Probe shape detection device, probe shape detection method, and probe shape detection program

Abstract

A probe shape detection device according to the present invention comprises a processor. The processor acquires prior information relating to a preset element design interval of a magnetic field-generating element disposed on the probe, acquires an element detection point indicating the position of the magnetic field-generating element, acquires information relating to the orientation of the magnetic field-generating element, sets a virtual first interpolation point at the periphery of the element detection point on the basis of the orientation information, calculates a first interpolation curve length of an interpolation curve formed by interpolation points obtained via an interpolation process that uses the element detection point and the first interpolation point as data points, sets a virtual second interpolation point on the basis of the first interpolation curve length and the element design interval, and estimates the shape of the probe via an interpolation process that uses the element detection point, the first interpolation point, and the second interpolation point as data points.

Description

Probe shape detection device, probe shape detection method, and probe shape detection program

[0001] This invention relates to a probe shape detection device, a probe shape detection method, and a probe shape detection program.

[0002] Endoscopic devices have long been widely used in the medical field. An endoscope is a medical device with a long, flexible insertion tube, which the operator inserts into the patient to observe the inside of the patient. Endoscopic images of the inside of the patient, captured by the endoscope, can be displayed on a monitor. However, it is difficult to determine from the endoscopic images how the endoscopic insertion tube is inserted into the patient.

[0003] Therefore, a probe shape detection device has been developed that allows the insertion status of an endoscope to be determined during endoscope insertion. This device includes a receiving antenna consisting of multiple transmitting coils built into the insertion section and multiple sensing coils arranged in a coil block, and a monitor that displays the insertion shape of the insertion section.

[0004] In this type of probe shape detection device, the shape of the endoscope can be estimated with high accuracy by narrowing the spacing between magnetic field generating elements placed within the endoscope insertion section and arranging a large number of magnetic field generating elements. However, in order to reduce the diameter of the endoscope insertion section, improve frame rate and noise immunity, and reduce costs, it is desirable to keep the number of elements placed within the endoscope as small as possible.

[0005] Therefore, Japanese Patent No. 5231681 (hereinafter referred to as Patent Document 1) and Japanese Patent No. 3722762 (hereinafter referred to as Patent Document 2) disclose a technology that enables high-precision shape estimation even with a reduced number of coils.

[0006] Patent No. 5231681 Patent No. 3722762

[0007] By adopting the proposals in Patent Documents 1 and 2, it is possible to accurately estimate the shape while reducing the number of elements placed inside the probe. However, even when adopting the proposals in Patent Documents 1 and 2, there was a problem that the shape estimation accuracy with a smaller number of elements was not sufficient. The present invention aims to provide a probe shape detection device, a probe shape detection method, and a probe shape detection program that can enable highly accurate shape estimation while further reducing the number of elements placed inside the probe.

[0008] A probe shape detection device according to one aspect of the present invention includes a processor, the processor acquires prior information regarding a pre-set element design interval of magnetic field generating elements arranged on the probe, acquires element detection points indicating the positions of the magnetic field generating elements, acquires information regarding the orientation of the magnetic field generating elements, sets a virtual first interpolation point around the element detection point based on the orientation information, calculates the length of a first interpolation curve of an interpolation curve obtained by interpolation processing using the element detection point and the first interpolation point as data points, sets a virtual second interpolation point based on the first interpolation curve length and the element design interval, and estimates the shape of the probe by interpolation processing using the element detection point, the first interpolation point and the second interpolation point as data points.

[0009] A probe shape detection method according to one aspect of the present invention involves acquiring prior information regarding a pre-set element design interval of magnetic field generating elements arranged on the probe, acquiring element detection points indicating the positions of the magnetic field generating elements, acquiring information regarding the orientation of the magnetic field generating elements, setting a virtual first interpolation point around the element detection point based on the orientation information, calculating the length of a first interpolation curve of an interpolation curve obtained by interpolation processing using the element detection point and the first interpolation point as data points, setting a virtual second interpolation point based on the first interpolation curve length and the element design interval, and estimating the shape of the probe by interpolation processing using the element detection point, the first interpolation point and the second interpolation point as data points.

[0010] A probe shape detection program according to one aspect of the present invention causes a computer to perform the following steps: acquire prior information regarding a predetermined element design interval of magnetic field generating elements arranged on the probe; acquire element detection points indicating the positions of the magnetic field generating elements; acquire information regarding the orientation of the magnetic field generating elements; set virtual first interpolation points around the element detection points based on the orientation information; calculate the length of a first interpolation curve of an interpolation curve obtained by interpolation processing using the element detection points and the first interpolation points as data points; set virtual second interpolation points based on the first interpolation curve length and the element design interval; and estimate the shape of the probe by interpolation processing using the element detection points, the first interpolation points and the second interpolation points as data points.

[0011] According to the present invention, it is possible to reduce the number of elements placed in the probe while enabling more accurate shape estimation.

