Medical instrument

A medical instrument includes an insertion portion, first transmitting coils, second transmitting coils, a signal control unit, a position detection unit, a memory, and a position estimating unit. The signal control unit controls the first transmitting coils to transmit magnetic fields during a first predetermined period and controls the second transmitting coils to transmit magnetic fields during a second predetermined period. The position detection unit detects positions of the first transmitting coils during the first predetermined period and detects positions of the second transmitting coils during the second predetermined period. The memory stores the positions of the first transmitting coils. The position estimating unit estimates a shape of the insertion portion based on the positions of the second transmitting coils and the positions of the first transmitting coils stored in the memory.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a medical instrument such as an endoscope which detects, for example, a shape when the medical instrument is inserted into a subject.

2. Description of the Related Art

There is known an observation apparatus for insertion-shape of an endoscope which detects, for example, a shape when an endoscope is inserted into a subject such as a patient. This apparatus comprises a large number of transmitting coils provided in an insertion portion of the endoscope, and also comprises an antenna including a receiving coil. This apparatus transmits magnetic fields from all the transmitting coils in a time-division manner, and receives the magnetic fields by the receiving coil of the antenna, thereby detecting the positions of all the transmitting coils, and from these positions, detecting the shape of the insertion portion of the endoscope.

In Jpn. Pat. Appln. KOKAI Publication No. 2003-290129, coils C1 to C30 arranged in the insertion portion of the endoscope are classified into groups A, B, and a C, each including ten coils. The coils C1 to 010 in the group A are connected to timing circuits P1 to P10, the coils C11 to C20 in the group B are connected to timing circuits P11 to P20, and the coils C21 to C30 in the group C are connected to timing circuits P21 to P30. In Jpn. Pat. Appln. KOKAI Publication No. 2003-290129, the timing circuits P1 to P30 are connected to 10 oscillators which have different oscillating frequencies. In such a configuration, according to Jpn. Pat. Appln. KOKAI Publication No. 2003-290129, each of ten timing circuits, for example, each of the timing circuits P1 to P10, P11 to P20, and P21 to P30, . . . is intermittently turned on by coil driving timing signals INTMT01 to 30 from a control circuit 51. Thus, Jpn. Pat. Appln. KOKAI Publication No. 2003-290129 discloses that each of the coils C1 to 010, C11 to C20, and C21 to C30 belonging to each of the groups A, B, and C is sequentially and intermittently driven, so that it is possible to handle cases in which the number of coils is large.

In Jpn. Pat. Appln. KOKAI Publication No. 2003-245242, a midpoint dPmi of an arc is found by interpolation processing of detection points Pi and Pi+1 of source coils arranged in the insertion portion. When the length of the arc is substantially equal to the actual arrangement interval of the source coils, the midpoint dPmi is set as an ideal point. When the length of the arc is much smaller than the actual arrangement interval of the source coils, a point Pvi extending from a midpoint of line segments Pi and Pi+1 in a direction to connect the midpoint dPmi of the arc is set as an ideal point, and the line segments Pi and Pi+1 including the ideal point Pvi are subjected to interpolation processing. Thus, Jpn. Pat. Appln. KOKAI Publication No. 2003-245242 discloses that the shape of the insertion portion can be accurately detected as if a source coil is disposed at the ideal point.

BRIEF SUMMARY OF THE INVENTION

A medical instrument according to an aspect of the invention is a medical instrument comprising: a medical instrument comprising: an insertion portion to be inserted into a subject; first transmitting coils provided in the insertion portion along a longitudinal direction of the insertion portion at predetermined intervals and generating magnetic fields; second transmitting coils provided at positions different from positions of the first transmitting coils in the insertion portion along the longitudinal direction of the insertion portion at predetermined intervals and generating magnetic fields; a signal control unit which controls the first transmitting coils to transmit the magnetic fields during a first predetermined period and controls the second transmitting coils to transmit the magnetic fields during a second predetermined period different from the first predetermined period; a position detection unit which detects positions of the first transmitting coils on the basis of the magnetic field during the first predetermined period and detects positions of the second transmitting coils on the basis of the magnetic field during the second predetermined period; a memory which stores the positions of the first transmitting coils detected by the position detection unit during the first predetermined period; and a position estimating unit which estimates a shape of the insertion portion on the basis of the positions of the second transmitting coils detected by the position detection unit during the second predetermined period and the positions of the first transmitting coils stored in the memory.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1shows a configuration diagram of a medical instrument (hereinafter referred to as the instrument)1. The instrument1is provided in, for example, an endoscope apparatus (tubular insertion system)10shown inFIG. 2. The endoscope apparatus10includes an insertion portion20to be inserted into a body cavity (lumen) of, for example, a patient who is a subject. The endoscope apparatus10inserts the insertion portion20into, for example, a body cavity to observe and treat an affected part or a lesioned part in the body cavity.

The present instrument1detects the position of the insertion portion20or a shape such as a looped shape when the insertion portion20is inserted in the body cavity of the patient. The instrument1is applicable to the detection of the position and shape of not only the endoscope apparatus10but also, for example, a forceps or a catheter used in the endoscope apparatus10.

The endoscope apparatus10includes an endoscope12, an image processor14such as a video processor, a monitor16, a light source18, an insertion shape estimating device18a, and a controller19. The endoscope12images the inside of the body cavity of, for example, the patient as shown inFIG. 2. The image processor14processes the image of the inside of the body cavity of, for example, the patient taken by the endoscope12. The monitor16displays the image of the inside of the body cavity of, for example, the patient processed by the image processor14.

The light source18emits illumination light which is output from the endoscope12to illuminate the inside of the body cavity of, for example, the patient. The insertion shape estimating device18asupplies electric power to transmitting coils as multiple elements such as transmitting coils50-1to50-n(n: natural number), and detects the voltages of receiving coils in an antenna as multiple elements such as receiving coils53-1to53-m(m: natural number) that is included in an antenna53and estimates an insertion shape. The controller19respectively controls the endoscope12, the image processor14, the monitor16, the light source18, and the insertion shape estimating device18ato control the operation of the whole endoscope apparatus10for observing and treating an affected part or a lesioned part in the body cavity of, for example, the patient.

Specific explanations are given below. The endoscope12is intended to observe and treat the body cavity of, for example, the patient. The insertion portion20and an operation unit are provided with the endoscope12. The operation unit30is coupled to the proximal end of the insertion portion20and serves to operate the endoscope12. The insertion portion20is formed into a hollow and elongated tubular shape.

The insertion portion20includes a distal rigid portion21, a curving portion23, and a flexible tubular portion25. The distal rigid portion21, the curving portion23, and the flexible tubular portion25are continuously formed from the distal end of the insertion portion20toward the proximal end. The distal rigid portion21is made of a rigid material. The proximal end of the distal rigid portion21is coupled to the distal end of the curving portion23. The distal rigid portion21is the distal end of the insertion portion20, i.e., the distal end of the endoscope12.

The curving portion23curves in a direction desired by an operator in UDLR directions in response to an operational instruction issued by the operator to a curving operation portion37. The curving portion23is formed to be curvable in, for example, upward, downward, leftward, and rightward (UDLR) directions. The proximal end of the curving portion23is coupled to the proximal end of the flexible tubular portion25. The position and direction of the distal rigid portion21change in accordance with the curving of the curving portion23. As a result, an image in which the inside of the body cavity of, for example, the patient is caught from a given direction can be brought into an observation field of the endoscope12. The illumination light output from the endoscope12is applied to the inside of the body cavity (lumen) of, for example, the patient. Joint rings of the curving portion23are rotatably joined along the longitudinal axis direction of the insertion portion20.

