Patent Publication Number: US-2011060185-A1

Title: Medical device system and calibration method for medical instrument

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2010/057456 filed on Apr. 27, 2010 and claims benefit of Japanese Application No. 2009-132390 filed in Japan on Jun. 1, 2009, the entire contents of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a medical equipment system provided with a medical instrument used while projecting from a distal end of an insertion portion of an endoscope inserted into the body of a subject and a medical instrument calibration method, and more particularly, to a medical equipment system and a medical instrument calibration method capable of detecting a precise direction of the distal end portion of the medical instrument. 
     2. Description of the Related Art 
     In recent years, an insertion navigation system is disclosed which forms a three-dimensional image of a tube, for example, the bronchus of the lung from three-dimensional image data of a subject obtained using a CT apparatus, determines a path up to a target point along the tube on the three-dimensional image and further forms a virtual endoscope image of the tube along the path based on the three-dimensional image data. Using, for example, an insertion navigation system disclosed in Japanese Patent Application Laid-Open Publication No. 2004-180940 allows an operator to correctly guide the distal end of the insertion portion of an endoscope to the vicinity of a region of interest in a short time. However, there is a limit to the thickness, that is, the diameter, of the tube through which the insertion portion can be inserted, and the insertion portion cannot be inserted up to the periphery of the bronchus. For this reason, after the distal end of the insertion portion reaches the vicinity of the region of interest, by causing a medical instrument such as treatment instrument or ultrasound probe of a smaller diameter to project from the distal end of the insertion portion, the operator can extract a sample of the region of interest or photograph an ultrasound image of target tissue. 
     To photograph an ultrasound image of target tissue or extract a sample of the region of interest, it is necessary to detect the position and direction of the distal end portion of the medical instrument. Japanese Patent Application Laid-Open Publication No. 2006-223849 and Japanese Patent Application Laid-Open Publication No. 2007-130154 propose a method of arranging a sensor at the distal end portion of the medical instrument to detect the position and direction of the distal end portion of a medical instrument. 
     SUMMARY OF THE INVENTION 
     A medical equipment system according to the present invention is provided with an insertion portion having a rigid portion disposed at a distal end portion of the insertion portion, a medical instrument whose medical instrument distal end portion projects from a projection port of the rigid portion, a channel that passes through the rigid portion and can linearly support the medical instrument distal end portion in the rigid portion, and a direction calculation section that calculates a longitudinal direction of the medical instrument distal end portion based on a positional variation caused by linear movement of the medical instrument distal end portion in the channel in the rigid portion. 
     Furthermore, another medical instrument calibration method of the present invention for a medical equipment system provided with an insertion portion having a rigid portion disposed at a distal end portion of the insertion portion, a medical instrument whose medical instrument distal end portion projects from a projection port of the rigid portion and a channel that passes through the rigid portion and can linearly support the medical instrument distal end portion in the rigid portion, includes an insertion step of inserting the medical instrument from an insertion port of the channel on a proximal end portion side, a first calculation step of calculating the position of the medical instrument distal end portion in a first place in the channel in the rigid portion based on information of a first sensor disposed at the medical instrument distal end portion, capable of detecting a position and a direction, a probe moving step of moving the position of the medical instrument distal end portion from the first place to a second place in the channel in the rigid portion on a straight line, a second calculation step of calculating the position of the medical instrument distal end portion in the second place, and a distal end portion direction calculation step of calculating the direction of the medical instrument distal end portion based on the position calculated in the first calculation step and the position calculated in the second calculation step. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a situation in which a region of interest of the lung of a subject is being inspected using an endoscope system according to a first embodiment; 
         FIG. 2  is a configuration diagram illustrating a configuration of the endoscope system of the first embodiment; 
         FIG. 3  is a schematic cross-sectional view illustrating an ideal structure of an ultrasound probe which is a medical instrument of the endoscope system of the first embodiment; 
         FIG. 4  is a schematic cross-sectional view illustrating an example of an actual structure of the ultrasound probe which is a medical instrument of the endo scope system of the first embodiment; 
         FIG. 5  is a configuration diagram illustrating a configuration of a navigation unit of the endoscope system of the first embodiment; 
         FIG. 6  is a flowchart illustrating a processing flow of the medical system of the first embodiment; 
         FIG. 7  is a schematic cross-sectional view illustrating operation of the medical system of the first embodiment; 
         FIG. 8  is a cross section schematic diagram illustrating the operation of the medical system of the first embodiment; 
         FIG. 9  is a schematic cross-sectional view illustrating the operation of the medical system of the first embodiment; 
         FIG. 10  is a schematic cross-sectional view illustrating operation of a medical system according to a second embodiment; 
         FIG. 11  is a schematic cross-sectional view illustrating the operation of the medical system of the second embodiment; 
         FIG. 12  is a schematic cross-sectional view illustrating the operation of the medical system of the second embodiment; 
         FIG. 13  is a display screen illustrating an example of image processing of a monitor illustrating an endoscope system according to a third embodiment of the present invention; 
         FIG. 14  is a flowchart illustrating a processing flow of the medical system of the third embodiment; 
         FIG. 15  is a schematic cross-sectional view of an endoscope illustrating an endoscope system according to a fourth embodiment; 
         FIG. 16  is a schematic cross-sectional view of the endoscope illustrating the endoscope system of the fourth embodiment; 
         FIG. 17  is a configuration diagram illustrating a configuration of the endoscope system of the fourth embodiment; 
         FIG. 18A  is a diagram illustrating a coordinate system in the endoscope system of the fourth embodiment; 
         FIG. 18B  is a diagram illustrating the coordinate system in the endoscope system of the fourth embodiment; and 
         FIG. 18C  is a diagram illustrating the coordinate system in the endoscope system of the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Hereinafter, an endoscope system  1 , which is a medical equipment system according to a first embodiment of the present invention, and a calibration method of an ultrasound probe (hereinafter also simply referred to as “probe”)  21  of a small diameter, which is a medical instrument, will be described with reference to the accompanying drawings. 
       FIG. 1  is a diagram illustrating a situation in which a region of interest of the lung of a subject is being inspected using an endoscope system according to the first embodiment of the present invention,  FIG. 2  is a configuration diagram illustrating a configuration of the endoscope system of the present embodiment,  FIG. 3  and  FIG. 4  are schematic cross-sectional views illustrating a structure of a probe, which is a medical instrument of the endoscope system of the present embodiment. 
       FIG. 1  shows a situation in which a rigid portion  13  making up an endoscope distal end portion, which is an insertion portion distal end portion of an insertion portion  12  of an endoscope apparatus  10  of the endoscope system  1  is inserted into a tube of a minimum diameter of the bronchus  7  of the subject  5  up to which insertion is possible. A probe distal end portion of the ultrasound probe (hereinafter also referred to as “probe”)  21  which is a medical instrument inserted into a channel  14  (see  FIG. 2 ) from a projection port  14 B on the proximal end portion side projects from the projection port  14 B of the rigid portion  13  and inspects tissue of a region of interest  8 . 
     As shown in  FIG. 1 , the insertion portion  12  of the endoscope apparatus  10  is as thin as on the order of diameter 3 mm so as to be insertable into a thin bronchus tube cavity, but the probe  21  is, for example, on the order of diameter 1 mm so as to be insertable into the thinner peripheral bronchus tube cavity. Since the region of interest  8  is within the thin peripheral bronchus, it often cannot be recognized using a CCD  19  or the like disposed in the rigid portion  13 . 
     Next, as shown in  FIG. 2 , the endoscope system  1  is provided with the endoscope apparatus  10 , which is insertion means, an ultrasound observation apparatus  20  and a navigation apparatus  30 . The endoscope apparatus  10  includes an endoscope  11  having the CCD  19  which is image pickup means in the rigid portion  13  of the insertion portion  12  having a flexible portion  15  and the rigid portion  13 , a light source  17  that supplies illumination light to the endoscope  11 , a CCU (camera control unit)  16  that controls the CCD  19  which is image pickup means and processes an image signal obtained from the CCD  19  into a video signal and a monitor  18  that displays an endoscope image. The channel  14  having openings at the insertion port  14 A on a proximal end portion side (PE) and at the projection port  14 B of the rigid portion  13  on the endoscope distal end portion side (DE) passes through the insertion portion  12 . While the flexible portion  15  is flexible, the rigid portion  13  is not flexible. 
     The ultrasound observation apparatus  20  has a probe  21  having an ultrasound transducer  23  at a probe distal end portion (hereinafter also simply referred to as “distal end portion”)  22 , which is a medical instrument distal end portion, an ultrasound observation unit  24  that controls the ultrasound transducer  23  and processes an ultrasound signal obtained and a monitor  25  that displays an ultrasound image. 
