Patent Publication Number: US-2012027170-A1

Title: Radiological image capturing and displaying method and apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a radiological image capturing and displaying method and apparatus that captures a subject in different radiographing directions to acquire radiological images from the different radiographing directions and displays a stereoscopic image using the radiological images. 
     2. Description of the Related Art 
     A technique is known which combines a plurality of images and displays the combined image, thereby enabling stereoscopically viewing using parallax. The image that can be stereoscopically viewed (hereinafter, referred to as a stereoscopic image or a stereo image) is generated based on a plurality of images which are acquired by capturing the same subject from different directions and have parallax therebetween. 
     Moreover, such way of generating stereoscopic image is utilized not only in the field of digital cameras and televisions but also in the field of capturing a stereoscopic radiological image. That is, a test subject is irradiated with radiation from different directions, and then the radiation passing through the test subject is detected by a radiological image detector to acquire plural radiological images having parallax, and a stereoscopic image is generated based on the radiological images. By generating a stereoscopic image in this way, a radiological image with a sense of depth can be observed thereby enabling the observation of a radiological image more suitable for diagnosis. 
     SUMMARY OF THE INVENTION 
     In the apparatus that captures the stereo image, one side of the radiological image detector needs to be parallel to a straight line connecting the two focal positions of a radiation source that radiates radiation in different directions. 
     However, for example, as shown in  FIG. 6 , when the side of a radiological image detector  15  is inclined with respect to a straight line connecting a focal position S 1  and a focal position S 2 , there is a shift in the Y direction between a radiological image which is captured by the radiation from the focal position S 1  and a radiological image which is captured by the radiation from the focal position S 2 . 
     That is, as shown in  FIGS. 7A and 7B , there is a shift between a subject image P 1  and a subject image P 2  indicating a subject OB in the Y direction. 
     As such, when there is a shift between two subject images P 1  and P 2  forming a stereo image in the Y direction and the observer observes the stereo image displayed on a monitor  3 , the burden on the observer to recognize the stereo image increases, which results in an increase in the fatigue of the observer. 
     JP2004-105568A discloses a technique that compensates the distortion of an image due to a change in the distance between a radiation source and a radiological image detector when the radiological image detector is moved and captures an image. However, JP-A-2004-105568 does not relate to the capture of a stereo image and does not disclose the above-mentioned problems in the capture of the stereo image and a solution for the problems. 
     JP-S59-40840A (JP19814-40840A) discloses an imaging apparatus that captures a stereo image. However, JP-S59-40840A (JP1984-40840A) does not disclose the above-mentioned problems in the capture of the stereo image and a solution for the problems. 
     The present invention has been made in view of the above-mentioned problems and an object of the present invention is to provide a radiological image capturing and displaying method and apparatus capable of displaying an appropriate stereo image even when one side of a radiological image detector is inclined with respect to a straight line linking two focal positions of radiation. 
     According to an aspect of the present invention , there is provided a radiological image capturing and displaying method that radiates radiation emitted from two focal positions to a subject in two different radiographing directions respectively to acquire two radiological images in the two different radiographing directions and displays a stereo image using the two acquired radiological images. The radiological image capturing and displaying method includes: acquiring the shift amount between the two radiological images in a direction perpendicular to a parallax direction; and displaying the stereoscopic image using the two radiological images which are relatively shifted in the direction perpendicular to the parallax direction as to reduce the acquired shift amount. 
     According to another aspect of the present invention, there is provided a radiological image capturing and displaying apparatus including: a radiological image acquiring unit that radiates radiation from two focal positions to a subject in two different radiographing directions to acquire two radiological images in the two different radiographing directions; a display unit that displays a stereoscopic image using the two radiological images acquired by the radiological image acquiring unit; and a shift amount acquiring unit that acquires the shift amount between the two radiological images in a direction perpendicular to a parallax direction. The display unit displays the stereoscopic image using the two radiological images which are relatively shifted in the direction perpendicular to the parallax direction as to reduce the shift amount acquired by the shift amount acquiring unit. 