The flexible tubular portion25is a tubular member extending from a body31of the operation unit30. The flexible tubular portion25is made of a flexible member, and curves by receiving external force.

The operation unit30is grasped by the operator, and operated to curve the insertion portion20in the upward, downward, leftward, and rightward (UDLR) directions. The operation unit30includes the body31which extends the flexible tubular portion25, a handle33which is coupled to the proximal end of the body31and which is held by the operator who operates the endoscope12, and a universal cord41connected to the handle33.

The curving operation portion37for curving the curving portion23is provided in the handle33. For example, an operation wire is extended between the curving operation portion37and the curving portion23. The curving operation portion37curves the curving portion23upward and downward (UD) and leftward and rightward (LR) by moving the operation wire in the axial direction of this operation wire between the operation wire and the curving portion23. The curving operation portion37includes an upward/downward curving operation knob37UD for curving the curving portion23upward/downward (UD), a leftward/rightward operation knob37LR for curving the curving portion23leftward/rightward (LR), and a fixing knob37cwhich fixes the position of the curved curving portion23.

The universal cord41electrically connects the handle33, the image processor14, the light source18, and the insertion shape estimating device18ato perform data communication. One end of the universal cord41extends from the side surface of the handle33. A connector42is provided at the other end of the universal cord41. The connector42can be connected to and disconnected from the image processor14, the light source device18, and the insertion shape estimating device18a, respectively.

The transmitting coils50-1to50-n, for example, 30 transmitting coils50-1to50-n(n=30) are provided in the insertion portion20along the longitudinal direction at predetermined intervals.FIG. 3shows the curving portion23of the insertion portion20in which five transmitting coils50-1to50-5among the 30 transmitting coils provided in the insertion portion20are provided.

The transmitting coils50-1to50-ngenerate alternating magnetic fields (hereinafter abbreviated as magnetic fields) by receiving electric power supply, and transmit these magnetic fields. The respective transmitting coils50-1to50-nare provided, for example, from the distal end of the insertion portion20in the order of the No.1transmitting coil50-1, the No.2transmitting coil50-2, . . . , and the No. n transmitting coil50-n.

Each of the transmitting coils50-1to50-nis connected to a transmission electric power supply52via a relay unit51for selectively supplying electric power to each of the transmitting coils50-1to50-nas shown inFIG. 1. The relay unit51is provided in, for example, the connector42or the operation unit30. The relay unit51comprises relays that are respectively connected to, for example, the transmitting coils50-1to50-n. The relay unit51turns on the relay corresponding to, for example, the transmitting coil50-1which transmits a magnetic field among the relays so that alternating electric power is supplied to the transmitting coil50-1from the transmission electric power supply52via the relay.

The transmission electric power supply52is provided in the insertion shape estimating device18a. The transmission electric power supply52outputs the alternating electric power having a predetermined frequency. The transmission electric power supply52supplies electric power to each of the transmitting coils50-1to50-nvia the relay unit51. The electric power is supplied via electric power supply lines provided in, for example, the universal cord41. A transmission unit includes, for example, each of the transmitting coils50-1to50-n, the relay unit51, and the transmission electric power supply52.

The receiving coils53-1to53-mincluded in the antenna53, for example, 12 (m=12) receiving coils are provided. Each of the receiving coils53-1to53-mdetects each of the magnetic fields transmitted from each of the transmitting coils50-1to50-n. Each of the receiving coils53-1to53-mis provided in an examination room or an operation room for, for example, observing and treating the inside of the body cavity of a subject such as a patient, outside the patient. When the inside of the body cavity of the patient lying in bed is observed and treated, each of the receiving coils53-1to53-mis provided within a range in which each of the receiving coils53-1to53-mcan detect each of the magnetic fields transmitted from each of the transmitting coils50-1to50-nof the insertion portion20inserted in the body cavity of, for example, the patient.

There are a total of 12 receiving coils among the receiving coils53-1to53-m: for example, four receiving coils having axes arranged in an x-direction, four receiving coils having axes arranged in a y-direction, and four receiving coils having axes arranged in a z-direction. Each of the receiving coils53-1to53-mis disposed at a different position in the area in which the magnetic field can be detected by the antenna53. The receiving coils53-1to53-mrespectively detect the magnetic fields transmitted from the transmitting coils50-1to50-nin the xyz directions, and generate voltages corresponding to the magnitude of the magnetic fields in the xyz directions at both ends of the receiving coils53-1to53-m.

Voltage detectors54are respectively connected to the output terminals of the receiving coils53-1to53-m. Each of the voltage detectors54is provided in the insertion shape estimating device18a. Each of the voltage detectors54detects the level of each of the voltages generated at the output terminal of each of the receiving coils53-1to53-m, and outputs each voltage detection signal corresponding to each of the voltage levels. Each of the voltage detection signals is sent to a position detection unit55provided in the insertion shape estimating device18a.

Each of the voltage detection signals output from the voltage detectors54is input to the position detection unit55. The position detection unit55detects the coil position and coil direction of each of the transmitting coils50-1to50-non the basis of the magnitude of each of the voltage levels indicated by each of the voltage detection signals, that is, the magnitude of each of the magnetic fields in the xyz directions. Each of the coil positions and directions of the transmitting coils50-1to50-nis stored in a memory19aas positional information. A receiving unit includes, for example, each of the receiving coils53-1to53-m, the voltage detector54, and the position detection unit55.

A signal control unit56is provided in the insertion shape estimating device18a. The signal control unit56sequentially drives to turn on and off the relays of the relay unit51. As a result of this on/off driving, electric power is sequentially supplied to the transmitting coils50-1to50-nfrom the transmission electric power supply52through the relays of the relay unit51. Thus, the magnetic fields are sequentially transmitted from the transmitting coils50-1to50-nin a time-division manner. In this case, magnetic fields are sequentially transmitted to the receiving coils53-1to53-mfrom the transmitting coils50-1to50-n.

A period up to the end of the transmission of the magnetic fields from all the transmitting coils50-1to50-nis one frame period. The signal control unit56performs, for multiple frame periods in succession, the operation of the one frame period for sequentially transmitting the magnetic fields from all the transmitting coils50-1to50-n.

The signal control unit56controls predetermined transmitting coils among the transmitting coils50-1to50-nto transmit magnetic fields in a time-division manner. The predetermined transmitting coils are, for example, even-numbered (first position) transmitting coils from the distal end of the insertion portion20among the transmitting coils50-1to50-n, that is, the No.2transmitting coil50-2, the No.4transmitting coil50-4, . . . , and the No. n transmitting coil50-n(n=30); and odd-numbered (second position) transmitting coils from the distal end of the insertion portion20, that is, the No.1transmitting coil50-1, the No.3transmitting coil50-3, . . . , and the No. n−1 transmitting coil50-n(n=30).

Therefore, the signal control unit56sequentially controls, for example, the even-numbered transmitting coils50-2,50-4, . . . , and50-n(n=30) one by one to transmit a magnetic field in a time-division manner.

The signal control unit56sequentially controls, for example, the odd-numbered transmitting coils50-1,50-3, . . . , and50-n(n=30) one by one to transmit a magnetic field in a time-division manner.

Specifically, the signal control unit56sequentially controls all the transmitting coils50-1to50-nto transmit magnetic fields in a time-division manner in an initial frame period (first) among multiple frame periods.

The signal control unit56sequentially controls the even-numbered transmitting coils50-2, . . . , and50-none by one to transmit a magnetic field in a time-division manner in a predetermined first frame period, for example, the even-numbered frame period among the successive frame periods (second and subsequent frame periods) after the initial frame period.

