magnetic sensors will be processed correctly. In some embodiments, the electromagnetic field formed by the generator is calibrated by the generator manufacturer. Alternatively or additionally, calibration may be updated locally at the client to take into consideration the influence of local magnetic fields, for example from other equipment in the vicinity.

[0056] In an embodiment of the disclosure, application 820 for constructing real-time images based on the electromagnetic field 840, CT and measurements of magnetic sensors 922 may be stored on a non-transitory storage medium, such as a DVD, CD, external USB disk, disk-on key or other storage medium. The medium may be provided to a general-purpose computer to be executed to serve as computer 810 to form images 875 as described above.

[0057] Exemplary embodiments:

[0058] System 100 according to some embodiments of the present disclosure is depicted schematically in Fig. 1 including a magnetic field generator 110; two fixed magnetic field sensors 120, each of them measures a vector along at least three axes of magnetic field 130 generated by generator 110; rigid connection 140 between fixed sensors 120; and positioning calculation module 150 receiving input 160 from fixed sensors 120.

[0059] Some embodiments of the disclosure are depicted schematically in Fig. 2A including two sensors 120 connected rigidly by connector 140, tip sensor 122 connected to one of sensors 120 by elastic connector 142, and object 144 fixedly connected to sensors 120. Object 144 can be equipment or work tools depending on the need such as a flashlight, camera, hose, scalpel, drill, soldering iron, cryotherapy device, endoscope, stent, syringe, nozzle, brush, steam hose, ejector, electrode, nozzle, heating coil, cooling coil, optic fiber, catheter, electric wire, tube, pump, laser, LiDAR, radar and sensor. Also shown, object A close to sensor 122. Object A can be an organ, tumor, dirt, rust, or sediment. The situation in which sensor 122 touches object A is depicted schematically in figure 2B. As a result a force is applied to sensor 122 a change occurs in an angle that is formed between the longitudinal dimension of rigid member 140 and a line connecting sensor 122 and sensor 120. As a result, this results in a change in the measurement of sensor 120 in particular. A non-transitory media readable by touch detection module 152, the media storing instructions that when executed by module 152, causes module 152 to determine whether the change in magnetic field measurement input 162 received from sensor 122 is a result of force exerted on sensor 122 due to contact object A. In some embodiments, not depicted in Fig. 2B, module 152 receives input also from sensor 120 to increase the reliability of touch detection. For example, if module 152 detects a change in the measurement of sensor 122, while the measurement of sensor 120 remains constant within the limits of measurement accuracy, such a situation is a more clear indication of touch, compared to a situation where a change in measurement was detected in both sensors (120, 122). That is, a combination of a condition for detecting a touch according to which the measurement of sensor 120 remains constant, while the measurement of sensor 122 changes. In some examples module 152 determines the force intensity exerted on sensor 122 based on input 162. In the example shown in Fig. 2B, mapping module 154 receives input 164 regarding contact occurrences from module 154. A collection of contact occurrences is then transformed by module 154 into a map or a model of object A.

[0060] In order to perform a variety of medical interventions, a catheter is to be inserted into the patient's body while monitoring its position. Furthermore, in many medical procedures such as heart ablation or biopsy, the catheter is guided through narrow internal body organs and is directed towards a target location. Monitoring the catheter position imprecisely may lead to carrying out the medical intervention in the wrong place, rendering it to be useless or even harmful. Therefore, the advantages of the present disclosure can be demonstrated through the following example, which involves the use of a catheter during a medical intervention or examination. It is important to note that this example is not meant to imply that the present disclosure is limited to medical applications only. The disclosure has applicability across various domains, including but not limited to industry, agriculture, space, research, and more. The example provided below is purely for demonstration purposes. A known method of locating the catheter is utilizing sensors located on the catheter which measure magnetic fields generated by one or more generators placed outside the body of the patient. In order to identify the position of the catheter tip with sufficient accuracy a number of generators and / or a number of magnetic sensors may be used due to the effect of the angles and distances of each of the sensors relative to the generators. Adding to this complexity is the need for a separate array of sensors and generators for detecting a contact (touch), of the catheter with the target organ, in addition to the above-mentioned sensors and generators used for the navigation of the catheter.

