Patent Publication Number: US-2012027166-A1

Title: Radiation image capturing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a radiation image capturing apparatus including a radiation source and a radiation conversion panel for detecting a radiation emitted from the radiation source and passing through a subject, and converting the detected radiation into radiation image information, and more particularly to a radiation image capturing apparatus for capturing an image of an elongate subject based on tomosynthesis. 
     2. Description of the Related Art 
     Radiation image capturing apparatus for capturing images of elongate subjects have been proposed in Japanese Laid-Open Patent Publication Nos. 2004-202069, 2005-066343, and 2006-141904. 
     Japanese Laid-Open Patent Publication No. 2004-202069 discloses an image reading apparatus for capturing an image of the outer side of a row of teeth as a single image. The image reading apparatus captures the images of a plurality of segments of the outer side of the row of teeth and then accurately combines the segmental images into an overall image of the outer side of the row of teeth. Specifically, the image reading apparatus comprises a digital camera for capturing the segmental images of the outer side of the row teeth segment by segment, a distance sensor for measuring the distance from the digital camera to the outer side of the row of teeth as an image capturing distance, a memory for storing the segmental images and the image capturing distance which is measured when the segmental images are captured, an image magnification converting means for converting the image capturing magnifications of all the segmental images into a life-size magnification based on the image capturing distance, and an image combining means for combining the segmental images into a single combined image. 
     Japanese Laid-Open Patent Publication No. 2005-066343 discloses a system for acquiring a radiographic tomosynthesis image using asymmetrical geometry, the system having an optimum total sweep angle for maximizing the image quality. The system includes an X-ray detector and an X-ray source capable of emitting X-rays directed at the X-ray detector. For acquiring a radiographic tomosynthesis image, the system utilizes asymmetric image acquisition geometry where θ1≠θ0 where θ1 represents a sweep angle on one side of a center line of the X-ray detector and θ0 a sweep angle on the opposite side of the center line of the X-ray detector. 
     SUMMARY OF THE INVENTION 
     Japanese Laid-Open Patent Publication No. 2006-141904 discloses an X-ray image capturing apparatus which operates as follows: A marker is disposed in an overlapping area on a subject, and the position of the marker is determined from a captured image of the marker. A distance to be traveled up to an image capturing range divided based on the position of the marker is determined by a distance calculating means. A position control means moves an X-ray detecting means to a position corresponding to the distance to be traveled, and automatically holds the X-ray detecting means in the image capturing range. The X-ray image capturing apparatus makes it possible to eliminate a complicated and time-consuming process of positioning a plane detector in capturing an image of an elongate subject. 
     According to the technology disclosed in Japanese Laid-Open Patent Publication No. 2004-202069, the segmental images captured by the digital camera are joined together into a single image of the outer side of the row of teeth. However, since the two-dimensional images are simply joined together in a planar array, the combined image is far from representing the actual three-dimensional outer side of the row of teeth. 
     The technology disclosed in Japanese Laid-Open Patent Publication No. 2005-066343 is effective in acquiring a three-dimensional radiographic image in a relatively small range such as a chest or the like. However, the disclosed system is unable to acquire a three-dimensional radiographic image of an elongate area such as the backbone or a leg bone of a human being. 
     Since the X-ray image capturing apparatus disclosed in Japanese Laid-Open Patent Publication No. 2006-141904 captures a two-dimensional image of an area, the apparatus is disadvantageous in that it needs to recapture another two-dimensional image of the area if the user wants to confirm the area from a different perspective. 
     It is an object of the present invention to provide a radiation image capturing apparatus which is capable of acquiring a two-dimensional projection image (tomographic image) of an elongate subject on an arbitrary image plane based on a three-dimensional image that is acquired by way of tomosynthesis, for thereby effectively shortening medical procedures that are performed using the radiation image capturing apparatus. 
