Improvements in or relating to sensitive probes for detecting surgical markers - Patents.com

Abstract

The present invention relates to a probe for locating a magnetic marker for use during surgery. The probe comprises at least two first coils (3a, 3b) and at least one second coil (5) arranged substantially coaxially on a longitudinal axis of the probe for measuring the proximity of a magnetic marker to the probe, and a baseline voltage sensing device (7) comprising a first elongated conductor defining a conductive path extending partially around the axis of the probe. The conductive path is constructed and arranged to induce a balanced voltage in the sensing coils that, in use, at least partially offsets the baseline voltage. Methods of manufacturing such a probe, methods of configuring such a probe for use in sensing magnetic markers, and detection devices for locating a magnetic marker during surgery are also disclosed.

Description

[Technical field]

[0001] The present disclosure relates to probes for sensing surgically implanted magnetic markers, as well as methods of manufacturing such probes, methods of configuring such probes, and detection systems including such probes. [Background technology]

[0002] In the field of sensitive probes for the detection of implanted magnetic markers for use in locating lesions and the like during surgery, it is known to use a combination of a drive coil and a sense coil to determine the proximity of a magnetic marker (also called a seed) to the probe. A current is supplied to the drive coil, which generates a drive magnetic field. The drive magnetic field induces a response from the magnetic marker, which in turn induces a sense voltage in the sense coil. By measuring and interpreting the sense voltage from the sense coil, the location of the marker relative to the probe can be determined. However, a voltage is also induced in the sense coil from the drive coil. This can prevent the location of the marker from being determined, as the voltage induced in the sense coil from the drive coil masks the sense voltage arising from the marker.

[0003] Known surgical probes, such as those disclosed in U.S. Pat. No. 5,399,333, use coil arrangements that can cancel the voltage induced directly from the drive coil and attribute a sense voltage to a magnetic marker. This is accomplished, for example, by placing the drive coil at the midpoint between two similar sense coils that are connected in anti-series or have windings in opposite directions. Alternatively, a single sense coil may be interposed between the two drive coils.

[0004] Due to manufacturing tolerances of the probe and coils, it may not be practical to precisely cancel or completely eliminate the voltage induced in the sense coil(s) directly from the drive coil(s). For example, two particular sense coils or drive coils may not be identical to each other, or the positioning of the drive coil and sense coil may not be precise enough. As a result, a residual baseline voltage may be induced in the sense coil(s) as a result of the drive coil(s): this may be problematic for precise identification of the marker's location. Although it is generally desirable for the probe to have a narrow diameter in order to reduce the size of the surgical incision required when using the probe, this problem becomes more severe in probes with small coils, because in such probes, even a small change in coil position or drive current results in a relatively large change in the drive magnetic field and therefore in the sense voltage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2014 / 140567 Summary of the Invention [Problem to be solved by the invention]

[0006] Thus, there is a need for an improved sensitive probe that allows for more accurate localization of marker locations, even with smaller probe diameters, without interference from the drive coil or coils. [Means for solving the problem]

[0007] According to a first aspect of the present disclosure, a probe for sensing an embedded magnetic marker for use in a surgical procedure is provided. The probe comprises at least two first coils and at least one second coil, which are 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 the other of the driving coil or the sensing coil. The one or more driving coils are adapted to be connected to a current source in use to generate a driving magnetic field through the driving coil. Meanwhile, the one or more sensing coils are adapted to be connected to a signal processor in use to process one or more sensing voltages induced in the respective one or more sensing coils to generate an output signal representative of the distance between the marker and the probe.

[0008] Preferably, the first coil or the second coil may be configured or arranged to minimize a baseline voltage component of the sense voltage induced in the one or more sense coils that is directly attributable to the drive 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 with respect to one another, or connected in series but wound in opposite directions, thereby minimizing the baseline voltage component of the sense voltage.

[0009] Alternatively, the two or more sense coils may be arranged to output separate sense voltages to a signal processor, allowing the signal processor to process the sense voltages and minimize baseline voltage components of the sense voltages that may be directly attributable to the drive magnetic field. For example, the signal processor may be operable to subtract the sense voltage from one sense coil from the sense voltage from another sense coil to substantially remove the component of the sense voltage that is directly attributable to the drive magnetic field.

[0010] After minimizing the baseline voltage, some baseline voltage may remain in the sensed voltage due to manufacturing tolerances or other reasons. According to the present disclosure, the probe further comprises a baseline voltage taring device comprising a first elongated conductor defining a conductive path extending partially around a longitudinal axis ("probe axis") defined by the probe in proximity to one or more sense coils. Preferably, the first conductor is located at a fixed position on the probe axis. The first conductor is preferably arc-shaped, preferably forming an arc in a plane perpendicular to the probe axis. Thus, the conductive path extends azimuthally but incompletely around the probe axis. The first conductor is adapted to connect to a current source to generate a balanced magnetic field in the vicinity of the one or more sense coils. The azimuth length of the conductive path around the probe axis is such that, in operation, the balanced magnetic field induces a balanced voltage in the one or more sense coils that at least partially cancels the residual baseline voltage, such that the sensed voltage is at least primarily due to a response magnetic field generated by the marker in response to a drive magnetic field corresponding to the proximity of the marker.

[0011] According to a second aspect, the present disclosure provides a method of manufacturing a probe for sensing a magnetic marker. The method may suitably include mounting at least two first coils and at least one second coil substantially coaxially on a longitudinal axis of the probe. The at least two first coils are one of a sensing coil or a driving coil. The at least one second coil is the other of a driving coil or a sensing coil. The one or more driving coils are mounted so as to be connectable to a current source for generating a magnetic driving field through the one or more driving coils. The one or more sensing coils are mounted so as to be connectable to a signal processor.

[0012] As described above, the first coil or the second coil may be configured or arranged to minimize a baseline voltage component of a sense voltage induced in one or more sense coils that is directly attributable to the drive magnetic field. Alternatively, the two or more sense coils may be arranged to output separate sense voltages to a signal processor, allowing the signal processor to process the sense voltages and minimize a baseline voltage component of the sense voltage that is directly attributable to the drive magnetic field. Thus, the first and second coils are attached to the probe such that they are configured and arranged to function as a gradiometer for measuring the proximity of a magnetic marker to the probe.

[0013] According to the present disclosure, the method further includes attaching a baseline voltage Tarling device to the probe, the baseline voltage Tarling device comprising a first elongated conductor defining a conductive path extending partially around the probe axis in juxtaposition with the one or more sensing coils. The Tarling device is attached such that the first conductor is connectable to a current source and generates a balanced magnetic field in the vicinity of the one or more sensing coils in use. The baseline Tarling device may be attached in juxtaposition with the one or more sensing coils, i.e. adjacent to or near the one or more sensing coils, such that when the first conductor is connected to a current source, the Tarling device generates a balanced magnetic field in the vicinity of the one or more sensing coils. In some implementations, the baseline Tarling device may be attached adjacent to one of the sensing coils. In some implementations, a drive coil may be interposed between the baseline Tarling device and the or at least one sensing coil. Those skilled in the art will appreciate that the at least two first coils and at least one second coil may typically be arranged to generate a magnetic field having substantial reflection symmetry in use around a transverse plane passing through a midpoint on the longitudinal axis of the probe. The first elongated conductor may be suitably positioned off-center relative to the midpoint such that the magnetic field generated by the baseline tering device is asymmetric about the midpoint. The azimuthal extent of the conductive path about the probe axis is such that the balanced magnetic field induces a balanced voltage in the one or more sense coils that at least partially offsets the baseline voltage. Thus, in use, the sense voltage is at least primarily due to a response magnetic field generated by the marker in response to the drive magnetic field, corresponding to the proximity of the marker.

[0014] The signal processor may be configured to generate an output signal, such as, for example, an audio, tactile, and / or display signal representative of the distance between the marker and the probe.

[0015] Preferably, the method of the present disclosure includes adjusting the azimuthal length of the conductive path about the probe axis to minimize the baseline voltage across one or more sensing coils.

[0016] Thus, according to a third aspect, the present disclosure provides a method of configuring a probe for sensing a magnetic marker during surgery. The probe preferably comprises at least two first coils and at least one second coil, which are arranged substantially coaxially on a 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 either sensing coils or driving coils. The at least one second coil is the other of the driving coil or the sensing coil. The one or more driving coils are adapted to connect to a current source to generate a driving magnetic field. The one or more sensing coils are adapted to connect to a signal processor for receiving and processing the sense voltage induced in the one or more sensing coils and generating an output signal. As described above, the first coil or the second coil may be configured or arranged to minimize a baseline voltage component of the sense voltage induced in the one or more sensing coils that is directly attributable to the driving magnetic field. Alternatively, the two or more sense coils may be arranged to output separate sense voltages to a signal processor, allowing the signal processor to process the sense voltages and minimize baseline voltage components of the sense voltages that may be directly attributable to the drive magnetic field. The probe further comprises a baseline voltage staring device comprising a first elongated conductor defining a conductive path extending at least partially around the probe axis juxtaposed to the one or more sense coils. The first conductor is connectable to a current source to generate a balanced magnetic field in the vicinity of the one or more sense coils.

[0017] A method of configuring a probe includes tuning the balance magnetic field by adjusting the azimuthal length of a conductive path about a probe axis and controlling the balance voltage to minimize or substantially eliminate a baseline voltage of one or more sensing coils. In some embodiments, the azimuthal length of the conductive path can be adjusted by connecting a first conductor to a current source at circumferentially spaced locations thereon, the azimuthal length of the conductive path corresponding to a length of the first conductor intermediate the spaced locations. Preferably, the length of the conductive path about the probe axis may be fixed.

[0018] According to a fourth aspect, the present disclosure includes a detection apparatus for locating a magnetic marker during surgery, the apparatus comprising a probe according to the first aspect of the present disclosure, at least one current source selectively operable to generate a magnetic drive field through one or more drive coils and conductive paths, and at least one signal processor configured to receive at least one sense voltage from the one or more sense coils and generate an output signal representative of a distance between the probe and the magnetic marker. In some embodiments, the apparatus may further comprise at least one magnetic marker.

[0019] It will be understood that features described in connection with one embodiment of the present disclosure may be incorporated in other embodiments of the present disclosure, for example, a method of the present disclosure may incorporate features described with reference to a probe and / or device of the present disclosure, and vice versa.

