Improvements in or related to sensitive probes for detecting surgical markers

Abstract

A probe for locating magnetic markers used in surgery. The probe includes: at least two first coils (3a, 3b) and at least one second coil (5), which are arranged substantially coaxially on the longitudinal axis of the probe for measuring the proximity of the magnetic marker to the probe; and a reference voltage balancing device (7) comprising a first elongated conductor defining a conductive path extending partially around the probe axis. The conductive path is configured and arranged such that, in use, a balancing magnetic field induces a balancing voltage in the sensing coil that at least partially cancels out the reference voltage. Methods for manufacturing such a probe, methods for setting such a probe for sensing magnetic markers, and detection devices for locating magnetic markers during surgery are also disclosed.

Description

Technical Field

[0001] This disclosure relates to a probe for sensing implanted magnetic markers during surgery, a method for manufacturing such a probe, a method for setting such a probe, and a detection system including such a probe. Background Technology

[0002] In the field of sensitive probes for detecting implantable magnetic markers used to locate lesions during surgery, it is known to use a combination of a drive coil and a sensing coil to determine the proximity of the magnetic marker (also called a seed) relative to the probe. Current is supplied to the drive coil, thereby generating a drive magnetic field. The drive magnetic field senses a response from the magnetic marker, which in turn senses a sensing voltage in the sensing coil. By measuring and interpreting the sensing voltage from the sensing coil, the position of the marker relative to the probe can be determined. However, a voltage is also induced in the sensing coil from the drive coil. This can interfere with the determination of the marker's position because the voltage induced in the sensing coil from the drive coil masks the sensing voltage generated by the marker.

[0003] In known surgical probes, such as those disclosed in WO2014 / 140567A2, a coil arrangement is used that allows for the elimination of voltage induced directly from the drive coil, making the sensed voltage attributable to a magnetic marker. This is achieved, for example, by arranging the drive coil at the midpoint between two similar sensing coils connected in anti-series or having opposing windings. Alternatively, a single sensing coil may be positioned between two drive coils.

[0004] Due to manufacturing tolerances of the probes and coils, eliminating or completely eliminating voltages induced directly from one or more drive coils in one or more sensing coils may be impractical. For example, two specific sensing or drive coils may differ from each other, or the positioning of the drive and sensing coils may not be precise enough. As a result, residual reference voltages induced in one or more sensing coils may exist due to one or more drive coils: this can be problematic for accurately determining the location of markers. While it is generally desirable for probes to have narrow diameters to reduce the size of the surgical incision required when using the probe, this problem becomes complicated in probes with small coils, where even small changes in coil position or drive current result in relatively large changes in the drive field, and therefore also in the sensing voltage.

[0005] Therefore, there is a need for an improved sensitivity probe that allows for more accurate determination of marker locations, even with a smaller probe diameter, without interfering with one or more drive coils. Summary of the Invention

[0006] According to a first aspect of this disclosure, a probe is provided for sensing an implanted magnetic marker used during surgery. The probe includes at least two first coils and at least one second coil, the at least two first coils and the at least one second coil being arranged to form a gradiometer for measuring the proximity of the magnetic marker to the probe. The at least two first coils are either sensing coils or driving coils. The at least one second coil is either a driving coil or a sensing coil. One or more driving coils are adapted to be connected to a current source to generate a driving magnetic field through the driving coils in use. Simultaneously, one or more sensing coils are adapted to be connected to a signal processor for processing one or more sensing voltages induced in the respective one or more sensing coils in use to generate an output signal that can represent the distance between the marker and the probe.

[0007] Suitable, the first or second coil may be configured or arranged to minimize the reference voltage component of the sensed voltage induced in one or more sense coils that is directly attributable to the driving magnetic field. For example, in some embodiments, as described herein, at least two drive coils or at least two sense coils may be connected in anti-series to each other, or they may be connected in series but with windings in opposite directions, thereby minimizing the reference voltage component of the sensed voltage.

[0008] Alternatively, two or more sensing coils can be arranged to output separate sensing voltages to a signal processor, allowing the signal processor to process the sensing voltages to minimize a reference voltage component of the sensing voltage directly attributable to the driving magnetic field. For example, the signal processor can be operated to subtract the sensing voltage from one sensing coil from the sensing voltage from the other sensing coil to substantially remove the component of the sensing voltage directly attributable to the driving magnetic field.

[0009] After minimizing the reference voltage, some reference voltage may remain in the sensed voltage due to manufacturing tolerances or other reasons. According to this disclosure, the probe also includes a reference voltage balancing device comprising a first elongated conductor defining a conductive path that extends partially around a longitudinal axis (“probe axis”) defined by the probe and adjacent to one or more sense coils. Suitably, the first conductor is positioned at a fixed location on the probe axis. The first conductor is suitably arcuate, preferably forming an arc in a plane perpendicular to the probe axis. Thus, the conductive path extends azimuthally, but not completely, around the probe axis. The first conductor is adapted to be connected to a current source to generate a balancing magnetic field near one or more sense coils. The azimuthal length of the conductive path around the probe axis such that, in operation, the balancing magnetic field induces a balancing voltage in one or more sense coils that at least partially cancels any residual reference voltage, such that the sensed voltage is at least primarily attributable to a response field generated by a marker in response to a driving field, corresponding to the proximity of the marker.

[0010] According to a second aspect, this disclosure provides a method for manufacturing a probe for sensing magnetic markers. The method may suitably include mounting at least two first coils and at least one second coil substantially coaxially along the longitudinal axis of the probe. The at least two first coils are either sensing coils or driving coils. The at least one second coil is either a driving coil or a sensing coil. One or more driving coils are mounted such that they can be connected to a current source to generate a driving magnetic field through the one or more driving coils. One or more sensing coils are mounted such that they can be connected to a signal processor.

[0011] As described above, the first or second coil can be configured or arranged to minimize the reference voltage component of the sensed voltage induced in one or more sense coils that is directly attributable to the driving magnetic field. Alternatively, two or more sense coils can be arranged to output individual sensed voltages to a signal processor, allowing the signal processor to process the sensed voltages to minimize the reference voltage component of the sensed voltage that is directly attributable to the driving magnetic field. Thus, the first and second coils are mounted to the probe such that they are configured and arranged to function as gradiometers for measuring the proximity of the magnetic marker to the probe.

[0012] According to this disclosure, the method further includes mounting a reference voltage taring device to the probe, the reference voltage taring device including a first elongated conductor defining a conductive path extending partially around the probe axis and juxtaposed with one or more sensing coils. The taring device is mounted such that the first conductor can be connected to a current source to generate a balanced magnetic field in the vicinity of the one or more sensing coils during use. The reference taring device may be mounted juxtaposed with one or more sensing coils, i.e., adjacent to or near one or more sensing coils, such that when the first conductor is connected to the current source, the taring device generates a balanced magnetic field in the vicinity of one or more sensing coils. In some implementations, the reference taring device may be mounted adjacent to one or more sensing coils. In some implementations, a drive coil may be positioned between the reference taring device and at least one of the sensing coils. Those skilled in the art will understand that at least two first coils and at least one second coil can generally be arranged to generate a magnetic field in use that has substantial reflection symmetry about a transverse plane passing through the midpoint of the longitudinal axis of the probe. The first elongated conductor may be suitably eccentrically positioned about the midpoint, such that the magnetic field generated by the reference taring device is asymmetrical about the midpoint. The angular extent of the conductive path around the probe axis causes the balancing magnetic field to induce a balancing voltage in one or more sensing coils that at least partially cancels out the reference voltage. Therefore, in use, the sensed voltage is at least primarily attributed to the response field generated by the marker in response to the driving field (which corresponds to the proximity of the marker).

[0013] The signal processor can be configured to generate output signals, such as audio, tactile, and / or display signals that represent the distance between the marker and the probe.

[0014] Appropriately, the method of this disclosure includes adjusting the angular length of the conductive path about the probe axis to minimize the reference voltage across one or more sensing coils.

[0015] Therefore, according to a third aspect, this disclosure provides a method for setting a probe for sensing a magnetic marker during surgery. The probe suitably includes at least two first coils and at least one second coil, which are arranged substantially coaxially on the longitudinal axis of the probe as a gradiometer for measuring the proximity of the magnetic marker to the probe. The at least two first coils are either sensing coils or driving coils. The at least one second coil is either a driving coil or a sensing coil. One or more driving coils are adapted to be connected to a current source to generate a driving magnetic field. One or more sensing coils are adapted to be connected to a signal processor for receiving and processing sensing voltages induced in the one or more sensing coils to generate an output signal. As described above, the first or second coils can be configured or arranged to minimize a reference voltage component of the sensing voltage induced in the one or more sensing coils that is directly attributable to the driving magnetic field. Alternatively, the two or more sensing coils can be arranged to output individual sensing voltages to the signal processor to allow the signal processor to process the sensing voltages in order to minimize the reference voltage component of the sensing voltage that is directly attributable to the driving magnetic field. The probe also includes a reference voltage balancing device comprising a first elongated conductor defining a conductive path that extends at least partially around the probe axis and is juxtaposed with one or more sensing coils. The first conductor may be connected to a current source to generate a balanced magnetic field in the vicinity of one or more sensing coils.

[0016] Methods for setting up the probe include balancing a balanced magnetic field by adjusting the angular length of a conductive path around the probe axis to control a balanced voltage, thereby minimizing or substantially eliminating a reference voltage in one or more sensing coils. In some embodiments, the angular length of the conductive path can be adjusted by connecting a first conductor to a current source at circumferentially spaced positions thereon, such that the angular length of the conductive path corresponds to the length of the first conductor at the midpoint of the space. Where appropriate, the length of the conductive path around the probe axis can then be fixed.

[0017] According to a fourth aspect, this disclosure includes a detection device for locating a magnetic marker during surgery. The device includes a probe according to a first aspect of this disclosure, at least one current source, and at least one signal processor. The at least one current source is selectively operable to generate a driving magnetic field through one or more drive coils and conductive paths. The at least one signal processor is configured to receive at least one sensing voltage from one or more sensing coils and generate an output signal representing the distance between the probe and the magnetic marker. In some embodiments, the device may further include at least one magnetic marker.

[0018] It should be understood that features described with respect to one aspect of this disclosure may be incorporated into other aspects of this disclosure. For example, the methods of this disclosure may be combined with features described with reference to the probes and / or apparatus of this disclosure, and vice versa. Attached Figure Description

[0019] Embodiments of this disclosure are described below by way of example with reference to the accompanying drawings, wherein:

[0020] Figure 1 This is a schematic diagram of a typical arrangement of sensitive probes and base stations used to detect magnetic markers during surgery.

[0021] Figure 2 This is a schematic diagram illustrating the use of sensitive probes to locate magnetic markers implanted in the breast to mark lesions.

[0022] Figure 3 This is a schematic longitudinal cross-sectional view of a mandrel through a probe according to an embodiment of the present disclosure, the mandrel carrying a long drive coil disposed between two sensing coils and a balancing device near one of the sensing coils;

[0023] Figure 4 This is a schematic longitudinal cross-sectional view of a mandrel through a probe according to different embodiments of the present disclosure, the mandrel carrying two sets of coils; each set of coils includes a drive coil and a sensing coil; and a balancing device near the first set of coils;

[0024] Figure 5 This is a schematic longitudinal cross-sectional view of a mandrel through a probe according to another embodiment of the present disclosure, the mandrel including two sets of coils; each set of coils including a pair of drive coils and a sensing coil therebetween; and a balancing device disposed between the sets of coils;

[0025] Figure 6(a) is a perspective view of a balancing device including a printed circuit board used in a probe according to another embodiment of the present disclosure;

[0026] Figure 6(b) is a plan view of the weighing device shown in Figure 6(a) in its unfolded configuration for reference;

[0027] Figure 7 This is a schematic plan view of different balancing devices including printed circuit boards according to another embodiment of the present disclosure;

[0028] Figure 8(a) is a perspective view of the coil arrangement of a probe according to another embodiment of the present disclosure, schematically showing a balancing device that extends angularly about part of the longitudinal axis of the probe.