     A radiation image capturing apparatus according to the present invention includes a tomosynthesis image capturing device comprising: a radiation source, a radiation conversion panel for detecting a radiation emitted from the radiation source and passing through an elongate subject, and converting the detected radiation into radiation image information, a first moving mechanism for moving the radiation source, a second moving mechanism for moving the radiation conversion panel, and a tomosynthesis control mechanism for moving the radiation source and the radiation conversion panel, which are disposed on the respective opposite sides of the subject, respectively in opposite directions in synchronism with each other; a image capturing range setting unit for setting a plurality of successive image capturing ranges in a longitudinal direction of the subject;_a longitudinal direction moving mechanism for moving an image capturing range of the tomosynthesis image capturing device in a longitudinal direction of the subject to allow the tomosynthesis image capturing device to capture the plurality of image capturing ranges such that the plurality of image capturing ranges are partly overlapped with each other;_an overlapping area specifying unit which acquires a plurality of radiation images of the plurality of image capturing ranges of an elongate test subject in advance, specifies overlapping areas in the radiation images, and registers information of the specified overlapping areas in an information table;_an image joining unit which acquires a plurality of radiation images of the plurality of image capturing ranges of the elongate subject, and joins the acquired plurality of radiation images based on the information of the overlapping areas registered in the information table to generate a single joined radiation image; and an image generating unit for generating a tomographic image on an arbitrary image plane based on the joined radiation image. The information of the overlapping areas may include a first relative number of pixels in a direction along the longitudinal direction and a second relative number of pixels in one direction perpendicular to the longitudinal direction or a direction opposite to the one direction. 
     The image joining unit may move any one of adjacent two radiation images in the longitudinal direction by the first relative number of pixels, move any one of the adjacent two radiation images in a direction perpendicular to the longitudinal direction by the second relative number of pixels, and then join the adjacent two radiation images. 
     The radiation image capturing apparatus may further include an input device for setting the image plane. 
     The tomosynthesis control mechanism of the tomosynthesis image capturing device may control the first moving mechanism and the second moving mechanism to move the radiation source and the radiation conversion panel in the longitudinal direction of the subject. 
     The tomosynthesis control mechanism of the tomosynthesis image capturing device may control the first moving mechanism and the second moving mechanism to move the radiation source and the radiation conversion panel in a direction perpendicular to the longitudinal direction of the subject. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a radiation image capturing apparatus according to an embodiment of the present invention; 
         FIGS. 2A through 2C  are side elevational views showing the manner in which a radiation source and a radiation conversion panel are moved in a longitudinal direction of a subject and a tomosynthesis image capturing apparatus is moved in the longitudinal direction of the subject; 
         FIGS. 3A through 3C  are plan views showing the manner in which the radiation source and the radiation conversion panel are moved in the longitudinal direction of the subject and the tomosynthesis image capturing apparatus is moved in the longitudinal direction of the subject; 
         FIGS. 4A through 4C  are plan views showing the manner in which the radiation source and the radiation conversion panel are moved in a direction perpendicular to the longitudinal direction of the subject and the tomosynthesis image capturing apparatus is moved in the longitudinal direction of the subject; 
         FIG. 5  is a block diagram of a circuit arrangement of the radiation conversion panel; 
         FIG. 6  is a view showing the manner in which three-dimensional images are joined together by a three-dimensional image joining unit; and 
         FIG. 7  is a view showing the manner in which the image plane of an elongate three-dimensional image is specified by an image generating unit. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A radiation image capturing apparatus according to an embodiment of the present invention will be described below with reference to  FIGS. 1 through 7 . 
     As shown in  FIG. 1 , a radiation image capturing apparatus  10  according to an embodiment of the present invention includes a tomosynthesis image capturing device  12 . 
