Patent Publication Number: US-8974373-B2

Title: Capsule-type medical device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. application Ser. No. 12/252,085 filed on Oct. 15, 2008, now U.S. Pat. No. 8,465,418, which is a continuation application of PCT/JP2007/058355 filed on Apr. 17, 2007 and claims benefit of Japanese Application No. 2006-115958 filed in Japan on Apr. 19, 2006, the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a capsule-type medical device that is inserted to a living body to perform image pickup, etc. 
     2. Description of the Related Art 
     Endoscopes, which enable diagnostic examinations, or treatments as necessary, of a body cavity by inserting an insertion portion to the body cavity have come into wide use in the medical and other fields. 
     Also, recently, a capsule-type medical device including a capsule-type in-vivo device having the shape of a capsule (abbreviated to “capsule”), which is swallowed from the mouth to pick up images in the body cavity, thereby enabling an endoscopic examination, has been put into practical use. 
     When a capsule is inserted into a body cavity, it ordinarily moves in the body cavity by means of peristaltic movement or the like, and accordingly, it is sometimes desirable to know information obtained by the capsule corresponds to which site in the body. 
     Therefore, as a first related art example, for example, Japanese Patent Application Laid-Open Publication No. 2003-524448 discloses the art in which a signal sent wirelessly from a capsule in a body cavity via an antenna is received by a plurality of antennae arranged outside the body to calculate the position of the capsule from, e.g., the intensity of the received signal. 
     Also, as a second related art example, Japanese Patent Application Laid-Open Publication No. 2005-198789 discloses the art in which a signal sent wirelessly via an antenna of a capsule in a body cavity is received by a plurality of antennae arranged outside the body to calculate the position and direction of the capsule from, e.g., the intensity of the received signal. 
     Meanwhile, when the position of a capsule is estimated, multiple positions may be estimated because of noise, etc. 
     Where multiple positions have been estimated as mentioned above, it is difficult to determine the track of the movement of the capsule unless the positions of the antenna in the capsule at respective times are determined, lowering the utility value of information on the inside of the body, etc., obtained by the capsule. 
     SUMMARY OF THE INVENTION 
     A capsule-type medical device according to the present invention includes: a capsule-type in-vivo device including an antenna, the capsule-type in-vivo device being inserted into a living body; a wireless transmission section for transmitting wirelessly an electromagnetic wave signal from the antenna in the capsule-type in-vivo device; a plurality of extracorporeal antennae arranged outside the living body; an estimation section for estimating a position of the antenna or the capsule-type in-vivo device from the electromagnetic wave signal at a time when the electromagnetic wave signal was received by the plurality of extracorporeal antennae; and a track calculating section for calculating a track of movement of the capsule-type in-vivo device according to a condition set for the case where a plurality of positions at mutually different times have been estimated by the estimation section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a diagram illustrating a configuration of a capsule-type endoscopic device, etc., according to embodiment 1 of the present invention; 
         FIG. 1B  is a diagram illustrating a state in which an extracorporeal device in  FIG. 1A  is connected to a terminal apparatus; 
         FIG. 2  is a schematic cross-sectional view of an inner configuration of a capsule-type endoscope; 
         FIG. 3  is a diagram illustrating an example arrangement of a plurality of antennae included in an antenna unit and a coordinate system set for one of the antennae; 
         FIG. 4A  is a diagram illustrating a schematic configuration of an electric system for transmission/reception of signals in a capsule-type endoscope; 
         FIG. 4B  is a diagram illustrating a schematic configuration of an electric system for transmission/reception of signals in an extracorporeal device; 
         FIG. 5A  is a diagram illustrating an example of an image signal, etc., sent wirelessly from a capsule-type endoscope; 
         FIG. 5B  is a diagram illustrating an example of an image signal, etc., sent wirelessly from a capsule-type endoscope, which is different from the example in  FIG. 5A ; 
         FIG. 6A  is a diagram indicating, by means of polar coordinates, components of an electromagnetic field, etc., at a given position, which is sent from an antenna formed of an circular coil in a capsule-type endoscope; 
         FIG. 6B  is a diagram indicating, by means of orthogonal coordinates, components of an electromagnetic field, etc., at a given position, which is sent from an antenna formed of a circular coil in a capsule-type endoscope; 
         FIG. 7  is a diagram illustrating an electromotive force detected when an electric field generated by the antenna in  FIG. 6  is received by a rod-like antenna in an antenna unit; 
         FIG. 8  is a diagram illustrating positions estimated at temporally adjacent times; 
         FIG. 9  is a diagram illustrating whether or not positions estimated at an adjacent time are within a sphere with a radius r set in advance; 
         FIG. 10  is a flowchart of processing for determining connection relations, which are candidates for a route constituting a track, from positions estimated at adjacent times; 
         FIG. 11  is a flowchart illustrating the content of processing for calculating a track after the processing in  FIG. 10 ; 
         FIG. 12A  is a diagram illustrating an example of a state of display where an image picked up by a capsule-type endoscope and positions forming a calculated track are both displayed; 
         FIG. 12B  is an example of a state of display where an image picked up by a capsule-type endoscope and positions forming a calculated track are both displayed, which is different from the example in  FIG. 12A ; 
         FIG. 13A  is a diagram illustrating a coordinate system X w Y w Z w  based on a human body; 
         FIG. 13B  is a diagram illustrating a state in which a space where a capsule-type endoscope  3  exists is divided into a plurality of regions; 
         FIG. 14  is a diagram illustrating the relationship between positions estimated at adjacent times and small regions; 
         FIG. 15  is a diagram illustrating a manner in which connection relations that are candidates for calculating a track are determined from a plurality of positions estimated at adjacent times; 
         FIG. 16  is a flowchart of the content of processing for determining connection relations, which are candidates for calculating a track, from a plurality of positions estimated at adjacent times; 
         FIG. 17  is a diagram illustrating two-dimensional array information stored in a second memory as a result of the processing in  FIG. 16 ; 
         FIG. 18  is a flowchart of the content of processing for calculating a track after the processing in  FIG. 16 ; and 
         FIG. 19  is a diagram illustrating two-dimensional array information stored in a third memory as a result of the processing in  FIG. 18 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     Embodiment 1 
       FIGS. 1 to 12B  relate to embodiment 1 of the present invention.  FIG. 1A  is a diagram illustrating the configuration of a capsule-type endoscopic device, etc., according to embodiment 1 of the present invention.  FIG. 1B  is a diagram illustrating a state in which an extracorporeal device in  FIG. 1A  is connected to a terminal apparatus.  FIG. 2  is a diagram illustrating the inner configuration of the capsule-type endoscope.  FIG. 3  is a diagram illustrating an example arrangement of a plurality of antennae included in an antenna unit and a coordinate system set for one of the antennae.  FIG. 4A  is a diagram illustrating a schematic configuration of an electric system for transmission/reception of signals in a capsule-type endoscope.  FIG. 4B  is a diagram illustrating a schematic configuration of an electric system for transmission/reception of signals in an extracorporeal device. 
     Also,  FIG. 5A  is a diagram illustrating an example of an image signal, etc., sent wirelessly from the capsule-type endoscope.  FIG. 5B  is a diagram illustrating an example of an image signal, etc., sent wirelessly from a capsule-type endoscope, which is different from the example in  FIG. 5A .  FIG. 6A  is a diagram indicating, by means of polar coordinates, components of an electromagnetic field, etc., at a given position, which is sent from an antenna formed of an circular coil in a capsule-type endoscope.  FIG. 6B  is a diagram indicating, by means of orthogonal coordinates, components of an electromagnetic field, etc., at a given position, which is sent from an antenna formed of a circular coil in a capsule-type endoscope.  FIG. 7  is a diagram illustrating the relationship with a direction Da of a rod-like antenna included in the antenna unit that receives an electric field generated by the antenna shown in  FIG. 6 . 
     Also,  FIG. 8  is a diagram illustrating multiple positions estimated at temporally adjacent times.  FIG. 9  is a diagram illustrating whether or not positions estimated at an adjacent time are within a sphere with a radius r d  of a value set in advance.  FIG. 10  is a diagram illustrating the content of processing for determining connection relations, which are candidates for a track, from positions estimated at adjacent times.  FIG. 11  is a diagram illustrating the content of processing for calculating the track after the processing in  FIG. 10 .  FIG. 12A  is a diagram illustrating an example of a state of display where an image picked up by the capsule-type endoscope and the positions forming the calculated track are both displayed.  FIG. 12B  is a diagram illustrating an example of a state of display where an image picked up by the capsule-type endoscope and the positions forming the calculated track are both displayed, which is different from the example illustrated in  FIG. 12A . 
     As shown in  FIG. 1A , a capsule-type endoscopic device  1  according to embodiment 1 of the present invention includes: a capsule-type endoscope  3  that, e.g., picks up an image of the inside of a body cavity, as a capsule-type in-vivo device that is inserted into the body cavity by being swallowed by a patient  2  from the mouth; and an extracorporeal device (or an external device)  5  that is arranged outside the body of the patient  2  and connected to an antenna unit  4  that wirelessly receives information on an image picked up by the capsule-type endoscope  3 , as its main components. 
     As shown in  FIG. 1B , this extracorporeal device  5  is attached to a cradle  6  and thereby electrically connected to a terminal apparatus  7 , which is a personal computer or the like. Also, the terminal apparatus  7  is capable of, e.g., loading an image stored in the extracorporeal device  5  in this terminal apparatus  7  via input and operating devices such as a keyboard  8   a  and/or a mouse  8   b  and displaying the loaded image on a monitor section  8   c.    
     As shown in  FIG. 1A , a jacket  10  worn by the patient  2 , which is used when he/she swallows the capsule-type endoscope  3  to undergo an endoscopic examination, is provided with the antenna unit  4  equipped with a plurality of antennae  11 . 
     Signals based on an image of a subject that is picked up by the capsule-type endoscope  3  and sent from an antenna  23  (see  FIG. 2 ) incorporated therein, are received by the plurality of antennae  11  in the antenna unit  4 . Consequently, the extracorporeal device  5  connected to the antenna unit  4  can store the image picked up by the capsule-type endoscope  3 . 
     Also, this extracorporeal device  5  has the shape of, e.g., a box, and on its front surface, a liquid-crystal monitor  12  that displays images and an operating section  13  for, e.g., performing an operation to give instructions are provided. 
     The extracorporeal device  5  may be constructed to only have, e.g., a LED for displaying a warning relating to the remaining battery level, and a power supply switch as the operating section  13 . Also, a portable display device (viewer), which is not shown, may be connected to the extracorporeal device  5  as a second extracorporeal device, the portable display device processing image signals sent from the capsule-type endoscope  3  and displaying an image on a liquid-crystal monitor equipped with the portable display device. 