     In the radiological image capturing and displaying apparatus according to the above-mentioned aspect, the shift amount acquiring unit may acquire the shift amount between marker images which appear in the two radiological images by radiographing reference marker in the two radiographing directions. 
     The radiological images including the marker images may be acquired before the subject is captured. 
     The reference marker may be provided on a radiography platform on which the subject is placed. 
     The radiological image capturing and displaying apparatus according to the above-mentioned aspect may further include a compression plate that compresses the subject. The subject may be a breast, and the reference marker may be placed on the compression plate. 
     The radiological image capturing and displaying apparatus according to the above-mentioned aspect may further include a radiation source that moves the two focal positions and radiates the radiation. The reference marker may be placed on a housing of the radiation source. 
     The shift amount acquiring unit may acquire the shift amount based on the specific portion of the subject in each of the radiological images. 
     The specific portion may be the outline of the subject. 
     The subject may be the breast and the specific portion may be the nipple of the breast. 
     The radiological image capturing and displaying apparatus according to the above-mentioned aspect may further include a radiological image detector that has a rectangular shape and detects the radiological image. The shift amount acquiring unit may acquire the shift amount based on the inclination of a side of the radiological image detector with respect to a straight line connecting the two focal positions. 
     The radiological image capturing and displaying apparatus according to the above-mentioned aspect may further include a radiological image compensating unit that performs a shift process on the two radiological images in the direction perpendicular to the parallax direction based on the shift amount acquired by the shift amount acquiring unit. 
     The radiological image capturing and displaying apparatus according to the above-mentioned aspect may further include a display control unit that controls the display unit to display the two radiological images shifted (  shifted   which are    ) in the direction perpendicular to the parallax direction based on the shift amount acquired by the shift amount acquiring unit. 
     The radiological image capturing and displaying apparatus according to the above-mentioned aspect may further include a cassette detecting unit that detects the insertion of a removable cassette. The radiological image detector may be provided in the removable cassette. When the cassette detecting unit detects the insertion of the cassette, the shift amount acquiring unit may automatically acquire the shift amount, or information prompting the acquisition of the shift amount may be notified. 
     According to the stereoscopic image capturing and displaying method and apparatus of the present invention, the shift amount between two radiological images in a direction perpendicular to the parallax direction is acquired, and a stereoscopic image is displayed using the two radiological images which are relatively shifted in the direction perpendicular to the parallax direction so that the acquired shift amount is reduced. Therefore, even when one side of the radiological image detector is inclined with respect to a straight line linking two focal positions of radiation, it is possible to display an appropriate stereoscopic image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically illustrating the structure of a breast image capturing and displaying system using a radiological image capturing and displaying apparatus according to an embodiment of the present invention. 
         FIG. 2  is a diagram illustrating an arm unit of the breast image capturing and displaying system shown in  FIG. 1 , as viewed from the right direction of  FIG. 1 . 
         FIG. 3  is a block diagram schematically illustrating the internal structure of a computer of the breast image capturing and displaying system shown in  FIG. 1 . 
         FIG. 4  is a diagram illustrating a marker member provided on a radiography platform. 
         FIG. 5  is a flowchart illustrating the operation of the breast image capturing and displaying system using the radiological image capturing and displaying apparatus according to the embodiment of the present invention. 
         FIG. 6  is a diagram illustrating a case in which a radiological image detector is provided so that one side thereof is inclined with respect to a straight line linking two focal positions of radiation. 
         FIGS. 7A and 7B  are diagrams illustrating an example of a first radiological image P 1  which is captured by the emission of radiation from one of the focal positions to a subject and a second radiological image P 2  which is captured by the emission of radiation from the other focal position to the subject in the arrangement position of the radiological image detector shown in  FIG. 6 . 
         FIG. 8  is a diagram illustrating the shift of the moving direction of the focal position of radiation from one side of the radiological image detector. 