     The tomosynthesis image capturing device  12  comprises a radiation source  14 , a radiation conversion panel  18  for detecting a radiation emitted from the radiation source  14  and passing through an elongate subject  16 , and converting the detected radiation into radiation image information, a first moving mechanism  20  for moving the radiation source  14 , a second moving mechanism  22  for moving the radiation conversion panel  18 , and a tomosynthesis control mechanism  24  for moving the radiation source  14  and the radiation conversion panel  18 , which are disposed on the respective opposite sides of the subject  16 , respectively in opposite directions in synchronism with each other. The radiation conversion panel  18  is housed in the casing of a cassette  26 , for example. In the present embodiment, the tomosynthesis control mechanism  24  moves the radiation source  14  and the radiation conversion panel  18 , which are disposed on the respective opposite sides of the subject  16 , respectively in the opposite directions in synchronism with each other, such that a line interconnecting the center of the radiation source  14  and the center of the radiation conversion panel  18  is held in substantial alignment with the direction in which the radiation is emitted from the radiation source  14  to the subject  16 . 
     The radiation image capturing apparatus  10  also includes, in addition to the tomosynthesis image capturing device  12 , a longitudinal direction moving mechanism  28  for moving an image capturing range of the tomosynthesis image capturing device  12  in a longitudinal direction of the subject  16 , a three-dimensional image reconstructing unit  30  for generating a single three-dimensional image from a plurality of radiation images captured in a single image capturing range, a three-dimensional image joining unit  32  for joining a plurality of three-dimensional images generated by the three-dimensional image reconstructing unit  30  with respect to a plurality of image capturing ranges, in the longitudinal direction of the subject  16 , an image generating unit  34  for generating a two-dimensional projection image (tomographic image) on an arbitrary image plane based on a joined three-dimensional image produced by the three-dimensional image joining unit  32 , and a computer  36  for controlling the above units  30 ,  32 ,  34 . 
     The tomosynthesis control mechanism  24  of the tomosynthesis image capturing device  12  controls the first moving mechanism  20  and the second moving mechanism  22  to move the radiation source  14  and the radiation conversion panel  18  (the cassette  26 ) in the longitudinal direction of the subject  16 , as shown in  FIGS. 2A through 2C  and  3 A through  3 C. The tomosynthesis control mechanism  24  may also control the first moving mechanism  20  and the second moving mechanism  22  to move the radiation source  14  and the radiation conversion panel  18  in a direction perpendicular to the longitudinal direction of the subject  16 , as shown in  FIGS. 4A through 4C . 
     As shown in  FIG. 5 , the radiation conversion panel  18  comprises an array of thin-film transistors (TFTs)  52  arranged in rows and columns, a photoelectric conversion layer  51  made of a material such as amorphous selenium (a-Se) for generating electric charges upon detection of the radiation, the photoelectric conversion layer  51  being disposed on the array of TFTs  52 , and an array of storage capacitors  53  connected to the photoelectric conversion layer  51 . When the radiation X is applied to the radiation conversion panel  18 , the photoelectric conversion layer  51  generates electric charges, and the storage capacitors  53  store the generated electric charges. Then, the TFTs  52  are turned on along each row at a time to read the electric charges from the storage capacitors  53  as an image signal. In  FIG. 5 , the photoelectric conversion layer  51  and one of the storage capacitors  53  are shown as a pixel  50 , and the pixel  50  is connected to one of the TFTs  52 . Details of the other pixels  50  are omitted from illustration. Since amorphous selenium tends to change its structure and lose its functionality at high temperatures, it needs to be used in a certain temperature range. Therefore, some means for cooling the radiation conversion panel  18  should preferably be provided in the cassette  26 . 
     The TFTs  52  connected to the respective pixels  50  are connected to respective gate lines  54  extending parallel to the rows and respective signal lines  56  extending parallel to the columns. The gate lines  54  are connected to a line scanning driver  58 , and the signal lines  56  are connected to a multiplexer  66  serving as a reading circuit. 