     As shown in  FIG. 2 , the capsule-type endoscope  3  includes: an exterior member  14  having the shape of a cylinder with its rear end closed, and a dome-shaped cover  14   a , which is rounded substantially in the shape of a hemisphere, connected by an adhesive to, and thereby closing, a distal end of this cylinder. Thus, the exterior of the capsule-type endoscope  3  has the shape of a capsule and a watertight construction in its entirety when the exterior member  14  and the cover member  14   a  are connected. 
     At a portion around the center of the cylinder in this transparent dome-shaped cover  14   a , an objective lens  15  that forms an image entered via the dome-shaped cover  14   a  is arranged in the state of being attached to a lens frame  16 . At the position where an image is formed by the objective lens  15 , here, a CCD imager  17  is arranged as an image pickup device. 
     Also, around the objective lens  15 , four white LEDs  18  are arranged on the same plane as an illumination system. Also, for example, on the back side of the CCD imager  17 , a processing circuit  19  that drives the white LEDs  18  to emit light and drives the CCD imager  17  to perform signal processing for generating image signals from image pickup signals inputted from the CCD imager  17 , a transceiver circuit  20  having a function that transmits image signals and receives signals from the extracorporeal device  5 , and button-shaped batteries  21  that supply power to the processing circuit  19  and the transceiver circuit  20  are arranged inside the exterior member  14 . 
     Also, at the rear end of the button-shaped batteries  21 , that is, inside the other semispherical shape, an antenna  23  having the shape of a circular coil (circular loop coil), which is connected to the transceiver circuit  20  and sends/receives radio waves, is arranged. Also, the CCD imager  17 , the white LEDs  18  and the respective circuits are provided on substrates, which are not shown, and the respective substrates are connected via flexible substrates. 
     The processing circuit  19  in the capsule-type endoscope  3  controls, by means of a control signal, the timing for the CCD imager  17  to pick up an image to make it pick up two frames of images per second in ordinary image pickup, and to make it pick up, e.g., 15 to 30 frames of image for a site where the capsule-type endoscope  3  moves at a relatively high speed like esophagus. 
     Also, the antenna  23  receives signals sent from the extracorporeal device  5 . Then, the signals received by the antenna  23  are processed by the transceiver circuit  20  and then sent to the processing circuit  19 . The processing circuit  19  controls, e.g., the image pickup timing for the CCD imager  17  and turning on/off of the white LEDs  18  based on the signals sent thereto. A circuit that can turn on/off the power in the capsule-type endoscope  3  by means of putting a magnetic body such as a magnet close thereto may be incorporated in the processing circuit  19  in the capsule-type endoscope  3  to acquire images by turning on the power of the capsule-type endoscope  3  before the patient swallows the capsule-type endoscope  3 . 
     The antenna unit  4  equipped with the jacket  10  worn by the patient  2  shown in  FIG. 1A  includes antennae  11   a ,  11   b , . . . , and  11   i  in close up, as shown in  FIG. 3 . 
     The transmission and reception portions of the capsule-type endoscope  3  and the extracorporeal device  5  are configured as shown in  FIGS. 4A and 4B . As shown in  FIG. 4A , the capsule-type endoscope  3  processes signals based on an image of a subject picked up by an image pickup circuit  31  (including the white LEDs  18  and the CCD imager  17 ) at the processing circuit  19 , modulates them to high frequency signals at the transceiver circuit  20 , and then sends them in the form of radio waves from the antenna  23  formed of a circular loop coil. 
     The signals sent from the antenna  23  are received by the plurality of antennae  11   a ,  11   b , . . .  11   i  included in the antenna unit  4  outside the body. Then, the signals are demodulated by a transceiver circuit  33  connected to the plurality of antennae  11   a ,  11   b , . . .  11   i , and inputted to a signal processing circuit  34 , and then converted into image signals by this signal processing circuit  34 , thereby an image of the subject being displayed on the liquid-crystal monitor  12  and image data corresponding to the image of the subject, etc., being stored in a memory  35 . 
     Also, the image data stored in the memory  35  can be sent to the liquid-crystal monitor  12  by a user&#39;s instruction via the operating section  13 . This enables the user to display images acquired in the past observations, etc., on the display surface of the liquid-crystal monitor  12 . 
     Also, in the present embodiment, the extracorporeal device  5  is provided with an antenna position and direction estimating section  36   a  configured using, e.g., a CPU  36 . This antenna position and direction estimating section  36   a  performs estimation processing for estimating the position and direction of the antenna  23  incorporated in the capsule-type endoscope  3  to calculate the position and direction of the antenna  23 . 
     As described later, in this estimation processing, an arbitrary position and direction are set in the initial state and the processing for estimating a position and direction relative to them using the Gauss-Newton method is repeatedly performed. At that time, estimation is repeated by the estimation processing until the displacement from the value before the estimation becomes equal to or lower than a small value. In the words, the extracorporeal device  5  in the present embodiment includes: estimation means for perform estimation processing; and update and correction means for updating and correcting an estimation value estimated by the estimation means (specifically, position and direction) so that the difference value between the estimation value and the value before the estimation becomes equal to or lower than a predetermined value. 
     Also, upon an instruction signal for, e.g., changing the image pickup cycle being inputted to the signal processing circuit  34  as a result of the operating section  13  provided in the extracorporeal device  5  being operated, this signal processing circuit  34  sends the instruction signal to the transceiver circuit  33 . Then, the transceiver circuit  33  modulates the instruction signal and send it from the antennae  11   a ,  11   b , . . .  11   i.    
     The instruction signal sent from the antennae  11   a ,  11   b , . . .  11   i  is received by the antenna  23 , and demodulated by the transceiver circuit  20 . Then, the transceiver circuit  20  performs an operation to, e.g., change the image pickup cycle according to the demodulated instruction signal. 
     In the present embodiment, when a signal of an image picked up by the image pickup circuit  31  is sent from the antenna  23  in the capsule-type endoscope  3  to the extracorporeal device  5 , for example, as shown in  FIG. 5A , a reception intensity detection signal that facilitates reception intensity detection is sent together with the image signal. 
     In other words, in each one frame period, a detection period Ta for sending a signal for reception intensity detection, and an image signal period Tb for sending an image signal are provided. Also, in the intensity detection period Ta, a signal for reception intensity detection with a certain intensity (amplitude) is sent. 
     Then, this signal for reception intensity detection is received by the antennae  11   a ,  11   b , . . .  11   i  in the antenna unit  4  and then inputted to the transceiver circuit  33 . The transceiver circuit  33  demodulates the signal for reception intensity detection and sends it to the signal processing circuit  34 . The signal processing circuit  34  compares the signals for reception intensity detection received by the antennae  11   s  (s=a, b, . . . i) with one another, selects an antenna suitable for receiving the image signal sent by the capsule-type endoscope  3  based on the result of the comparison and receives the image signal. As shown in  FIG. 5B , similar comparison processing may be performed omitting the signal for reception intensity detection and using the image signal only. 
     Also, the signal processing circuit  34  sends the image signal obtained via the antenna suitable for reception and the signals for reception intensity detection of the antennae  11   s  to the nonvolatile memory  35 , such as a CompactFlash (registered trademark), connected to the signal processing circuit  34  to store the signals in the memory  35 . 
     In this case, multiple, for example, two antennae may be selected as antennae for receiving the image signal to record two sets of image signals with the same content at the same time. Furthermore, at that time, the signal processing circuit  34  may sum up the intensities of image signals to be recorded in an amount corresponding to one frame, and leave one with the larger summation result in the memory  35  and delete the other. 
     Also, the signal processing circuit  34  sends the image signal obtained via the antenna that is most suitable for reception to the liquid-crystal monitor  12  connected to the signal processing circuit  34  to display an image of a subject picked up by the capsule-type endoscope  3 . 
     In the present embodiment, as described above, the extracorporeal device  5  is provided with, e.g., the antenna position and direction estimating section  36   a  configured by the CPU  36 . This antenna position and direction estimating section  36   a  calculates the position and direction of the antenna  23  incorporated in the capsule-type endoscope  3 . 
     Also, in the present embodiment, the CPU  36  also functions as a track estimating section (track calculating section)  36   b  that recognizes the respective positions of the antenna  23  obtained chronologically (temporally), which have been calculated by the processing function of the antenna position and direction estimating section  36   a , as the positions of the capsule-type endoscope  3 , determines whether or not the respective positions meet the condition that the distances between the respective positions and their respective adjacent positions are equal to or lower than a predetermined value, and calculates a more accurate track (route) using those meeting the condition. 
     This antenna position and direction estimating section  36   a , as described later, sets an initial value for the position and direction of the antenna  23  in the initial state (for example, the center position of the measurement space and any of X, Y and Z-axis directions). 
     Then, the CPU  36  estimates the detection value of a magnetic field generated at the extracorporeal antennae  11   a ,  11   b , . . .  11   i  using the zeroth update value, and calculates an amount of update for the zeroth position and direction, from a square sum of the difference between the estimated detection value and the detection value actually detected (measured). Furthermore, the CPU  36  calculates the first position and/or direction from the zeroth position and direction and the update value from the zeroth position and direction. 
     The CPU  36  repeatedly performs similar estimation processing on this first position and/or direction and performs estimation value correction processing for determining an update value in which a change in the update value before and after the estimation has become equal to or lower than a sufficiently small value, as a position and direction for the antenna  23 . The CPU  36  calculates the positions and directions with high accuracy in this manner. The information on the positions and directions calculated by the CPU  36  is stored in, e.g., the memory  35 . 
     Next, a method for estimating a position and direction of the capsule-type endoscope  3  from a reception intensity signal detected using the plurality of antennae  11   a ,  11   b , . . .  11   i  in antenna unit  4  in the present embodiment will be described. 
     As shown in  FIG. 6A , in a coordinate system X L Y L Z L  based on the antenna  23  formed of a circular coil or a circular loop arranged in the capsule-type endoscope  3 , an electromagnetic field (electrostatic field, radiation electromagnetic field and induction electromagnetic field components) H r , H θ  and E φ  at a given position P (x L , y L , z L ) can be expressed by the following expressions.
 