[0012] This is a configuration diagram showing the probe shape detection device of the present invention. This is an explanatory diagram for explaining the state of receiving a magnetic field. This is an explanatory diagram showing the insertion state of the endoscope insertion section 1 into the large intestine C. Figure 4 is an explanatory diagram for explaining the method for accurately estimating the loop shape disclosed in Patent Document 2. This is an explanatory diagram for explaining the tangent virtual point Pvt as the first interpolation point. This is an explanatory diagram for explaining the tangent virtual point Pvt as the first interpolation point. This is a flowchart for explaining the operation of the first embodiment. This is an explanatory diagram for explaining the operation of the first embodiment. This is an explanatory diagram for explaining the operation of the first embodiment. This is an explanatory diagram showing the shape estimation result when the first embodiment is adopted. This is an explanatory diagram showing the shape estimation result when the first embodiment is adopted. This is a flowchart for explaining the operation of the second embodiment of the present invention. This is an explanatory diagram for explaining the method for determining the order j of the coil detection point and the tangent virtual point Pvt. This is a block diagram showing a modified example.

[0013] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0014] (First Embodiment) Figure 1 is a configuration diagram showing the probe shape detection device of the present invention. This embodiment makes it possible to estimate the shape with a relatively small number of coils with higher accuracy by using not only the three-dimensional position information of each coil in the probe but also the orientation information to determine the direction of the tangent to the shape curve at each coil position. In this embodiment, even when the spacing between coils is wide, the direction of the tangent at the coil position can be correctly determined, so the estimated shape is less likely to deviate significantly from the actual probe shape. In particular, this embodiment makes it possible to prevent the curves connecting the coils from bulging in a direction different from the actual shape.

[0015] The probe shape detection device shown in Figure 1 is equipped with a drive detection timing control circuit 11. The drive detection timing control circuit 11 controls the drive signal transmission circuit 7, the magnetic field detection signal receiving circuit 8, and the position and orientation estimation circuit 9. Each part of the probe shape detection device, including the probe shape estimation circuit 10, may be composed of a processor using a CPU (Central Processing Unit) or FPGA (Field Programmable Gate Array), or it may operate according to a program stored in a memory (not shown) to control each part, or some or all of the functions may be realized by hardware electronic circuits.

[0016] In Figure 1, the flexible, elongated endoscope insertion section 1 has an imaging device (not shown) at its tip. Images of the inside of the subject's body obtained by this imaging device are supplied to a video processor (not shown) for predetermined signal processing. The images processed by the video processor are supplied to a display device (not shown), and the endoscopic images of the inside of the body are displayed on the display screen of the display device.

[0017] To estimate the shape of the endoscope insertion section 1, multiple transmitting coils (filled areas) 2 are arranged in the endoscope insertion section 1, and the magnetic field generated by these coils 2 is received by a magnetic field detection device 4. Figure 2 is an explanatory diagram illustrating the state in which the magnetic field is received.

[0018] As shown in Figure 2, a probe 3 having multiple magnetic field generating elements (coils) 2 (filled area) is inserted into the endoscope insertion section 1. Multiple coils 2-1, 2-2, ... (hereinafter referred to simply as coil 2 when there is no need to distinguish between them) are attached to the probe 3 at predetermined intervals along its axis. By fixing the tip or rear end of the probe 3, multiple coils 2 are arranged at predetermined intervals in the axial direction of the insertion section 1. A high-frequency signal (drive signal) is applied to the multiple coils 2 from the drive signal transmission circuit 7, causing them to radiate electromagnetic waves 6 accompanied by a magnetic field into the surroundings. These electromagnetic waves 6 are received by the magnetic field detection device 4.

[0019] The magnetic field detection device 4 is positioned near a bed (not shown) on which the patient lies. The magnetic field detection device 4 is equipped with a coil unit 5A, and multiple magnetic field detection elements (sense coils) are arranged within this coil unit 5A. For example, the coil unit 5A is composed of, for example, three sense coils 5 wound in three directions, each with its coil surface orthogonal to the others. The magnetic field detection device 4 as a whole is equipped with, for example, four coil units 5A, i.e., twelve sense coils 5. Each sense coil 5 is configured to detect a signal proportional to the strength of the magnetic field in the axial component perpendicular to its coil surface. For example, the coil unit 5A receives the generated magnetic field, converts it into a voltage signal, and outputs this voltage signal as the detection result.

[0020] The sense coil 5 is connected to the magnetic field detection signal receiving circuit 8 via a cable (not shown). The magnetic field detection signal receiving circuit 8 receives the signal detected by the sense coil 5 in the coil unit 5A, performs predetermined signal processing such as amplification, and then outputs it to the position and orientation estimation circuit 9.

[0021] The drive signal transmission circuit 7 is configured, for example, by an FPGA, and is controlled by a timing control signal from the drive detection timing control circuit 11 to generate and output a sine wave signal, for example, to drive the coil 2. The drive signal transmission circuit 7 is controlled by the drive detection timing control circuit 11 to supply a sine wave to each coil 2 individually. In other words, the drive detection timing control circuit 11 can control which coil 2 at which position on the probe 3 receives the sine wave.

[0022] Each coil 2 radiates electromagnetic waves accompanied by a magnetic field when a high-frequency sine wave is applied to it. The drive detection timing control circuit 11 can sequentially drive each transmitting coil 2-1, 2-2, ... at appropriate time intervals, for example, several milliseconds. The drive detection timing control circuit 11 can also individually specify the timing at which each transmitting coil 2-1, 2-2, ... generates a magnetic field.