     The gate lines  54  are supplied with control signals Von, Voff for turning on and off the TFTs  52  along the rows from the line scanning driver  58 . The line scanning driver  58  comprises a plurality of first switches SW 1  for switching between the gate lines  54 , and a column address decoder  60  for outputting a selection signal for selecting one of the first switches SW 1  at a time. The column address decoder  60  is supplied with an address signal from the cassette controller  46 . 
     The signal lines  56  are supplied with electric charges stored in the storage capacitors  53  of the pixels  50  through the TFTs  52  arranged in the columns. The electric charges supplied to the signal lines  56  are amplified by amplifiers  62  connected respectively to the signal lines  56 . The amplifiers  62  are connected through respective sample and hold circuits  64  to the multiplexer  66 . The multiplexer  66  comprises a plurality of second switches SW 2  for switching between the signal lines  56 , and a row address decoder  68  for outputting a selection signal for selecting one of the second switches SW 2  at a time. The row address decoder  68  is supplied with an address signal from the cassette controller  46 . The multiplexer  66  has an output terminal connected to an A/D converter  70 . A radiation image signal generated by the multiplexer  66  based on the electric charges from the sample and hold circuits  64  is converted by the A/D converter  70  into a digital signal representing radiation image information, which is supplied to the cassette controller  46 . The cassette controller  46  supplies the digital image signal to the computer  36 , which stores the digital image signal, i.e., the radiation image information, in an image storage memory  38 . 
     In other words, each time the tomosynthesis image capturing device  12  captures a radiation image of the subject  16 , the radiation conversion panel  18  supplies radiation image information representing the radiation image to the computer  36 , which stores the radiation image information in a first storage area  100  of the image storage memory  38 . 
     Each time the tomosynthesis image capturing device  12  completes the capturing of images in an image capturing range, for example, the three-dimensional image reconstructing unit  30  reads out a plurality of pieces of radiation image information corresponding to the one image capturing range from the first storage area  100  of the image storage memory  38 , reconstructs a single three-dimensional image from the read pieces of radiation image information according to a known three-dimensional image reconstructing algorithm, and stores the reconstructed three-dimensional image in a second storage area  102  of the image storage memory  38 . 
     When the tomosynthesis image capturing device  12  completes the capturing of images in all image capturing ranges, therefore, the second storage area  102  of the image storage memory  38  stores reconstructed three-dimensional images corresponding to the respective image capturing ranges. 
     For imaging the elongate subject  16  in a plurality of image capturing ranges, it is preferable to set the image capturing ranges such that they partly overlap each other for the purpose of accurately imaging the elongate subject  16 . Accordingly, the three-dimensional images generated in the adjacent two image capturing ranges include images of the overlapping areas. If the three-dimensional images are simply joined together according to the sequence of the image capturing ranges, then the images of the overlapping areas are juxtaposed in the joined part, and the resultant combined image is not accurately representative of the subject  16 . 
     To avoid the above drawback, the three-dimensional image joining unit  32  specifies the overlapping areas. The overlapping areas may be specified by a first process based on a table of positional information, which has been recognized in advance, of the overlapping areas, or a second process based on pattern matching. 
