Patent Publication Number: US-8977020-B2

Title: Image processing device and image processing method

Description:
TECHNICAL FIELD 
     The present invention relates to an image processing device and an image processing method of generating a three-dimensional image from a plurality of tomographic images. 
     BACKGROUND ART 
     Conventionally, a method of generating a three-dimensional image of an object using a group of a series of tomographic images scanned by, for example, an X-ray CT (computed tomography) apparatus, an MRI (magnetic resonance imaging) apparatus, or an ultrasonic diagnostic apparatus is known. For example, PTL 1 discloses an image display device that generates and displays an inside-out image, which is obtained when the inside surface of an organ is turned over to the outer surface, by extracting the contour of a hollow organ from a medical image constructed by scanning the hollow organ, setting a radial line from the radiation center set inside the hollow organ towards the contour of the lumen, and copying a pixel value of a point inside the hollow organ onto the radial line outside a contour point. 
     In addition, PTL 2 discloses a three-dimensional image construction method capable of checking the irregularities inside an object from the outside by generating a two-dimensional image by a perspective transformation of a volume image, which is formed by stacking tomographic images of the object, to a coordinate system on an arbitrary perspective plane, calculating a distance between a position of a virtual linear light source set inside the object and an inside contour point of the object, and reflecting the distance in the shading of the two-dimensional image. In addition, PTL 3 discloses a medical image processing device that displays an image, which has a central portion in which a virtual endoscopic image equivalent to an image observed with an endoscope is displayed and a peripheral portion in which the inside of a hollow organ is spread, for example, by setting a viewpoint inside the hollow organ and setting the projection directions in different directions in the central portion and the peripheral portion of a projection plane. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] JP-A-2010-17490 
     [PTL 2] JP-A-9-237352 
     [PTL 3] JP-A-2009-22411 
     SUMMARY OF INVENTION 
     Technical Problem 
     As described above, there are various techniques of generating an image showing the inside of an object outside. 
     However, in order to make the irregularities of the inner surface or portions hidden in plicae observable more easily, it is preferable to be able to change the shape of the surface of an organ even on the image as if the surface is spread by pressing from the back side of the organ using fingers. In addition, when deforming a portion to be observed, the portion may become an image far from the original shape or position. Since this interferes with understanding rather, it is preferable to display the original shape or position so as to be able to be understood intuitively. 
     The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide an image processing device and an image processing method capable of generating and displaying a folded image, in which a part of the inner surface of a hollow organ is exposed outside, by changing the shape of the hollow organ to a shape in which sleeves of clothes are folded. 
     Solution to Problem 
     In order to achieve the object described above, the present invention is an image processing device characterized in that it includes: a coordinate transformation unit that performs coordinate transformation so as to fold each point inside a hollow organ, which is extracted from a volume image formed by stacking a plurality of tomographic images, along a predetermined convex surface set outside the hollow organ and gives a pixel value of an original position to a corresponding point after the coordinate transformation; and a generation unit that generates a folded volume image using image information after the coordinate transformation by the coordinate transformation unit. 
     In addition, the present invention is an image processing method characterized in that it includes a coordinate transformation step of performing a coordinate transformation so as to fold each point inside a hollow organ, which is extracted from a volume image formed by stacking a plurality of tomographic images, along a predetermined convex surface set outside the hollow organ and giving a pixel value of an original position to a corresponding point after the coordinate transformation; and a generation step of generating a folded volume image using image information after the coordinate transformation in the coordinate transformation step. 
     Advantageous Effects of Invention 
     By the image processing device and the image processing method of the present invention, it is possible to generate and display a folded image, in which a part of the inner surface of a hollow organ is exposed outside, by changing the shape of the hollow organ to a shape in which sleeves of clothes are folded. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing the overall configuration of an image processing device  100 . 
         FIG. 2  is a flow chart illustrating the flow of a folded image generation process executed by the image processing device  100  related to the present invention. 