     The navigation apparatus  30  has transmission antennas  33  which are magnetic field generating means for generating magnetic fields for a first sensor  40  disposed at the distal end portion  22  and a second sensor  41  disposed in the rigid portion  13  of the insertion portion  12  to detect the position and direction, a sensor unit  32  that processes output data of the first sensor  40  and the second sensor  41 , a navigation unit  31  that calculates positions and directions of the distal end portion  22  of the probe  21  and the distal end of the insertion portion  12  based on information of the sensor unit  32  and is insertion supporting means for supporting the insertion operation, and a monitor  34  that performs display for navigation. The sensor unit  32  and the navigation unit  31  need not be independent units, but may be integrated in one single unit. 
     The sensor unit  32  shown in  FIG. 2  sends an AC current to coils (not shown) located at a plurality of different positions in the transmission antennas  33  and the transmission antennas  33  generate AC magnetic fields. The first sensor  40  and the second sensor  41  detect the AC magnetic fields from the transmission antennas  33  and can detect the position and direction based on the detected magnetic field strength. 
     That is, as shown in  FIG. 3  and  FIG. 4 , the first sensor  40  is a magnetic field detection sensor that has, for example, two coils  40 A and  40 B that detect magnetic fields in directions orthogonal to each other. That is, a coil axis which is a magnetic field detection direction of the coil  40 A is orthogonal to a coil axis which is a magnetic field detection direction of the coil  40 B. 
     Therefore, the first sensor  40  can detect distances from and directions of the respective coils located at a plurality of different positions in the transmission antennas  33 . Thus, the sensor unit  32  can detect a position (x, y, z) and a direction (α, β, γ) of the first sensor  40  using the positions of the transmission antennas  33  as references, that is, parameters of six degrees of freedom. The sensor position is, for example, three-dimensional coordinate values of the coil center point of the coils  40 A and  40 B and the sensor direction is the direction of, for example, the coil axis of the coil  40 A. 
     As shown in  FIG. 2 , the second sensor  41  disposed at the rigid portion  13  is a magnetic field detection sensor that has a structure similar to that of the first sensor  40 , that is, having two coils that detect magnetic fields in directions orthogonal to each other. The coil axis which is the magnetic field detection direction of one coil of the second sensor  41  is parallel to the longitudinal direction of the elongated distal end portion  22  (rigid portion  13 ) and the coil axis which is the magnetic field detection direction of the other coil is parallel to the vertical direction of the endoscope image out of the directions orthogonal to the longitudinal directions of the distal end portion  22 . Hereinafter, when the sensor direction is indicated, suppose the direction substantially parallel to the longitudinal direction of the distal end portion  22  will be referred to as an “axial direction” and the direction substantially orthogonal to the longitudinal direction will be referred to as a “radial direction.” 
     The sensor unit  32  detects the positions and directions of the first sensor  40  and the second sensor  41  and calculates the position and direction of the ultrasound transducer  23  disposed at the distal end portion  22 . The navigation unit  31  then performs navigation based on the positions and directions of the ultrasound transducer  23  and the distal end portion  22  calculated by the sensor unit  32 . The position of the ultrasound transducer  23  is, for example, the center position of the ultrasound transducer  23 , the direction thereof is a direction orthogonal to the direction in which ultrasound is generated, and the position of the distal end portion  22  is the center position of the distal end face of the probe  21  and the direction thereof is the longitudinal direction of the elongated distal end portion  22 . 
     However, as shown in  FIG. 3 , when a smaller magnetic field sensor is disposed at the distal end portion  22  of the probe  21  of a small diameter, it is ideal that the magnetic field detection direction of the coil  40 A be disposed so as to be parallel to the longitudinal direction of the distal end portion  22 , but this is not easy. That is, as shown in  FIG. 4 , the magnetic field detection direction of the coil  40 A may be actually not parallel to the longitudinal direction of the distal end portion  22 .  FIG. 4  shows an example where the magnetic field detection direction of the coil  40 A is exaggeratedly deviated from the longitudinal direction of the distal end portion  22  for ease of explanation. 
     As shown in  FIG. 4 , when the magnetic field detection direction of the coil  40 A does not coincide with the longitudinal direction of the distal end portion  22 , there is an error between the magnetic field detection direction of the coil  40 A calculated by the sensor unit  32  and the longitudinal direction of the distal end portion  22 . However, as will be described later, the endoscope system  1  can calibrate the probe  21 , and can thereby calculate the direction with high accuracy. 
     Here,  FIG. 5  is a configuration diagram illustrating a configuration of a navigation unit  31  of the endoscope system  1  of the present embodiment. As shown in  FIG. 5 , the navigation unit  31  includes a position calculation section  31 A which is position calculation means for calculating the position and direction of the first sensor  40  from information of the first sensor  40 , a direction calculation section  31 B which is direction calculation means for calculating the longitudinal direction of the distal end portion  22 , a direction correction section  31 C which is direction correction means for correcting the direction detected by the first sensor  40 , and a navigation section  31 E which is navigation means for performing navigation that inserts the distal end portion  22  up to the region of interest  8  based on the position of the distal end portion  22 . As has already been described, since the region of interest  8  is located in the small peripheral bronchus, the region of interest  8  may not always be recognized using the CCD  19  or the like disposed at the rigid portion  13 . 
     As will be described later, the direction calculation section  31 B calculates the longitudinal direction of the distal end portion  22  based on the place to which the distal end portion  22 , that is, the first sensor  40  moves on a straight line, for example, the position of the first sensor  40  before and after the movement when the channel  14  in the rigid portion  13  is moved, and thereby calculates the amount of difference between the magnetic field detection direction of the coil  40 A and the longitudinal direction of the distal end portion  22 , the direction correction section  31 C corrects the direction detected by the first sensor  40  and calculates the longitudinal direction of the distal end portion  22 , and the endoscope system  1  can thereby calculate the direction with high accuracy. 
     Here, the operation of the endoscope system  1  will be described using  FIG. 6 ,  FIG. 7 ,  FIG. 8  and  FIG. 9 .  FIG. 6  is a flowchart illustrating a processing flow of the medical system of the present embodiment and  FIG. 7  to  FIG. 9  are schematic cross-sectional views illustrating the operation of the medical system according to the present embodiment. Hereinafter, the processing flow of the endoscope system  1  of the present embodiment will be described according to the flowchart in  FIG. 6 . 
     &lt;Step S 10 &gt; Insertion Portion Insertion Step 
     The operator inserts the insertion portion  12  of the endoscope apparatus  10  into the bronchus  7  of the subject  5 . In that case, by forming a virtual endoscope image of the bronchus  7  using a publicly known insertion navigation system based on the three-dimensional image data and performing insertion support, the operator can correctly guide the distal end of the insertion portion  12  to the vicinity of the region of interest  8  in a short time. 
     &lt;Step S 11 &gt; Probe Insertion Step 
     As shown in  FIG. 7 , the operator inserts the probe  21  from the insertion port  14 A of the channel  14  of the insertion portion  12  so that the first sensor  40  is located at the position P 2  close to the proximal end portion in the channel  14  of the rigid portion  13 . 
     &lt;Step S 12 &gt; First Calculation Step 
     The operator instructs the navigation unit  31  on the first direction correction processing. 
     Upon receiving the instruction on the first direction correction processing, the navigation unit  31  acquires data (position and direction) of the first sensor  40  and the second sensor  41  from the sensor unit  32 . 
     In this case, suppose the position data of the second sensor  41  is P 1 , the axial direction data is vector V 1 , radial direction data is vector W 1 , the magnetic field detection direction data of the coil  40 A of the first sensor  40  is vector V 2 , and the magnetic field detection direction data of the coil  40 B is vector W 2 . 
     &lt;Step S 13 &gt; Probe Moving Step 
     Next, as shown in  FIG. 8 , the operator moves the position of the probe  21  with respect to the rigid portion  13  to the distal end direction P 4  within a range in which the first sensor  40  of the probe  21  is located in the channel  14  of the rigid portion  13 . Since the channel  14  in the rigid portion  13  is linear, the distal end portion  22 , that is, the first sensor  40  moves on a straight line. 
     &lt;Step S 14 &gt; Second Calculation Step 
     The operator instructs the navigation unit  31  on second direction correction processing. 
     Upon receiving the instruction of the second direction correction processing, the navigation unit  31  acquires data (position and direction) of the second sensor  41  and data (position and direction) of the first sensor  40  form the sensor unit. 
     In this case, suppose the position data of the second sensor  41  is P 3 , the axial direction data is vector V 3 , radial direction data is vector W 3 , magnetic field detection direction data from the coil  40 A of the first sensor  40  is vector V 4 , and magnetic field detection direction data from the coil  40 B is vector W 4 . 
     &lt;Step S 15 &gt; Correction Coefficient Calculation Step 
     Assuming that the moving direction of the probe  21  coincides with the longitudinal direction of the distal end portion  22  of the probe  21 , the navigation unit  31  estimates the longitudinal direction of the distal end portion  22  of the probe  21 . However, while the probe  21  is moving, the endoscope  11  may move due to movement, breathing or heart beat of the subject. To cancel out the movement of the endoscope  11 , it is preferable to calculate the moving direction of the probe  21  as the longitudinal direction of the distal end portion  22  of the probe  21  based on the relative position of the probe  21  with respect to the endoscope  11 . 
     The method of calculating the longitudinal direction VV of the distal end portion  22  will be described in (Equation 1) to (Equation 6) described below. 
     First, the navigation unit  31  sets vector X 1 , vector X 3  and vector X 4  as (Equation 1), (Equation 2) and (Equation 3) below respectively. 
         X 1 =V 1 ×W 1 (vector product)  (Equation 1)
 
