Determining the roll angle of the distal end of a deflectable or non-deflectable invasive medical device

Abstract

The system includes a medical device, a position sensor, and a processor. The medical device includes a handle and a head, the head configured for insertion into a patient's organ and having a feature that is rotationally asymmetric with respect to a longitudinal axis of the medical device. The position sensor is disposed on the head and configured to generate a signal in response to an externally applied magnetic field. The processor is configured to receive the signal generated by the position sensor on the head and to estimate a roll angle of the rotationally asymmetric feature of the head based on the received signal.

Description

[Technical Field]

[0001] The present invention relates generally to medical devices, and more particularly to tracking invasive devices within a patient's organ. [Background technology]

[0002] Techniques for tracking medical devices within a patient's organ have previously been proposed in the patent literature. For example, U.S. Patent Application Publication No. 2018 / 0280049 describes a medical device including a disposable ear-nose-throat (ENT) tool, a reusable handle, and a processor. The ENT tool is configured to perform a medical procedure within the patient's ENT organ. The reusable handle is configured to hold and control the disposable ENT tool and includes a position sensor configured to generate one or more position signals indicative of a first position of the reusable handle. The processor is configured to receive the position signals from the position sensor and, based on the position signals, estimate a second position of the disposable ENT tool within the patient's ENT organ.

[0003] As another example, U.S. Patent No. 6,272,371 describes an invasive probe device that includes a flexible, elongated probe having a distal portion adjacent a distal tip of the flexible, elongated probe for insertion into a subject's body. The distal portion assumes a predetermined curve when a force is applied thereto. First and second sensors are fixed to the distal portion of the probe at known locations relative to the distal tip, and the sensors generate signals responsive to bending of the probe. Signal processing circuitry receives and processes the signals responsive to bending to find position and orientation coordinates of at least the first sensor and to determine the locations of multiple points along the length of the distal portion of the probe. Summary of the Invention [Means for solving the problem]

[0004] One embodiment of the present invention provides a system including a medical device, a position sensor, and a processor. The medical device includes a handle and a head, the head configured for insertion into a patient's organ and having a feature that is rotationally asymmetric about a longitudinal axis of the medical device. The position sensor is disposed on the head and configured to generate a signal in response to an externally applied magnetic field. The processor is configured to receive the signal generated by the position sensor on the head and estimate a roll angle of the rotationally asymmetric feature of the head based on the received signal.

[0005] In some embodiments, the position sensor includes at least a coil having an axis oriented at a given rotational angle relative to the rotationally asymmetric feature of the head.

[0006] In some embodiments, the rotationally asymmetric feature comprises a medical tool.

[0007] In one embodiment, the medical tool comprises an ear, nose and throat (ENT) shaver. In another embodiment, the medical tool comprises an ENT suction tool. In yet another embodiment, the medical tool comprises an ENT microbrider. In a further embodiment, the rotationally asymmetric feature comprises an opening in the medical tool. In an additional embodiment, the medical tool is curved relative to the longitudinal axis.

[0008] In some embodiments, the position sensor is a single axis sensor (SAS) printed on a circuit board.

[0009] In some embodiments, the position sensor is a dual axis sensor (DAS) printed on a circuit board.

[0010] In one embodiment, the system further includes a location pad including at least one magnetic field emitter configured to transmit a magnetic field near the organ.

[0011] In another embodiment, the system further includes a display, and the processor is configured to (a) track the location of the head in response to the received signals, and (b) render on the display an image including a representation of at least a portion of the organ and a representation of at least a portion of the head within the body.

[0012] Furthermore, in accordance with another embodiment of the present invention, there is provided a method including inserting a medical instrument including a handle and a head into an organ of a patient, the head having a feature that is rotationally asymmetric with respect to a longitudinal axis of the medical instrument, a position sensor disposed on the head is used to generate a signal in response to an externally applied magnetic field, the signal generated by the position sensor on the head is received, and a roll angle of the rotationally asymmetric feature of the head is estimated based on the received signal.