         FIG. 3  is a view illustrating an example of dividing a hollow organ  50  in a volume image  40  using a plane  20 . 
         FIG. 4  is a view showing the matching of the coordinates when folding the hollow organ  50  along the convex surface (a circle  30 ) (when performing coordinate transformation). 
         FIG. 5  is an example of a folded image  80  of the hollow organ  50  on the plane  20 . 
         FIG. 6  is an example of a folded three-dimensional image  90  which is displayed in a three-dimensional manner like an endoscopic image. 
         FIG. 7  is a display example in which a scale is added to the folded three-dimensional image  90 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail on the basis of the drawings. 
     First, the configuration of an image processing system  1  to which an image processing device  100  of the present invention is applied will be described with reference to  FIG. 1 . 
     As shown in  FIG. 1 , the image processing system  1  includes: the image processing device  100  having a display device  107  and an input device  109 ; an image database  111  connected to the image processing device  100  through a network  110 ; and a medical image scanning apparatus  112 . 
     The image processing device  100  is a computer which performs processing, such as image generation and image analysis. For example, a medical image processing device installed in a hospital and the like is included. 
     As shown in  FIG. 1 , the image processing device  100  includes a CPU (Central Processing Unit)  101 , a main memory  102 , a storage device  103 , a communication interface (communication I/F)  104 , a display memory  105 , and an interface (I/F)  106  with an external device such as a mouse  109 , and the respective units are connected to each other through a bus  113 . 
     The CPU  101  loads a program stored in the main memory  102  or the storage device  103  to a work memory region on a RAM of the main memory  102  and executes the program and performs driving control of the respective units connected to each other through the bus  113 , thereby realizing various kinds of processing performed by the image processing device  100 . 
     In addition, the CPU  101  executes a folded image generation process (refer to  FIG. 2 ), which will be described later, to generate a folded three-dimensional image  90  and displays it on the display device  107 . The folded three-dimensional image  90  and the folded image generation process will be described later. 
     The main memory  102  is configured to include a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The ROM permanently holds a boot program of a computer, a program such as BIOS, data, and the like. In addition, the RAM temporarily holds a program, data, and the like loaded from the ROM, the storage device  103 , and the like, and has a work area used when the CPU  101  performs various kinds of processing. 
     The storage device  103  is a storage device which performs reading/writing of data from/into a HOD (hard disk drive) or other recording media. Programs executed by the CPU  101 , data required to execute the programs, an OS (operating system), and the like are stored in the storage device  103 . As programs, a control program equivalent to an OS and application programs are stored. Each of program codes thereof is read by the CPU  101  when necessary and moved to the RAM of the main memory  102 , thereby being executed as various kinds of means. 
     The communication I/F  104  has a communication control device, a communication port, and the like, and mediates communication between the image processing device  100  and the network  110 . In addition, the communication I/F  104  performs communication control with the image database  111 , other computers, or the medical image scanning apparatus  112 , such as an X-ray CT apparatus or an MRI apparatus, through the network  110 . 
     The I/F  106  is a port for connection with a peripheral device and performs transmission and reception of data to and from the peripheral device. For example, a pointing device, such as the mouse  108  or a stylus pen, maybe connected through the I/F  106 . 
     The display memory  105  is a buffer which temporarily accumulates display data input from the CPU  101 . The accumulated display data is output to the display device  107  at a predetermined timing. 
     The display device  107  is formed by a display device such as a liquid crystal panel or a CRT monitor, and a logic circuit which cooperates with the display device to execute display processing, and is connected to the CPU  101  through the display memory  105 . The display device  107  displays the display data accumulated in the display memory  105  under control of the CPU  101 . 
     The input device  109  is an input device such as a keyboard, and outputs to the CPU  101  various kinds of instructions or information input by an operator. The operator operates the image processing device  100  interactively using the display device  107 , the input device  109 , and an external device such as the mouse  108 . 