 H   r =( IS/ 2π)( jk/r   2 +1 /r   3 )exp(− jkr )cos θ
 
 H   θ =( IS/ 4π)(− k   2   /r+jk/r   2 +1 /r   3 )exp(− jkr )sin θ  (1)
 
 E   φ =−( jωμIS/ 4π)( jk/r+ 1 /r   2 )exp(− jkr )sin θ
 
     Here, H r  and H θ  represent magnetic field components, and E φ  represents an electric field component. Also, I and S represent current flowing in the antenna  23  and the area of the circular coil forming the antenna  23 . Also, r represents the distance r=(x 2 +y 2 +z 2 ) 1/2  between the antenna  23  and the given position, and k represents k=ω(εμ) 1/2  (ε is permittivity and μ is permeability), and j represents an imaginary unit. 
     Where an electromagnetic field generated by the antenna  23  arranged in the capsule-type endoscope  3  has a high frequency and as shown in  FIG. 1A , there is a sufficient distance between the capsule-type endoscope  3  and the antennae  11   s  attached to the body surface of the patient  2 , the radiation electromagnetic field components becomes the largest in the electromagnetic field reaching the antennae  11   s  (accordingly, the electrostatic field and induction electromagnetic field components become smaller than the radiation electromagnetic field component, and thus, they can be ignored). Accordingly, formula (1) can be expressed by formula (2) below.
 
H r =0
 
 H   θ =( IS/ 4π)(− k   2   /r )exp(− jkr )sin θ  (2)
 
 E   φ =−( jωμIS/ 4π)( jk/r )exp(− jkr )sin θ
 
     Where the antennae  11   s  attached to the body surface of the patient  2  are antennae for detecting an electric field, the expression in formula (2) that is necessary for the detection is the electric field E φ . 
     The electric field E φ  in formula (2) represents a radiation electric field, which can be considered as a result based on alternating current phenomena. Accordingly, the instantaneous value of the electric field E φ  can be obtained by both sides of the expression (2) for the electric field E φ  being multiplied by exp(jωt) to extract the real part. 
                             E   ϕ     ⁢     exp   ⁡     (     j   ⁢           ⁢   ωt     )         =           -     (     jωμ   ⁢           ⁢     IS   /   4     ⁢   π     )               (     j   ⁢           ⁢     k   /   r       )     ⁢     exp   ⁡     (       -   j     ⁢           ⁢   k   ⁢           ⁢   r     )               sin   ⁢           ⁢     θexp   ⁡     (   jωt   )                 =         (     ωμ   ⁢           ⁢     ISk   /   4     ⁢   π   ⁢           ⁢   r     )           (       cos   ⁢           ⁢   U     +     j   ⁢           ⁢   sin   ⁢           ⁢   U       )           sin   ⁢           ⁢   θ                 (   3   )               
provided that U=ωt−kr.
 
     Here, when the real part in expression (3) is extracted, the instantaneous value of the electric field E′ φ  can be expressed as follows.
 
 E′   φ =(ωμ ISk/ 4 πr )cos  U  sin θ  (4)
 
     Also, when formula (4) is converted from a polar coordinate system (r, θ, φ) to an orthogonal coordinate system (X L , Y L , Z L ) as shown in  FIG. 6B , the electric field components E Lx , E Ly  and E Lz  of X L , Y L , Z L  can be expressed as follows.
 
 E   Lx′   =E′   φ  sin φ=(ωμ ISk/ 4 πr   2 )cos  U ·(− y   L )
 
 E   Ly′   =E′   φ  cos φ=(ωμ ISk/ 4 πr   2 )cos  U·x   L   (5)
 
E Lz =0
 
     Also, in the coordinate system X L , Y L , Z L  based on the antenna  23  in the capsule-type endoscope  3 , an expression for converting the position P (x L , y L , z L ) into a coordinate system X W Y W Z W  based on the body of the patient  2  can be expressed as follows: 
                     (           X   Lp               Y   Lp               Z   Lp           )     =         R     -   1       ⁡     [       (           X   Wp               Y   Wp               Z   Wp           )     -     (           X   WG               Y   WG               Z   WG           )       ]       =       (           R   00           R   10           R   20               R   01           R   11           R   21               R   02           R   12           R   22           )     ⁡     [       (           X   Wp               Y   Wp               Z   Wp           )     -     (           X   WG               Y   WG               Z   WG           )       ]                 (   6   )               
provided that (x WP , y WP , z WP ) and (x WG , y WG , z WG ) represent the position P and the position of the antenna  23  in the coordinate system X W Y W Z W , respectively. Also, R, which is used in the first term on the right side of expression (6), represents a rotation matrix between the coordinate system X W Y W Z W  and the coordinate system X L Y L Z L , and can be calculated by the following expression.
 
                       (           R   00           R   01           R   02               R   10           R   11           R   12               R   20           R   21           R   22           )     =     (           cos   ⁢           ⁢   α   ⁢           ⁢   cos   ⁢           ⁢   β             -   sin     ⁢           ⁢   α           cos   ⁢           ⁢   α   ⁢           ⁢   sin   ⁢           ⁢   β               sin   ⁢           ⁢   α   ⁢           ⁢   cos   ⁢           ⁢   β           cos   ⁢           ⁢   α           sin   ⁢           ⁢   α   ⁢           ⁢   sin   ⁢           ⁢   β                 -   sin     ⁢           ⁢   β         0         cos   ⁢           ⁢   β           )       ,           (   7   )               
provided α and β represent the rotation amount of the polar coordinate system.
 
     Accordingly, an electric field E W  at the certain position P (x WP , y WP , z WP ) in the coordinate system X W Y W Z W  based on the body of the patient  2  can be expressed as 
                       (           E   Wx               E   Wy               E   Wz           )     =       R   ⁡     (           E   Lx               E   Ly               E   Lz           )       =       (           R   00           R   01           R   02               R   10           R   11           R   12               R   20           R   21           R   22           )     ⁢     (           E   Lx               E   Ly               E   Lz           )           ,           (   8   )               
and expression (9) for the electric field E W  below can be obtained by assigning expressions (5), (6) and (7) to expression (8).
 
                       (           E   Wx               E   Wy               E   Wz           )     =         k   1       r   2       ⁢     (         0         (       z   Wp     -     z   WG       )           -     (       y   Wp     -     y   WG       )                 -     (       z   Wp     -     z   WG       )           0         (       x   Wp     -     x   WG       )               (       y   Wp     -     y   WG       )           -     (       x   Wp     -     x   WG       )           0         )     ⁢     (           g   x               g   y               g   z           )         ,           (   9   )               
provided that k 1  is a constant, and (g x , g y , g z ) represents the direction of the antenna  23 .
 
     An electromotive force Va detected when the electric field E W  generated by the antenna  23  is received by, e.g., an antenna  11   a  included in the antenna unit  4 , which is, e.g., a rod-like antenna as shown in  FIG. 7 , that is, a dipole antenna, can be calculated by the following expression.
 
 Va=k   2   E   w  cos γ= k   2 ( E   Wx   D   xa   +E   Wy   D   ya   +E   Wz   D   za )  (10)
 
provided that k 2  represents a constant, and Da (see  FIG. 7 ) represents the direction (D xa , D ya , D za ) of the antenna  11   a  in the antenna unit  4  in the coordinate system based on the patient.
 
