Magnetic and optical alignment

Abstract

In one embodiment, an apparatus for calibrating a probe including an image sensor and a magnetic field sensor includes a fixture configured to hold the probe; a magnetic field generator configured to generate at least one magnetic field having a predetermined direction aligned with the fixture; an optical target aligned with the fixture so that an image sensor in the probe can capture an image of the optical target while the probe is held in the fixture; and a processing circuit configured to receive from the probe a signal output by the magnetic field sensor in response to at least one magnetic field and an image captured by the image sensor while the probe is held in the fixture, and to calibrate the alignment of the image sensor relative to the magnetic field sensor in response to the received signal and the received image.

Description

Technical Field

[0001] The present invention relates to optical alignment of probes. Background Art

[0002] A large number of medical procedures involve placing probes such as guidewires and catheters in the patient's body. Position sensing systems have been developed to track such probes. Magnetic position sensing is a method known in the art. In magnetic position sensing, a magnetic field generator is usually placed at a known position outside the patient's body. A magnetic field sensor in the distal end of the probe generates electrical signals in response to these magnetic fields, and these electrical signals are processed to determine the coordinate position of the distal end of the probe. These methods and systems are described in U.S. Patents 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT International Patent Publication WO 1996 / 005768, and in U.S. Patent Application Publication 2003 / 0120150 and 2004 / 0068178, the disclosures of which are all incorporated herein by reference.

[0003] U.S. Patent 6,266,551 to Osadchy et al. (hereinafter the '551 patent), which is incorporated herein by reference, describes a probe for insertion into a subject's body, the probe having a distal end and a proximal end, and including an electronic microcircuit that stores information related to the calibration of the probe. Preferably, the microcircuit stores a calibration code, the calibration code being encrypted. Alternatively or additionally, the microcircuit stores a usage code that controls the availability of the probe to its user. The probe includes access control circuitry that allows the usage code to be changed so as to reduce the availability of the probe, but not increase its availability.

[0004] The '551 patent describes that a system for electromagnetic detection of catheter position and orientation is typically located in the catheter at a small distance near the distal tip of the catheter because the distal tip is typically occupied by an electrode or other functional element. Therefore, it is necessary to calibrate the position and orientation detection system to account for the displacement of the distal tip of the catheter relative to the position of the coil. Due to manufacturing variations, this displacement typically varies from one catheter to another. In addition, the coils used to generate the position signals may not be precisely orthogonal. For the purpose of calculating the position and orientation of the catheter, the axes of the coils define corresponding axes of a coordinate system fixed to the catheter tip, and the directions of these axes must be known relative to the catheter. If these axes deviate from orthogonality, the corresponding degree of deviation must be known and corrected for position and orientation calculations. In addition, the relative gain of the coil determines the strength of the corresponding position signal generated by the coil in response to an externally applied field. Since these signal strengths are used to calculate the position and orientation of the catheter, deviations of the gain from its expected value will result in inaccuracies in the calculated position and orientation. Therefore, the corresponding gain of the coil must be known and corrected for position and orientation calculations.

[0005] The '551 patent provides a method of calibrating a device for determining the position and orientation of a catheter, wherein calibration information is retained in the catheter. The calibration information is digitally stored in a microcircuit located in a location that is easily accessible to a signal processing circuit and a computing device, such that the catheter need not house digital signal wires, and such that digital electronic signals transmitted from the microcircuit to the signal processing circuit and computing device do not interfere with low level analog signals transmitted by the wires from the distal end of the catheter to the circuit.

[0006] The '551 patent describes a device for determining the position and orientation of a catheter inside the body. The device, such as a Helmholtz calibration chamber, includes a plurality of coils adjacent to the distal end of the catheter. The catheter also includes an electronic microcircuit adjacent to the proximal end of the catheter. The microcircuit stores information related to the calibration of the device.

[0007] U.S. Patent 6,427,314 to Acker describes a magnetic position and orientation determination system that uses magnetic fields, advantageously including uniform fields from Helmholtz coils positioned on opposite sides of a sensing volume and gradient fields generated by the same coils. By monitoring the field components detected at the probe during application of these fields, the position and orientation of the probe in the field can be derived. A representation of the probe can be superimposed on a separately acquired image of the subject to show the position and orientation of the probe relative to the subject.

[0008] U.S. Patent Publication 2019 / 0044784 to Cohen et al. describes an apparatus for displaying a moving region of interest located within a body, the apparatus comprising a positioning system to determine a position and orientation (P&O) of a medical device and tracking the movement of the region of interest over time using an internal position reference sensor. A compensation function block generates a motion compensation function based on the movement of the region of interest, the motion compensation function being configured to compensate for the movement of the region of interest between a first time, such as a time when the image is acquired, and a second time, such as a time when the P&O of the device is measured. The measured P&O is corrected using the compensation function. A representation of the medical device is superimposed on the image based on the corrected P&O.