     The network  110  includes various communication networks, such as a LAN (Local Area Network), a WAN (Wide Area Network), an intranet, and the Internet, and mediates communication connection between the image database  111 , a server, or other information devices and the image processing device  100 . 
     The image database  111  accumulates and stores image data obtained by the medical image scanning apparatus  112 . Although the image processing system  1  shown in  FIG. 1  has a configuration in which the image database  111  is connected to the image processing device  100  through the network  110 , the image database  111  may be provided, for example, in the storage device  103  of the image processing device  100 . 
     Next, the operation of the image processing device  100  will be described with reference to  FIGS. 2 to 6 . The CPU  101  of the image processing device  100  reads from the main memory  102  a program and data regarding the folded image generation process shown in  FIG. 2  and executes the process on the basis of the program and data. 
     In addition, it is assumed that data of a volume image  40  to be calculated is acquired from the image database  111  or the like through the network  110  and the communication I/F  104  and stored in the storage device  103  of the image processing device  100  at the start of execution of the following processing. The volume image  40  is image data formed by stacking a plurality of tomographic images  41 ,  42 ,  43 , . . . , as shown in  FIG. 3 . Each pixel (voxel) of the volume image  40  has a pixel value. 
     In the folded image generation process shown in  FIG. 2 , the CPU  101  of the image processing device  100  first reads the volume image  40 , which is formed by stacking the series of tomographic images  41 ,  42 , . . . obtained by scanning a target region, as input image data. The volume image  40  read herein is a group of a series of tomographic images of a region including a hollow organ  50  such as the colon. As appropriate examples of the input image data, an ultrasonic image, a CT image, or an MR image may be described. In addition, the target region is not limited to the colon, and may be other hollow organs, for example, blood vessels or bronchi. 
     First, the CPU  101  sets an arbitrary viewpoint  21  inside the hollow organ  50  extracted from the volume image  40  and divides the hollow organ  50  by a plurality of planes including an arbitrary eye vector  23  set inside the hollow organ  50  or a plurality of planes along the centerline of the hollow organ  50  (step S 1 ). In the following explanation, the plane which divides the hollow organ  50  is called a plane  20 . 
     In the case of generating a virtual endoscopic image finally as in the present embodiment, the above-described view point  21  is preferably a view point of the virtual endoscopic image. The eye vector  23  is set from the view point  21  toward an arbitrary direction in the depth direction of the hollow organ  50 . 
     The centerline of the hollow organ  50  is a line formed by connecting the coordinates of the center of gravity of each cross section of the hollow organ  50  along the hollow organ  50 . The coordinates of the center of gravity can be calculated using the coordinates of a wall (boundary between an organ region and other regions) of the hollow organ. 
       FIG. 3  is a view showing an example of division by the plane  20  including the eye vector  23  of the hollow organ  50 . 
     As shown in  FIG. 3 , the arbitrary view point  21  is set inside the hollow organ  50  in the volume image  40 , and the eye vector  23  is set in the depth direction of the hollow organ  50 . The hollow organ  50  is divided by the plurality of planes  20  including the eye vector  23 . The hollow organ  50  is divided radially by the plurality of planes  20  with the view point  21  as the center. 
     As shown in  FIG. 4 , each plane  20  which divides the hollow organ  50  has image information of the wall, inside region, and outside region of the hollow organ  50 . 
     In addition,  FIG. 4  is an example where the X axis of the plane  20  and the eye vector  23  match each other. When the plane  20  is a region shown by a dotted line in  FIG. 3 , a lower part of the X axis in  FIG. 4  is not included in the plane  20 . 
     However, the lower part of the X axis in  FIG. 4  is included in other planes which divide the hollow organ  50 . In addition, as shown in  FIG. 4 , the hollow organ  50  may be divided so that upper and lower parts of the X axis are included in the same plane. 