         X 3 =V 3 ×W 3 (vector product)  (Equation 2)
 
         X 4 =V 4 ×W 4 (vector product)  (Equation 3)
 
     Next, assuming the relative position of the probe  21  with respect to the endoscope  11  in the first calculation step before moving the probe is vector P 1 P 2  from P 1  to P 2 , relative position coefficients a, b and c are calculated when expressed by (Equation 4) below using V 1 , W 1  and X 1 . 
         P 2 P 1 =aV 1 +bW 1 +cX 1  (Equation 4)
 
     Likewise, assuming the relative position of the probe  21  relative to the endoscope  11  in the second calculation step after moving the probe is vector P 1 P 2  from P 3  to P 4 , relative position coefficients a 1 , b 1  and c 1  are calculated when expressed by (Equation 5) below using V 3 , W 3  and X 3 . 
         P 4 P 3 =a   1   V 3 +b   1   W 3 +c   1   X 3  (Equation 5)
 
     The axial direction of the probe  21  in the second calculation step, that is, the longitudinal direction VV of the distal end portion  22  is calculated from the moving direction of the probe  21 , and is calculated based on the relative position with respect to the endoscope  11 . Thus, VV can be calculated as expressed in (Equation 6) below using a, b, c, a 1 , b 1  and c 1  which are relative position coefficients. 
         VV=P 3 P 4 −P 1 P 2=( a   1   −a ) V 3+( b   1   −b ) W 3+( c   1   −c ) X 3  (Equation 6)
 