     Then, the CPU  36  calculates the position and direction of the antenna  23  based on the arrangement of the antennae  11   s  in the antenna unit  4 , which are arranged on the body of the patient  2 , the arrangement being, e.g., one illustrated in  FIG. 3 , by means of iterative refinement (using the Gauss-Newton method). 
     Here, it is assumed that x is a parameter for the position (x WG , y WG , z WG ) and direction (g x , g y , g z ) of the antenna  23  and an initial value for the parameter is x (0) . 
     Here, where the k-th order estimation value x (k)  has been obtained by iterative refinement, and a model function V(x) for the electromotive force generated at the coils of the antennae  11   s  is expanded around x (k)  using Taylor expansion, the first-order approximation can be expressed as follows. 
     
       
         
           
             
               
                 
                   
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                             x 
                             
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     At this time, where Vm is the electromotive force measured by the coils of the antennae  11   s , the observation equation can be represented by 
                   Vm   ≅       V   ⁡     (     x     (   k   )       )       +         [       δ   ⁢           ⁢     V   ⁡     (   x   )           δ   ⁢           ⁢   x       ]       x   =     x     (   k   )           ⁢     (     x   -     x     (   k   )         )     ⁢           ⁢   with   ⁢           ⁢   error   ⁢           ⁢   σ   ⁢           ⁢   included               (   12   )               
Here, the approximately equal sign includes an error σ.
 
     Also, movement of the first term on the right side of equality (11) to the left side results in:
 
ΔVm (k) ≅A (k) Δx (k)  with error σ included  (13),
 
provided that,
 
Δ Vm   (k)   =Vm−V ( x   (k) )= Vm−Vm   (k)   (14)
 
Δ x   (k)   =x−x   (k)   (15)
 
 A   js   =[∂V   j ( x )/∂ x   s ] x=x   (k) ( j= 1 ˜n,s=a˜i )  (16)
 
(the number of rows is an unknown number n, and the number of columns is the number i of coils for the antennae  11   s ). The solution Δx (k)  can be expressed based on expression (15) as follows:
 
Δ x   (k) =( A   t(k)   WA   (k) ) −1   A   t(k)   WΔVm   (k)   (17)
 
provided that A t  is a transposed matrix for A and W is a weighting matrix.
 
     Accordingly, the estimation value of the parameter refined according to expression (14) can be obtained by
 
 x   (k+1)   =x   (k)   +Δx   (k)   (18)
 
     As shown in  FIG. 3 , where nine antennae  11   a ,  11   b , . . .  11   i  are provided to a patient, the matrix A can be expressed by 
                     A   =     [             δ   ⁢           ⁢     V   a         x   Wg               δ   ⁢           ⁢     V   a         y   Wg               δ   ⁢           ⁢     V   a         z   Wg               δ   ⁢           ⁢     V   a         g   x               δ   ⁢           ⁢     V   a         g   y               δ   ⁢           ⁢     V   a         g   z                   δ   ⁢           ⁢     V   b         x   Wg               δ   ⁢           ⁢     V   b         y   Wg               δ   ⁢           ⁢     V   b         z   Wg               δ   ⁢           ⁢     V   b         g   x               δ   ⁢           ⁢     V   b         g   g               δ   ⁢           ⁢     V   b         g   z               ⋮       ⋮       ⋮       ⋮       ⋮       ⋮               δ   ⁢           ⁢     V   i         x   Wg               δ   ⁢           ⁢     V   i         y   Wg               δ   ⁢           ⁢     V   i         z   Wg               δ   ⁢           ⁢     V   i         g   x               δ   ⁢           ⁢     V   i         g   g               δ   ⁢           ⁢     V   i         g   z             ]       ,           (   19   )               
and the weighting matrix W can be expressed by
 
                     W   =     [           σ   0   2         0       0       …       0           0         σ   1   2         0       …       0           0       0         σ   2   2         …       0           ⋮       ⋮       ⋮       ⋱       ⋮           0       0       0       …         σ   8   2           ]       ,           (   20   )               
provided that σ j  (j=0, 1, . . . , 8) in the weighting matrix W is fluctuation amounts of measured voltages of the antennae  11   j , such as environmental noise, for example.
 
     Also, since the k-th ΔVm can be expressed by 
                       Δ   ⁢           ⁢   Vm     =     [             Vm   a     -       V   a     ⁡     (     x     (   k   )       )                     Vm   b     -       V   b     ⁡     (     x     (   k   )       )                     Vm   c     -       V   c     ⁡     (     x     (   k   )       )                 ⋮               Vm   i     -       V   i     ⁡     (     x     (   k   )       )               ]       ,           (   21   )               
and accordingly, a position and direction of the antenna  23  in the capsule-type endoscope  3  can be calculated by steps (a) to (d) below.
 