[0023] Such a magnetic field is detected by the magnetic field detection device 4, and the voltage signal of the detection result is supplied to the position and orientation estimation circuit 9. The position and orientation estimation circuit 9 is also supplied with a timing control signal from the drive detection timing control circuit 11. The position and orientation estimation circuit 9 is controlled by the timing control signal and detects the spatial position coordinates of each coil 2. In the following explanation, the detected position of the coil 2 will be referred to as the coil detection point. That is, the coil detection point as an element detection point indicates the position of the coil 2 on a predetermined spatial coordinate system.

[0024] Figure 3 is an explanatory diagram showing the insertion state of the endoscope insertion section 1 into the large intestine C. In Figure 3, the coil 2 in the probe 3 is positioned within the large intestine C as a result of inserting the endoscope insertion section 1 into the large intestine C. That is, by determining the position coordinates of the coil 2, the insertion shape of the endoscope insertion section 1 can be estimated. The left column of Figure 3 shows a configuration in which the spacing between the coils 2 placed within the probe 3 is narrowed, and a large number of coils 2 are arranged. This allows for highly accurate (high-precision) estimation of the endoscope shape.

[0025] In contrast, the right column of Figure 3 shows a configuration where the number of coils in coil 2 is reduced compared to the left column. Reducing the number of coils reduces the number of connection wires to coil 2. Furthermore, reducing the number of coils allows coil 2 to be driven more frequently, even if the performance of the drive circuit is the same, thus improving the frame rate. Also, reducing the number of coils allows for a longer driving time for coil 2, which extends the sampling time and improves noise immunity (S / N). Therefore, it is desirable to place as few coils as possible within the probe 3. However, if the number of coils 2 placed in the endoscope is reduced further, the estimated shape of the endoscope may differ significantly from its original shape.

[0026] Therefore, in this embodiment, similar to Patent Document 2, when a loop-shaped curvature is detected, a method is adopted in which a virtual point is set and a highly accurate loop shape is estimated.

[0027] First, with reference to Figure 4, the method described in Patent Document 2 will be briefly explained. Figure 4 is an explanatory diagram illustrating the method for accurately estimating loop shape disclosed in Patent Document 2.

[0028] The probe is equipped with multiple coils, and Figure 4 shows two of these coils, Pi and Pi+1. When the number of coils is relatively small and the probe bends sharply, the curve created by normal spline interpolation between the two coils Pi and Pi+1 placed inside the probe may be shorter than the actual distance between the coils. In this case, the estimation accuracy of the interpolated curve by normal spline interpolation is considered to be low. Therefore, a virtual point Pv is set on the curve so that the length of the interpolated curve by spline interpolation matches the actual distance between the coils, and this virtual point Pv is treated as if it were a coil position. By performing interpolation using the virtual point Pv and the coil detection point, the inference accuracy is improved.

[0029] In the following explanation, among the spline interpolation processes that interpolate between existing known data points, the spline interpolation process that uses coil detection points as data points will be referred to as the first interpolation process, and the interpolation curve obtained by the multiple interpolation points from the first interpolation process will be referred to as the first interpolation curve.

[0030] First, a first interpolation process is performed on the coil detection point Pi to obtain a first interpolation curve using multiple interpolation points. The dashed curve between coil detection point Pi and Pi+1 in Figure 2 represents the first interpolation curve. Next, the distance along the interpolation points between coil Pi and Pi+1 (length of the first interpolation curve) is determined as Lri. Then, it is determined whether the distance Lri along the interpolation points is greater than or equal to the value obtained by multiplying the actual distance between coils in the probe (hereinafter referred to as the coil design interval) Li (e.g., 100 mm) by a predetermined coefficient value (e.g., 0.8). In other words, it is determined whether Lri1 ≥ Li × 0.8. If this condition is met, it is determined that the distance Lri calculated by interpolation is calculated as the normal coil distance. In this case, the first interpolation curve shown by the dashed line is used for shape estimation.

[0031] On the other hand, if Lri ≥ Li × 0.8 is not met, the interpolated points (first interpolation curve) obtained by the first interpolation process are judged not to be the result of accurately calculating the probe shape, and a virtual point Pv is calculated by correcting the interpolated points.

[0032] To calculate the virtual point Pv, first, the midpoint of the arc of the interpolated point (first interpolation curve) obtained by the first interpolation process is defined as the interpolation midpoint Di. Next, the midpoint of the line segment PiPi+1 is found and defined as the line segment midpoint Mi. Then, assuming that a circular arc representing the probe shape (hereinafter referred to as the virtual circular arc) exists on the extension of the vector drawn from the line segment midpoint Mi to the interpolation midpoint Di, the center of the virtual circular arc is defined as Oi, and the intersection point of the virtual circular arc on the extension of the line segment midpoint Mi and the interpolation midpoint Di is defined as the arc midpoint Ni. Then, the arc midpoint Ni is set so that the length of the arc PiNiPi+1 becomes the coil design interval Li, which is the element design interval.

[0033] Now, if we consider a triangle with vertices Pi, Pi+1, and Oi, and let θi be one angle PiOiPi+1, and let ri be the radius of the virtual arc, then equation (1) below holds. From equation (1) above, we find θi and ri, and then we find the coordinates of the midpoint Ni of the arc using equation (2) below. Instead of the interpolation midpoint Di, the arc midpoint Ni is used as the coil position, and spline interpolation is performed using the arc midpoint Ni.