The signal control unit56sequentially controls the odd-numbered transmitting coils50-1, . . . , and50-n−1 one by one to transmit a magnetic field in a time-division manner in a second frame period, for example, the odd-numbered frame period which is a frame period after a predetermined frame period among the frame periods (second and subsequent frame periods).

A shape estimating unit57is provided in the insertion shape estimating device18a. The shape estimating unit57estimates the coil positions (the odd-numbered transmitting coils50-1, . . . , and50-n−1 or the even-numbered transmitting coils50-2, . . . , and50-n) other than the predetermined coils (the even-numbered transmitting coils50-2, . . . , and50-nor the odd-numbered transmitting coils50-1, . . . , and50-n−1) on the basis of the positional information comprising the coil positions and coil directions of the transmitting coils50-1to50-n.

The shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20on the basis of the estimated coil positions and coil directions of the coils (the odd-numbered transmitting coils50-1, . . . , and50-n−1 or the even-numbered transmitting coils50-2, . . . , and50-n), the coil positions and coil directions of the predetermined coils (the even-numbered transmitting coils50-2, . . . , and50-nor the odd-numbered transmitting coils50-1, . . . , and50-n−1) detected by the signal control unit56when the magnetic fields are transmitted from the predetermined coils, and each of distances between the transmitting coils50-1to50-n(which is a distance along a scope shape and which is a value, e.g., 100 mm known from a design value of a scope). Here, the scope corresponds to the insertion portion20of the endoscope apparatus10.

In the initial frame period, when the magnetic fields are sequentially transmitted from the transmitting coils50-1to50-nin a time-division manner, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-non the basis of the coil positions and coil directions of the transmitting coils50-1to50-ndetected by the position detection unit55, and each of the distances between the transmitting coils50-1to50-n(e.g., 100 mm).

In each of the frame periods after the initial frame period, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-non the basis of the estimated coil positions, that is, the coil positions of the even-numbered transmitting coils50-2, . . . , and50-n, the positions and magnetic field directions of the predetermined coils already detected by the position detection unit55in a frame period closest to (e.g., a frame period which is one frame period before) the current frame period, and each of the distances between the transmitting coils50-1to50-n(e.g., 100 mm). The positions of the predetermined coils already detected in the frame period closest to the current frame period are, for example, the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1.

In each of the frame periods after the initial frame period, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-non the basis of the estimated coil positions, that is, the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1, the positions of the predetermined coils already detected by the position detection unit55in a frame period closest to the current frame period, for example, a frame period which is one frame period before the current frame period, for example, the coil positions and coil directions of the even-numbered transmitting coils50-2, . . . , and50-n, and each of the distances between the transmitting coils50-1to50-n(e.g., 100 mm).

The associated operations of the signal control unit56and the shape estimating unit57are specifically described.

In each of the first frame periods, for example, the even-numbered frame periods among the successive frame periods after the initial frame period, the signal control unit56sequentially controls the even-numbered transmitting coils50-2, . . . , and50-namong all the transmitting coils50-1to50-nto transmit magnetic fields in a time-division manner.

In addition, in each of the even-numbered frame periods, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-non the basis of the coil positions and coil directions of the even-numbered transmitting coils50-2, . . . , and50-ndetected by the position detection unit55when the magnetic fields are transmitted from the even-numbered transmitting coils50-2, . . . , and50-nin a time-division manner, the coil positions and coil directions of the transmitting coils other than the even-numbered transmitting coils50-2, . . . , and50-nalready detected by the position detection unit55in a frame period closest to each of this even-numbered frame periods, for example, in a previous frame period, that is, the odd-numbered transmitting coils50-1, . . . , and50-n−1, and each of the distances between the transmitting coils50-1to50-n.

For example, in each of the even-numbered frame periods, each of the coil positions of the even-numbered transmitting coils50-2,50-4, and others is detected by the position detection unit55as shown inFIG. 4when the magnetic fields are sequentially transmitted from the even-numbered transmitting coils50-2,50-4, and others in a time-division manner.

In the same frame period, the coil positions already detected by the position detection unit55in the recent frame period, for example, in the previous frame period and then stored in the memory19aare used as the coil positions of the odd-numbered transmitting coils50-1,50-3, and others which have not been detected by the position detection unit55.

Therefore, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20on the basis of each of the coil positions of the even-numbered transmitting coils50-2,50-4, and others, each of the coil positions of the odd-numbered transmitting coils50-1,50-3, and others which have been already detected by the position detection unit55and then stored in the memory19a, and each of the distances between the transmitting coils50-1to50-n.

On the other hand, in the second frame period, for example, the odd-numbered frame period among the frame periods after the initial frame period, the signal control unit56sequentially controls the odd-numbered transmitting coils50-1, . . . , and50-n−1 among all the transmitting coils50-1to50-nto transmit magnetic fields in a time-division manner.

In addition, in each of the odd-numbered frame periods, the shape estimating unit57finds each of the coil positions of all the transmitting coils50-1to50-non the basis of each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 detected by the position detection unit55when the magnetic fields are transmitted from the odd-numbered transmitting coils50-1, . . . , and50-n−1 in a time-division manner, and the coil positions and coil directions of the even-numbered transmitting coils50-2, . . . , and50-nalready detected by the position detection unit55and then stored in the memory19ain a frame period closest to each of this odd-numbered frame periods, for example, in a previous frame period. The shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20on the basis of each of the coil positions of all the transmitting coils50-1to50-n, the direction of each of the coils50-1to50-n, and each of the distances between the transmitting coils50-1to50-n.

The position of the insertion portion20and a shape such as a looped shape are estimated by the shape estimating unit57based on the following assumed conditions of the endoscope12. The first condition is that the insertion portion20of the endoscope12does not extend or contract. The second condition is that there is a limit to how the endoscope12curves.

Each of the spaces between the transmitting coils50-1to50-ndoes not change because the insertion portion20does not extend or contract. Each of the spaces between the transmitting coils50-1to50-nis a distance along the scope shape, and is known from a design value of the scope. The endoscope12has a limit in the way of curving; for example, the endoscope12cannot rapidly be bent in a curvature radius R 30 mm or less. A circumference at a curvature radius R of 30 mm is about 188 mm. Therefore, if each of the distances between the transmitting coils50-1to50-nis 100 mm, at least one transmitting coil exists in the loop formed by the insertion portion20. As a result, even the position of the insertion portion20having the loop is identified.

In the present embodiment, in the even- or odd-numbered frame period, the magnetic fields are sequentially transmitted from the even- or odd-numbered transmitting coils in a time-division manner, and each of the coil positions of the even- or odd-numbered transmitting coils is detected. The undetected coil positions of the even- or odd-numbered transmitting coils are detected by use of each of the coil positions of the even- or odd-numbered transmitting coils that have been already detected in the closest frame period. The positions of all the transmitting coils are linked to estimate the position of the insertion portion20and a shape such as a looped shape.

A method of shape estimation between two transmitting coils in the transmitting coils50-1to50-nis specifically described below with reference toFIG. 5toFIG. 10.

The shapes of the parts between the transmitting coils50-1to50-nare estimated by sequentially finding pairs of interpolation points from two interpolation target transmitting coils, for example, the transmitting coils50-1and50-2, and linking all these interpolation points. Terms and abbreviations used in the explanation of the method of shape estimation between two coils are as follows, and some of them are shown inFIG. 5.