[0061] One of the objects of the present disclosure is using pairs of digital magnetic sensors with a constant rigid displacement therebetween to determine the precise six degrees of freedom (DOF) position of the magnetic sensors. Optionally, a single magnetic field generator can be used.

[0062] In a device according to some embodiments of the present disclosure, a number, in some cases, an even number, of catheter body sensors are fixed to the catheter with a rigid segment (connection) between them in a maimer that the displacement (distance and angle) between sensors are constant. With the distance and the angle between the sensors known, the use of a single magnetic field to determine the catheter tip location becomes possible as opposed to the prior art systems. Each body sensor measures the magnetic field vector- its strength along the x, y, and z axes. Hence, the exact position of the tip of the catheter can be determined with the output from the sensors in six degrees of freedom. The reading from the sensors can be transmitted via the catheter or wirelessly to a positioning system that calculates the position of the catheter tip and allows the medical staff to be informed graphically or otherwise, of it.

[0063] Location and orientation estimation of objects

[0064] Location and orientation of objects can be estimated using magnetometers, which measure the magnetic field over time. In the non-limiting example below, a way to estimate the location and orientation of a catheter over time will be shown, when the sensors from which measurement input is received are several magnetometers located on the catheter or in its vicinity, as well as in some cases an IMU which is attached to the catheter. Sometimes the source of the magnetic field is also part of the system.

[0065] Static case

[0066] In the static case the continuous position of the catheter is defined as follows: posj is the position of sensor j relative to the center of the catheter.

[0067] The continuous orientation of the catheter is defined as follows:

[0068] The equation describing the measurement of the magnetic field measured by sensor j at time t is:

[0069] Rj is the rotation matrix of sensor j with respect to the orientation of the catheter, where R can be defined by the angles that make it up:

[0070] The general function of the magnetic field is defined as: where x is the position and x is a multidimensional vector that includes all the parameters of the function. These parameters can be represented in a wide variety of ways. We will refer to them later when we define the model of the magnetic field. The location or shape of the generator affects these parameters. Hence, the position calculation model includes a predetermined three dimensional intensity profile of the magnetic field produced by the generator. The determination of the magnetic field intensity profile is done through pre-calibration and calibration stages detailed below.

[0071] Calculation of the error

[0072] Magnetometers are not necessarily in the same axis system, both in terms of position and orientation. In order to get the position of any sensor (e.g. magnometers), we move between the axis systems as follows:

[0073] Where Ra2wis the rotation matrix defined by the orientation of the magnetometer (with the catheter), that is and therefore the field at the point where the sensor is located is:

[0074] In order to get the magnetic field that the sensor measures, we rotate the magnetic field to the orientation of the sensor which is affected by the matrix of the basis between the world and the catheter and between the catheter and the specific magnetometer:

[0075] And this is how the transformation function that imposes the state on the measurement space of the specific sensor is defined when state consists of: where is the rotation matrix between the sensor and the arm defines the relationship between our state space and the measurement space from sensor j at time t, so the definition of an error function is:

[0076] Where Wj tis the weight we give to the j measurement at time t in the state. This weight is subject to choice as will be explained below. Optimization

[0077] It can be understood from the very definition of state that it is a vector with a dimension that can be large and this dimension is defined by the number of magnetometers we use and also by the complexity of the model of the magnetic field. We are looking for the state that will give as small an error as possible. The smaller the error, the higher the accuracy.

[0078] To avoid a degenerate / non-singular solution we use a number of equations higher than the number of degrees of freedom. In order to optimize for finding a state that minimizes the error there are several methods, such as the

[0079] Levenberg-marquardt method used in the example below.