     The longitudinal direction VV of the distal end portion  22  of the probe  21  calculated here is expressed as a function of magnetic field detection direction data of the coil  40 A which is output data of the first sensor  40  and magnetic field detection direction data of the coil  40 B. By expressing VV with this function, the output data of the first sensor  40  of the probe  21  is corrected and a correction coefficient for accurately calculating the longitudinal direction of the distal end portion  22  is calculated. 
     When VV is expressed as a function of V 4 , W 4  and X 4 , VV is expressed by (Equation 7) below and the navigation unit  31  can calculate a 2 , b 2  and c 2  which are correction coefficients using (Equation 6) and (Equation 7). 
         VV=a   2   V 4 +b   2   W 4 +c   2   X 4  (Equation 7)&lt;
 
     &lt;Step S 16 &gt; Detection Direction Correction Step (Navigation Step) 
     The navigation apparatus  30  changes the navigation target from the rigid portion  13  of the insertion portion  12  to the distal end portion  22  of the probe  21 . The navigation apparatus  30  creates navigation information based on the corrected longitudinal direction VV(t) of the distal end portion  22  and the detected position of the distal end portion  22 . The operator inserts the probe  21  up to the vicinity of the region of interest  8  according to navigation information of the navigation apparatus  30  and performs observation using the ultrasound transducer  23 . 
     As shown in  FIG. 9 , a longitudinal direction VV(t) of the distal end portion  22  at an arbitrary time t during navigation is calculated according to the following (Equation 8) based on the magnetic field detection direction data V(t) of the coil  40 A which is the output data of the first sensor  40  at the arbitrary time t, the magnetic field detection direction data W(t) of the coil  40 B and a 2 , b 2  and c 2  which are correction coefficients calculated in step S 15 . 
         VV ( t )= a   2   V ( t )+ b   2   W ( t )+ c   2 ( V ( t )× W ( t ))  (Equation 8)
 