[0029] Figures 8(b) to 8(d) This is a perspective view of the coil arrangement of the probe according to different corresponding embodiments of the present disclosure, schematically showing different balancing devices extending angularly around the probe axis to different degrees.

[0030] Figure 9This is a perspective view of a portion of a probe according to another embodiment of the present disclosure, the probe comprising two sets of coils and a balancing device on a mandrel between the two sets of coils;

[0031] Figure 10 This is a schematic diagram of a general arrangement of a detection apparatus according to another embodiment of the present disclosure, the detection apparatus including a probe, the probe including... Figure 5 The type shown has a mandrel with two sensing coils, wherein the sensing voltage is output separately from each sensing coil to a signal processor; and

[0032] Figure 11 This is a flowchart illustrating a method for manufacturing a probe according to yet another embodiment of the present disclosure. Detailed Implementation

[0033] As shown in the attached figure Figure 1 and Figure 2 As shown, a detection device 1001 used in surgery to locate an implantable magnetic marker 1002 for marking non-touchable lesions (i.e., lesions too small to be felt or seen during surgery) typically includes a probe 1004 connected to a base station 1007. As shown, the probe 1004 suitably includes a handheld rod 1005 and can be connected to the base station 1007 via a suitable cable 1006, or it can be wirelessly connected. Figure 2 As shown, probe 1004 is used during surgery to guide the surgeon to lesion 1003 and allows for accurate removal of the lesion while minimizing the amount of healthy tissue removed.

[0034] The marker 1002 suitably comprises one or more sheets of magnetic material. A suitable marker 1002 is disclosed, for example, by WO2016 / 193753A2. The probe 1004 typically includes: at least one drive coil for generating a driving magnetic field, which produces a response field from the marker; and at least one sensing coil for detecting the response field from the marker. The response field generates a sensing voltage in the sensing coil, which is detected by a suitable signal processor housed in the base station 1007. WO2014 / 140567A2 discloses a known probe. The sensing voltage corresponds to the distance between the marker 1002 and the probe 1004. Therefore, as disclosed in WO2011 / 067576A1, the signal processor is configured to calculate the marker distance, for example, from the detected sensing voltage. The signal processor can generate an output signal representing the marker distance. The output signal may be, for example, a display signal for displaying the distance to a marker on a screen 1008 on a base station 1007, or, for example, an audio or tactile signal as disclosed in WO 2022 / 008922A1.

[0035] This disclosure provides for the above-mentioned types of probes and improvements thereof.

[0036] Therefore, according to a first aspect, this disclosure provides a probe for locating magnetic markers used in surgery, the probe comprising:

[0037] At least two first coils and at least one second coil, the at least two first coils and the at least one second coil being arranged substantially coaxially on the longitudinal axis of the probe as a gradiometer for measuring the proximity of a magnetic marker to the probe; the at least two first coils are one of a sensing coil or a driving coil, and the at least one second coil is the other of a driving coil or a sensing coil; the one or more driving coils are adapted to be connected to a current source to generate a driving magnetic field, and the one or more sensing coils are adapted to be connected to a signal processor for processing one or more sensing voltages induced in the respective one or more sensing coils to generate an output signal representing the distance between the marker and the probe; the first coils or second coils are configured or arranged to minimize a reference voltage component of the sensing voltage induced in one or more sensing coils that is directly attributable to the driving magnetic field, or to output individual sensing voltages from the two or more sensing coils to the signal processor to allow the signal processor to process the sensing voltages, thereby minimizing the reference voltage component of the sensing voltage that is directly attributable to the driving magnetic field; and

[0038] A reference voltage balancing device includes a first elongated conductor that defines a conductive path extending partially around a probe axis and can be connected to a current source to generate a balancing magnetic field near one or more sensing coils.

[0039] The conductive paths are configured and arranged such that, in use, the balancing magnetic field induces a balancing voltage in one or more sensing coils that at least partially cancels out the reference voltage; thus, the sensed voltage is at least primarily attributable to a response field generated by the marker in response to the driving field, which corresponds to the proximity of the marker.

[0040] Suitable, at least two first coils and at least one second coil may be centered on the longitudinal axis of the probe (“probe axis”). The coils may be separated from each other along the probe axis. A first elongated conductor may extend partially around the probe axis and be juxtaposed with one or more sensing coils. Typically, the first elongated conductor may be eccentrically positioned with respect to at least two first coils and at least one second coil.

[0041] At least two first coils and at least one second coil can be suitably housed within a hollow probe housing. The probe housing can have an elongated shape. In some embodiments, the probe housing can be substantially cylindrical. In some embodiments, the probe housing can include multiple segments with the same or different outer diameters. The probe housing can be stepped or include a frustoconical transition between adjacent segments with different outer diameters.

[0042] The outer diameter of the probe housing can depend on the intended use of the probe. Generally, a narrow diameter is desirable for the probe housing to reduce the size of the surgical incision required when using the probe. In some implementations, the maximum outer diameter of the probe housing can be between about 3 mm and about 20 mm; typically between about 4 mm and about 15 mm, or between about 6 mm and about 10 mm, depending on the intended use of the probe. For example, the diameter of a probe used in laparoscopic or robotic surgery can be between about 4 mm and about 6 mm.

[0043] Appropriately, the wall thickness of the probe housing can be between about 0.2 mm and 3 mm; typically between about 0.5 mm and about 1 mm.

[0044] An air gap may be required between at least two first coils and at least one second coil and the inner surface of the probe housing to reduce thermal effects. The air gap may suitably be between about 0.2 mm and about 3 mm in radial dimension; typically between about 0.5 mm and about 1 mm.

[0045] Suitablely, at least some, and preferably all, of the coils, along with the reference voltage balancing device, may be disposed within the head of the probe housing near the distal sensing end or tip of the probe. Preferably, at least one sensing coil is positioned as close as possible to the distal end to optimize probe sensitivity, for example, within about 5 mm of the distal end; preferably within about 3 mm of the distal end; more preferably within 2 mm of the distal end.

[0046] In some embodiments, the coil may be mounted on an elongated forming element or other support within the housing. Suitablely, the forming element or other support may be formed of an insulating material, or an insulating layer may be included between the forming element or support and the coil.

[0047] Alternatively, in some embodiments, at least one coil of the coil may be disposed outside the probe housing. For example, at least one coil of the coil may be wound around and supported thereon on the outer surface of the probe housing.

[0048] One or more drive coils are suitably connected to a selectively operable AC current source (not shown) that provides the drive current for operating the probe. In some embodiments, the probe may include more than one drive coil. In this case, the drive coils may be connected in series or anti-series as described herein, and may be connected to the same current source. One or more drive coils are excited by a drive current to generate a drive magnetic field. The strength of the drive magnetic field depends on the number and configuration of the drive coils, the current through one or more drive coils, and the number of turns of said or each drive coil.

[0049] In use, the driving magnetic field induces magnetic markers near the probe to generate a response field.

[0050] In some embodiments, the magnetic marker may be a ferromagnetic marker. Suitable exemplary markers are disclosed in WO2014013235A1, WO2016 / 193753, WO2019180580A1, UK Patent Application No. 2115827.4 and UK Patent Application No. 2115826.6, the disclosures of which are incorporated herein by reference.

[0051] The response field from the marker depends on the strength of the driving magnetic field experienced by the marker, which in turn depends on the proximity of the marker to one or more driving coils. It should be understood that in the presence of two or more driving coils spaced apart along the probe axis, the driving magnetic field experienced by the marker can primarily originate from the driving coil of the closer marker; typically, it originates from those driving coils positioned more distally to the probe. The response field also depends on the permeability of the marker.

[0052] The response field from the marker is detected as a sense voltage by one or more sensing coils. Similar to the drive coils, when the probe has more than one sensing coil, the response field can be more strongly detected by a sensing coil positioned closer to the marker in use (typically at or near the distal end of the probe). When two or more sensing coils are provided, one or more can be provided to sense the voltage across the sensing coil directly generated by the drive magnetic field, such that it can be subtracted from the sense voltage, as described below. However, when the probe tip moves past the marker in use, the marker can respond more strongly to the drive magnetic field generated by a drive coil positioned further from the distal end, and the response field can be more strongly detected by a sensing coil positioned further from the distal end.

[0053] The sensed voltage across one or more sensing coils generated by the response field produced by the marker is related to the distance between the probe and the marker, and is appropriately output to a signal processor (not shown) for calculating the proximity of the marker relative to the probe, and for outputting a suitable dynamic audible, visible or other perceptible signal representing the proximity; for example, a visible indication of digital distance on a display.

[0054] However, the voltage (referred to herein as the “reference voltage”) is also induced in one or more sensing coils by the driving magnetic field generated by one or more driving coils. Both the magnetic marker and the one or more driving coils can increase or decrease the magnetic flux through the sensing coils. The closer the driving coils are to the sensing coils for positioning, and the stronger the driving magnetic field, the larger the reference voltage. Those skilled in the art will understand that the reference voltage is typically much larger than the component of the sensed voltage generated by the response field. When a probe is used to detect a marker, the reference voltage induced in one or more sensing coils by the driving magnetic field should therefore be minimized so that the sensed voltage across one or more sensing coils is primarily generated by the marker's response field, thus allowing for accurate determination of the marker's proximity. A significant reference voltage is undesirable because it can obscure the sensed voltage originating from the marker.

[0055] The reference voltage can be reduced and potentially eliminated in several different ways. In some implementations, the first or second coil can be configured or arranged to minimize the reference voltage component of the sensed voltage induced in one or more sensing coils that is directly attributable to the driving magnetic field. For example, the first coil may include two or more driving coils connected in anti-series or having opposite windings to generate a driving field of minimum (ideally zero) strength at the location of at least one sensing coil, which is the second coil, such that the sensed voltage across the sensing coil is primarily (ideally entirely) generated by the response field of the marker. This may require, for example, arranging the sensing coil at the midpoint between two substantially identical driving coils.

[0056] Alternatively, the first coil may include at least two sensing coils. One sensing coil may be positioned near the distal end of the probe for marker detection, while the other sensing coil may be positioned distal to the distal end. At least one drive coil may be provided as a second coil to generate a drive field in use. Typically, one or more drive coils may be positioned between the sensing coils. Alternatively, one or more drive coils may be arranged close to each sensing coil to form two sets of coils; each set of coils includes a sensing coil and at least one drive coil. For example, as described herein, a single drive coil may be positioned adjacent to each sensing coil, or each sensing coil may be positioned between two adjacent drive coils. The two sensing coils may be symmetrically positioned within the drive field such that each sensing coil experiences substantially the same drive field. The two sensing coils may be far enough apart that a marker located in the drive field generates a significant sensing voltage only in one of them; typically the one closer to the probe tip. The sensing voltage generated across one sensing coil may be subtracted from the sensing voltage generated across one sensing coil such that the net sensing voltage across the sensing coils is primarily generated by the response field. For example, two sensing coils can be connected in anti-series or have opposite winding directions, such that the sensed voltages induced across them have opposite polarities.

[0057] In alternative arrangements, the sensed voltages from two or more sensing coils can be individually input to a signal processor, which can be configured to process the sensed voltages in use to minimize a reference voltage generated by the driving field. Thus, in some embodiments, the reference voltage across one or more sensing coils can be physically reduced by appropriately configuring or arranging the coils, while in other embodiments, the reference voltage can be reduced by processing a signal representing the voltage sensed by the sensing coils at the signal processor.

[0058] In practice, due to manufacturing tolerances of the probes and coils, it is difficult to eliminate the reference voltage using only an arrangement of at least one drive coil or sensing coil. This is especially true for relatively narrow probes incorporating small-diameter coils, such as probes with a diameter less than about 15 mm or even more particularly less than about 10 mm. According to this disclosure, a reference voltage balancing device including a first conductor can be used to further reduce the reference voltage, the first conductor defining a juxtaposed arcuate conductive path that extends angularly to ground around the probe axis, i.e., close to or adjacent to, or more generally, near one or more sensing coils. The first conductor is connected to a selectively operable current source such that it also generates a magnetic field in use, referred to herein as a balancing magnetic field. The conductive path extends partially (i.e., incompletely) around the probe axis and is configured, as disclosed herein, to counteract residual reference voltages across one or more sensing coils generated directly from one or more drive coils.