[0020] Embodiments of the present disclosure are described below, by way of example only, with reference to the accompanying drawings. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram of a typical arrangement of a susceptometry probe and base station for use in detecting magnetic markers in surgery. [Diagram 2]FIG. 1 is a schematic showing the use of a susceptometry probe to locate magnetic markers that are implanted in the breast to mark lesions. [Diagram 3] FIG. 1 is a schematic longitudinal cross-sectional view of a mandrel for a probe according to one embodiment of the present disclosure, in which the mandrel carries a long drive coil disposed between two sense coils and a tarring device adjacent one of the sense coils. [Figure 4] FIG. 1 is a schematic longitudinal cross-sectional view of a mandrel for a probe according to a different embodiment of the present disclosure, in which the mandrel carries two coil sets and a tarring device proximate to the first coil set, each set including a drive coil and a sense coil. [Diagram 5] FIG. 13 is a schematic cross-sectional view of a mandrel for a probe according to another embodiment of the present disclosure, the mandrel comprising two coil sets and a tarring device disposed between the coil sets, each set comprising a drive coil pair and a sense coil interposed therebetween; [Figure 6(a)] FIG. 13 is a perspective view of a tarring device including a printed circuit board for use with a probe according to another embodiment of the present disclosure; [Figure 6(b)] For ease of reference, a top view of the tarring device shown in FIG. 6(a) in an uncoiled configuration. [Figure 7] FIG. 1 is a schematic plan view of a different tering device with a printed circuit board according to yet another embodiment of the present disclosure; [Figure 8(a)] FIG. 13 is a perspective view of a coil arrangement of a probe according to another embodiment of the present disclosure, showing a tarring device extending partially azimuthally about the longitudinal axis of the probe; [Figure 8(b)] 1A-1C are perspective views of coil arrangements of probes according to different respective embodiments of the present disclosure, which diagrammatically show different terling arrangements that extend azimuthally to different degrees about the probe axis; [Figure 8(c)] 1A-1C are perspective views of coil arrangements of probes according to different respective embodiments of the present disclosure, which diagrammatically show different terling arrangements that extend azimuthally to different degrees about the probe axis; [Figure 8(d)]1A-1C are perspective views of coil arrangements of probes according to different respective embodiments of the present disclosure, which diagrammatically show different terling arrangements that extend azimuthally to different degrees about the probe axis; [Figure 9] FIG. 13 is a perspective view of a portion of a probe according to yet another embodiment of the present disclosure, comprising two coil sets on a mandrel and a tarring device interposed therebetween; [Figure 10] FIG. 6 is a schematic diagram of a general layout of a detection apparatus according to yet another embodiment of the present disclosure, comprising a mandrel-containing probe of the type shown in FIG. 5 having two sensing coils with sense voltages output separately from each sensing coil to a signal processor; [Figure 11] 1 is a flow chart illustrating a method for manufacturing a probe according to yet another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] As shown in Figures 1 and 2 of the accompanying drawings, a detection device 1001 for use during surgery to locate implantable magnetic markers 1002 used to mark non-palpable lesions (i.e., those that are too small to be felt or seen during surgery) typically comprises a probe 1004 connected to a base station 1007. The probe 1004 suitably comprises a hand-held wand 1005 and is connected to the base station 1007 via a suitable cable 1006 as shown, or may be connected wirelessly. As shown in Figure 2, the probe 1004 is used during surgery to guide the surgeon to the lesion 1003 and enable precise excision of the lesion while minimizing the amount of healthy tissue removed.

[0023] The marker 1002 preferably comprises one or more pieces of magnetic material. A suitable marker 1002 is disclosed, for example, by WO 2016 / 193753. The probe 1004 typically comprises at least one driving coil for generating a driving magnetic field that generates a response magnetic field from the marker, and at least one sensing coil for detecting the response magnetic field from the marker. The response magnetic field generates a sense voltage in the sensing coil, which sense voltage is detected by a suitable signal processor housed in the base station 1007. A known probe is disclosed by WO 2014 / 140567. The sense voltage corresponds to the distance between the marker 1002 and the probe 1004. The signal processor is therefore configured to calculate the marker distance from the detected sense voltage, as disclosed, for example, by WO 2011 / 067576. The signal processor can generate an output signal representative of the marker distance. The output signal may be a display signal, for example for displaying the marker distance on a screen 1008 on the base station 1007, or an audio or tactile signal, for example as disclosed by WO 2022 / 008922.

[0024] The present disclosure provides improvements to and relating to probes of the type described above.

[0025] Thus, according to a first aspect, the present disclosure provides a probe for locating a magnetic marker for use in a surgical procedure, the probe comprising: at least two first coils and at least one second coil arranged substantially coaxially on a 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 either one of a sense coil or a drive coil, and the at least one second coil is the other of a drive coil or a sense coil; the one or more drive coils adapted to connect to a current source to generate a drive magnetic field, and the one or more sense coils adapted to connect to a signal processor for processing one or more sense voltages induced in the respective one or more sense coils to generate an output signal representative of the distance between the marker and the probe; the at least two first coils and at least one second coil configured or arranged to minimize a baseline voltage component of the sense voltage induced in the one or more sense coils that is directly attributable to the drive magnetic field, or to output separate sense voltages from the two or more sense coils to the signal processor and enable the signal processor to process the sense voltages to minimize a baseline voltage component of the sense voltage that is directly attributable to the drive magnetic field; and a baseline voltage tering apparatus comprising a first elongated conductor defining a conductive path extending partially around the probe axis and connectable to a current source to generate a balanced magnetic field in the vicinity of the one or more sensing coils; Equipped with The conductive path is constructed and arranged such that, in use, the balanced magnetic field induces a balanced voltage in one or more sensing coils that at least partially offsets the baseline voltage; whereby the sensed voltage is attributable at least primarily to a response magnetic field generated by the marker in response to the drive magnetic field, which corresponds to the proximity of the marker.

[0026] Preferably, the at least two first coils and the at least one second coil may be centered on a longitudinal axis of the probe ("probe axis"). The coils may be spaced apart from one another along the probe axis. The first elongated conductor may extend partially around the probe axis juxtaposed with the one or more sensing coils. Typically, the first elongated conductor may be positioned off-center with respect to the at least two first coils and the at least one second coil.

[0027] The at least two first coils and the at least one second coil may be suitably housed within a hollow probe housing. The probe housing may have an elongated shape. In some embodiments, the probe housing may be substantially cylindrical in shape. In some embodiments, the probe housing may comprise a plurality of segments of the same or different outer diameters. The probe housing may comprise a stepped or frustoconical transition between adjacent segments of different outer diameters.

[0028] The outer diameter of the probe housing may depend on the intended use of the probe. In general, it is desirable for the probe housing to have a narrow diameter to reduce the size of the surgical incision required when using the probe. In some embodiments, the probe housing may have a maximum outer diameter of about 3 mm to about 20 mm; typically, about 4 mm to about 15 mm or about 6 mm to about 10 mm, depending on the intended use of the probe. Probes for use in laparoscopy or robotic surgery may have a diameter of, for example, about 4 mm to about 6 mm.

[0029] Suitably, the probe housing may have a wall thickness of about 0.2 mm to about 3 mm; typically, about 0.5 mm to about 1 mm.

[0030] To reduce thermal effects, an air gap may be required between the at least two first coils and the at least one second coil and the inner surface of the probe housing. The air gap may suitably have a radial dimension of about 0.2 mm to about 3 mm; typically about 0.5 mm to about 1 mm.

[0031] Suitably, at least some, and preferably all, of the coils, and the baseline voltage targeting device may be located within a head portion of the probe housing proximate the distal sensing end or tip of the probe. Preferably, at least one sensing coil is located as close as possible to the distal end to optimize the sensitivity of the probe, 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.

[0032] In some embodiments, the coil may be mounted on an elongated former or other support within the housing. Suitably, the former or other support may be formed of an insulating material or may include an insulating layer between the former or support and the coil.

[0033] Alternatively, in some embodiments, at least one of the coils may be disposed outside the probe housing, for example, at least one of the coils may be wrapped around and supported by an outer surface of the probe housing.

[0034] The one or more drive coils are suitably connected to a selectively operable alternating current source (not shown) that provides a drive current for operating the probe. In some embodiments, the probe may include multiple drive coils. In such cases, the drive coils may be connected in series or anti-series as described herein and may be connected to the same current source. The 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 passing through the one or more drive coils, and the number of turns in the or each drive coil.

[0035] In use, the drive magnetic field induces magnetic markers in the vicinity of the probe to generate a response magnetic field.

[0036] In some embodiments, the magnetic marker may be a ferromagnetic marker. Suitable exemplary markers are disclosed by International Publication Nos. WO 2014013235, WO 2016 / 193753, WO 2019180580, GB 2115827.4 and GB 2115826.6, the disclosures of each of which are incorporated herein by reference.

[0037] The response field from the marker depends on the strength of the drive field experienced by the marker, which in turn depends on the proximity of the marker to one or more drive coils. It will be appreciated that if there are two or more drive coils spaced axially along the probe, the drive field experienced by the marker may arise primarily from the drive coil closer to the marker; typically the one located closer to the distal end of the probe. The response field also depends on the magnetic permeability of the marker.

[0038] The response magnetic field from the marker is detected by one or more sensing coils as a sense voltage. As with the drive coil, if the probe has multiple sensing coils, the response magnetic field may be detected more strongly by the sensing coils located closer to the marker in use; typically, those at or near the distal tip of the probe. If more than one sensing coil is provided, one or more sensing coils may be provided to sense a voltage across the sensing coil resulting directly from the drive magnetic field so that it can be subtracted from the sense voltage, as described below. However, if the tip of the probe is moved beyond the marker in use, the marker will respond more strongly to the drive magnetic field generated by the drive coil located further from the distal end, and the response magnetic field may be detected more strongly by the sensing coil located further from the distal end.

[0039] The sensed voltage across one or more sensing coils resulting from the response magnetic field generated by the marker is correlated to the distance between the probe and the marker, calculated the proximity of the marker to the probe, and suitably output to a signal processor (not shown) to output a suitable dynamic audible, visible, or other perceptible signal representative of the proximity; for example, a visual indication of the distance in numbers on a display.

[0040] However, a voltage (herein referred to as "baseline voltage") is also induced in the one or more sensing coils by the driving magnetic field generated by the one or more driving coils. Both the magnetic marker and the one or more driving coils can increase or decrease the magnetic flux passing through the sensing coil. The closer the driving coil is placed to the sensing coil and the stronger the driving magnetic field, the larger the baseline voltage will be. Those skilled in the art will understand that the baseline voltage is typically much larger than the component of the sense voltage resulting from the response magnetic field. Therefore, when the probe is used to detect a marker, the baseline voltage induced in the one or more sensing coils by the driving magnetic field should be minimized so that the sense voltage across the one or more sensing coils results mainly from the response magnetic field of the marker, thereby allowing the proximity of the marker to be accurately determined. A baseline voltage that is too large is undesirable because it can obscure the sense voltage due to the marker.

[0041] The baseline voltage can be reduced and potentially eliminated in several different ways. In some embodiments, the first coil or the second coil can be configured or arranged to minimize the baseline voltage component of the sense voltage induced in one or more sense coils that is directly due to the drive magnetic field. For example, the first coil may comprise two or more drive coils that are connected in anti-series or wound in opposite directions to generate a drive magnetic field of minimum, ideally zero strength, in the position of at least one sense coil as the second coil, so that the sense voltage across the sense coil arises primarily, ideally entirely, from the response magnetic field of the marker. This may require, for example, placing the sense coil at the midpoint between two substantially identical drive coils.

[0042] Alternatively, the first coil may comprise at least two sensing coils. One sensing coil may be located close to the distal end of the probe to detect the markers, and another sensing coil may be located away from the distal tip. At least one driving coil may be provided as a second coil for generating a driving magnetic field during use. Typically, one or more driving coils may be interposed between the sensing coils. Alternatively, one or more driving coils may be located close to each sensing coil to form two coil sets; each set includes a sensing coil and at least one driving coil. For example, as described herein, a single driving coil may be positioned adjacent to each sensing coil, or each sensing coil may be interposed between two adjacent driving coils. The two sensing coils may be symmetrically positioned within the driving magnetic field such that each sensing coil is subjected to substantially the same driving magnetic field. The two sensing coils may be sufficiently separated such that a marker located in the driving magnetic field generates a significant sensing voltage only in one of them; typically the one close to the probe tip. The sense voltage generated across the other sense coil is subtracted from the sense voltage generated across the other sense coil, resulting in a net sense voltage generated across the sense coil that results primarily from the response magnetic field. For example, the two sense coils may be connected in anti-series or wound in opposite directions such that the sense voltages induced across them have opposite polarities to each other.

