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

Abstract

A probe (303; 403) for sensing a magnetic marker, comprising a first coil set (313; 413) including a first coil of a first coil type, e.g., a sense coil (305; 405), disposed between a first pair of coils of a second coil type, e.g., a drive coil (301a, 301b; 401a, 401b) connected in series, and a balance element (317; 417) axially spaced from the first coil set (313; 413) along the length of the probe (303; 403). The balance element (317; 417) is configured or arranged to generate a sense voltage that fully offsets, partially offsets, or minimizes a sense voltage induced in one or more sense coils (305; 405) of the first coil set from the drive coil or coils (301a, 301b; 401a, 401b). A detection system is also disclosed, comprising the probe (303; 403), a magnetic field generator configured to drive an alternating magnetic field through the drive coils (301a, 301b; 401a, 401b) of the first coil set and the balance element (317; 417), and at least one detector configured to receive a signal indicative of a sensed voltage.

Description

[Technical field]

[0001] The present disclosure relates to a probe for surgical use for sensing magnetic markers, and a detection system including such a probe. [Background technology]

[0002] In the field of sensitive probes for the detection of magnetic markers, it is known to use a combination of a drive coil and a sense coil to determine the proximity of a magnetic marker to the probe. A drive magnetic field may be generated by supplying an alternating current to the drive coil. The drive magnetic field induces a response from the magnetic marker, which in turn induces a sense voltage in the sense coil. The sense voltage induced in the sense coil may be processed by a signal processor and a signal indicative of the marker position may be output to a user. Thus, by measuring and interpreting the sense voltage from the sense coil, the proximity of the marker to the probe may be determined.

[0003] In known probes, a single drive coil may be positioned in juxtaposition with a sense coil positioned near the tip of the probe. A relatively long drive coil is used to generate a relatively strong drive magnetic field, which increases the sensitivity of the probe, allowing the marker to be detected at a greater distance from the probe. However, the magnetic field generated by a long drive coil exhibits significant magnetic flux variations. When the long drive coil moves axially (i.e., parallel to its long axis) relative to the magnetic marker, the marker experiences a varying magnetic flux and a reversal of flux direction. This causes a varying sense voltage induced from the marker to the sense coil. The cube root of the sense voltage (typically measured in microvolts, μV) can be used to map the varying sense voltage around the probe, due to the wide range of sense voltage values ​​typically recorded. When the cube root of the sense voltage is mapped in two dimensions, significant "side lobes" that project laterally (i.e., perpendicular to the longitudinal axis of the drive coil) can be observed. In three dimensions, these side lobes extend circumferentially around the probe. These side lobes result in phase reversals or phase shifts in the sense voltage measured from the marker as the probe moves axially relative to the marker alongside the drive coil. These phase reversals can interfere with the signal output to the user and can make it difficult for the probe user to determine the position of the marker relative to the probe.

[0004] The size of the side lobes in the sense voltage, and the extent to which they extend away from the drive coil, depends on the strength of the drive field and the dimensions of the drive coil. If a long drive coil is used, the side lobes in the sense voltage may extend beyond or outside the probe housing. Thus, a phase reversal of the sense voltage occurs when the probe moves axially relative to a marker that is outside the probe housing. This can be avoided by increasing the diameter of the probe housing so that the side lobes in the sense voltage do not extend beyond the probe housing. In this case, no phase reversal is observed when the probe moves axially relative to a marker that is outside the probe housing. Thus, the sense voltage may be easier to interpret. However, large diameter probes are often undesirable for use in surgical procedures because of the increased size of the surgical incision required when the probe is used.

[0005] The extent to which the side lobes extend away from the drive coil can be reduced by using a drive coil of shorter length. However, using a shorter drive coil typically reduces the strength of the drive field beyond what can be produced without increasing the drive current and creating excessive thermal effects. Using a smaller drive field reduces the sensitivity of the probe. Summary of the Invention [Problem to be solved by the invention]

[0006] There remains a need for a probe that does not experience phase reversal in the sense voltage as the probe moves axially relative to the marker. It is desirable for the probe to have a small diameter, thereby enabling its use in a variety of surgical applications, while retaining high sensitivity, and allowing the marker to be detected at a relatively large distance from the probe. [Means for solving the problem]

[0007] According to a first aspect, the present disclosure provides a surgical probe for sensing a magnetic marker. The probe comprises a first coil set, the first coil set including a first coil of a first coil type disposed between a first pair of coils of a second coil type connected in series. The first coil type can be either a sensing coil or a driving coil, and the second coil type can be either a driving coil or a sensing coil, respectively. Electromagnetically, the two possible arrangements are interchangeable, and the result is electromagnetically the same when the sensing coil and the driving coil are swapped. However, preferably, the first coil type is a sensing coil and the second coil type is a driving coil. This allows the driving coil to be located at the distal end of the probe to maximize the driving field in the vicinity of the magnetic marker, as disclosed below. Furthermore, the driving coil typically uses a larger gauge wire than the sensing coil, and carries more current without excessive heating. Thus, providing two driving coils allows for more space and potentially more turns to be added. Thus, the first coil set preferably includes a first sense coil disposed between a first pair of series-connected drive coils.

[0008] The probe further includes a balance element, the balance element axially spaced from the first coil set along the length of the probe.

[0009] The first coil set and balance element may be suitably configured such that as the probe moves axially along its length relative to the magnetic marker, the marker induces a sense voltage exhibiting a monophasic change. The balance element may generate a sense voltage that fully or partially offsets a sense voltage induced in one or more sense coils of the first coil set by one or more drive coils of the first coil set. For example, the balance element may generate a sense voltage that fully or partially offsets a sense voltage induced in the first sense coil by the first drive coil pair. This means that the net sense voltage may be attributable entirely or mostly to the voltage induced from the magnetic marker.

[0010] In some implementations, the balance element may include a second coil set including a second coil disposed between a second pair of coils. Preferably, the second coil may be of the same coil type as the first coil, and each of the second pair of coils may be of the same coil type as each of the first pair of coils.

[0011] In some implementations, the balance element may comprise a second coil set including a second coil disposed axially proximate to the first coil set and a third coil disposed axially away from the first coil set such that the second coil is interposed between the first coil set and the third coil. Preferably, the second coil may be of the same coil type as the first coil and the third coil may be of the same coil type as each of the first coil pairs.