[0009] U.S. Patent Publication 2006 / 0058647 to Strommer et al. describes a method for delivering a medical device coupled to a catheter to a selected location within a lumen of a patient's body, the method comprising the following procedures: aligning a three-dimensional coordinate system with a two-dimensional coordinate system, associating the three-dimensional coordinate system with a medical positioning system (MPS), associating the two-dimensional coordinate system with a two-dimensional image of the lumen, which is further associated with an organ timing signal of an organ of the patient; acquiring MPS data corresponding to a plurality of points within the lumen, each of the points being associated with the three-dimensional coordinate system, each of the points being further associated with a corresponding activity state of the organ; and associating the two-dimensional image with the corresponding activity state. The invention relates to a method for controlling a medical device and a plurality of medical devices, comprising: determining a time three-dimensional trajectory representation for each corresponding activity state based on the acquired MPS data; superimposing the time three-dimensional trajectory representation on a two-dimensional image according to the corresponding activity state; receiving position data corresponding to the selected position by selecting at least one of the points along the time three-dimensional trajectory representation; determining the coordinates of the selected position in a three-dimensional coordinate system by the at least one selected point; determining a current position of the medical device in the three-dimensional coordinate system according to an output of an MPS sensor of a catheter attached to the vicinity of the medical device; manipulating the medical device toward the selected position through an inner cavity according to the current position relative to the selected position; and generating a notification output when the current position substantially matches the selected position. Summary of the invention

[0010] According to one embodiment of the present disclosure, there is provided a device for calibrating a probe including an image sensor and a magnetic field sensor, the device including a fixture configured to hold the probe; a magnetic field generator configured to generate at least one magnetic field having a predetermined direction aligned with the fixture; an optical target aligned with the fixture so that the image sensor in the probe can capture an image of the optical target when the probe is held in the fixture; and a processing circuit configured to receive from the probe a signal output by the magnetic field sensor in response to at least one magnetic field and an image captured by the image sensor when the probe is held in the fixture, and calibrate the alignment of the image sensor relative to the magnetic field sensor in response to the received signal and the received image.

[0011] Also in accordance with an embodiment of the present disclosure, the processing circuit is configured to calibrate an alignment of the magnetic field sensor with at least one magnetic field generated by the magnetic field generator in response to the received signal.

[0012] Also in accordance with an embodiment of the present disclosure, the processing circuit is configured to store an alignment of the image sensor relative to the magnetic field sensor and an alignment of the magnetic field sensor with the at least one magnetic field in a storage device included in the probe.

[0013] Additionally, according to one embodiment of the present disclosure, the processing circuit is configured to calculate a sensitivity of the magnetic field sensor in response to the received signal.

[0014] In addition, according to one embodiment of the present disclosure, the optical target includes a plurality of alignment features, the received image includes at least some of the plurality of alignment features, and the processing circuit is configured to calculate optical aberration corrections for the image sensor in response to corresponding positions of corresponding alignment features of at least some of the alignment features in the received image.

[0015] Also in accordance with an embodiment of the present disclosure, the processing circuit is configured to calculate optical aberration corrections for the image sensor in response to a curvature of at least one line defined by corresponding ones of the at least some of the alignment features at corresponding locations in the received image.

[0016] Also in accordance with an embodiment of the present disclosure, the optical target includes a plurality of alternating rectangular portions, and the processing circuit is configured to find respective boundaries between respective ones of the rectangular portions corresponding to respective ones of the plurality of alignment features.

[0017] In addition, according to one embodiment of the present disclosure, the central boundaries between some of the rectangular parts correspond to the central alignment features among the multiple alignment features, and the processing circuit is configured to calibrate the alignment of the image sensor relative to the magnetic field sensor in response to the position of the central alignment feature in the received image.

[0018] In addition, according to one embodiment of the present disclosure, the optical target is configured to rotate about a central alignment feature, and the processing circuit is configured to receive a plurality of corresponding images captured by an image sensor of the optical target at a plurality of corresponding rotational positions of the optical target, and to calculate optical aberration corrections of the image sensor in response to corresponding positions of corresponding alignment features of at least some of the alignment features in the received corresponding images.

[0019] Also according to one embodiment of the present disclosure, the magnetic field generator includes three calibration coil groups respectively aligned with three orthogonal axes of the magnetic coordinate system, the magnetic field sensor includes three position coils, and the processing circuit is configured to actuate the calibration coil groups to generate a magnetic field for detection by the position coils, and for each of the position coils, calibrate the alignment with the magnetic coordinate system in response to a signal received from the position coil.

[0020] Also in accordance with an embodiment of the present disclosure, each of the calibration coil sets is a Helmholtz coil.

[0021] According to another embodiment of the present disclosure, a method for calibrating a probe including an image sensor and a magnetic field sensor is also provided, the method including setting the probe in a fixture, generating at least one magnetic field having a predetermined direction aligned with the fixture, capturing an image of an optical target aligned with the fixture with the image sensor while the probe is held in the fixture, receiving from the probe a signal output by the magnetic field sensor in response to at least one magnetic field and an image captured by the image sensor when the probe is held in the fixture, and calibrating the alignment of the image sensor relative to the magnetic field sensor in response to the received signal and the received image.

[0022] Additionally, according to an embodiment of the present disclosure, the method includes calibrating an alignment of the magnetic field sensor with the at least one magnetic field in response to the received signal.

[0023] Furthermore, according to an embodiment of the present disclosure, the method includes storing an alignment of the image sensor relative to the magnetic field sensor and an alignment of the magnetic field sensor with the at least one magnetic field in a storage device included in the probe.

[0024] Also in accordance with an embodiment of the present disclosure, the method includes calculating a sensitivity of the magnetic field sensor in response to the received signal.

[0025] Also according to an embodiment of the present disclosure, the optical target includes a plurality of alignment features, the received image includes at least some of the plurality of alignment features, and the method includes calculating an optical aberration correction of the image sensor in response to corresponding positions of corresponding alignment features of at least some of the alignment features in the received image.

[0026] Additionally, according to one embodiment of the present disclosure, calculation of the optical aberration correction is performed in response to a curvature of at least one line defined by respective positions of respective ones of at least some of the alignment features in the received image.