[0013] The present invention will be more fully understood from the following detailed description taken in conjunction with the drawings, in which: [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic, pictorial illustration of an ear, nose and throat (ENT) device tracking system, in accordance with one embodiment of the present invention; [Figure 2] 2 is a schematic diagram of an ear, nose and throat (ENT) device used in FIG. 1 and a representation of a paranasal sinus with an inserted interchangeable head of the ENT device, according to one embodiment of the present invention. [Figure 3] 3 is a schematic diagram of the handle and interchangeable head of the ear, nose and throat (ENT) instrument of FIG. 2, in accordance with one embodiment of the present invention. [Figure 4] 3 is a schematic diagram of interchangeable heads of the ear, nose and throat (ENT) instrument of FIG. 2, each including a magnetic sensor disposed on the distal end of the head, according to one embodiment of the present invention. [Figure 5] 5 is a flow chart that schematically illustrates a method and algorithm for tracking the head roll angle of the ear, nose and throat (ENT) device of FIG. 4 within a patient's head, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Overview Some invasive medical procedures may require tracking the rotational orientation of the distal end of a medical instrument within a patient's organ. The medical instrument may include a handle with multiple interchangeable heads, which may be rigid and straight, rigid and curved (e.g., curved distal edges), or deflectable distal edges. Furthermore, even straight heads may include features or components that are rotationally asymmetric. Interchangeable heads with rotationally asymmetric shapes, such as those including tools positioned at preferred rotational orientations relative to the head, are configured to perform different therapeutic functions and / or access different organs, including cavities. Thus, for use within an organ, such as to cut tissue, a physician needs to know the rotational orientation of the tool relative to the target tissue in the organ.

[0016] Additionally, some medical devices may allow interchangeable rigid heads to be inserted into the handle in one of many rotational positions. Additionally or alternatively, some medical devices may allow the inserted head to be rotated to multiple positions. These options may further increase a physician's uncertainty about the actual rotational orientation of the tool (e.g., a cutting tool) relative to the target tissue.

[0017] As another example, rigid heads of ear, nose, and throat (ENT) instruments may have at their distal ends rotationally asymmetrically aligned electrical cutting elements (e.g., partially covered rotary blades or burrs) positioned on the heads at a given rotational orientation and used to remove tissue within a patient's sinuses. Again, to perform this task, the physician must know how to precisely rotate the heads so that the heads of the electrical cutting elements face the target tissue.

[0018] Embodiments of the invention described below enable accurate tracking of the roll angle of rotationally asymmetric features, such as tools, relative to the longitudinal axis of a medical instrument head within an organ. The disclosed techniques enable a physician to precisely manipulate a tool located at the distal end of the head (e.g., precisely manipulate an ENT shaver or ENT suction device within a patient's sinuses) when treating target tissue. The medical instrument head may be replaceable or fixed.

[0019] The disclosed embodiments provide a position sensor, such as a magnetic position sensor, coupled to the head of the instrument that can respond to an externally applied magnetic field to indicate to the user the rotational orientation (i.e., roll angle) of a component of the head, such as the cutting tool described above, or, as another example, a curved distal edge with irrigation ports.

[0020] In some embodiments, using a magnetic tracking system, the processor determines the roll angle of the distal tip using signals from the magnetic sensors.

[0021] In one embodiment, the disclosed magnetic sensor is a single-axis sensor (SAS) whose coil axis is aligned at a given rotational angle relative to the rotational orientation of a feature (e.g., of a cutting tool) to track the roll angle of the feature (e.g., cutting tool) inside an organ, e.g., relative to a rendered anatomical structure.

[0022] In another embodiment, the sensor is a dual-axis sensor (DAS) comprising, for example, two orthogonally wound coils capable of tracking the position, orientation, and roll angle of each feature, with one axis of its coils aligned at a given rotational angle relative to the rotational orientation feature.

[0023] The SAS or DAS may be printed on a printed circuit board (PCB) for attachment to the head.