[0059] In some embodiments, the probe may include at least two sensing coils axially separated along the probe axis, and a drive coil between the at least two sensing coils. In this case, the at least two sensing coils may be connected in anti-series or wound in opposite directions, as described above. A voltage can be induced in each sensing coil by a driving magnetic field. At least one of the sensing coils may be wound in the same direction as at least one drive coil, and at least one of the sensing coils may be wound in the opposite direction to at least one drive coil. Therefore, in use, opposite voltages are induced in sensing coils wound in opposite directions. In this embodiment, the reference voltage is the sum of the voltages induced in the sensing coils due to the driving field.

[0060] In some embodiments, the probe may include two sensing coils and a single drive coil disposed between the two sensing coils. One sensing coil may be positioned near the distal end of the probe; the drive coil may be positioned proximal to one sensing coil; the other sensing coil may be positioned proximal to the drive coil. Suitably, the distance between the two sensing coils is such that a marker positioned at or far from the distal end of the probe will not generate any significant sensing voltage in the other proximal sensing coil. The drive coil may suitably have a length between about 2 mm and about 10 mm. The drive coil may include a wire with between about 10 and about 150 turns; typically between about 10 and about 60 turns. Each sensing coil may have a length between about 0.5 mm and about 6 mm. Each sensing coil may include a wire with between about 50 and about 1000 turns; typically between about 100 and about 500 turns. The two sensing coils may include the same number of turns and have approximately the same length. The spacing between each coil may be between about 0.5 mm and about 1.0 mm.

[0061] For two sensing coils wound in anti-series configuration but otherwise identical, and a drive coil centered precisely at the midpoint between the two sensing coils, when a drive current flows through the drive coil, in the absence of a magnetic marker, the drive magnetic field induces approximately equal and opposite voltages in the two sensing coils, resulting in a net sensed voltage of zero. In reality, due to manufacturing tolerances, the two sensing coils may not be identical, or the drive coil may not be precisely centered at the midpoint between the two sensing coils. Therefore, the voltages induced in the two sensing coils may be opposite but not equal, and a net reference voltage may exist.

[0062] Therefore, a reference voltage balancing device can be used according to this disclosure to reduce or preferably eliminate the resulting net reference voltage. A drive current can pass through the first conductor along a conductive path to generate a balanced voltage that is opposite to and at least partially cancels out the reference voltage. The conductive path can be suitably positioned off-center from the midpoint between the two sensing coils, close to or adjacent to one of the sensing coils. If the conductive path is positioned off-center from the midpoint between the two sensing coils, the passage of current in the conductive path can induce voltages in both sensing coils, but the magnitude of the voltage induced in one sensing coil can be greater than the voltage induced in the other sensing coil. The conductive path can be arranged close to or adjacent to one of the sensing coils and can be at a small axial distance from the other sensing coil. Thus, the conductive path can induce an additional balanced voltage in one of the sensing coils, reducing any difference in the magnitude of the sensed voltages induced in the two sensing coils by the drive field, and thereby at least reducing the net reference voltage, such that the sensed voltage is at least primarily attributable to the response field generated by the marker in response to the drive field.

[0063] As described above, in some embodiments, the probe may include at least two drive coils separated along the length axis of the probe and a sensing coil disposed between the at least two drive coils. Suitably, one of the drive coils is positioned as close as possible to the distal end of the probe. In this case, the at least two drive coils may be connected in anti-series or wound in opposite directions. In use, two similar drive coils connected in anti-series or opposite winding manner generate opposite magnetic fields, resulting in symmetrical opposite magnetic fields on both sides of the zero and midpoint at or near the midpoint between the two drive coils. The sensing coil may be disposed between the two drive coils. The sensing coil may have a length between about 0.5 mm and about 6 mm. The sensing coil may include a wire with about 50 turns to about 1000 turns; typically between about 100 turns and about 500 turns. Each drive coil may have a length between about 0.75 mm and about 6 mm. Each drive coil may include a wire with about 10 turns to about 150 turns; typically between about 10 turns and about 60 turns. The two drive coils may include the same number of turns and have approximately the same length. The spacing between each coil may be between about 0.5 mm and about 1.0 mm.

[0064] In use, each drive coil induces a voltage in the sensing coil. Drive coils connected in anti-series or opposite windings induce opposite voltages in the sensing coil. The net voltage induced in the sensing coil is a reference voltage. If the sensing coil is precisely positioned at the midpoint between the drive coils, and if the drive coils are identical but connected in anti-series, the induced balance voltage in the sensing coil will be zero. In practice, the drive coils may not be identical, and the sensing coil may not be precisely centered at the midpoint between the drive coils; for example, due to manufacturing tolerances. Therefore, a small reference voltage may result.

[0065] The reference voltage balancing device can be suitably configured and arranged to at least reduce and preferably eliminate the reference voltage. In use, a drive current is passed through a conductive path, causing the conductive path to generate a balancing magnetic field. The balancing magnetic field from the conductive path induces a balancing voltage in the sensing coil. The conductive path is configured such that the balancing voltage substantially cancels out the reference voltage. In particular, the angular length of the conductive path around the probe axis can such that the balancing voltage substantially cancels out the reference voltage. The conductive path can be suitably located between two drive coils, eccentrically from the midpoint between the two drive coils. The conductive path can be positioned close to or adjacent to one of the coils.

[0066] In some embodiments, the probe may include a first set of coils and a second set of coils. The first set of coils includes at least one drive coil and at least one sensing coil, and the second set of coils includes at least one drive coil and at least one sensing coil. The first and second sets of coils may be separated along the length axis of the probe. Preferably, one set of coils is positioned closer to the distal end of the probe.

[0067] In some embodiments, the first set of coils may include a drive coil and a sensing coil, and the second set of coils may also include a drive coil and a sensing coil. The first and second sets of coils may be substantially identical. Suitably, two sensing coils may be positioned in a similar relationship to their respective drive coils. Each sensing coil may be positioned proximal or distal to its associated drive coil. In some embodiments, the two sensing coils may be positioned distal to their respective drive coils. In other embodiments, the two sensing coils may be positioned proximal to their respective drive coils. In other embodiments, one sensing coil may be positioned distal to its drive coil, and the other sensing coil may be positioned proximal to its respective drive coil. Preferably, one sensing coil is positioned at or near the distal end of the probe. Suitable coil arrangements are disclosed in UK Patent Application No. 2204999.3 and International Patent Application No. PCT / GB2023 / 050909, the disclosures of each of which are incorporated herein by reference.

[0068] Appropriately, each set of coils may include two substantially identical drive coils; that is, the drive coils may have substantially the same dimensions as each other and may include the same number of turns of wire.

[0069] In some implementations, each drive coil may have an outer radius between about 0.5 mm and 10 mm; typically between about 1.5 mm and about 6 mm. The radius of the drive coil can be selected to suit the diameter of the probe, for example as described above.

[0070] In some implementations, the axial length of each drive coil can be between about 0.2 mm and 10 mm; typically between about 0.5 mm and about 2.5 mm.

[0071] In some implementations, each drive coil may have between about 10 and about 150 turns of wire, typically between about 10 and about 60 turns of wire.

[0072] The axial length of the sensing coil in each coil group can be between approximately 0.5 mm and 6 mm; typically between approximately 0.75 mm and approximately 2 mm.

[0073] The average radius of the sensing coil in each group of coils can be between about 0.5 mm and 10 mm; typically between about 1.5 mm and about 6.5 mm. Conveniently, the first sensing coil can have an average radius similar to that of the driving coil in the corresponding group of coils.

[0074] Typically, the sensing coil in each coil group can include wire with between about 50 and 1,000 turns. In some implementations, the sensing coil may have wire with between about 100 and 500 turns.

[0075] Appropriately, the sensing coil in each group of coils can be formed from wires with a diameter between about 0.01 mm and 0.3 mm; typically between about 0.025 mm and 0.1 mm.

[0076] In some implementations, the sensing coil of each group of coils may include about 3 to 20 stacked layers; typically about 8 to 10 turns; wherein each layer has about 5 to 50 turns; typically between about 15 and 20 turns.

[0077] As disclosed in UK Patent Application No. 2204999.3 and International Patent Application No. PCT / GB2023 / 050909, the distance between the center of each sensing coil and the center of each driving coil within the same set of coils can advantageously be between about 1 mm and about 3 mm.

[0078] The total axial distance spanned by the first and second sets of coils can be between approximately 10 mm and 100 mm; typically between approximately 19 mm and approximately 30 mm. In some implementations, the axial spacing between the sensing coils of the first and second sets of coils can be between approximately 3 mm and approximately 100 mm; typically between approximately 12 mm and approximately 15 mm.

[0079] Suitablely, the distance between the two sensing coils is such that, in use, a marker positioned far from the far sensing coil generates essentially no sensing voltage in the far sensing coil, thereby the sensing voltage in the near sensing coil is almost entirely generated by the driving field and is substantially the same as the component of the sensing voltage induced in the far sensing coil by the driving field. Therefore, as described above, the sensing voltage in one of the sensing coils can be used to isolate the sensing voltage generated by the sensing response of the marker in the other sensing coil. Thus, the sensing coils of the first set of coils and the sensing coils of the second set of coils can be connected in anti-series or have opposite winding directions. Simultaneously, the driving coils of the first set of coils and the driving coils of the second set of coils can be suitably connected in series.

[0080] Therefore, the voltage induced in one of the sensing coils by the respective drive coil can be approximately equal and opposite to the voltage induced in the other sensing coil by its respective drive coil. If the first set of coils is not identical to the second set of coils, or if the axial spacing between the first and second sets of coils is insufficient, the voltage induced in the second sensing coil may not completely cancel the voltage induced in the first sensing coil, potentially resulting in a residual reference voltage. A reference voltage balancing device can be configured to cancel this residual reference voltage. Therefore, a conductive path defined by the reference voltage balancing device can be positioned between the first and second sets of coils. The conductive path can be positioned close to or near one of the first or second sets of coils. A drive current can pass through the conductive path, thereby generating a magnetic field. The magnetic field from the conductive path can generate a balanced voltage in one of the sensing coils (or unequal voltages in both sensing coils). The angular length of the conductive path ensures that the balanced voltage induced in the sensing coil from the conductive path substantially cancels any residual reference voltage from the drive coil.

[0081] In some implementations, the first set of coils may include a first sensing coil disposed between a first pair of drive coils. The second set of coils may include a second sensing coil disposed between a second pair of drive coils. Suitablely, the first set of coils may be substantially identical to the second set of coils.

[0082] The first set of coils may include a pair of substantially identical drive coils. The first pair of drive coils may be connected in series.

[0083] The second set of coils can be substantially the same as the first set of coils. The second set of coils may include a substantially identical second pair of drive coils. The second pair of drive coils can be substantially the same as the first pair of drive coils. The second pair of drive coils can be connected in series. The second pair of drive coils can be connected in series with the first pair of drive coils. Appropriately, the first pair of drive coils and the second pair of drive coils can be connected to the same current source.

[0084] Suitablely, one of the first and second sensing coils can be connected with the same polarity as its corresponding pair of drive coils. The other of the second and first sensing coils can be connected with opposite polarities as its corresponding pair of drive coils. Thus, in some embodiments, the two pairs of drive coils can be connected in series with each other, having the same polarity as one of the sensing coils, while one sensing coil is connected with opposite polarities to both the drive coil and the other sensing coil. In some embodiments, the two sensing coils can be anti-series or series-series, but with windings in opposite directions. In an alternative arrangement, as described above, the sensing coils can be adapted to be individually connected to a signal processor, such that the sensing voltage induced in one of the sensing coils by the drive magnetic field can be processed to strip the component of the sensing voltage in the other sensing coil from the drive magnetic field, leaving only the sensing voltage generated by the marker response field and any residual reference voltage.