     &lt;Step S 17 &gt; End Instruction 
     The navigation apparatus  30  continues the navigation until the operator sends an end instruction. 
     The correction coefficients a 2 , b 2  and c 2  used by the direction correction section  31 C for correction are values specific to the probe  21 . Therefore, the navigation apparatus  30  also has a storage section that stores the relationship between the probe whose correction coefficient is calculated once, in other words, the calibrated probe and the correction coefficient, and it is also possible to preferably use an endoscope system that informs the operator that the correction coefficient has already been calculated when the probe stored in the storage section is used. 
     An example has been described above where the position of the distal end portion  22  is corrected based on information of the second sensor  41 . Even when the relative position of the bronchus  7  with respect to the region of interest  8  of the distal end portion  22  does not change, the position of the distal end portion  22  changes due to breathing or the like of the subject  5 . However, in the case of movement of the distal end portion  22  due to breathing or the like of the subject  5 , it is possible to assume that the second sensor  41  also simultaneously moves by the same amount. Thus, by correcting the position of the distal end portion  22  based on the information of the second sensor  41 , it is possible to estimate the movement due to breathing or the like of the subject  5  and calculate the position of the distal end portion  22  more accurately. 
     When the region of interest  8  is located at a region where there is little influence of breathing or the like of the subject, the position of the distal end portion  22  need not be corrected based on the information of the second sensor  41 . In other words, the second sensor  41  is unnecessary. 
     Although the ultrasound probe  21  has been illustrated above as an example of the medical instrument, the medical instrument is not limited to this, but a treatment instrument such as puncture needle, brush or forceps whose distal end is suitable for sampling of tissue may be used as the medical instrument. 
     As described so far, in the endoscope system  1  which is the medical equipment system of the present embodiment, when the first sensor  40  is disposed at the probe  21 , even if the probe  21  is not disposed accurately, the probe  21 , which is the medical instrument, calibrates the probe  21 , and can thereby detect a precise longitudinal direction of the distal end portion  22 . Thus, the endoscope system  1  can perform high accuracy inspection or treatment. 
     Furthermore, a magnetic field sensor made up of two coils whose coil axes are orthogonal to each other as the first sensor  40  and second sensor  41  has been illustrated in the present embodiment, but these need not be orthogonal to each other as long as the coil axis directions of the two coils are different. Furthermore, the magnetic field sensor may be made up of three or more coils or may be an MR sensor, MI sensor, FG sensor or the like. 
     Second Embodiment 
     Hereinafter, an endoscope system  1 B which is a medical equipment system according to a second embodiment of the present invention will be described with reference to the accompanying drawings. The endoscope system  1 B of the present embodiment is similar to the endoscope system  1  of the first embodiment, and therefore the same components will be assigned the same reference numerals and descriptions thereof will be omitted.  FIG. 10 ,  FIG. 11  and  FIG. 12  are schematic cross-sectional views illustrating the operation of the endoscope system of the second embodiment. 
     As shown in  FIG. 10 , since the endoscope  11  of the endoscope system  1 B of the present embodiment has a structure in which the probe  21  projects in a diagonal direction, the linear region of the channel  14  in the rigid portion  13  is short. For this reason, it is not easy to calibrate the probe  21  in the rigid portion  13 . 
     However, as shown in  FIG. 11 , while the amount of projection is small even after projecting from the projection port  14 B, the probe  21  maintains the linear state by its own rigidity, in other words, the distal end portion  22  of the probe  21  moves on a straight line. The endoscope system  1 B performs calibration at a place where the distal end portion  22  moves on a straight line after projecting from the projection port  14 B. 
     That is, the first calculation step is performed in the state shown in  FIG. 10 , the probe  21  moves by an amount for maintaining the linear state in the probe moving step, performs the second calculation step in the state shown in  FIG. 11 , and the navigation unit  31  thereby sets the axial direction of the probe  21  at an arbitrary time t, that is, the longitudinal direction VV(t) of the distal end portion  22  as a function of the magnetic field detection direction data V(t) from the coil  40 A of the first sensor  40  and magnetic field detection direction data W(t) from the coil  40 B. 
     That is, the endoscope system  1 B of the present embodiment and the endoscope system  1  of the first embodiment only differ in the place where calibration is performed, but are basically the same in the system configuration and calibration method. 
     Even in the case of a side-viewing endoscope or oblique-viewing endoscope having a structure in which the probe  21  projects in the diagonal direction as in the case of the endoscope  11 B, the endoscope system  1 B of the present embodiment can obtain effects similar to those of the endoscope system  1 B of the first embodiment. 
     Third Embodiment 
     Hereinafter, an endoscope system  1 C which is a medical equipment system according to a third embodiment of the present invention will be described with reference to the accompanying drawings. The endoscope system  1 C of the present embodiment is similar to the endoscope system  1  of the first embodiment, and therefore the same components will be assigned the same reference numerals and descriptions thereof will be omitted. 
       FIG. 13  is a display screen illustrating an example of image processing of the monitor  18  for illustrating the endoscope system of the third embodiment and  FIG. 14  is a flowchart illustrating a processing flow of the endoscope system of the third embodiment. 
     In the endoscope system  1 C, as shown in  FIG. 13 , the direction calculation section  31 B in the navigation unit  31  projects from the projection port  14 B and calculates the longitudinal direction of the distal end portion  22  through image processing based on an image of the probe  21  in the endoscope image  18 A picked up by the CCD  19 .  FIG. 13  shows an example where the probe  21  is bent by gravity. 
     A direction calculation section  31 BA which is different from the direction calculation section  31 B of the first embodiment calculates the longitudinal direction of the distal end portion  22  of the probe  21  with respect to the direction of the second sensor  41  based on the shape of the probe  21  in the endoscope image  18 A first. 
     There are several methods thereof and two of those methods will be described. A first method will be described below first. According to the first method, the endoscope image  18 A is preliminarily photographed with the probe  21  projected in various projection directions and projection lengths, the direction of the distal end  22 A of the probe  21  with respect to the direction of the second sensor  41  at that time is physically measured and a database is created according to the following procedure. The portion corresponding to the probe  21  and the other portion in each endoscope image  18 A are identified, binarized and a binarized reference endoscope image is thereby created. At the time of photographing an endoscope image, the binarized reference endoscope image and the measured distal end direction of the probe  21  are associated with each other and saved, and a database is thereby created. 
     During use, an outer edge shape of the probe  21  is extracted from the current endoscope image  18 A. The positions and shapes of the probe  21  are compared using the outer edge shape of the probe  21  extracted from the endoscope image  18 A, a plurality of binarized reference endoscope images saved in the database and the endoscope image, a binarized reference endoscope image that best matches the position and shape of the probe  21  of the current endoscope image  18 A is selected. The longitudinal direction of the distal end portion  22  associated with the selected binarized reference ultrasound image is assumed to be the longitudinal direction of the distal end portion  22  corresponding to the direction of the current second sensor  41 . 
     Next, the second method will be described. In the second method, the outer edge shape of the probe  21  is extracted from the current endoscope image  18 A during use. As shown in  FIG. 13 , a center line  52  is calculated on a longitudinal axis of the outer edge shape of the distal end portion  22  of the extracted probe  21  and two reference points  50  and  51  are set on the center line  52 . Furthermore, reference line segments  53  and  54  which pass through reference points  50  and  51  and are orthogonal to the center line  52  are calculated. Here, a two-dimensional coordinate system is set assuming that the origin is the center position of the endoscope image  18 A, the rightward direction is +x direction and the upward direction is +y direction. In this coordinate system, suppose the upper side of the endoscope image is y=1, the lower side is y=−1, the right side is x=1 and the left side is x=−1. Coordinates (x, y) of the two reference points in the coordinate system are calculated respectively. 
     Furthermore, lengths of the reference line segments  53  and  54  are calculated and assumed to be the values of z. Next, since the value of the angle of view which is a design value of the endoscope and the value of the outer diameter of the distal end portion  22  which is a design value of the probe  21  are known, it is possible to judge an approximate apparent outer diameter of the probe  21  on the endoscope image  18 A in proportion to the distance between the probe  21  and the CCD  19 . In other words, when the probe  21  is far from the CCD  19 , its endoscope image  18 A appears small and when the probe  21  is in the vicinity, its endoscope image  18 A appears large. Thus, it is possible to calculate the distance between the CCD  19  in the three-dimensional space and the reference points  50  and  51  on the probe  21  from the values of z. On the other hand, it is possible to judge the direction of the (x, y) coordinates on the endoscope image  18 A with respect to the CCD  19  in the three-dimensional space from the value of the angle of view which is a design value of the endoscope. To be exact, the (x, y) coordinate points on the endoscope image correspond to points on radial straight lines centered on the position of the CCD  19  in the three-dimensional space. From this, it is possible to calculate the directions of the reference points  50  and  51  on the probe  21  from the CCD  19  in the three-dimensional space from the (x, y) values. The positions of the reference points  50  and  51  of the probe  21  with respect to the CCD can be calculated from the distances between the CCD  19  and the reference points  50  and  51  on the probe  21  calculated from z described above, the directions of the reference points  50  and  51  on the probe  21  from the CCD  19  in the three-dimensional space calculated from (x, y). 
     Furthermore, the three-dimensional positional relationship between the CCD  19  and the second sensor  41  is known. For this reason, it is possible to convert the positions of the reference points  50  and  51  of the probe  21  with respect to the CCD  19  to positions of the reference points  50  and  51  of the probe  21  with respect to the second sensor  41  when assuming the position of the second sensor  41  is the origin and the directions of the second sensor  41  are x-, y- and z-axes. The direction of the vector connecting the two reference points on the probe  21  is the longitudinal direction of the distal end portion  22 , and the longitudinal direction of the distal end portion  22  with respect to the direction of the second sensor  41  can be calculated. 
     Next, the direction calculation section  31 B converts the longitudinal direction of the distal end portion  22  with respect to the direction of the second sensor  41  to the longitudinal direction of the distal end portion  22  with respect to the direction of the first sensor  40 . That is, the direction calculation section  31 B performs coordinate transformation from the detection value of the first sensor  40  and the detection value of the second sensor  41  using the relationship between the position and direction of the first sensor  40  and the position and direction of the second sensor  41 . 
     Next, a processing flow of the endoscope system  1 C of the present embodiment will be described according to the flowchart in  FIG. 14 . 
     &lt;Steps S 20  and S 21 &gt; 
     These are the same as steps S 10  and S 11  in the description of the endoscope system  1  according to the first embodiment. 
     &lt;Step S 22 &gt; Projection Step 
     The operator causes the probe  21  to project from the projection port  14 B up to a sufficiently recognizable position in the endoscope image  18 A as shown in  FIG. 13 . 
     &lt;Step S 23 &gt; Distal End Portion Direction Calculation Step 
     The navigation unit  31  performs image analysis of the state of the probe  21  in the endoscope image  18 A using the aforementioned method and thereby calculates the longitudinal direction VV of the distal end portion  22  of the probe  21  with respect to the second sensor  41 . In this case, VV is calculated using the direction of the second sensor  41  as shown in (Equation 9) as a reference. 
     The navigation unit  31  acquires direction data of the second sensor  41  simultaneously with the distal end portion direction calculation step. Of the direction data of the second sensor in this case, the longitudinal direction data of the distal end portion  22  (rigid portion  13 ) is assumed as a vector V 6  and the direction data on the endoscope image  18 A is assumed as a vector W 6 . 
         VV=a   4   V 6 +b   4   W 6 +c   4   X 6  (Equation 9)
 
       where 
         X 6 =V 6 ×W 6 (vector product)  (Equation 10)
 