     Then, the CPU  101  transforms the coordinates of each point inside the hollow organ  50  using each divided plane  20  so that the point is folded outside (step S 2 ). That is, the CPU  101  calculates a corresponding point when folding each point inside the hollow organ  50  along a predetermined convex surface, which is set outside the hollow organ  50 , on each divided plane  20  and gives a pixel value of the original position to the calculated corresponding point. 
     Referring to  FIG. 4 , coordinate transformation processing of step S 2  will be described. 
     As shown in  FIG. 4 , on the plane  20  including the eye vector  23 , a direction of the eye vector  23  is an X direction and a direction perpendicular to the eye vector  23  is a Y direction. In addition, the predetermined convex surface is set outside the hollow organ  50 . In the example shown in FIG.  4 , a circle  30  with a radius r0 is set as the convex surface, and the circle  30  is set so as to be adjacent to the outer surface of the hollow organ  50 . 
     The CPU  101  transforms the coordinates of each point P(X1, Y1) inside the hollow organ  50  along the convex surface (circle  30 ). 
     For example, when folding the point P(X1, Y1), which is located inside the hollow organ  50  by a distance r from a point P′(X1, Y1′) on the surface of the hollow organ  50 , along the circle  30 , the point P(X1, Y1) is moved by a distance L along the circumference of the circle  30 , and a point Q separated from the point by the distance r in the normal direction of the circle  30  is set as the corresponding point after the coordinate transformation. The above-described distance L is a distance between a contact point R of the circle  30  and the hollow organ  50  and the point P′. 
     The coordinates of the corresponding point Q(X, Y) of the point P(X1, Y1) inside the hollow organ  50  are calculated from the following Expressions.
 
 X 1= X 0− L=X 0−Ψ· r 0= X 0−(2π−θ−π/2)· r 0
 
 Y 1= Y 0− r 0− r  
 
 X=X 0+( r+r 0)·cos θ
 
 Y=Y 0+( r+r 0)·sin θ
 
     Here, (X0, Y0) is the coordinates of a center 0 of the circle  30 , θ is an angle between a straight line 0W extending in the positive direction of the X axis from the center 0 of the circle  30  and a straight line 0Q, r0 is the radius of the circle  30 , and r is the distance from the point P to the surface of the hollow organ  50 . 
     A pixel value of the original point P(X1, Y1) is assigned to a pixel value of the corresponding point Q(X, Y), and an image (a folded image  80 ) after the coordinate transformation is obtained. 
     As shown in  FIG. 5 , in a folded portion  82  of the folded image  80  formed on the plane  20 , the corresponding point Q is calculated more coarsely as a distance of a pixel from the circle  30  increases since the coordinates of each point P inside the hollow organ  50  are transformed along the convex surface (circle  30 ). For this reason, the CPU  101  calculates pixel values other than the corresponding point Q by interpolating the pixel value of the peripheral corresponding point Q. 
     In addition, when virtual endoscopic display of the folded hollow organ  50  is performed in step S 4  described later, a range of the coordinate transformations (range of the point P whose the corresponding point Q is calculated) maybe limited to the point P in a range from the distance between the points P′ and R in  FIG. 4  of L=0 (contact point between the hollow organ  50  and the circle  30 ) to L=π·r0 (half circumference of the circle  30 ). This is because a range farther than L=π·r0 is located on the rear side of the circle  30  and does not appear on the virtual endoscopic image at the time of the virtual endoscopic display in step S 4  described later. 
     In addition, when calculating the corresponding point Q of the point P in the range of L&gt;π·r0, the corresponding point Q may be calculated along the circle  30  for the range of up to L=π·r0 and a straight line UV parallel to the X axis for the range exceeding L=π·r0. 
     When the coordinate transformation is performed as in step S 2 , for example, the folded image  80  shown in  FIG. 5  is obtained. 
