Magnetically tracked sensor

Abstract

Magnetic field sensor assembly, comprising: a hollow core comprising a ferromagnetic material, wherein the hollow core has a proximal end and a distal end; conductive material arranged around the hollow core and forming at least one turn of a coil, the coil comprising at least one start terminal and at least one end terminal; and wherein at least first and second lead wires are provided, wherein the first lead wire is connected to the start terminal to form a first termination, and wherein the second lead wire is connected to the end terminal to form a second termination, and wherein the first and second lead wires can transmit electrical signals from the coil to a magnetic position measuring system for determining a sensor position, characterized by the fact that The first and second supply wires run inside the hollow core, thus reducing the fragility of the sensor assembly.

Description

AREA OF INVENTION

[0001] This revelation concerns a magnetically tracked sensor. STATE OF THE ART

[0002] Magnetic tracking of instruments relative to imaged anatomy is widely used in medical practice. Imaging systems enhanced with magnetic tracking can be used to track and display the position and orientation of a diagnostic or therapeutic instrument relative to the imaging plane. This can help the clinician guide the instrument to a chosen target with reduced error compared to an unguided instrument. Furthermore, the visual representation of the tracked instrument is not necessarily limited to the ultrasound imaging plane, thus providing the clinician with greater freedom of movement.

[0003] For magnetic tracking of an instrument, an electromagnetic sensor can be added to the instrument's location. Electromagnetic sensors can be electromagnetic coils that surround or come close to the objects whose location is being tracked. When an instrument with an embedded sensor is placed in a changing electromagnetic field, a voltage can be generated in the electromagnetic sensor. This generated voltage can be used to determine and track the location and relative positioning of the instrument within the electromagnetic field. An ultrasound system enhanced by magnetic tracking sensors can provide a three-dimensional representation of ultrasound-generated anatomical features and a visual representation of the instrument's position and orientation. US Patent 4,905,698 A shows a detector consisting of a hollow guide wire with a magnetically permeable solid cylindrical core inside it. The core protrudes from the free end of the guide wire and encloses a coil wound coaxially to the guide wire. Lead wires to the coil are routed outside the core and inside the lead wire. US 2010 / 130851A1 shows a sensor consisting of a hollow and flexible tube around which a coil is wound. The tube is filled by a mechanical amplifier made of magnetic material, which establishes an electrical connection to the coil. SUMMARY

[0004] According to the invention, a magnetic field sensor assembly comprises a hollow core comprising a ferromagnetic material, wherein the hollow core has a proximal end and a distal end, conductive material arranged around the hollow core and forming at least one turn of a coil, wherein the coil comprises at least one start terminal and at least one end terminal, wherein at least first and second lead wires run inside the hollow core, wherein the first lead wire is connected to the start terminal to form a first termination, and wherein the second lead wire is connected to the end terminal to form a second termination, and wherein the first and second lead wires can transmit electrical signals from the coil to a magnetic position measuring system for determining a sensor position.

[0005] Implementations can include one or more of the following features. The hollow core is a hollow cylindrical core. The first and second terminations are located within the hollow core. The first and second terminations are located within the distal end of the hollow core. The first and second terminations are located within the proximal end of the hollow core. The first and second lead wires and the first and second terminations are permanently fixed within the hollow core. The hollow core contains ferrite material. The hollow core contains magnetic material. The hollow core contains hardened austenitic stainless steel. The conductive material includes magnetic wire. The conductive material comprises structured conductive material deposited on a dielectric material. The first and second terminations are formed by soldering, welding, or bonding with a conductive adhesive.In a further embodiment, a method generally comprises providing a hollow core containing ferromagnetic material, wherein the hollow core has a proximal end and a distal end, arranging conductive material around the hollow core, forming at least one turn of a coil, wherein the coil comprises at least one start terminal and at least one end terminal, passing at least first and second lead wires through the hollow core, connecting the first lead wire to the start terminal to form a first termination, and connecting the second lead wire to the end terminal to form a second termination, wherein the first and second lead wires can transmit electrical signals from the coil to a magnetic position measuring system for determining a sensor position.

[0006] Implementations can include one or more of the following features. The hollow core is a hollow cylindrical core. The first and second terminations are located within the hollow core. The first and second terminations are located within the distal end of the hollow core. The first and second terminations are located within the proximal end of the hollow core. The process involves permanently attaching the first and second lead wires and the first and second terminations within the hollow core. The hollow core contains ferrite material. The hollow core contains magnetic material. The hollow core contains hardened austenitic stainless steel. The conductive material contains magnetic wire. The conductive material contains structured conductive material deposited on a dielectric material. The first and second terminations are formed by soldering, welding, or bonding with a conductive adhesive.