[0080] Each optimization step is calculated as follows:

[0081] The state in the n iteration is represented by sn.

[0082] Dynamic case

[0083] In the dynamic case we include the speed in the calculation. Below are definitions according to a non-limiting example.

[0084] The velocity defined as:

[0085] The angular velocity is defined by: Error calculation for the dynamic case

[0086] The magnetic field including the velocity in the system of the world's axes is defined as follows:

[0087] The velocity of each sensor relative to the world axis system:

[0088] While

[0089] The field at the location and speed where the sensor is located is:

[0090] In order to get the magnetic field that the sensor measures, we rotate the magnetic field to the orientation of the sensor which is affected by the matrix of the basis between the world and the arm and between the arm and the specific sensor:

[0091] We define the transformation function that imposes the state on the measurement space of the specific sensor, when state consists of:

[0092] The error equation is:

[0093] We add a component of time advancement based on the state from a previous time and also on IMU in case there is information available from it. The time advance function for the model is:

[0094] In case we don't have data from an IMU then the function will be linear advancement:

[0095] In case we have an IMU then the advancement will be carried out more precisely with the help of the output of the IMU which includes relative position and relative orientation:

[0096] This is how we expand the error function to also include consideration of previous times:

[0097] Where Wpis a controllable weight in order to increase or decrease the constraint of the similarity to the state in the previous time.

[0098] For each iteration:

[0099] Model of three dimensional magnetic field profile

[0100] There are differences in the operation between magnetic field generators among other things due to some imperfect replicability of their structure even if they are assembled in the same assembly line. Hence, according to an embodiment of the present disclosure the position calculation is based on a model that includes a three dimensional intensity profile of the magnetic field produced by each generator. The determination of the magnetic field intensity profile is done through pre-calibration and calibration stages as exemplified below.

[0101] According to some embodiments of the disclosure, to allow the determination of the catheter tip location using the above body sensors measuring a single magnetic field, the above device is a device pre-calibrated using a model based on measurement input received from these body sensors. This precalibration is a controlled measurement of the magnetic field at known positions and speeds combined with the implementation of a Weighted Information Filtering method. The resulting model is then calculated for the entire space where we want to move the catheter, commonly in close proximity to the treated organ. The magnetic field is calculated around a predefined location (point). Each measurement is weighted during the pre-calibration process, with greater weight given to measurements closer to the predefined location.

[0102] According to some embodiments of the disclosure the pre-calibration, or as also called generator calibration, is performed with the magnetic field generator that later will be used during the medical intervention, and with a plurality of magnetometers, typically installed on a calibration board. In some embodiments the generator is a generator specifically produced, yet in some embodiments the generator is an off-the-shelf generator.

[0103] In some embodiments of the disclosure, when a calibration board is used, the number of magnetometers installed on the calibration board can reach 100 to 200. Before the first use of each calibration board, a calibration of the calibration board is performed using a calibrated magnetic field generator in order to verify and, if necessary, correct the information regarding the position of each of the sensors installed on the board. After the board calibration, during the generator calibration, the board is in motion while the magnetometers installed on it measure the magnetic field generated by the magnetic field generator at different locations. In some embodiments of the disclosure the board is in motion once during the generator calibration for a distance of around 50 centimeters, when the magnetometers measure the magnetic field generated by the generator every approximately 2 centimeters (approximately every half of a second). In some embodiments the board travels from one side to the other and back. The board may travel the same track more than once, thus enabling calculation of an average of magnetic field measurements done in each point. The distance the board travels can be different than 50 centimeter. The board velocity can vary too. In some embodiments more than one calibration board is used. The measurements of the magnetic field and the locations where they were done are collected and recorded in pre-calibration module, as well as the velocity at which the board was moving. The need for the generator calibration stems from the differences existing between the generators, even if they were produced in a controlled production line. During the generator calibration, the parameters of function A are determined. In function A, the independent variable is the position within a three-dimensional axis system, while the dependent (calculated) variable is the magnetic field. In some cases, there may be an additional independent variable, which is the velocity of the magnetometer within a three-dimensional axis system. The mathematical definition of function A is the polynomial where its parameters are: and its weights are: for a predetermined sigma

[0104] At a later stage function A is converted into function B that is used during the medical intervention or examination to calculate the location of the catheter according to the measurement of the magnetic field produced by the generator.