[0024] As described above, the SAS can be used to render an image on a display that includes a representation of at least a portion of an organ and a representation of a distal end of an inserted interchangeable head of a medical device within the organ in response to a tracked roll angle of the distal end of the inserted interchangeable head. The DAS can be used to render a representation on a display that corresponds to the tracked position, orientation, and roll angle of the distal end of the inserted interchangeable head.

[0025] By providing accurate rotational information of the distal tip, features positioned at a given rotational orientation at the distal tip (e.g., a distal suction opening with a rotationally asymmetric shape, or a tool such as a blade) can be used more effectively and safely in interventional procedures.

[0026] System Description 1 is a schematic, pictorial illustration of an ear, nose, and throat (ENT) device tracking system 20, in accordance with one embodiment of the present invention. Medical procedures for which the system 20 is typically used include invasive and / or investigative procedures on the paranasal sinuses and other ENT structures, such as the adenoids or Eustachian tubes, that are accessible via the nasal cavity. However, the system may also be used, mutatis mutandis, to treat other body organs (such as the brain) of a patient 22.

[0027] In the illustrated embodiment, the magnetic field emission assembly 24 is positioned behind and / or around the head of the patient 22, for example, by fastening the assembly 24 to a chair 25 (or bed) on which the patient is sitting (or lying). The magnetic field emission assembly 24 in the illustrated example includes five magnetic field emitters 26 fixed within a horseshoe-shaped frame, which is positioned under or around the patient 22 so that the magnetic field emitters 26 surround the head of the patient 22. Alternatively, fewer or more emitters 26 may be used in a variety of different configurations. The magnetic field emitters 26 are configured to emit alternating magnetic fields at respective frequencies into a region 30 in which the head of the patient 22 is located.

[0028] The alternating magnetic field induces signals in magnetic position sensors 32 and 36. Position sensor 32 is shown positioned on ENT instrument 28 to track the position, orientation, and roll angle of distal end 34 of ENT equipment 28. Position sensor 36 is shown positioned on patient 22 (e.g., on the forehead of patient 22) to track the position of the patient's head and compensate for movement of the patient's head relative to magnetic field emitting assembly 24. By way of example only, ENT instrument 28 may include any one or more of a suction tool, a microdebrider, or a shaver.

[0029] The distal tip 34 of the ENT instrument 28 and the head of the patient 22 are tracked using a tracking subsystem operating on the processor 38. The position sensor 32 includes at least one coil, which is described in more detail in FIG. 4. To determine the roll angle of the distal tip 34 of the ENT instrument 28 within the sinus of the patient 22, the position sensor 32 is fixed to the ENT instrument 28 with the axis of the at least one coil of the sensor 32 positioned at a given rotational orientation relative to a physical feature or component of the distal end (e.g., a cutting tool disposed on the distal end) whose roll angle is to be tracked, as described above.

[0030] A system using magnetic field emitters to track entities such as magnetic field emitter 26 inserted into a patient is described in U.S. Patent Application Publication No. 2016 / 0007842, which is incorporated herein by reference. Additionally, the Carto® system (manufactured by Biosense Webster, Irvine, California) uses a tracking system similar to that described herein to determine the location and orientation of coils within the irradiated magnetic field region.

[0031] In some embodiments, the medical device 28 is attached to and held by a robotic arm 40 that includes multiple robotic joints configured to control the movement of the robotic arm 40 and manipulate the ENT device 28. In other embodiments, the ENT device 28 is held and manipulated by a physician 54. The robotic arm 40 generally has its own robotic coordinate system. The robotic coordinate system is aligned with the magnetic coordinate system of the magnetic field emitter 26, or vice versa. Alignment of the robotic coordinate system with the magnetic coordinate system can be performed, for example, by moving the robotic arm 40 or the ENT device 28 attached to the robotic arm 40 to one or more locations known to the magnetic field emitter 26, such as locations on the magnetic field emission assembly 24. Once alignment of the robotic coordinate system with the magnetic coordinate system is performed, locations in the magnetic coordinate system can be transformed to the robotic coordinate system for proper manipulation of the robotic arm 40.