[0012] Preferably, all of the coils of one of the first and second types are connected in series and may be wound in the same direction, while the coils of the other of the second and first types may be connected in anti-series or may be wound in opposite directions to each other.

[0013] Preferably, all of the drive coils of the first and second coil sets are connected in series and the first and second sense coil sets are connected in anti-series, particularly when each set includes a single sense coil. However, in some implementations, all of the first and second sense coil sets may be connected in series and the first and second drive coil sets may be connected in anti-series, particularly when each set includes a single drive coil.

[0014] Thus, the drive coils of the first and second coil sets may be connected in series. One or more sense coils of the second coil set may be coupled in anti-series with one or more sense coils of the first coil set. Alternatively, one or more sense coils of the second coil set may be wound in the opposite direction to one or more sense coils of the first coil set.

[0015] According to a second aspect, the present disclosure provides a detection system for identifying the location of a magnetic marker. The system includes a probe for surgical use. The probe may include any of the features described above. The system includes a magnetic field generator arranged to drive an alternating magnetic field through one or more drive coils and balance elements of a first coil set; preferably through a first drive coil pair and balance element. The system includes at least one detector arranged to receive a signal indicative of a sensed voltage.

[0016] It will be understood that features described in connection with one aspect of the present disclosure may be incorporated in other aspects of the present disclosure, for example, a system of the present disclosure may incorporate features described with reference to an apparatus of the present disclosure, and vice versa.

[0017] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: [Brief description of the drawings]

[0018] [Figure 1(a)] 13 is a plot showing the cube root of the sensed voltage over 2D space for a probe with a single long drive and sense coil; [Figure 1(b)] Plot showing the sidesense response of the probe of Figure 1(a) to a marker moving axially relative to the probe, plotted for different lateral distances from the axial center of the probe. [Figure 2(a)] 13 is a plot showing the cube root of the sensed voltage over 2D space for a probe with a single short drive and sense coil; [Figure 2(b)] Plot showing the sidesense response to a marker moving axially relative to the probe in Figure 2(a), plotted for different lateral distances from the axial center of the probe. [Figure 3(a)] 1 is a plot showing the cube root of the sense voltage across 2D space for a probe according to one embodiment of the present disclosure, the probe comprising a sense coil sandwiched between a pair of drive coils; [Figure 3(b)] A schematic diagram showing the cube root of the sensed voltage in the region between two adjacent side lobes of the probe in Figure 3(a). [Figure 3(c)] Plot showing the sidesense response to a marker moving axially relative to the probe in Figure 3(a), plotted for different lateral distances from the axial center of the probe. [Figure 4(a)] FIG. 1 is a schematic longitudinal section through a probe according to one embodiment of the present disclosure, comprising two coil sets, each set comprising a sense coil sandwiched between a pair of drive coils. [Figure 4(b)] A plot showing the sensitivity of the probe in Figure 4(a) as a function of distance from the probe tip. [Figure 4(c)] Plot showing sensing range as a function of probe front diameter [Figure 4(d)] Plot showing sidesense response as a function of axial position along the probe for a marker moving along the probe in Figure 4(a). [Diagram 5] FIG. 1 is a schematic longitudinal cross-sectional view of a probe according to one embodiment of the present disclosure, comprising two coil sets, the first set including a sense coil sandwiched between a pair of drive coils, and the second set including a drive coil and a sense coil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] According to a first aspect, the present disclosure provides a probe for sensing a magnetic marker. The probe comprises a first coil set, the first coil set including a first coil of a first coil type disposed between a first pair of coils of a second coil type connected in series. The first coil type is either a sensing coil or a drive coil. The second coil type is either a drive coil or a sensing coil, respectively. Preferably, as described above, the first coil set comprises a first sensing coil disposed between a first pair of drive coils connected in series.

[0020] The probe further includes a balance element, the balance element being axially spaced from the first coil set along the length of the probe.

[0021] The first coil set and balance element are configured such that when the probe moves axially (ie, parallel to the long axis of the probe) relative to the magnetic marker, the marker induces a sensed voltage that exhibits a monophasic change.

[0022] The balance element may generate a sense voltage that fully offsets, partially offsets, or minimizes the sense voltage induced in the sense coil or coils by the drive coil or coils, respectively. Thus, if the first coil set comprises a first sense coil disposed between a first drive coil pair, the balance element may generate a voltage that cancels the voltage induced in the first sense coil from the first drive coil pair. This means that the net sense voltage measured as the marker moves axially relative to the probe may be attributable entirely, or at least in large part, to the sense voltage induced from the magnetic marker. The balance element may also cancel any environmental magnetic fields, such as the Earth's magnetic field.

[0023] The first coil set and balance element may be housed within a probe housing. The probe housing may have an elongated shape with a long axis. Here, a direction substantially parallel to the long axis is referred to as the axial direction. The probe housing may be substantially cylindrical in shape. The probe housing may have a graduated cylindrical profile such that the diameter of the probe housing increases or decreases in stages along the length of the probe. The maximum outer diameter of the probe housing may depend on the intended use of the probe. It is often desirable for the probe housing to have a narrow diameter to minimize the size of the surgical incision required when using the probe. The probe housing may have a maximum outer diameter of about 3 mm to about 20 mm, or 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 smaller diameter, for example, about 4 mm to about 6 mm. The first coil set and balance element may be disposed within the head of the probe housing proximate to the distal end of the probe.

[0024] The first coil set may be located within about 5 mm of the distal end of the probe, preferably within about 3 mm of the distal end of the probe, more preferably within 2 mm of the distal end of the probe. Advantageously, when the first coil set comprises a first sense coil located between a first drive coil pair, one of the drive coils of the first drive coil pair may be located closest to the distal end to maximise the magnetic drive field generated by the drive coil in the vicinity of the marker.

[0025] In operation, one or more drive coils of the first coil set may be excited by an alternating drive current to generate such a drive field. When the first coil set comprises a first drive coil pair, the first drive coil pair may be connected in series and may be conceptually considered as a single long drive coil split into two parts (i.e., a "split" long drive coil). The drive field extends around the first coil set and outside the probe housing. The strength of the drive field depends on the magnitude of the current passing through the or each drive coil and the number of turns of the or each drive coil. The drive field may induce a sensing response from a magnetic marker in proximity to the probe. The magnetic marker may suitably be a ferromagnetic marker, for example, as described in WO 2016 / 193753, WO 2019 / 180580, WO 2014 / 013235, the disclosures of each of which are incorporated by reference. The sensed response from the marker depends on the magnetic field experienced by the marker, which in turn depends on the magnitude of the current passing through the one or more drive coils and the relative positioning of the marker and the drive coil. The sensed response also depends on the magnetic permeability of the marker. The sensed response from the marker may be detected by one or more sense coils of the first coil set, preferably the first sense coil, as a sensed voltage. The sensed voltage may be processed by a signal processor, which may generate an output. The output from the signal processor may be, for example, an audible signal, a visual signal, or a tactile signal. The output may be interpreted by a user and used to determine the position of the marker relative to the probe.