     &lt;Step S 24 &gt; Correction Coefficient Calculation Step 
     The navigation unit  31  acquires magnetic field detection direction data of the first sensor  40  simultaneously with the distal end portion direction calculation step. Suppose magnetic field detection direction data of the coil  40 A of the first sensor  40  is a vector V 5  and the magnetic field detection direction data of the coil  40 B is a vector W 5  in this case. 
     VV is expressed as a function of V 5 , W 5  and X 5  as (Equation 11) below. Relative position coefficients a 5 , b 5  and c 5  can be calculated from VV calculated according to (Equation 9) and the detected values of V 5 , W 5  and X 5 . 
         VV=a   5   V 5 +b   5   W 5 +c   5   X 5  (Equation 11)
 
     &lt;Step S 25 &gt; Detection Direction Correction Step 
     The detection direction correction step of the endo scope system  1 C is the same as the detection direction correction step S 16  of the endoscope system  1  of the first embodiment. 
     The endo scope system  1 C of the present embodiment has the effects of the endoscope system  1  of the first embodiment and can further detect the longitudinal direction of the distal end portion  22  of the probe accurately even when the probe  21  is bent due to influences of gravity or the like. 
     Fourth Embodiment 
     Hereinafter, an endoscope system  1 D according to a fourth embodiment will be described with reference to the accompanying drawings. The endoscope system  1 D of the present embodiment is similar to the endoscope system  1  of the first embodiment, and therefore the same components will be assigned the same reference numerals and descriptions thereof will be omitted. 
       FIG. 15  and  FIG. 16  are schematic cross-sectional views of the endoscope illustrating the endoscope system of the present embodiment and  FIG. 17  is a configuration diagram illustrating a configuration of a navigation unit of the endoscope system of the present embodiment. 
     In navigation, it is important to accurately detect the longitudinal direction of the distal end portion  22  of the medical instrument of a small diameter to be made to project from the insertion portion of the endoscope as in the case of the endoscope system  1  of the first embodiment, and at the same time, it is also important to accurately detect a reference azimuth which is a predetermined azimuth within a plane (radial direction) perpendicular to the longitudinal direction. When, for example, the medical instrument is an ultrasound probe which radially scans a plane perpendicular to the longitudinal axis of the probe, detecting the vertical and horizontal directions within the scanning plane of the ultrasound transducer is important in judging the position of a lesioned region. Furthermore, when the medical instrument is forceps, it is important and necessary that the opening/closing direction of the forceps match the direction of the lesioned region. 
     Therefore, when, for example, a sensor made up of two coils, directions of coil axes of which are orthogonal to each other, is disposed at the distal end portion  22  of the ultrasound probe  21 , it is ideal to ensure that the magnetic field detection direction of one coil be parallel to the longitudinal direction of the distal end portion  22  of the ultrasound probe  21  and the magnetic field detection direction of the other coil be parallel to the reference azimuth (e.g., upward direction of the ultrasound image). 
     However, as has already been described, it is not easy to dispose on the distal end portion  22  of the probe  21  of an extremely small diameter, a two-axis magnetic field sensor of a still smaller diameter so that one detection axis thereof is parallel to the longitudinal direction of the distal end portion  22  and the other detection axis is parallel to the upward direction of the ultrasound image. Thus, as shown in  FIG. 4 , the coil axis direction which is the magnetic field detection direction of the coil  40 B may not be completely parallel to the reference azimuth. The operator cannot accurately grasp the vertical and horizontal directions of the ultrasound image. 
     For this reason, the endoscope system  1 D detects variations in the position and direction of the sensor  40  due to a rotation operation of the probe  21  and the direction calculation section  31 B calculates the exact longitudinal direction of the distal end portion  22 . On the other hand, variations in the position and direction of the sensor  40  due to a bending operation of the bending portion  12 A of the probe  21  (see  FIG. 15 ) are detected and the reference azimuth calculation section  31 D (see  FIG. 16 ) which is reference azimuth calculation means calculates a precise reference azimuth. That is, the endoscope system  1 D calculates a distal end direction correction value for correcting the direction of the sensor  40  to the distal end longitudinal direction of the probe  21  through calibration by the rotation operation of the probe  21  and calculates a reference azimuth correction value for correcting the direction of the sensor  40  to a reference azimuth through calibration by a bending operation. 
     As shown in  FIG. 15 , the endoscope  11 D of the endoscope system  1 D of the present embodiment includes a bending portion  12 A disposed between the flexible portion  15  and the rigid portion  13  of the insertion portion  12 . Furthermore, image pickup means such as a CCD  13 B is disposed in the rigid portion  13  and the operator can recognize an endoscope image picked up by the CCD  13 B and displayed on the monitor  18 . The bending portion  12 A is connected to a bending knob  12 C of an operation portion  12 B via a bending wire (not shown). As shown in  FIG. 16 , when the operator rotates the bending knob  12 C, the bending portion  12 A performs bending operation and the distal end  13 A of the insertion portion  12  performs rotational motion. 
     As shown in  FIG. 17 , in the endoscope system  1 D of the present embodiment, the navigation unit  31 Z includes a reference azimuth calculation section  31 D that calculates a reference azimuth of an ultrasound image picked up by the ultrasound transducer  23  based on the positions before and after movement of the first sensor  40  by the rotation operation of the probe  21  and the bending operation of the bending portion  12 A. 
     Next, sections in the navigation unit  31 Z of the endoscope system  1 D of the present embodiment will be described. Since the position calculation section  31 A is the same as that of the first embodiment, the direction calculation section  31 B will be described first. 
       FIG. 18A  to  FIG. 18C  are diagrams for illustrating a coordinate system in a rotation operation of the probe  21  of the endoscope system  1 D of the present embodiment. Suppose a position of the first sensor  40  in a state (time t 0 ) before the rotation operation of the probe  21  is H(t 0 ) and an orthonormal basis in the direction of the first sensor  40  is (U(t 0 )V(t 0 )W(t 0 )) as shown in  FIG. 18A , a position of the first sensor  40  in a state (time t 1 ) after the rotation operation of the probe  21  is H(t 1 ) and an orthonormal basis in the direction of the first sensor  40  is (U(t 1 )V(t 1 )W(t 1 )) as shown in  FIG. 18B , and an orthonormal basis provided in the center of the transmission antenna  33  is (ijk) as shown in  FIG. 18C . 
     First, the operator twists the probe  21  in the channel  14  in such a way that the bending portion  12 A as shown in  FIG. 15  is not bent, that is, is straight, in other words, rotates the probe  21  around the center direction of its longitudinal axis. The direction of the axis of rotation of the probe  21  is a distal end direction Q of the probe  21 . Since the rotation operation is an operation for calculating the axis of rotation from a state variation before and after the rotation, the rotation operation may be a half turn or so. 
     (U(t 0 ), V(t 0 ), W(t 0 )) and (U(t 1 ), V(t 1 ), W(t 1 )) can be expressed using matrices S(t 0 ) and S(t 1 ) of three rows and three columns respectively as follows. The respective components of S(t 0 ) and S(t 1 ) are successively outputted from the sensor unit  32 . 
       [ i ( t   0 ) j ( t   0 ) k ( t   0 )]=[ U ( t   0 ) V ( t   0 ) W ( t   0 )] S ( t   0 )  (Equation 12)
 