[0027] Furthermore, according to an embodiment of the present disclosure, the optical target includes a plurality of alternating rectangular portions, and the method further includes finding respective boundaries between respective ones of the rectangular portions corresponding to respective ones of the plurality of alignment features.

[0028] Also according to one embodiment of the present disclosure, a central boundary between some of the rectangular portions corresponds to a central alignment feature among the plurality of alignment features, and alignment of the calibration image sensor relative to the magnetic field sensor is performed in response to a position of the central alignment feature in the received image.

[0029] Also in accordance with one embodiment of the present disclosure, the method includes rotating the optical target about a central alignment feature to a plurality of rotational positions, receiving a plurality of corresponding images captured by an image sensor of the optical target at corresponding rotational positions of the plurality of rotational positions of the optical target, and wherein computational correction of optical aberrations of the image sensor is performed in response to corresponding positions of corresponding alignment features of at least some of the alignment features in the received corresponding images.

[0030] In addition, according to one embodiment of the present disclosure, the method includes actuating three calibration coil groups respectively aligned with three orthogonal axes of the magnetic coordinate system to generate a magnetic field for detection by three position coils of the magnetic field sensor, and for each of the position coils, calibrating the alignment with the magnetic coordinate system in response to a signal received from the position coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0032] Figures 1 to 3 A schematic diagram of a probe constructed and operated according to one embodiment of the present invention;

[0033] Figure 4 for Figure 1 a cross-sectional view of a distal end of a probe;

[0034] Figure 5 An isometric view of a correction apparatus constructed and operative in accordance with one embodiment of the present invention;

[0035] Figure 6 for Figure 5 A front view of the calibration device;

[0036] Figure 7 for Figure 5 A side view of a calibration device;

[0037] Figure 8 for Figure 5 A schematic diagram of a captured image analyzed in a device;

[0038] Fig. 9 To show Figure 5 A schematic diagram of an optical aberration correction method in a device;

[0039] Fig.10 for Figure 5 a schematic diagram of another captured image in a device; and

[0040] Fig.11 To include Figure 5 A flowchart of the steps in the method of operating the device. DETAILED DESCRIPTION

[0041] Overview

[0042] For a probe (such as a catheter, guidewire, or medical tool, e.g., ENT tool) having an image sensor (e.g., a camera) and a magnetic field sensor, both the image sensor and the magnetic field sensor may need to be aligned with the axis of the probe, or alternatively may need to be calibrated to compensate for any misalignment. The need for alignment or calibration typically arises from inaccuracies incorporated during probe manufacture, especially when the probe is manually assembled. It should be noted that for an image sensor, even a small misalignment may result in relatively large errors in registering the image sensor image, e.g., when the image is displayed side by side or superimposed on a different image (e.g., a CT, MRI, or ultrasound image) of the same body part.

[0043] One solution is to calibrate the magnetic field sensor in a magnetic field calibration device (such as the calibration device described in the '551 patent) and separately calibrate the image sensor in the optical calibration device, for example by placing the probe in a fixture with a fixed orientation aligned with the optical target and analyzing images captured by the image sensor to determine alignment corrections for the image sensor. Such separate calibrations are time consuming and prone to errors due to differences between the two calibration devices.

[0044] Embodiments of the present invention solve the above problems by providing an apparatus that combines calibration of an image sensor and a magnetic field sensor while the probe is held in the same fixture.

[0045] The magnetic field generator generates at least one time-varying magnetic field having a predetermined direction aligned with the fixture. The optical target is aligned with the fixture so that the image sensor in the probe can capture an image of the optical target when the probe is held in the fixture. The processing circuit receives from the probe a signal output by the magnetic field sensor in response to one or more magnetic fields and an image captured by the image sensor when the probe is held in the fixture. The processing circuit calibrates the alignment of the image sensor relative to the magnetic field sensor in response to the one or more received signals and the received image. The processing circuit also calibrates the alignment of the magnetic field sensor with the one or more magnetic fields generated by the magnetic field generator in response to the one or more received signals.

[0046] In some embodiments, the optical target includes a plurality of alignment features, such as alternating rectangular portions, e.g., alternating black and white squares, similar to a chess or checkers board. Thus, the image received from the image sensor includes at least some of the plurality of alignment features, and the processing circuit finds respective boundaries between respective rectangular portions corresponding to respective alignment features. The center boundary between the rectangular portions at the center of the optical target corresponds to the center alignment feature, and the processing circuit calibrates the alignment of the image sensor relative to the magnetic field sensor in response to the location of the center alignment feature and / or other features in the received image.

[0047] In some embodiments, the processing circuitry calculates optical aberration corrections (spherical aberration and / or chromatic aberration) for the image sensor in response to the respective positions of the respective alignment features in the received image. The processing circuitry calculates optical aberration corrections for the image sensor in response to the curvature of one or more lines defined by the respective positions of the respective alignment features in the received image.

[0048] In some embodiments, the optical target is configured to rotate about a central alignment feature of the alignment features (e.g., a central intersection of the central black and white squares). The processing circuit receives a corresponding image captured by an image sensor of the optical target at a corresponding rotational position of the optical target. The processing circuit calculates an optical aberration correction of the image sensor in response to the corresponding position of the corresponding alignment feature in the received corresponding image.