[0026] The variation in the sense voltage occurs because the magnetic marker, preferably the first sense coil, changes the magnetic flux passing through one or more sense coils of the first coil set. The magnetic marker can increase or decrease the magnetic flux passing through one or more sense coils of the first coil set. Thus, the sense voltage resulting from the marker depends on whether the magnetic marker increases or decreases the magnetic flux through one or more sense coils of the first coil set. The effect of the magnetic marker on the one or more sense coils depends on the drive magnetic field experienced by the marker. When the probe moves axially relative to the magnetic marker, the marker is exposed to a changing magnetic field from the one or more drive coils, respectively. Thus, the magnetic response induced in the magnetic marker changes and the magnetic flux induced in the one or more sense coils changes accordingly.

[0027] The one or more sense coils also detect a sense response from the drive magnetic field arising from the adjacent one or more drive coils of the first coil set. The sense response from the one or more drive coils, e.g., the first drive coil pair, is significantly greater than the sense response from the marker. Without the balance element, the response detected in the one or more sense coils is dominated by the response from the one or more drive coils, respectively. The balance element is used to offset the sense response from the one or more drive coils of the first coil set, e.g., the first drive coil pair, thereby allowing the sense response from the magnetic marker to be detected. The balance element can generate a voltage that offsets or minimizes the voltage induced in the one or more sense coils of the first coil set, e.g., the first sense coil, from the respective one or more drive coils of the first coil set, e.g., the first drive coil pair.

[0028] When mapping sensed voltages from magnetic markers around the periphery of the probe, the sensed voltage map shows side lobes that extend laterally away from the probe (i.e., perpendicular to the long axis of the probe). In three dimensions, the side lobes extend circumferentially around the probe.

[0029] For probes according to embodiments of the present disclosure, one or more sensing coils of the first coil set, e.g., the first sensing coil, may be coupled in series or anti-series to one or more drive coils or coils of the first coil set, e.g., the first drive coil pair, or may be wound in the same or opposite direction.

[0030] Preferably, the first pair of drive coils, if provided, are connected in series. This allows for the generation of a significant magnitude of the drive magnetic field, since the drive magnetic field is generated by both coils. By providing a pair of drive coils instead of a single drive coil, the length of each coil can be reduced. This can advantageously result in a lower overall inductance and reduced thermal distortion.

[0031] The inductance of each drive coil is, for example, proportional to the square of the number of turns in the coil, i.e.

number

[0032] By providing a shorter drive coil pair instead of a single drive coil, good magnetic flux density and a strong drive field can be maintained at the distal end of the probe. Axially spaced drive coils have less variation in magnetic flux density with axial position than a single long drive coil. The magnetic flux density pattern of axially spaced drive coils has less change in axial sign compared to the magnetic flux density pattern of a single long drive coil. By using a short drive coil pair rather than a single long drive coil, the extent of side lobes in the sense voltage extending laterally from the side of the probe as the marker moves axially relative to the marker is reduced. Good probe sensitivity is maintained because a strong drive field is maintained at the distal end of the probe. In some embodiments, the size of the side lobes can be minimized by placing a sense coil next to at least one drive coil. In embodiments of the present disclosure, the distance between the center of the first coil of the first coil type and the center of each coil of the first coil pair of the second type of coil, for example, the distance between the center of the first sense coil and the center of each drive coil, can be about 1 mm to about 3 mm.

[0033] The first coil pair of the second coil type, e.g. the drive coil, may include two identical coils, i.e. the coils may have the same dimensions as each other and include the same number of turns of wire.

[0034] Each drive coil may have, for example, an axial length of about 0.2 mm to 10 mm, preferably about 0.5 mm to about 2.5 mm.

[0035] The first sensing coil may have an axial length of about 0.5 mm to about 6 mm, more preferably about 0.75 mm to about 2 mm.

[0036] Each drive coil may include from about 10 to about 150 turns of wire, preferably from about 10 to about 60 turns of wire.

[0037] Each drive coil may have an outer diameter of about 0.5 mm to about 10 mm, more preferably about 1.5 mm to about 6 mm. The radius of the drive coil may be selected to suit the diameter of the probe.

[0038] The first sensing coil may have an average radius of about 0.5 mm to about 10 mm, more preferably about 1.5 mm to about 6.5 mm. The first sensing coil may have an average radius similar to that of the drive coil.

[0039] The first sensing coil may include about 50 to about 1000 turns of wire, preferably about 100 to about 500 turns of wire.

[0040] The first sensing coil may be formed from a wire having a diameter of about 0.01 to 0.3 mm, more preferably about 0.025 mm to 0.1 mm.

[0041] The first sensing coil can include about 3 to 20 layers, preferably about 8 to 10 turns, with each layer having about 5 to 50 turns, preferably about 15 to about 20 turns.

[0042] The probe housing may be hollow and may define a recess to accommodate the coil. The probe housing may have a wall thickness of about 0.2 mm to 3 mm, more preferably about 0.5 mm to about 1 mm.

[0043] To reduce thermal effects, an air gap may be required between the coil and the inner surface of the probe housing. The air gap may be about 0.2 mm to 3 mm, more preferably about 0.5 mm to about 1 mm in radial dimension.

[0044] The total axial distance spanned by the first coil set and balance element may be from about 10 mm to about 100 mm, more preferably from about 19 mm to about 30 mm. The axial spacing between the first sensing coil and the balance element may be from about 3 mm to about 100 mm, preferably from about 12 mm to about 15 mm.

[0045] Exemplary plots showing sense voltages across 2D space and sense response plots of a probe including comparative drive and sense coil arrangements are shown in Figures 1(a), 1(b), 2(a) and 2(b). Exemplary plots showing sense voltages across 2D space and sense response plots of a probe having a coil arrangement according to an embodiment of the present disclosure are shown in Figures 3(a) and 3(c). For simplicity, balance elements are not shown in Figures 1(a)-3(c).