[0007] In a further embodiment, an electromagnetic position measuring system generally comprises a magnetic field sensor assembly designed to measure position and angular orientation data of at least 3 degrees of freedom when placed in an electromagnetic field, and includes a hollow core comprising a ferromagnetic material, wherein the hollow core has a proximal end and a distal end, conductive material arranged around the hollow core and forming at least one turn of a coil, wherein the coil includes at least one start terminal and at least one end terminal, and wherein at least first and second lead wires run inside the hollow core, the first lead wire being connected to the start terminal to form a first termination, and the second lead wire being connected to the end terminal to form a second termination.wherein the first and second terminations are located inside the hollow core and wherein the first and second connecting wires can transmit electrical signals from the coil to the electromagnetic position measuring system to determine a sensor position.

[0008] Implementations can include one or more of the following features. The hollow core is a hollow cylindrical core. The first and second terminations are located within the hollow core.

[0009] Two or more features described in this disclosure, including those described in this summary section, can be combined to form implementations not specifically described herein.

[0010] The details of one or more implementations are set out in the accompanying drawings and descriptions below. Other features, objectives, and benefits will become apparent from the description, drawings, and claims. DESCRIPTION OF THE DRAWINGS Fig. Figure 1 illustrates an ultrasound imaging system augmented by magnetic instrument tracking. Fig. 2A - Fig. Figure 2C illustrates a state-of-the-art method for attaching and encapsulating a sensor element. Fig. 3A - Fig. Figure 3C shows cross-sectional views of a sensor according to the invention with a hollow ferromagnetic core. Fig. 4A - Fig. Figure 4C shows cross-sectional views of a further implementation of a sensor according to the invention with a hollow ferromagnetic core. Fig. 5A - Fig. Figure 5C shows cross-sectional views of a further implementation of a sensor according to the invention with a hollow ferromagnetic core. Fig. Figure 6 shows a flowchart that lists the individual steps for manufacturing a magnetic field sensor assembly according to the invention.

[0011] Identical reference symbols in the different drawings indicate the same elements. DETAILED DESCRIPTION

[0012] With reference to Fig. 1 Imaging tools, such as an ultrasound system 10, are used to generate images of detailed anatomical features in a spatial slice (or imaging plane) 16. The ultrasound system 10 comprises a portable probe 12, a display 10a, and electronics 10b. To magnetically track an instrument 14 with the ultrasound system 10, electromagnetic sensors 11 and 13 are inserted into the portable probe 12 and at a location on the instrument 14, respectively. The sensors 11 and 13 can be electromagnetic coils that surround or approach the objects whose location is being tracked. In the example of Fig. In instrument 14, a needle assembly is located, and sensor 13 is positioned close to the needle tip 19. When sensor 13 is placed in a changing electromagnetic field, a voltage is generated in the electromagnetic sensor 13. Similarly, when the portable ultrasound probe 12 with the embedded sensor 11 is placed in the changing electromagnetic field, a voltage is generated in the electromagnetic sensor 11. These generated voltages in sensors 11 and 13 are used to determine and track the positions and relative positioning of the ultrasound probe 12 and the needle tip 19, respectively, within the electromagnetic field. The ultrasound system 10, enhanced by the magnetic tracking of sensors 11 and 13, provides a three-dimensional reconstruction of ultrasound-generated anatomical features 16 in the area of ​​interest 15 and an optical representation of the position and orientation of instrument 14.