[0085] Advantageously, the first set of coils can be positioned near the distal sensing end of the probe. When a drive current passes through the first set of drive coils, a drive magnetic field is generated. The drive magnetic field can induce a response field from a magnetic marker near the distal end of the probe, which can be detected as an induced voltage in the first sensing coil. A voltage is also induced in the first sensing coil from at least the first pair of drive coils. Those skilled in the art will understand that the sensed voltage generated by the drive field is typically much larger than the sensed voltage from the response field.

[0086] The driving field passing through the second pair of driving coils generates a driving magnetic field and induces a voltage in the second sensing coil. When the second sensing coil is wound in anti-series with the first sensing coil and the second pair of driving coils is substantially identical to the first pair of driving coils, the voltage induced in the second sensing coil from the second pair of driving coils is ideally equal to and opposite to the voltage induced in the first sensing coil from the first pair of driving coils. Therefore, the net voltage induced in the sensing coil from the driving coils (which is a reference voltage) can be zero or close to zero, thus allowing the detection of any sensing response from the marker.

[0087] In practice, due to manufacturing tolerances, for example, the first pair of drive coils is unlikely to be identical to the second pair of drive coils, the first sensing coil is unlikely to be identical to the second sensing coil, and the first and second sensing coils are unlikely to be located at the exact midpoint between the drive coils. As a result, the reference voltage is unlikely to be exactly zero. This is especially true in small-diameter probes (e.g., less than about 15 mm, particularly less than about 10 mm), where the magnetic field in and around the coils is higher than that in wider probes due to their smaller size. Therefore, small changes in positioning or drive current often result in large changes in the drive field, and thus also large changes in the sensed voltage. This can obscure or interfere with measurements of the sensed voltage induced from the marker.

[0088] The conductive path of the reference voltage balancing device can be further configured, according to this disclosure, to reduce or even substantially eliminate the reference voltage. The conductive path provided by the first conductor can be suitably positioned between the first and second sets of coils. The conductive path can be positioned at a fixed axial location between the first and second sets of coils. The conductive path can be configured to be off-center from the midpoint between the first and second sets of coils. Therefore, the conductive path can be positioned closer to one of the first and second sensing coils. Conveniently, the conductive path can be connected to the same current source as the first or second set of driving coils. When current flows through the conductive path, a balancing magnetic field is generated, which induces an additional balancing voltage in the first or second sensing coil. The voltage induced in the first or second sensing coil can be larger. The conductive path can be configured such that the balancing voltage induced by the current flowing through the conductive path is opposite to the reference voltage.

[0089] As described herein, the conductive path is formed by a first conductor. Typically, the first conductor may be positioned between two drive coils or two sensing coils to generate a balancing voltage in one or more sensing coils. The conductive path defined by the first conductor should be eccentrically positioned between the two drive coils or two sensing coils in the direction of the probe axis. The first conductor may be connected to a suitable current source in any convenient manner known to those skilled in the art. Conveniently, the first conductor may be connected to the same current source as at least one drive coil. Typically, the first conductor is connected to the current source at two spaced-apart locations on the first conductor, thereby defining a conductive path between the two locations. The balancing voltage provided by the reference voltage balancing device is a function of the angular length of the conductive path between the two locations.

[0090] In some implementations, the reference voltage balancing device may conveniently include a second elongated conductor extending around the probe and at least one conductive bridge extending in the axial direction to interconnect the first and second conductors. Thus, the conductive bridge defines the angular length of the conductive path on the first conductor at the midpoint of the conductive bridge. The second conductor may also define a conductive path around the probe axis, juxtaposed with the conductive path defined by the first conductor. In some implementations, the conductive path defined by the second conductor may be aligned with the midpoint between the two sensing coils or the two drive coils, and therefore, for convenience, it does not contribute to voltage balancing. However, in some embodiments, the conductive path of the second conductor may also be eccentrically positioned, thereby contributing to field balancing.

[0091] One or both of the first and second conductors may extend completely or partially around the probe. Therefore, in some embodiments, one or both of the first and second conductors may form a complete loop. Alternatively, one or both of the first and second conductors may form an arc extending partially but not completely around the probe axis. In some implementations, one or both of the first and second conductors may extend angularly around the probe axis in a plane perpendicular to the probe axis. In some embodiments, the first and second conductors may be substantially parallel to each other.

[0092] Suitablely, one or both of the first and second conductors may comprise a wire or strip; for example, a copper wire or strip. Therefore, in some implementations, the first or second conductor may comprise a copper wire loop. A suitable conductive strip may comprise a flexible insulating film coated with a thin layer of conductive material. A suitable insulating film is a polyimide film, which can be trademarked... It was purchased from DuPont de Nemours and Company in Wilmington, Delaware, USA. Copper is a suitable conductive material.

[0093] Suitablely, each of the first and second conductors is connected to a current source, and at least one conductive bridge connects the first and second conductors together to complete the circuit. In some implementations, at least one conductive bridge may extend between the first and second conductors in a direction substantially perpendicular to at least one of the first and second conductors. Suitablely, at least one conductive bridge may comprise a conductive wire or strip. The materials described above for the first and second conductors may also be suitable for the conductive bridge.

[0094] In some implementations, at least one conductive bridge can be moved between multiple angular positions about the probe axis. A single conductive bridge can extend between a first conductor and a second conductor and can be moved by sliding between the multiple angular positions. The conductive bridge can move between the multiple angular positions at discrete distances.

[0095] In some embodiments, one or both of the first and second conductors may include a plurality of conductive pads at a series of angularly spaced locations around the probe axis. The pads on this or each conductor may extend toward the other conductor in a direction substantially parallel to the probe axis. Each pad on a conductor appropriately terminates where no other conductor is present, thereby defining a short gap therebetween. A conductive bridge may include a conductive strip adapted to form a connection at selected angular locations around the probe axis across the gap between the pads on one conductor and the other conductor. By moving the conductive bridge between the plurality of angular locations, the angular length of the conductive path can be adjusted to control the magnitude of the balancing magnetic field, thereby minimizing the reference voltage across one or more sensing coils. Alternatively, the conductive bridge may be positioned at a fixed angular location between the first and second conductors. Advantageously, the fixed angular location of the conductive bridge can be selected such that the angular length of the conductive path defined by the first conductor is optimized to at least partially offset the reference voltage.

[0096] In some embodiments, the reference voltage balancing device may include a flexible circuit board at least partially wound around the probe axis. Suitably, the circuit board may be a printed circuit board. The circuit board may include two conductive traces defining a first conductor and a second conductor, and a plurality of conductive pads extending from one or both of the first and second conductors at a series of angularly spaced locations as described above. One or more conductive bridges may be provided to extend between a pad on one conductor and the other conductor, thereby defining the angular length of the conductive path. One or more conductive bridges may be formed, for example, by a suitable conductive strip fixed across a gap between a pad on one conductor and the other conductor, or by soldering between a pad on one conductor and the other conductor. Other methods of interconnecting pads on one conductor and the other conductor will be apparent to those skilled in the art.

[0097] According to a second aspect, this disclosure provides a method for manufacturing a probe for sensing magnetic markers during a surgical procedure, the method comprising:

[0098] At least two first coils and at least one second coil are mounted substantially coaxially on the longitudinal axis of the probe. The at least two first coils are either sensing coils or driving coils, and the at least one second coil is either a driving coil or a sensing coil. One or more driving coils can be connected to a current source to generate a driving magnetic field through the driving coils, and one or more sensing coils can be connected to a signal processor to process one or more sensing voltages induced in the respective sensing coils to generate an output signal. The first or second coils are configured or arranged to minimize a reference voltage component of the sensing voltage induced in one or more sensing coils that is directly attributable to the driving magnetic field, or to output individual sensing voltages from the two or more sensing coils to the signal processor, allowing the signal processor to process the sensing voltages and thus minimize the reference voltage component of the sensing voltage that is directly attributable to the driving magnetic field. Thus, the first and second coils are configured and arranged as a gradiometer to measure the proximity of a magnetic marker to the probe, and the output signal represents the distance between the marker and the probe.

[0099] A reference voltage balancing device comprising a first elongated conductor is mounted to a probe such that the first conductor defines a conductive path extending partially around the probe axis and can be connected to a current source to generate a balancing magnetic field near one or more sensing coils, such that in use, the balancing magnetic field induces a balancing voltage in one or more sensing coils, which at least partially cancels the reference voltage; thereby the sensed voltage is at least primarily attributable to a response field generated by the marker in response to the driving field, the response field corresponding to the proximity of the marker.

[0100] The probe can be any of the features disclosed above. Therefore, the conductive path can extend partially around the probe axis and be juxtaposed with one or more sensing coils. The conductive path can typically be eccentrically or asymmetrically fitted to the probe with respect to an arrangement of at least two first coils and at least one second coil.

[0101] The method may also include adjusting the angular length of the conductive path around the probe to minimize the reference voltage across one or more sensing coils.

[0102] Adjusting the angular length of the conductive path can include moving the aforementioned type of conductive bridge to an angular position around the probe circumference, thereby minimizing the reference voltage. Multiple conductive pads or tabs can extend between the first and second conductors at different angular positions. Adjusting the length of the conductive path can include completing a connection between at least two corresponding pads or tabs, thereby forming a conductive bridge. The connection can be appropriately completed by soldering connectors between the conductors.

[0103] According to a third aspect, this disclosure provides a method for setting a probe for sensing magnetic markers used in surgery, the probe comprising:

[0104] At least two first coils and at least one second coil, the at least two first coils and the at least one second coil being arranged substantially coaxially on the longitudinal axis of the probe as a gradiometer for measuring the proximity of a magnetic marker to the probe; the at least two first coils are one of a sensing coil or a driving coil, and the at least one second coil is the other of a driving coil or a sensing coil; the one or more driving coils are adapted to be connected to a current source to generate a driving magnetic field, and the one or more sensing coils are adapted to be connected to a signal processor for processing sensing voltages induced in the one or more sensing coils to generate an output signal; the first coils or second coils are configured or arranged to minimize a reference voltage component of the sensing voltage induced in the one or more sensing coils that is directly attributable to the driving magnetic field, or to output the sensing voltages from the two or more sensing coils to the signal processor to allow the signal processor to process the sensing voltages, thereby minimizing a reference voltage component of the sensing voltage that is directly attributable to the driving magnetic field;

[0105] A reference voltage balancing device includes a first elongated conductor that defines a conductive path extending partially around a probe axis, the conductive path being juxtaposed with one or more sensing coils and connectable to a current source to generate a balancing magnetic field in the vicinity of one or more sensing coils;

[0106] The method involves adjusting the angular length of the conductive path around the probe axis to control a balanced magnetic field, thereby inducing a balanced voltage across one or more sensing coils that at least partially cancels out a reference voltage.

[0107] The probe can include any of the features disclosed above.

[0108] It should be understood that the method includes effectively tuning the balance magnetic field by changing the angular length of the conductive path around the probe axis, so that the balance voltage minimizes the reference voltage.

[0109] Changing the angular length of the conductive path around the probe axis can include moving the conductive bridge to an angular position around the probe axis such that the reference voltage is minimized. Changing the angular length of the conductive path around the probe axis can include completing a connection between at least two conductors to form a conductive bridge. Multiple conductive strips can partially extend between at least two conductors at different angular positions and can be connected by soldering selected copper strips and conductive connections between at least two conductors.

[0110] The method for setting up the probes disclosed herein can be performed as part of the fabrication of the probes. In some embodiments, the position of the conductive bridge can be adjustable to allow the probes to be recalibrated periodically or as needed.

[0111] According to a fourth aspect, this disclosure provides a detection device for locating a magnetic marker during surgery, the device comprising: a probe as described above according to a first aspect of this disclosure; a current source selectively operable to generate a driving magnetic field through one or more driving coils and a first conductor; and at least one signal processor configured to receive one or more sensing voltages from one or more sensing coils and generate an output signal representing the distance between the probe and the magnetic marker.