[0049] Various methods for correcting optical aberrations using chessboards are described in the art. One such example is described in a paper titled "A Robust Chessboard Detector for Geometric Camera Calibration" by Mathis Hoffmann, Andreas Ernst, Tobias Bergen, Sebastian Hettenkofer, and Jens-Uwe Garbas of the Fraunhofer Institute for Integrated Circuits IIS (Am Wolfsmantel 33, 91058 Erlangen, Germany).

[0050] In some embodiments, the magnetic field generator includes three calibration coil groups (e.g., three Helmholtz coils) aligned with three orthogonal axes of the magnetic coordinate system, respectively. The magnetic field sensor may also include three position coils (e.g., a three-axis magnetic sensor). In these embodiments, the processing circuit actuates the calibration coil group to generate a magnetic field for detection by the position coils. The calibration coil groups can be actuated one by one or simultaneously (if different corresponding frequencies are used for corresponding calibration coil groups). If the magnetic field sensor is a three-axis sensor whose coils are completely aligned with the generated magnetic field, if only one Helmholtz coil is actuated, only one signal is present on one coil. If there is a signal on another coil, the misalignment of these other coils is measured by the processing circuit using the signals on these other coils, and thus for each position coil in the position coils, the alignment with the magnetic coordinate system is calibrated in response to the signal received from the position coil.

[0051] In some embodiments, the magnetic field sensor may include only one or only two position coils (eg, a single-axis or dual-axis magnetic sensor). In these embodiments, the processing circuit calibrates the alignment of the single-axis or dual-axis sensor with one or more generated magnetic fields.

[0052] In some embodiments, the processing circuit calculates a sensitivity of the magnetic field sensor in response to one or more signals from the magnetic field sensor.

[0053] The processing circuit stores the calculated parameters (e.g., alignment of the image sensor relative to the magnetic field sensor, alignment of the magnetic field sensor with one or more generated magnetic fields, sensitivity of the magnetic field sensor, and optical aberration corrections) in a storage device (such as an electrically erasable programmable read-only memory (EEPROM)), which is typically included in the probe. The stored parameters can then be retrieved by the processing device during use of the probe to correct for misalignment of the magnetic field sensor, image sensor, aberrations of the image sensor, and sensitivity mismatch of the magnetic field sensor.

[0054] System Description

[0055] Documents incorporated herein by reference shall be considered to be an integral part of this application, except that, to the extent that any term is defined in these incorporated documents in a manner that contradicts a definition explicitly or implicitly made in this specification, only the definition in this specification shall prevail.

[0056] See now Figures 1 to 3 , which is a schematic diagram of a probe 10 constructed and operated in accordance with an embodiment of the present invention. Probe 10 can be any suitable probe, such as a catheter, a guidewire, or a medical tool, such as an ENT tool. Probe 10 includes a distal end 12, a proximal end 22 (by way of example, from which a guidewire extends), and a handle 24 that allows an operator to control probe 10 via various operating controls 26. Handle 24 may include a storage device 25, such as an EEPROM. Storage device 25 may be disposed in any suitable portion of probe 10, such as, but not limited to, proximal end 22. Reference Fig.11 The use of the storage device is described in more detail.

[0057] See now Figure 2 and Figure 3 The distal end 12 includes an image sensor 14 (such as a camera) and a magnetic field sensor 16. The probe 10 may optionally include other elements, such as one or more irrigation tubes (and / or aspiration tubes) 18, and one or more illumination (illumination) elements 20, by way of example only. The distal end 12 may be deflectable. Figure 2 and Figure 3 The image sensor 14, illumination element 20, and irrigation tube 18 are shown connected directly or indirectly to a support bar 27 formed of any suitable deflectable and resilient material, such as, but not limited to, Nitinol or stainless steel.

[0058] The magnetic field sensor 16 may include a plurality of position coils 28 , such as two or three position coils. Figure 3 Two orthogonally disposed position coils 28-1, 28-2 are shown disposed around the proximal portion of the distal end 12. The axis of each of the position coils 28-1, 28-2 is disposed perpendicular to the longitudinal axis of the probe. The position coils 28-1, 28-2 may be wound coils disposed within the distal end 12, or may be formed as Figure 3 The printed circuit board (PCB) printed coils shown (eg, printed on a flexible PCB), or any other suitably placed coils, may be used to determine the position and / or orientation (winding) of the distal end 12 .

[0059] See now Figure 4 , the figure is Figure 11 is a cross-sectional view of the distal end 12 of the probe 10 . Figure 4 A third position coil 28-3 is shown disposed proximate to the image sensor 14. The position coil 28-3 is disposed so that its axis is parallel to the longitudinal axis of the probe 10. By way of example only, the position coil 28-3 may be a wound coil or a PCB printed coil. The position coil 28-3 may be used to determine the position and / or orientation (excluding winding) of the distal end 12. It should be understood that the positioning of the position coil 28 is shown in the accompanying drawings by way of example only. The position coil 28 may be disposed in the distal end 12 in any suitable position and / or orientation.

[0060] See now Figure 5 , which is an isometric view of a calibration apparatus 30 constructed and operative in accordance with an embodiment of the present invention. The calibration apparatus 30 includes a magnetic field generator 32, a fixture 34, an optical target 36, and processing circuitry 38.

[0061] The magnetic field generator 32 is configured to generate at least one time-varying magnetic field having a predetermined direction aligned with the fixture 34. In some embodiments, the magnetic field generator 32 is configured to generate two or three magnetic fields corresponding to two or three orthogonal axes. Each of the magnetic fields is typically generated so as to generate a uniform magnetic field within the area of ​​the fixture 34.