[0032] The processor 38 includes a processing unit in communication with one or more memories. Typically, components may be connected to the processor 38 by cables. Alternatively, or in addition, components may be wirelessly coupled to the processor 38. The processor 38 may be mounted on a console 50, which includes motion controls 51, typically including a keypad and / or a pointing device such as a mouse or trackball. The console 50 also connects to other components of the system 20, such as a proximal end 52 of the ENT equipment 28. A physician 54 interacts with the processor 38 using the motion controls 51 while performing a procedure, and the processor 38 may present results generated by the system 20 on a display 56.

[0033] In some embodiments, a CT image of the patient 22 is acquired prior to performing the medical procedure. The CT image is stored in memory (not shown) by the processor 38 for subsequent retrieval. In FIG. 1 , the display 56 displays various views 59 of the previous CT scan (or other suitable scan), which can be used to assist the physician 54 in guiding the ENT equipment 28 within the sinuses. The display screen 56 also shows an image 61 captured by a camera (not shown) of the ENT equipment 28. As explained in more detail in FIG. 2 , the CT image can be aligned with a magnetic coordinate system so that a representation of the ENT equipment 28 can be displayed along with the CT image on the display 56.

[0034] In practice, some or all of these functions of processor 38 may be combined into a single physical component or may be embodied using multiple physical components. These physical components may comprise hardwired or programmable devices, or a combination of the two. In some embodiments, at least some of the processor's functions may be performed by a programmable processor under the control of suitable software. This software may be downloaded to the device in electronic form, for example, over a network. Additionally or alternatively, this software may be stored on a non-transitory computer-readable medium, such as an optical, magnetic, or electronic storage medium.

[0035] Determining the roll angle of the distal end of a deflectable or non-deflectable invasive medical device Figure 2 is a schematic diagram of the ear, nose, and throat (ENT) device 28 used in Figure 1 and a representation of a paranasal sinus into which an interchangeable head 64 of the ENT device 28 has been inserted, according to one embodiment of the present invention. The ENT device 28 includes a handle 62 into which a plurality of interchangeable heads 64 of varying stiffness are individually and reversibly insertable. Figure 2 shows one of the interchangeable heads 64 inserted into the handle 62. Another example of an interchangeable head 64 is shown in Figure 3, described below. The ENT device 28 shown in Figure 2 further includes an irrigation or drainage tube 66.

[0036] 2 shows the ENT instrument 28 before position sensors have been added to the ENT tool. Indeed, in some embodiments, as described in detail in FIG. 4, the ENT instrument 28 may be embodied as an off-the-shelf medical device sold without a position sensor, with the position sensor added at an appropriate location on the ENT instrument 28. For example, a Bien Air® S120 handpiece and replaceable reusable blades available without a position sensor may be adapted to provide the ENT instrument 28 described below. In other embodiments, the ENT instrument 28 may be embodied as a dedicated medical device with an integrated position sensor.

[0037] Inset 35 of FIG. 2 shows a schematic diagram of an image 146 of a representation 148 of a paranasal sinus and a representation 150 of an inserted interchangeable head 64 rendered by processor 38 system 20 of FIG. 1. Processor 38 is configured to render image 146 on display 56 ( FIG. 1 ), including representation 148 of at least a portion of the paranasal sinus and a representation 150 of at least a portion of the inserted interchangeable head 64 of ENT equipment 28 within the paranasal sinus, corresponding to the tracked location, orientation, and roll angle of the distal end of the interchangeable head 64. Because the interchangeable head 64 is rigid, representation 150 of the inserted interchangeable head 64 can be rendered based on the coordinates of a single point on the inserted interchangeable head 64 and the known shape of the identified inserted interchangeable head 64. A treatment tool, such as a cutting element 78, can also be indicated using an indicator 152 on representation 150.