[0112] In some embodiments, the device may also include at least one implantable magnetic marker. Suitablely, the magnetic marker may include a ferromagnetic marker; for example, one commercially available from Endomagnetics, Cambridge, UK. Marker.

[0113] Figure 3 This is a schematic longitudinal cross-sectional view of a portion of a probe according to an embodiment of the present disclosure. Specifically, Figure 3 A generally cylindrical mandrel 1 is shown. The shape and dimensions of the mandrel 1 are designed to be received within a correspondingly shaped recess in a probe housing (not shown) with very small tolerances, and a small air gap (e.g., about 1 mm) between the outer surface of the mandrel 1 and the inner surface of the housing. The mandrel 1 is suitable for securely attaching to the distal end of a handheld rod, for example, as shown in the image. Figure 1 As shown, this allows the mandrel 1 to be mounted at the distal end of the probe.

[0114] A spindle 1 defines a longitudinal axis 2, which is aligned with the longitudinal axis of the probe, and carries two sensing coils 3a and 3b axially separated along the probe axis 2. One of the sensing coils 3a is juxtaposed with the distal end 4 of the spindle 1, which is positioned at the distal sensing end (also referred to herein as the end) of the probe during assembly. The other sensing coil 3b is juxtaposed with the proximal end 6 of the spindle 1. A long drive coil 5 is positioned approximately midway between the sensing coils 3a and 3b. The sensing coils 3a and 3b are connected in anti-series, such that the sensing voltages induced therein by the magnetic field have opposite polarities. Alternatively, the sensing coils 3a and 3b can be wound in opposite directions and connected in series to achieve the same effect. The long drive coil 5 is connected to a suitable current source (not shown), which can be housed in... Figure 1 In the type of base station shown, the probe can be connected to the base station via a suitable cable. When current passes through the drive coil 5, a drive magnetic field is generated.

[0115] Sensing coils 3a and 3b are arranged for connection to a signal processor (not shown), which may also be housed in, for example, a base station. When the probe is in use, a driving magnetic field from the long drive coil 5 generates a response field from a magnetic marker (also not shown) near the probe; typically near the distal end of the probe. The response field is detected by the signal processor as a sense voltage in sensing coil 3a closest to the probe tip. Voltages are also induced from the drive coil 5 in both the distal sensing coil 3a and the proximal sensing coil 3b. Since sensing coils 3a and 3b are connected in anti-series with the drive coil 5 at substantially equal distances, the drive coil 5 induces approximately equal and opposite voltages in sensing coils 3a and 3b. Therefore, the net reference voltage in sensing coils 3a and 3b generated by the drive coil 5 is close to zero. However, due to manufacturing tolerances (e.g., sensing coils 3a and 3b are unlikely to be identical, and the drive coil is unlikely to be precisely centered between the two sensing coils 3a and 3b), the net reference voltage induced from the drive coil 5 in sensing coils 3a and 3b is not precisely zero.

[0116] A reference voltage balancing device, comprising a conductor 7 formed of an elongated, bow-shaped strip of conductive material, is mounted proximal to the spindle 1 on the distal sensing coil 3a. The conductor 7 is connected to a current source at circumferentially spaced terminals (not shown) and defines a conductive path extending partially circumferentially around the spindle 1 between the connectors. Figure 3 As shown, conductor 7 thus forms a conductive path extending angularly to the ground around probe axis 2, but does not form a complete loop. When current flows through the conductive path, the conductive path generates a balancing magnetic field, which induces a balancing voltage in sensing coil 3a. The angular length of the conductive path causes the induced balancing voltage in sensing coil 3a to decrease the reference voltage from drive coil 5. Advantageously, this means that the sensed voltage detected in sensing coil 3a is primarily attributable to the marker. Therefore, the signal processor can process the sensed voltage to calculate the proximity of the marker to the probe and generate an output signal representing that proximity. The output signal can be a display signal for displaying the distance between the marker and the probe on a suitable display, an audio signal having one or more parameters that vary according to the proximity, and / or a tactile signal for generating a tactile response in the probe or another device in contact with the user indicating the distance between the probe and the marker.

[0117] Figure 4 This is a schematic longitudinal cross-sectional view taken through a mandrel 101 forming a portion of a probe, according to another embodiment of this disclosure. The mandrel 101 is generally connected to... Figure 3 The mandrel 1 is similarly constructed and arranged, and is adapted to be securely fixed to the distal end of the handheld rod, such that the mandrel 1 is mounted at the distal end of the probe. The rod is appropriately configured for connection to the base station, such as... Figure 1As shown. A spindle 101 supports a first pair of coils 110a adjacent to the distal end 104 of the spindle 101 and a second pair of coils 110b adjacent to the proximal end 106 of the spindle 101, the first pair of coils 110a and the second pair of coils 110b being axially separated along the probe axis 102. The first pair of coils 110a includes a first drive coil 105a and a first sensing coil 103a; the second pair of coils 104b includes a second drive coil 105b and a second sensing coil 103b. The second drive coil 105b and the second sensing coil 103b are substantially identical to the first drive coil 105a and the first sensing coil 103a, respectively. The first drive coil 105a and the second drive coil 105b are connected to a current source (not shown) that can be housed in a base station and connected in series. The first sensing coil 103a and the second sensing coil 103b are connected in anti-series and are arranged for connection to a suitable signal processor as described above. In an alternative arrangement, as described above regarding... Figure 3 The first sensing coil 103a and the second sensing coil 103b can be connected in series but wound in opposite directions.

[0118] When current is passed through the first drive coil 105a and the second drive coil 105b during use, a driving magnetic field is generated. As a result, a voltage is induced primarily from the first drive coil 105a in the first sensing coil 103a, and primarily from the second drive coil 105b in the second sensing coil 103b. Since the sensing coils 103a and 103b are connected in anti-series, the voltages induced in the sensing coils 103a and 103b from their associated drive coils 105a and 105b are approximately equal and opposite. However, due to manufacturing tolerances, the first drive coil 105a is unlikely to be identical to the second drive coil 105b, the first sensing coil 103a is unlikely to be identical to the second sensing coil 103b, and the spacing between coils 103a and 105a in the first pair of coils 110a is unlikely to be equal to the spacing between coils 103b and 105b in the second pair of coils 110b. As a result, the net reference voltage summed from the two sensing coils 103a and 103b is unlikely to be zero.

[0119] A reference voltage balancing device, comprising a conductor 107 formed of an arcuate strip of conductive material, is also mounted to the spindle 201 and connected to a current source to generate a balancing magnetic field as described above. The arcuate strip of conductive material defines a circumferentially extending conductive path on the conductor 107 between spaced terminals (not shown) near the first drive coil 105a. The conductive path extends around the probe axis 102 and has an angular length between the terminals, such that the balancing magnetic field induces a balancing voltage in the first sensing coil 103a that at least partially cancels the reference voltage. Advantageously, this means that the voltage detected in the sensing coil 103a will be at least primarily attributable to a marker near the probe, thereby allowing the signal processor to determine the distance between the marker and the probe.

[0120] Figure 5 This is a schematic longitudinal cross-sectional view taken through a mandrel 201 of a probe according to yet another embodiment of this disclosure. The mandrel 201 is similar to the mandrels 1; 101 of the first and second embodiments described above, and is adapted to be securely fixed to the distal end of a handheld rod, such that the mandrel 201 is mounted at the distal end of the probe. The mandrel 201 supports a first set of distal coils 210a and a second set of proximal coils 210b axially separated along the longitudinal axis 202 of the mandrel 201. The first set of coils 210a includes a first pair of drive coils 205a, 205c and a first sensing coil 203a between the first pair of drive coils 205a, 205c; the second set of coils 210b includes a second pair of drive coils 205b, 205d substantially identical to the first pair of drive coils 205a, 205c and a second sensing coil 203b. The first pair of drive coils 205a, 205c and the second pair of drive coils 205b, 205d are connected in series to a current source (not shown) that can be accommodated in a suitable base station, such as... Figure 1 As shown. As described above, the first sensing coil 203a and the second sensing coil 203b are connected in anti-series connection and arranged for connection to the signal processor. In an alternative arrangement, as described above... Figure 3 and Figure 4 The first sensing coil 203a and the second sensing coil 203b can be connected in series but wound in opposite directions.

[0121] When current flows through the first pair of drive coils 205a, 205c and the second pair of drive coils 205b, 205d during operation, a driving magnetic field is generated. The axial spacing of the two sets of coils 210a, 210b ensures that the voltage induced in the first sensing coil 203a mainly originates from the first pair of drive coils 205a, 205c, and the voltage induced in the second sensing coil 203b mainly originates from the second pair of drive coils 205b, 205d. Since the sensing coils 203a, 203b are connected in anti-series, the voltages induced in the sensing coils 203a, 203b from their respective pairs of drive coils 205a, 205c; 205b, 205d are approximately equal and opposite to each other. However, due to manufacturing tolerances, the first pair of drive coils 205a, 205c is unlikely to be identical to the second pair of drive coils 205b, 205d, the first sensing coil 203a is unlikely to be identical to the second sensing coil 203b, and the spacing between the coils in the first set of coils 210a is unlikely to be equal to the spacing between the coils in the second set of coils 210b. As a result, the net reference voltage across the two sensing coils 203a, 203b is unlikely to be exactly zero.

[0122] A reference voltage balancing device, comprising an arcuate conductor 207 formed of an elongated arcuate strip of conductive material, is mounted to the outer surface of a spindle 201, defining a circumferentially extending conductive path between spaced-apart terminals (not shown) on the conductor 207, the spaced-apart terminals being intermediate between a first set of coils 210a and a second set of coils 210b. The conductor 207 is conveniently connected via terminals suitably located at or near corresponding axial ends 208, 209 of the conductor 207 to generate a balanced magnetic field in use. It should be understood that, in some embodiments, separate current sources may be provided for the conductive path if desired. The conductor 207 is positioned closer to one set of coils 210b, 210a than one set of coils in the plurality of sets of coils 210a, 210b, such that, in operation, it generates a magnetic field that induces a larger voltage across the sensing coils 203a, 203b in one set of coils 210a, 210b. Conductor 207 is configured such that the angular length of the conductive path between terminals 208 and 209 results in a net balance voltage across sensing coils 203a and 203b, which at least partially cancels out the reference voltage. Advantageously, this means that the voltage detected in sensing coils 203a and 203b is primarily attributable to a magnetic marker near the probe, thereby allowing the signal processor to determine the distance between the marker and the probe. In an alternative arrangement, conductor 207 may be as shown below with reference to Figures 6(a) and 6(b) or Figure 7 The reference voltage balancing device of one of the described types is replaced.

[0123] Figure 6(a) is a perspective view of a reference voltage balancing device 401 according to another embodiment of the present disclosure; Figure 6(b) is a plan view of the reference voltage balancing device 401 in an unfolded configuration for ease of reference. The balancing device 401 is formed of a flexible printed circuit board including an insulating backing layer 402 and a conductive layer 403. Suitably, the conductive layer 403 may comprise a copper film in a manner known to those skilled in the art. The backing layer 402 may comprise any suitable insulating material having sufficient flexibility to be wound and secured to the cylindrical mandrels 1, 101, 201, similar to the materials described above. Alternatively, the backing layer 402 may comprise an insulating tape, such as a polyimide tape (e.g., the aforementioned...). bring).

[0124] The balancing device 401 forms an incomplete ring as shown in FIG. 6(a), having two axial ends 405, 406 and defining a central axis 404, which, during assembly, is aligned with the longitudinal axes 2, 102, 202 of the spindles 1, 101, 201. A connecting piece 407 is attached to one of the circumferential ends 405, which is configured to be received in a corresponding recess (not shown) formed in the spindle for positioning the device 401 relative to the spindle.

[0125] A copper layer 403 is etched in a manner known to those skilled in the art to form a first axially spaced elongated conductor 409a and a second axially spaced elongated conductor 409b, which extend circumferentially around the device 401, one substantially parallel to the other. Each conductor 409a, 409b includes a plurality of circumferentially spaced pads 411 in a rung manner, which extend at a series of different angular locations between the conductors 409a, 409b in a direction substantially parallel to the axis 404 of the device 401 and terminate at a free end 412 near the other conductor 409b, 409a. Each conductor 409a, 409b is formed with terminals 413a, 413b, which are juxtaposed with a terminal block 407 for connecting the balancing device 401 to a current source.