[0034] Thus, in the method of Patent Document 2, Pi and Pi+1 in FIG. 4 are used as coil detection points, the arc PiDiPi+1 is used as the interpolation shape of the first interpolation curve, the length Lri of the first interpolation curve is compared with the coil design interval Li (for example, 100 mm), and when Lri≥Li×0.8, the interpolation midpoint Di is used as the virtual point Pv. When Lri<Li×0.8, the arc midpoint Ni of the virtual arc centered at Oi is obtained as the virtual point Pv, and the virtual point Pv as the second interpolation point is added to the coil detection points of the coils arranged on the probe for interpolation, so that the probe shape can be accurately obtained even when it is bent into a predetermined loop shape. In the following description, the spline interpolation process using the coil detection point and the virtual point Pv as data points is referred to as the second interpolation process.

[0035] (Virtual point in this embodiment) Further, in this embodiment, not only the three-dimensional position of the coil but also the information on the orientation is used. By determining the orientation obtained from this orientation information as the tangent direction of the probe 3, more accurate (higher accuracy) shape estimation can be achieved.

[0036] In Patent Document 2 described above, the shape of the probe 3 is estimated by obtaining the positions of the coils 2. In contrast, in this embodiment, in the position and orientation estimation circuit 9, not only the coil position but also the orientation of the coil 2 is obtained. That is, the position and orientation estimation circuit 9 performs frequency extraction processing on the signal input from the magnetic field detection signal reception circuit 8, separates and extracts the magnetic field detection information of the frequency components corresponding to the high-frequency sine waves of each transmission coil 2, and calculates the three-dimensional position coordinates and orientation (three-dimensional unit direction vector) of each transmission coil 2 provided on the probe 3 from each digital data of the separated magnetic field detection information. The calculation results of the position coordinates and orientation by the position and orientation estimation circuit 9 are supplied to the probe shape estimation circuit 10.

[0037] The probe shape estimation circuit 10 is also given probe information as prior information including the number of coils of the probe 3 and information on the coil design interval Li. The probe shape estimation circuit 10 sets a virtual point (hereinafter referred to as a tangent virtual point Pvt) around the coil detection point based on the calculation results of the position and orientation of the coil detection point of the probe 3, and connects the coil detection point, the virtual point Pv, and the tangent virtual point Pvt to generate a linear image as an insertion shape image.

[0038] FIGS. 5 and 6 are explanatory diagrams for explaining the tangent virtual point Pvt as the first interpolation point.

[0039] FIG. 5 shows the coil detection points (square marks) of each coil 2 arranged in the probe 3 and the three-dimensional unit direction vector v representing the direction of each coil 2 by an arrow. As shown in FIG. 6, the probe shape estimation circuit 10 sets a tangent virtual point Pvt indicated by a solid circle before and after in the direction of the three-dimensional unit direction vector v at the coil detection point (open circle mark) of the coil 2. That is, the tangent virtual point Pvt is provided in the tangent direction of the probe 3 at the coil position of each coil 2. Therefore, when the coil position and the position of the tangent virtual point Pvt are relatively close, the position of the tangent virtual point Pvt is considered to be close to the position of the actual probe 3.

[0040] In the present embodiment, the probe shape estimation circuit 10 treats the tangent virtual point Pvt in the same manner as the actual coil detection point, and adopts the method of the above-mentioned Patent Document 2 by combining the coil detection point of the coil 2 and the tangent virtual point Pvt as data points for spline interpolation. In the following description, the spline interpolation process using the coil detection point and the tangent virtual point Pvt as data points is referred to as the third interpolation process.

[0041] Assuming that the distance between the coil 2 and the tangent virtual point Pvt is L (for example, 1 cm), L is sufficiently smaller than the coil design interval Li, and the coil interval between adjacent tangent virtual points Pvt is approximately Li - 2L. Compared with Patent Document 2, the distance between data points for spline interpolation can be shortened, and the accuracy of shape estimation can be improved.

[0042] (Operation) Next, the operation of the embodiment configured as described above will be explained with reference to Figures 7 to 11. Figure 7 is a flowchart illustrating the operation of the first embodiment. Figures 8 to 9 are explanatory diagrams illustrating the operation of the first embodiment.

[0043] The drive signal transmission circuit 7 is controlled by the drive detection timing control circuit 11 to generate and output, for example, a sinusoidal signal for driving the coil 2. As a result, each transmitting coil 2-1, 2-2... is driven sequentially at appropriate time intervals, radiating electromagnetic waves accompanied by a magnetic field into the surroundings.

[0044] Each sense coil 5 in the coil unit 5A of the magnetic field detection device 4 receives the magnetic field generated by each coil 2 and converts it into a voltage signal, which is then output to the magnetic field detection signal receiving circuit 8 as the detection result. The magnetic field detection signal receiving circuit 8 receives a timing control signal from the drive detection timing control circuit 11, receives the signal detected by the sense coil 5 for each coil 2, performs predetermined signal processing such as amplification, and then outputs it to the position and orientation estimation circuit 9. The position and orientation estimation circuit 9 determines the three-dimensional position coordinates and three-dimensional unit direction vectors of each coil 2. The position and orientation estimation circuit 9 outputs the determined position coordinates and orientation information of each coil 2 to the probe shape estimation circuit 10.