[0043] In an alternative configuration, the sensed voltages from two or more sensing coils may be input separately to a signal processor which may be configured to process the sensed voltages to minimize the baseline voltage resulting from the drive magnetic field, in use. Thus, in some embodiments, the baseline voltage across one or more sensing coils may be physically reduced by suitable configuration or placement of the coils, while in other embodiments the baseline voltage may be reduced by processing signals representing the voltages sensed by the sensing coils with a signal processor.

[0044] In practice, due to manufacturing tolerances of the probe and coils, it is difficult to eliminate the baseline voltage using only the placement of at least one drive coil or sense coil. This may be particularly true for relatively narrow probes incorporating small diameter coils, for example, probes having a diameter of less than about 15 mm, or more particularly less than about 10 mm. In accordance with the present disclosure, the baseline voltage can be further reduced using a baseline voltage staring device comprising a first conductor that defines an arcuate conductive path extending azimuthally around the probe axis, juxtaposed to, i.e., near, adjacent to, or more generally in the vicinity of, the one or more sense coils. The first conductor is connected to a selectively operable current source and, in use, generates a magnetic field, referred to herein as a balance magnetic field. The conductive path extends partially (i.e., not completely) around the probe axis and is configured as disclosed herein to offset residual baseline voltages across the one or more sense coils that arise directly from the one or more drive coils.

[0045] In some embodiments, the probe may include at least two sense coils axially spaced apart along the probe axis and a drive coil interposed between the at least two sense coils. In this case, at least two of the sense coils may be connected in anti-series or wound in opposite directions, as described above. A voltage may be induced in each sense coil by the drive magnetic field. At least one of the sense coils may be wound in the same direction as the at least one drive coil, and at least one of the sense coils may be wound in the opposite direction to the at least one drive coil. Thus, in use, opposite voltages are induced in the sense coils wound in opposite directions. In this embodiment, the baseline voltage is the sum of the voltages induced in the sense coils as a result of the drive magnetic field.

[0046] In some embodiments, the probe may comprise two sensing coils and a single drive coil disposed between the two sensing coils. One of the sensing coils may be disposed proximal to the distal end of the probe; the drive coil may be disposed proximal to one sensing coil; the other sensing coil may be disposed proximal to the drive coil. Suitably, the distance between the two sensing coils may be such that a marker disposed at or distal to the distal end of the probe does not cause a significant sensing voltage in the other proximal sensing coil. The drive coil may suitably have a length of about 2 mm to about 10 mm. The drive coil may comprise about 10 to about 150 turns; typically about 10 to about 60 turns of wire. Each sensing coil may have a length of about 0.5 mm to about 6 mm. Each sensing coil may comprise about 50 to about 1000 turns; typically about 100 to about 500 turns of wire. The two sensing coils may comprise the same number of turns and be approximately the same length. The spacing between each coil may be about 0.5 to about 1.0 mm.

[0047] For two sense coils wound in anti-series but otherwise identical, and a drive coil centered exactly at the midpoint between the two sense coils, when a drive current is passed through the drive coils, in the absence of a magnetic marker, approximately equal and opposite voltages will be induced in the two sense coils by the drive magnetic field, resulting in a net sense voltage of zero. In practice, the two sense coils may not be identical, or the drive coil may not be centered exactly at the midpoint between the two sense coils due to manufacturing tolerances. Thus, the voltages induced in the two sense coils may be opposite but unequal, and there may be a net resulting baseline voltage.

[0048] Thus, the baseline voltage tering device may be used in accordance with the present disclosure to reduce or preferably eliminate the net resulting baseline voltage. A drive current may be passed through the first conductor along the conductive path to generate a balanced voltage that opposes and at least partially cancels the baseline voltage. The conductive path may be appropriately positioned off-center from the midpoint between the two sense coils, close to or adjacent to one of the sense coils. If the conductive path is positioned off-center from the midpoint between the two sense coils, the passage of current in the conductive path may induce a voltage in both sense coils, but the magnitude of the voltage induced in one of the sense coils may be greater than the voltage induced in the other sense coil. The conductive path may be positioned close to or adjacent to one of the sense coils, and may be slightly axially spaced from one of the sense coils. Thus, the conductive path induces an additional balancing voltage in one of the sensing coils, reducing any magnitude difference in the sense voltages induced in the two sensing coils by the drive magnetic field, thereby at least reducing the net baseline voltage, the sense voltage being at least primarily attributable to the response magnetic field generated by the marker in response to the drive magnetic field.

[0049] As mentioned above, in some embodiments, the probe may comprise at least two drive coils spaced axially along the length of the probe and a sense coil disposed between the at least two drive coils. Preferably, one of the drive coils is disposed as close as possible to the distal end of the probe. In this case, at least two of the drive coils may be connected in anti-series or wound in opposite directions. In use, two similar drive coils connected in anti-series or wound in opposite directions will generate opposing magnetic fields, resulting in a null point at or near the midpoint between the two drive coils, resulting in symmetrically opposing magnetic fields on either side of the midpoint. A sense coil may be disposed between the two drive coils. The sense coil may have a length of about 0.5 mm to about 6 mm. The sense coil may include about 50 to about 1000 turns; typically about 100 to about 500 turns of wire. Each drive coil may have a length of about 0.75 to about 6 mm. Each drive coil may include about 10 to about 150 turns of wire; typically, about 10 to 60 turns. The two drive coils may have the same number of turns and be about the same length. The spacing between each coil may be about 0.5 to about 1.0 mm.

[0050] In use, each drive coil induces a voltage in the sense coil. Drive coils wound in anti-series or oppositely wound induce opposing voltages in the sense coil. The net voltage induced in the sense coil is the baseline voltage. If the sense coil is positioned exactly at the midpoint between the drive coils, and if the drive coils are identical but connected in anti-series, the balanced voltage induced in the sense coil will be zero. In practice, for example due to manufacturing tolerances, the drive coils may not be identical and the sense coil may not be centered exactly at the midpoint between the drive coils. Thus, there may be a small resulting baseline voltage.

[0051] The baseline voltage tering device may be suitably constructed and arranged to at least reduce and preferably eliminate the baseline voltage. In use, a drive current is passed through the conductive path, which generates a balanced magnetic field. The balanced magnetic field from the conductive path induces a balanced voltage in the sense coil. The conductive path is configured such that the balanced voltage substantially offsets the baseline voltage. In particular, the azimuthal length of the conductive path about the probe axis may be such that the balanced voltage substantially offsets the baseline voltage. The conductive path may be suitably located between the two drive coils off-center from the midpoint of the two drive coils. The conductive path may be located close to or adjacent to one of the coils.

[0052] In some embodiments, the probe may include a first coil set comprising at least one drive coil and at least one sense coil, and a second coil set comprising at least one drive coil and at least one sense coil. The first coil set and the second coil set may be axially spaced apart along the length of the probe. Preferably, one of the coil sets is located proximate the distal end of the probe.

[0053] In some embodiments, the first coil set may comprise a drive coil and a sense coil, and the second coil set may comprise a drive coil and a sense coil. The first coil set and the second coil set may be substantially identical. Preferably, the two sense coils may be arranged in a similar relationship to their respective drive coils. Each sense coil may be arranged proximal or distal to its associated drive coil. In some embodiments, both sense coils may be arranged distal to their respective drive coils. In other embodiments, both sense coils may be arranged proximal to their respective drive coils. In still other embodiments, one of the sense coils may be arranged distal to its drive coil and the other sense coil may be arranged proximal to its respective drive coil. Preferably, one sense coil is arranged at or near the distal end of the probe. Suitable coil arrangements are disclosed by 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.

[0054] Preferably, each coil set 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.

[0055] In some implementations, each drive coil may have an outer diameter of about 0.5 mm to 10 mm; typically about 1.5 mm to about 6 mm. The radius of the drive coil may be selected to suit the diameter of the probe, for example, as described above.

[0056] In some implementations, each drive coil may have an axial length of about 0.2 mm to 10 mm; typically about 0.5 mm to about 2.5 mm.

[0057] In some implementations, each drive coil can have from about 10 to about 150 turns of wire, typically from about 10 to about 60 turns of wire.

[0058] The sensing coil of each coil set may have an axial length of about 0.5 mm to 6 mm; typically about 0.75 mm to about 2 mm.

[0059] The sensing coil of each coil set may have an average radius of about 0.5 mm to 10 mm; typically about 1.5 mm to about 6.5 mm. Conveniently, the first sensing coil may have an average radius similar to that of the drive coil of its respective coil set.

[0060] Typically, the sensing coil of each coil set can include about 50 to about 1000 turns of wire. In some embodiments, the sensing coil can have about 100 to about 500 turns of wire.

[0061] Preferably, the sensing coils of each coil set may be formed from wire having a diameter of about 0.01 to 0.3 mm; typically about 0.025 mm to 0.1 mm.

[0062] In some implementations, the sensing coil of each coil set may include about 3 to 20 superimposed layers; typically about 8 to 10 turns; each layer having about 5 to 50 turns; typically about 15 to about 20 turns.

[0063] As disclosed by UK Patent Application No. 2204999.3 and International Patent Application No. PCT / GB2023 / 050909, the distance between the centre of each sense coil and the centre of each drive coil within the same coil set may advantageously be from about 1 mm to about 3 mm.

[0064] The total axial distance spanned by the first and second coil sets can be between about 10 mm and 100 mm; typically between about 19 mm and about 30 mm. In some implementations, the axial spacing between the sensing coils of the first and second coil sets can be between about 3 mm and about 100 mm; typically between about 12 mm and about 15 mm.

[0065] Preferably, the distance between the two sensing coils is such that, in use, a marker located distal to the distal sensing coil does not generate substantially a sensing voltage in the distal sensing coil, so that the sensing voltage in the proximal sensing coil arises almost entirely from the driving magnetic field and is substantially the same as the component of the sensing voltage induced in the distal sensing coil as a result of the driving magnetic field. Thus, as described above, the sensing voltage in one of the sensing coils can be used to separate the sensing voltage in the other sensing coil resulting from the sensing response of the marker. Thus, the sensing coils of the first coil set and the sensing coils of the second coil set may be connected in anti-series or have opposite winding directions. Meanwhile, the driving coils of the first coil set and the driving coils of the second coil set may be connected in series as appropriate.

[0066] Thus, the voltage induced in one of the sense coils by the respective drive coils may be approximately equal and opposite to the voltage induced in the other sense coil by the respective drive coil. If the first coil set is not identical to the second coil set, or if there is insufficient axial separation between the first and second coil sets, the voltage induced in the second sense coil may not fully offset the voltage induced in the first sense coil, resulting in a residual baseline voltage. The baseline voltage tarring device may be configured to offset this residual baseline voltage. Thus, the conductive path defined by the baseline voltage tarring device may be positioned between the first and second coil sets. The conductive path may be located in close proximity to or adjacent to one of the first or second coil sets. A drive current may pass through the conductive path, thereby generating a magnetic field. The magnetic field from the conductive path may generate a balanced voltage in one of the sense coils (or unequal voltages in both of the sense coils). The azimuthal length of the conductive paths is such that a balanced voltage from the conductive paths induced in the sense coil substantially cancels any residual baseline voltage from the drive coil.

[0067] In some embodiments, the first coil set may comprise a first sense coil disposed between a first drive coil pair, and the second coil set may comprise a second sense coil disposed between a second drive coil pair. Preferably, the first coil set may be substantially identical to the second coil set.

[0068] The first coil set may comprise a first pair of substantially identical drive coils. The first pair of drive coils may be connected in series.