[0105] Function B is an iterative function that can be expressed as follows: Where "s" are the parameters of the position (including orientation) and sometimes the speed of the catheter, H is a function that maps between the position of a fixed sensor and the magnetic field, and z are the measurements of the magnetic field. "W" are the weights of given to various sensors. In the example here, all weights are 1, but may be changed if there exists a difference in the accuracy of the sensors' measurements.

[0106] Continued discussion of the above functions and description of their variables below.

[0107] Magnetic model for the static case - zero board velocity:

[0108] Given N measurements of a magnetic field BLaccompanied by position measurements according to xta state describing the function of the magnetic field is calculated using a general polynomial. The polynomial of x is defined to be and the error function to be

[0109] Where x is the starting position around which we want to calculate the magnetic field and is the weight function of the measurements according to their distance from x.

[0110] Where is the matrix that represents the degree of locality of the solution.

[0111] Since in the polynomial the coefficients are linear in the polynomial function, the calculation of the parameters for each point or weight chosen is as follows:

[0112] And so, a calculation can for the polynomial of the magnetic field be made for any point in space according to local measurements, and thus a solution with higher local accuracy is achieved compared to a calculation of a single polynomial for the entire space.

[0113] Magnetic model for the dynamic case:

[0114] There is no significant difference compared to what was described above, i.e., considering both position and velocity instead of only position since x can be defined both as a vector of three axes of position and as a vector of six axes for position and velocity with the same solution. It should be appreciated that more measurements may be required to adequately cover the space for six axes.

[0115] Selecting hyperparameters:

[0116] To perform a local polynomial adjustment instead of the whole space, we can choose how local we want the adjustment. Therefore, additional optimization is carried out to calculate the size of the environment which is expressed in

[0117] For each chosen, we will get the total error of the model in relation to the measurements:

[0118] This error reflects the squared sum of all the errors of all the measurements in relation to the model when they are weighted according to proximity to the point of interest hence assisting in understanding how accurate our model is in relation to all the points that make it up. For too large an environment, not fitting to a polynomial will cause the error to increase.

[0119] The sum of the weights of the measurements being carried out is expressed by:

[0120] The average or normalized error according to the weights is:

[0121] On one hand, the aim is to minimize the average or normalized error, yet in order to avoid a degenerate solution where the error will be zero, for example, due to too few measurements, a calculation is done of the eigenvalues of: which is the Fisher information matrix for the parameters of the polynomial. If there is zero or very low eigenvalues, this indicates that the solution is degenerate or sensitive to small changes. So to determine the working point, an examination of several values for is done and which of them provides a solution with sufficiently high eigenvalues yet with a lower error (e).

[0122] Pick up and run times:

[0123] Once having the cluster of samples that includes the measured magnetic field together with position (and velocity) the operation of calculating the local model is an operation of complexity of 0(N*MA2) where N is the number of measurements and M is the degree of the polynomial. Even when collecting a very large number of samples, the above-described method allows running in real-time with far less complexity compared to the solutions of neural networks that contain hundreds of thousands and millions of parameters. Nevertheless, the option to carry out the calculation for all the points in real-time can be done by calculating the model in a grid of points, and basically, every time the device is switched on, the user can simply access the appropriate model according to the grid. In this way, the user translates running time into a place on the storage media, e.g. disk. Although saving the models takes up space, here, too, it is significantly smaller than using neural networks.