     As shown in  FIG. 5 , in the folded portion  82  in which the hollow organ  50  has been deformed into a shape in which sleeves of clothes are rolled up, the inside of the hollow organ  50  is exposed outward. Since the folded portion  82  is deformed into the shape along the convex surface (circle  30 ), plicae in the folded portion  82  are spread. Accordingly, a portion hidden behind the plicae can easily be observed. 
     Then, the CPU  101  performs reverse processing of step S 1 . That is, the respective planes  20  having image information of the folded image  80  are combined in the reverse procedure of step S 1 , thereby obtaining a folded volume image (step S 3 ). 
     The CPU  101  creates a folded three-dimensional image  90  from the folded volume image (step S 4 ). The folded three-dimensional image  90  created herein may be any of a shaded three-dimensional image, a stereoscopic image, and the like. 
     The shaded three-dimensional image is an image viewed in a three-dimensional manner by setting an arbitrary view point and an arbitrary eye vector and performing predetermined shading on each pixel of a two-dimensional image obtained by projecting the volume image to the projection plane. Any of a volume rendering method, a ray casting method, a surface method, a depth method, and the like may be used as a shading method. In addition, the projected image may be either a parallel projection image or a central projection image. When performing central projection by setting a view point inside the hollow organ  50  and setting an eye vector in the depth direction of the lumen, it is possible to obtain a virtual endoscopic image as when the hollow organ  50  is observed with an endoscope (refer to  FIG. 6 ). The stereoscopic image is intended to achieve a stereoscopic image in an observer&#39;s brain by generating binocular parallax intentionally. A stereoscopic image using a lenticular lens or a stereoscopic image using a parallax barrier is known (JP-A-2004-78086 and the like). 
       FIG. 6  is an example of the folded three-dimensional image  90  under the virtual endoscopic display. When the virtual endoscopic display of a folded volume image in which a part of the hollow organ  50  is folded is performed, a normal virtual endoscopic image is displayed in a central portion  92  of the image  90  and the folded portion  82  is displayed on a peripheral portion  94  of the image  90 , as shown in  FIG. 6 . Inside plicae of the hollow organ  50  are displayed in the central portion  92  of the image  90  without being folded, while the inside plice of the hollow organ  50  are displayed in the peripheral portion  94  so as to be exposed outward. 
     Thus, the hollow organ  50  is folded as if the sleeves of clothes are rolled up and as a result, the inside plicae are spread and displayed in a part of the image (in the case of the virtual endoscopic image, displayed in the peripheral portion  94  of the image). For this reason, the inside of the hollow organ  50  in the folded portion  82  can easily be observed. In addition, since the coordinate transformation of the folded portion  82  is performed along the convex surface (circle  30 ), the folded portion  82  is deformed as if the inner surface is pressed and spread by pressing from the back side (outside of the hollow organ  50 ) using fingers. As a result, a portion hidden behind the plicae expands and can easily be observed. In addition, since portions other than the folded portion  82  are displayed in the same manner as a normal three-dimensional image (in the case of the virtual endoscopic image, a central portion of the image becomes a normal endoscopic image), the portions can be observed with the same sense as in the image diagnosis that a doctor or the like usually performs. Accordingly, it becomes easy to intuitively grasp the original position or the original shape of an observed portion. 
     In addition, a display state of the folded three-dimensional image  90  may be changed according to a predetermined order or the operation of the operator. 
     For example, as shown in  FIG. 6 , a stop button  95 , a rotation button  96 , a move button  97 , a surface deformation button  98 , and an end button  99  which are operated by the user are provided, and the CPU  101  changes the display state of the folded three-dimensional image  90  in response to a clicking operation of each button. 
     Examples of the display state include not only a stop display mode specified instep S 4  but also a rotational display mode, a moving display mode, and a surface deformation mode. 
     In the rotational display mode, the direction of the eye vector  23  under the virtual endoscope display is changed. The direction of the eye vector  23  is changed according to a setting operation. The CPU  101  generates a folded three-dimensional image  90  by executing the above-described folded image generation process on the basis of the changed eye vector  23  and displays the folded three-dimensional image  90 . 