[0069] The second coil set may be substantially identical to the first coil set. The second coil set may comprise a substantially identical second drive coil pair. The second drive coil pair may be substantially identical to the first drive coil pair. The second drive coil pair may be connected in series. The second drive coil pair may be connected in series with the first drive coil pair. Preferably, the first drive coil pair and the second drive coil pair may be connected to the same current source.

[0070] Preferably, one of the first and second sensing coils can be connected with the same polarity as the respective pair of driving coils. The other of the second and first sensing coils can be connected with the opposite polarity to the respective pair of driving coils. Thus, in some embodiments, the two driving coil pairs can be connected in series with each other with the same polarity as one of the sensing coils, while the other sensing coil is connected with the opposite polarity to the driving coil and one sensing coil. In some embodiments, the two sensing coils are connected in anti-series or in series but with the windings in the opposite direction. In an alternative configuration, as described above, the sensing coils can be adapted to be separately connected to a signal processor, and the sense voltage induced in one of the sensing coils by the driving magnetic field can be used in processing to remove the component of the sense voltage in the other sensing coil from the driving magnetic field, leaving only the sense voltage and any residual baseline voltage resulting from the marker response magnetic field.

[0071] Advantageously, the first coil set may be positioned proximate the distal sensing end of the probe. When a drive current is passed through the first drive coil set, a drive magnetic field is generated. The drive magnetic field may induce a response magnetic field from a magnetic marker proximate the distal end of the probe, which response magnetic field may be detected as an induced voltage in the first sensing coil. Also, a voltage is induced in the first sensing coil from at least the first drive coil pair. Those skilled in the art will appreciate that the sense voltage resulting from the drive magnetic field is typically much larger than the sense voltage from the response magnetic field.

[0072] The drive magnetic field passing through the second drive coil pair generates a drive magnetic field and induces a voltage in the second sense coil. If the second sense coil is wound in anti-series with the first sense coil and the second drive coil pair is substantially the same as the first drive coil pair, the voltage induced in the second sense coil from the second drive coil pair is ideally equal and opposite to the voltage induced in the first sense coil from the first drive coil pair. Thus, the net voltage induced in the sense coil from the drive coil, which is the baseline voltage, may be zero or close to zero, allowing any sense response from the marker to be detected.

[0073] In practice, the first drive coil pair is unlikely to be identical to the second drive coil pair, the first sense coil is unlikely to be identical to the second sense coil, and the first and second sense coils are unlikely to be located exactly at the midpoint between the drive coils, for example due to manufacturing tolerances. As a result, the baseline voltage is unlikely to be exactly zero. This is particularly noticeable in probes with small diameters (e.g., less than about 15 mm, especially less than about 10 mm), where the smaller dimensions make the magnetic field in and around the coils stronger than in wider probes. Thus, small changes in positioning or drive current generally result in large changes in the drive magnetic field and therefore in the sense voltage. This can obscure or interfere with the measurement of the sense voltage induced from the marker.

[0074] The conductive path of the baseline voltage Tarling device may be configured to further reduce or substantially eliminate the baseline voltage according to the present disclosure. The conductive path provided by the first conductor may be preferably disposed between the first coil set and the second coil set. The conductive path may be provided at a fixed axial position between the first coil set and the second coil set. The conductive path may be disposed off-center from a midpoint between the first coil set and the second coil set. Thus, the conductive path may be disposed closer to one of the first and second sense coils. Conveniently, the conductive path may be connected to the same current source as the first or second drive coil set. When a current passes through the conductive path, a balanced magnetic field is generated, which induces an additional balanced voltage in the first or second sense coil. The induced voltage may be greater in the first or second sense coil. The conductive path may be configured such that the balanced voltage induced by the current passing through the conductive path opposes the baseline voltage.

[0075] As disclosed herein, the conductive path is formed by a first conductor. Generally, the first conductor can be disposed between two drive coils or two sense coils to generate a balanced voltage in one or more sense coils. The conductive path defined by the first conductor should be disposed off-center between the two drive coils or two sense coils in the direction of the probe axis. The first conductor can be connected to a suitable current source in any convenient manner known to those skilled in the art. Conveniently, the first conductor can be connected to the same current source as at least one drive coil. Typically, the first conductor is connected to a current source at two spaced apart locations on the first conductor, thereby defining a conductive path between the two locations. The balanced voltage provided by the baseline voltage tering device is a function of the azimuthal length of the conductive path between the two locations.

[0076] In some implementations, the baseline voltage tering device may conveniently comprise a second elongated conductor extending around the probe and at least one conductive bridge extending axially to interconnect the first and second conductors. The conductive bridge thus determines the azimuthal length of the conductive path on the first conductor intermediate the conductive bridge. The second conductor may also define a conductive path around the probe axis that is juxtaposed with the conductive path defined by the first conductor. In some implementations, the conductive path defined by the second conductor may conveniently be aligned with the midpoint between the two sense coils or the two drive coils so as not to contribute to the balanced voltage. However, in some embodiments, the conductive path of the second conductor may be positioned off-center so as to contribute to the balanced magnetic field.

[0077] One or both of the first and second conductors may extend completely or partially around the probe. Thus, 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 that extends partially but not completely around the probe axis. In some implementations, one or both of the first and second conductors may extend azimuthally 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.

[0078] Suitably, one or both of the first and second conductors may comprise a conductive wire or strip; for example, a copper wire or strip. Thus, in some implementations, the first or second conductor may comprise a loop of copper wire. 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 is commercially available under the trade name Kapton® from EI du Pont de Nemours and Company, Wilmington, Del., USA. A suitable conductive material is copper.

[0079] Preferably, 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 to each other to complete the circuit. In some implementations, the 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. Preferably, the at least one conductive bridge may include a conductive wire or strip. The materials mentioned above for the first and second conductors may also be suitable for the conductive bridge.

[0080] In some embodiments, at least one conductive bridge may be movable between a plurality of azimuthal positions about the probe axis. A single conductive bridge may extend between the first conductor and the second conductor and may be movable by sliding between the plurality of azimuthal positions. The conductive bridge may be movable in discrete steps between the plurality of azimuthal positions.

[0081] In some embodiments, one or both of the first and second conductors may comprise a plurality of conductive lands at a series of azimuthally spaced locations around the probe axis. The lands on each conductor may extend toward the other conductor in a direction substantially parallel to the probe axis. Each land on one conductor preferably terminates short of the other conductor, thereby defining a short gap therebetween. The conductive bridge may comprise a conductive strip adapted to form a connection across the gap between the land on one conductor and the other conductor at a selected azimuth position around the probe axis. By moving the conductive bridge between a plurality of azimuth positions, the azimuth length of the conductive path can be adjusted to control the magnitude of the equilibrium magnetic field, thereby minimizing the baseline voltage across one or more sensing coils. Alternatively, the conductive bridge may be provided between the first and second conductors at a fixed azimuth position. Advantageously, the fixed azimuth position of the conductive bridge may be selected such that the azimuth length of the conductive path defined by the first conductor is optimized to at least partially offset the baseline voltage.

[0082] In some embodiments, the baseline voltage tarring device may include a flexible circuit board that is at least partially wrapped around the probe shaft. Suitably, the circuit board may be a printed circuit board. The circuit board may include two conductive traces that define the first and second conductors, and a plurality of conductive lands that extend from one or both of the first and second conductors at a series of azimuthally spaced locations, as described above. One or more conductive bridges may be provided to extend between the land on one conductor and the other conductor, thereby defining the azimuth length of the conductive path. The one or more conductive bridges may be formed, for example, from a suitable conductive tape that is applied across the gap between the land on one conductor and the other conductor, or the conductive bridge may be formed by soldering between the land on one conductor and the other conductor. Other methods of interconnecting the land on one conductor and the other conductor will be apparent to those skilled in the art.

[0083] According to a second aspect, the present disclosure provides a method of manufacturing a probe for sensing a magnetic marker during a surgical procedure, the method comprising: mounting at least two first coils and at least one second coil substantially coaxially on a longitudinal axis of the probe, the at least two first coils being one of a sense coil or a drive coil and the at least one second coil being the other of a drive coil or a sense coil, the one or more drive coils connectable to a current source for generating a drive magnetic field through the one or more drive coils, and the one or more sense coils connectable to a signal processor for processing one or more sense voltages induced in the respective one or more sense coils to generate an output signal; the one or second coils are configured or arranged to minimize a baseline voltage component of a sense voltage induced in the one or more sense coils that is directly attributable to the drive magnetic field, or to output separate sense voltages from the two or more sense coils to a signal processor and enable the signal processor to process the sense voltages to minimize a baseline voltage component of the sense voltage that is directly attributable to the drive magnetic field; whereby the first and second coils are configured and arranged as a gradiometer for measuring the proximity of a magnetic marker to the probe, the output signal being indicative of the distance between the marker and the probe; and Attaching to the probe a baseline voltage targeting device comprising a first elongated conductor defining a conductive path extending partially around the probe axis and connectable to a current source to generate a balanced magnetic field in the vicinity of one or more sensing coils, wherein, in use, the balanced magnetic field induces a balanced voltage in the one or more sensing coils that at least partially offsets the baseline voltage; whereby the sensed voltage is at least primarily attributable to a response magnetic field generated by the marker in response to the drive magnetic field, which corresponds to the proximity of the marker.

[0084] The probe may be a probe including any of the features disclosed above. Thus, the conductive path may extend partially around the probe axis juxtaposed to the one or more sensing coils. The conductive path may typically be attached to the probe off-center or asymmetrically with respect to the arrangement of the at least two first coils and the at least one second coil.

[0085] Preferably, the method may further include adjusting the azimuthal length of the conductive path around the probe to minimize the baseline voltage across the one or more sensing coils.

[0086] Adjusting the azimuthal length of the conductive path may include moving a conductive bridge of the type described above in an azimuthal direction around the probe such that the baseline voltage is minimized. The plurality of conductive lands or tabs may extend partway between the first and second conductors at different azimuthal positions. Adjusting the length of the conductive path may include completing a connection between at least two corresponding lands or tabs, thereby forming a conductive bridge. The connection may be suitably completed by soldering a connector between the conductors.

[0087] According to a third aspect, the present disclosure provides a method of configuring a probe for sensing a magnetic marker for use in a surgical procedure, the probe including: at least two first coils and at least one second coil disposed substantially coaxially on a longitudinal axis of the probe as a gradiometer for measuring proximity of a magnetic marker to the probe; the at least two first coils are one of a sense coil or a drive coil and the at least one second coil is the other of a drive coil or a sense coil; the one or more drive coils are adapted to connect to a current source to generate a drive magnetic field and the one or more sense coils are adapted to connect to a signal processor for processing sense voltages induced in the one or more sense coils to generate an output signal; the first or second coils are configured or arranged to minimize a baseline voltage component of the sense voltages induced in the one or more sense coils that is directly attributable to the drive magnetic field or to output separate sense voltages from the two or more sense coils to the signal processor and enable the signal processor to process the sense voltages to minimize a baseline voltage component of the sense voltages that is directly attributable to the drive magnetic field; a baseline voltage tering device comprising a first elongated conductor defining a conductive path extending partially around the probe axis juxtaposed to the one or more sensing coils and connectable to a current source to generate a balanced magnetic field in the vicinity of the one or more sensing coils; The method includes adjusting the azimuthal length of a conductive path about a probe axis to control a balance magnetic field and induce a balance voltage across one or more sensing coils that at least partially offsets the baseline voltage.

[0088] The probe may include any of the features disclosed above.

[0089] It will be appreciated that the method includes the step of effectively adjusting the balance magnetic field by varying the azimuthal length of the conductive path about the probe axis such that the balance voltage minimizes the baseline voltage.