[0124] Generator calibration according to some embodiments is depicted schematically in Fig. 3. Shown are calibration sensors 320 that are fixed to calibration board 323 which is moving at velocity C. Sensors 320 measure magnetic field 130 generated by the magnetic field generator 110 at predefined locations along the path of movement of board 323 to identify the form of the magnetic field 130. Input of the measurements of sensors 320 is received in a precalibration module 350 which is associated with the locations where these measurements were done. The velocity C is already stored or received as input in module 350. In an embodiment of the disclosure, the calibration board is used to identify the form of the electromagnetic field as a function of space and time.

[0125] Additionally, the calibration board can be used to calibrate the magnetic sensors 320 of the board or independent magnetic sensors by testing measurements of each magnetic sensor 320 on the board 323 relative to the neighbor magnetic sensors 320 and relative to given parameters provided for the sensor, for example parameters provided by the manufacturer on the package of sensor. Likewise, the testing is performed at different electromagnetic field intensities and different distances from the magnetic field generator 110.

[0126] At a specific moment a single magnetic sensor 320 is designated as the magnetic sensor under calibration 324 either on the board 323 or as an independent magnetic sensor as shown in Fig. 3, by comparing the measurements of the sensor under calibration 324 with the expected values from previous measurements to verify that the magnetic sensor under calibration 324 is functioning correctly, matches the recorded parameters and / or to adjust its parameters if needed.

[0127] Final calibration

[0128] As explained above, the model is calculated in the pre-calibration stage, typically in the factory, for each generator separately. The final calibration performed in-situ, also referred to here as catheter calibration is done for several reasons:

[0129] 1. To allow more precision in the calculated location of the catheter based on the magnetic field measurements by finding the relative position and orientation between each of the magnetometers and a predefined point on the catheter, e.g. the center of the catheter.

[0130] 2. To find the timing delays between the sensors in order to synchronize them.

[0131] 3. To check and screen for external disturbances such as the Earth's magnetic field or distant magnetic sources present in situ (e.g., from other equipment in the vicinity of performing the process on the patient). These disturbances are generally at a much lower frequency than the generator of the current system.

[0132] The final calibration is done while using the mentioned function B. The catheter travels in a similar maimer to the board in the pre-calibration while recording the positions and orientations of each magnetometer installed on the catheter at a number of points along the catheter's path. This too resembles the precalibration procedure with one of the differences compared to the pre-calibration that this time the locations of the magnetometers are calculated based on their measurements of the magnetic field generated by the magnetic field generator. Accurately finding the relative position and orientation of each of the magnetometers relative to a predefined point on the catheter allow improving the precision of the calculation of the catheter's location during the medical procedure based on the magnetometer’s measurements.

[0133] The time when each measurement was done is recorded as well to determine the difference in the measurement times between the magnetometers. These time differences which are due to specific characteristic of each magnetometer are taken into account to reduce inaccuracy in location determination during a medical procedure. In some embodiments an increase in the calculated position of the catheter is achieved by applying data fusion techniques. For example, by comparing the positions of the magnetometers at a previous time with their current positions. In some embodiments IMU measurements are integrated in data fusion techniques to further improve the estimation of the location of the catheter during a medical procedure.

[0134] In some embodiments of the disclosure, one or more sensors are used that measure the rotation of the catheter such as a gyro meter. That information is incorporated into the model which determines the location of the catheter tip in six degrees of freedom with greater ease. In addition, incorporating a rotation sensor, allows for determining the correct catheter tip position when two or more positions are mathematically possible due to symmetry of the magnetic field.

[0135] Final calibration according to some embodiments is depicted schematically in Fig. 4. During the final calibration generator 110 generates its characteristic magnetic field 130. As can be understood from the explanation given, magnetic field 130 can be compared to a sort of fingerprint of the generator 110. This fingerprint is converted into a model by module 350 and transmitted to module 150 for position calculations based on sensor measurements 120. For the reasons explained above, the pre-calibration is accompanied by the final calibration in order to obtain maximum accuracy in the position calculations. Also shown in Fig. 4 is rotation sensor 124 providing complementary input to module 150 for enhancement of the position calculation based on magnetic field 130 profile model.