[0062] In some embodiments, the magnetic field generator includes three calibration coil sets 40 respectively aligned with three orthogonal axes of the magnetic coordinate system 44. In some embodiments, each calibration coil set in the calibration coil sets 40 includes two coils, for example, Helmholtz coils that provide a uniform magnetic field. Helmholtz coil systems are commercially available, for example, from Bartington Instruments (Oxford, England).

[0063] The calibration coil sets 40 are coupled to a drive circuit (not shown) which causes the calibration coil sets 40 to generate a magnetic field. Each calibration coil set 40 generates a magnetic field that is substantially orthogonal to the plane defined by the calibration coil set 40 and therefore substantially orthogonal to the fields generated by the other two calibration coil sets 40.

[0064] Each calibration coil set 40 is configured to generate a predetermined substantially uniform magnetic field ( Figure 3 and Figure 4 ). The drive circuit is adjusted so that the amplitudes of the respective magnetic fields generated by the three calibration coil sets 40 are equal.

[0065] References below Fig.11The processing circuit 38 is described in more detail. In implementation, some or all of the functions of the processing circuit 38 may be combined in a single physical component, or alternatively, implemented using multiple physical components. These physical components may include hard-wired or programmable devices, or a combination of the two. In some embodiments, at least some of the functions of the processing circuit may be implemented by a programmable processor under the control of suitable software. The software may be downloaded to the device in electronic form via a network, for example. Alternatively or in addition, the software may be stored in a tangible, non-transient computer-readable storage medium, such as an optical, magnetic or electronic memory.

[0066] See now Figure 6 and Figure 7 . Figure 6 for Figure 5 Front view of the calibration device 30. Figure 7 for Figure 5 A side view of the calibration device 30 is shown.

[0067] The clamp 34 is configured to hold the distal end 12 of the probe 10. The clamp 34 is fixed to one of the calibration coil assemblies 40 and aligned with the axis of the magnetic coordinate system 44. The clamp 34 may include a clamp assembly that is constructed and configured so that the distal end 12 of the probe 10 is held in the clamp 34 in a substantially uniform magnetic field region adjacent to the center of the clamp 34, and so that the long axis of the probe 10 will be substantially orthogonal to the plane defined by the calibration coil assembly in the calibration coil assembly 40. The clamp 34 includes a corresponding semicircular groove, the radius of which is substantially equal to the outer radius of the distal end 12 of the probe 10.

[0068] The clamp 34 may include a heating element (not shown) and at least one temperature sensor (not shown) for heating the distal end 12 of the probe 10 to a temperature substantially equal to the temperature of the body into which the probe 10 is to be inserted and maintaining the distal end 12 at that temperature during calibration. As is known in the art, the position coil 28 ( Figure 3 , 4 )'s response to a magnetic field may vary with temperature. For example, when a coil is wound around a ferrite core, its inductance may change with temperature, which may introduce errors into the calibration of the magnetic field sensor 16 ( Figure 3 , Figure 4 Thus, distal end 12 is typically heated to and maintained at a temperature of 37° C. during calibration, although other temperatures may be selected, for example, when probe 10 is to be used under cryogenic conditions, such as those typically encountered during open heart surgery.

[0069] The probe 10 is inserted into the fixture 34 and rotated about its long axis to a desired rotational orientation, wherein the axis of the position coil 28 ( Figure 3 and Figure 4 ) are substantially aligned with the respective axes of the magnetic coordinate system 44 defined by the respective calibration coil set 40. The desired rotational orientation may be indicated, for example, by a fiducial mark or other feature (not shown) on the outer surface of the probe 10. In this way, the probe 10 is fixed in a known orientation relative to the magnetic field generated by the calibration coil set 40. The probe 10 is also connected to the processing circuit 38.

[0070] The corresponding gain and angular orientation of the position coils 28 are then calibrated by sequentially activating the calibration coil set 40 to generate a predetermined known magnetic field and measuring the amplitude of the signal generated by the position coils 28 .

[0071] First, to calibrate the gain (sensitivity) of the position coils 28, the total amplitude of the corresponding position coil signals is derived by summing the squares of the signal amplitudes generated by each of the position coils 28 in response to each of the calibration coil groups 40 in sequence. Since the magnetic field near the position coils 28 has equal and substantially uniform components along each of the axes of the position coils 28, the total signal amplitude will be independent of the respective orientation and position of the position coils 28, and will depend only on the respective coil gain. Therefore, the measured total signal amplitude can be used to determine the respective normalization factor of the position coils 28 by dividing the measured amplitude by the expected standard value. Subsequently, the amplitude of the signals received from these coils can be multiplied by the respective normalization factor to correct for gain variations.

[0072] The normalized amplitude of the signal generated by each of the position coils 28 in response to each of the magnetic fields will be proportional to the cosine of the angle between the respective axis of the position coil 28 and the applied magnetic field direction. Thus, for each of the position coils 28, the cosines of three such angles corresponding to the directions of the three orthogonal magnetic fields applied by the calibration coil set 40 can be derived. Since, as described above, the probe 10 is held in the fixture 34 in such a manner that the axis of the probe 10 is substantially aligned with the three orthogonal magnetic field directions of the magnetic coordinate system 44, the orientation of the position coil 28 relative to the axis of the probe 10 can be determined.