[0090] Varying the azimuthal length of the conductive path about the probe axis may include moving a conductive bridge in an azimuthal direction about the probe axis such that the baseline voltage is minimized. Varying the azimuthal length of the conductive path about the probe axis may include completing a connection between the at least two conductors, thereby forming a conductive bridge. The plurality of conductive strips may extend partway between the at least two conductors at different azimuthal positions, and the connection may be completed by soldering the conductive connection between selected copper strips and the at least two conductors.

[0091] The methods of configuring the probes of the present disclosure can be performed as part of the manufacture of the probe, in some embodiments, the position of the conductive bridges can be adjustable so that the probe can be recalibrated periodically or as needed.

[0092] According to a fourth aspect, the present disclosure provides a detection apparatus for locating a magnetic marker during surgery, the apparatus comprising a probe according to the first aspect of the present disclosure as described above, a current source selectively operable to generate a drive magnetic field through one or more drive coils and a first conductor, and at least one signal processor configured to receive one or more sense voltages from the one or more sense coils and generate an output signal representative of a distance between the probe and the magnetic marker.

[0093] In some embodiments, the device may further comprise at least one embedded magnetic marker. Suitably, the magnetic marker may comprise a ferromagnetic marker; for example, a Magseed® marker available from Endomagnetics Ltd, Cambridge, UK.

[0094] Figure 3 is a schematic longitudinal cross-sectional view of a portion of a probe according to one embodiment of the present disclosure. In particular, Figure 3 shows a generally cylindrical mandrel 1 that is shaped and dimensioned to close tolerances within a correspondingly shaped recess in a probe housing (not shown) with a small 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 suitably adapted to be secured to the distal end of a hand-held wand such that the mandrel 1 is attached to the distal end of the probe, for example as shown in Figure 1.

[0095] The mandrel 1 defines a longitudinal axis 2 aligned with the longitudinal axis of the probe and carries two sense coils 3a, 3b spaced axially along the probe axis 2. One of the sense coils 3a is positioned in juxtaposition at the distal end 4 of the mandrel 1, which when mated will be at the distal sense end (also referred to herein as the tip) of the probe. The other sense coil 3b is positioned in juxtaposition at the proximal end 6 of the mandrel 1. A long drive coil 5 is interposed between the sense coils 3a, 3b approximately midway between them. The sense coils 3a, 3b are connected in anti-series such that the sense voltages induced by the magnetic field are of opposite polarity. Alternatively, the sense coils 3a, 3b can be wound in opposite directions and connected in series to a similar effect. The long drive coil 5 is connected to a suitable current source (not shown), which may be housed in a base station of the type shown in FIG. 1, to which the probe may be connected via a suitable cable. When a current flows through the drive coil 5, a drive magnetic field is generated.

[0096] The sensing coils 3a, 3b are arranged to connect to a signal processor (not shown), which may be housed, for example, in a base station. When the probe is in use, the driving magnetic field from the long driving coil 5 generates a response magnetic field from a magnetic marker (not shown) in the vicinity of the probe; typically near the distal end of the probe. The response magnetic field is detected by the signal processor as a sensed voltage in the sensing coil 3a closest to the probe tip. Voltage is also induced from the driving coil 5 in both the distal and proximal sensing coils 3a, 3b. When the sensing coils 3a, 3b are connected in anti-series substantially equidistant from the driving coil 5, the driving coil 5 induces approximately equal and opposite voltages in the sensing coils 3a, 3b. Thus, the net baseline voltage in the sensing coils 3a, 3b resulting from the driving coil 5 is close to zero. However, due to manufacturing tolerances (e.g., the sense coils 3a, 3b are unlikely to be identical and the drive coil is unlikely to be located in the middle of the two sense coils 3a, 3b), the net baseline voltage induced in the sense coils 3a, 3b from the drive coil 5 will not be exactly zero.

[0097] A baseline voltage tering device including a conductor 7 formed from an arc-shaped elongated strip of conductive material is attached to the mandrel 1 proximal to 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 between connections that extends partially circumferentially around the mandrel 1. As shown in FIG. 3, the conductor 7 forms a conductive path that extends azimuthally around the probe axis 2, but does not form a complete loop. When a current passes through the conductive path, the conductive path generates a balanced magnetic field that induces a balanced voltage in the sensing coil 3a. The azimuth length of the conductive path is such that the balanced voltage induced in the sensing coil 3a reduces the baseline voltage from the drive coil 5. Advantageously, this means that the sensed voltage detected at the sensing coil 3a is primarily due to the marker. The sensed voltage can therefore be processed by a signal processor to calculate the proximity of the marker to the probe and generate an output signal representative of the proximity. The output signal may 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.

[0098] Figure 4 is a schematic longitudinal section through a mandrel 101 forming part of a probe according to another embodiment of the present disclosure. The mandrel 101 is generally constructed and arranged similarly to the mandrel 1 of Figure 3 and is adapted to be fixedly attached to the distal end of a hand-held wand such that the mandrel 1 is attached to the distal end of the probe. The wand is suitably configured to connect to a base station as shown in Figure 1. The mandrel 101 supports a first coil pair 110a adjacent the distal end 104 of the mandrel 101 and a second coil pair 110b adjacent the proximal end 106 of the mandrel 101, the first coil pair 110a and the second coil pair 110b being axially spaced apart along the axis 102 of the probe. The first coil pair 110a comprises a first drive coil 105a and a first sense coil 103a; the second coil pair 104b comprises a second drive coil 105b and a second sense coil 103b. The second drive coil 105b and the second sense coil 103b are substantially the same as the first drive coil 105a and the first sense coil 103a, respectively. The first drive coil 105a and the second drive coil 105b are connected to a current source (not shown) that may be housed in a base station and are connected in series. The first sense coil 103a and the second sense coil 103b are connected in anti-series and arranged to connect to a suitable signal processor as described above. In an alternative configuration, the first and second sense coils 103a, 103b may be connected in series but wound in opposite directions, as described above in connection with FIG. 3.

[0099] In use, applying current to the first drive coil 105a and the second drive coil 105b generates a drive magnetic field. As a result, a voltage is induced in the first sense coil 103a primarily from the first drive coil 105a, and a voltage is induced in the second sense coil 103b primarily from the second drive coil 105b. Because the sense coils 103a, 103b are connected in anti-series, the voltages induced in the sense coils 103a, 103b from their associated drive coils 105a, 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 sense coil 103a is unlikely to be identical to the second sense coil 103b, and the spacing between the coils 103a, 105a of the first coil pair 110a may not be equal to the spacing between the coils 103b, 105b of the second coil pair 110b. As a result, the net baseline voltage summed from the two sense coils 103a, 103b is likely to be non-zero.

[0100] A baseline voltage staring device comprising a conductor 107 formed from an arc-shaped elongated strip of conductive material defining a conductive path extending circumferentially between spaced terminals (not shown) on the conductor 107 proximate the first drive coil 105a is also mounted on the mandrel 201 and connected to a current source to generate a balanced magnetic field as described above. The conductive path extends about the probe axis 102 and has an azimuthal length between the terminals, and the balanced magnetic field induces a balanced voltage in the first sense coil 103a, which at least partially offsets the baseline voltage. Advantageously, this means that the voltage detected in the sense coil 103a is at least primarily due to a marker proximate the probe, enabling the signal processor to determine the distance between the marker and the probe.

[0101] 5 is a schematic longitudinal section through a mandrel 201 of a probe according to yet another embodiment of the present disclosure. The mandrel 201 is similar to the mandrels 1;101 of the first and second embodiments described above, and is adapted to be fixedly attached to the distal end of a hand-held wand such that the mandrel 201 is attached to the distal end of the probe. The mandrel 201 supports a first distal coil set 210a and a second proximal coil set 210b spaced axially along a longitudinal axis 202 of the mandrel 201. The first coil set 210a comprises a first drive coil pair 205a, 205c and a first sense coil 203a interposed between the first drive coil pair 205a, 205c; the second coil set 210b comprises a second drive coil pair 205b, 205d that is substantially the same as the first drive coil pair 205a, 205c, and a second sense coil 203b. The first drive coil pair 205a, 205c and the second drive coil pair 205b, 205d are connected in series to a current source (not shown) that may be housed in a suitable base station, as shown in FIG. 1. The first sense coil 203a and the second sense coil 203b are connected in anti-series to each other and arranged to connect to a signal processor as described above. In an alternative configuration, the first and second sensing coils 203a, 203b may be connected in series but wound in opposite directions, as described above in connection with Figures 3 and 4.

[0102] In use, a magnetic drive field is generated when current flows through the first drive coil pair 205a, 205c and the second drive coil pair 205b, 205d. The axial separation of the two coil sets 210a, 210b is such that the voltage induced in the first sense coil 203a comes primarily from the first drive coil pair 205a, 205c, and the voltage induced in the second sense coil 203b comes primarily from the second drive coil 205b, 205d. When the sense coils 203a, 203b are connected in anti-series, the voltages induced in the sense coils 203a, 203b from the respective drive coil pairs 205a, 205c; 205b, 205d are approximately equal and opposite to each other. However, due to manufacturing tolerances, the first drive coil pair 205a, 205c is unlikely to be identical to the second drive coil pair 205b, 205d, the first sense coil 203a is unlikely to be identical to the second sense coil 203b, and the spacing between the coils of the first coil set 210a is unlikely to be equal to the spacing between the coils of the second coil set 210b. As a result, the net baseline voltage across the two sense coils 203a, 203b is unlikely to be exactly zero.

[0103] A baseline voltage tering device comprising an arc-shaped conductor 207 formed from an arc-shaped elongated strip of conductive material is attached to the outer surface of the mandrel 201 and defines a conductive path extending circumferentially between spaced apart terminals (not shown) on the conductor 207 intermediate the first coil set 210a and the second coil set 210b. The conductor 207 is conveniently connected to a current source, preferably via terminals disposed at or near each circumferential end 208, 209 of the conductor 207, to generate a balanced magnetic field in use. It will be appreciated that in some embodiments, a separate current source for the conductive path may be provided if desired. The conductor 207 is positioned closer to one of the coil sets 210a, 210b than to the other 210b, 210a, thereby generating a magnetic field that induces a greater voltage across the sense coils 203a, 203b of one of the coil sets 210a, 210b in operation. Conductor 207 is configured such that the azimuthal length of the conductive path between terminals 208, 209 results in a net balanced voltage across the sensing coils 203a, 203b that at least partially cancels the baseline voltage. Advantageously, this means that the voltage detected in the sensing coils 203a, 203b is primarily due to a magnetic marker in close proximity to the probe, allowing the signal processor to determine the distance between the marker and the probe. In an alternative configuration, conductor 207 may be replaced by a baseline voltage staring device of one of the types described below with reference to Figures 6(a) and 6(b) or 7.

[0104] FIG. 6(a) is a perspective view of a baseline voltage tarring device 401 according to another embodiment of the present disclosure; FIG. 6(b) is a plan view of the baseline voltage tarring device 401 in an unfolded state for ease of reference. The tarring device 401 is formed from a flexible printed circuit board including an insulating backing layer 402 and a conductive layer 403. Suitably, the conductive layer 403 may comprise a thin film of copper in a manner known to those skilled in the art. The backing layer 402 may comprise any suitable insulating material that is sufficiently flexible to be wrapped and secured to a cylindrical mandrel 1;101;201, similar to those described above. Alternatively, the backing layer 402 may comprise an insulating tape, such as, for example, a polyimide tape (e.g., the Kapton® tape described above).