       [ i ( t   1 ) j ( t   1 ) k ( t   1 )]=[ U ( t   1 ) V ( t   1 ) W ( t   1 )] S ( t   1 )  (Equation 13)
 
     Here, S(t 0 ) and S(t 1 ) can be expressed as (Equation 14) and (Equation 15) below using row vectors s 1 , s 2  and s 3  of three elements shown below. 
     where, 
     
       
         
           
             
               
                 
                   
                     
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     On the other hand, assuming the respective azimuth components corresponding to (ijk) of U(t 0 ), V(t 0 ), W(t 0 ), U(t 1 ), V(t 1 ) and W(t 1 ) are column vectors u(t 0 ), v(t 0 ), w(t 0 ), u(t 1 ), v(t 1 ) and w(t 1 ) of three elements, the following (Equation 18) and (Equation 19) hold. 
       [ U ( t   0 ) V ( t   0 ) W ( t   0 )]=[ i ( t   0 ) j ( t   0 ) k ( t   0 )][ u ( t   0 ) v ( t   0 ) w ( t   0 )]  (Equation 18)
 
       [ U ( t   1 ) V ( t   1 ) W ( t   1 )]=[ i ( t   1 ) j ( t   1 ) k ( t   1 )][ u ( t   1 ) v ( t   1 ) w ( t   1 )]  (Equation 19)
 
     Since [i, j, k] are orthonormal bases, the following (Equation 20) is obtained from (Equation 16) and (Equation 18). 
         u ( t   0 )= T   s   1 ( t   0 ),  v ( t   0 )= T   s   2 ( t   0 ),  w ( t   0 )= T   s   3 ( t   0 )  (Equation 20)
 
     Likewise, the following (Equation 21) is obtained from (Equation 17) and (Equation 19). 
         u ( t   1 )= T   s   1 ( t   1 ),  v ( t   1 )= T   s   2 ( t   1 ),  w ( t   1 )= T   s   3 ( t   1 )  (Equation 21)
 
     The distal end direction Q is invariable before and after the rotation, that is, independent of time. Therefore, the following (Equation 22), (Equation 23) and (Equation 24) hold. 
         U ( t   0 )· Q=U ( t   1 )· Q   (Equation 22)
 
         V ( t   0 )· Q=V ( t   1 )· Q   (Equation 23)
 
         W ( t   0 )· Q=W ( t   1 )· Q   (Equation 24)
 
     Here, assuming the matrix whose elements are the respective direction components corresponding to [ijk] of Q is q, the following (Equation 25), (Equation 26) and (Equation 27) hold. 
       0 =U ( t   0 )· Q−U ( t   1 )· Q =( U ( t   0 )− U ( t   1 ))· Q=   T ( u ( t   0 )− u ( t   1 )) q=   T ( T   s   1 ( t   0 )− T   s   1 ( t   1 )) q =( s   1 ( t   0 )− s   1 ( t   1 )) q   (Equation 25)
 
       0 =V ( t   0 )· Q−V ( t   1 )· Q =( V ( t   0 )− V ( t   1 ))· Q=   T ( v ( t   0 )− v ( t   1 )) q=   T ( T   s   2 ( t   0 )− T   s   2 ( t   1 )) q =( s   2 ( t   0 )− s   2 ( t   1 )) q   (Equation 26)
 
       0 =W ( t   0 )· Q−W ( t   1 )· Q =( W ( t   0 )− W ( t   1 ))· Q=   T ( w ( t   0 )− w ( t   1 )) q=   T ( T   s   3 ( t   0 )− T   s   3 ( t   1 )) q =( s   3 ( t   0 )− s   3 ( t   1 )) q   (Equation 27)
 
       where, 
     
       
         
           
             
               
                 
                   
                     
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                     28 
                   
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     That is, 
       ( S ( t   0 )− S ( t   1 )) q= 0  (Equation 29)
 
     Q is the axis of rotation and since the position H of the sensor  40  moves within a plane perpendicular to the axis of rotation during rotation, the following (Equation 30) holds. 
         Q ·( H ( t   0 )− H ( t   1 ))=0  (Equation 30)
 
     That is, assuming matrices whose elements are the respective direction components corresponding to {ijk} of H(t 0 ) and H(t 1 ) are h(t 0 ) and h(t 1 ), the following (Equation 31) holds. The respective components of H(t 0 ) and H(t 1 ) are outputted from the sensor unit  32 . 
         T ( h ( t   1 )− h ( t   0 )) q= 0  (Equation 31)
 
     Furthermore, since the Q is a basic vector, the following (Equation 32) holds. 
       |q|=1  (Equation 32)
 
     Therefore, the q is calculated from (Equation 29), (Equation 31) and (Equation 32). 
     When the calculated Q is expressed as a function of U(t 1 ), V(t 1 ) and W(t 1 ), the Q is expressed by the following (Equation 33) and relative position coefficients a 6 , b 6  and c 6  are calculated. 
         Q=a   6   U ( t   1 )+ b   6   V ( t   1 )+ c   6   W ( t   1 )  (Equation 33)
 
     Next, the operation of the direction correction section  31 C will be described. The operation of the direction correction section  31 C is basically the same as the operation of the first embodiment, that is, corrects the direction of the first sensor  40  and successively calculates the longitudinal direction of the distal end portion  22 . To be more specific, the direction correction section  31 C operates as follows. 
     Assuming the direction of the first sensor  40  at an arbitrary time t is U(t), V(t) and W(t), the navigation unit  31  can calculate the distal end direction Q(t) of the probe from the following (Equation 34). 
         Q ( t )= a   6   U ( t )+ b   6   V ( t )+ c   6   W ( t )  (Equation 34)
 
