Selecting cursor location on medical image using direction from distal end of probe

Abstract

To provide a medical probe, particularly an ear-nose-throat (ENT) tool.SOLUTION: A medical probe 21 includes a tubular distal end section, which is configured to be inserted into a cavity of a patient, and includes (a) a visually guiding object disposed over a perimeter of the distal end section, and (b) a magnetic field sensor including two sensor coils aligned non-parallel with each other, the sensor attached to the distal end section, and having:(i) a first axis of symmetry, of one of the coils, which is aligned perpendicular to a central longitudinal axis of the distal end section, and (ii) a second axis of symmetry, of the remaining coil, which is aligned perpendicular to the central longitudinal axis of the distal end section and not parallel to the first axis of symmetry.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates generally to medical probes, and more particularly to ear-nose-throat (ENT) tools. [Background technology]

[0002] Techniques for guiding invasive probes inside organ cavities to target tissue have been previously proposed in the patent literature. For example, US Patent Application Publication No. 2019 / 0090959 describes several improvements related to computer aided surgery (CAS) utilizing on-board tool tracking (OTT) systems. Some improvements relate to methods of providing feedback during a procedure to improve the efficiency or quality, or both, of the procedure, including the speed and type of data processed depending on the CAS mode. In one embodiment, to provide navigational assistance during an OTT CAS procedure, an OTT device monitors the position of an associated surgical tool within the surgical field. The OTT CAS system may not use one or more coordinate systems, including one or more position sensors or one or more fiducial markers, depending on the requirements of the OTT CAS procedure performed.

[0003] As another example, US Patent Application Publication No. 2016 / 0183841 describes a method of guiding an interventional instrument within a patient's anatomy, including processing a target location within the patient's anatomy and receiving a location of a tip portion of the interventional instrument at a first location within the patient's anatomy. The method also includes determining a three-dimensional distance between the first location and the target location, and displaying a symbol representing the target location and a symbol representing the tip portion of the interventional instrument. In one embodiment, the rotational orientation of features of the distal tip portion may also be displayed with a rotational aid by the navigation aid image. For example, if the biopsy instrument has a lateral opening, the side of the opening may be indicated with a rotational aid in the navigation aid image.

[0004] U.S. Patent Application Publication No. 2007 / 0208252 describes devices, systems and methods for performing image-guided interventional and surgical procedures, including various procedures for treating sinusitis and other disorders of the sinuses, ear, nose or throat. In some applications, a pre-operative tomographic scan (e.g., CT scan) may be acquired, and the image-guidance system may be programmed to display the tomographic image on a video monitor along with real-time indications (e.g., crosshairs, illuminated dots, etc.) of the position of the working device relative to the anatomical structures depicted in the tomographic image. Summary of the Invention [Means for solving the problem]

[0005] One embodiment of the present invention comprises a medical probe including a tubular distal end portion configured to be inserted into a cavity of a patient, the distal end portion including (a) a visual guidance object disposed about the distal end portion, and (b) a magnetic field sensor including two sensor coils aligned non-parallel to one another, the sensor being attached to the distal end portion and having (i) a first axis of symmetry of one of the coils aligned perpendicular to a central longitudinal axis of the distal end portion, and (ii) a second axis of symmetry of the remaining coil aligned perpendicular to the central longitudinal axis of the distal end portion and not parallel to the first axis of symmetry.

[0006] In some embodiments, the visual guidance object includes a guidance bump, hi other embodiments, the visual guidance object includes one or more colored sloped portions around the distal end portion.

[0007] In one embodiment, the two sensor coils are orthogonal to each other.

[0008] According to another embodiment of the present invention, there is further provided a system including a magnetic tracking system probe and a processor, the probe including a tubular distal end portion configured to be inserted into a cavity of a patient, the probe including (a) a visual guidance object disposed about the distal end portion, and (b) a magnetic field sensor including two sensor coils aligned non-parallel to each other, the sensor being attached to the distal end portion and having (i) a first axis of symmetry of one of the coils aligned perpendicular to a central longitudinal axis of the distal end portion and (ii) a second axis of symmetry of the remaining coil aligned perpendicular to the central longitudinal axis of the distal end portion and not parallel to the first axis of symmetry. The processor of the magnetic tracking system is configured to (a) use signals received from the magnetic field sensor coils to calculate a position, orientation, and rotational orientation of the distal end within the patient's cavity, (b) register the measured position to the medical image, (c) use the calculated orientation and rotational orientation to find a first position in the medical image along the direction of the central longitudinal axis and a second position along a direction from the calculated position to the object, and (d) toggle a cursor between the first and second positions on the medical image.