         FIGS. 9A and 9B  are diagrams illustrating an example of the first radiological image P 1  which is captured by the emission of radiation from one of the focal positions to the subject and the second radiological image P 2  which is captured by the emission of radiation from the other focal position to the subject in the relationship between the moving direction of the focal position and the arrangement position of the radiological image detector shown in  FIG. 8 . 
         FIG. 10  is a diagram illustrating an example in which the marker member is provided on a compression plate. 
         FIG. 11  is a diagram illustrating an example in which the marker member is provided on a housing of a radiation source. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a breast image capturing and displaying system using a radiological image capturing and displaying apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.  FIG. 1  is a diagram schematically illustrating the overall structure of the breast image capturing and displaying system according to this embodiment. 
     As shown in  FIG. 1 , a breast image capturing and displaying system  1  according to this embodiment includes a breast imaging apparatus  10 , a computer  2  that is connected to the breast imaging apparatus  10 , and a monitor  3  and an input unit  4  that are connected to the computer  2 . 
     As shown in  FIG. 1 , the breast imaging apparatus  10  includes a base  11 , a rotating shaft  12  that is movable in the vertical direction (Z direction) relative to the base  11  and is rotatable, and an arm unit  13  that is connected to the base  11  by the rotating shaft  12 .  FIG. 2  shows the arm unit  13 , as viewed from the right direction of  FIG. 1 . 
     The arm unit  13  has a C-shape and includes one end to which a radiography platform  14  is attached and the other end to which a radiation radiating unit  16  is attached so as to face the radiography platform  14 . The rotation and vertical movement of the arm unit  13  are controlled by an arm controller  31  that is incorporated into the base  11 . 
     The radiography platform  14  includes a radiological image detector  15 , such as a flat panel detector, and a detector controller  33  that controls the reading of a charge signal from the radiological image detector  15 . In addition, the radiography platform  14  includes, for example, a circuit board provided with a charge amplifier that converts the charge signal read from the radiological image detector  15  into a voltage signal, a correlated double sampling circuit that samples the voltage signal output from the charge amplifier, and an A/D converter that converts the voltage signal into a digital signal. 
     The radiography platform  14  is configured so as to be rotatable with respect to the arm unit  13 . Therefore, even when the arm unit  13  is rotated with respect to the base  11 , the direction of the radiography platform  14  can be fixed with respect to the base  11 . 
     The radiological image detector  15  can repeatedly record and read the radiological image and may be a so-called direct radiological image detector that directly receives radiation and generates charge or a so-called indirect radiological image detector that converts radiation into visible light and then converts the visible light into a charge signal. As a method of reading a radiological image signal, it is preferable to use a so-called TFT reading method of turning on or off a TFT (thin film transistor) switch to read the radiological image signal or a so-called optical reading method of radiating reading light to read the radiological image signal. However, the reading method is not limited thereto, but other methods may be used. 
     The radiation radiating unit  16  includes a radiation source  17  and a radiation source controller  32 . The radiation source controller  32  controls the time when radiation is radiated from the radiation source  17  and the radiation generation conditions (for example, a tube current, time, and a tube current-time product) of the radiation source  17 . 
     In addition, a compression plate  18  that is provided above the radiography platform  14  and compresses the breast, a supporting portion  20  that supports the compression plate  18 , and a moving mechanism  19  that moves the supporting portion  20  in the vertical direction (Z direction) are provided at the center of the arm unit  13 . The position and compression pressure of the compression plate  18  are controlled by a compression plate controller  34 . 
     The computer  2  includes, for example, a central processing unit (CPU) and a storage device, such as a semiconductor memory, a hard disk, or an SSD. A control unit  8   a,  a radiological image storage unit  8   b,  a shift amount acquiring unit  8   c,  an image correcting unit  8   d,  and a display control unit  8   e  shown in  FIG. 3  are formed by these hardware components. 