The front (coil) is the coil (the transmitting coil50-1) on the distal side of the endoscope12of the two interpolation target coils (e.g., the transmitting coils50-1and50-2). The coordinates of the front coil are P1. The reference sign21aindicates the distal direction of the insertion portion20.

The rear (coil) is the coil (the transmitting coil50-2) on the proximal side of the endoscope12of the interpolation target coils (e.g., the transmitting coils50-1and50-2). The coordinates of the rear coil are P2.

The number of interpolations is a number to which 1 is added to the number of interpolation points.

One interpolation distance (1FD) is a value obtained by dividing the distance between the interpolation target coils (e.g., the transmitting coils50-1and50-2) by the number of interpolations. For example, when the distance is 100 mm and the number of interpolations is 10, one interpolation distance is 10 mm.

A current point is an interpolation point determined at the time of the determination of the previous interpolation point. The first interpolation point determination current point is a point indicating each of the two interpolation target coils.

Current directional vectors Pd1and Pd2are interpolation orbit directional vectors VD1and VD2determined at the time of the determination of the previous interpolation point. The current directional vectors used at the time of the determination of the first interpolation point are directional vectors indicating each of the two interpolation target coils.

The interpolation orbit directional vectors VD1and VD2are unit directional vectors which have been corrected by an interpolation ratio to determine the coordinates of the next interpolation point. For the interpolation ratio, refer to the setting of one interpolation ratio, which will be described later, and the interpolation orbital directions VD1and VD2.

Object directional vectors Po1and Po2are unit directional vectors facing toward the interpolation points to pair with, on the side of the other coil side from the current points. The object directional vector used at the time of the determination of the first interpolation point is a unit directional vector facing from the coordinates indicating one interpolation target coil toward the coordinates indicating another interpolation target coil.

The interpolation points are points located at the coordinates which have moved one interpolation distance from the current points toward the interpolation orbital directions VD1and VD2. The number of interpolation points existing between the interpolation target coils is the number of interpolations−1.

During interpolation processing, the inverted vector of the actual directional vector is treated as the directional vector of the front coil.

[Setting of Interpolation Ratio and Interpolation Orbital Directions]

The basic ratio to find the interpolation ratio is defined as follows.

The basic ratio starts from (1−(1/number of interpolations)), and is a value which decreases by (2/number of interpolations) whenever a pair of front and rear interpolation points are determined.

Two points are determined in one interpolation process, so that, for example, when the number of interpolations is N, the basic ratio is
(1−1/N)→(1−3/N)→(1−5/N)→(1−7/N).

The value obtained by multiplying the length of a line segment connecting the end points of the current directional vectors Pd1and Pd2and the endpoints of the object directional vectors Po1and Po2by the basic ratio is an interpolation ratio 1. The value of the length of a line segment connecting the end points of the current directional vectors Pd1and Pd2and the end points of the object directional vectors Po1and Po2is an interpolation ratio 2.

(a) Case in which Interpolation Ratio 2≥Interpolation Ratio 1 is Satisfied

m(interpolation ratio 1), n(interpolation ratio 2−interpolation ratio 1). Unit vectors of vectors in which the current points are starting points and in which points that internally divide line segments connecting the end points of the current directional vectors Pd1and Pd2and the end points of the object directional vectors Po1and Po2by m:n from the side of the end points of the object directional vectors Po1and Po2are endpoints are the interpolation orbital direction vectors VD1and VD2.

(b) Case in which Interpolation Ratio 2<Interpolation Ratio 1 is Satisfied

n(interpolation ratio 1), m(interpolation ratio 1−interpolation ratio 2). Unit vectors of vectors in which the current points are starting points and in which points that externally divide line segments connecting the end points of the current directional vectors Pd1and Pd2and the end points of the object directional vectors Po1and Po2by n:m from the side of the end point of the object directional vector Po are end points are the interpolation orbital direction vectors VD1and VD2.

The interpolation ratio and the interpolation orbital direction VD to determine the first interpolation point and the second interpolation point are as follows. The third and subsequent points are found in a manner similar to the second point, and are therefore omitted.

Here, N is the number of interpolations.

L1is the length (front) of a line segment which connects the end point of the current directional vector Pd1started from the coil position of the distal side coil (the transmitting coil50-1) and the end point of the object directional vector Po1as shown inFIG. 6.

L2is the length (rear) of a line segment which connects the end point of the current directional vector Pd2started from the coil position of the proximal side coil (the transmitting coil50-2) and the end point of the object directional vector Po2.

(At the Time of the Determination of the First Interpolation Point)

An explanation is given with reference toFIG. 6. An internally dividing point is used because interpolation ratio 2≥interpolation ratio 1 is always satisfied.
L1×(1−1/N),L2×(1−1/N)  Interpolation ratio 1
L1,L2Interpolation ratio 2
m1:L1×(1−1/N)
m2:L2×(1−1/N)
n1:L1×N
n2:L2×N

Unit vectors of the vectors indicated by dotted arrows are the interpolation orbital direction vectors VD1and VD2.

FIG. 7shows the rear coil by way of example, and the same method is also applied to the front coil.

(At the Time of the Determination of the Second Interpolation Point)
L1×(1−3/N),L2×(1−3/N)  Interpolation ratio 1
L1′,L2′  Interpolation ratio 2
(for L2′, seeFIG. 7. L2′ corresponds to L2in the case of the second point)

Unit vectors of the vectors indicated by dotted arrows are the interpolation orbital direction vectors VD1and VD2.

Points of coordinates which have moved one interpolation distance from the current points toward the interpolation orbital direction vectors VD1and VD2found in the previous chapter are next interpolation points, for example, P1′ and P2′ shown inFIG. 9.

These interpolation points P1′ and P2′ are found by moving one interpolation distance from the current points in a straight line. However, when the actual shape of the insertion portion is taken into account, it is considered that a smooth movement distance corresponding to a circular arc should be the one interpolation distance. Thus, the interpolation points that have been found, the current points, and the previous interpolation point are used to reset interpolation points.

At the time of the determination of the first interpolation point, the current point is the coil position, and the previous interpolation point is the position which has moved one interpolation distance from the point of the coil position in a direction opposite to the current directional vector. At the time of the second point, the previous interpolation point is the point of the coil position.

FIG. 10can be drawn when Q0is the previous interpolation point, Q1is the current point, Q2is the interpolation point that has been found, and Q3is the midpoint between the current point Q1and the interpolation point Q2.

A sphere is desirable if a three-dimensional coordinate system is considered. However, it is assumed here that three points are on a two-dimensional coordinate system, and an auxiliary circle is created, and then an interpolation point is reset so that the circular arc of the auxiliary circle will be the one interpolation distance.

(a) An area S of ΔQ0Q1Q2is found by use of Heron's formula.

When s=(a+b+c)/2, the area S of ΔQ0Q1Q2can be found by

(b) Coordinates (w, h) of Q2existing in the third quadrant when Q1is assumed to be an origin are the following values.
S=a×(−h)/2
∴h=−2×S/a

ΔQ1Q2W is a right triangle. Therefore, w is as follows:

(c) A central point R(0, r) of a circle passing through Q1and Q2is found.

A linear equation with two unknowns that represents a straight line passing through a line segment Q1-Q2is represented by
y=a1×x
when the inclination is a1(=−h/w).

ΔQ1Q2W is an isosceles triangle, so that

the central point R exists on a straight line which passes through a midpoint Q3(w/2, h/2) of the line segment Q1-Q2and which intersects at right angles with this line segment Q1-Q2.