     (a) Assume that k=0 and the initial value of the antenna  23  is a position (x Wg   (0) , y Wg   (0) , z Wg   (0) ) and a direction (g x   (0) , g y   (0) , g z   (0) ) (for example, the center position of the space in which the antenna  23  is measured, and the Z-axis vector (0, 0, 1)); 
     (b) Calculate the k-th matrix using expressions (9), (20) and (21); 
     (c) Calculate the k-th update amount Δx (k)  using expression (18); and 
     (d) Repeat steps (b) to (d) until the update amount Δx (k)  becomes small. 
     The estimation processing as described above enables highly-accurate position and direction estimation (calculation). 
     Also, in the present embodiment, as described below, even when multiple positions are estimated, a highly-accurate or highly-reliable track can be calculated by performing track estimation processing on the chronologically estimated and calculated positions at the track estimating section  36   b.    
     In the aforementioned position and direction estimation steps, multiple positions of the antenna  23  or the capsule-type endoscope  3  may be estimated depending on the number and arrangement position of antennae  11  for reception, the manner to provide the position (x Wg , y Wg , z Wg ) (0)  at the initial value for the antenna  23 , and noise, etc. The antenna  23  is secured in the capsule-type endoscope  3 , and thus, if the position of the antenna  23  is estimated, the position of the capsule-type endoscope  3  is also determined. 
     Since the capsule-type endoscope  3  make relative small movements in a body cavity and picks up images at short intervals, the position estimated at a certain time and the position estimated at a time immediately before or after the certain time can be considered to be positions that are substantially the same or close to each other. 
     Accordingly, when the positions meeting the condition of adjacency are extracted from the multiple positions estimated at the time immediately before or after the certain time to obtain the connection relations between the positions estimated at the respective times, and the smallest route is calculated from the routes of the overall connection relations, the final track and the correct positions of the capsule-type endoscope  3  at the respective times can be calculated. 
     As shown in  FIG. 8 , it is assumed that the positions estimated at a time t−1 are P(t−1) 1 , P(t−1) 2 , . . . , and the positions estimated at a time t are Pt 1 , Pt 2 , . . . . 
     At this time, for the positions Pti (i=1, 2, 3, . . . ) estimated at the time t, the CPU  36 , as shown in  FIG. 9 , sets a sphere with a radius r d  whose value has been set in advance, corresponding to the distance that the capsule-type endoscope  3  can move during the time between position estimations of the capsule-type endoscope  3 . 
     Then, the CPU  36  detects the estimated positions P(t−1)j (j=1, 2, 3, . . . ) at the time t−1, which are present in the sphere. Also, the CPU  36  calculates the distances dij between the positions Pti estimated at the time t and the detected estimated positions P(t−1)j at the time t−1, and then calculates the estimated positions P(t−1)j at the time t−1 providing the smallest distances dij. 
     The CPU  36  calculates the estimated positions at the time t−1 that are the closest to the respective estimated positions Pti (i=1, 2, 3, . . . ) at the time t, and stores such connection relations. For example, the CPU  36  relates information on addresses at which the estimated positions at the time t−1 is stored thereto to store as connection information. 
     In  FIG. 8 , the estimated position at the time t−1 that is the closest to the estimated position Pt 3  is P(t−1) 3 . However, the distance between these two points is larger than r d , the CPU  36  determines that the estimated position at the time t−1 connected to the estimation position Pt 3  is one resulting from noise, etc., and does not store it as information to be used for a connection relation for the estimated position Pt 3 . 
     As described above, the CPU  36  performs position estimation for all the recorded data to obtain the connection relations. Then, the CPU  36  sets the estimated positions stored at the last as the starting points and the estimated positions stored at the first as the endpoints to search for the routes of the connection relations from the starting points and the endpoints using the connection information stored together with the respective estimated positions. Then, the CPU  36  calculates the smallest one of the obtained routes as a track, and determines the estimated positions at the respective times from the track. 
     As a modification, the CPU  36  may calculate the route including the largest number of points (estimated positions), select the route as a track, and determine the estimated positions at the respective times from the track. In this case, where multiple routes including the largest number of points have been obtained, the CPU  36  may select one whose overall route length is the smallest as a track. 
     Next, a track estimation operation will be described. As processing prior to track estimation, the CPU  36  performs processing for calculating (determining) whether or not two adjacent positions are positions in the connection relation meeting the condition for forming a track. The processing for calculating this connection relation will be described with reference to  FIG. 10 .  FIG. 10  shows the content including an image pickup operation in a chronological manner. 
     Upon the processing for calculating the connection relation being started, as shown in step S 1  in  FIG. 10 , the CPU  36  in the extracorporeal device  5  sets a time t to an initial value of 1, that is, t=1. In this way, the description with reference to  FIGS. 10 and 11  shall be given in a simplified manner using a parameter obtained by making the time t to an integer. 
     Then, the CPU  36 , as shown in step S 2  in  FIG. 10 , acquires an electromotive force Vmt (which expresses that it is a value of the aforementioned electromotive force Vm at the time t) obtained at the time t via the antennae  11  on the extracorporeal device  5  side, and stores the value of the electromotive force Vmt in the memory  35 , which is storing means. 
     Also, as shown in step S 3  in  FIG. 10 , the CPU  36  estimates a position Pti of the capsule-type endoscope  3  at the time t using the value of electromotive force Vmt (acquired via the plurality of antennae  11  at the time t) stored in the memory  35 , and stores the position Pti in the memory  35 . 
     As described below, there is a case where multiple positions Pti at the time t are estimated, and in that case, the multiple positions Pti are stored in the memory  35 . Also, in general, the number of positions Pti obtained varies if the time t varies. Accordingly, it is assumed that the number of positions obtained at the time t is Ni, and the number of positions obtained at a time t−1 is Nj. 
     Then, at the next step S 4 , the CPU  36  determines whether or not the parameter value for the time t is the initial value of 1. 
     In this case, since the parameter value for the time t is 1, the CPU  36  proceeds to step S 5 , and the parameter value is incremented by one, and then the processing at steps S 1  and S 2  is performed, and the CPU  36  proceeds to step S 6  as a result of the determination at step S 4 . Then, in the processing at step S 6  onward, processing for connecting the positions Pti estimated (calculated) at the time t, which include those affected by noise, to positions P(t−1)j estimated at a time t−1 one time before the time t as routes is performed. 
     At step S 6 , for the entire positions Pt estimated at the time t, that is, Ni positions Pti (i=1 to Ni), a parameter i indicating those positions is set to an initial value of 1, that is, i=1. 
     Then, at the next step S 7 , as shown in  FIG. 9 , the CPU  36  sets a prescribed radius r d  as a value for a minimum distance d min . Furthermore, at the next step S 8 , the CPU  36  sets a parameter j indicating the respective positions P(t−1)j estimated at the time t−1, that is, Nj positions P(t−1) (j=1 to Nj) to an initial value of 1, that is, j=1. 
     Then, at the next step S 9 , the CPU  36  calculates the distance between the position Pti of the capsule-type endoscope  3  estimated at the time t and the position P(t−1)j estimated at the time t−1. 
     Furthermore, at the next step S 10 , the CPU  36  determines whether or not the calculated distance dij is shorter than the minimum distance dmin set in advance at step S 7 . Then, if the result of the determination does not meet the condition of dij&lt;dmin, the CPU  36  determines if the parameter j is smaller than the number of positions P(t−1)j estimated at the time t−1, that is, Nj at step S 14 . If this condition is met, the CPU  36 , as shown in step S 11 , increments the value of the parameter j by one and returns to step S 9 , and repeats similar processing. The positions not meeting the condition at step S 10  are not used for the processing for calculating a track of the movement of the capsule-type endoscope  3 , which can be understood from the following steps. 
     Meanwhile, if it has been determined that the condition at step S 10  is met, the CPU  36 , as shown in step S 12 , updates the value of the minimum distance dmin by the distance dij. Furthermore, at the next step S 13 , the CPU  36  relates positional information on the position P(t−1)j of the capsule-type endoscope  3  estimated at the time t−1 one time before the time t to the position Pti estimated at the time t, and stores the same in the memory  35  as connection information. Also, in  FIG. 10  (also in  FIG. 11 , etc.), the capsule-type endoscope is abbreviated simply to “capsule”. 
     At the next step S 14 , the CPU  36  determines if the parameter j is smaller than the number Nj of positions P(t−1)j estimated at the time t−1. Also, if the condition at step S 14  in  FIG. 10  is met, the CPU  36  increments the value of j by one via step S 11 , and retunes to step S 9  to repeat the same processing. 
     Then, if this value of j corresponds to the number Nj, the CPU  36  proceeds to the next step S 15  to determine if the parameter i is smaller than the number Ni of positions Pti estimated at the time t. Furthermore, if the condition at step S 15  in  FIG. 10  is met, the CPU  36  proceeds to step S 16  to increment the value of i by one, and retunes to step S 7  and then repeats the same processing. 
     Subsequently, if this value of i corresponds to the number Ni, the CPU  36  proceeds to step S 17  to determine if the parameter t is smaller than a time tend measured at the last. Then, if the condition of this parameter t being smaller than tend is met, the CPU  36  retunes to step S 5  to increment the value of t by one and returns to step S 2 , and then repeats similar processing. 
     As described above, if the time t corresponds to the last time tend, the CPU  36  terminates this processing, and as shown in  FIG. 11 , performs processing for searching for the positions meeting the connection relation (which have been determined in the processing shown in  FIG. 10 ), that is, searching for a route (calculating a track) to calculate (estimate) a track. 
     Upon the start of the processing for route search shown in  FIG. 11 , the CPU  36 , at the first step S 21 , sets the time t, which is the time for performing the processing, to tend−1, which is a time one time before the last time tend used in the processing shown in  FIG. 10 . Then, the CPU  36 , at the next step S 22 , sets the parameter i indicating one of the positions Pti estimated at the time t to an initial value of 1. 
     In the next step S 23 , the CPU  36  reads the position Pti of the capsule-type endoscope  3  and its connection information from the memory  35 . Then, at the next step S 24 , the CPU  36  determines whether or not connection information exists in the read information. 
     If no connection information exists, the CPU  36 , at step S 29 , determines if the position parameter i is smaller than Ni. If this condition is met, the CPU  36 , as shown in step S 25 , increments the position parameter i by one, and performs the processing at steps S 23  and S 24  for the parameter i+1. Also, if it has been determined as a result of step S 24  that connection information exists, the CPU  36  proceeds to the processing at step S 26 . 
     At step S 26 , the CPU  36  determines whether or not there is any connection with a position Pt+1 of the capsule-type endoscope  3  at a time t+1 following the time t (in the case of the time t=tend−1, t+1=tend). Then, if there is no such connection, the CPU  36  proceeds to step S 27 . At step S 27 , the CPU  36  stores new route information (for example, route information to the effect that the connection is discontinued) in the memory  35  and then returns to the processing at step S 23 , via step S 25  depending on the condition at step S 29 . 
     Meanwhile, if the CPU  36  has determined at step S 26  that connection with a position Pt+1 of the capsule-type endoscope  3  at the following time t+1 exists, it proceeds to step S 28 . Then, in this case, at step S 28 , the CPU  36  stores information to the effect that they are connected, in the memory  35  as route information. 
     At the next step S 29 , the CPU  36  determines whether or not the position parameter i is smaller than Ni. Then, if the parameter i is smaller than Ni, the CPU  36  increments the value of the position parameter i by one via step S 25 , and then returns to the processing at step S 22 . 
     As described above, the CPU  36  repeats the processing at steps S 22  to S 29  while sequentially incrementing the value of the parameter i by one. Then, when the parameter i corresponds to Ni, the CPU  36  proceeds to step S 30 . At step S 30 , the CPU  36  determines whether or not the time t is equal to or lower than an initial value of 2. 