[0105] The tarring device 401, as shown in Figure 6(a), has two circumferential ends 405, 406 and when attached forms an incomplete loop defining a central axis 404 that is aligned with the longitudinal axis 2;102;202 of the mandrel 1;101;201. A tab 407 is attached to one of the circumferential ends 405 that is configured to be received in a corresponding recess (not shown) formed in the mandrel to position the device 401 relative to the mandrel.

[0106] The copper layer 403 is etched in a manner known to those skilled in the art to form first and second axially spaced apart elongated conductors 409a, 409b which extend circumferentially around the device 401, one substantially parallel to the other. Each conductor 409a, 409b includes a plurality of circumferentially spaced lands 411 in a ladder-like fashion which extend in a direction substantially parallel to the axis 404 of the device 401 between the conductors 409a, 409b at a series of different azimuthal positions and terminate at a free end 412 adjacent the other conductor 409b, 409a. Each conductor 409a, 409b is formed with a terminal 413a, 413b juxtaposed to the tab 407 for connecting the terminaling device 401 to a current source.

[0107] In use, the balanced magnetic field generated by the tering apparatus 401 can be adjusted by selecting a land (e.g., 411', 411" or 411'") on one of the conductors 409b, 409a and forming an electrical connection (not shown) between the selected land 411'; 411"; 411'" and the other conductor 409a, 409b to form a bridge across the short gap between the free end 412 of the land 411'; 411"; 411'" and the other conductor 409a, 409b. The electrical connection may be made, for example, by soldering from the free end 412 across to the other conductor, thereby forming a continuous electrical path as indicated by the arrows in FIG. 6(b). The selection of a given land 411'; 411"; 411'" determines the azimuthal length of the conductive path defined by the conductors 409a, 409b. As disclosed herein, the azimuthal length of the conductive path determines the strength of the balance magnetic field and therefore the balance voltage induced in one or more sense coils from the tering device 401. The axially extending land 411 when attached to the mandrel 1;101;201 does not contribute to the balance magnetic field. Advantageously, the tering device 401 is attached to the mandrel 1;101;201 such that one of the first and second conductors 409a, 409b is positioned midway between the two sense coils 3a, 3b;103a, 103b;203a, 203b such that the magnetic field generated by that conductor affects the two sense coils substantially equally. In such a case, the balance magnetic field is governed by the axial position of the other conductor 409b, 409a and the azimuthal length of the other conductor between the terminal 413b, 413a and the selected land 411';411";411'".

[0108] 7 is a plan view of a balanced voltage tering device 501 according to another embodiment of the present disclosure in an unfolded state. The tering device 501 comprises a flexible printed circuit board 510. The circuit board 510 is etched with two elongated copper traces 509a, 509b forming first and second parallel conductors, and a number of spaced apart copper lands 511 extending partway between the traces 509a, 509b. In this embodiment, all lands 511 are connected to one of the traces 509a. By wiring or soldering the connection between a selected one of the copper rungs 511a and the other trace 509b, as shown at 521, a complete conductive path can be created, thereby allowing current to flow around the path, as shown by the arrows. In use, the tering apparatus 501 can induce balanced voltages in one or more sensing coils as disclosed herein depending on the azimuthal length of the conductive path defined by the traces 509a, 509b and the position of the traces 509a, 509b relative to the one or more sensing coils.

[0109] FIG. 8(a) is a schematic diagram of an arrangement of two coil sets 604a, 604b forming a gradiometer for a susceptibility probe (not shown) according to another embodiment of the present disclosure, illustrating how a conductive path 607 provided by a balanced voltage staring device of the type described herein interposed between the pair of coils 604a, 604b provides a balanced magnetic field and induces balanced voltages across the two sensing coils 603a, 603b of the two coil sets to reduce the baseline voltage in the sensing coil resulting from the drive magnetic field generated by the drive coil set of coils, such that the sense voltage across the sensing coil is primarily due to the response magnetic field from a magnetic marker present within the drive magnetic field.

[0110] This configuration comprises a first coil set 604a and a second coil set 604b arranged coaxially on a longitudinal probe axis 602; each coil set comprises two spaced apart drive coils 605a, 605c; 605b, 605d and a sense coil 603a; 603b interposed between the drive coils 605a, 605c; 605b, 605d. The coils may be supported on a suitable coaxial former or mandrel (not shown) of the type described above and housed within a probe housing (also not shown), with the first coil set 604a positioned proximate the distal tip of the probe for maximum sensitivity.

[0111] The drive coils 605a, 605b; 605c, 605d are connected in series with each other and are suitably adapted for connection to an alternating current source (not shown) to generate a drive magnetic field during use. The sense coils 603a, 603b of the two coil sets are connected in anti-series and arranged for connection to a signal processor housed, for example, in a base station as shown in Figure 1, which processes sense voltages induced in the sense coils to calculate the distance between the probe and the magnetic marker. In an alternative configuration, the sense coils 603a, 603b may be connected in series but wound in opposite directions.

[0112] In use, the drive coils 605a, 605b, 605c, 605d generate approximately equal and opposite voltages in the two sense coils 603a, 603b, but due to manufacturing tolerances, the net baseline voltage (i.e., the net voltage across the sense coils 603a, 603b) is unlikely to be exactly zero. This is particularly true for narrow probes (e.g., less than about 10 mm) having small coil diameters, as discussed above.

[0113] As disclosed herein, the conductive path 607 is provided at an off-center position between the first coil set 604a and the second coil set 604b in a direction parallel to the probe axis 602. In FIG. 8(a), the conductive path 607 is shown as a complete circuit for illustrative purposes, but in reality includes terminals for connection to a current source for passing a current through the conductive path. The conductive path 607 is suitably connected to the same current source as the drive coils 605a, 605b, 605c, 605d, although in other embodiments a separate current source may be provided. Current flowing along the conductive path 607 in an azimuth direction at an off-center position along the probe axis 602 (as indicated by solid arrow 613) contributes to a balance magnetic field, which induces a balance voltage in at least one of the sense coils 603a, 603b. Axial currents and currents flowing in an azimuth direction at a midpoint between the two sense coils 604a, 604b do not contribute to the balance magnetic field. The conductive path 607 is arranged to induce a balancing voltage that at least partially cancels any baseline voltage across the sense coils 604a, 604b generated by the drive coils 605a, 605b, 605c, 605d.

[0114] As disclosed above, the conductive path 607 may be suitably provided by a balanced voltage staring device that includes at least one arcuate conductor extending azimuthally about the probe axis 602. The balanced magnetic field is determined by the azimuth length of the conductive path 607.

[0115] 8(b)-8(d) are a series of schematic diagrams illustrating the effect of varying the azimuthal length of a conductive path 707a, 707b, 707c interposed between two coil sets 704a, 704b arranged coaxially on a longitudinal probe axis 702 for use in a sensitive probe according to the present disclosure. The coil sets 704a, 704b, similar to those described above with reference to FIG. 8(a), comprise a first coil set 704a and a second coil set 704b. Each coil set 704a, 704b comprises a spaced apart pair of drive coils 705a, 705c; 705b, 705d, and a sense coil 703a; 703b interposed between the respective drive coils 705a, 705c; 705b, 705d. A balanced voltage Tarling apparatus (not shown) is interposed between the coil sets 704a, 704b and defines conductive paths 707a, 707b, 707c comprising first and second circumferentially extending conductors and two conductive bridges extending between the circumferential conductors in a direction substantially parallel to the probe axis 702. As with Figure 8(a), in Figures 8(b)-8(d) each of the conductive paths 707a, 707b, 707c is shown as a complete circuit for illustrative purposes, although in practice the Tarling apparatus would include terminals for connecting the conductive paths to a current source for passing a current through the conductive paths.

[0116] FIG. 8(b) shows a conductive path 707a that spans only a short azimuthal distance around the probe axis 702. The off-center portion of the conductive path 707, which extends in a circumferential direction, indicated by arrow 713, contributes to the equilibrium magnetic field. FIG. 8(c) shows a conductive path 707b that spans a larger azimuthal distance around the probe axis 702. This can be achieved, for example, by connecting different lands 411 in a tering device of the type described above with reference to FIGS. 6(a) and 6(b) or 7, or by moving the conductive bridges to include a longer length of the first and second conductors 409a, 409b; 509a, 509b in the conductive path 707b. The conductive path 707b generates a stronger equilibrium magnetic field than the conductive path 707a of FIG. 8(b). On the other hand, FIG. 8(d) shows a conductive path 707c that extends almost completely around the probe axis 702. This path can be formed, for example, by connecting lands 411 at the ends of the first and second conductors 409a, 409b; 509a, 509b in a tering device of the type described above with reference to Figures 6(a) and 6(b) or 7, or by including substantially the entire length of the conductors in the conductive path by placing a conductive bridge at or near the ends of the first and second circumferential conductors remote from the connecting terminals. This conductive path 707c generates a stronger balanced magnetic field than the conductive path 707b of Figure 8(c).

[0117] 9 is a perspective view of a distal end portion of a probe 800 according to one embodiment of the present disclosure. The probe 800 comprises a coil arrangement supported on a mandrel 901 secured to a distal end 902 of a wand 900, as described in more detail below. The wand 900 is adapted to connect to a suitable base station (not shown) comprising a signal processor. The probe 800 is typically connected to the base station by a wired connection through the wand 900, although in some embodiments it may be connected wirelessly.

[0118] The mandrel 901 defines a longitudinal axis 902 with a first distal cylindrical portion 903 having a diameter of approximately 10 mm supporting a first coil set 804a proximate the distal sensing end 904 of the probe 800, a second proximal cylindrical portion 905 similarly dimensioned as the distal portion 903 and supporting a second coil set 804b axially spaced apart from the first coil set 804a, and a narrower cylindrical intermediate portion 907 supporting a balanced voltage staring device 807 between the first and second coil sets 804a, 804b. The mandrel 901 has the coil arrangement fixedly mounted thereon and is housed within a substantially cylindrical hollow probe housing (not shown) having an outer diameter of approximately 12 mm.

[0119] The first coil set 804a comprises a first drive coil pair 805a, 805c and a first sense coil 803a interposed between the drive coils 805a, 805c. The second pair of coils 805b, 805d similarly comprises a second drive coil pair 805b, 805d and a second sense coil 803b interposed between the drive coils 805b, 805d.

[0120] The drive coils 805a, 805c; 805b, 805d in each coil set 804a, 804b are substantially identical to one another. Each drive coil includes about 10 to about 60 turns of wire, has an outer diameter of about 1.5 mm to about 6 mm, and an axial length of about 0.5 mm to about 2.5 mm.

[0121] The sensing coils 803a; 803b of each coil set 804a, 804b include about 100 to about 500 turns of wire, have an axial length of about 0.75 mm to about 2 mm, and an average radius of about 1.5 mm to about 6.5 mm. In this embodiment, each sensing coil 803a, 803b has an average radius similar to the average radius of the driving coils 805a, 805c; 805b, 805d of the respective coil sets 804a, 804b.

[0122] Each sensing coil 803a; 803b is formed from a wire having a diameter of approximately 0.025 mm to 0.1 mm.

[0123] The coils are constructed and arranged such that the distance between the centre of each sensing coil 803a; 803b and the centre of each drive coil 805a, 805c; 805b, 805d in the same coil set 804a; 804b is from about 1 mm to about 3 mm.

[0124] The total axial distance spanned by the first and second coil sets 804a, 804b is about 19 mm to about 30 mm, while the axial spacing between the sensing coils 803a, 803b of the first coil set 804a and the second coil set 804b is about 12 mm to about 15 mm.

[0125] In this embodiment, the spacing between the first coil set 804a and the second coil set 804b is approximately 12 mm in a direction parallel to the probe axis 902, although it will be understood that in other embodiments a different spacing between the coil sets 804a, 804b may be used.