[0045] In S1 of Figure 7, the probe shape estimation circuit 10 reads probe information including the number of coils placed in the probe 3 and the coil design interval Li. Next, the probe shape estimation circuit 10 reads the three-dimensional position coordinates and three-dimensional unit direction vector for each coil 2 (S2).

[0046] The probe shape estimation circuit 10 sets tangent virtual points Pvt before and after the three-dimensional unit direction vector v at the coil position. The distance between the coil detection point and the tangent virtual point Pvt is L (for example, 1 cm). Therefore, the distance between adjacent tangent virtual points Pvt is the coil design interval Li - 2L. The probe shape estimation circuit 10 updates the number of coils (number of data points) to (number of coils in coil 2 + number of tangent virtual points Pvt) = (number of coils in coil 2 × 3) (S3).

[0047] Next, the probe shape estimation circuit 10 calculates the coordinates of the tangent virtual point Pvt (S4). In the following description, vector A is represented as vec{A}.

[0048] Now, each coil of the plurality of coils 2 is represented by coil i (i = 0, 1, 2,..., n), the coordinates of coil i are vec{p ３ｉ＋１ ,

[0049] , ０ , ０ , , ,

[0051] , ３ｉ , , ３ｉ ,

[0050] }, and the unit direction vector is vec{v ３ｉ}. Also, the order j of the coil detection point and the tangent virtual point Pvt is set as j = Top, 0, 1, 2, 3,..., 3n + 1 from the beginning. Therefore, the following formula is derived. vec{p ３ｉ－１} = vec{p ３ｉ} + Lvec{v ３ｉ} (i = 1, 2,..., n) vec{p Ｔｏｐ} = vec{p ０} + Lvec{v{ ０} vec{p ３ｉ＋１} = vec{p ３ｉ} - Lvec{v ３ｉ} (i = 1, 2,..., n) Next, the probe shape estimation circuit 10 treats the tangent virtual point Pvt in the same way as the coil detection point, and performs third interpolation processing on each section between the coil detection point and the tangent virtual point Pvt as data points, and calculates interpolation points (for example, 20 points) (S5).

[0049] FIG. 8 shows the third interpolation processing. FIG. 8 shows the positions of the coils 2 in the probe 3 (coil detection points (open circles)) and the tangent virtual point Pvt (filled circle) with relatively large circles, and shows the interpolation points Ps by the third interpolation processing with relatively small circles. In the example of FIG. 8, one interpolation point Ps is calculated between the coil detection point of the coil 2 and the tangent virtual points Pvt before and after it.

[0050] Next, in S6, the probe shape estimation circuit 10 extracts the interpolation midpoint Psm (× mark) of the interpolation curve (hereinafter referred to as the third interpolation curve) obtained by the third interpolation processing using the coil detection point and the tangent virtual point Pvt as data points (see FIG. 9).

[0051] Next, the probe shape estimation circuit 10 determines whether the length Lpi of the third interpolation curve obtained by the third interpolation process using the coil detection point and the tangent virtual point Pvt as data points is less than or equal to a predetermined value shorter than the coil design interval Li, for example, less than or equal to m times (for example, m = 0.9) (S7). If the length Lpi of the third interpolation curve is not less than or equal to a predetermined value shorter than the coil design interval Li, for example, if Lpi > MLi, the probe shape estimation circuit 10 sets the interpolation midpoint Psm as the virtual point Pvl (S8). Also, if Lpi ≤ MLi, the probe shape estimation circuit 10 sets the arc midpoint Ni obtained based on equations (1) and (2) above as the virtual point Pvl (S9). In the explanation using Figure 4 above, equations (1) and (2) were used to determine θi and ri by setting a virtual arc between two coil detection points. However, in this embodiment, the difference is that a virtual arc is set between the coil detection point and the tangent virtual point Pvt, or between two tangent virtual points Pvt, to determine θi and ri, and the coordinates of the arc midpoint Ni are calculated.

[0052] The probe shape estimation circuit 10 estimates the shape of the probe 3 by performing interpolation using the coil detection point, the tangent virtual point Pvt, and the virtual point Pvl as data points for spline interpolation (S10). In the following description, the spline interpolation process using the coil detection point, the tangent virtual point Pvt, and the virtual point Pvl as data points will be referred to as the fourth interpolation process.

[0053] Figures 10 and 11 are explanatory diagrams showing the shape estimation results when this embodiment is adopted. The examples in Figures 10 and 11 show the coil detection point, the coil detection point and the tangent virtual point Pvt, and the coil detection point, the tangent virtual point Pvt and the virtual point Pvl, relative to the actual shape (true shape) of the probe, as well as the result of shape estimation (estimated shape) by a fourth interpolation process using the coil detection point, the tangent virtual point Pvt and the virtual point Pvl as data points for spline interpolation. As shown in the examples in Figures 10 and 11, it can be seen that high-precision shape estimation is possible in this embodiment.

[0054] In this embodiment, the orientation of the tangent to the shape curve at each coil position is determined using not only the three-dimensional position information of each coil in the probe, but also the orientation information. Virtual tangent points are defined before and after the tangent direction at the coil detection point, and the interpolation curve is obtained by a third interpolation process using the coil detection point and virtual tangent points as data points, and the method of the second patent document is applied. The data point interval in spline interpolation is narrower than in patent document 2, enabling more accurate shape estimation. In particular, it is possible to prevent the curve connecting the coils from expanding in a direction different from the actual direction.