[0073] In some embodiments of the present invention, when the Z-axis magnetic field is activated, the position coil 28-3 ( Figure 4 ) The normalized amplitude of the signal received by the position coil 28-3 is calculated. The X-axis field and the Y-axis field are similarly activated and corresponding normalized signals are received from the position coil 28-3. The received signals are used to calculate the coil angle calibration factor for the position coil 28-3, which is then recorded in the probe 10 and used to determine the position and orientation of the probe. A similar procedure is used to calibrate the coils 28-1, 28-2 ( Figure 3 ).

[0074] The optical target 36 is also aligned with the fixture 34 so that the image sensor 14 in the probe 10 can capture an image of the optical target 36 while the probe 10 is held in the fixture 34. The optical target 36 includes a plurality of alignment features 46 (only some are labeled for simplicity). In some embodiments, the optical target 36 includes a plurality of alternating rectangular (e.g., square) black and white (or darker and lighter) portions, similar to a chess or checkerboard. In other embodiments, a single suitably shaped alignment feature, such as a cross, may be used instead of a checkerboard pattern. In other embodiments, other suitably shaped alignment techniques may be used.

[0075] In some embodiments, alignment features 46 may include a central alignment feature 48 that is substantially centrally disposed in optical target 36 such that central alignment feature 48 is substantially aligned with the X and Y positions of a central longitudinal axis of distal end 12 of probe 10 (indicated by dashed line 52).

[0076] In some embodiments, the optical target 36 is configured to rotate about the center alignment feature 48, for example using a bearing 50 about the Z-axis. The rotational motion of the optical target 36 may be controlled using a motor (not shown), which may be controlled by the processing circuit 38. A corresponding image of the optical target 36 may be captured by the image sensor 14 at a corresponding rotational position of the optical target 36.

[0077] Calibration of the position and orientation of the image sensor 14 and correction of optical aberrations are performed based on one or more captured images, as shown in FIG. Figures 8 to 11 Described in more detail.

[0078] See now Figure 8 , which is in Figure 5 Schematic diagram of a captured image 54 analyzed in the calibration device 30.

[0079] Processing circuit 38 ( Figures 5 to 7 ) is configured to find, for example but not limited to, using image processing techniques such as edge detection, respective boundaries between respective rectangular (e.g., square) portions corresponding to respective alignment features of the plurality of alignment features 46 (only some of which are labeled for simplicity) in the captured image 54. A circle 56 (only some of which are labeled for simplicity) is centered around the boundary (detected point) found between the rectangular portions. The boundary may be used to calibrate the image sensor 14 based on the following: Figure 3 , Figure 4 ), for example, relative to the magnetic field sensor 16 ( Figure 3 , Figure 4 ) alignment: the position of the center alignment feature 48 in the captured image 54 and / or the position and orientation of the alignment feature 46 in the captured image 54; the alignment feature 46 ( Figure 6 , Figure 7 ) and the magnetic coordinate system 44 (composed of the calibration coil set 40 ( Figure 6 , Figure 7 ) generates a magnetic field defining a given spatial relationship between); the fixture 34 ( Figure 6 , Figure 7 ) and a given spatial relationship between alignment features 46 of optical target 36; optical properties of image sensor 14; and optionally, alignment between magnetic field sensor 16 and magnetic coordinate system 44. The calibration of the alignment of image sensor 14 described above may be based on the corrected position of alignment features 46 in captured image 54 corrected for optical aberrations, as described below with reference to Fig. 9 described.

[0080] See now Fig. 9 , which shows Figure 5 Schematic diagram of the optical aberration correction method in the calibration device 30. As mentioned above Figure 8 As shown, circle 56 is centered around the boundary between the rectangular portions of alignment feature 46 ( Figure 8 If the image sensor 14 does not contain optical defects, the captured image 54 ( Figure 8 ) will include alignment features 46 that are identical to those included on optical target 36, with the correct positioning, spacing, and orientation. Specifically, the lines defined by the centers of circles 56 (only some are labeled for simplicity) will be straight, parallel, and equally spaced. Conversely, the lines defined by the centers of circles 56 will be straight, parallel, and equally spaced. Fig. 9 The lines defined by the centers of the circles 56 in are not straight, parallel and equally spaced. Fig. 9 Also shown are crosses 58 (only some are labeled for simplicity), the centers of which define straight, parallel, and equally spaced lines based on the geometry of the alignment features 46 of the optical target 36. The pattern of crosses 58 is centered around the center of the captured image 54. The displacement between the center of the corresponding circle 56 and the center of the corresponding cross 58 defines an optical aberration (e.g., spherical aberration) correction for the image sensor 14, and can optionally be used to calibrate the alignment of the image sensor 14 with the magnetic field sensor 16. The above process can be repeated for different rotational positions of the optical target 36. The rotational position of the optical target 36 does not need to be known by the processing circuit 38 in order to perform the optical aberration correction. Other optical aberration corrections, such as chromatic aberration corrections, can be calculated based on a suitable analysis of the captured image 54 using methods known to those skilled in the art.

[0081] See now Fig.10 , which is Figure 5 Schematic diagram of another captured image 60 in the calibration device 30 of FIG. The captured image 60 is captured when the optical target 36 is rotated so that the side of the optical target 36 is not aligned with the X-axis and Y-axis of the magnetic coordinate system 44 ( Figure 6 , Figure 7 ). The captured image 60 clearly shows that the lines defined by the alignment features 46 are not straight, parallel, and equally spaced lines, and therefore, the image sensor 14 exhibits spherical aberration.

[0082] See now Fig.11 , which includes Figure 5 Flowchart 70 of steps in a method of operating the calibration device 30. See also Figure 6 and Figure 7 .