If the inclination of this straight line is a2, a linear equation with two unknowns that represents this straight line is represented by
y=a2×x+r.
a2=−1/a1=−w/h
so that r is found.
∴r=(w2/2h)+(h/2)

(d) A central angle ∠Q1RQ2of a sector in which the line segment Q1-Q2is a chord is found.

ΔQ1Q2W and ΔQ1RQ3are similar to each other, so that if central angle ∠Q1RQ2is θ(rad),

∠Q2Q1W is represented by θ/2.
tan(θ/2)=h/w
so that θ is found.
∴θ=2×tan−1(h/w)

If the length of the arc Q1Q2is L, the length of the arc Q1Q2is found by radius×central angle, so that

the length L is represented by
L=|r|×θ.

r is y-coordinate of the third quadrant, and therefore needs to take an absolute value.

(f) For a point Q2′ such that the length L of the arc Q1Q2′ will be the one interpolation distance to be the actual interpolation point, it is necessary to find a length l of a line segment Q1-Q2′.

This length l is represented by

As a result, the next interpolation point Q2′ is represented by the point of a position which has moved in a straight line by the length l from the current point Q1along the interpolation orbital direction vectors VD1and VD2.

The shape estimation method based on the interpolation method described above is One example. Various other shape estimation methods are possible, such as where the positions of multiple coils are linked by a spline curve. Any one of the methods may be used.

Next, the position of the insertion portion20and the operation of detecting a shape such as a looped shape by the apparatus having the above configuration are described.

The insertion portion20of the endoscope apparatus10is inserted into the body cavity of, for example, the patient in accordance with an operation by the operator. The curving portion23of the insertion portion20curves in, for example, the desired upward, downward, leftward, and rightward (UDLR) directions by the operator's operation. Illumination light is output from the distal end of the insertion portion20to illuminate the inside of the body cavity. In this state, an affected part or a lesioned part in the body cavity is observed and treated. When the insertion portion20of the endoscope apparatus10is inserted into the body cavity in this way, the insertion portion20may be looped, for example, as shown inFIG. 18.

First, the signal control unit56drives to turn on and off each of the relays of the relay unit51in the initial frame period (first), supplies electric power to the transmitting coils50-1,50-2, . . . , and50-nin this order from the transmission electric power supply52through the relay unit51, and sequentially transmits magnetic fields from the transmitting coils50-1to50-nin a time-division manner.

The receiving coils53-1to53-mrespectively detect the magnetic fields transmitted from the transmitting coils50-1to50-nin the xyz directions, and generate voltages corresponding to the magnitude of the magnetic fields in the xyz directions at both ends of the receiving coils53-1to53-m.

The voltage detector54connected to the output terminal of each of the receiving coils53-1to53-mdetects each voltage level generated at the output terminal of each of the receiving coils53-1to53-m, and outputs each voltage detection signal corresponding to each of the voltage levels. Each of the voltage detection signals is sent to the position detection unit55.

Each of the voltage detection signals output from the voltage detectors54is input to the position detection unit55. The position detection unit55detects each of the coil positions of the transmitting coils50-1to50-non the basis of the magnitude of each of the voltage levels indicated by each of the voltage detection signals, that is, the magnitude of each of the magnetic fields in the xyz directions, and also detects the direction of each of the receiving coils53-1to53-mfrom the magnitude of each of the magnetic fields in the xyz directions. The coil positions and coil directions of the transmitting coils50-1to50-ndetected by the position detection unit55are stored in the memory19ain the controller19as positional information.

After the end of the initial frame period and the end of the transmission of the magnetic fields from the transmitting coils50-1to50-n, the shape estimating unit57estimates the shape of the insertion portion20which is inserted in a body cavity of a subject such as a human body and thus curved, for example, a shape such as a looped shape, on the basis of each of the coil positions of all the transmitting coils50-1to50-ndetected by the position detection unit55in the initial frame period by the inter-transmission-coil shape estimation method described above in the section [Inter-coil shape estimation method], that is, by sequentially finding pairs of interpolation points from the transmitting coils50-1and50-2and linking all these interpolation points.

The signal control unit56then sequentially controls the even-numbered transmitting coils50-2, . . . , and50-nto transmit magnetic fields in a time-division manner in a frame period (second) that is, the even-numbered frame period. That is, the signal control unit56drives to turn on each of the relays in the relay unit51corresponding to the even-numbered transmitting coils50-2, . . . , and50-n, sequentially supplies electric power to the even-numbered transmitting coils50-2, . . . , and50-nfrom the transmission electric power supply52through the relay unit51, and sequentially transmits magnetic fields from the transmitting coils50-1to50-nin a time-division manner.

The receiving coils53-1to53-msequentially detect the magnetic fields respectively transmitted from the even-numbered transmitting coils50-2, . . . , and50-nin a time-division manner in the xyz directions, and generate voltages corresponding to the magnitude of the magnetic fields in the xyz directions at both ends of the receiving coils53-1to53-m. Thus, as described above, the position detection unit55detects each of the coil positions of the even-numbered transmitting coils50-2, . . . , and50-n. Each of the coil positions of the even-numbered transmitting coils50-2, . . . , and50-nis stored in, for example, the memory19ain the controller19.

The shape estimating unit57reads each of the coil positions of the even-numbered transmitting coils50-2, . . . , and50-ndetected by the position detection unit55from the memory19ain the frame period (second).

The shape estimating unit57reads, from the memory19a, each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 among all the transmitting coils50-1to50-nalready detected from the memory19aby the position detection unit55in a frame period closest to the second frame period, that is, the previous first frame period.

The shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-nin accordance with the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], on the basis of each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 detected by the position detection unit55, and the coil positions and coil directions of the even-numbered transmitting coils50-2, . . . , and50-nread from the memory19a.

The signal control unit56then sequentially controls the odd-numbered transmitting coils50-1, . . . , and50-n−1 to transmit magnetic fields from in a time-division manner in a third frame period, that is, the odd-numbered frame period.

The receiving coils53-1to53-msequentially detect the magnetic fields respectively transmitted from the odd-numbered transmitting coils50-1, . . . , and50-n−1 in a time-division manner in the xyz directions, and generate voltages corresponding to the magnitude of the magnetic fields in the xyz directions at both ends of the receiving coils53-1to53-m. Thus, as described above, the position detection unit55detects each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1. Each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 is stored in, for example, the memory19ain the controller19.

As described above, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by interpolating and linking the coils in accordance with the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], on the basis of each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 detected by the position detection unit55when the magnetic fields are sequentially transmitted from the odd-numbered transmitting coils50-1, . . . , and50-n−1 in a time-division manner, and each of the coil positions of the even-numbered transmitting coils50-2, . . . , and50-nalready detected by the position detection unit55and stored in the memory19ain a frame period closest to this third frame period, for example, in the previous second frame period.

Subsequently, in the even-numbered frame period, the shape, for example, looped shape of the insertion portion20is estimated by interpolating and linking the coils in accordance with the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], on the basis of each of the coil positions of the even-numbered transmitting coils50-2, . . . , and50-ndetected when the magnetic fields are sequentially transmitted from the even-numbered transmitting coils50-2, . . . , and50-nin a time-division manner, and each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 already detected in a frame period closest to this even-numbered frame period, for example, in the previous frame period.

In the odd-numbered frame period, the shape, for example, looped shape of the insertion portion20is estimated by interpolating and linking the coils in accordance with the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], on the basis of each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 detected when the magnetic fields are sequentially transmitted from the odd-numbered transmitting coils50-1, . . . , and50-n−1 in a time-division manner, and each of the coil positions of the even-numbered transmitting coils50-2, . . . , and50-nalready detected in a frame period closest to this odd-numbered frame period, for example, in the previous frame period.