[0046] FIG. 1(a) shows the cube root of the sense voltage in microvolts, μV, over a 2D space 2 for a probe 3 moving axially relative to a marker, which includes a long drive coil 1 that extends axially along the probe 3. The cube root of the sense voltage is plotted due to the large variation in the sense voltage. The drive coil 1 is approximately 5 mm long. The long drive coil 1 is placed in juxtaposition with a sense coil 5 located towards the distal tip of the probe 3. The drive coil 1 and sense coil 5 are coiled in opposite directions. Mapping the cube root of the sense voltage 2 around the drive coil 3 in two dimensions for the probe 3 moving axially relative to the marker, one can see prominent side lobes 4a, 4b that extend laterally away from the drive coil 1 beyond the outer housing of the probe 3 (not shown). In three dimensions, these side lobes 4a, 4b form part of a ring that extends circumferentially around the probe 3. In operation, as the probe 3 moves axially outside the probe housing (i.e., parallel to the length of the probe 3) relative to the marker, the marker is subjected to a varying magnetic flux that reverses direction multiple times. As a result, the sensing response induced in the sensing coil from the marker reverses phase as the marker moves axially relative to the probe 3.

[0047] This is shown in Figure 1(b), which plots the side-sense response in μV as a function of position in mm for a marker moving axially relative to the probe 3 along the length of the probe 3 at different distances from the axial centre of the coil. The side-sense response is proportional to the sense voltage induced in the first sense coil. The x-axis shows the relative position of the magnetic marker along the length of the probe 3, which is superimposed on the plot for reference. In this example, the drive coil 1 is a 5 mm drive coil extending from -1 mm to -6 mm, with the tip of the probe at 0. The sense voltage depends on the strength of the drive magnetic field at the location of the marker (which depends on the length and diameter of the drive coil 1, the current passing through the drive coil 1, and the lateral proximity of the marker to the probe 3). The sense voltage also depends on the lateral distance between the marker and the first sense coil 7a (i.e. the distance orthogonal to the length of the probe). The different plots show the sense response for markers positioned at different lateral distances from the centre of the probe 3. As the lateral distance from the probe 3 increases, the variation in the sensed response flattens out. At relatively small distances from the center of the probe 3, for example 6 mm from the center of the probe coil, phase inversions 8a, 8b can be seen in the sensed response. As the distance from the center to the marker increases, the sensed response flattens out. For example, at a distance of 10 mm from the center of the probe, a ripple 9 can be seen in the sensed response as the probe 1 moves axially relative to the marker, but no phase inversions are observed. For the probe 3 shown in FIG. 1(a) with a single long drive coil, two phase inversions can be observed as the probe 3 moves axially relative to the marker, even at a relatively large distance from the center of the drive coil 1. For example, at a distance of 7.5 mm from the center of the probe, phase inversions 10a, 10b can be seen in the sensed response as the probe 3 moves axially relative to the marker. Thus, even for a relatively large diameter probe, for example a 15 mm diameter probe, phase inversions can be observed in the sensed response as the probe 3 moves axially relative to the marker. The sensed response is processed by a signal processor and output to a user.Phase reversals in the sensed response can affect the output, which can be confusing for a probe user when interpreting the sensed response to identify the location of a marker relative to the probe.

[0048] It will be appreciated that phase reversal outside the probe housing can be avoided by simply using a larger diameter probe housing so that a greater distance is maintained between the drive coil and the magnetic marker. However, this may be undesirable as it increases the size of the surgical incision required when the probe is used. From a surgical standpoint, it is preferable that the probe housing diameter be no larger than required to accommodate the coil, the wall thickness of the housing, and any air gaps (if used). Phase reversal can also be avoided by reducing the length of the drive coil, as shown in FIG. 2(a). This reduces the size of the side lobes in the sense voltage, but also reduces the strength of the drive magnetic field extending from the probe tip. This reduces the sensitivity of the probe.

[0049] The probe 301 of FIG. 2(a) includes a shorter drive coil 101 having a length of 2.5 mm, positioned adjacent to the sense coil 105. The magnetic flux generated by the drive coil 101 has less axial variation than the drive coil 1 shown in FIG. 1(a). The side lobes 104a, 104b of the cube root sense voltage map 102 that extend laterally away from the probe 103 are less pronounced. The magnetic flux extending from the tip of the probe 103 is also less than the probe 3 of FIG. 1, which means that the sensitivity of the probe 103, or the distance at which the probe 103 can detect a marker, is reduced.

[0050] FIG. 2(b) is the same type of plot as shown in FIG. 1(b) and shows the side sense response as a function of position as the marker moves axially relative to the probe 103 of FIG. 2(a) for markers placed at different lateral distances from the central axis of the probe. Similar to plot 7 for probe 3 of FIG. 1(b), phase reversals 108a, 108b in the sense response are observed at relatively short distances from the center of the probe 103 (shown for curves at 6 mm and 6.5 mm from the center of the drive coil). However, the sense response flattens out at shorter lateral distances from the center of the probe 103 because the side lobes 104a, 104b are less pronounced. For lateral distances greater than about 7 mm from the center of the probe 103, no phase reversals are observed in the sense response. Thus, for larger probe sizes with a diameter of about 15 mm, no phase reversals are observed outside the probe housing as the marker moves axially along the length of the probe 103. However, the sensitivity of the probe 103 shown in FIG. 2 is less than that of the probe 3 of FIG. 1 due to the reduced magnetic flux extending from the probe tip.

[0051] FIG. 3(a) illustrates an exemplary probe 203 and the cube root of the sense voltage in 2D space 202 generated from the current passing through the drive coils 201a, 201b of the probe 203, according to one embodiment of the present disclosure. For simplicity, balance elements are not shown. A sense coil 205 is interposed between the first pair of drive coils 201a, 201b. Each drive coil 201a, 201b has a length of about 2.5 mm, so that the combined length of the drive coils 201a, 203(b) is similar to the length of the single long drive coil 1 described above with reference to FIG. 1(a). The magnetic flux extending from the tip of the probe 203 resulting from the current flowing through the drive coils 201a, 201b is similar to the magnetic flux from the tip of the probe 3 of FIG. 1(a), and the sensitivity of the probe 203 of FIG. 3(a) is comparable to that of the probe 3 of FIG. 1(a). Advantageously, because the drive coils 203a, 203b are provided as a pair, the total inductance of the drive coils 203a, 203b is lower than that of the drive coil 1 of FIG. 1(a), thus reducing thermal distortion.