     According to the first process, an elongate test subject is imaged to generate a plurality of three-dimensional images thereof, and the three-dimensional images are displayed on a display monitor. Then, the overlapping areas of the three-dimensional images are specified while the three-dimensional images are being moved on the display monitor using a CAD program or the like. After the overlapping areas are specified, information of the overlapping areas included in the three-dimensional images is registered in an information table. If the longitudinal direction of the subject  16  is indicated as an x direction (see  FIG. 6 ) and the direction perpendicular to the longitudinal direction of the subject  16  is indicated as a y direction, then the information of the overlapping areas may include the relative number of pixels in the x direction, i.e., the relative number of overlapping pixels in the longitudinal direction of the subject  16 , a sign (a positive sign or a negative sign) with respect to the y direction, and the relative number of pixels in the y direction. The positive sign represents a rightward direction from a central line m in the x direction, and the negative sign represents a leftward direction from the central line m in the x direction.  FIG. 6  shows the manner in which a first three-dimensional image G 1 , a second three-dimensional image G 2 , and a third three-dimensional image G 3  are joined together. In  FIG. 6 , the second three-dimensional image G 2  is moved in the x direction by the relative number Pa of pixels and moved to the left by the relative number Pb of pixels, and is joined to the first three-dimensional image G 1 , and the third three-dimensional image G 3  is moved in the x direction by the relative number Pc of pixels and moved to the right by the relative number Pd of pixels, and is joined to the second three-dimensional image G 2 . The overlapping areas of the three-dimensional images G 1  through G 3  are shown hatched in  FIG. 6 . The first process requires the test subject to be imaged and also requires the information table to be generated while the overlapping areas of the three-dimensional image are being confirmed on the monitor display. However, the first process is advantageous in that once the information table is generated, it can be used repeatedly until the next maintenance. 
     According to the second process, each of the pixels or each of a group of several pixels is regarded as a block, and pattern matching is carried out for each block. The pattern matching is readily applicable because it has been used to detect interframe motion vectors for image processing. Though the pattern matching is a simple process as there is no need for imaging a test subject and generating an information table while the overlapping areas of three-dimensional image are being confirmed on the monitor display, the pattern matching is problematic in that it requires time-consuming image processing. 
     The first process and the second process may be combined with each other. Specifically, an information table may be registered for rough ranges that may be regarded as overlapping areas according to the first process, and pattern matching is performed on the rough ranges according to the second process. The combination of the first and second processes makes it possible to specify the overlapping areas accurately at a high speed. 
     After the three-dimensional image joining unit  32  has specified the overlapping areas in each three-dimensional image, the three-dimensional image joining unit  32  calculates weighted averages of the pixels included in the overlapping areas. For example, the three-dimensional image joining unit  32  calculates weighted averages of the pixels included in a first overlapping area of a first three-dimensional image and a second three-dimensional image, for example, and generates a three-dimensional image of the first overlapping area based on the weighted averages. Then, the three-dimensional image joining unit  32  calculates weighted averages of the pixels included in a second overlapping area of the second three-dimensional image and a third three-dimensional image, for example, and generates a three-dimensional image of the second overlapping area based on the weighted averages. The three-dimensional image joining unit  32  calculates weighted averages of the pixels included in a third overlapping area of the third three-dimensional image and a fourth three-dimensional image, and generates a three-dimensional image of the third overlapping area based on the weighted averages. The three-dimensional image joining unit  32  operates similarly on other overlapping areas to generate three-dimensional images of the other overlapping areas. 
     Accordingly, the three-dimensional image joining unit  32  generates a single combined elongate three-dimensional image free of overlapping areas which is accurately representative of the elongate subject  16 . The elongate three-dimensional image is stored in a third storage area  104  of the image storage memory  38 . The elongate three-dimensional image stored in the third storage area  104  will be supplied to a printer  108  or a display monitor  110  via a first output unit  106 . 
     The image generating unit  34  generates a tomographic image on an arbitrary image plane based on the elongate three-dimensional image stored in the third storage area  104 . The image plane is set using an input device  112  (a keyboard, a mouse, etc.) connected to the computer  36 . If signals are entered via a GUI (Graphic User Interface), for example, then, as shown in  FIG. 7 , an image plane  116  is designated on an elongate three-dimensional image  114  displayed on the display monitor  110 , as a sectional image across the elongate three-dimensional image  114 , using a coordinate input device such as a mouse, for example. At this time, the image plane  116  may be specified by entering vertex coordinates. Alternatively, the image plane  116  may be specified simply by entering a distance from the radiation conversion panel  18 . 