[0055] (Second Embodiment) Figure 12 is a flowchart illustrating the operation of the second embodiment of the present invention. In Figure 12, the same reference numerals are used for the same steps as in Figure 7, and their descriptions are omitted. The hardware configuration of this embodiment is the same as in Figure 1.

[0056] In the first embodiment, the orientation of the coil 2 was determined to determine the tangent virtual point Pvt. However, it is assumed that the direction of the coil detection point is known (detectable in the previous step) as to whether it is towards the tip of the endoscope insertion section 1 (hereinafter referred to as the tip direction) or towards the rear end (hereinafter referred to as the rear end direction), which are two tangent directions. For this reason, the assignment of the above order j between the coil detection point and the tangent virtual point Pvt may be incorrect. If this is incorrect, the direction of the probe's movement will be determined in reverse in that part, and the estimated shape may differ significantly from the actual shape. Therefore, in this embodiment, by determining whether the orientation of the coil 2 is towards the tip direction or the rear end direction, highly accurate shape estimation is made possible.

[0057] In this embodiment, first, the approximate shape is estimated by adopting the method of Patent Document 2, so that it is possible to determine whether the orientation of the coil is towards the front end or the rear end. That is, in S11 of Figure 12, the probe shape estimation circuit 10 obtains an interpolation point (third interpolation point) by normal spline interpolation processing (first interpolation processing) using the coil detection point of the coil 2, and obtains the interpolation midpoint Di on the first interpolation curve using the obtained interpolation point (S12). Next, it is determined whether the length Lri of the first interpolation curve obtained by the first interpolation processing is m times or less (for example, m = 0.9) of the coil design interval Li (S13). If it is not m times or less, the interpolation midpoint Di on the first interpolation curve is set as a virtual point Pv (S14), and if it is m times or less, the arc midpoint Ni is set as a virtual point Pv (S15). Next, the coil detection point and the virtual point Pv are used as data points for spline interpolation, and spline interpolation processing (second interpolation processing) is performed.

[0058] Next, the shape of probe 3 is estimated using the method of the first embodiment. First, the probe shape estimation circuit 10 sets tangent virtual points Pvt before and after the three-dimensional unit direction vector v at the coil position, similar to the first embodiment, and updates the number of coils (number of data points) to (number of coils of coil 2 + number of tangent virtual points Pvt) = (number of coils of coil 2 × 3) (S3). Next, the probe shape estimation circuit 10 calculates the coordinates of the tangent virtual points Pvt (S4). Then, the probe shape estimation circuit 10 sets the order j of the coil detection point and the tangent virtual point Pvt (S17).

[0059] Figure 13 is an explanatory diagram illustrating the method for determining the order j of the coil detection point and the tangent virtual point Pvt. In other words, Figure 13 illustrates a method for determining which of the two tangent virtual points Pvt (hereinafter referred to as tangent virtual point Pvt0 and tangent virtual point Pvt1) set for each coil detection point is on the leading edge side (or trailing edge side) using the processing result of S16. Since the second interpolation process in S16 does not use the tangent virtual point Pvt as a data point, it is considered that the interpolation points before and after the coil detection point will be correctly positioned in the leading edge direction or trailing edge direction relative to the coil detection point, even if the accuracy is not sufficient. Therefore, by comparing the orientation of the interpolation points relative to the coil detection point with the orientation of the tangent virtual point Pvt relative to the coil detection point, it is determined whether the tangent virtual points Pvt0 and Pvt1 are on the leading edge side or trailing edge side relative to the coil detection point.

[0060] In Figure 13, the large circles indicate the coil detection points of coil 2, the filled circles indicate the interpolation points obtained as a result of the second interpolation process in S16, and the small white circles indicate the tangent virtual points Pvt(Pvt0, Pvt1). Also, one of the vectors from the coil detection point to the interpolation point is vec{V ｆｒｏｎｔ Let the other vector be vec{V ｂａｃｋ Let} be the case. Also, let vec{V0} be the three-dimensional unit vector from the coil detection point to the tangent virtual point Pvt0, and let (-vec{V0}) be the three-dimensional unit vector from the coil detection point to the tangent virtual point Pvt1. Note that for the coil detection point of coil 2, vec{V ｆｒｏｎｔ} indicates the tip side, vec{V ｂａｃｋ The direction indicated by} is the direction towards the rear end.

[0061] The probe shape estimation circuit 10 calculates the angle between the vectors extending on both sides of the interpolation point closest to the coil detection point and the three-dimensional unit vector, and adopts the combination with the smaller angle.

[0062] vec{V ｆｒｏｎｔ Let cos_front0 and vec{V0} be the cos of the angle between} and vec{V0}. ｆｒｏｎｔ Let cos_front1 be the cos of the angle between} and (-vec{V0}), and vec{V ｂａｃｋLet cos_back0 and vec{V0} be the cos of the angle between} and vec{V0}. ｂａｃｋ Let cos_back1 be the cos of the angle between} and (-vec{V0}).

[0063] The probe shape estimation circuit 10 determines which of the tangent virtual points Pvt0 and Pvt1 is the front end (rear end) based on the following conditions (a) to (f). Then, it determines the order j of the coil detection point and the tangent virtual points Pvt0 and Pvt1 from the beginning as j = Top, 0, 1, 2, 3, ...