     The control unit  8   a  outputs predetermined control signals to various kinds of controllers  31  to  35  to control the entire system. A detailed control method will be described below. 
     The radiological image storage unit  8   b  stores the radiological image signals acquired by the radiological image detector  15  in advance. 
     The shift amount acquiring unit  8   c  acquires the shift amount between two radiological images forming a stereo image in a direction perpendicular to the parallax direction. 
     A marker member  40  is provided in the radiography platform  14  according to this embodiment, as shown in  FIG. 4 . The shift amount acquiring unit  8   c  acquires the shift amount between marker images appearing on the two radiological images by the marker member  40  as the shift amount between the two radiological images. In this embodiment, the marker member  40  is a radiation absorption member, such as lead, and is provided at the corner of the radiography platform  14  so that the marker image does not overlap the breast image. The shift amount acquiring operation of the shift amount acquiring unit  8   c  will be described in detail below. 
     The image correcting unit  8   d  performs a shift process of relatively shifting two radiological image signals so that the shift amount acquired by the shift amount acquiring unit  8   c  is reduced. Performing the shift process so that the shift amount is reduced means performing the shift process so that the shift amount is zero. 
     The display control unit  8   e  displays the stereo image of the breast on the monitor  3  based on the two radiological image signals shifted by the image correcting unit  8   d.    
     The input unit  4  is, for example, a keyboard or a pointing device, such as a mouse, and receives imaging conditions or an imaging start instruction input from a photographer. 
     The monitor  3  is configured so that it can display a stereo image using two radiological image signals output from the computer  2  when the stereo image is captured. As a structure that displays the stereo image, for example, the following structure may be used in which two radiological images are respectively displayed on two screens based on two radiological image signals and, for example, a half mirror or a polarization glass is used so that one of the two radiological images is incident on the right eye of the observer and the other radiological image is incident on the left eye of the observer, thereby displaying a stereo image. Alternatively, for example, the following structure may be used: a structure in which two radiological images are displayed so as to overlap each other with a positional shift corresponding to a predetermined amount of parallax therebetween and a polarization glass is used to generate a stereo image so that the observer can view the stereo image; or a structure, such as a parallax barrier type or a lenticular type, in which two radiological images are displayed on a 3D liquid crystal display that can three-dimensionally display the radiological images, thereby generating a stereo image. 
     Next, the operation of the breast image capturing and displaying system according to this embodiment will be described with reference to the flowchart shown in  FIG. 5 . 
     First, the breast M of the patient is placed on the radiography platform  14  and the compression plate  18  compresses the breast M with a predetermined pressure (S 10 ). 
     Then, the input unit  4  sequentially receives various kinds of imaging conditions and an image start instruction from the photographer. 
     When the input unit  4  receives the imaging start instruction, the stereo image of the breast M is captured (S 12 ). Specifically, first, the control unit  8   a  reads the angle θ of convergence for capturing a predetermined stereo image and outputs the information of the read angle θ of convergence to the arm controller  31 . In this embodiment, in this case, it is assumed that θ=±2° is stored as the information of the angle θ of convergence in advance, but the present invention is not limited thereto. The photographer may use the input unit  4  to set an arbitrary angle of convergence. 
     The arm controller  31  receives the information of the angle θ of convergence output from the control unit  8   a.  Then, the arm controller  31  outputs a control signal based on the information of the angle θ of convergence so that the arm unit  13  rotates +θ° with respect to the direction vertical to the radiography platform  14 , as shown in  FIG. 2 . That is, in this embodiment, the arm controller  31  outputs a control signal so that the arm unit  13  rotates +2° with respect to the direction vertical to the radiography platform  14 . 
     The arm unit  13  rotates +2° in response to the control signal output from the arm controller  31 . Then, the control unit  8   a  outputs control signals to the radiation source controller  32  and the detector controller  33  so as to perform the emission of radiation and the reading of the radiological image signal, respectively. In response to the control signals, the radiation source  17  radiates radiation, the radiological image detector  15  detects the radiological image of the breast captured in a +2° direction, and the detector controller  33  reads the radiological image signal. Then, predetermined signal processing is performed on the radiological image signal, and the radiological image signal is stored in the radiological image storage unit  8   b  of the computer  2 . 