[0038] Figure 3 is a schematic diagram of the handle 62 and interchangeable head 64 of the ear, nose, and throat (ENT) instrument 28 of Figure 2, according to one embodiment of the present invention. The interchangeable heads 64 are shown without position sensors in Figure 3. The interchangeable heads 64 differ from one another with respect to head shape and functionality.

[0039] Each interchangeable head 64 includes a plastic proximal end 68 that is inserted into a socket 70 in the handle 62. The socket 70 in the handle 62 includes multiple rotational positions for inserting interchangeable heads 64 of various stiffnesses. For example, in the S120 handpiece, reusable blades can be inserted into eight different rotational positions. In some embodiments, the interchangeable head 64 may only be inserted into a single rotational position within the socket 70.

[0040] The handle 62 includes multiple rotational positions for rotating interchangeable heads 64 of different stiffness. Thus, when one of the interchangeable heads 64 is inserted into the socket 70, the inserted interchangeable head 64 can be rotated to multiple rotational positions using the rotation adjustment cogwheel 72. In other embodiments, the inserted interchangeable head 64 cannot be rotated to another position.

[0041] 3, each of the interchangeable heads 64 is embodied as an elongated shaft 74 having a distal end 76, the distal end 76 of which includes at least one cutting element 78 or distal opening 79, the opening 79 being rotationally asymmetric. The distal opening 79 may be used to expose the shaver only over a given azimuthal range, for example, to prevent collateral damage to surrounding tissue after the tool is rotated to face the target tissue. The cutting element(s) 78 may include a shaving burr (e.g., a roughened cylindrical or ball-shaped element), a rotating shaving blade within the elongated shaft 74, or any other suitable cutting element.

[0042] Further aspects of ENT devices of the type described above can be found in U.S. patent application Ser. No. 16 / 375,485, entitled "Medical Instrument Identification," filed April 4, 2019, which is assigned to the assignee of the present patent application and the disclosure of which is incorporated herein by reference.

[0043] FIG. 4 is a schematic diagram of interchangeable heads 64 of ear, nose and throat (ENT) instrument 28 of FIG. 2, each including a magnetic sensor 82 disposed on the distal end 76 of the head, according to one embodiment of the present invention.

[0044] The sensor 82 is typically formed as a printed coil on a PCB. Among other advantages, using a PCB sensor is that (a) the PCB sensor is not adversely affected by metallic interference, (b) the PCB sensor can be positioned on the head with very precise orientation, and (c) because the PCB sensor is not a wound coil but a standard printed coil, each PCB has substantially the same magnetic susceptibility. Therefore, based on the above advantages, PCB sensors generally do not require calibration and therefore do not require a controller (e.g., an EEPROM), which is generally too bulky to place on the head.

[0045] As mentioned above, each interchangeable head 64 includes a position sensor 82 disposed on and at the distal end 76 of the elongated shaft 74 of the interchangeable head 64. The position sensor 82 is electrically insulated from the elongated shaft 74 and the cutting element(s) 78. Wires extending from the head position sensor 82 are secured to the elongated shaft 74 by, for example, using adhesive tape 75.

[0046] 4 , the sensor 82 of each interchangeable head 64 includes at least one coil whose axis 84 is aligned with a given rotation angle α relative to a physical feature of the distal end 76 to track the roll angle of the physical feature. In the embodiment shown, the angle α is defined with respect to the bent distal end in the yz plane (defined by a longitudinal z-axis 81 and a lateral y-axis 85). As can be seen, the direction 84 has a projection 86 onto the lateral xy plane defined by the x-axis 83 and y-axis 85, and the given rotation angle α is defined between the projection 86 and the yz plane.

[0047] In another embodiment, the angle α is defined relative to the rotational orientation of a rotationally asymmetrically positioned distal opening 79 that is tracked, for example, to precisely rotate the electric shaver to directly face the target tissue.