[0052] Advantageously, by effectively splitting the single drive coil of FIG. 1(a) into a drive coil pair 201a, 201b having the same overall length, the cube root of the sense voltage 202 to the side of the probe 203 of FIG. 3(a) is reduced compared to the probe 3 of FIG. 1(a) without sacrificing sensitivity. When the cube root of the sense voltage is mapped in two dimensions, each drive coil 201a, 201b results in a small side lobe pair 204a, 204c and 204b, 204d (in three dimensions, the pairs of side lobes 204a, 204c and 204b, 204d form part of two rings extending circumferentially around the probe 203). Because there is a small spacing between the two drive coils 201a, 201b, the side lobes 204a, 204b and 204c, 204d on the same side of the probe overlap each other. This is shown in Figure 3(b), which results in a generally flat sensed voltage region 212 between the side lobes 204a / 204b and 204c / 204d. Advantageously, these smaller side lobes 204a, 204b, 204c, 204d, compared to the larger side lobes 4a, 4b of Figure 1, are less problematic for a user attempting to interpret a marker position using the probe 203 because the side lobes 204a, 204b, 204c, 204d may not extend outside the probe 203 housing. Additionally, the overlap between the side lobes 204a, 204b and 204c, 204d on the same side of the probe 203 results in a generally flat sensed voltage region 212 between the side lobes 204a, 204b and 204c, 204d, which may allow for more accurate positioning of the sense coil 205 between the drive coils 201a, 201b.

[0053] FIG. 3(c) is a plot 207 showing the sensed response from the probe 203 of FIG. 3(a) as it moves axially relative to the marker, for markers positioned at a range of different transverse distances from the center of the probe 203. As a result of the side lobes 204a, 204b and 204c, 204d, at short lateral distances from the center of the coil, the sensed response shows multiple phase reversals 208a, 208b, 208c, 208d as the marker moves axially relative to the probe 203. However, similar to the plot 107 of the probe 103 of FIG. 2(a), the sensed response flattens out at larger distances from the center of the probe 203. At lateral distances greater than about 6.5 mm from the center of the probe, the sensed response is generally flat and does not show phase reversals in the sensed voltage. This means that even for smaller probe diameters, such as a 13 mm diameter probe, no phase reversals are observed outside the probe housing as the probe 203 moves axially relative to the marker.

[0054] Thus, the coil arrangement of probe 203 of FIG. 3(a) can enable good sensitivity, as a result of the combined length of the two drive coils 201a, 201b, which is comparable to the sensitivity of the coil configuration of probe 3 of FIG. 1(a). The coil arrangement of probe 203 of FIG. 3(a) provides lower inductance, and therefore less thermal distortion, and smaller side lobes, than the coil configuration of probe 3 of FIG. 1(a). The smaller side lobes of the coil arrangement of probe 203 of FIG. 3(a) mean that a smaller diameter probe housing can be used without phase reversal occurring outside the probe housing.

[0055] For simplicity, Figures 1(a)-3(c) omit a balance element that counteracts the effect of the drive coils on the sense response. The balance element is configured and arranged to counteract a sense response generated in the first sense coil that is directly attributable to the first drive coil pair, and can detect a sense response from the marker.

[0056] While any balancing element that acts in use to generate voltages that counteract the voltages induced in the one or more sense coils from the one or more drive coils, respectively, may be used, in some embodiments the balancing element may suitably comprise a second coil set. The second coil set may include a second coil disposed between a second pair of coils. The second coil may be of the same coil type as the first coil. Each of the second pair of coils may be of the same coil type as each of the first pair of coils. Thus, preferably the second coil set may comprise a second sense coil interposed between a second pair of drive coils.

[0057] In some implementations, the second coil set may include a second coil disposed axially proximate to the first coil set and a third coil disposed axially away from the first coil set, with the second coil interposed between the first coil set and the third coil. The second coil may be of the same coil type as the first coil. The third coil may be of the same coil type as each of the first coil pairs. Thus, preferably, the second coil set may include a second sense coil interposed between the first coil set and the second drive coil.

[0058] The second coil set may be axially spaced from the first coil set such that the second coil set is positioned proximal to the probe distal tip. Preferably, the distance between the first coil set and the balance element should be such that when the marker is positioned proximal to the distal end of the probe, the response signal from the marker is primarily due to the drive field from the first coil set without being significantly affected by the drive field generated by the balance element. When the marker is positioned proximal to the second coil set, the response signal from the marker is primarily due to the drive field from the second coil set and the first coil set may act as the balance element.

[0059] One or more drive coils of the second coil set, eg, a second drive coil pair, may be suitably connected in series with one or more drive coils of the first coil set.

[0060] One or more drive coils of the second coil set may be similar to one or more drive coils of the first coil set, respectively. Thus, for example, the second drive coil pair may be similar to the first drive coil pair.

[0061] The second coil set may be substantially identical to the first coil set.

[0062] The one or more sensing coils of the second coil set may be coupled in anti-series with the one or more sensing coils of the first coil set, or alternatively, the one or more sensing coils of the second coil set may be wound in the opposite direction to the one or more sensing coils of the first coil set, to produce the same effect in use.

[0063] Thus, the second sense coil may, for example, be coupled in series or anti-series with the drive coils of the first and second coil sets and coupled anti-series with the first sense coil. Alternatively, the second sense coil may be wound in the opposite direction to the first sense coil, which will have the same effect in use.

[0064] Similar to the one or more drive coils of the first coil set, the one or more drive coils of the second coil set may be excited by an alternating drive current to generate a drive magnetic field. For example, when both the first drive coil pair and the second drive coil pair are generating a drive magnetic field, a sense voltage is induced in both the first and second sense coils as a result of the drive magnetic field from their adjacent drive coils. When the first and second drive coil pairs are wound in the same direction and the first and second sense coils are coupled in anti-series or wound in opposite directions, opposing sense voltages are induced in the first and second sense coils from their adjacent drive coils. This means that the sense voltages due to the drive coils adjacent to a sense coil cancel each other. Thus, the sense voltage and sense response may be substantially entirely due to the sense voltage induced by the magnetic marker in proximity to the probe.