Thus, according to the first embodiment described above, in the even-numbered frame period, the magnetic fields are sequentially transmitted from the even-numbered transmitting coils50-2, . . . , and50-nin a time-division manner, and the shape, for example, looped shape of the insertion portion20is estimated on the basis of each of the coil positions of the even-numbered transmitting coils50-2, . . . , and50-nand each of the coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1 already detected in the closest frame period. In the odd-numbered frame period, the magnetic fields are sequentially transmitted from the odd-numbered transmitting coils50-1, . . . , and50-n−1 in a time-division manner, and the shape, for example, looped shape of the insertion portion20is estimated by linking the coil positions of the transmitting coils50-1to50-non the basis of the coil positions of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1, and the coil positions and directions of each of the even-numbered transmitting coils50-2, . . . , and50-nalready detected in the closest frame period.

For example, as shown inFIG. 4, the position of the insertion portion20and a shape such as a looped shape are estimated on the basis of each of the coil positions of the even-numbered transmitting coils50-2,50-4, and others and each of the coil positions of the odd-numbered transmitting coils50-1,50-3, and others already detected by the position detection unit55and stored in the memory19a. Therefore, when magnetic fields are transmitted from the even-numbered transmitting coils50-2, . . . , and50-n, the shape, for example, looped shape of the insertion portion20can be estimated even if the even-numbered transmitting coils50-2, . . . , and50-nare not detected in the looped shape of the insertion portion20.

Thus, magnetic fields are not transmitted from all the transmitting coils50-1to50-nin a time-division manner in every frame period, and the coil positions of all the transmitting coils50-1to50-nare not detected, so that the frame rate does not decrease. For example, the configuration of the present instrument1is not greatly changed in comparison with the case in which the magnetic fields are sequentially transmitted from all the transmitting coils50-1to50-nin every frame period to estimate the shape of the insertion portion20. The frame rate to estimate the shape of the insertion portion20can be about twice as high. The size of the instrument1is not changed. Moreover, the price does not increase either.

When the position of each of the transmitting coils detected by sequentially transmitting magnetic fields from the transmitting coils50-2, . . . , and50-nand the already detected coil position of each of the transmitting coils are used, this is equivalent to the detection of the coil positions of all the transmitting coils50-1to50-n, so that the shape, for example, looped shape of the insertion portion20can be certainly estimated even if the insertion portion20is looped.

Second Embodiment

Next, a second embodiment of the present invention is described with reference to the drawings.

The configuration of the present instrument1in this embodiment is the same, so that the differences are only described usingFIGS. 1 and 2together.

In the initial frame period (first), the signal control unit56controls all the transmitting coils50-1to50-nto transmit magnetic fields in a time-division manner.

In the first frame period (even-numbered frame) among the frame periods after the initial frame period, the signal control unit56sequentially controls the even-numbered transmitting coils50-2, . . . , and50-nas the predetermined coils among the transmitting coils50-1to50-nto transmit magnetic fields.

In the same even-numbered frame period, the shape estimating unit57estimates the coil position of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 on the basis of the coil position adjacent to each of the odd-numbered transmitting coils50-1, . . . , and50-n−1. The shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-non the basis of the estimated coil positions, the coil position and coil direction of each of the even-numbered transmitting coils50-2, . . . , and50-nalready detected in the closest frame period, and each of the distances between the transmitting coils50-1to50-n.

In the frame period of the second frame period (odd-numbered frame), the signal control unit56sequentially controls the odd-numbered transmitting coils50-1, . . . , and50-n−1 as the predetermined coils among the transmitting coils50-1to50-nto transmit magnetic fields.

In the same odd-numbered frame period, the shape estimating unit57estimates the coil position of each of the even-numbered transmitting coils50-2, . . . , and50-non the basis of the coil position adjacent to each of the even-numbered transmitting coils50-2, . . . , and50-n. The shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-non the basis of the estimated coil positions, the coil position and coil direction of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 already detected in the closest frame period, and each of the distances between the transmitting coils50-1to50-n.

The shape estimating unit57estimates the coil position of each of the predetermined coils, that is, the coil position of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 and the coil position of each of the even-numbered transmitting coils50-2, . . . , and50-non the basis of the positions of the predetermined coils, that is, the coil position of each of the even-numbered transmitting coils50-2, . . . , and50-nor the coil position of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1, and one or both of the coil position of each of the transmitting coils provided adjacent to the predetermined coil and the adjacent direction.

Specifically, in the initial frame period, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-non the basis of the coil position and coil direction of each of the transmitting coils50-1to50-ndetected by the position detection unit55when the magnetic fields are transmitted from the transmitting coils50-1to50-n, and each of the distances between the transmitting coils50-1to50-n.

In each of the frame periods after the initial frame period, the shape estimating unit57estimates the smooth shape of the insertion portion20from the coil directions and coil positions of the predetermined coils (the even-numbered transmitting coils50-2, . . . , and50-nand the odd-numbered transmitting coils50-1, . . . , and50-n−1) on the basis of each of the voltage detection signals output from the voltage detectors54, that is, each of the voltage detection signals corresponding to each of the voltage levels generated at the output terminal of each of the receiving coils53-1to53-m. The shape estimating unit57estimates the coil position of the transmitting coil50-2that may actually exist, from the shape of the insertion portion20, and the coil direction and coil position of the transmitting coil50-1in the previous frame period of the transmitting coil other than the predetermined coil (each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 or each of the even-numbered transmitting coils50-2, . . . , and50-n).

The shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20by linking the coil positions of the transmitting coils50-1to50-nin accordance with the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], on the basis of the coil position estimated by use of the predicted position of the coil (existence probability of the coil), each of the coil positions and magnetic field directions of the predetermined coils already detected in the closest frame period, and each of the distances between the transmitting coils50-1to50-n.

A specific shape estimation method that uses the predicted position of the coil (existence probability of the coil) is described.

In the first embodiment, for example, the looped shape of the insertion portion20can be estimated with a certain degree of accuracy even if the number of the transmitting coils50-1to50-nis small. However, for example, when the movement of the scope including the insertion portion20is fast or when the scope tends to move, there is a greater difference in the coil position of each of the transmitting coils50-1to50-nbetween the recent frame period and the current frame period, and the estimated shape differs from the actual shape. Even in such a case, according to the present second embodiment, the shape, for example, looped shape of the insertion portion20can be accurately estimated.

A specific example in which the scope tends to move is shown, and a phenomenon that occurs in the above-described first embodiment in which the estimated shape differs from the actual shape is described, wherein given successive two frames are the first frame and the second frame, respectively, as shown by (1) and (2) below. In the explanation below, both the first frame and the second frame are frames in the frame periods after the initial frame period, and the first frame is an odd-numbered frame, and the second frame is an even-numbered frame.

(1) First Frame

FIG. 11shows an actual shape K1of the insertion portion20and the coil position of each of the transmitting coils50-1to50-nprovided therein in the first frame.FIG. 11shows each of the transmitting coils50-2to50-4.

In the first frame, the signal control unit56sequentially controls the odd-numbered transmitting coils50-1to50-n−1 to transmit magnetic fields in a time-division manner.

The shape estimating unit57detects the coil position and coil direction of each of the transmitting coils50-1to50-n−1 detected by the position detection unit55when the magnetic fields are sequentially transmitted from the odd-numbered transmitting coils50-1to50-n−1 in a time-division manner in the initial one frame.