[0009] In some embodiments, the system includes a colored sloped portion around a distal edge of the distal end portion, and based on a known orientation of the colored sloped portion relative to the second axis of symmetry, the processor is further configured to define the object as any of the colored sloped portions displayed using an endoscope inserted into the cavity and switch a cursor between a first and second location on the medical image accordingly.

[0010] According to another embodiment of the present invention, there is further provided a method for switching a cursor on a medical image of a patient's organ, the method comprising inserting a tubular distal end portion of a probe into a cavity of the patient's organ, the distal end portion including (a) a visual guidance object arranged around the distal end portion, and (b) a magnetic field sensor including two sensor coils aligned non-parallel to each other, the sensor being attached to the distal end portion and having (i) a first axis of symmetry of one of the coils aligned perpendicular to a central longitudinal axis of the distal end portion, and (ii) a second axis of symmetry of the remaining coil aligned perpendicular to the central longitudinal axis of the distal end portion and not parallel to the first axis of symmetry. Using signals received from the magnetic field sensor coils, calculate a position, orientation, and rotational orientation of the distal end within the cavity of the patient. Register the measured position to the medical image. Using the calculated orientation and rotational orientation, a first position along the direction of the central longitudinal axis and a second position along a direction from the calculated position to the object are found on the medical image. Toggle a cursor between a first and a second location on the medical image.

[0011] In some embodiments, the method includes defining the object as one of a plurality of colored sloped portions around a distal edge of the distal end portion viewed using an endoscope inserted into the cavity, and responsively switching a cursor between a first location and a second location on the medical image based on a known orientation of the colored sloped portion relative to a second axis of symmetry.

[0012] The invention will be more fully understood from consideration of the following detailed description taken in conjunction with the drawings, in which: [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of an ear-nose-throat (ENT) system, in accordance with an embodiment of the present invention; FIG. [Diagram 2]2 is a side view of the distal end of the ear-nose-throat (ENT) tool used in FIG. 1 according to one embodiment of the present invention. [Diagram 3] 1 is a top view of a distal end of an ear-nose-throat (ENT) tool according to another embodiment of the present invention. FIG. [Figure 4] FIG. 4 is a perspective view of a distal end of an ear-nose-throat (ENT) tool showing implementation of elements of the ENT tool of FIGS. 2 and 3 according to an embodiment of the present invention. [Diagram 5] 3 is a flowchart of a method for switching a cursor between locations on a medical image using the distal end of the ear-nose-throat (ENT) tool of FIG. 2 in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Overview The distal end portion of a probe, such as an ear-nose-throat (ENT) probe used in the guidance system, may be tracked for visual use as a location cursor (i.e., pointer) in a 3D view (e.g., medical image) of the patient's cavity. For example, an ENT suction tool or shaver may be used in this manner with the TruDi™ ENT Tracking System (Acclarent, Irvine, Calif.). The medical image may be generated, for example, from a CT or MRI image.

[0015] The distal tip portion of a probe (e.g., an ENT aspiration device) can be tracked using a magnetic sensor attached to the distal tip, and the tracked position is projected to a position on the medical image along the direction of the central longitudinal axis of the distal tip (e.g., the center of the aspiration opening of an aspiration tool). In this way, the physician can see the cursor position on the medical image (on the display) as it "displayed" distally from the tool itself.

[0016] However, in some clinical procedures, it may be preferable for the user to switch an image cursor between an image location projected along the direction of the central longitudinal axis and another image location corresponding to a visual guidance object located around the distal edge of the distal end of the probe, the other image location being interchangeably displayed, for example, as viewed distally from the tool by the physician using a user interface of the position tracking system via virtual crosshairs placed at tracked locations centered around the distal edge of the distal end of the probe.

[0017] The embodiments of the invention described below provide a means to allow a user to switch a cursor displayed on a 3D view (e.g., a medical image) between medical image locations received by projecting tracked locations along the two different directions described above. In one embodiment, the tracked object is a guiding bump, as described below. In another embodiment, the distal edge of a tubular distal end portion (e.g., a revolver) is colored to indicate multiple sloped portions (e.g., four quadrants) that can each be tracked based on a user determination of where to place the crosshairs.

[0018] Using video images from an endoscope (e.g., an otoscope) inserted into the cavity, the physician can see at least a portion of the bump or bevel in real time and can view the target tissue and nearby tissue (e.g., brain tissue) without affecting the tool. Based on the known orientation of the colored bevel relative to the object, the processor redefines the object as any of the colored bevels displayed using the endoscope and switches the cursor on the medical image accordingly.