[0013] The Fig. 2A - Fig. Figure 2C shows two prior art methods for constructing magnetic sensor assemblies with five degrees of freedom. The magnet wire 32 is wound around the ferromagnetic core 30. In Fig. 2A is a pair of supply wires 31 with magnet wires 32 connected at each of the two termination points 33a, 33b (winding start and end). The end diameter 13b of sensor 13 is typically in the range of 1 mm and can even be as small as 0.3 mm, so the components, especially the connection points 33a, 33b, are particularly fragile and difficult to handle without damaging them. These design methods result in a very sensitive area between the termination points 33a, 33b and the core 30, since the coil wire 32 typically has a diameter of 0.0005'' (0.0127 mm) and is therefore easily damaged or broken. In certain cases, it is advantageous to connect a conductor of the supply wire 31 directly to the core 30 by soldering or gluing, as shown in Fig. Figure 2B shows this. This allows the larger conductor of the supply wire 31 to absorb the mechanical forces experienced by the sensor 13 during assembly and use. This joining process has the disadvantage of requiring precise application and curing of the adhesive, or exposing the coil assembly to soldering temperatures that can damage the insulation if not performed precisely. A second common method for dealing with the fragility of the termination area 33 is to place a tube 35 over the sensor 13 so that it surrounds the termination area 33 and provides mechanical support. The tube 35 and sensor 13 assembly is then injection-molded with adhesive. This tube must extend well beyond the termination area 33 to provide an overlap between the supply wires and the tube, thus creating an area for the formation of the tensile shear adhesive bond.This has the disadvantage that either the rigid length 13a of sensor 13 increases or a shorter core is required, which reduces the sensor's signal output and its usable range. Adhesive injection methods require costly sensor-tube alignment devices and precise flow controllers. Furthermore, the rigid nature of tube 35 and the extended tensile shear range create a lever arm with the weak point at the termination point 33. Great care must be taken during the assembly process to avoid breaking or damaging the connecting wires 31, 32 or the termination points 33a, 33b when inserting them into tube 35. Tube 35 is often made of a metallic material, such as stainless steel, or a plastic material, such as polyester, depending on the desired properties of the finished product.If the tube 35 is made of a plastic material, it must have sufficient wall thickness to prevent the termination area 33 from bending, as the connections in this area are prone to breakage. Although the tube 35 is often filled with a stress-relieving adhesive, the termination area 33 remains a point of low stress and is susceptible to breakage. The termination of these sensors is also exposed to a magnetic field, which the sensors detect. Since a single coil sensor cannot detect rotation about its axis, it must be assumed that the magnetic axis and the body axis of the coil are collinear. If the termination process results in an undesired deviation from the plane, the loop 36 is formed. This loop 36 can lead to misalignment of the magnetic axis of the sensor 13 relative to its body axis.Such a loop is actually difficult to avoid in some construction methods, since the conductors in the termination area 33 are separated to prevent short circuits, and this separation results in a relatively large loop.

[0014] With reference to the Fig. 3A - Fig. Figure 3C comprises an example of a ferromagnetic sensor 13 according to the invention, comprising a twisted lead wire 31 placed in a ferromagnetic hollow core 50. The coil wire 32 is wound around the ferromagnetic core 50, and the ends 32a, 32b are connected to the terminal ends 33a, 33b of the lead wire 31, which appears at the opposite end of the core 50 compared to the sensors located in the Fig. 2A - Fig. Figure 2C shows the adhesive coating 51 being applied after the termination connections 33a, 33b are completed and is drawn into the space between the core 50 and the lead wire 31, creating a strong bond along the inner surface of the core 50. The terminations 33a, 33b can be made in close proximity to the end 50a of the core 50, thus minimizing the length of the sensor 13. Because the bonding surfaces between the lead wire 31 and the coil wire 32 are located internally within the core 50, the strain relief area 52 can have zero length, which is not possible with other design techniques. This allows the rigid section of the sensor to be shorter without sacrificing the strength of the assembly, enabling instruments equipped with the sensor to more easily navigate highly tortuous anatomy, such as blood vessels.

[0015] As in Fig. As shown in Figure 2A, in a conventional sensor design, the coil wire 32 and the connecting wire 31 are sometimes deformed during the termination process. This deformation is difficult to avoid because the connecting wire 31 must be somewhat separated so that it can be joined with the coil wires 32 at the termination 33 without creating a short circuit caused by removing the insulation in the area of ​​the termination 33. Likewise, some bending and manipulation of the coil wires 32 and connecting wires 31 is usually required. Due to these factors, a small, undesirable parasitic loop 36 can form. This loop has an axis of maximum sensitivity that may differ from the physical axis of the sensor 13. By shielding the magnetic field of this loop, its effect on the sensor output can be eliminated.