(2) Second Frame

FIG. 12shows an actual shape K2of an insertion portion20-1and the actual coil position of each of the transmitting coils50-1to50-nprovided therein in the frame next to the first frame (i.e., the second frame).FIG. 12shows the shape K1of the insertion portion20in the first frame over the actual shape K2of the insertion portion20-1in the second frame.

The second frame is an even-numbered frame, so that the signal control unit56sequentially controls the even-numbered transmitting coils50-2, . . . , and50-namong the transmitting coils50-1to50-nto transmit magnetic fields in a time-division manner. Thus, the shape estimating unit57estimates the shape of the insertion portion20-1in the second frame on the basis of the coil position and coil direction of each of the even-numbered transmitting coils50-2, . . . , and50-ndetected in the second frame, and the coil position and coil direction of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 already detected in the previous initial frame period.

In the state shown in the second frame, the insertion portion20is pressed from the side of the operation unit30(the right side in the drawing) (press direction M), and the transmitting coil50-3close to the operation unit30moves to the left side, whereas the transmitting coil50-1close to the distal end of the insertion portion20does not smoothly move to the left side. Due to this state, in the second frame period, the shape K2of the insertion portion20is curved into, for example, a bow shape, and is different from the shape K1of the insertion portion20in the initial frame period. In such a situation in which the transmitting coil50-2tends to move and the difference in the transmitting coil positions between frames is great, the estimated shape of the insertion portion may be different from the actual shape K2of the insertion portion20in the first embodiment.

In the present embodiment, when the difference in the transmitting coil positions between frames is great, the shape estimation method that uses the smoothness of the shape and the existence probability of the coil is also employed to reduce the difference between the actual shape K2of an insertion portion20and the estimated shape of the insertion portion20.

An overview of the shape estimation method that uses the existence probability is described.

In the first embodiment described above, the shape of the insertion portion20in the endoscope apparatus10may be estimated to be a non-smooth unnatural shape such as the shape K2shown inFIG. 12.

In contrast, the shape estimation method according to the present embodiment allows a smoother shape of the insertion portion20, and still sets the position of the transmitting coil50-3at the position which is not that far from the coil position of the transmitting coil50-3in the closest frame, for example, the previous frame.

The shape estimation method that uses the existence probability as the shape estimation method according to the present embodiment is specifically described below along with a shape estimation flowchart shown inFIG. 13.

FIG. 14shows the coil position of the transmitting coil50-3estimated by the estimation method according to the first embodiment in the first frame, and the actual shape K2of the insertion portion20in the second frame.

In step S1, in the second frame, the shape estimating unit57estimates, for example, the looped shape of the insertion portion20in accordance with the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], on the basis of the coil position and coil direction of each of the even-numbered transmitting coils50-2, . . . , and50-ndetected by an estimation method similar to that in the first embodiment, that is, by sequentially transmitting magnetic fields from the even-numbered transmitting coils50-2, . . . , and50-nin a time-division manner in the even-numbered frame period, and the coil position and coil direction of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 already detected in the recent frame (previous frame).

In step S2, the shape estimating unit57estimates the shape of the part between the transmitting coil50-2(a coil position J1) and the transmitting coil50-4(a coil position J3) by the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], using the coil position J1and coil direction of the transmitting coil50-2detected in the second frame shown inFIG. 15, the coil position J3and coil direction of the transmitting coil50-4detected in the second frame, and the distance between the transmitting coils (e.g., 200 mm). The distance between the transmitting coils (e.g., 200 mm) corresponds to the distance between the transmitting coil50-2and the transmitting coil50-4that is the distance of two coils.

FIG. 15shows the shape of the insertion portion20estimated by the shape estimating unit57. The shape of the insertion portion20estimated by step S1is represented as K1, and the shape of the insertion portion20estimated by step S2is represented as K2.

In step S3, the shape estimating unit57determines a point located at half of the length of the insertion portion20along the second shape K2(when the transmitting coils50-2,50-3, and50-4are arranged at equal intervals) as an estimated point C2of the transmitting coil50-3.

In step S4, the shape estimating unit57determines a direction along the shape K2at the estimated point C2of the transmitting coil50-3as an estimated direction F2of the transmitting coil50-3.

In step S5, the shape estimating unit57determines a midpoint between the estimated point C2of the transmitting coil50-3and the coil position C1of the transmitting coil50-3in the recent frame (first frame) as an estimated point C3of the transmitting coil50-3.

Similarly, in step S6, the shape estimating unit57determines the average of the estimated direction F2of the transmitting coil50-3and a direction F1of the transmitting coil50-3in the recent frame (first frame) as an estimated direction F3of the transmitting coil50-3at the estimated point C3.

In step S7, the shape estimating unit57finds a third shape K3of the insertion portion20by the inter-coil shape estimation method described above in the section [Inter-coil shape estimation method], using the estimated point C3of the transmitting coil50-3and the estimated direction F3of the transmitting coil50-3, the coil position K1and the coil direction of the transmitting coil50-2detected in the second frame, the coil position J3and the coil direction of the transmitting coil50-4detected in the second frame, and the distance between the transmitting coils (e.g., 100 mm). The shape K3can be said to be an intermediate shape between the shape K1and the shape K2.

The shape estimating unit57may repeat processing similar to that in step S5to step S7, and find more intermediate shapes, for example, an intermediate shape between the shape K1and the shape K3and an intermediate shape between the shape K2and the shape K3.

In step S8, the shape estimating unit57calculates the smoothness of the first to third shapes K1, K2, and K3of the insertion portion20as follows:

The shape estimating unit57divides the shape of the part between the coil position J1of the transmitting coil50-2and the coil position J3of the transmitting coil50-4into N equal parts as shown inFIG. 16. Here, the shape is divided into 6(═N) equal parts.

The shape estimating unit57links the N equal parts by a line, and determines line segments thus obtained as a line L1, a line L2, . . . , and a line LN from the distal end as shown inFIG. 17.

The shape estimating unit57determines a reciprocal of the total value of the N−1 angular differences α as the value of smoothness.

In step S9, the shape estimating unit57calculates the existence probability of each of the estimated points C1, C2, and C3of the transmitting coil50-3in the first, second, and third shapes K1, K2, and K3as follows:

The shape estimating unit57respectively calculates distances X1, X2, and X3(mm) between the coil position C1of the transmitting coil50-3in the recent frame (first frame) and the estimated points C1, C2, and C3of the transmitting coil50-3in the first to third shapes K1, K2, and K3. The coil position C1of the transmitting coil50-3in the first shape K1is the coil position of the transmitting coil50-3in the recent frame.

The shape estimating unit57respectively determines the existence probabilities of the first to third shapes as 100−100·X1/(X1+X2+X3), 100−100·X2/(X1+X2+X3), and 100−100·X3/(X1+X2+X3).

For example, the estimated point C1of the transmitting coil50-3in the first shape K1is the coil position of the transmitting coil50-3in the recent frame, so that the existence probability is 100 when X1=0.

In step S10, the shape estimating unit57determines, as a determination value, the value in which the value of smoothness in each shape is added to the value of the existence probability multiplied by k. k is a coefficient representing the difficulty in the change of the position of the scope between frames, and varies depending on the type of scope, the frame rate, and the part in the body in which the scope is located.

In step S11, the shape estimating unit57selects and displays a shape having a high determination value from the first to third shapes K1to K3.

Next, an operation of detecting the position of the insertion portion20and a shape such as a looped shape by the apparatus having the above configuration is described.

The insertion portion20of the endoscope apparatus10is inserted into the body cavity of, for example, the patient by the operator's operation. When the insertion portion20is inserted into the body cavity, the insertion portion20may be looped, for example, as shown inFIG. 18.