     When the image plane  116  is set, the image generating unit  34  determines a plurality of vertex coordinates where the elongate three-dimensional image  114  and the image plane  116  overlap each other based on coordinates and vectors on an image memory (VRAM) of the elongate three-dimensional image  114  and coordinates and vectors on an image memory (VRAM) of the image plane  116 , and projects the elongate three-dimensional image  114  parallel onto the image plane  116  which is given as a plane specified by the vertex coordinates, thereby generating a two-dimensional image (tomographic image). The tomographic image is stored in a forth storage area  118  of the image storage memory  38 . The tomographic image stored in the fourth storage area  118  will be supplied to the printer  108  or the display monitor  110  via a second output unit  120 . 
     In addition to the above parallel projection, the image generating unit  34  is also capable of generating a two-dimensional image on an image plane according to a perspective transformation process having a viewpoint at the radiation source and a screen on the image plane, in response to a selective command entered via the input device. Specifically, based on preset world coordinates of the radiation source  14  and the world coordinates of the image plane  116  which are set as described above, the elongate three-dimensional image  114  is processed by a perspective transformation process having a viewpoint at the radiation source  14  and a screen on the image plane, thereby generating a tomographic image on the image plane  116 . The tomographic image is different in overlapping and magnification from the elongate three-dimensional image  114  depending on the positional relationship between the radiation source  14 , the subject  16 , and the image plane  116 . The tomographic image is also stored in the forth storage area  118  of the image storage memory  38 . The tomographic image stored in the fourth storage area  118  will be supplied to the printer  108  or the display monitor  110  via the second output unit  120 . 
     As described above, the radiation image capturing apparatus  10  according to the present embodiment comprises the longitudinal direction moving mechanism  28  for moving an image capturing range of the tomosynthesis image capturing device  12  in the longitudinal direction of the subject  16 , the three-dimensional image reconstructing unit  30  for generating a single three-dimensional image from a plurality of radiation images captured in a single image capturing range, the three-dimensional image joining unit  32  for joining a plurality of three-dimensional images generated by the three-dimensional image reconstructing unit  30  with respect to a plurality of image capturing ranges, in the longitudinal direction of the subject  16 , and the image generating unit  34  for generating a tomographic image on an arbitrary image plane  116  based on a joined three-dimensional image produced by the three-dimensional image joining unit  32 . Using the three-dimensional image acquired in the tomosynthesis image capturing, the radiation image capturing apparatus  10  is capable of easily producing a tomographic image on the image plane  116  across the elongate subject  16 , for thereby effectively shortening medical procedures that are performed using the radiation image capturing apparatus  10 . 
     The radiation conversion panel  18  of the radiation image capturing apparatus  10  described above converts the incident radiation directly into an electrical signal corresponding to the amount of the radiation by means of the photoelectric conversion layer  51  (i.e., direct conversion type). Instead, the radiation conversion panel may, however, convert the incident radiation into visible light with a scintillator and then the visible light into an electrical signal using solid-state detecting elements such as a-Si (i.e., indirect conversion type, see Japanese Patent No. 3494683). 
     The radiation image information may also be acquired with light readout type radiation conversion panels. In light readout type radiation conversion panels, a two-dimensional array of solid-state detecting elements receives radiation and stores an electrostatic latent image corresponding to the amount of radiation. Readout of the latent image is carried out by applying reading light onto the radiation conversion panel and utilizing the value of the electrical current generated by the radiation conversion panel as radiation image information. After reading out the radiation image information, the latent image and the radiation image information of the radiation conversion panel can be erased by irradiating the radiation conversion panel with erasing light, so that the radiation conversion panel can be reused (see Japanese Laid-Open Patent Publication No. 2000-105297). 
     While the radiation conversion panel  18  of the radiation image capturing apparatus  10  utilizes the thin-film transistors (TFTs)  52  in the above-mentioned embodiments, such a device as a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor) device or the like may also be used instead of the TFTs  52 . 
     Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.