     In the moving display mode, the CPU  101  generates a plurality of the folded three-dimensional images  90  by calculating the corresponding point Q of the point P within a predetermined range (performing the coordinate transformation in step S 2 ) while moving the circle  30  (convex surface) sequentially along the hollow organ  50  and displays the plurality of folded three-dimensional images  90  sequentially like moving images. 
     Therefore, since the folded three-dimensional images  90  can be displayed sequentially while moving the folded position of the hollow organ  50  in the depth direction, it becomes easy to observe the entire hollow organ. 
     In the surface deformation mode, the CPU  101  generates the plurality of folded three-dimensional images  90  with different surface shapes at the folded positions by calculating the corresponding point Q by changing the shape of the convex surface used for folding (performing the coordinate transformation instep S 2 ) and displays the plurality of folded three-dimensional images  90  sequentially. For example, the folded three-dimensional image  90  is generated by changing a value of the radius of the circle  30 , or the folded three-dimensional image  90  along an arbitrary curve such as an ellipse, a parabola, or a hyperbola, a triangle, a rectangle, and other polygons instead of the circle  30  is generated. In this manner, it is possible to display the plurality of various folded three-dimensional images  90  of different plica spreading methods or different viewing angles. 
     In addition, display states of the stop display mode, the rotational display mode, the moving display mode, and the surface deformation mode may be appropriately combined and displayed. 
     When an end instruction is input by operating the end button  99 , the series of folded image generation processes are ended. 
     In addition, the folded three-dimensional image  90  may be displayed together with a scale added in the circumferential direction. 
     For example, as shown in  FIG. 7 , scales  71  in which scale marks indicating distances in the circumferential direction inside the hollow organ are added on the circumference of an ellipse are displayed in folded portions of the folded three-dimensional image  90  so as to overlap each other. Although two scales  71  are arranged in the radial direction and displayed in the example shown in  FIG. 7 , the number of displayed scales  71  is not limited to two. 
     The ellipticity of the scale  71  may be changed according to the viewing direction or the position of the view point. That is, when the viewing direction is parallel to the depth direction of the hollow organ or when the position of the view point is on the centerline of the hollow organ, the ellipse may be made similar to a true circle. On the other hand, the ellipticity may be made to increase as the inclination of the viewing direction and the depth direction of the hollow organ increases and as a distance of the position of the view point from the centerline of the hollow organ increases. 
     Since the inside of the hollow organ  50  expands outward in the folded portion, the distance between the scale marks on the circumference of the ellipse is increased by the outside scale. In addition, the distance between the scale marks may be changed according to the shape of the folded portion. For example, the distance between the scale marks maybe increased in the folded portion which is more pressed and spread. 
     The position of the scale mark of the scale  71  may be matched to the position of the plane when the hollow organ  50  is divided in step S 1  or to the middle of the adjacent planes. In this manner, the operator can know the position of the pixel value calculated by interpolation. 
     Switching of display and non-display of the scale  71  is performed when the operator performs an operation of clicking on a scale button  70  displayed on the display device  107 . 
     By displaying the scale  71  on the folded three-dimensional image  90  so as to overlap each other, the operator can see the size of the folded portion displayed in a deformed state while comparing it with other portions. 
     As described above, the image processing device  100  of the present invention divides the hollow organ  50 , which is extracted from the volume image  40  formed by stacking the plurality of tomographic images, using the plurality of planes  20  including the arbitrary eye vector  23  set in the depth direction of the hollow organ or the plurality of planes along the centerline of the hollow organ and deforms the divided portions along the predetermined convex surface (for example, the circle  30 ), which is set outside the hollow organ  50 , on each plane  20 . That is, the CPU  101  calculates the corresponding point Q when folding each point P in a predetermined range inside the hollow organ  50  along the convex surface (circle  30 ) and gives the pixel value of the original position to the corresponding point Q. The respective planes  20  on which the coordinate-transformed image is placed as described above are combined in a reverse procedure of the division procedure, thereby generating the folded volume image. Then, the shaded folded three-dimensional image  90  is generated by projecting the folded volume image to the projection plane from the arbitrary viewing direction, and is displayed on the display device  107 . 