[0083] The probe 10 is disposed (block 72) in the fixture 34, as described above with reference to Figure 6 and Figure 7 The processing circuit 38 is configured to actuate (block 74) the calibration coil set 40 of the magnetic field generator 32 to generate a magnetic field using the calibration coil set 40. When the probe 10 is held in the fixture 34, the generated magnetic field ( Figure 3 and Figure 4 ). Then, the calibration coil assembly 40 can be as described above with reference to Figure 6 or Figure 7 The calibration coil sets 40 may be actuated simultaneously, or if different respective frequencies are used for different respective calibration coil sets 40 (i.e., the first calibration coil set 40 generates a first frequency, the second calibration coil set 40 generates a second frequency, and the third calibration coil set 40 generates a third frequency).

[0084] The processing circuit 38 is configured to actuate (block 76 ) the image sensor 14 of the probe 10 to capture an image of the optical target 36 while the probe 10 is held in the fixture 34 .

[0085] Processing circuit 38 is optionally configured to actuate a motor (not shown) to rotate optical target 36 (block 78) to a new rotational position. The steps of block 76 are repeated at the new rotational position. The steps of blocks 76 and 78 may be repeated any suitable number of times. Increasing the number of images used to calibrate image sensor 14 may improve the accuracy of calibration of image sensor 14.

[0086] The processing circuit 38 is configured to receive (box 80) the following from the probe: a signal (or multiple signals) output by the magnetic field sensor 16 (from the position coil 28) in response to one or more magnetic fields; and one or more images captured by the image sensor 14 of the optical target 36 when the probe 10 is held in the fixture 34 (e.g., at multiple corresponding rotational positions of the optical target 36).

[0087] Each received image includes at least some of the plurality of alignment features 46. In some embodiments, the processing circuit 38 is configured to find respective boundaries between respective rectangular portions corresponding to respective alignment features of the plurality of alignment features 46, as described above with reference to Figure 8 The central boundaries between some of the rectangular portions correspond to the central alignment features 48 .

[0088] Processing circuitry 38 is configured to calibrate (block 82) the alignment of image sensor 14 relative to magnetic field sensor 16 in response to the received signal, the received image, and other factors, such as, but not limited to, the location of center alignment feature 48 in captured image 54 ( Figure 8 ) and / or the position and orientation of alignment features 46 in captured image 54, a given spatial relationship between alignment features 46 of optical target 36 and magnetic coordinate system 44 (defined by the magnetic field generated by calibration coil set 40), a given spatial relationship between alignment features 46 of fixture 34 and optical target 36, optical properties of image sensor 14, and optionally, alignment between magnetic field sensor 16 and magnetic coordinate system 44. The above-described calibration of the alignment of image sensor 14 may be based on the corrected position of alignment features 46 in captured image 54 corrected for optical aberrations, as described below with reference to Fig. 9 described.

[0089] The processing circuitry 38 is configured to calculate (block 84) an optical aberration correction for the image sensor 14 in response to the respective positions of respective ones of the at least some of the alignment features 46 in the received image. In some embodiments, the processing circuitry 38 is configured to calculate the optical aberration correction for the image sensor in response to the curvature of at least one line defined by the respective ones of the at least some of the alignment features 46 in the received image at the respective positions.

[0090] In some embodiments, when multiple corresponding images are captured at multiple rotational positions of optical target 36, processing circuitry 38 is configured to calculate optical aberration corrections for image sensor 14 in response to corresponding positions of corresponding ones of alignment features 46 in the received corresponding images.

[0091] The processing circuit is configured to calibrate (block 86) the alignment of the magnetic field sensor 16 with one or more magnetic fields generated by the magnetic field sensor 32 in response to one or more signals received from the magnetic field sensor 16, as described above with reference to Figure 6 and Figure 7 In some embodiments, the processing circuit 38 is configured to position the coil 28 ( Figure 3 , Figure 4) in order to calibrate the alignment with the magnetic coordinate system 44 in response to the signals received from the position coils 28.

[0092] The processing circuit 38 is configured to calculate (block 88) the sensitivity of the magnetic field sensor 16 in response to one or more signals received from the magnetic field sensor 16, as shown in reference Figure 6 and Figure 7 Described in more detail.

[0093] The processing circuit is configured to store the storage device 25 ( Figure 1 ), an alignment of the image sensor 14 relative to the magnetic field sensor 16 , an alignment of the magnetic field sensor 16 with one or more magnetic fields generated by the magnetic field generator 32 , and a sensitivity of the magnetic field sensor 16 are stored (block 90 ).

[0094] The probe 10 is then removed (block 92 ) from the fixture 34 .

[0095] If desired, the software components of the present invention may be implemented in ROM (read-only memory) form. If desired, the software components may generally be implemented in hardware using conventional techniques. The software components may be instantiated, for example, as a computer program product or on a tangible medium. In some cases, the software components may be instantiated as signals that can be interpreted by an appropriate computer, but such instantiations may be excluded in certain embodiments of the present invention.

[0096] For the sake of clarity, various features of the present invention described in the context of independent embodiments may also be provided in combination in a single embodiment. Conversely, for the sake of simplicity, various features of the present invention are described in the context of a single embodiment and may also be provided separately or in any suitable sub-combination.

[0097] The above embodiments are cited by way of example, and the present invention is not limited by what is specifically shown and described above. On the contrary, the scope of the present invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications thereof, which should occur to those skilled in the art when reading the above description, and which are not disclosed in the prior art.