[0126] The balanced magnetic field generated by the balancing device 401 in use can be tuned by selecting pads (e.g., 411', 411" or 411"') on one of the conductors 409b, 409a and forming an electrical connection (not shown) between the selected pads 411', 411" or 411"' and the other conductor 409a, 409b to bridge the short gap between the free end 412 of the pads 411', 411" or 411" and the other conductor 409a, 409b. For example, the electrical connection can be made by soldering from the free end 412 to the other conductor, thereby forming a continuous electrical path, as indicated by the arrows in Figure 6(b). The selection of pads 411'; 411"; 411"' determines the angular length of the conductive path defined by the conductors 409a, 409b. As disclosed herein, the conductive path The angular length determines the strength of the balancing magnetic field, and thus the balancing voltage induced from the balancing device 401 in one or more sensing coils. When mounted to mandrels 1, 101, 201, the axially extending pads 411 do not contribute to the balancing field. Conveniently, the balancing device 401 is mounted on mandrels 1, 101, 201 such that one of the first conductor 409a and the second conductor 409b is positioned midway between the two sensing coils 3a, 3b; 103a, 103b; 203a, 203b, such that the field generated by this conductor affects the two sensing coils substantially equally. In this case, the balancing field is controlled by the axial position of the other conductor 409b, 409a and the angular length of the other conductor between the terminals 413b, 413a and the selected pads 411'; 411"; 411"'.

[0127] Figure 7 This is a plan view of a balanced voltage balancing device 501 in an unfolded configuration according to another embodiment of this disclosure. The balancing device 501 includes a flexible printed circuit board 510. The circuit board 510 is etched with two elongated copper traces 509a, 509b forming a first parallel conductor and a second parallel conductor, and a plurality of spaced copper pads 511 extending partially between the traces 509a, 509b. In this embodiment, all pads 511 are connected to one of the traces 509a. A complete conductive path can be formed, as shown in 521, by wiring or soldering a connection between a selected copper crossbar 511a and the other trace 509b, thereby allowing current to flow around the path, as indicated by the arrows. In use, the balancing device 501 can induce a balanced voltage in one or more sensing coils, as disclosed herein, depending on the angular length of the conductive path defined by the traces 509a, 509b and the position of the traces 509a, 509b relative to one or more sensing coils.

[0128] Figure 8(a) is a schematic diagram of the arrangement of two sets of coils 604a, 604b of a gradiometer forming a sensitive probe (not shown) according to another embodiment of the present disclosure. It shows how the conductive path 607 provided by the type of balancing voltage balancing device described herein provides a balancing magnetic field to induce a balancing voltage across the two sensing coils 603a, 603b of the two sets of coils, for reducing the reference voltage in the sensing coil caused by the driving magnetic field generated by the driving coil of the multiple sets of coils, whereby the sensing voltage across the sensing coil is mainly attributed to the response field from the magnetic marker present in the driving field.

[0129] The arrangement includes a first set of coils 604a and a second set of coils 604b coaxially arranged on the longitudinal probe axis 602; each set of coils includes two spaced-apart drive coils 605a, 605c; 605b, 605d and sensing coils 603a, 603b between the drive coils 605a, 605c, 605b, 605d. The coils can be supported on a suitable coaxial formwork or mandrel (not shown) of the type described above and housed within a probe housing (also not shown), wherein the first set of coils 604a is positioned close to the distal end of the probe for maximum sensitivity.

[0130] The drive coils 605a, 605b; 605c, 605d are connected in series with each other and are adapted to be connected to an AC current source (not shown) so that they generate a drive magnetic field during use. The sensing coils 603a, 603b of the two sets of coils are connected in anti-series and arranged for connection to a signal processor, for example, housed in a... Figure 1 Within the base station shown, the sensed voltage induced in the sensing coil is processed to calculate the distance between the probe and the magnetic marker. In an alternative arrangement, sensing coils 603a and 603b may be connected in series but wound in opposite directions.

[0131] In use, the drive coils 605a, 605b, 605c, and 605d generate approximately equal and opposite voltages in the two sensing coils 603a and 603b. However, due to manufacturing tolerances, the net reference voltage (i.e., the net voltage across sensing coils 603a and 603b) cannot be exactly zero. This is especially true for narrow probes with small coil diameters (e.g., less than about 10 mm), as described above.

[0132] As disclosed herein, conductive path 607 is positioned off-center between the first set of coils 604a and the second set of coils 604b in a direction parallel to probe axis 602. In FIG. 8(a), conductive path 607 is shown as a complete circuit for illustrative purposes, but in practice includes terminals for connection to a current source to drive current through the conductive path. Conductive path 607 is suitably connected to the same current source as the driving coils 605a, 605b, 605c, 605d, but in other embodiments, a separate current source may be provided. The current flowing angularly along conductive path 607 at the off-center position along probe axis 602 (as indicated by solid arrow 613) helps to balance the magnetic field, which induces a balancing voltage in at least one of sensing coils 603a, 603b. Current in the axial direction and current flowing angularly at the midpoint between the two sensing coils 604a, 604b do not contribute to the balancing magnetic field. The conductive path 607 is arranged such that it induces a balancing voltage that at least partially cancels any reference voltage across the sensing coils 604a and 604b generated by the drive coils 605a, 605b, 605c, and 605d.

[0133] As disclosed above, the conductive path 607 can be suitably provided by a balancing voltage device comprising at least one arcuate conductor extending angularly to the ground around the probe axis 602. The balancing field is determined by the angular length of the conductive path 607.

[0134] Figures 8(b) to 8(d) These are a series of schematic diagrams illustrating the effect of altering the angular length of conductive paths 707a, 707b, 707c between two sets of coils 704a, 704b, which are coaxially arranged on a longitudinal probe axis 702 for use in a sensitive probe according to this disclosure. Similar to the multiple sets of coils 704a, 704b described above with reference to FIG8(a), they include a first set of coils 704a and a second set of coils 704b. Each set of coils 704a, 704b includes a pair of spaced-apart drive coils 705a, 705c; 705b, 705d and sensing coils 703a, 703b between the respective drive coils 705a, 705c; 705b, 705d. A voltage balancing device (not shown) is positioned between multiple sets of coils 704a, 704b to define conductive paths 707a, 707b, 707c. These conductive paths include a first circumferentially extending conductor and a second circumferentially extending conductor, as well as two conductive bridges extending between the circumferential conductors in a direction substantially parallel to the probe axis 702. As shown in Figure 8(a), conductive paths 707a, 707b, 707c are... Figures 8(b) to 8(d)The circuits shown are for illustrative purposes, but in reality, the balancing device includes terminals for connecting the conductive path to a current source to drive current through the conductive path.

[0135] Figure 8(b) shows a conductive path 707a spanning only a short azimuth distance around the probe axis 702. The eccentric portion of the conductive path 707, extending in the axial direction indicated by arrow 713, helps to balance the magnetic field. Figure 8(c) shows a conductive path 707b spanning a larger azimuth distance around the probe axis 702. This can be seen, for example, by referring above to Figures 6(a) and 6(b) or... Figure 7 In the type of balancing device described, different pads 411; 511 are connected, or the conductive bridge is moved to include first and second conductors 409a, 409b; 509a, 50b of greater length in the conductive path 707b. The conductive path 707b generates a stronger balancing magnetic field than the conductive path 707a in FIG8(b). Meanwhile, FIG8(d) shows a conductive path 707c that extends almost completely around the probe axis 702. This path can be, for example, by referring above to FIG6(a) and FIG6(b) or Figure 7 In the balancing device of the described type, the ends of the first and second conductors 409a, 409b; 509a, 509b are connected to pads 411; 511, or formed by positioning conductive bridges at or near the ends of the first circumferential conductor and the second circumferential conductor away from the connection terminals, thereby substantially encompassing the entire length of the conductor in the conductive path. This conductive path 707c generates a stronger balancing magnetic field than the conductive path 707b of FIG. 8(c).

[0136] Figure 9 This is a perspective view of the distal portion of a probe 800 according to an embodiment of the present disclosure. The probe 800 includes a coil arrangement, as described in more detail below, supported on a mandrel 901 fixedly attached to the distal end 902 of a rod 900. The rod 900 is adapted to connect to a suitable base station (not shown) including a signal processor. The probe 800 is typically connected to the base station via a wired connection to the rod 900, but in some embodiments, it can be connected wirelessly.

[0137] The mandrel 901 defines a longitudinal axis 902, which includes: a first distal cylindrical portion 903 having a diameter of approximately 10 mm, supporting a first set of coils 804a near the distal sensing end 904 of the probe 800; a second proximal cylindrical portion 905, similar in size to the distal portion 903 and supporting a second set of coils 804b axially spaced relative to the first set of coils 804a; and a narrower cylindrical intermediate portion 907 supporting a balancing voltage matching device 807 between the first set of coils 804a and the second set of coils 804b. The mandrel 901, with its coil arrangement fixedly mounted thereon, is housed within a substantially cylindrical hollow probe housing (not shown) having an outer diameter of approximately 12 mm.

[0138] The first pair of coils 804a includes a first pair of drive coils 805a and 805c and a first sensing coil 803a between the drive coils 805a and 805c. Similarly, the second pair of coils 805b and 805d includes a second pair of drive coils 805b and 805d and a second sensing coil 803b between the drive coils 805b and 805d.

[0139] The drive coils 805a, 805c; 805b, 805d within each set of coils 804a, 804b are substantially identical to each other. Each drive coil includes a conductor with approximately 10 to approximately 60 turns and has an outer radius between approximately 1.5 mm and approximately 6 mm and an axial length between approximately 0.5 mm and approximately 2.5 mm.

[0140] The sensing coils 803a and 803b in each group of coils 804a and 804b include wires with approximately 100 to approximately 500 turns and have an axial length between approximately 0.75 mm and approximately 2 mm and an average radius between approximately 1.5 mm and approximately 6.5 mm. In this embodiment, each sensing coil 803a and 803b has an average radius similar to that of the driving coils 805a and 805c, 805b and 805d of the corresponding group of coils 804a and 804b.

[0141] Each sensing coil 803a; 803b is formed of a wire with a diameter between approximately 0.025 mm and 0.1 mm.

[0142] The coils are configured and arranged such that the distance between the center of each sensing coil 803a; 803b and the center of each driving coil 805a, 805c; 805b, 805d within the same set of coils 804a; 804b is between approximately 1 mm and approximately 3 mm.

[0143] The total axial distance spanned by the first group of coils 804a and the second group of coils 804b is between approximately 19 mm and approximately 30 mm. Meanwhile, the axial spacing between the sensing coils 803a and 803b of the first group of coils 804a and the second group of coils 804b is between approximately 12 mm and approximately 15 mm.

[0144] In this embodiment, the spacing between the first coil group 804a and the second coil group 804b is approximately 12 mm in the direction parallel to the probe axis 902. However, it should be understood that in other embodiments, different spacings between the coil groups 804a and 804b may be used.

[0145] The voltage balancing device 807, essentially as described above with reference to Figures 6(a) and 6(b), includes a flexible printed circuit board etched thereon to form two substantially parallel elongated copper traces forming a first arcuate conductor 809a and a second arcuate conductor 809b, the angular portions of which extend about ground around a probe axis 902. The flexible circuit board is circumferentially wound around and secured to the middle portion 907 of a mandrel 901, such that the first conductor 809a and the second conductor 809b extend about ground around the probe axis 902. Figure 9 As shown. One of the conductors 809a extends circumferentially around the spindle 901 in a direction parallel to the axis 902 of the spindle 901, at an off-center position between the first set of coils 804a and the second set of coils 804b, and more specifically between the first sensing coil 803a and the second sensing coil 803b. The other conductor 809b extends circumferentially around the spindle 901 at a point equidistant from the first set of coils 804a and the second set of coils 804b, and more specifically at a point equidistant from the first sensing coil 803a and the second sensing coil 803b. In other arrangements, the two conductors 809a, 809b may be positioned away from the midpoint between the multiple sets of coils 804a, 804b, but they should be arranged asymmetrically about the midpoint. In this embodiment, each of the elongated conductors 809a, 809b extends in a corresponding plane substantially perpendicular to the axis 902 of the spindle 901. In other embodiments, one of the two conductors 809a, 809b may be configured differently such that they also extend in a direction parallel to axis 902, provided that at least one of the conductors 809a, 809b extends angularly about axis 902 and has an average eccentric position along axis 902.