     Then, as shown in  FIG. 2 , the arm controller  31  returns the arm unit to the initial position once and outputs a control signal so that the arm unit rotates −0° with respect to the direction vertical to the radiography platform  14  (S 14 ). That is, in this embodiment, the arm controller  31  outputs a control signal so that the arm unit  13  rotates −2° with respect to the direction vertical to the radiography platform  14 . 
     Then, the arm unit  13  rotates −2° in response to the control signal output from the arm controller  31 . Then, the control unit  8   a  outputs control signals to the radiation source controller  32  and the detector controller  33  so as to perform the emission of radiation and the reading of the radiological image, respectively. In response to the control signals, the radiation source  17  radiates radiation, the radiological image detector  15  detects the radiological image of the breast captured in a −2° direction, and the detector controller  33  reads the radiological image signal. Then, predetermined signal processing is performed on the radiological image signal and the radiological image signal is stored in the radiological image storage unit  8   b  of the computer  2 . 
     When, the radiological image detector  15  is arranged so that the side thereof is inclined with respect to a straight line linking the focal position S 1  of the radiation source  17  when an image is captured in the +θ° direction and the focal position S 2  of the radiation source when an image is captured in the −θ° direction, as shown in  FIG. 6 , the radiological image captured by radiation radiated from the focal position S 1  deviates from the radiological image captured by radiation radiated from the focal position S 2  in a direction perpendicular to the parallax direction. 
     For ease of explanation,  FIG. 6  shows a subject OB which schematically shows the breast M,  FIG. 7A  shows a first radiological image P 1  which is captured by the emission of radiation from the focal position S 1  to the subject OB, and  FIG. 7B  shows a second radiological image P 2  which is captured by the emission of radiation from the focal position S 2  to the subject OB. 
     When the radiological image detector  15  is provided so as to be inclined as shown in  FIG. 6 , a shift between the subject image P 1  and the subject image P 2  indicating the subject OB occurs in a direction perpendicular to the parallax direction, that is, the y direction shown in  FIGS. 7A and 7B , as shown in  FIGS. 7A and 7B . The x-y directions shown in  FIG. 6  and  FIGS. 7A and 7B  are the coordinate axes of the radiological image detected by the radiological image detector  15 . 
     When the radiological image detector  15  is normally provided, but the straight line linking the two focal positions is inclined with respect to the side of the radiological image detector  15  due to the shift of the moving direction of the focal position of the radiation source  17  as shown in  FIG. 8 , the shift between the subject image P 1  and the subject image P 2  indicating the subject OB also occurs in the direction perpendicular to the parallax direction, that is, the y direction shown in  FIGS. 9A and 9B , as shown in  FIGS. 9A and 9B . The x-y directions shown in  FIG. 8  and  FIGS. 9A and 9B  are also the coordinate axes of the radiological image detected by the radiological image detector  15 . 
     As such, when the shift between the two subject images P 1  and P 2  forming the stereo image occurs in the y direction and the observer observes the stereo image displayed on the monitor  3 , the burden on the observer to recognize the stereo image increases, which results in an increase in the fatigue of the observer. 
     Therefore, in the breast image capturing and displaying system according to this embodiment, the shift amount between the subject image P 1  and the subject image P 2  in the y direction is acquired and a process of shifting the two radiological images in the y direction is performed based on the shift amount. 
     Specifically, as described above, the two acquired radiological image signals are read from the radiological image storage unit  8   b  and are then input to the shift amount acquiring unit  8   c.  The shift amount acquiring unit  8   c  extracts the marker images from the input two radiological image signals and acquires the shift amount between the marker images in the y direction (S 16 ). For example, when a marker image MP 1  appears in one of the radiological images as shown in  FIG. 7A  or  FIG. 9A  and a marker image MP 2  appears in the other radiological image as shown in  FIG. 7B  or  FIG. 9B , the amount d of shift between the marker image MP 1  and the marker image MP 2  in the y direction is acquired. 