[0019] Typically, at the start of a medical procedure, the coordinate systems of the medical image and the magnetic tracking system are aligned. The position, direction, and angular orientation of the sensor are tracked by the system, so that a crosshair can be placed at various tracked positions, and thus the cursor on the medical image can be switched between center and tilt orientations, as described above.

[0020] The disclosed technique enables a physician to optimally align the distal edge of an ENT tool in position, direction, and rotational orientation to perform a therapeutic procedure, such as ENT suction, and direct the distal edge of the ENT tool toward a targeted internal location.

[0021] System Description 1 is a schematic diagram of an ear-nose-throat (ENT) system 20, according to an embodiment of the present invention. In the following description, it is assumed that an ENT tool 21 of the system 20 is used to perform a suction procedure on the sinuses of a patient 28, although it is understood that the tool may be used to perform other procedures on the patient.

[0022] As described below, in one embodiment, the tool 21 includes a tilted dual-axis magnetic sensor 34 attached to a distal end of the tool 21 (distal end and sensor described in FIG. 2 ), which is tracked by the magnetic tracking system 23 during the procedure. To enable tracking in the system 20, the coordinate systems of a medical image 60, e.g., a computed tomography (CT) image of the patient 28, and the magnetic tracking system 23 are aligned. Meanwhile, the CT image 60 may typically include a magnetic resonance imaging (MRI) image or a fluoroscopic image, and in the description herein, it is assumed that the image includes, e.g., a fluoroscopic CT image.

[0023] Before and during sinus surgery, a magnetic tracking system includes a magnetic emitter assembly 24 that is positioned under the patient's head. The assembly 24 includes a magnetic field emitter 26 that is fixed in place and transmits an alternating magnetic field to a region 30 in which the head of a patient 28 is located. In response to the magnetic field, electrical potentials generated by sensors 34 in region 30 allow the position, direction, and angular orientation thereof in the coordinate system of the magnetic tracking system to be measured.

[0024] By way of example, the five emitters 26 of assembly 24 are arranged in a general horseshoe shape around the head of patient 28. However, alternative configurations for the emitters of assembly 24 may be used, and all such configurations are contemplated as falling within the scope of the present invention.

[0025] Prior to treatment, alignment of the coordinate system of the magnetic tracking system to the CT image can be performed by placing a magnetic sensor at a known location in the image, such as the tip of the patient's nose, however, any other convenient system for aligning the coordinate systems may be used.

[0026] The elements of system 20 are under the overall control of a system processor 40. The processor 40 may be mounted on a console 50, which includes a motion control 58, which typically includes a keypad and / or a pointing device, such as a mouse or trackball. The console 50 is connected wirelessly and / or via one or more cables to the emitters 26 and the sensors 34. A physician 54 uses the motion control 58 to interact with the processor while performing an ENT procedure using the system 20. When performing the procedure, the processor presents a cursor 15 over a medical image 60 on a screen 56 to assist the physician in guiding the distal tip to a target tissue location within the paranasal sinus.

[0027] Processor 40 operates system 20 using software stored in memory 42. The software may be downloaded in electronic form to processor 40, for example over a network, or alternatively or additionally, the software may be provided and / or stored on a non-transitory, tangible medium, such as magnetic, optical, or electronic memory.

[0028] The cursor is toggled between positions on the medical image according to the bump direction and center direction. 2 is a side view of the distal end portion 22 of the ear-nose-throat (ENT) tool 21 used in FIG. 1, according to an embodiment of the present invention. The distal end portion 22 includes a dual-axis coil sensor 34 whose two coils (34a, 34b) are aligned non-parallel to each other. Both coils 34a and 34b are aligned with their axes of symmetry (340a, 340b) perpendicular to the direction 44 of the central axis of the distal end. For any given orientation of the distal end relative to the direction of the magnetic field of the system 20, and any roll angle about the axis 44, the dual-axis sensor 34 allows the system 20 to find the tilt direction 33 and the direction 44 of the central longitudinal axis, and use the directions described below.