Claims

1. A device for calibrating a probe including an image sensor and a magnetic field sensor, the device comprising: a fixture configured to hold the probe; a magnetic field generator configured to generate at least one magnetic field having a predetermined direction aligned with the fixture; an optical target aligned with the fixture so that the image sensor in the probe can capture an image of the optical target while the probe is held in the fixture; as well as a processing circuit configured to receive from the probe a signal output by the magnetic field sensor in response to the at least one magnetic field and the image captured by the image sensor while the probe is held in the fixture, and to calibrate an alignment of the image sensor relative to the magnetic field sensor in response to the received signal and the received image.

2. The device according to claim 1, wherein The processing circuit is configured to calibrate alignment of the magnetic field sensor with the at least one magnetic field generated by the magnetic field generator in response to the received signal.

3. The device according to claim 2, wherein: The processing circuit is configured to store the alignment of the image sensor relative to the magnetic field sensor and the alignment of the magnetic field sensor with the at least one magnetic field in a storage device included in the probe.

4. The device according to claim 1, wherein: The processing circuit is configured to calculate a sensitivity of the magnetic field sensor in response to the received signal.

5. The apparatus of claim 1, wherein: The optical target includes a plurality of alignment features; the received image includes at least some of the plurality of alignment features; And the processing circuit is configured to calculate optical aberration corrections for the image sensor in response to respective positions of respective ones of the at least some of the alignment features in the received image.

6. The device according to claim 5, wherein: The processing circuit is configured to calculate an optical aberration correction for the image sensor in response to a curvature of at least one line defined by corresponding ones of the at least some alignment features at the corresponding location in the received image.

7. The apparatus of claim 6, wherein: The optical target includes a plurality of alternating rectangular portions; and the processing circuit is configured to find respective boundaries between respective ones of the rectangular portions corresponding to respective ones of the plurality of alignment features.

8. The device according to claim 7, wherein: A central boundary between some of the rectangular portions corresponds to a central alignment feature among the plurality of alignment features, and the processing circuit is configured to calibrate the alignment of the image sensor relative to the magnetic field sensor in response to the position of the central alignment feature in the received image.

9. The apparatus according to claim 8, wherein: The optical target is configured to rotate about the central alignment feature; and the processing circuit is configured to: receiving a plurality of respective images captured by the image sensor of the optical target at a plurality of respective rotational positions of the optical target; as well as The optical aberration correction of the image sensor is calculated in response to the respective positions of respective ones of the at least some alignment features in the respective received images.

10. The apparatus of claim 1, wherein: The magnetic field generator comprises three calibration coil groups, wherein the three calibration coil groups are respectively aligned with three orthogonal axes of the magnetic coordinate system; The magnetic field sensor comprises three position coils; and The processing circuit is configured to: actuating the calibration coil assembly to generate a magnetic field for detection by the position coil; as well as For each of the position coils, alignment with the magnetic coordinate system is calibrated in response to a signal received from the position coil.

11. The device according to claim 10, wherein: Each of the calibration coil groups is a Helmholtz coil.

12. A method for calibrating a probe comprising an image sensor and a magnetic field sensor, the method comprising: placing the probe in a fixture; generating at least one magnetic field having a predetermined direction aligned with the fixture; capturing, with the image sensor, an image of an optical target aligned with the fixture while the probe is held in the fixture; receiving from the probe a signal output by the magnetic field sensor in response to the at least one magnetic field and the image captured by the image sensor while the probe is held in the fixture; as well as An alignment of the image sensor relative to the magnetic field sensor is calibrated in response to the received signal and the received image.

13. The method of claim 12, further comprising calibrating an alignment of the magnetic field sensor with the at least one magnetic field in response to the received signal.

14. The method of claim 13, further comprising storing the alignment of the image sensor relative to the magnetic field sensor and the alignment of the magnetic field sensor with the at least one magnetic field in a storage device included in the probe.

15. The method of claim 12, further comprising calculating a sensitivity of the magnetic field sensor in response to the received signal.

16. The method according to claim 12, wherein: The optical target includes a plurality of alignment features; the received image includes at least some of the plurality of alignment features; and the method further includes calculating an optical aberration correction of the image sensor in response to respective positions of respective ones of the at least some of the alignment features in the received image.

17. The method according to claim 16, wherein: The calculation of the optical aberration correction is performed in response to a curvature of at least one line defined by respective ones of the at least some alignment features at the respective locations in the received image.

18. The method of claim 17, wherein: The optical target includes a plurality of alternating rectangular portions; and the method further includes finding respective boundaries between respective ones of the rectangular portions corresponding to respective ones of the plurality of alignment features.

19. The method of claim 18, wherein: A central boundary between some of the rectangular portions corresponds to a central alignment feature of the plurality of alignment features; calibrating the alignment of the image sensor relative to the magnetic field sensor is performed in response to the position of the central alignment feature in the received image.

20. The method according to claim 19, further comprising: rotating the optical target about the central alignment feature to a plurality of rotational positions; receiving a plurality of respective images captured by the image sensor of the optical target at respective ones of the plurality of rotational positions of the optical target, and wherein calculating the optical aberration correction of the image sensor is performed in response to the respective positions of respective ones of the at least some alignment features in the received respective images.

21. The method according to claim 12, further comprising: actuating three calibration coil sets, the three calibration coil sets being respectively aligned with three orthogonal axes of the magnetic coordinate system to generate magnetic fields for detection by three position coils of the magnetic field sensor; as well as For each of the position coils, alignment with the magnetic coordinate system is calibrated in response to a signal received from the position coil.

Images