[0146] As described above, the first conductor 809a and the second conductor 809b have a plurality of pads 811 formed at a series of angular locations around the probe axis 902. These pads 811 extend between the conductors 809a and 809b in a direction substantially parallel to the probe axis 902. Each pad 811 extends from one of the conductors 809a and 809b and terminates only where there is no other conductor 809b or 809a. Each of the conductors 809a and 809b has a terminal (not shown) at one end for connection to a current source, and the conductors 809a and 809b are interconnected at one of the pads 811 to form a continuous conductive path through the first conductor 809a and the second conductor 809b, as described in more detail below.

[0147] Drive coils 805a, 805b, 805c, and 805d are connected in series with each other, while the first sensing coil 803a and the second sensing coil 803b are connected in anti-series. In an alternative arrangement, sensing coils 803a and 803b may be connected in series but have opposite windings. Sensing coils 803a and 803b are provided with connectors for connection to a signal processor as described herein, for processing the sensed voltage detected by the sensing coils to calculate the distance between probe 800 and the magnetic marker. Drive coils 805a, 805b, 805c, and 805d and balancing device 807 are connected to an AC current source. The first pair of drive coils 805a and 805c generates a driving magnetic field and induces a voltage in the first sensing coil 803a. The second pair of drive coils 805b and 805d also generates a driving magnetic field and generates approximately equal and opposite voltages in the second sensing coil 803b. The net voltage induced in the first sensing coil 803a and the second sensing coil 803b from the first pair of drive coils 805a, 805c and the second pair of drive coils 805b, 805d is close to zero, but is unlikely to be exactly zero due to manufacturing tolerances and differences between the first set of coils 804a and the second set of coils 804. Therefore, a residual reference voltage is typically generated. In use, a magnetic marker present in the driving magnetic field generates a response field that induces a sensing voltage in one or both of the sensing coils 803a, 803b. Typically, the marker is located distal to the end 904 of the probe 800, such that the sensing voltage is primarily generated in the first sensing coil 803a of the first distal coil set 804a. The reference voltage generated by the drive coils tends to mask the sensing voltage from the marker, and therefore it is desirable to minimize the reference voltage as much as possible so that the sensing voltage is primarily attributed to the response field and indicates the distance between the first sensing coil 803a and the marker, allowing the signal processor to process the sensing voltage to determine the distance and generate an output signal representing the distance.

[0148] A current is passed through the conductive path of the balancing device 807 to generate a balancing magnetic field as disclosed herein. The strength of the balancing field depends on the angular length of the conductive path, which can be controlled by selecting where the first conductor 809a and the second conductor 809b are interconnected. Because one of the conductors 809a and 809b is eccentrically positioned between the coil groups 804a and 804b as described above, the balancing field induces unequal voltages in the first sensing coil 803a and the second sensing coil 803b, thereby generating a net balancing voltage to at least partially offset the reference voltage. Therefore, the magnitude of the balancing field can be tuned by properly setting the angular length of the conductive path to minimize the residual reference voltage generated by the drive coils 805a, 805b, 805c, and 805d. As will be apparent to those skilled in the art, this is achieved by forming a conductive bridge at an angular position between a pad 811 on one of the conductors 809a, 809b and the other conductor 809b, 809a, such that the angular length of the conductive path causes the current flowing eccentrically from the midpoint between the first set of coils 804a and the second set of coils 804b in the circumferential direction to induce a balanced voltage in the first sensing coil 803a and the second sensing coil 803b, thereby minimizing the reference voltage and allowing the sensing voltage induced in one or both sensing coils 803a, 803b from the response field generated by the magnetic marker in the driving field to be detected with improved sensitivity and accuracy.

[0149] See above for reference. Figures 3 to 5 , Figures 8(a) to 8(d) and Figure 9 In a variation of the described arrangement, instead of connecting the two sensing coils in anti-series (or in series with opposite windings), the two sensing coils can be adapted to be connected individually to a signal processor. Figure 10 The mandrel 1201 for the probe is shown, which is similar to the reference above. Figure 5 The mandrel 201 is described. However, it should be understood that this is purely for illustrative purposes, and any other implementation according to this disclosure may be similarly configured.

[0150] therefore, Figure 10The spindle 1201 includes two sets of coils 1210, 1210, which are coaxially supported on the spindle 1201 with respect to the longitudinal axis 1202 of the spindle. Each set of coils includes two axially spaced drive coils 1205a, 1205c; 1205b, 1205d and sensing coils 1203a, 1203b between their respective drive coils. A voltage balancing device 1207 is also supported on the spindle 1201 between the two sets of coils 1210a, 1210b. The drive coils 1205a, 1205c; 1205b, 1205d are connected in series to an AC current source 1221 housed within the base station 1220. Each sensing coil 1203a, 1203b is connected to a signal processor 1222 within the base station. In this way, the signal processor 1222 can use the reference voltage directly induced in one of the sensing coils 1203a and 1203b by the driving magnetic field to remove the corresponding reference voltage component directly caused by the driving magnetic field from the voltage induced in the other sensing coil 1203b and 1203a, thereby leaving only the sensing voltage component generated by the response field generated by the magnetic marker in the driving field and any residual reference voltage. Then, according to this disclosure, a balancing device 1207 of the type described above can be used to minimize the residual reference voltage.

[0151] Figure 11 This is a flowchart of a method 1100 for manufacturing a probe for sensing a magnetic marker according to another embodiment of the present disclosure. In a first step 1101, the method includes mounting at least two first coils and at least one second coil substantially coaxially on the longitudinal axis of the probe, the at least two first coils being either sensing coils or drive coils, and the at least one second coil being either a drive coil or a sensing coil, such that one or more drive coils can be connected to a current source to generate a drive magnetic field through the one or more drive coils, and one or more sensing coils can be connected to a signal processor to process one or more sensing voltages induced in the respective one or more sensing coils to generate an output signal; the first coils or second coils are configured or arranged to minimize a reference voltage component of the sensing voltage induced in the one or more sensing coils, the reference voltage component being directly attributable to the drive magnetic field; thereby the first coils and second coils are configured and arranged as a gradiometer for measuring the proximity of the magnetic marker to the probe, and the output signal represents the distance between the marker and the probe.

[0152] In the second step 1102, the method includes assembling a reference voltage balancing device comprising a first elongated conductor to a probe, such that the first conductor defines a conductive path extending partially around the probe axis and is juxtaposed with one or more sensing coils, and may be connected to a current source to generate a balancing magnetic field in the vicinity of one or more sensing coils, such that in use, the balancing magnetic field induces a balancing voltage in one or more sensing coils, the balancing voltage at least partially offsetting the reference voltage; thereby the sensed voltage is at least primarily attributed to a response field generated by a marker in response to a driving field, the response field corresponding to the proximity of the marker.

[0153] In an alternative implementation, in the first step 1101, two or more sensing coils may be arranged to output individual sensing voltages to a signal processor to allow the signal processor to process the sensing voltages to minimize the reference voltage component of the sensing voltage that can be directly attributed to the driving magnetic field.

[0154] Step 1102 may optionally include adjusting the angular length of the conductive path around the probe to minimize the reference voltage across one or more sensing coils.

[0155] Although various aspects of this disclosure have been described with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of this disclosure. Therefore, it should be understood that many modifications can be made to the illustrative embodiments, and other arrangements can be designed without departing from the scope of this disclosure as defined by the appended claims.

[0156] Those skilled in the art will understand that the features of these exemplary embodiments can be combined in other embodiments falling within the scope of this disclosure.

[0157] While various details have been set forth in the foregoing description, it should be understood that various aspects of the techniques for operating diagnostic and / or surgical guidance systems suitable for identifying, locating, tracking, and detecting the position of one or more implanted markers can be practiced without these specific details. Those skilled in the art will recognize that, for clarity of concept, the components (e.g., operations), devices, objects, and the discussions accompanying them described herein are used as examples, and various configuration modifications are contemplated. Therefore, as used herein, the specific examples illustrated and the accompanying discussions are intended to represent their more general categories. Generally, the use of any particular example is intended to represent its category, and the exclusion of specific components (e.g., operations), devices, and objects should not be considered limiting.

[0158] Furthermore, although several forms have been shown and described, the applicant does not intend to limit the scope of the appended claims to or confine them to these details. Many modifications, variations, alterations, substitutions, combinations, and equivalents of these forms can be implemented and will be apparent to those skilled in the art without departing from the scope of this disclosure. Moreover, the structure of each element associated with a described form can alternatively be described as means for providing the function performed by that element. Furthermore, where materials for certain components are disclosed, other materials may be used. Therefore, it should be understood that the foregoing description and the appended claims are intended to cover all such modifications, combinations, and variations falling within the scope of the disclosed forms. The appended claims are intended to cover all such modifications, variations, alterations, substitutions, modifications, and equivalents.

[0159] Although integers or elements of known obvious or foreseeable equivalents have been mentioned in the foregoing description, such equivalents are incorporated herein as if set forth separately. Reference should be made to the claims used to determine the true scope of this disclosure, which should be interpreted as covering any such equivalents. The reader will also understand that entire or specific features of this disclosure described as advantageous, convenient, etc., are optional and do not limit the scope of the independent claims. Furthermore, it should be understood that while such optional integers or features may be beneficial in some embodiments of this disclosure, they may not be desirable and therefore may not be present in other embodiments.

[0160] For the sake of brevity and clarity, selected aspects of the foregoing disclosure have been shown in block diagram form rather than in detail. Some portions of the detailed description provided herein can be presented as instructions for operating on data stored in one or more computer memories or one or more data storage devices or processors (e.g., floppy disks, hard disks, caches, random access memory, and other optical and magnetic storage devices and media) in a base station. Such descriptions and representations are used by those skilled in the art to describe the substance of their work and to convey it to others skilled in the art. Generally, an algorithm refers to a self-consistent sequence of steps that leads to a desired result, where a “step” refers to the manipulation of physical quantities and / or logical states, which may, but not necessarily, take the form of electrical or magnetic signals capable of being stored, transmitted, combined, compared, and otherwise manipulated. These signals are commonly referred to as bits, values, elements, symbols, characters, items, numbers, etc. These and similar terms may be associated with appropriate physical quantities and are merely convenient labels applied to these quantities and / or states. The various methods and steps disclosed herein can be implemented or programmed as algorithms, data structures, and instructions that can operate on inputs from data channels and generate outputs containing various types of data, such as user action data, user feedback signals, information, and images.

[0161] Unless otherwise specifically stated, as is apparent from the foregoing disclosure, it should be understood that throughout the foregoing disclosure, discussions using terms such as “processing” or “computing” or “speculating” or “determining” or “displaying” refer to the actions and processes of a computer system, a processor-based base station or similar electronic computing device, which manipulate and convert data represented as physical (electronic) quantities in the registers and memories of the computer system into other data similarly represented as physical quantities in the computer system’s memory or registers or other such information storage, transmission or display devices.

[0162] In a general sense, those skilled in the art will recognize that the various aspects described herein, which may be implemented individually and / or collectively by various hardware, software, firmware, or any combination thereof, can be considered as comprising various types of “circuits.” Thus, as used herein, “circuit” includes, but is not limited to, circuits having at least one discrete circuit, circuits having at least one integrated circuit, circuits having at least one application-specific integrated circuit, circuits forming a general-purpose computing device configured by a computer program (e.g., a general-purpose computer configured by a computer program that at least partially performs the processes and / or devices described herein, or a microprocessor configured by a computer program that at least partially performs the processes and / or devices described herein), circuits forming a memory device (e.g., in the form of random access memory), and / or circuits forming a communication device (e.g., a modem, communication switch, or optoelectronic device). Those skilled in the art will recognize that the subject matter described herein can be implemented in an analog or digital manner, or some combination thereof.