[0065] The second drive coil pair, if provided, may comprise two substantially identical coils, i.e. the coils may have substantially identical dimensions and may comprise the same number of turns of wire. Each drive coil may have an axial length of about 0.2 mm to about 10 mm, preferably about 0.5 mm to about 2.5 mm. The second sense coil may have an axial length of about 0.5 mm to about 6 mm, preferably about 0.75 mm to about 2 mm. Each drive coil may comprise about 10 to about 150 turns of wire, preferably about 10 to about 60 turns of wire. Each drive coil may have an average radius of about 0.5 mm to about 10 mm, preferably about 1.5 mm to about 6 mm. The radius of the drive coil may be suitable for the diameter of the probe. The second sense coil may have an average radius of about 0.5 mm to about 10 mm, preferably about 1.5 mm to about 6.5 mm. The second sense coil may have an average radius similar to that of the drive coil. The second sensing coil may include about 50 to about 1000 turns of wire, preferably about 100 to 500 turns of wire. The distance between the second sensing coil and the adjacent drive coil may be about 0.4 to about 0.8 mm, preferably about 0.7 mm.

[0066] The second sensing coil may be formed from a wire having a diameter of about 0.01 to 0.3 mm, preferably about 0.025 to 0.1 mm. The second sensing coil may include about 8 to about 10 layers, each layer having 5 to 50 turns, preferably about 15 to 20 turns.

[0067] The total axial length occupied by the first and second coil sets, including the space between adjacent coils, may be from about 10 mm to about 100 mm, preferably from about 19 mm to about 30 mm. The axial spacing between the midpoint of a first coil of a first coil type, e.g., the first sensing coil, and the midpoint of the balance element may be from about 3 mm to about 100 mm, preferably from about 12 mm to about 15 mm. For example, the axial spacing between the first and second sensing coils may be at least 10 mm to reduce the risk that the second sensing coil will sense a magnetic marker and interfere with the sensing signal from the first sensing coil.

[0068] In some implementations of the present disclosure, as described above, the second coil set may include a second coil of the same coil type as the first coil positioned axially proximate to the first coil set, and a third coil of the same coil type as each of the first coil pair positioned axially away from the first coil set, such that the second coil is interposed between the first coil set and the third coil.

[0069] Thus, the probe may, for example, comprise a second sensing coil and a drive coil disposed distal to the second sensing coil, but no additional drive coil proximal to the second sensing coil. Instead, the proximal drive coil furthest from the probe tip of the first drive coil pair may serve as the proximal drive coil for the first drive coil pair and also as the distal drive coil for a coil arrangement corresponding to the second drive coil pair of the kind described above. The drive coil furthest from the probe tip may thus play a role in both the first and second coil sets, allowing one drive coil to be omitted compared to the above configuration. A similar arrangement is obtained when the first coil set comprises a single drive coil between two sensing coils: the second coil set may comprise a single distal drive coil and at least one proximal sensing coil, whereby the distal drive coil is interposed between the proximal one of the sensing coils of the first coil set and at least one proximal sensing coil of the second set.

[0070] Conversely, in some implementations, the second coil set may comprise a single drive coil proximal to the sense coil and may be axially spaced from the first coil set such that the second coil set is positioned proximal to the probe distal tip.

[0071] According to a second aspect, the present disclosure provides a detection system for identifying the location of a magnetic marker. The detection system includes a probe. The probe may include any of the features described above. The system includes one or more drive coils of a first coil set, preferably a first drive coil pair, and a magnetic field generator arranged to drive an alternating magnetic field through a balance element. The system suitably includes at least one detector configured to receive a signal indicative of a sense voltage. In some embodiments, the detection system may further include one or more magnetic markers for inducing a sense voltage in one or more sense coils, e.g., the first sense coil. The system may include a signal processor for processing the sense voltage.

[0072] 4(a) shows a schematic cross-sectional view of a distal end portion of a probe 303 according to one embodiment of the present disclosure. The probe 303 includes a substantially cylindrical probe housing 311 having a diameter of 10 mm. In other embodiments, the housing may include sections of different diameters and / or have a maximum outer diameter in the range of about 3 mm to about 20 mm, depending on the intended use of the probe. The relatively small probe diameter of the probe may facilitate improved visualization of the examined surgical site and increased accuracy in identifying marker locations, and may reduce the size of the incision that needs to be made by the surgeon when using the probe.

[0073] The probe housing 311 has a thickness of 1 mm, indicated by the letter "a". In other embodiments, the probe housing may have a thickness of about 0.5 mm to about 2 mm. There is an air gap of about 1 mm, indicated by the letter "b", between the inner surface 312 of the probe housing 311 and the coil within the housing 311, which helps to avoid thermal drift. For smaller diameter probes, for example having an outer diameter of about 4 mm to about 6 mm, an air gap may not be required between the inner surface of the probe housing and the coil. Instead, a coating can be applied to the inner surface of the housing. Advantageously, this may allow for further reduction in probe size and may allow less material to be used within the probe. This may allow a constant probe temperature to be more easily achieved and thermal drift to be reduced.

[0074] The probe housing 311 defines a recess that accommodates a first coil set 313 proximate the distal sensing end 315 of the probe 303 and a second coil set 317 axially separated from the first coil set 313 along the length of the probe 303. There is a gap (indicated by the letter "b") of approximately 2 mm between the inner surface of the probe housing at the probe tip and the molding material surrounding the coils 313, 317.

[0075] The first coil set 313 comprises a first sense coil 305 interposed between the first drive coil pair 301a, 301b. The second coil set 317 comprises a second sense coil 319 interposed between the second drive coil pair 321a, 321b. All four drive coils 301a, 301b, 321a, 321b are wound in the same direction (i.e., in series) and connected to an alternating current source (not shown). In operation, the drive coils 301a, 301b, 321a, 321b generate a drive field that induces a magnetic moment in a marker (not shown) in proximity to the probe 303.

[0076] The axial spacing between the first and second coil sets is 12.6 mm, indicated by the letter "j." By spacing the first and second coil sets 313, 317 to span a significant length of the distal end portion of the probe 303, the sensitivity or sensing distance of the probe 303 can be increased, such that markers can be detected at a greater distance from the probe tip 315. Each drive coil 301a, 301b, 321a, 321b has a length of about 2 mm and an average radius of about 4 mm. The four drive coils 301a, 301b, 321a, 321b are substantially identical to one another, and each drive coil 301a, 301b, 321a, 321b includes six radially stacked layers, each layer having six turns of 330 μm diameter wire (totaling 36 turns). By using a relatively short drive coil pair 301a, 301b, 321a, 321b to generate the drive field rather than a single long drive coil, the inductance of the drive coils 301a, 301b, 321a, 321b is reduced and a lower voltage can be used to generate an appropriate drive field, which may reduce heating in the probe 303.