[0136] Palpation is an important part of the physical examination. It is the process of feeling an object in or on the body to determine its size, shape, firmness, or location. Manual palpation has several important limitations: it is limited to tissues accessible to the physician's hand, it is distorted by any intervening tissue, and it is qualitative but not quantitative. Tactile imaging translates input from tactile sensors into digital images similar to manual palpation, using a pressure sensor array. In addition to the catheter tip position, according to some embodiments of the disclosure the medical team is able to determine when the surface of an organ is touched by the tip of the catheter. For this, at least one catheter tip magnetic field sensor is placed on the tip of the catheter on an elastic or spring-like member. When the catheter tip touches the target organ, the angle between the tip sensor and the fixed pair of magnetic sensors changes. When the contact between the tip sensor and the target organ ceases, the position of the tip sensor returns to its position before contact with the target organ. The magnetic field signal varies by this change in the above angle between the sensors, thus enabling to determine whether contact is made between the tip of the catheter and the target organ, or other organs. In some cases, alteration in the above angle causes changes in the magnetic field signal correlated with the intensity of contact between the catheter tip and the organ. When more force is applied the angle of the tip sensor relative to at least one of the fixed sensors will change more significantly and the signal from the sensor will change accordingly. This information provided according to some embodiments of the disclosure regarding contact between the catheter tip and the organ allows the medical staff to decide when to start the medical intervention, (e.g. ablation, measurement, biopsy, obstruction, and clearance). This information also assists in avoiding applying too much force during the medical intervention that can harm the organ.

[0137] According to an embodiment of the disclosure, a collection of contact points between the catheter tip at various locations on the organ surface is used to assist in generating a 3D map or a model of the organ. Optionally, data from a CT may also be used.

[0138] Some embodiments are depicted schematically in Figures 5A-B, illustrating various components such as fixed sensors 120, rigid connector 140, elastic connector 142, and sensor 122. The example demonstrates the navigation of elongated flexible part 210 (e.g., a catheter), through a curved cavity B using the system depicted in Figs. 1 and 2A-B, with certain components also visible in Figure 5B. Furthermore, capsule 220, flexible cap 230, and rotation sensor 124 are shown. Rotation sensor 124 output received by module 150 is used in combination with input from sensors 120 for the calculation of the position of part 210. Capsule 220 connects part 210 to rigid connector 140 to which sensors 120 and 124 are attached. In addition, capsule 220 serves as an enclosure for sensors 120 and 124 for their protection from the environment. Cap 230 is connected to capsule 220 serves as an enclosure to sensor 122. The flexibility of cap 230 allows the transfer of force to sensor 122 when object A (shown in Figs. 2A-B) presses cap 230 during contact.

[0139] The flowchart presented in Fig. 6 provides an overview of the primary stages in accordance with some embodiments of the present disclosure. Before the first use of each calibration board, calibration stage 410 is performed using a calibrated magnetic field generator in order to verify and, if necessary, correct the information regarding the position of each of the sensors installed on the board. According to some embodiments "calibrated generator" means that for the generator in use, there exists a refined model representing this generator's characteristic magnetic field profile. After verifying and correcting the information regarding the position of each of the sensors installed on the board in stage 410, the calibration board is used in stage 420 for creating the magnetic field model of the generator that will be in used in-situ, e.g., during a medical intervention in a hospital. As can be understood this is not the same generator that was used in stage 410. For this generator that will be used in-situ, there is still no magnetic field profile model. In some cases, stages 410 and 420 are performed in the factory supplying systems described in the disclosure. Once the model is created, it undergoes a refinement process in stage 430, which takes place in-situ. This refinement step aims to enhance the accuracy and quality of the model by making adjustments or improvements while situated in its operational environment. Stage 440 is an actual use of a system according to the disclosure which allows navigating equipment based on measurements of the magnetic field generated by a magnetic field generator.