[0016] With reference to the Fig. 4A - Fig. In a method according to the invention for aligning the magnetic and physical axes of sensor 13, the terminations 33a, 33b are connected to the coil wire ends 32a, 32b at the distal end 50a of the core 50, and then the connected termination points are inserted into the distal end 50a of the core 50 and pushed into the hollow core 50. Since the magnetic field is attenuated within a ferromagnetic tube, the core 50 acts as a magnetic shield for unwanted parasitic loops that may have formed during the fabrication of the terminations 33a, 33b. This is advantageous in terms of improving the alignment of the magnetic and physical axes of the sensor 13. The alignment of the magnetic and physical axes of the sensor 13 is important because the sensor 13 cannot detect angular rotation parallel to its magnetic axis; therefore, if the magnetic and physical axes of the sensor 13 do not coincide, imaging errors will occur.Therefore, if the magnetic and physical axes are not aligned, the insertion of sensor 13 into a biopsy needle, such as the tubular instrument 14, causes errors in the displayed trajectory of instrument 14 relative to the depicted anatomy 10. A calibration step can be used to reduce this trajectory error, but this complicates the manufacturing process. By incorporating terminations 33a and 33b into core 50, a major source of error is eliminated for applications requiring accurate instrument trajectory display without additional calibration steps.

[0017] In certain applications, it may not be possible to access the distal end 50a of the hollow core 50. This is the case when the sensor 13 is molded into an instrument, with only the proximal end 50b of the core 50 exposed. In this case, with reference to the Fig. 5A - Fig. 5C The terminations 33a, 33b are made at the proximal end 50b of the core 50. The ends 32a, 32b of the feed cable 31 are connected to the terminations 33a, 33b, and the connected points are inserted into the proximal end 50b and pushed into the hollow core 50. The core 50 then acts as a magnetic shield for the terminations 33a, 33b, and the improvements in imaging accuracy are similar to those obtained by shielding the terminations 33a, 33b at the distal end 50b of the core 50.

[0018] Fig. Figure 6 shows a flowchart 100 that lists the steps for producing a magnetic field sensor assembly individually, for example, the magnetic field sensor assembly that is used in the Fig. 3A - Fig.Figure 3C shows that step 102 involves providing a hollow core (for example, a hollow cylindrical core) comprising ferromagnetic material. The hollow core has a proximal and a distal end. In some implementations, the hollow core comprises ferrite material. The hollow core may also comprise magnetic material. In some examples, the hollow core may comprise hardened austenitic stainless steel. Step 104 involves arranging conductive material around the hollow core and forming at least one turn of a coil. The coil has at least one start terminal and at least one end terminal. In some implementations, the conductive material may comprise magnet wire. In some implementations, the conductive material may comprise structured conductive material deposited on a dielectric material. Step 106 involves pushing first and second lead wires through the center of the hollow core.Step 108 involves connecting the first lead wire to the start terminal to form a first termination. Step 110 involves connecting the second lead wire to the end terminal to form a second termination. In some examples, the first and second terminations may be located within the distal or proximal end of the hollow core. In some implementations, the first and second lead wires and the first and second terminations may be permanently fixed within the hollow core. Step 112 involves optionally positioning the first and second terminations within the hollow core. The first and second lead wires may be configured to carry electrical signals from the coil to a magnetic position sensing system to determine a sensor position.

[0019] The magnetic field sensor assembly described here aims to have a termination area that is less fragile than other types of sensors. Several implementations of the assembly are possible. The ferromagnetic core can be made hollow; an example is a ferrite bead core. The lead wire can be pushed through the center of the hollow bead core and secured with an adhesive pin before the difficult process of connecting the fragile coil wires to the lead wire is carried out. The termination process can be performed at the distal end of the assembly. Applying adhesive to the proximal end of the coil is much simpler because capillary action draws the adhesive to the center of the hollow core in a controlled manner.

[0020] In some examples, the sensor can be immersed in adhesive, causing the adhesive to flow into and around the sensor, securing all the wires within the core and encapsulating the sensor. The self-locking nature of this process allows the termination process to proceed without fixing the coil assembly and lead wire in a fixed position relative to each other. Positioning the terminations at the distal end or within the sensor core also shortens the sensor for a given core length because the lead wires are under reduced stress on the inside of the core. A lever arm, where the point of highest stress coincides with the point of lowest stress above the termination area, is not required.

[0021] The termination can be applied to either the distal or proximal end without first securing the lead wire to the inside of the hollow sensor core. The termination can be pushed or pulled into the hollow core before adhesive is applied. In this way, the termination area does not contribute to the sensor's length, and the lead wire can still be securely attached to the inside of the sensor core. With this configuration, the parasitic loops formed by the terminations are shielded by the hollow core, and the sensor's magnetic axis is better aligned with the physical axis.