     If the time t is not equal to or lower than 2 (that is, not smaller than 3), the CPU  36 , as shown in step S 31 , decrements the value of the time t by one, and then returns to the processing at step S 22 . Then, the CPU  36  sets the time t to the time t−1 one time before the time t and repeats similar processing. Thus, when the time t has the initial value of 2, the CPU  36  terminates this processing. 
     Through the processing at the aforementioned series of steps, routes from the positions Pti of the capsule-type endoscope  3  at the time t having the initial value of 1 to the positions Ptend of the capsule-type endoscope  3  at the last time tend are calculated. 
     Then, as described above, the CPU  36  calculates the shortest route, from among the routes from the starting point to the endpoint that have been obtained in such a manner as described above to determine it to be a track, and determines the estimated positions at the respective times from the track. 
     As a modification of the present embodiment, the CPU  36  may set the route obtained from the starting point to the end point that includes the largest number of estimated position, as a track. Also, if multiple routes including the largest number of points have been calculated based on, e.g., the preset value of the distance r d , the CPU  36  may determine one whose entire length is the shortest to be a track. Also, in that case, the CPU  36  may determine the estimated positions at the respective times from the shortest route, that is, the track. 
     Alternatively, the CPU  36  may rank the routes according to the number of points included in the routes, and calculate the lengths of the entire routes only for the highly-ranked routes to determine the route whose entire length is the shortest as a track. Also, the CPU  36  may determine the estimated positions at the respective times from the track in that case. 
     Alternatively, the CPU  36  calculates the total sum of the cost values obtained when position estimation has been performed, for the routes highly ranked when the routes have been ranked according to the number of points included in the routes (e.g., the sums of the squares of the residual differences between the measured values and the calculated values) to determine the route whose total sum of the cost values is the smallest to be a track, and determines the estimated positions at the respective times from the track. 
     When one track has been calculated in such a manner as described above, the track is displayed on, e.g., the monitor section  8   c  shown in  FIG. 1B . 
       FIGS. 12A and 12B  show examples of display on the monitor section  8   c . In  FIG. 12A , on the left side of the display screen, a track of the movement of the capsule-type endoscope  3  in a body cavity is displayed by connecting the estimated positions of the capsule-type endoscope  3  in the body cavity with straight lines, and on the right side of this display screen, the image picked up at an estimated position Pti, which has been designated (via, e.g., a cursor on the left side), is displayed. 
     Also, signs A, B and C appearing on the right side of the track formed by the estimated positions on the left side of the display screen indicate the general positions of organs in the body cavity, and more specifically, sign A indicates the esophagus, sign B indicates the small intestine, and sign C indicates the large intestine. 
     Other than the display method shown in  FIG. 12A , for example, display may also be provided as shown in  FIG. 12B . 
     In this case, the display is provided by performing interpolation, such as spline interpolation, between the respective adjacent positions to connect the respective positions of the capsule-type endoscope  3  estimated for the respective frames with a smooth curve. 
     As described above, since the estimated positions in the body cavity and the corresponding picked up images can be displayed, it is possible to easily determine in which site in the body cavity the image was picked up, enabling efficient diagnosis. 
     Also, in the case where a possible lesion has been found from an obtained image and there has arisen a need for a closer endoscopic examination of the site, a re-examination or treatment, etc., can efficiently be conducted since the position can be estimated with high accuracy, enabling approaching the site smoothly in a short time. 
     The present embodiment provides the following advantageous effects. 
     Even when multiple positions of the capsule-type endoscope  3  have been estimated depending on the number of antennae included in the antenna unit  4 , the arrangement position of the antennae included in the antenna unit  4 , the manner to provide the position (x Wg , y Wg , z Wg ) (0)  of an initial value for an antenna  23 , and noise, etc., the position of the capsule-type endoscope  3  can uniquely be determined by means of a proper method, enabling a track to be calculated. 
     Also, since a track is calculated by selecting positions meeting a predetermined condition, the calculated track and the respective positions in the track are highly reliable, and can effectively be utilized for diagnosis, etc. 
     Embodiment 2 
     Next, embodiment 2 of the present invention will be described with reference to  FIGS. 13A to 15 . The configuration of the present embodiment is similar to that of embodiment 1, and is different from that of embodiment 1 in the content of processing provided by the program in the track estimating section to estimate a track. 
     In the present embodiment, as described below, a living body in which the positions of the capsule-type endoscope  3  are estimated is divided into a plurality of regions to calculate the regions including the respective estimated positions of the capsule-type endoscope  3  in a chronological manner. Then, processing for calculating the routes from the starting point to the endpoint for the estimated positions to determine the route including the largest number of regions to be a track is performed. 
     Next, the operation of the present embodiment will be described with reference to  FIG. 13A  onward. 
       FIG. 13A  is a diagram illustrating a coordinate system X W Y W Z W  based on a human body.  FIG. 13B  is a diagram illustrating a state in which a space where the capsule-type endoscope  3  exists is divided into a plurality of regions (x=1, 2, 3, . . . , y=1, 2, 3, . . . , and z=1, 2, 3, . . . ) (for example, cubes 2 cm on a side). 
     In embodiment 1, as shown in  FIG. 9 , the connections that meet the condition that the distance dij between positions Pti and P(t−1)j at adjacent times t and t−1 is equal to or shorter than a distance r d  are extracted and used as connection information for determining routes or a track. 
     Meanwhile, in the present embodiment, in order to further increase the speed of arithmetic processing, or connections to be saved as connection information are further narrowed down. The CPU  36  divides a space where the capsule-type endoscope  3  exists into a plurality of regions R xyz , and searches for regions R xyz  including positions Pti estimated at a time t to determine the region including many estimated positions to be a connected region used for route search (or track estimation). 
     In this case, the positions Pti estimated at the time t are dispersed in multiple regions, the CPU  36  determines the region including the largest number of positions to be the connected region, and the positions included in the regions other than that region are not used for route search. As described above, even when there are a large number of estimated positions due to noise, etc., a track can be calculated in a short time by reducing the number of positions used for route search. 
     Also, the CPU  36  determines whether or not the regions R xy , including the positions Pti and P(t−1)j estimated at the times t and t−1 are connected regions from their positional relationship. 
     More specifically, if two regions including the positions Pti and P(t−1)j estimated at the times t and t−1 are not in the same region, the CPU  36  determines only regions that meet the relationship in which they are adjacent regions, in other words, regions meeting a particular region relationship in which they are close to each other within a small distance, to be regions connected by the movement of the capsule-type endoscope  3 . Then, the CPU  36  does not determine the regions that are not in the relationship in which they are adjacent to each other, for example, the regions in the relationship in which they are remote from each other to be connected regions. 
       FIG. 14  is a diagram illustrating the respective positions P(t−1)j (j=1, 2, 3, . . . ) and Pti (i=1, 2, 3, . . . ) estimated as positions of the capsule-type endoscope  3  from multiple output values of the antennae  11  obtained at the times t−1 and t. 
     The CPU  36  in the extracorporeal device  5  calculates regions R xyz  including the respective estimated positions Pti (i=1, 2, 3, . . . ). 
     In  FIG. 14 , the positions estimated at the time t are Pt 1  to Pt 4 , and the positions estimated at the time t−1 are P(t−1) 1  to P(t−1) 3 . In this case, the positions Pt 1  and Pt 4  are included in a region R 122 , the position Pt 2  is included in a region R 121 , and the position Pt 3  is included in a region R 211 . Also, the positions P(t−1) 1  and P(t−1) 2  are included in a region R 112 , and the position P(t−1) 3  is included in a region R 111 . 
     Also, the CPU  36  determines whether or not each of the spatial relationships between the estimated positions at the times t−1 and t meets the connection relationship for connected regions to be saved as connection information. In this case, whether or not the regions are connected regions is determined depending on whether or not they are adjacent regions. 
     Then, the CPU  36  stores information on connected regions obtained from the regions obtained at the time t and the regions obtained at the time t−1, in the memory  35 . Also, the CPU  36  records the extracted region and its connection information for all the stored data. 
     The CPU  36  sets the region stored at the last to be a starting point, and the region stored at the first to an endpoint, and performs processing similar to the track estimation processing described in embodiment 1, using the connection information stored together with the extracted regions to calculate the routes from the starting point to the endpoint. 
     The CPU  36  calculates the route including the largest number of regions, and determines the estimated positions at the respective times from the obtained route. The estimated positions in this case are the center positions (barycentric positions) of the regions. 
     In the specific example in  FIG. 14 , as described above, the largest number of positions, i.e., Pt 1  and Pt 4 , are included in the region R 122  at the time t and the largest number of positions, i.e., P(t−1) 1  and P(t−1) 2 , are included in the region R 112  adjacent to the region R 122  at the time t−1. 
     These regions R 122  and R 112  are recognized as connected regions. The positions Pt 2 , Pt 3  and P(t−1) 3  included in the other regions are not used for route search. 
     Also, since these regions R 122  and R 112  are adjacent to each other, they are recognized as connected regions used for route search. 
       FIG. 15  illustrates a manner in which connected regions are specifically determined in the state shown in  FIG. 14 . In other words,  FIG. 15  is a diagram illustrating a manner to determine the connection relations with the regions at the time t−1 from the regions obtained at the time t. 
     In  FIG. 15 , in the case of the connected regions R 122  and R 112  adjacent to each other, each having the largest number of estimated positions, the estimated position at the time t is the center position (barycenter position) Qt 1  of the region R 122 , and the estimated position at the time t−1 is the center position (barycenter position) Q(t−1) 1  of the region R 112 . In  FIG. 15 , these two connected regions R 112  and R 122  are indicated with solid lines. 
     As described above, the CPU  36  searches for routes from the starting point to the endpoint and finally calculates one track. 
     Next, processing for determining connection regions will be described with reference to  FIG. 16 . Upon the start of the operation, at the first step S 41 , the CPU  36  performs processing for dividing a space where the capsule-type endoscope exists into a plurality of regions R xyz . 
     Then, at the next step S 42 , the CPU  36  sets the time t to an initial value of 1, and then, at the next step S 43 , acquires an electromotive force Vmt obtained at the time t via the antennae  11 . 
     In the next step S 44 , the CPU  36  estimates the position Pti of the capsule-type endoscope  3  using the value of the electromotive force Vmt at the time t, and stores it in the memory  35 . Since multiple positions Pti may exist, they are distinguished from one another by providing the subscript i thereto. 
     In the next step S 45 , the CPU  36  detects the region R xyztk  including the largest number of estimated positions Pti of the capsule-type endoscope  3  and stores it in, e.g., a first memory in the memory  35 . In this case, multiple regions R xyztk  may exist. Here, the subscript t indicates a time, k indicates a parameter k (k=1, 2, . . . N k ) for distinguishing multiple regions R xyzt  detected at the time t from one another. 
     In the next step S 46 , the CPU  36  determines whether or not the time t is its initial value, that is, t=1. Then, in the case of t=1, at step S 47 , the CPU  36  stores the information on the regions R xyztk  stored in the first memory in the memory  35 , in a second memory, and the next step S 48 , sets the time t to t+1, and then returns to step S 43 . 
     Then, the CPU  36  performs the processing at steps S 43  to S 46 . In this case, the CPU  36  determines in the determination at step S 46  that t is not 1, and proceeds to the processing at step S 49 . 