[0048] The sensor 82 of each interchangeable head 64 may include a dual-axis sensor (e.g., with two coils aligned orthogonally or at least non-parallel to one another) that can be used to detect the location, orientation, and roll angle of the interchangeable head 64. The head position sensor 82 may be printed on one or two printed circuit boards. For example, two coils may be printed on one or two printed circuit boards connected to the distal end 76 of the elongated shaft 74, with each coil aligned orthogonally to the other coil. Printing the coils on a printed circuit board results in a more compact and standard sensor than using a wire-wound coil. The coils may be coated with an electrically insulating material.

[0049] At least a portion of the elongate shaft 74 may be disposed within a plastic, biocompatible sleeve prior to inserting the elongate shaft 74 into a body part. In some embodiments, the sleeve may cover the elongate shaft 74 from the plastic proximal end 68 up to and including the sensor 82.

[0050] Figure 5 is a flowchart 90 that generally illustrates a method and algorithm for tracking the roll angle of the head 64 of the ear, nose, and throat (ENT) device 28 of Figure 4 within a patient's head, in accordance with one embodiment of the present invention. The process begins with the physician 54 inserting one of the interchangeable heads 64 into the device 62 at a head insertion step 92.

[0051] When the physician 54 brings the distal end of the ENT equipment 28 into the region 30 where the alternating magnetic field is present, the processor 38 begins tracking at least the roll angle of the distal end 76 of the ENT equipment 28 using the signals generated by the sensor 82, at a tracking step 94. The detected roll angle may be accurate to a given tolerance, such as up to a 5 or 10% roll angle accuracy.

[0052] In an insertion step 96, the physician 54 inserts the head of the instrument into the sinus with the distal end 76 at some initial preferred roll angle.

[0053] At decision step 98, processor 38 renders a query on display 56 asking physician 54 whether the roll angle at which the distal tip is rotationally aligned is acceptable. Physician 54 provides a response via motion controller 51 that is received by processor 38. If the physician responds negatively, the physician rotates inserted interchangeable head 64 to a new rotational position (block 100), and the method returns to step 94. If interchangeable head 64 is free to rotate relative to handle 62, the physician may continuously rotate inserted interchangeable head 64 while evaluating whether the roll angle of head 64 (e.g., distal end 76) is acceptable until the rotation angle is approved.

[0054] Next, the physician further steers (e.g., rotates and orients) the tool located on the distal end in a tool steering step 102, so that the tool is correctly oriented relative to the target tissue within the sinus using the tracked roll angle of the tool.

[0055] Finally, in a treatment step 104, the physician performs the necessary treatment, such as shaving the tissue, once the physician has successfully aligned the tool to face the target tissue.

[0056] It should be understood that various features of the solution of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the solution that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

[0057] The above-described embodiments are cited by way of example, and the present invention is not limited to that particularly shown and described in the foregoing specification. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described in the foregoing specification, as well as variations and modifications thereof not disclosed in the prior art that will occur to those skilled in the art upon reading the above description.

[0058] [Embodiment] (1) A system comprising: a medical instrument comprising a handle and a head, the head configured for insertion into an organ of a patient and having features that are rotationally asymmetric about a longitudinal axis of the medical instrument; a position sensor disposed on the head and configured to generate a signal in response to an externally applied magnetic field; 1. A processor, comprising: receiving the signal generated by the position sensor on the head; and a processor configured to estimate a roll angle of the rotationally asymmetric feature of the head based on the received signals. (2) The system of embodiment 1, wherein the position sensor comprises at least a coil having an axis oriented at a given rotational angle relative to the rotationally asymmetric feature of the head. (3) The system of claim 1, wherein the rotationally asymmetric feature comprises a medical tool. (4) The system of claim 1, wherein the medical tool comprises an ear, nose and throat (ENT) shaver. (5) The system of embodiment 1, wherein the medical tool comprises an ENT suction tool.

[0059] (6) The system of claim 1, wherein the medical tool comprises an ENT microbrider. (7) The system of claim 3, wherein the rotationally asymmetric feature comprises an opening in the medical tool. (8) The system of embodiment 3, wherein the medical tool is curved relative to the longitudinal axis. (9) The system of embodiment 1, wherein the position sensor is a single-axis sensor (SAS) printed on a circuit board. (10) The system of embodiment 1, wherein the position sensor is a dual-axis sensor (DAS) printed on a circuit board.