[0022] The magnetic sensor can be movable within the instrument so that it can be replaced with a therapeutic device after the instrument tip has been successfully placed in the target area. Furthermore, the magnetic sensor can be reinserted for the purpose of navigating to a different target. The magnetic sensor can be designed to accommodate this movement. Due to the curved nature of many surgical instruments and most passageways in the human body, the length of the magnetic sensor can also be limited while maintaining its mechanical strength.

Claims

[1] Magnetic field sensor assembly comprising: a hollow core comprising a ferromagnetic material, wherein the hollow core has a proximal end and a distal end; conductive material arranged around the hollow core and forming at least one turn of a coil, the coil comprising at least one start terminal and at least one end terminal; and wherein at least first and second lead wires are provided, wherein the first lead wire is connected to the start terminal to form a first termination, and wherein the second lead wire is connected to the end terminal to form a second termination, and wherein the first and second lead wires can transmit electrical signals from the coil to a magnetic position measuring system for determining a sensor position, characterized by , that The first and second supply wires run inside the hollow core, thus reducing the fragility of the sensor assembly. [2] Assembly according to claim 1, wherein the hollow core is a hollow cylindrical core. [3] Assembly according to claim 1, wherein the first and second closures are located inside the hollow core. [4] Assembly according to claim 3, wherein the first and the second termination are located within the distal end of the hollow core. [5] Assembly according to claim 3, wherein the first and second terminations are located within the proximal end of the hollow core. [6] Assembly according to claim 3, wherein the first and second supply wire and the first and second termination are permanently fixed in the hollow core. [7] Assembly according to claim 1, wherein the hollow core comprises ferrite material. [8] Assembly according to claim 1, wherein the hollow core comprises magnetic material. [9] Assembly according to claim 1, wherein the hollow core comprises hardened austenitic stainless steel material. [10] Assembly according to claim 1, wherein the conductive material comprises magnet wire. [11] Assembly according to claim 1, wherein the conductive material comprises structured conductive material deposited on a dielectric material. [12] Assembly according to claim 1, wherein the first and second terminations are formed by soldering, welding or joining with a conductive adhesive. [13] Procedures, including: Providing a hollow core comprising ferromagnetic material, wherein the hollow core has a proximal end and a distal end; Arranging conductive material around the hollow core and forming at least one turn of a coil, the coil comprising at least one start terminal and at least one end terminal; Pushing at least the first and second supply wires through the hollow core; Connect the first supply wire to the start terminal to form a first termination; and connect the second supply wire to the end terminal. to form a second termination, thereby reducing the fragility of the sensor assembly, wherein the first and second supply wires carry electrical signals from the coil to a magnetic Position measurement system to determine a sensor position can be transmitted. [14] Method according to claim 13, wherein the hollow core is a hollow cylindrical core. [15] Method according to claim 13, wherein the first and second closures are located inside the hollow core. [16] Method according to claim 15, wherein the first and second closures are located within the distal end of the hollow core. [17] Method according to claim 15, wherein the first and second closures are located within the proximal end of the hollow core. [18] Method according to claim 15, further comprising permanently fixing the first and second lead wire and the first and second termination inside the hollow core. [19] Method according to claim 13, wherein the hollow core comprises ferrite material. [20] Method according to claim 13, wherein the hollow core comprises magnetic material. [21] Method according to claim 13, wherein the hollow core comprises hardened austenitic stainless steel material. [22] Method according to claim 13, wherein the conductive material comprises magnet wire. [23] Method according to claim 13, wherein the conductive material comprises structured conductive material deposited on a dielectric material. [24] Method according to claim 13, wherein the first and second terminations are formed by soldering, welding or joining with a conductive adhesive. [25] Electromagnetic position measuring system comprising: a magnetic field sensor assembly designed to measure position and angular orientation data of at least 3 degrees of freedom when placed in an electromagnetic field, and comprising: a hollow core comprising a ferromagnetic material, wherein the hollow core has a proximal end and a distal end; conductive material arranged around the hollow core and forming at least one turn of a coil, the coil comprising at least one start terminal and at least one end terminal; and wherein at least first and second supply wires are provided, wherein the first supply wire is connected to the start terminal to form a first termination, and wherein the second supply wire is connected to the end terminal to form a second termination, and wherein the first and second supply wires can transmit electrical signals from the coil to an electromagnetic position measuring system for determining a sensor position, characterized by , that The first and second supply wires run inside the hollow core, thus reducing the fragility of the sensor assembly. [26] System according to claim 25, wherein the hollow core is a hollow cylindrical core. [27] System according to claim 25, wherein the first and the second closure are located inside the hollow core.

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