First, in the initial frame period (first), the signal control unit56sequentially controls all the transmitting coils50-1to50-nto transmit magnetic fields in a time-division manner.

In the initial frame period, the shape estimating unit57estimates the shape, for example, looped shape of the insertion portion20inserted in the body cavity of the subject and thus curved on the basis of each of the coil positions of all the transmitting coils50-1to50-ndetected by the position detection unit55.

In the first frame (odd-numbered frame) among the frame periods after the initial frame period, the signal control unit56then sequentially controls the odd-numbered transmitting coils50-1, . . . , and50-n−1 as the predetermined coils among the transmitting coils50-1to50-nto transmit magnetic fields.

The shape estimating unit57then detects the positions and directions of the predetermined coils, that is, the odd-numbered transmitting coils50-1, . . . , and50-n−1 on the basis of each of the voltage detection signals corresponding to each of the voltage levels generated at the output terminal of each of the receiving coils53-1to53-m. The shape estimating unit57estimates the smooth shape of the insertion portion20from the position and direction of each of the odd-numbered transmitting coils among the odd-numbered transmitting coils (step S2).

In this instance, when the even-numbered transmitting coils50-2, . . . , and50-nalone exist in the loop as shown inFIG. 18, it is not known by the odd-numbered transmitting coils50-1, . . . , and50-n−1 alone which direction the looped shape is in, so that one second shape K2is not determined in contrast to the above, and there are countless second shapes K2.

In this case, the shape estimating unit57carries on the processing in and after step S3in accordance with representative i second shapes K2(K2-1, K2-2, . . . , and K2-i), and finds i×2+1 candidate shapes from the position and direction of each of the transmitting coils50-2, . . . , and50-nalready detected by the position detection unit55in the previous frame. The shape estimating unit57selects the shape of the part between the odd-numbered transmitting coils50-1, . . . , and50-n−1 from the candidate shapes in accordance with the smoothness of the shapes and the existence probability.

Thus, the shape estimating unit57estimates the shape of the whole insertion portion20by selecting the shapes of the parts between the odd-numbered transmitting coils50-1, . . . , and50-n−1.

On the other hand, in the second (even-numbered frame) frame period among the frame periods after the initial frame period, the signal control unit56sequentially controls the even-numbered transmitting coils50-2, . . . , and50-nas the predetermined coils among the transmitting coils50-1to50-nto transmit magnetic fields.

As in the odd-numbered frame, the shape estimating unit57then detects the positions and directions of the predetermined coils, that is, the even-numbered transmitting coils50-2, . . . , and50-non the basis of each of the voltage detection signals corresponding to each of the voltage levels generated at the output terminal of each of the receiving coils53-1to53-m. The shape estimating unit57estimates the smooth shape of the insertion portion20from the position and direction of each of the even-numbered transmitting coils50-2, . . . , and50-namong the even-numbered transmitting coils50-2, . . . , and50-n.

The shape estimating unit57then finds candidate shapes from the position and direction of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 already detected by the position detection unit55in the previous frame. The shape estimating unit57selects the shapes of the parts between the even-numbered transmitting coils50-2, . . . , and50-nfrom the candidate shapes in accordance with the smoothness of the shapes and the existence probability.

Thus, the shape estimating unit57estimates the shape of the whole insertion portion20by selecting the shapes of the parts between the even-numbered transmitting coils50-2, . . . , and50-n.

Thus, according to the second embodiment described above, the coil positions and coil directions of the predetermined coils (the even-numbered transmitting coils50-2, . . . , and50-nor the odd-numbered transmitting coils50-1, . . . , and50-n−1) are detected, and the existence probability of the predetermined coils already detected in the recent frame existing around each coil position is set, and then the shape, for example, looped shape of the insertion portion20is estimated using this existence probability and the smoothness of the shapes. Therefore, in the second embodiment described above, advantageous effects similar to those in the previously described first embodiment are provided, and the shape, for example, looped shape of the insertion portion20can be more accurately estimated, for example, even when the movement of the scope including the insertion portion20is fast or when the scope tends to move.

As another embodiment, when some of the transmitting coils50-1to50-nare determined to be continuously out of magnetic field detection ranges of the receiving coils53-1to53-min a predetermined period, for example, in a period of several frames or more, the signal control unit56may control these transmitting coils to transmit magnetic fields and directly detect the coil positions of the transmitting coils50-1to50-nin the initial frame period after the period of several frames or more.

Thus, whenever the scope goes out of the magnetic field detection range and then returns to the detection range, magnetic fields are always transmitted and the positions are directly detected. As a result, the shape is not detected on the basis of old coil position information of several frames or more before. It is possible to more accurately estimate the shape even when the scope temporarily goes out of the detection range and then returns to the detection range.

As another embodiment, the signal control unit56sequentially controls the odd-numbered transmitting coils50-1, . . . , and50-n−1 as the predetermined coils among the transmitting coils50-1to50-nto transmit magnetic fields in the second frame period (odd-numbered frame period) among the frame periods after the initial frame period.

In the odd-numbered frame period, the shape estimating unit57estimates the coil position of each of the even-numbered transmitting coils50-2, . . . , and50-non the basis of the coil position of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 adjacent to each of the even-numbered transmitting coils50-2, . . . , and50-n. The shape estimating unit57estimates the coil position of each of new even-numbered transmitting coils50-2, . . . , and50-non the basis of the distance between the coil position of each of the even-numbered transmitting coils50-2, . . . , and50-nalready detected by the position detection unit55in a frame period closest to the odd-numbered frame period and the estimated coil positions of the odd-numbered transmitting coils50-1, . . . , and50-n−1. The shape estimating unit57estimates the shape of the insertion portion20on the basis of the newly estimated coil positions of the even-numbered transmitting coils50-2, . . . , and50-nand the coil position of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1.

The shape estimating unit57estimates the coil position and the coil direction of each of the even-numbered transmitting coils50-2, . . . , and50-non the basis of the coil position and the coil direction of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1 adjacent to each of the even-numbered transmitting coils50-2, . . . , and50-n. The shape estimating unit57estimates the shape of the insertion portion20on the basis of the coil position and the coil direction that have been estimated and the coil position and the coil direction of each of the odd-numbered transmitting coils50-1, . . . , and50-n−1.

The shape estimating unit57estimates the coil position of each of the new even-numbered transmitting coils50-2, . . . , and50-non the basis of the smoothness of the shape of the insertion portion20as well.

The present invention is not completely limited to the embodiments described above, and modifications of components can be made at the stage of carrying out the invention without departing from the spirit thereof. Further, various inventions can be made by properly combining the components disclosed in the embodiments described above. For example, some of all the components shown in the embodiments may be eliminated. Moreover, the components in different embodiments may be properly combined.

The transmitting coils50-1to50-nare provided in, but not exclusively, the insertion portion20of the endoscope apparatus10in each of the embodiments described above. The receiving coils53-1to53-mmay be provided in the insertion portion20and the transmitting coils may be provided in the antenna53. In this case, the shape of the insertion portion20is estimated on the basis of the position of each of the receiving coils provided in the insertion portion20. In this instance, the receiving coils which process received signals output from the receiving coils53-1to53-mare selected from the receiving coils53-1to53-min each frame period. Consequently, it is possible to reduce the size of the circuit configuration which processes the received signals without a decrease in frame rate.

Although the coils transmit and receive magnetic fields in the embodiments described above, any material that can transmit and receive magnetic fields is possible. For example, hall elements, MI sensors, or tunnel magnetoresistive (TMR) sensors are also possible.