[0140] According to some embodiments of the disclosure, a device for navigation of equipment and for locating and mapping objects includes a cable made from flattened round copper wires serving for communication and power supply to the sensors described above. In some cases, the process for producing such a device may include the flattening of the copper wires. The flattening can be done for a number of tendons together or for each tendon separately. The wires are combined as one reel with a predefined space between them. The wires are jointly coated / extruded to form a flat cable. The coating is removed at predefined locations (for example by using a laser). The combining of the wires forms a cable as depicted schematically in Fig. 7A where cable 510 with four tendons 512 is shown. Also shown are coating 514 and cavities 520 where coating 514 was removed. Afterward, a soldering paste is applied for example by a pick-and-place robot in the locations where the coating was removed. In another example, a mask can be placed on the cable with holes corresponding to the locations where the coating was removed, and soldering paste is placed via screen printing. Body sensors or other components are attached to their positions, where the soldering paste was applied. Cable 510 with body sensors 120 and rotation sensor 124 is depicted schematically in Fig. 7B. This can be done by a pick-and-place robot. After that, soldering is performed via reflow, laser heating, or any other means. After that, the cable may be coated for mechanical and environmental protection, or to protect the patient in cases of biomedical applications.

[0141] The use of the term “include,” “includes,” “including,” “have,” “has,” “having,” including grammatical equivalents thereof, should be understood generally as open-ended and non-limiting, for example, not excluding additional unrecited elements or steps, unless otherwise specifically stated or understood from the context.

[0142] The use of the singular herein, for example, “a,” “an,” and “the,” includes the plural (and vice versa) unless specifically stated otherwise.

[0143] The use of any and all examples, or exemplary language herein, for example, “such as,” “including,” or “for example,” is intended merely to better illustrate the present teachings and does not pose a limitation on the scope of the disclosure unless claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the present teachings.

[0144] The present teachings encompass embodiments in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the present teachings described herein.

[0145] Further, one skilled in the art will recognize that functional units in this description have been labeled as modules throughout the specification. The person skilled in the art will also recognize that a module may be implemented as processor, circuits, logic chips or any sort of discrete component. Still further, one skilled in the art will also recognize that a module may be implemented in software which may then be stored on a non-transitory medium and the software may be executed by a variety of processor architectures. In embodiments of the disclosure, a module may also comprise computer instructions or executable code that may instruct a computer processor to carry out a sequence of events based on instructions received. The choice of the implementation of the modules is left as a design choice to a person skilled in the art and does not limit the scope of this disclosure in any way.

[0146] Within the disclosure:

[0147] The terms “touch”, and "contact" may be used interchangeably;

[0148] The terms “magnetic field sensor”, "sensor" and "magnetometer" may be used interchangeably;

[0149] The terms “fixed sensor”, and "body sensor" may be used interchangeably;

[0150] The terms “magnetic field generator”, "generator" and "coil" may be used interchangeably;

[0151] The terms “device", and "system" may be used interchangeably;

[0152] The terms “wire”, and "tendon" may be used interchangeably;

[0153] The terms “calibration board”, and "board" may be used interchangeably;

[0154] The terms “pre-calibration”, and "generator calibration" may be used interchangeably;

[0155] The term "position" used in herein may refer to a location; however, it may also be extended to both location and orientation combined; The terms “equipment”, "part" and "tool" may be used interchangeably; and

[0156] The terms “rigid member”, "rigid connector" and "rigid connection" may be used interchangeably.