     Then, the amount d of shift acquired by the shift amount acquiring unit  8   c  is output to the image correcting unit  8   d.  The image correcting unit  8   d  performs a shift process on the two radiological image signals in the y direction based on the shift amount so that the amount d of shift is zero (S 18 ). In this case, the shift process may be performed to shift only one radiological image signal in the y direction by the amount d of shift or the shift process may be performed to shift each of the two radiological image signals in the y direction by half the amount d of shift (d/2). 
     Then, the image correcting unit  8   d  outputs the two radiological image signals subjected to the shift process to the display control unit  8   e  and the display control unit  8   e  displays the stereo image of the breast on the monitor  3  based on the input two radiological image signals (S 20 ). 
     In the above-described embodiment, the marker member  40  is provided on the radiography platform  14 , but the present invention is not limited thereto. For example, as shown in  FIG. 10 , the marker member  40  may be provided at the corner of the compression plate  18 . In addition, as shown in  FIG. 11 , the marker member  40  may be provided on a housing of the radiation radiating unit  16  provided with the radiation source  17 . 
     The marker image may be captured at the same time as the subject is captured as in the above-described embodiment, or it may be captured in advance by pre-exposure before the subject is captured. 
     In the above-described embodiment, the marker image of the marker member  40  is used to acquire the shift amount, but the marker image is not necessarily used. For example, the shift amount may be acquired based on the image of a specific portion in each radiological image. 
     For example, when the image of the specific portion is the radiological image of the breast, the skin line (outline) of the breast may be detected and the shift amount of the skin line in the y direction may be acquired. As a method of detecting the skin line, for example, a known edge detecting method may be used. 
     In addition, the position of a nipple in the radiological image of each breast may be detected and the shift amount at the position of the nipple in the y direction may be acquired. As a method of detecting the position of the nipple of the breast, for example, the following methods may be used: a method which detects the skin line of the breast and detects the position of the top of the skin line as the position of the nipple; and a method which detects a mammary gland pattern and detects the position where the density of the mammary gland pattern is the highest as the position of the nipple. In addition, other known methods may be used to detect the position of the nipple. 
     In addition, the inclination of the side of the rectangular radiological image detector  15  with respect to the straight line linking two focal positions may be directly detected and the shift amount of the breast image in the y direction may be acquired based on the inclination. For example, a laser displacement meter may be used to detect the inclination. In addition, the inclination may be measured in advance, the inclination may be input by the input unit  4 , and the shift amount acquiring unit  8   c  may calculate the shift amount based on the input inclination. 
     In the above-described embodiment, the image correcting unit  8   d  performs the shift process on the radiological image signal based on the shift amount acquired by the shift amount acquiring unit  8   c.  However, instead of performing the shift process, the display control unit  8   e  may generate a display control signal based on the shift amount and two radiological image signals so that the two radiological images are displayed on the monitor  3  so as to be shifted by the shift amount, and output the display control signal to the monitor  3 . 
     In addition, the radiological image detector  15  may be provided in a cassette that is removable from the radiography platform  14 . In this case, when the cassette is inserted, the radiological image detector  15  can be inclined and the apparatus can detect the insertion of the cassette. When the insertion of the cassette is detected, the shift amount may be automatically acquired or information prompting the acquisition of the shift amount may be displayed. For example, the marker image may be automatically captured or information prompting the capture of the marker image may be displayed. 
     In the above description, the stereo image display apparatus according to an embodiment of the present invention is applied to the breast image capturing and displaying system, but the subject of the present invention is not limited to the breast. For example, the present invention can be applied to a radiological image capturing and displaying system that captures an image of the chest or the head.