     Therefore, since the hollow organ  50  is folded as if the sleeves of clothes are rolled up and accordingly the inside plicae are displayed outside, it becomes easy to observe the inside the hollow organ  50 . In addition, since the hollow organ  50  is folded along the convex surface, portions hidden behind the plicae are spread and displayed. Accordingly, the portions hidden behind the plicae can easily be observed. In addition, the plicae behind folded portion are displayed near the image of the normal hollow organ  50 . Since the position or the shape before folding can easily be grasped intuitively, this is effective for diagnosis of a doctor or the like. 
     In addition, the above-described convex surface may be either an arbitrary curved surface or an arbitrary polygon including a circle or an ellipse adjacent to the outer surface of the hollow organ  50 . If an appropriate convex surface is selected according to the state of the plicae of the inner surface, it is possible to generate the folded three-dimensional image that can easily be observed. 
     In addition, the folded three-dimensional image  90  may be displayed in various display formats as well as the virtual endoscope display in the example described above. For example, the moving display mode is preferred in which the plurality of folded three-dimensional images  90  are generated by transforming the coordinates of each point inside the hollow organ  50  along the above-described convex surface while moving the convex surface sequentially along the outer surface of the hollow organ and the plurality of folded three-dimensional images  90  are displayed sequentially like moving images. In the moving display mode, the folded image can be displayed such that movement in the depth direction is made while folding the hollow organ  50  sequentially. Therefore, it becomes easy to observe the entire hollow organ. 
     In addition, the surface deformation mode is preferred in which the plurality of folded three-dimensional images  90  with different surface shapes at the folded positions are generated by transforming the coordinates of each point inside the hollow organ  50  along the above-described convex surface by changing the shape of the convex surface sequentially or according to the operation of the operator and the plurality of folded three-dimensional images  90  are displayed sequentially. 
     In the surface deformation mode, the shape of the folded portion is changed to various shapes. Therefore, it is possible to display the plurality of folded three-dimensional images  90  of different fold spreading methods or different viewing angles. 
     In addition, the folded volume image may be generated by projecting the pixel value of the hollow organ to the trumpet-shaped curved surface. 
     Although the preferred embodiments of the image processing device related to the present invention have been described with reference to the accompanying drawings, the present invention is not limited to such examples. It is apparent to those skilled in the art that various changes and modifications can be made within the range of the technical idea disclosed in this specification, and it should undoubtedly be understood that they also belong to the technical range of the present invention. 
     REFERENCE SIGNS LIST 
       1 : image processing system 
       100 : image processing device 
       101 : CPU 
       102 : main memory 
       103 : storage device 
       104 : communication I/F 
       105 : display memory 
       106 : I/F 
       107 : display device 
       108 : mouse 
       109 : input device 
       20 : plane including an eye vector or plane along the centerline of a hollow organ 
       30 : circle 
       40 : volume image 
       41 ,  42 , . . . : tomographic image 
       50 : hollow organ 
       80 : image formed by folding a point inside the hollow organ  50  on the plane  20   
       82 : folded portion 
       90 : folded three-dimensional image under virtual endoscopic display 
       92 : central portion of the folded three-dimensional image  90   
       94 : peripheral portion of the folded three-dimensional image  90   
       95 : stop button 
       96 : rotation button 
       97 : move button 
       98 : surface deformation button 
       99 : end button 
     P: point inside a hollow organ 
     Q: corresponding point after coordinate transformation 
     R: contact point of the circle  30  and the hollow organ  50