[0064] (a) When cos_front0 > cos_front1 and cos_back1 > cos_back0, the virtual tangent point Pvt0 is on the front end side and the virtual tangent point Pvt1 is on the back end side. (b) When cos_front0 < cos_front1 and cos_back1 < cos_back0, the virtual tangent point Pvt0 is on the back end side and the virtual tangent point Pvt1 is on the front end side. (c) When cos_front0 <= cos_front1 and cos_front0 <= cos_back0 and cos_front0 <= cos_back1, the virtual tangent point Pvt0 is on the back end side and the virtual tangent point Pvt1 is on the front end side. (d) When cos_front1 <= cos_front0 and cos_front1 <= cos_back0 and cos_front1 <= cos_back1, the virtual tangent point Pvt0 is on the front end side and the virtual tangent point Pvt1 is on the back end side. (e) When cos_back0 <= cos_front0 and cos_back0 <= cos_front1 and cos_back0 <= cos_back1, the virtual tangent point Pvt0 is on the front end side and the virtual tangent point Pvt1 is on the back end side. (f) In all other cases, When the probe shape estimation circuit 10 determines the order j, it performs a third interpolation process using the coil detection point and the tangent virtual points Pvt0 and Pvt1 as data points. The subsequent processes S6 to S10 are the same as in the first embodiment.

[0065] Thus, in this embodiment, the same effects as in the first embodiment can be obtained, and since the order of the data points is determined after determining which of the pair of tangent virtual points set with respect to the coil detection point is the front end and which is the rear end, there is an advantage that the shape can be estimated with high accuracy even if the front end / rear end cannot be identified in the stage prior to shape estimation.

[0066] (Modified Example) Figure 14 is a block diagram showing a modified example. In Figure 14, the same reference numerals are used for components identical to those in Figure 1, and their descriptions are omitted.

[0067] A modified version of Figure 14 shows that probe information is supplied from the endoscope 12 to the probe shape estimation circuit 10. The endoscope 12 in Figure 14 includes an endoscope insertion section 1. Depending on the model of the endoscope, the coil design interval and the number of coils of the probe 3 may differ. The endoscope 12 is equipped with a memory 12a that stores probe information, including information on the coil design interval and the number of coils. During an endoscopic examination, the endoscope 12 reads the probe information stored in the memory 12a and provides it to the probe shape estimation circuit 10.

[0068] This enables highly accurate shape estimation regardless of differences in endoscopic design, such as different endoscope models.

[0069] The present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the embodiments described above. For example, some components of all the components shown in the embodiments may be deleted. Moreover, components from different embodiments may be appropriately combined.

[0070] For example, in the above description, an example was described in which the coil 2 inside the probe 3 is used as the magnetic field generating element and the sense coil 5 of the magnetic field detection device 4 is used as the magnetic field detection element. However, the arrangement may be reversed, with the magnetic field generating element placed outside the body and the magnetic field detection element placed inside the probe.

[0071] Of the technologies described in the specification, the controls, mainly those explained in flowcharts, can often be configured by program and may be stored on recording media or recording units. The method of recording on these recording media or recording units may vary; recording may be done at the time of product shipment, using distributed recording media, or by downloading data via the internet.

[0072] Furthermore, each step in the flowchart may be executed in a different order, executed simultaneously, or executed in a different order each time, as long as it does not contradict its nature.

[0073] In the embodiments, the parts referred to as "circuits" may be configured as dedicated circuits, or they may be configured by combining multiple general-purpose circuits. If necessary, they may also be configured by combining a computer, a processor such as a CPU, or a sequencer such as an FPGA, which operate according to pre-programmed software.

Claims

1. The probe shape detection device includes a processor, which acquires prior information regarding a pre-set element design interval (Li) of a magnetic field generating element placed on the probe, acquires an element detection point indicating the position of the magnetic field generating element, acquires information regarding the orientation of the magnetic field generating element, sets a virtual first interpolation point (tangential virtual point Pvt) around the element detection point based on the orientation information, calculates a first interpolation curve length (Lri) of an interpolation curve obtained by interpolation processing using the element detection point and the first interpolation point as data points, sets a virtual second interpolation point (virtual point Pv) based on the first interpolation curve length and the element design interval, and estimates the shape of the probe by interpolation processing using the element detection point, the first interpolation point and the second interpolation point as data points.

2. The probe shape detection device according to claim 1, wherein the processor compares the element design interval with the first interpolation curve length, and if the first interpolation curve length is shorter than the element design interval by a predetermined value or more, sets the midpoint of a virtual arc connecting two adjacent element detection points with an arc as the second interpolation point.

3. The probe shape detection device according to claim 1, wherein the processor compares the element design interval with the first interpolation curve length, and sets the midpoint of the first interpolation curve as the second interpolation point if the first interpolation curve length is not shorter than the element design interval by a predetermined value or more.

4. A probe shape detection device according to claim 1, wherein the processor sets a third interpolation point based on the shape of the probe estimated by interpolation processing with the element detection point as a data point, and sets the first interpolation point based on the third interpolation point.

5. A probe shape detection device according to claim 4, wherein the processor sets a virtual pair of first interpolation points before and after the element detection point in the tangential direction at the element detection point, and uses the third interpolation point to determine whether the pair of first interpolation points is located on the tip side or the rear end side of the probe.