[0029] Upon insertion of tool 21, distal end portion 22 of the tool is typically in air, i.e., within a cavity region 200 of the diagrammatically illustrated anatomical structure 100, which corresponds to a Hounsfield Unit (HU) value of zero in three planes of a medical image, such as a CT image 205 of the anatomical structure. During a medical procedure, the revolver is conveniently viewed with an endoscope (not shown), which is typically manipulated by the physician to obtain and display video images so that the physician can see the position of the revolver relative to the anatomical structure 100. As shown in FIG. 2, anatomical structure 100 includes anatomical features at surface locations 62 and 64 that the physician would like to view with the endoscope.

[0030] In the embodiment shown, the processor projects the position of the sensor 34 onto the anatomy in a direction defined by the tracked center position 11 and bump 32 position around the distal edge of the distal tip portion 22. In the embodiment shown, positions 11, 32 define directions 33, 44, respectively. Because the coordinate systems of the CT image 205 and the magnetic tracking system are aligned, the processor 40 can use the anatomical position actually pointed to by the distal tip 22 and mark the corresponding position on the image 205 with a cursor. Thus, the tracking system relates the visual positions 62 and 64 that a physician wishing to resolve to point an ENT tool for these purposes to respective positions 202 and 204 in the three planes of the CT image 205.

[0031] To select the direction 33 or 44 of the tool relative to the anatomical structure, the physician uses the user interface to place the virtual crosshairs 102 and 104 at a position such as positions 11 and 32, respectively. The physician can move the crosshairs to any other tilt position around the distal tip, so that the cursor marks a position other than position 62 on the CT image 205. Thus, the physician can toggle the cursor on the medical image between a first position 302 and a second position 304 that matches the preselected crosshair position 102 or 104 on the tool, so that the anatomical position 62 or 64 is visible from the direction 33 and 44, respectively.

[0032] The cursor switches in the plane of the CT image 205 between positions 302 and 304 corresponding to the actual anatomical positions 62 and 64, respectively, indicated by different portions of the distal end portion 22, thereby allowing the physician to better control the use of the tool at the marked tissue position.

[0033] It should be noted that only a single cursor is shown on the plane of the CT image 205 at any one time, and showing both cursors at positions 302 and 304 in FIG. 2 is done merely to illustrate the switching of the cursors according to the selected positions on the medical tool for placement at the crosshairs 102 and 104 (by the software).

[0034] The magnetic navigation system can further tell the physician how far the closest tissue location (e.g., location 62 or 64) is from bump 32 or center location 11. The processor can display the distance from a selected tracking location on the tool to the closest tissue region (an area with a non-zero HU value) to assist the physician in assessing proximity.

[0035] The cursor is switched between positions on the medical image according to the direction of the tilted portion. 3 is a top view of a distal end portion 122 of an ear-nose-throat (ENT) tool according to another embodiment of the present invention. In the embodiment shown, the dual-axis magnetic sensor 34 is the same as in FIG.

[0036] As shown in FIG. 3, the revolver at the distal end 122 is visually marked (e.g., colored) in the quadrants 48. In the embodiment shown, one of the colored quadrants 48 defines a direction 55a, and another of the colored quadrants 48 defines a direction 55b. Based on the known shape of the distal end, using the sensor 24, the crosshairs can be placed in any of the position tracking quadrants 48, where in the embodiment shown, the physician places the crosshairs 112 and 114 in the quadrant positions that define the directions 55a and 55b, respectively. As described above, the cursors displayed on the registered medical image, such as the three-plane CT image 305, can be switched between the corresponding positions 302 and 304, respectively. Furthermore, it should be noted that only one cursor is displayed on each plane of the medical image at any one time.

[0037] When viewing the revolver with the endoscope, the physician can switch between different quadrants, and thus select the cursor in the 3D view at a position and direction that corresponds to the tilted portion that the physician has selected to place the crosshairs on. For example, based on the physician's selection, the processor 40 can select one of the quadrants 48 and direct the cursor to a position 302 on the medical image that corresponds to an anatomical location 67 within a region 301 of the anatomical structure 101 projected along a direction 55a via a crosshair (102) positioned on that quadrant, or to a position 304 on the medical image that corresponds to an anatomical location 68 within a region 301 of the anatomical structure 101 having a non-zero HU projected along a direction 55b via a crosshair 104 positioned (104) as seen in another quadrant.

[0038] Hardware implementation of the probe Figure 4 is a perspective view of a distal end portion 222 of an ear-nose-throat (ENT) tool 211 showing an implementation of elements of the ENT tool of Figures 2 and 3, according to an embodiment of the present invention. Such a perspective view of the distal end portion 222 may be part of a video image taken by the aforementioned endoscope.