[0163] The foregoing detailed description has illustrated various forms of devices and / or processes using block diagrams, flowcharts, and / or examples. Where such block diagrams, flowcharts, and / or examples contain one or more functions and / or operations, those skilled in the art will understand that each function and / or operation within such block diagrams, flowcharts, and / or examples can be implemented individually and / or collectively by various hardware, software, firmware, or virtually any combination thereof. In one form, several portions of the subject matter described herein can be implemented via application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the forms disclosed herein can be implemented, wholly or partially, equivalently in an integrated circuit, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing circuits and / or writing code for software and / or firmware according to this disclosure will be within the skill of those skilled in the art.

[0164] Furthermore, those skilled in the art will understand that the mechanisms of the subject matter described herein can be distributed as one or more program products in various forms, and that the illustrative form of the subject matter described herein applies regardless of the specific type of signal-bearing medium used to actually perform the distribution. Examples of signal-bearing media include, but are not limited to, the following: recordable media, such as floppy disks, hard disks, optical discs (CDs), digital video discs (DVDs), digital magnetic tapes, computer memory, etc.; and transmission media, such as digital and / or analog communication media (e.g., fiber optic cables, waveguides, wired communication links, wireless communication links (e.g., transmitters, receivers, transmission logic, receiving logic, etc.)).

[0165] Furthermore, as described, some aspects can be implemented as one or more methods. Actions performed as part of a method can be ordered in any suitable manner. Therefore, implementations can be constructed in which actions are performed in a different order than those shown, which may include performing some actions simultaneously, even if they are shown as sequential in the illustrative implementation.

[0166] The phrase “and / or” as used herein in the specification and claims should be understood to mean “any one or both” of the elements so combined, that is, elements that exist together in some cases and separately in others.

[0167] As used herein in the specification and claims, the phrase "at least one" relating to a list of one or more elements should be understood to mean at least one element selected from any one or more elements in the list, but does not necessarily include at least one of every element specifically listed in the list, and does not exclude any combination of elements in the list. This definition also allows for the optional presence of elements other than those specifically identified in the list of elements referred to by the phrase "at least one," whether related to or unrelated to those specifically identified elements.

[0168] The terms “approximately” and “about” can be used to indicate within ±20% of the target value in some embodiments, within ±10% of the target value in some embodiments, within ±5% of the target value in some embodiments, and within ±2% of the target value in some embodiments. The terms “approximately” and “about” can include the target value.

[0169] In the claims and in the foregoing description, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “consisting of,” etc., shall be understood as open-ended, meaning including but not limited to. The transitional phrases “consisting of” and “substantially consisting of” shall be closed or semi-closed transitional phrases, respectively.

[0170] When a range or list of values ​​is provided, each intermediate value between the upper and lower limits of that range or list is individually anticipated and encompassed within this disclosure as if each value were specifically listed herein. Furthermore, smaller ranges between and including the upper and lower limits of a given range are anticipated and encompassed within this disclosure. The list of exemplary values ​​or ranges is not a declaration of other values ​​or ranges between and including the upper and lower limits of a given range.

[0171] The use of headings and sections in this application is not intended to limit this disclosure; each section may be applied to any aspect, implementation, or feature of this disclosure. Those claims that use only the phrase "means for..." are intended to be interpreted according to 35 USC 112, paragraph 6, and even only in the United States. Where the phrase "means for..." is not recited in the claims, these claims should not be interpreted under 35 USC 112. Outside the United States, the phrase "means for..." is intended to have its natural meaning. Limitations in the specification are not intended to be construed as applicable to any of the claims unless such limitations are expressly included in the claims.

[0172] The embodiments disclosed herein can be implemented as systems, methods, or computer program products. Therefore, embodiments can take the form of entirely hardware implementations, entirely software implementations (including firmware, resident software, microcode, etc.), or implementations combining software and hardware aspects, which are generally referred to herein as “circuit,” “module,” or “system.” Furthermore, embodiments can take the form of computer program products implemented on one or more computer-readable media having computer-readable program code embodied thereon.

[0173] Although various aspects of the invention have been described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the illustrative embodiments, and other arrangements can be designed, without departing from the scope of the invention as defined by the appended claims.

Claims

1. A probe for locating magnetic markers used in surgical procedures, the probe comprising: At least two first coils and at least one second coil, the at least two first coils and the at least one second coil being arranged substantially coaxially on the longitudinal axis of the probe as a gradiometer for measuring the proximity of the magnetic marker to the probe; The at least two first coils are one of a sensing coil or a driving coil, and the at least one second coil is the other of a driving coil or a sensing coil; The one or more drive coils are adapted to be connected to a current source to generate a drive magnetic field, and the one or more sensing coils are adapted to be connected to a signal processor for processing one or more sensing voltages induced in the respective one or more sensing coils to generate an output signal representing the distance between the marker and the probe; the first coil or the second coil is configured or arranged to minimize a reference voltage component of the sensing voltage induced in the one or more sensing coils that is directly attributable to the drive magnetic field, or to output individual sensing voltages from two or more sensing coils to the signal processor to allow the signal processor to process the sensing voltages, thereby minimizing the reference voltage component of the sensing voltages that is directly attributable to the drive magnetic field; as well as A reference voltage balancing device includes a first conductor that defines a conductive path juxtaposed with the one or more sensing coils and extending partially around the longitudinal axis, and is connectable to a current source to generate a balancing magnetic field in the vicinity of the one or more sensing coils. The conductive path is configured and arranged such that, in use, the balancing magnetic field induces a balancing voltage in one or more sensing coils that at least partially cancels out the reference voltage; thereby the sensed voltage is at least primarily attributable to a response field generated by the marker in response to the driving magnetic field, the response field corresponding to the proximity of the marker.

2. The probe according to claim 1, the probe comprising at least two sensing coils separated from each other along the longitudinal axis and a drive coil between the at least two sensing coils.

3. The probe according to claim 2, wherein the probe comprises a first set of coils and a second set of coils, the first set of coils comprising at least one driving coil and at least one sensing coil, and the second set of coils comprising at least one driving coil and at least one sensing coil; wherein, The first set of coils and the second set of coils are separated from each other along the longitudinal axis.

4. The probe according to claim 3, wherein, The first set of coils includes a first sensing coil located between a first pair of drive coils; and the second set of coils includes a second sensing coil located between a second pair of drive coils.

5. The probe according to claim 3, wherein, The first conductor is positioned at a fixed axial location between the first group of coils and the second group of coils.

6. The probe according to any one of claims 2 to 5, wherein, The at least two sensing coils are connected in anti-series connection to each other or have opposite windings, thereby minimizing the reference voltage component of the sensing voltage induced in the sensing coils that is directly attributable to the driving magnetic field.

7. The probe according to any one of claims 2 to 5, wherein, The at least two sensing coils are adapted to be individually connected to the signal processor, such that the signal processor can process the sensing voltage induced in the respective sensing coil to minimize the reference voltage component of the sensing voltage directly attributable to the driving magnetic field.

8. The probe according to claim 1, wherein the probe comprises at least two drive coils axially separated from each other along the length of the longitudinal axis and a sensing coil between the at least two drive coils; wherein, The at least two drive coils are connected in anti-series connection to each other or have opposite windings, thereby minimizing the reference voltage component of the sensed voltage induced in the sense coil that can be directly attributed to the drive magnetic field.

9. The probe according to claim 1, wherein, The balancing device further includes a second conductor and at least one conductive bridge extending between the first conductor and the second conductor, the conductive bridge defining the angular length of the conductive path.

10. The probe according to claim 9, wherein, The first conductor and the second conductor are defined by two conductive rings, each extending about the longitudinal axis.

11. The probe according to claim 9 or claim 10, wherein, One or both of the first conductor and the second conductor include a plurality of pads at a series of angularly spaced locations around the longitudinal axis for connecting the at least one conductive bridge, thereby defining the conductive path.

12. The probe according to claim 1, wherein, The first conductor includes conductive traces and / or wires.

13. The probe according to claim 1, wherein, The balancing device includes a flexible circuit board, which is circumferentially wound around the longitudinal axis.

14. The probe according to claim 13, wherein, The balancing device includes a flexible printed circuit board, which includes at least one conductive trace defining the first conductor.

15. A method of manufacturing a probe for sensing magnetic markers during a surgical procedure, the method comprising: At least two first coils and at least one second coil are mounted substantially coaxially on the longitudinal axis of the probe, the at least two first coils being either sensing coils or driving coils, and the at least one second coil being either driving coils or sensing coils, such that one or more driving coils can be connected to a current source to generate a driving magnetic field through the one or more driving coils, and the one or more sensing coils can be connected to a signal processor for processing one or more sensing voltages induced in the respective one or more sensing coils to generate an output signal; the first coils or the second coils are configured or arranged to minimize a reference voltage component of the sensing voltage induced in the one or more sensing coils that is directly attributable to the driving magnetic field, or to output individual sensing voltages from the two or more sensing coils to the signal processor to allow the signal processor to process the sensing voltages, thereby minimizing the reference voltage component of the sensing voltage that is directly attributable to the driving magnetic field; Thus, the first coil and the second coil are configured and arranged as a gradiometer for measuring the proximity of the magnetic marker to the probe, and the output signal represents the distance between the marker and the probe; A reference voltage balancing device, including a first conductor, is mounted to the probe such that the first conductor defines a conductive path juxtaposed with the one or more sensing coils and extending partially around the longitudinal axis, and is connectable to a current source to generate a balancing magnetic field near the one or more sensing coils, such that, in use, the balancing magnetic field induces a balancing voltage in the one or more sensing coils that at least partially cancels the reference voltage; thereby, the sensed voltage is at least primarily attributable to a response field generated by the marker in response to the driving magnetic field, the response field corresponding to the proximity of the marker.

16. The method according to claim 15, further comprising: Adjust the angular length of the conductive path around the probe to minimize the reference voltage across the one or more sensing coils.

17. A method for setting a probe for sensing magnetic markers used in surgery, the probe comprising: At least two first coils and at least one second coil, the at least two first coils and the at least one second coil being arranged substantially coaxially on the longitudinal axis of the probe as a gradiometer for measuring the proximity of the magnetic marker to the probe; The at least two first coils are one of a sensing coil or a driving coil, and the at least one second coil is the other of a driving coil or a sensing coil; The one or more drive coils are adapted to be connected to a current source to generate a drive magnetic field, and the one or more sensing coils are adapted to be connected to a signal processor for processing the sensing voltage induced in the one or more sensing coils to generate an output signal; The first or second coil is configured or arranged to minimize the reference voltage component of the sensed voltage induced in the one or more sense coils that is directly attributable to the driving magnetic field, or to output individual sensed voltages from two or more sense coils to the signal processor to allow the signal processor to process the sensed voltages, thereby minimizing the reference voltage component of the sensed voltage that is directly attributable to the driving magnetic field. A reference voltage balancing device includes a first conductor that defines a conductive path juxtaposed with the one or more sensing coils and extending partially around the longitudinal axis, and is connectable to a current source to generate a balancing magnetic field in the vicinity of the one or more sensing coils. The method includes: adjusting the angular length of the conductive path around the longitudinal axis to control the balancing magnetic field, thereby inducing a balancing voltage on one or more sensing coils that at least partially cancels out the reference voltage.

18. A detection device for locating magnetic markers during surgery, the detection device comprising: The probe according to any one of claims 1 to 14; A current source, operable to generate a driving magnetic field through the one or more driving coils and the first conductor; At least one signal processor is configured to receive one or more sensing voltages from the one or more sensing coils and generate an output signal representing the distance between the probe and the magnetic marker.

19. The detection device according to claim 18, wherein the detection device further comprises at least one implantable magnetic marker.

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