     At step S 49 , the CPU  36  sets the parameter k to its initial value, that is, k=1. Subsequently, at the next step S 50 , the CPU  36  further sets a parameter j to its initial value, that is, j=1. 
     Then, at the next step S 51 , the CPU  36  determines whether or not the region R xyztk  and the region R xyzt−1j  are adjacent to each other. Here, the region R xyzt−1j  indicates a parameter j (j=1, 2, . . . N j ) for distinguishing, from one another multiple, the regions R xyzt−1  estimated to include the largest number of positions P t−1j  of the capsule-type endoscope  3  detected at the time t−1. 
     If the CPU  36  has determined at step S 51  that the region R xyztk  and the region R xyzt−1j  are not adjacent to each other, it further determines if j&lt;N j  at step S 54 . If this condition is met, the CPU  36  increments j by one at step S 52 , and then performs the processing at step S 51 . 
     If the CPU  36  has determined that the region R xyztk  and the region R xyzt−1j  are adjacent to each other, the CPU  36 , at step S 53 , stores the connection relation in which the region R xyztk  and the region R xyzt−1j  are adjacent to each other in the second memory in the memory  35 .  FIG. 17  is a diagram illustrating an example of the case where connection relations between the regions R xyztk  and the regions R xyzt−1j  are stored in the second memory by means of a two-dimensional array. 
     In  FIG. 17 , the relationship between the regions R xyz , the times t and the parameters k are shown in a two-dimensional array to easily find out the connection relation of two regions R xyztk  and R xyzt−1j  at the times t and t−1 as to whether or not they are adjacent to each other. In  FIG. 17 , where they are arranged in a line in the temporal axis (vertical axis which is the direction in which the times are arrayed) direction, they are region adjacent to each other. 
     After performing the aforementioned processing at step S 53 , at the next step S 54 , the CPU  36  determines if j&lt;N j . Then, if the CPU  36  has determined that this condition is met, it performs the processing at step S 52 , and then returns to step S 51 . 
     After the processing is repeated until j≦N j  is reached as described above, j&gt;N j  is reached, and thus, the CPU  36  proceeds to the next step S 55  via determination at step S 54 . The CPU  36 , at step S 55 , determines if k&lt;N k , and if this condition is met, it increments k by one at the next step S 56  and then returns to the processing at step S 50 . 
     As described above, the CPU  36  repeats the processing from steps S 50  to S 56 . Then, upon k&gt;N k  being reached as a result of the processing at steps S 50  to S 56  being repeated, the CPU  36  proceeds to step S 57  via determination at step S 55 . 
     At step S 57 , the CPU  36  determines if t&lt;tend, and if this condition is met, it returns to step S 48 , and at step S 48 , sets t to t+1 and returns to step S 43 . 
     As described above, the CPU  36  repeats the processing from steps S 43  to S 57 . Then, upon reaching a time not meeting the condition of t&lt;tend, it terminates this processing. 
     As a result of the processing at the aforementioned series of steps, information on all the connection relations at the adjacent times is stored in the second memory in the memory  35 . Then, the CPU  36 , as shown in  FIG. 18 , proceeds to processing for searching for a track from the connection relation information. Upon the start of this processing, at the first step S 61 , the CPU  36  sets the time for processing t to the last time tend, that is, t=tend. 
     The CPU  36 , at step S 62 , determines if the condition of t=tend is met. Then, if this condition is met, the CPU  36 , at step S 63 , regards information on the connection relations at the time tend to be new route information and stores all the regions R xyztendk  (k=1, 2, 3 . . . ) stored in the second memory in the memory  35 , in the third memory in the memory  35 . Subsequently, the CPU  36 , at step S 64 , sets the time t to a time one time before, that is, t=t−1 and returns to the processing at step S 62 . 
     At this step S 62 , the CPU  36  determines that the condition of t=tend is not met and proceeds to step S 65 , and sets the parameter k to k=1, and then proceeds to the next step S 66 . 
     At step S 66 , the CPU  36  determines whether or not any region R xyzt−1j  adjacent to the region R xyztk  exists in the second memory. 
     Then, if the CPU  36  determines that no such adjacent region exists, it proceeds to step S 73 , and further determines whether or not any region R xyzt+1m  adjacent to the region R xyztk  exists in the second memory. Here, m represents a parameter for, if multiple regions R xyzt+1  exist at the time t+1, distinguishing such regions from one another. 
     Then, if the CPU  36  has determined that no such adjacent region exists, it proceeds to step S 71 . Meanwhile, if the CPU  36  has determined at step S 73  that an adjacent region R xyzt+1m  exists, it proceeds to step S 70 , and stores this information in the third memory as route information, and then proceeds to the next step S 71 . 
     Meanwhile, if the CPU  36  has determined at step S 66  that an adjacent region R xyzt−1j  exists, it proceeds to step S 68 , and further determines whether or not a region R xyzt+1m  adjacent to the region R xyztk  exists in the second memory. Here, m represent a parameter for, if multiple regions R xyzt+1  exist for the time t+1, distinguishing them from one another. 
     If the CPU  36  has determined that no such adjacent region exists, at step S 69 , it stores that information in the third memory as new route information, and then returns to step S 66  via the processing at step S 67 . 
     Meanwhile, if the CPU  36  has determined at step S 68  that an adjacent region R xyzt+1m  exists, it proceeds to step S 70 , and stores this information in the third memory as route information, and proceeds to the next step S 71 . 
     Then, at step S 71 , the CPU  36  determines if the condition of k&lt;N k  is met, if this condition is met, the CPU  36  returns to step S 66  via step S 67 . 
     Meanwhile, if the CPU  36  has determined that the condition of k&lt;N k  is not met, it proceeds to the next step S 72 , and further determines if the condition of 2&lt;t is met. Then, if this condition is met, the CPU  36  returns to step S 62  via step S 64 . 
     Then, the CPU  36  sets the time to the time t−1 one time before and repeats similar processing. When the time t has become the first time t=1 as a result of that, the CPU  36  terminates this processing. 
     As a result of the above-described processing being performed, route information such as that shown in  FIG. 19 , for example, is stored in the third memory. In  FIG. 19 , the regions are included in the respective rows, and the row including the largest number of regions is extracted, and the temporal route, that is, the track of the capsule-type endoscope  3  is formed by connecting (joining) the regions for the respective times. 
     Alternatively, the CPU  36  may calculate the route (track) in such a manner as described below. 
     Where multiple adjacent regions exist, the CPU  36  calculates the minimum value of the cost values for the estimated positions in the respective regions (e.g., the sums of the squares of the residual differences between the measured values and the calculated values), and determines the extracted region with the smallest cost value to be the connected region. 
     The CPU  36  records the information on the estimated positions with the smallest cost values in the respective regions, together with the extracted regions and the connection information. Then, the CPU  36  ranks the routes according to the number of regions included in the routes, and calculates the lengths of the entire routes for the highly-ranked routes to calculate the route whose entire length is the shortest as a track. Also, the CPU  36  may calculate the route whose total sum of the cost values is the smallest to determine it to be a track. 
     The present embodiment provides the following advantageous effects. 
     According to the present embodiment, regions are set to reduce the number of positions to be estimated, enabling searching for routes at a speed higher than in embodiment 1. Besides, likewise in embodiment 1, the positions and track of the capsule-type endoscope  3  can be estimated with high accuracy. 
     Embodiment 3 
     Next, embodiment 3 of the present invention will be described. The configuration of the present embodiment is similar to that of embodiment 1, and is different from that of embodiment 1 in the content of processing provided by the program in the track estimating section. In the present embodiment, the CPU  36  performs track estimation processing using the Dijkstra method as described below. 
     Next, the operation of the present embodiment will be described. The operation is similar to that of embodiment 1 or 2 up to the steps of calculating and recording the estimated positions or regions and the connection information. In the present embodiment, the Dijkstra method is employed as a technique for determining routes. This Dijkstra method is described in, e.g., “Data Structures and Algorithms” (coauthored by Nobuo Saito and Seiichi Nishihara, Corona Publishing Co., Ltd., pp. 124-129). 
     In the Dijkstra method, for example, in embodiment 1, the processing for setting a plurality of routes connecting the positions estimated at the respective adjacent times t and t−1 from the time t=1 to tend via lines L using such positions as nodes is performed. 
     Then, the CPU  36  properly assigns weights to, e.g., the lengths of the lines L for them (as a matter of course, the same weight may be assigned as 1), calculates the accumulated value (cost value) obtained by adding up the values in the route for all possible routes, and determines the route whose accumulated value (cost value) is the smallest to be the final route, that is, the track. 
     In the present embodiment, the CPU  36 , upon the estimation of the positions, performs the processing for calculating cost values for them and comparing the calculated cost values to calculate the final route. Thus, the present embodiment provides the following advantageous effect. 
     In the present embodiment, the use of the Dijkstra method enables search for routes at a speed higher than in embodiment 1 or 2. 
     Embodiment 4 
     Next, embodiment 4 of the present invention will be described. The configuration of the present embodiment is similar to that of embodiment 1, and different from that of embodiment 1 in the content of processing provided by the program in the track estimating section. 
     For the operation of the present embodiment, the CPU  36 , where a route from the starting point and the endpoint is disconnected in the middle, connects the disconnected routes so that the distance between the endpoint of one route and the starting point of the other route is as short as possible. 
     As an advantageous effect of the present embodiment, it is possible to search for a route from the starting point to the endpoint even if the route is disconnected in the middle. 
     Embodiment 5 
     Next, embodiment 5 of the present invention will be described. The configuration of the present embodiment is similar to that of embodiment 1, and different from that of embodiment 1 in the content of processing provided by the program in the track estimating section. 
     For the operation of the present embodiment, the CPU  36  constrains estimated positions/regions from forecast information relating to a site of a living body. For example, in a site such as esophagus, the capsule-type endoscope  3  can be considered to move substantially linearly from the mouth to the stomach, and accordingly, it is almost possible to forecast estimated positions, and the estimated positions outside the forecasted area are excluded from the targets of the processing by the CPU  36 . 
     Also, since the moving direction of the capsule-type endoscope (direction from the mouth toward the stomach) can be forecasted, when connecting the estimated positions or regions, the connections from the stomach toward the mouth are excluded from the targets of the processing by the CPU  36 . 
     As an advantageous effect of the present embodiment, it is possible to search routes at high speed. 
     Embodiment 6 
     Next, embodiment 6 of the present invention will be described. The configuration of the present embodiment is similar to that of embodiment 1, and different from that of embodiment 1 in the content of processing provided by the program in the track estimating section. 
     Next, the operation of the present embodiment will be described. 
     Multiple positions of the capsule-type endoscope  3  may be estimated depending on the number and arrangement of antennae  11  for reception, the manner to provide an initial value for the position (x wg , y wg , z wg ) (0)  of the antenna  23 , and noise, etc. Since the capsule-type endoscope  3  makes relative small movements in a body cavity and picks up images at short intervals, the position of the capsule-type endoscope  3  estimated at a certain time and the position of the capsule-type endoscope  3  estimated at a time immediately before or after the certain time can be considered to be positions that are substantially the same or close to each other. 
     Accordingly, the CPU  36  connects multiple positions of the capsule-type endoscope  3  estimated at temporally adjacent times using the distance or cost values, etc., as a condition, to calculate the positions of the capsule-type endoscope  3  at the respective times from the entire connection state. 
     The CPU  36 , as shown in  FIG. 8 , sets positions estimated at a time t−1 to P(t−1)j (j=1, 2, . . . Nj), and positions estimated at a time t to Pti (i=1, 2, . . . , Ni). Also, the CPU  36  sets an evaluation function h (t−1)j,ti  for the positions P(t−1)j and Pti estimated at the times t−1 and t as described below.
 