[0157] It should be appreciated that the above-described methods and apparatus may be varied in many ways, including omitting or adding elements or steps, changing the order of steps and the type of devices used. It should be appreciated that different features may be combined in different ways. In particular, not all the features shown above in a particular embodiment are necessary in every embodiment of the disclosure. Further combinations of the above features are also considered to be within the scope of some embodiments of the disclosure.

[0158] It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims, which follow.

Claims

CLAIMSI / We claim:

1. A navigation system for navigating within a magnetic field, comprising: a catheter with a head that is moved through the magnetic field by moving a handle of the catheter; the head comprises one or more pairs of magnetic sensors; wherein the magnetic sensors are solid-state sensors that measure an electrical signal indicating a three dimensional intensity of the magnetic field at the location of the magnetic sensor; wherein each pair of magnetic sensors are rigidly connected together with a fixed displacement; and wherein the measurements of the magnetic sensors of each pair are processed together with details of the fixed displacement between the magnetic sensors of the pair to determine the location and the angular orientation of the pair of magnetic sensors.

2. The system of claim 1, wherein the navigation system functions with a DC and / or time constant magnetic field.

3. The system of claim 1, wherein the system forms images of the path followed by the head of the catheter based on data from a CT of a user, information of a form of the magnetic field, and the measurements of the magnetic sensors.

4. The system of claim 1, wherein the head comprises multiple pairs identifying curvature of the cavity while the catheter is held stationary.

5. The system of claim 1, wherein a rotation sensor that comprises an accelerometer or gyroscope is connected to one of the pairs of magnetic sensors.

6. The system of claim 1, wherein a touch sensor that comprises a single magnetic sensor or a pair of magnetic sensors is connected by a spring or flexible member to a last pair of magnetic sensors along an elongated axis of the head; wherein the touch sensor tilts when coming into contact with an obstacle in the path of the catheter head.

7. The system of claim 1, wherein the head comprises multiple pairs and the measurements of each pair are given a different weight for being considered in determining the location or curve of the catheter head.

8. The system of claim 7, wherein the weights are location dependent or time dependent.

9. The system of claim 1, wherein the pairs are connected in parallel over a common cable.

10. The system of claim 1, wherein each pair has a unique address to be addressed for transferring measurements.

11. The system of claim 1, wherein specific pairs deliver measurements more frequently than other pairs.

12. A method of navigating within a magnetic field with a navigation system, comprising: moving a handle of a catheter that moves a head through the magnetic field; wherein the head comprises one or more pairs of magnetic sensors that are solid state sensors; Wherein each pair of magnetic sensors are rigidly connected together with a fixed displacement;measuring an electrical signal indicating a three dimensional intensity of the magnetic field at the location of the magnetic sensor; and processing the measurements of the magnetic sensors of each pair together with details of the fixed displacement between the magnetic sensors of the pair to determine the location and the angular orientation of the pair of magnetic sensors.

13. The method of claim 12, wherein the navigation system functions with a DC and / or time constant magnetic field.

14. The system of claim 12, wherein the system forms images of the path followed by the head of the catheter based on data from a CT of a user, information of a form of the magnetic field, and the measurements of the magnetic sensors.

15. The method of claim 12, wherein the head comprises multiple pairs identifying curvature of the cavity while the catheter is held stationary.

16. The method of claim 12, wherein a rotation sensor that comprises an accelerometer or gyroscope is connected to one of the pairs of magnetic sensors.

17. The method of claim 12, wherein a touch sensor that comprises a single magnetic sensor or a pair of magnetic sensors is connected by a spring or flexible member to a last pair of magnetic sensors along an elongated axis of the head; wherein the touch sensor tilts when coming into contact with an obstacle in the path of the catheter head.

18. The method of claim 12, wherein the head comprises multiple pairs and the measurements of each pair are given a different weight for being considered in determining the location or curve of the catheter head.

19. The system of claim 18, wherein the weights are location dependent or time dependent.

20. A non-transitory computer readable medium comprising an executable program configured to perform the method of claim 12.

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