6. The probe shape detection device according to claim 1, wherein the processor employs spline interpolation as the interpolation process.

7. The probe shape detection device according to claim 1, wherein the processor sets two adjacent points among the element detection point, first interpolation point, and second interpolation point as Pi and Pi+1, respectively, sets the midpoint of the line segment connecting Pi to Pi+1 as Mi, and sets the point formed by extending a line perpendicular to the line segment through the midpoint as Oi, forming a triangle with Pi, Pi+1 and Oi as vertices, sets the midpoint of the virtual arc passing over Pi and Pi+1 such that the length of the arc PiNiPi+1, which is the interpolation curve length, is equal to the element design interval Li, and estimates the coordinates of the midpoint of the arc Ni by the following formula, with the angle PiOiPi+1 being θi and the radius of the virtual arc being ri.

8. The probe shape detection method involves: acquiring prior information regarding a pre-set element design interval (Li) of magnetic field generating elements arranged on the probe; acquiring element detection points indicating the positions of the magnetic field generating elements; acquiring information regarding the orientation of the magnetic field generating elements; setting a virtual first interpolation point (tangential virtual point Pvt) around the element detection point based on the orientation information; calculating the first interpolation curve length (Lri) of an interpolation curve obtained by interpolation processing using the element detection point and the first interpolation point as data points; setting a virtual second interpolation point (virtual point Pv) based on the first interpolation curve length and the element design interval; and estimating the probe shape by interpolation processing using the element detection point, the first interpolation point and the second interpolation point as data points.

9. A probe shape detection method according to claim 8, wherein the element design interval is compared with the first interpolation curve length, and if the first interpolation curve length is shorter than the element design interval by a predetermined value or more, the midpoint of a virtual arc connecting two adjacent element detection points with an arc is set as the second interpolation point.

10. A probe shape detection method according to claim 8, wherein the element design interval is compared with the first interpolation curve length, and if the first interpolation curve length is not shorter than the element design interval by a predetermined value or more, the midpoint of the first interpolation curve is set as the second interpolation point.

11. A probe shape detection method according to claim 8, wherein a third interpolation point is set based on the probe shape estimated by interpolation processing with the element detection point as a data point, and the first interpolation point is set based on the third interpolation point.

12. A probe shape detection method according to claim 11, wherein a pair of virtual first interpolation points are set before and after the element detection point in the tangential direction at the element detection point, and the third interpolation point is used to determine which of the pair of first interpolation points is located on the tip side or the rear end side of the probe.

13. The probe shape detection method according to claim 8, wherein spline interpolation is employed as the interpolation process.

14. A probe shape detection method according to claim 8, wherein two adjacent points among the element detection point, first interpolation point, and second interpolation point are defined as Pi and Pi+1, respectively; the midpoint of the line segment connecting Pi to Pi+1 is defined as Mi; the point formed by extending a line perpendicular to the line segment through the midpoint of the line segment is defined as Oi; a triangle is formed with Pi, Pi+1, and Oi as its vertices; the midpoint of the arc is set as Ni, the midpoint of a virtual arc passing over Pi and Pi+1 such that the length of the arc PiNiPi+1, which is the interpolation curve length, is equal to the element design interval Li; the coordinates of the midpoint of the arc are estimated by the following formula, with angle PiOiPi+1 as θi and radius of the virtual arc as ri.

15. The probe shape detection program causes the computer to perform the following steps: acquire prior information regarding the pre-set element design interval (Li) of the magnetic field generating elements placed on the probe; acquire element detection points indicating the positions of the magnetic field generating elements; acquire information regarding the orientation of the magnetic field generating elements; set a virtual first interpolation point (tangential virtual point Pvt) around the element detection point based on the orientation information; calculate the first interpolation curve length (Lri) of the interpolation curve obtained by interpolation processing using the element detection point and the first interpolation point as data points; set a virtual second interpolation point (virtual point Pv) based on the first interpolation curve length and the element design interval; and estimate the shape of the probe by interpolation processing using the element detection point, the first interpolation point and the second interpolation point as data points.

16. A probe shape detection program according to claim 15, wherein the computer is instructed to perform the following steps: compare the element design interval with the first interpolation curve length, and if the first interpolation curve length is shorter than the element design interval by a predetermined value or more, set the midpoint of a virtual arc connecting two adjacent element detection points with an arc as the second interpolation point.

17. A probe shape detection program according to claim 15, wherein the computer is instructed to perform the procedure of comparing the element design interval with the first interpolation curve length, and if the first interpolation curve length is not shorter than the element design interval by a predetermined value or more, setting the midpoint of the first interpolation curve as the second interpolation point.

18. A probe shape detection program according to claim 15, wherein the computer is instructed to set a third interpolation point based on the shape of the probe estimated by interpolation processing with the element detection point as a data point, and to set the first interpolation point based on the third interpolation point.

19. A probe shape detection program according to claim 18, wherein the computer is instructed to set a virtual pair of first interpolation points before and after the element detection point in the tangential direction at the element detection point, and to use the third interpolation point to determine which of the pair of first interpolation points is located on the tip side or the rear end side of the probe.

20. A probe shape detection program according to claim 15, wherein the computer is instructed to perform a procedure in which spline interpolation is used as the interpolation process.

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