[0077] The sensing coils 305, 319 are wound in opposite directions but are otherwise substantially identical to one another. Each sensing coil 305, 319 comprises nine radially stacked layers, with each layer having 18 turns, for a total of 162 turns per coil.

[0078] Both the first and second sense coils 305, 319 have an average radius of about 4.5 mm and a length of about 2 mm. Each sense coil 305, 319 is formed from 110 μm diameter wire. The spacing between each sense coil 305, 319 and its adjacent drive coil is about 0.7 mm, indicated by the letter "e".

[0079] Each sense coil 305;319 is disposed between two drive coils 301a,301b;321a,321b, and the sense coils 305,319 are wound in opposite directions such that the drive coils 301a,301b,321a,321b generate opposing signals in the sense coils in use. Thus, the direct effects of the drive coils 301a,301b,321a,321b on the sense coils 305,319 can be cancelled out during processing of the sensed voltage signals.

[0080] As disclosed herein, in variations of this embodiment, each of the drive coils 301a, 301b; 321a, 321b and the sense coils 305, 319 may be replaced with other types of coils (i.e., sense coils or drive coils, respectively), and each of the first and second coil sets 313, 317 comprises a single drive coil interposed between a pair of sense coils, the first and second drive coil sets 313, 317 are wound in opposite directions to each other or connected in anti-series, and the sense coil pairs of the first and second coil sets are wound in the same direction and connected in series.

[0081] The probe 303 of this embodiment is capable of detecting magnetic markers at a distance or sensing range of up to about 15 mm from the tip 315 of the probe 303. This is shown in Figure 4(b), which plots the sensitivity (measured as the cube root of the sense voltage in μV) as a function of distance (mm) from the tip of the probe. Below 0.2 μV (shown by the dashed line), which corresponds to a sense voltage of 8 nV, the signal is considered too weak for accurate detection.

[0082] 4(c) is a plot showing how sensing range (mm) varies with probe front diameter (mm) for a probe according to an embodiment of the present disclosure, the front portion being provided within a probe housing, the probe front diameter being determined, at least in part, by the coil diameter and spacing.

[0083] As the probe moves axially relative to the marker, the magnetic fields from the first and second drive coil pairs 301a, 301b, 321a, 321b induce a magnetic moment in the marker. The induced magnetic moment in the marker induces a sense voltage in the sense coil 305 proximate the probe tip 315. The drive coils 301a, 301b, 321a, 321b also induce equal and opposite sense voltages in the sense coils 305, 319. Thus, the net sense voltage from the two sense coils 305, 319 can be substantially entirely attributable to the sense response from the marker, as the sense voltages from the drive coils cancel each other. The change in sense voltage as the probe 303 moves axially relative to the marker is shown in FIG. 4(d).

[0084] Plot 307 shown in FIG. 4(d) shows the side sense response from the sense coils 305, 319 of the probe 303 shown in FIG. 4(a) as the probe 303 moves axially relative to the marker. The sense response is plotted for markers at lateral distances of 6.5 mm, 7 mm, and 7.5 mm from the center of the probe. The x-axis shows the relative position of the magnetic marker along the length of the probe 303, which is superimposed on the plot 307 for reference. Each of the drive coil pairs 301a, 301b; 321a, 321b results in two corresponding side lobes of sense voltage that extend circumferentially around the probe 303. For a marker moving axially relative to the probe 303, at a fixed lateral distance from the probe 303, the four drive coils 301a, 301b; 321a, 321b give rise to four peaks 325, 327, 329, 331 in the sense response, which correspond to the side lobes. Because the spacing between the drive coils in each pair is small (approximately 5.5 mm center-to-center), the side lobes arising from the drive coils in a pair overlap each other as described above, and the peaks partially overlap as shown in Figure 4(d).

[0085] As discussed above with reference to FIG. 3(a), the coil configuration of FIG. 4(a) may result in relatively small side lobes compared to the coil configuration of FIG. 1(a) because the drive coil configuration reduces the magnetic flux extending from the sides of the probe 303 while retaining a moderately strong magnetic flux extending from the probe tip 315. Side lobes in the sense response are further reduced as a result of the small center-to-center spacing of about 3.5 mm for each drive coil 301a, 301b and 321a, 321b in the pair. As a result of these smaller side lobes, no phase reversals are observed in the sense response where either the first or second coil set passes along the marker outside the probe housing (i.e., in this embodiment, at a lateral distance of more than 5 mm from the center of the coil). A single phase reversal is observed as the marker moves relative to the probe 303 in the region intermediate the first and second coil sets. This is in contrast to the sensing response observed for a probe having the coil configuration shown in Figure 1(a), which shows multiple phase reversals outside the probe housing with the probe moving axially relative to the marker. Thus, the probe 303 of Figure 4(a) advantageously exhibits strong sensitivity and low thermal distortion, and only a single phase reversal as the probe moves axially relative to the marker as a result of the short pair of drive coils and small spacing between the drive coils.

[0086] FIG. 5 shows a schematic longitudinal cross-sectional view of a distal end portion of a probe 403 according to a different implementation of the present disclosure. The probe 403 is similar to the probe 303 of FIG. 4(a) and includes a substantially cylindrical probe housing 411. The probe housing 411 defines an internal recess that accommodates a first coil set 413 proximate a distal sensing end 415 of the probe 403. The first coil set 413 includes a first sense coil 405 interposed between a first drive coil pair 401a, 401b. A second coil set 417 is axially spaced apart from the first coil set 413 along the length of the probe 403. In this implementation, the second coil set 417 includes a second sense coil 419 and a drive coil 421 disposed proximal to the second sense coil 419, but the drive coil is not disposed distal to the second sense coil 419, but intermediate the first coil set 413.

[0087] 4(a), the first drive coil pair 301a, 301b and the second drive coil pair 321a, 321b are all wound in the same direction (i.e., in series) and connected to an alternating current source (not shown). The sense coils 305, 319 are wound in opposite directions but are otherwise substantially identical to one another.