[0039] In the embodiment shown, coils 34a and 34b of transverse dual-axis sensor 134 are formed such that their axes of symmetry 340a and 340b have an angle α between them. The axes are non-parallel to one another and typically approach orthogonal (α ∼ 120 degrees in the embodiment shown). Dual-axis sensor 34 is configured to provide different sets of voltage signals according to the rotational orientation of distal end 22 about axis 44 (shown in FIG. 2).

[0040] Forming a multi-axis magnetic sensor at a distal end, such as sensor 134, is described in commonly assigned U.S. Patent Application Publication No. 2018 / 0228392, which describes a position sensor including a flexible substrate formed into a three-dimensional (3D) shape, where at least a first magnetic field sensing coil and a second magnetic field sensing coil are formed in first and second layers, respectively, of the flexible substrate, such that in the 3D shape, the first magnetic field sensing coil and the second magnetic field sensing coil have first and second axes, respectively, that are non-parallel to one another.

[0041] FIG. 4 also visualizes the aforementioned guiding bumps 32 and angled portions 48 (eg, quadrants 48) visually marked (eg, colored) on the distal end 22 (ie, revolver).

[0042] Switching the action at the cursor position 5 is a flow chart of a method for switching a cursor between locations on a medical image using the distal end portion 22 of the ear-nose-throat (ENT) tool 21 of FIG. 2 according to another embodiment of the present invention. The process begins at a first step 70 where the coordinate systems of the magnetic tracking system 23 and the medical image, such as obtained from a CT image of the patient 28, are registered as described above. To perform the registration with the medical image, the magnetic tracking system 23 is activated and used to track the position, orientation, and angular orientation of the dual-axis sensor 34, as described above. The tracking is assumed to be updated in real time.

[0043] In an insertion step 72, the physician 54 inserts the distal end portion 22 of the tool 21 into the nostril of the patient 28. Once inserted, using the signal from the sensor 34, the processor 40 in a range detection step 74 locates on the medical image the closest internal feature of the patient 28 from a virtual crosshair located on the distal end portion 22 of the tool 21.

[0044] Next, in a cursor placement step 76 , processor 40 places a cursor on the medical image to point to the nearest internal feature of patient 28 to the specified location of distal end portion 22 of tool 21 .

[0045] In a cursor switching step 78, the physician 54 switches the cursor on the medical image between two imaged locations that correspond to crosshairs placed at the two tracked locations on the distal tip portion 22 of the tool 21. As the physician moves the distal tip, as indicated by the dashed arrow, the process is repeated, with the cursor position on the medical image changing as the physician moves the device and switches cursors.

[0046] The example flowchart shown in Figure 5 has been selected solely for conceptual clarity. Figure 5 shows only steps relevant to an embodiment of the present invention. Other steps such as selecting and marking crosshairs at tracking locations other than the center 11 and bump 32 on the distal end portion 22 of the tool 21, followed by switching the cursor between each newly selected location on the medical image, are omitted.

[0047] Although the embodiments described herein primarily address ENT applications, the methods and systems described herein may also be used in other applications, such as cardiac, neurological, or ophthalmic applications.

[0048] It will therefore be understood that the above-described embodiments have been cited by way of example, and that the present invention is not limited to what has been particularly shown and described above. 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 foregoing description.

[0049] [Embodiment] (1) A medical probe including a tubular distal end portion configured for insertion into a cavity of a patient, the distal end portion comprising: a visual guidance object disposed about the distal end portion; and a magnetic field sensor including two sensor coils aligned non-parallel to one another, the sensor being attached to the distal end portion; a first axis of symmetry of one of the coils aligned perpendicular to a central longitudinal axis of the distal end portion; a second axis of symmetry for the remainder of the coil aligned perpendicular to the central longitudinal axis of the distal end portion and not parallel to the first axis of symmetry. (2) A probe as described in embodiment 1, wherein the visual guidance object includes a guidance bump. (3) A probe as described in embodiment 1, wherein the visual guidance object includes one or more colored sloped portions around the distal end portion. (4) A probe as described in embodiment 1, wherein the two sensor coils are mutually orthogonal. (5) A system comprising: 1. A probe comprising a tubular distal end portion configured for insertion into a cavity of a patient, the distal end comprising: a visual guidance object disposed around a distal edge of the distal end; a magnetic field sensor including two sensor coils aligned non-parallel to one another, the sensor being attached to the distal end portion; a first axis of symmetry of one of the coils aligned perpendicular to a central longitudinal axis of the distal end portion; a magnetic field sensor having a second axis of symmetry of the remaining coil aligned perpendicular to the central longitudinal axis of the distal end portion and not parallel to the first axis of symmetry; 1. A processor for a magnetic tracking system, comprising: calculating a position, direction, and rotational orientation of the distal tip within the cavity of the patient using signals received from the magnetic field sensor coils; Registering the measured position to a medical image; Using the calculated direction and rotational orientation, in the medical image: a first position along the central longitudinal axis; and finding a second position along a direction from the calculated position to the object; a processor of a magnetic tracking system configured to switch a cursor between the first location and the second location on the medical image.