[0126] The balanced voltage tering apparatus 807 is substantially similar to that described above with reference to Figures 6(a) and 6(b) and comprises a flexible printed circuit board that is etched to form two substantially parallel elongated copper traces thereon, forming first and second arcuate conductors 809a, 809b that extend partially azimuthally around the probe axis 902. The flexible circuit board is wrapped circumferentially around an intermediate portion 907 of the mandrel 901 and secured thereto, such that the first and second conductors 809a, 809b extend azimuthally around the probe axis 902, as shown in Figure 9. One of the conductors 809a extends circumferentially around the mandrel 901 in a direction parallel to the axis 902 of the mandrel 901 at an off-center location between the first and second coil sets 804a, 804b, more specifically between the first and second sense coils 803a, 803b. The other conductor 809b extends circumferentially around the mandrel 901 at a point equidistant from the first and second coil sets 804a, 804b, more specifically from the first and second sense coils 803a, 803b. In other configurations, both conductors 809a, 809b may be positioned away from the midpoint between the coil sets 804a, 804b, but they should be positioned asymmetrically relative to the midpoint. In this embodiment, each of the elongated conductors 809a, 809b extends in a respective plane that is substantially perpendicular to the axis 902 of the mandrel 901. In other embodiments, one of the conductors 809a, 809b may have a different configuration such that it also extends in a direction parallel to the axis 902, where at least one of the conductors 809a, 809b extends in an azimuth direction about the axis 902 at an average off-center position along the axis 902.

[0127] As described above, the first and second conductors 809a, 809b are formed with a plurality of lands 811 at a series of azimuthal positions about the probe axis 902, the lands 811 extending between the conductors 809a, 809b in a direction substantially parallel to the probe axis 902. Each land 811 extends from one of the conductors 809a, 809b and terminates just short of the other conductor 809b, 809a. Each of the conductors 809a, 809b has a terminal (not shown) at one end for connection to a current source, and the conductors 809a, 809b are interconnected at one of the lands 811 to form a continuous conductive path through the first and second conductors 809a, 809b, as described in more detail below.

[0128] The drive coils 805a, 805b, 805c, 805d are connected in series with each other, and the first and second sense coils 803a, 803b are connected in anti-series. In an alternative configuration, the sense coils 803a, 803b may be formed connected in series but wound in opposite directions. The sense coils 803a, 803b include connectors for connecting to a signal processor for processing sense voltages detected by the sense coils as described herein and calculating the distance between the probe 800 and the magnetic marker. The drive coils 805a, 805b, 805c, 805d and the turner 807 are connected to an alternating current source. The first drive coil pair 805a, 805c generates a drive magnetic field and induces a voltage in the first sense coil 803a. The second drive coil pair 805b, 805d also generates a drive magnetic field and generates an approximately equal and opposite voltage in the second sense coil 803b. The net voltage induced in the first and second sense coils 803a, 803b from the first drive coil pair 805a, 805c and the second drive coil pair 805b, 805d is close to zero, but is unlikely to be exactly zero as a result of manufacturing tolerances and differences between the first set of coils 804a and the second set of coils 804. Thus, a residual baseline voltage typically results. In use, a magnetic marker present in the drive magnetic field generates a response magnetic field, which induces a sense voltage in one or both of the sense coils 803a, 803b. Typically, the marker is located distal to the tip 904 of the probe 800, so that the sense voltage is primarily generated in the first sense coil 803a of the first distal coil set 804a. The baseline voltage resulting from the drive coil tends to mask the sensed voltage from the marker and therefore it is desirable to minimize the baseline voltage as much as possible so that the sensed voltage is due primarily to the response magnetic field and is indicative of the distance between the first sense coil 803a and the marker and a signal processor can process the sensed voltage to determine the distance and generate an output signal representative of the distance.

[0129] By passing a current through the conductive paths of the tering device 807, a balanced magnetic field is generated as disclosed herein. The strength of the balanced magnetic field depends on the azimuthal length of the conductive paths, which can be controlled by selecting the location of interconnecting the first and second conductors 809a, 809b. Because one of the conductors 809a, 809b is positioned off-center between the coil sets 804a, 804b, as described above, the balanced magnetic field induces unequal voltages in the first and second sense coils 803a, 803b, thereby generating a net balanced voltage that serves to at least partially cancel the baseline voltage. Thus, the magnitude of the balanced magnetic field can be adjusted to minimize the residual baseline voltage resulting from the drive coils 805a, 805b, 805c, 805d by precisely setting the azimuthal length of the conductive paths. As will be apparent to one skilled in the art, this is accomplished by forming a conductive bridge between the land 811 on one of the conductors 809a, 809b and the other conductor 809b, 809a at an azimuthal position, where the azimuthal length of the conductive path is such that current flowing circumferentially of the conductive path off-center from the midpoint between the first coil set 804a and the second coil set 804b induces balanced voltages in the first and second sensing coils 803a, 803b, thus minimizing the baseline voltage, thereby allowing the sense voltage induced in one or both of the sensing coils 803a, 803b from the response magnetic field generated by a magnetic marker in the drive magnetic field to be detected with improved sensitivity and accuracy.

[0130] In a variation of the configurations described above with reference to Figures 3-5, 8(a)-8(d) and 9, 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 separately to a signal processor. Figure 10 shows a mandrel 1201 for a probe similar to mandrel 201 described above with reference to Figure 5. However, it will be understood that this is purely for illustrative purposes and that any other embodiment according to the present disclosure may be similarly configured.

[0131] Thus, the mandrel 1201 of Figure 10 comprises two coil sets 1210, 1210 supported on the mandrel 1201 coaxially with the longitudinal axis 1202 of the mandrel. Each coil set comprises two axially spaced drive coils 1205a, 1205c; 1205b, 1205d and a sense coil 1203a; 1203b interposed between the respective drive coils. A balanced voltage turner 1207 is also supported on the mandrel 1201 intermediate the two coil sets 1210a, 1210b. The drive coils 1205a, 1205c; 1205b, 1205d are connected in series to an alternating current source 1221 housed within a base station 1220. Each sense coil 1203a, 1203b is separately connected to a signal processor 1222 within the base station. In this manner, the baseline voltage induced directly in one of the sensing coils 1203a, 1203b by the drive field can be used by the signal processor 1222 to remove the corresponding baseline voltage component caused directly by the drive field from the voltage induced in the other sensing coil 1203b, 1203a, leaving only the sense voltage component resulting from the response field produced by the magnetic marker in the drive field and any residual baseline voltage. A tering device 1207 of the type described above can then be used to minimize the residual baseline voltage in accordance with the present disclosure.

[0132] 11 is a flow chart of a method 1100 of 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 a longitudinal axis of the probe, the at least two first coils being either a sensing coil or a driving coil, and the at least one second coil being the other of a driving coil or a sensing coil, the one or more driving coils being connectable to a current source and generating a driving magnetic field through the one or more driving coils, and the one or more sensing coils being connectable to a signal processor for processing one or more sense voltages induced in the respective one or more sense coils to generate an output signal; the first coil or the second coil is configured or arranged to minimize a baseline voltage component of the sense voltage induced in the one or more sense coils that is directly attributable to the driving magnetic field; the first and second coils are thereby configured and arranged as a gradiometer for measuring the proximity of a magnetic marker to the probe, the output signal being indicative of the distance between the marker and the probe.

[0133] In a second step 1102, the method includes attaching a baseline voltage targeting device to the probe, the first conductor defining a conductive path extending partially around the probe axis in juxtaposition to the one or more sensing coils and connectable to a current source to generate a balanced magnetic field in the vicinity of the one or more sensing coils, wherein, in use, the balanced magnetic field induces a balanced voltage in the one or more sensing coils that at least partially offsets the baseline voltage, whereby the sensed voltage is at least primarily attributable to a response magnetic field generated by the marker in response to the drive magnetic field, which corresponds to the proximity of the marker.

[0134] In an alternative embodiment, in the first step 1101, two or more sensing coils may be configured to output separate sense voltages to a signal processor, allowing the signal processor to process the sense voltages to minimize baseline voltage components in the sense voltages that may be directly attributable to the drive magnetic field.

[0135] Step 1102 may optionally include adjusting the azimuthal length of the conductive path around the probe to minimize a baseline voltage across one or more sensing coils.

[0136] Although aspects of the present disclosure have been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It is therefore to be understood that numerous modifications can be made to these exemplary embodiments and that other arrangements can be devised without departing from the scope of the present disclosure as defined by the appended claims.

[0137] It will be understood by those skilled in the art that features of these exemplary embodiments may be combined in other embodiments that are within the scope of the present disclosure.

[0138] Although various details are described in the above description, it will be understood that various aspects of the techniques for operating a diagnostic and / or surgical guide system suitable for identifying, locating, tracking, and detecting one or more embedded markers may be performed without these specific details. Those skilled in the art will recognize that the components (e.g., operations), devices, objects, and the accompanying descriptions described herein are used as examples for conceptual clarity, and that various modifications of the configurations are contemplated. Thus, as used herein, the above-mentioned specific examples and the accompanying descriptions are intended to be representative of more general classes of these examples. In general, the use of any specific exemplar is intended to be representative of the class, and should not be construed as a limitation that the specific components (e.g., operations), devices, objects are not included.

[0139] Furthermore, while several embodiments have been illustrated and described, it is not the intention of the applicant to restrict or limit the scope of the appended claims to such details. Numerous modifications, variations, changes, substitutions, combinations, and equivalents to those embodiments may be implemented and will occur to those skilled in the art without departing from the scope of the present disclosure. Furthermore, the structure of each element associated with the described embodiments may be alternatively described as a means for providing the function performed by the element. Also, where materials are disclosed for a particular component, 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 that fall within the scope of the disclosed embodiments. The appended claims are intended to cover all such modifications, variations, changes, substitutions, modifications, and equivalents.

[0140] In the above description, integers or elements having known obvious or foreseeable equivalents are referred to, and such equivalents are incorporated herein as if set forth individually. Reference should be made to the claims to determine the true scope of the present disclosure, and the claims should be interpreted to encompass any such equivalents. The reader will also understand that integers or features of the present disclosure described as advantageous, convenient, etc. are optional and do not limit the scope of the independent claims. Furthermore, it should be understood that such optional integers or features may be beneficial in some embodiments of the present disclosure, but may be undesirable and therefore absent in other embodiments.

[0141] For brevity and clarity of the disclosure, 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 may be presented in terms of instructions operating on data stored in one or more computer memories or one or more data storage devices of the base station, or one or more processors or microprocessors operating therein (e.g., floppy disks, hard disk drives, caches, random access memories, and other optical and magnetic storage devices and media). Such descriptions and representations are used by those skilled in the art to describe the substance of their work and 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, and the "steps" refer to manipulations of physical quantities and / or logical states, which may, but need not necessarily, take the form of electrical or magnetic signals that can be stored, transferred, combined, compared, and otherwise manipulated. It is common to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. These and similar terms may be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities and / or states. The various method steps disclosed herein can be implemented or programmed as algorithms, data structures, and instructions that can operate based on input from data channels and generate output including various types of data, such as user action data, user feedback signals, information, and images.

[0142] Unless otherwise specifically stated as will be apparent from the foregoing disclosure, discussions using terms such as "processing" or "calculating" or "computing" or "determining" or "displaying" throughout the foregoing disclosure will be understood to refer to operations and processes of a computer system, processor-based base station, or similar electronic computing device that manipulates and converts data represented as physical (electronic) quantities in the computer system's registers and memory into other data that is similarly represented as physical quantities in the computer system's memory or registers or other such information storage, transmission, or display devices.