[0088] In the embodiment shown in FIG. 5, the first coil set 413 includes a drive coil pair 401a, 401b, while the second coil set 417 includes only a single drive coil 421. All of the drive coils 401a, 401b, 421 are wound in the same direction (i.e., in series) and connected to an alternating current source (not shown). In operation, at least the drive coils 401a, 401b generate a drive field to induce a magnetic moment in a marker (not shown) proximate to the probe 403. The proximal drive coil 401b of the first coil set 413, which is further from the edge of the probe tip, performs the function of the corresponding proximal drive coil 301b in FIG. 4(a) and also performs the function of the distal drive coil 321a of the second drive coil set 317, which is closer to the probe tip, as shown in FIG. 4(a).

[0089] The drive coils 401a, 401b, 421 are all wound in the same direction (i.e., in series) and connected to an alternating current source (not shown). In operation, the drive coils 401a, 401b, 421 generate a drive field that induces a magnetic moment in a marker (not shown) proximate to the probe 403. The outer drive coils 401a, 421 (i.e., the drive coil 401a closest to the sensing end of the probe 415 and the single drive coil 421 forming part of the second coil set 417) each comprise ten radially stacked layers, each layer having ten turns of 330 μm diameter wire (totaling 100 turns). The proximal coil 401b (i.e., the central drive coil) of the first coil set 413 comprises seven radially stacked layers, each layer having seven turns of 330 μm diameter wire (totaling 49 turns). The proximal coil 401b has fewer turns than each of the outer drive coils 401a, 421, and the proximal coil 401b has fewer turns than the combined central drive coils 321a, 301b in the configuration shown in Figure 4(a) (the central drive coils 321a, 301b in Figure 4(a) have a total of 72 turns). The fewer turns in the proximal coil 401b compared to the outer drive coils 401a, 421 helps maintain a constant detection signal along the axial length of the probe 403 and can facilitate easier manufacture of the probe.

[0090] Similar to the probe 303 of FIG. 4(a), the sense coils 405, 419 of FIG. 5 are wound in opposite directions but are otherwise substantially identical to each other. Each sense coil 405, 419 comprises nine radially stacked layers, each layer having 18 turns, totaling 162 turns per coil. Each sense coil 405; 419 is disposed between two adjacent ones of the drive coils 401a, 401b; 421, and the sense coils 405, 419 are wound in opposite directions to each other, so that the drive coils 401a, 401b, 421 generate opposite signals in the sense coils 405, 419 in use. Thus, the direct effect of the drive coils 401a, 401b, 421 on the sense coils 405, 419 can be substantially cancelled out during processing of the sensed voltage signal.

[0091] 4(a), in a variation of this embodiment, each of the drive coils 401a, 401b; 421 and sense coils 405, 419 can be replaced with the other type of coil (i.e., sense coil or drive coil, respectively), such that the first coil set 413 comprises a single drive coil interposed between a pair of sense coils, and the second coil set 417 comprises a single drive coil and a single sense coil, with the single drive coil interposed between the single sense coil and the first coil set. In such a case, the first and second drive coil sets 413, 417 can be wound in opposite directions to each other or connected in anti-series, but the sense coils of the first and second coil sets can all be wound in the same direction and connected in series.

[0092] 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 thus to be understood that numerous modifications can be made to the exemplary embodiments and other configurations can be devised without departing from the scope of the present disclosure as defined by the appended claims.

[0093] 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.

[0094] Although various details have been described in the foregoing description, it will be understood that various aspects of the techniques for operating a diagnostic and / or surgical guidance system suitable for identifying, locating, tracking, and detecting the position of one or more implanted markers may be practiced without these specific details. Those skilled in the art will recognize that the components (e.g., operations), devices, objects, and the accompanying discussions described herein are used as examples to clarify the concepts, and various configuration modifications are contemplated. Thus, as used herein, the specific examples described and the accompanying discussions are intended to be representative of their more general classes. In general, the use of any specific example is intended to represent its class, and the absence of a particular component (e.g., operation), device, and object should not be construed as limiting.

[0095] 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 without departing from the scope of the present disclosure and will occur to those skilled in the art. 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.

[0096] 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. It will also be understood by the reader 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 not be desirable and therefore may not be present in other embodiments.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

Claims

1. A surgical probe for detecting magnetic markers, A first coil set including a first sensing coil positioned between a first pair of drive coils connected in series; and Balance elements spaced axially away from the first coil set along the length of the probe Equipped with, The balancing element is configured and arranged to generate a sensing voltage that completely offsets, partially offsets, or minimizes the sensing voltage induced in the first sensing coil from the first drive coil pair. A probe characterized by the following features.

2. The probe according to claim 1, characterized in that the balancing element comprises a second coil set including a second sensing coil disposed between a second pair of drive coils.

3. The probe according to claim 1, characterized in that the total axial distance reached by the first coil set and the balance element is 19 mm to 30 mm.

4. The probe according to claim 1, characterized in that the aforementioned or each drive coil has an axial length of 0.5 mm to 2.5 mm.

5. The probe according to claim 1, characterized in that the aforementioned or each sensing coil has an axial length of 0.75 mm to 2 mm.

6. The probe according to claim 1, characterized in that the axial distance between the first sensing coil and the balance element is 12 mm to 15 mm.

7. The probe according to claim 1, characterized in that each drive coil has an average radius of 1.5 mm to 6 mm.

8. The probe according to claim 1, characterized in that each sensing coil has an outer diameter of 1.5 mm to 6.5 mm.

9. The probe according to claim 1, characterized in that each drive coil includes a wire with 10 to 60 turns.

10. The probe according to claim 1, characterized in that each sensing coil includes a wire of 100 to 500 turns.

11. The probe according to any one of claims 2 to 10, characterized in that the first drive coil pair and the second drive coil pair are connected in series.

12. The probe according to any one of claims 2 to 10, characterized in that the second sensing coil is coupled in reverse series with the first sensing coil.

13. The probe according to any one of claims 2 to 10, characterized in that the second sensing coil is wound in the opposite direction to the first sensing coil.

14. The probe according to any one of claims 1 to 10, characterized in that the first coil set and the balance element are housed within a probe housing, and the probe housing has a maximum outer diameter of 4 mm to 15 mm.

15. A detection system for determining the location of a magnetic marker, A surgical probe according to any one of claims 1 to 10; A magnetic field generator configured to drive an alternating magnetic field through the first pair of drive coils and the balance element; and At least one detector configured to receive a signal indicating a sensed voltage. A system equipped with these features.

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