     The Q(t) calculated here is transmitted to the navigation section  31 E. 
     Furthermore, the operation of the reference azimuth calculation section  31 D will be described. 
     The operator bends the bending portion  12 A in an upward direction of the ultrasound image using the bending knob  12 C as shown in  FIG. 16 . Suppose the axis of rotation of the bending operation in this case is P. Moreover, suppose time before the bending operation is t 2  and time after the bending operation is t 3 . Using a method similar to the above described method of calculating the Q, the direction P of the bending axis of rotation when performing a bending operation is calculated. 
     When the calculated P is expressed as a function of U(t 3 ), V(t 3 ) and W(t 3 ), the P is expressed as (Equation 35) below, and the reference azimuth calculation section  31 D can calculate relative position functions a 7 , b 7  and c 7  according to (Equation 35). 
         P=a   7   U ( t   3 )+ b   7   V ( t   3 )+ c   7   W ( t   3 )  (Equation 35)
 
     Furthermore, the reference azimuth calculation section  31 D which is reference azimuth calculation means calculates the reference azimuth V 12 (t 3 ) according to the following (Equation 36). 
         V   12 ( t   3 )= P×Q ( t   3 )=( b   7   c   6   −c   7   b   6 ) U ( t   3 )+( c   7   a   6   −a   7   c   6 ) V ( t   3 )+( b   7   c   6   −c   7   b   6 ) W ( t   3 )  (Equation 36)
 
     Next, the operation of the reference azimuth correction section  31 F which is the reference azimuth correction means will be described. The reference azimuth correction section  31 F corrects the direction of the first sensor  40  and successively calculates the reference azimuth. To be more specific, the reference azimuth correction section  31 F operates as follows. 
     When the direction of the first sensor  40  at an arbitrary time t is assumed to be U(t), V(t) and W(t), the navigation unit  31  calculates the reference azimuth V 12 (t) of the probe according to the following (Equation 37). 
         V   12 ( t )=( b   7   c   6   −c   7   b   6 ) U ( t )+( c   7   a   6   −a   7   c   6 ) V ( t )+( b   7   c   6   −c   7   b   6 ) W ( t )  (Equation 37)
 
     The Q(t) calculated here is transmitted to the navigation section  31 E. 
     Finally, the operation of the navigation section will be described. The navigation section performs navigation based on the Q(t) calculated by the direction correction section and the V 12 (t) calculated by the reference azimuth correction section  31 F. 
     As described above, the endoscope system  1 D corrects the direction of the first sensor  40  to the distal end direction of the probe  21  through calibration by a rotation operation of the probe  21  and corrects the direction of the first sensor  40  to the reference azimuth through calibration by a bending operation. Thus, the operator can accurately grasp the vertical and horizontal directions of an ultrasound image and perform inspection or treatment with high accuracy. 
     When the direction of the first sensor  40  and the upward direction of the ultrasound image are matched through calibration by the bending operation, if the probe is provided with a bending mechanism, the operator may perform a bending operation of the probe. 
     An ultrasound probe has been described above as an example of medical instrument of the medical equipment system and an upward direction of the endoscope image has been described above as a reference method, but in the case where the medical instrument is forceps, the opening/closing direction of the forceps is set as the reference azimuth. Furthermore, in the case where the medical instrument is a single-edged knife, the direction of the edge is set as the reference azimuth. Furthermore, when the medical instrument is a small endoscope inserted into the channel of the endoscope, the upward direction of an endoscope image of the small endoscope is set as the reference azimuth. 
     The distal end direction Q is calculated above from (Equation 29), (Equation 31) and (Equation 32), but when the value of H in (Equation 30) has substantially no difference between times t 0  and t 1 , the error of the distal end direction Q increases. For this reason, when the distance between H(t 0 ) and H(t 1 ) is equal to or below a predetermined value, the medical equipment system preferably displays a message on the screen of the monitor  18  and instruct the operator to further rotate the probe  21 . 
     The calculation in this case is as follows. Assuming the time after a second rotation is t 4 , the following (Equation 38) holds in the same way as (Equation 29). 
       ( S ( t   0 )− S ( t   4 )) q= 0  (Equation 38)
 
     The distal end direction Q of the distal end portion  22  is calculated from (Equation 29), (Equation 32) and (Equation 38). In this way, the error becomes smaller. 
     Furthermore, as in the cases of the first to third embodiments, the second sensor may be provided at the endoscope distal end and the position and direction information of the probe may be corrected based on information of the second sensor. 
     The present invention is not limited to the aforementioned embodiments, but various changes, modifications or the like can be made without departing from the spirit and scope of the present invention. 
     For example, the detection means for detecting the position and direction may not necessarily be a magnetic sensor. For example, a gyro sensor may be disposed at the distal end portion to detect the position and direction, a light-emitting marker such as LED may be disposed at the operation portion of a rigid endoscope, the light-receiving apparatus may detect the position and direction of the operation portion of the endoscope, convert the position to the position of the endoscope distal end portion or a fiber grating (FBG) sensor may be disposed at the insertion portion of the endoscope to detect the position and direction of the distal end portion. 
     Furthermore, although the flexible endoscope having the flexible portion  15  and the rigid portion  13  disposed on the distal end side of the flexible portion  15  has been described above as an example of the insertion means of the medical equipment system, the present invention is not limited to this but the insertion means may be a rigid endoscope, trocar or the like as long as the insertion means has a channel. 
     That is, the probe is moved in the channel of the endoscope above to correct the probe direction, but in an endoscope operation, the endoscope or treatment instrument may be moved in the trocar to correct the direction of the endoscope or treatment instrument. 
     As described above, the endoscope system  1 D is as follows. 
     (1) A medical equipment system including: 
     insertion means including a flexible portion, a bending portion, a rigid portion and a channel that passes through the flexible portion, the bending portion and the rigid portion; 
     a medical instrument that is inserted from an insertion port on a proximal end portion side of the channel, projects from a projection port of the rigid portion and includes a sensor for detecting a position and direction at a distal end portion; 
     position calculation means for calculating the position and direction of the distal end portion from information of the sensor; and 
     reference azimuth calculation means for calculating, when the medical instrument rotates in the channel, a reference azimuth of the distal end portion based on the position and direction of the distal end portion before and after movement when the bending portion is bent. 
     (2) The medical equipment system described in (1) above, wherein the insertion means is an insertion portion of an endoscope, and 
     the reference azimuth is an azimuth of an image picked up by the endoscope. 
     (3) The medical equipment system described in (1) above, wherein the medical instrument is an ultrasound probe, and 
     the reference azimuth is an azimuth of an ultrasound image picked up by the ultrasound probe.