[0050] (6) The system of embodiment 5, wherein the visual guidance object is a guidance bump. (7) The system of embodiment 5, further comprising: a colored sloped portion extending around the distal edge of the distal end portion; and based on a known orientation of the colored sloped portion relative to the second axis of symmetry, the processor is further configured to define the object as any of the colored sloped portions displayed using an endoscope inserted within the cavity, and to switch a cursor between the first and second positions on the medical image accordingly. (8) A method for switching a cursor on a medical image of a patient's organ, comprising: Inserting a tubular distal end portion of the probe into a cavity of an organ of a patient, the distal end comprising: a visual guidance object disposed around a distal edge of the distal end; a magnetic field sensor including two sensor coils aligned non-parallel to one another, the sensor being attached to the distal end portion; a first axis of symmetry of one of the coils aligned perpendicular to a central longitudinal axis of the distal end portion; a magnetic field sensor having a second axis of symmetry of the remaining coil aligned perpendicular to the central longitudinal axis of the distal end portion and not parallel to the first axis of symmetry; calculating a position, direction, and rotational orientation of the distal tip within the cavity of the patient using signals received from the magnetic field sensor coils; registering the measured position to a medical image; Using the calculated direction and rotational orientation, in the medical image: a first position along the central longitudinal axis; and finding a second position along a direction from the calculated position to the object; and and switching a cursor between the first and second locations on the medical image. (9) The method of claim 8, wherein the object is an induction bump. (10) A method as described in embodiment 8, comprising defining the object as one of a plurality of colored sloped portions around a distal edge of the distal end portion displayed using an endoscope inserted into the cavity, and correspondingly switching a cursor between the first and second positions on the medical image based on a known orientation of the colored sloped portion relative to the second axis of symmetry.

Claims

1. 1. A magnetic tracking system comprising:

1. A probe including a tubular distal end portion configured for insertion into a cavity of a patient, the tubular distal end portion comprising: a visual guidance object disposed about a distal edge of the tubular distal end portion; a magnetic field sensor including two sensor coils aligned non-parallel to one another, the magnetic field sensor being attached to the tubular distal end portion; a first axis of symmetry of one of the two sensor coils aligned perpendicular to a central axis of the tubular distal end portion; a magnetic field sensor having a second axis of symmetry of the remaining one of the two sensor coils aligned perpendicular to the central axis of the tubular distal end portion and not parallel to the first axis of symmetry; 1. A processor for a magnetic tracking system, comprising: aligning a coordinate system of the magnetic tracking system with a coordinate system of a medical image of the patient, the medical image being generated from a CT or MRI image, the medical image including the cavity; calculating a position, orientation, and rotational orientation of the tubular distal end portion within the lumen of the patient using signals received from the two sensor coils; registering the calculated location to the medical image by placing the magnetic field sensor at a known location on the medical image; projecting the position of the magnetic field sensor onto the medical image in a direction defined from a center position of the tubular distal end portion tracked by the magnetic tracking system toward a position of the visual guidance object; Using the calculated direction and the rotational orientation, in the medical image: a first anatomical location on a surface of the cavity of the patient along the central axis; and finding a second anatomical location of the surface within the cavity of the patient along a direction from the calculated location to the visual guidance object; a processor of the magnetic tracking system configured to be capable of switching a cursor between the first anatomical location and the second anatomical location of the medical image based on a request from a user interface of the magnetic tracking system.

2. The magnetic tracking system of claim 1 , wherein the visual guiding object is a guiding bump.

3. the probe includes a plurality of colored ramps around the periphery of the distal edge of the tubular distal end portion; 2. The magnetic tracking system of claim 1, wherein the processor is further configured to define the visual guidance object as one of the plurality of colored sloped portions displayed using a video image including the tubular distal end portion from an endoscope inserted within the cavity based on a known orientation of the colored sloped portion relative to the second axis of symmetry, and to switch the cursor between the first anatomical location and the second anatomical location on the medical image in response to the defined visual guidance object.

Images