 h   (t−1)j,ti   =d   (t−1)j,ti   +w (cos  t   (t−1)j +cos  t   ti )
 
 d   (t−1)j,ti =[( P   xt1   −P   x(t−1)j ) 2 +( P   yti   −P   y(t−1)j ) 2 +( P   zti   −P   z(t−1)j ) 2 ] 1/2 ,
 
provided that d (t−1)j,ti  indicates the distance between the respective estimated positions, and cost (t−1)j  and cost ti  indicates the cost values obtained when the positions are estimated, and w indicates a weighting factor. This w is calculated from, for example, a distance of 3 cm and a value obtained by tripling the minimum cost cost min  at the time of the position estimation.
 
     In other words,
 
 w= 0.03/(3cost min )
 
The CPU  36  calculates an evaluation function for all the combination of the positions P(t−1)j and Pti estimated at the times t−1 and t. Then, the CPU  36  arranges the position combinations in ascending order of value according to the evaluation function, and extracts the high-order combinations from those with the smallest values in that case and stores them.
 
     For example, the CPU  36  sets a threshold value for the evaluation function, and where a value according to the evaluation function is equal to or larger than the threshold value, the CPU  36  does not store the connection information and the value according to the evaluation function. Also, where there is a large distance, e.g., a distance of 5 cm or more, between two points, the CPU  36  cancels the calculation according to the evaluation function and does not store the connection information, etc. 
     Lastly, the CPU  36  connects the estimated positions at the respective times according to the connection information with the position of the capsule-type endoscope  3  stored together with the connection information as the starting point, and calculates the total sum of the values according to the evaluation function. The CPU  36  extracts the route whose connection is the longest to calculate the track as the positions of the capsule-type endoscope  3  at the respective times. Also, where multiple routes are calculated, the CPU  36  estimates the positions of the capsule-type endoscope  3  at the respective times from the route whose sum of the values according to the evaluation function is small. Where all the routes are disconnected in the middle (e.g., all the values according to the evaluation function are equal or larger than the threshold value, or the distances are 5 cm or more), the CPU  36  performs processing similar to the above-described processing with the position at the time when the route is disconnected as the starting point, and the connection between the disconnection parts, as in the embodiment 4, is made so that the distance between the endpoint of one route and the starting point of the other route is as short as possible. 
     The CPU  36  calculates an value according to the evaluation function for all the combinations of the positions P(t−1)j and Pti at the times t−1 and t. Then, the CPU  36  arranges the position combinations in ascending order of value according to the evaluation function, and extracts the high-order combinations from those with the smallest values in that case and stores them. 
     For example, the CPU  36  sets a threshold value for the evaluation function, and where a value according to the evaluation function is equal to or larger than the threshold value, the CPU  36  does not store the connection information and the value according to the evaluation function. Also, where there is a large distance, e.g., a distance of 5 cm or more, between two points, the CPU  36  cancels the calculation according to the evaluation function and does not store the connection information, etc. 
     The present embodiment provides the following advantageous effect. 
     According to the present embodiment, even where multiple positions of the capsule-type endoscope  3  have been estimated depending on the number and arrangement of antennae  11  for reception, the manner to provide the position (x wg , y wg , z wg ) (0)  of an initial value for an antenna  23 , and noise, etc., the position of the capsule-type endoscope  3  can uniquely be determined. Also, according to the present embodiment, since an evaluation function is set using the distance between two points and the cost values, the correct positions of the capsule-type endoscope  3  can be estimated using this evaluation function. 
     Embodiment 7 
     Next, embodiment 7 of the present invention will be described. The configuration of the present embodiment is similar to that of embodiment 1, and is different from that of embodiment 1 in the content of processing provided by the program in the track estimating section. 
     Next, the operation of the present embodiment will be described. 
     As described above,  FIG. 13B  a diagram illustrating a state in which a space where the capsule-type endoscope  3  exists is divided into a plurality of regions R XYZ  (x=1, 2, 3, . . . , y=1, 2, 3, . . . , and z=1, 2, 3, . . . ). Also,  FIG. 14  is a diagram illustrating respective positions P(t−1)j (j=1, 2, 3, . . . ) and Pti (i=1, 2, 3, . . . ) estimated as positions of the capsule-type endoscope  3  from multiple output values of the antennae  11  obtained at times t−1 and t. 
     The CPU  36  calculates regions R xyz  including the positions Pti (i=1, 2, 3, . . . ) estimated at the time t. Also, when the CPU  36  connects them with the regions obtained at the time t−1, it calculates the following evaluation function.
 
 h   (t−1)j,ti   =d   (t−1)j,ti   +w   1 (cos  t   (t-1)j +cos  t   ti   +w   2 /( n   Q1mn′   +n   Q1m+1n )
 
 d   (t−1)j,ti =[( Q   xlmn   −Q   xlm+ln ) 2 +( Q   ylmn   −Q   ylm+ln ) 2 +( Q   zlmn   −Q   zlm+ln ) 2 ] 1/2 ,
 
provided that d (t−1)j,ti  indicates the distance between the barycentric positions Q t−1  and Q t t of regions R xyz  including respective estimated positions, and cost (t−1)j  and cost ti  indicate cost values obtained when positions are estimated, and also, w 1  and w 2  indicate weighting factors. For example, w 1  is a value calculated from a distance of 3 cm and a value obtained by tripling the minimum cost at the time of the position estimation, and w 2  is a value calculated from the number of divided regions and the number (n Qlmn , n Qlm+1n ) of estimated positions included in each of the relevant region.
 
     In other words, the weighting factors w 1  and w 2  are values that can be expressed as follows:
 
 w 1=0.03/(3cost min )
 
w2=1000.0
 
     The CPU  36  determines the connection relations of the estimated positions at the times t and t−1, which have been extracted based on the valuation function, in the divided regions. The connections are limited to those for movements between adjacent regions. Also, where there are multiple adjacent regions, the region including the largest number of estimated positions is determined to be the connected region.  FIG. 15  shows a state of connection from a region obtained at the time t to that obtained at the time t−1. The CPU  36  records information on the region obtained at the time t−1 connected to the region obtained at the time t. Furthermore, the CPU  36  records extracted positions and connection information for all the recorded data. 
     The CPU  36 , as in embodiment 2, sets the region stored at the last to be a stating point, and the region stored at the first to be an endpoint, and calculates routes from the starting point to the endpoint using the connection information stored together with the extracted regions. The CPU  36  calculates the route including the largest number of regions and determines the estimated positions at the respective times from the obtained route. Also, the estimated positions in this case are the center positions (barycentric positions) of the regions. 
     Where there are multiple adjacent regions, the CPU  36  calculates the minimum value in the cost values (e.g., the sums of the squares of the residual differences between the measured values and the calculated values) of the estimated positions included in the respective regions, and determines the extracted region with the smallest cost value to be the connected region. 
     Then, the CPU  36  records the information on the estimated positions whose cost values are the smallest in the respective regions together with the extracted regions and the connection information. Furthermore, the CPU  36  ranks the routes according to the number of regions included in the routes, and calculates the lengths of the entire routes for the highly-ranked routes to calculate the route whose entire length is the shortest. Also, the CPU  36  may calculate the route whose total sum of the cost values is the smallest. 
     The present embodiment provides the following advantageous effect. 
     According to the present embodiment, regions are set to reduce the number of positions to be estimated, enabling search for routes at a speed higher than in embodiment 1. 
     In the above-described embodiments, etc., in addition to the estimated positions of the antenna  23  (or the capsule-type endoscope  3 ), information on the directions thereof may be used for the processing for calculating a track. The use of information on the directions as mentioned above enables calculation of a track and positions with higher accuracy or with higher reliability compared to the case where only the positions are used. 
     In the above-described embodiments, an embodiment formed by, e.g., combining parts of different embodiments also falls under the scope of the present invention. Also, an embodiment partially modified without departing from the scope and spirit of the present invention also falls under the scope of the present invention. 
     Although the above-described examples have been described for the case where information on images of a body cavity optically picked up is acquired as information on the inside of a living body, the present invention is not limited thereto, and can also be employed in a capsule-type medical device for pH calculation by providing a pH sensor to the device. Alternatively, a medicinal solution and mean for spraying the medicinal solution may be provided to provide medical treatment.