[0143] In a general sense, those skilled in the art will recognize that the various aspects described herein, which may be individually and / or collectively implemented by a wide range of hardware, software, firmware, or any combination thereof, may be considered to be composed of various types of "electrical circuitry." Thus, "electrical circuitry" as used herein includes, but is not limited to, electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry 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 executes the processes and / or devices described herein, or a microprocessor configured by a computer program that at least partially executes the processes and / or devices described herein), electrical circuitry forming a storage device (e.g., in the form of random access memory), and / or electrical circuitry forming a communication device (e.g., a modem, a communication switch, or an optoelectronic device). Those skilled in the art will recognize that the subject matter described herein may be implemented in an analog or digital manner, or in any combination thereof.

[0144] The foregoing detailed description has described various forms of apparatus and / or processes through the use of block diagrams, flow charts, and / or examples. To the extent that such block diagrams, flow charts, and / or examples include one or more functions and / or operations, those skilled in the art will appreciate that each function and / or operation within such block diagrams, flow charts, and / or examples may be individually and / or collectively implemented by a wide range of hardware, software, firmware, or virtually any combination thereof. In one form, some portions of the subject matter described herein may be implemented via an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), or other integrated format. However, those skilled in the art will recognize that some aspects of the forms disclosed herein may equivalently be implemented, in whole or in part, in integrated circuits, 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 operating on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing circuitry and / or writing code for the software and / or firmware will be within the skill of those of ordinary skill in the art in light of this disclosure.

[0145] Moreover, those skilled in the art will appreciate that the subject matter mechanisms described herein can be distributed as one or more program products in a variety of forms, and that the exemplary forms of the subject matter described herein apply regardless of the particular type of signal-bearing medium actually used to effect the distribution. Examples of signal-bearing media include, but are not limited to, recordable media such as floppy disks, hard disk drives, compact disks (CDs), digital video disks (DVDs), digital tape, computer memory, and the like; and transmission-type media such as digital and / or analog communications media (e.g., fiber optic cables, wave guides, wired communications links, wireless communications links (e.g., transmitters, receivers, transmitting logic, receiving logic, etc.), etc.).

[0146] Also, as described, some aspects may be implemented as one or more methods. Acts performed as part of a method may be ordered in any suitable manner. Thus, while shown in an exemplary embodiment as sequential operations, embodiments may be constructed in which operations are performed in a different order than described and may include performing some operations simultaneously.

[0147] The term "and / or" as used in the specification and claims should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctive in some cases and disjunctive in other cases.

[0148] As used herein and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed in the list of elements, and not necessarily excluding any combination of elements in the list of elements. This definition also allows that elements other than those specifically identified in the list of elements to which the phrase "at least one" refers may optionally be present, whether or not related to the specifically identified elements.

[0149] The terms "approximately" and "about" may be used in some embodiments to mean within ±20% of a target value, in some embodiments within ±10% of a target value, in some embodiments within ±5% of a target value, and in some embodiments within ±2% of a target value. The terms "approximately" and "about" may include the target value.

[0150] In the claims as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "consisting of," and the like, are to be understood to be open-ended, i.e., meaning including but not limited to. The transitional phrases "consisting of" and "consisting essentially of" are intended to be closed or semi-closed transitional phrases, respectively.

[0151] When a range or list of values ​​is provided, each intervening value between the upper and lower limits of that range or list of values ​​is individually contemplated and encompassed within the disclosure as if each value were specifically recited herein. Additionally, smaller ranges between and including the upper and lower limits of a given range are contemplated and encompassed within the disclosure. The recitation of exemplary values ​​or ranges is not a disclaimer of other values ​​or ranges between and including the upper and lower limits of a given range.

[0152] The use of headings and sections in this application is not meant to limit the disclosure; each section may apply to any aspect, embodiment, or feature of the disclosure. Only claims using the term "means for" are intended to be interpreted only in the United States under 35 USC 112, paragraph 6. Unless the claim contains the recitation "means for," such claims should not be interpreted under 35 USC 112. Outside the United States, the term "means for" is intended to have its natural means. No limitations from this specification are intended to be read into any claims unless such limitations are expressly included in the claims.

[0153] The embodiments disclosed herein may be embodied as a system, method, or computer program product. Accordingly, the embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, all of which may be referred to generally herein as a "circuit," "module," or "system." Additionally, the embodiments may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied therein.

[0154] Although aspects of the invention have been described herein with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is thus to be understood that numerous modifications can be made to the illustrative embodiments and other arrangements can be devised without departing from the scope of the invention as defined by the appended claims.

Claims

1. 1. A probe for locating a magnetic marker for use in surgery, the probe comprising: at least two first coils and at least one second coil disposed substantially coaxially on a longitudinal axis of the probe as a gradiometer for measuring the proximity of a magnetic marker to the probe; and a baseline voltage Tarling device comprising a first elongated conductor defining a conductive path extending partially around the probe axis and connectable to a current source to generate a balanced magnetic field in the vicinity of one or more sensing coils; Equipped with the at least two first coils are either sensing coils or drive coils, and the at least one second coil is the other of a drive 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 sense voltages induced in each one or more sensing coils to generate an output signal representative of the distance between the marker and the probe; the first or second coils are configured or arranged to minimize a baseline voltage component of the sense voltages induced in one or more sensing coils that is directly attributable to a drive magnetic field, or to output separate sense voltages from two or more sensing coils to a signal processor and enable the signal processor to process the sense voltages to minimize a baseline voltage component of the sense voltages that is directly attributable to a drive magnetic field; The conductive pathway is constructed and arranged such that, in use, a balanced magnetic field induces a balanced voltage in the one or more sense coils that at least partially offsets the baseline voltage; whereby the sense voltage is at least primarily attributable to a response magnetic field generated by the marker in response to the drive magnetic field, which corresponds to the proximity of the marker. A probe characterized by:

2. 2. The probe of claim 1, including at least two sense coils spaced apart from one another along the probe axis, and a drive coil interposed between the at least two sense coils.

3. 2. The probe of claim 1, comprising a first coil set including at least one drive coil and at least one sense coil, and a second coil set including at least one drive coil and at least one sense coil, the first coil set and the second coil set being spaced apart from each other along the probe axis.

4. 4. The probe of claim 3, wherein the first coil set includes a first sense coil interposed between a first pair of drive coils, and the second coil set includes a second sense coil interposed between a second pair of drive coils.

5. 5. The probe of claim 3, wherein the first conductor is disposed at a fixed axial position between the first coil set and the second coil set.

6. 5. The probe of claim 2, wherein the at least two sense coils are connected in anti-series with each other or have windings in opposite directions, thereby minimizing a baseline voltage component of the sense voltage induced in the sense coils that is directly attributable to the drive magnetic field.

7. 5. The probe of claim 2, wherein the at least two sensing coils are adapted for individual connection to the signal processor, the signal processor being capable of processing sense voltages induced in each sensing coil to minimize baseline voltage components of the sense voltages that are directly attributable to the drive magnetic field.

8. at least two drive coils axially spaced apart from one another along the length of the probe shaft, and a sense coil interposed between the at least two drive coils; The at least two drive coils are connected in anti-series with each other or have windings in opposite directions, thereby minimizing a baseline voltage component of the sense voltage induced in the sense coil that is directly attributable to the drive magnetic field. The probe according to claim 1 .

9. 9. The probe of claim 1, wherein the tering device further comprises a second conductor and at least one conductive bridge extending between the first conductor and the second conductor, the conductive bridge defining an azimuthal length of the conductive path.

10. 10. The probe of claim 9, wherein the first and second conductors are each defined by two conductive loops extending around the probe axis.

11. 10. The probe of claim 9, wherein one or both of the first and second conductors comprises a plurality of lands at a series of azimuthally spaced locations about the probe axis for connecting at least one conductive bridge, thereby defining a conductive path.

12. The probe of any one of claims 1 to 4 and 8, wherein the first conductor comprises a conductive trace and / or a wire.

13. A probe according to any one of claims 1 to 4 and 8, characterized in that the turning device comprises a flexible circuit board wrapped circumferentially around the probe shaft.

14. 14. The probe of claim 13, wherein the tering device comprises a flexible printed circuit board including at least one conductive trace that defines the first conductor.

15. 1. A method of manufacturing a probe for sensing magnetic markers during a surgical procedure, comprising: - mounting at least two first coils and at least one second coil substantially coaxially on a longitudinal axis of the probe, wherein the at least two first coils are either sensing coils or drive coils, and the at least one second coil is the other of a drive coil or a sensing coil, the one or more drive coils connectable to a current source to generate a magnetic drive field through the one or more drive coils, and the one or more sensing coils connectable to a signal processor for processing one or more sense voltages induced in each of the one or more sensing coils to generate an output signal; the first or second coils are configured or arranged to minimize a baseline voltage component of a sense voltage induced in the one or more sense coils that is directly attributable to a drive magnetic field, or to output separate sense voltages from two or more sense coils to the signal processor and enable the signal processor to process the sense voltages to minimize a baseline voltage component of the sense voltage that is directly attributable to a drive magnetic field; whereby the first and second coils are configured and arranged as a gradiometer for measuring the proximity of the magnetic marker to the probe, the output signal being indicative of the distance between the marker and the probe; - attaching to the probe a baseline voltage Tarling device comprising a first elongated conductor, the first conductor defining a conductive path extending partially around the probe axis and connectable to a current source to generate a balanced magnetic field in the vicinity of the one or more sensing coils, wherein in use the balanced magnetic field induces a balanced voltage in the one or more sensing coils that at least partially offsets a baseline voltage; whereby a sense voltage is at least primarily attributable to a response magnetic field generated by the marker in response to a drive magnetic field, which corresponds to the proximity of the marker; A method comprising:

16. 16. The method of claim 15, further comprising adjusting the azimuthal length of a conductive path around the probe to minimize a baseline voltage across the one or more sensing coils.

17. 1. A method of configuring a probe for sensing magnetic markers for use in a surgical procedure, the probe comprising: at least two first coils and at least one second coil disposed substantially coaxially on a longitudinal axis of the probe as a gradiometer for measuring the proximity of the magnetic marker to the probe; a baseline voltage Tarling device comprising a first elongated conductor defining a conductive path extending partially around the probe axis and connectable to a current source to generate a balanced magnetic field in the vicinity of the one or more sensing coils; Equipped with the at least two first coils are either sense coils or drive coils, and the at least one second coil is the other of a drive coil or a sense 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 sense coils are adapted to be connected to a signal processor for processing sense voltages induced in the one or more sense coils to generate an output signal; the first or second coils are configured or arranged to minimize a baseline voltage component of the sense voltages induced in the one or more sense coils that is directly attributable to a drive magnetic field, or to output separate sense voltages from two or more sense coils to the signal processor and enable the signal processor to process the sense voltages to minimize a baseline voltage component of the sense voltage that is directly attributable to a drive magnetic field; The method includes adjusting the azimuthal length of a conductive path about the probe axis to control a balance magnetic field and induce a balance voltage across the one or more sense coils that at least partially offsets a baseline voltage. A method characterized by:

18. 1. A detection device for locating a magnetic marker during surgery, the device comprising: A probe according to any one of claims 1 to 4 and 8; a current source selectively operable to generate a magnetic drive field through the one or more drive coils and the first conductor; and at least one signal processor configured to receive at least one sense voltage from the one or more sense coils and to generate an output signal representative of the distance between the probe and the magnetic marker; A detection device comprising:

19. The detection device of claim 18, further comprising at least one embedded magnetic marker.

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