[0060] (11) The system of embodiment 1, further comprising a location pad including at least one magnetic field emitter configured to transmit the magnetic field near the organ. (12) The display further includes: tracking the location of the head in response to the received signals; 2. The system of claim 1, wherein the system is configured to: render on the display an image including a representation of at least a portion of the organ and a representation of at least a portion of the head within the body. (13) A method comprising: inserting a medical instrument having a handle and a head into a patient's organ, the head having features that are rotationally asymmetric about a longitudinal axis of the medical instrument; generating a signal in response to an externally applied magnetic field using a position sensor located on the head; receiving the signal generated by the position sensor on the head; and estimating a roll angle of the rotationally asymmetric feature of the head based on the received signals. (14) The method of claim 13, wherein the position sensor comprises at least a coil having an axis oriented at a given rotational angle relative to the rotationally asymmetric feature of the head. (15) The method of claim 13, wherein the rotationally asymmetric feature comprises a medical tool.

[0061] (16) The method of claim 15, wherein the medical tool comprises an ear, nose and throat (ENT) shaver. (17) The method of embodiment 15, wherein the medical tool comprises an ENT suction tool. (18) The method of embodiment 15, wherein the medical tool comprises an ENT microbrider. (19) The method of claim 15, wherein the rotationally asymmetric feature comprises an opening in the medical tool. (20) The method of embodiment 15, wherein the medical tool is curved relative to the longitudinal axis.

[0062] (21) The method of embodiment 13, wherein the position sensor is a single axis sensor (SAS) printed on a circuit board. (22) The method of embodiment 13, wherein the position sensor is a dual-axis sensor (DAS) printed on a circuit board. (23) The method of embodiment 13, further comprising transmitting the magnetic field near the organ using a location pad including at least one magnetic field emitter. (24) tracking the location of the head in response to the received signal; 14. The method of claim 13, further comprising: rendering on a display an image including a representation of at least a portion of the organ and a representation of at least a portion of the head within the body.

Claims

1. 1. A system comprising: a medical instrument comprising a handle and a head, the head configured for insertion into an organ of a patient and having features that are rotationally asymmetric about a longitudinal axis of the medical instrument, the head comprising an elongate shaft having a distal end with a bend; a position sensor disposed on the head and configured to generate a signal in response to an externally applied magnetic field, the position sensor being located at a portion of the distal end proximal to the bend such that the position sensor is located at a portion of the head coaxial with the longitudinal axis of the medical device; 1. A processor, comprising: receiving the signal generated by the position sensor on the head; and estimating a roll angle of the rotationally asymmetric feature of the head relative to the longitudinal axis of the medical device based on the received signal; A system wherein the position sensor comprises at least one coil having an axis oriented at a given rotational angle relative to the rotationally asymmetric feature of the head.

2. The system of claim 1 , wherein the medical device comprises an ear, nose and throat (ENT) shaver.

3. The system of claim 1 , wherein the medical device comprises an ENT suction tool.

4. The system of claim 1 , wherein the medical device comprises an ENT microbrider.

5. The system of claim 1 , wherein the rotationally asymmetric feature comprises an opening formed in the distal end of the elongate shaft.

6. The system of claim 1 , wherein the position sensor is a single axis sensor (SAS) printed on a circuit board.

7. The system of claim 1 , wherein the position sensor is a dual-axis sensor (DAS) printed on a circuit board.

8. The system of claim 1 , further comprising a location pad including at least one magnetic field emitter configured to transmit the magnetic field near the organ.

9. a display, wherein the processor: tracking the location of the head in response to the received signal; and rendering on the display an image including a representation of at least a portion of the organ and a representation of at least a portion of the head within a body.

10. 10. The system of claim 1, further comprising a fixation tape disposed on the head and located proximal to the position sensor, the fixation tape configured to secure a position sensor wire extending proximally from the position sensor to the elongate shaft of the head.

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