Abstract:
An X-ray image display apparatus for exposing a subject to an X-ray to obtain an X-ray image of the subject, picking up the X-ray image, converting it to a digital video signal, performing necessary signal processing on the digital video signal in an image processor to obtain X-ray image data, and displaying, on a display device, an image of a display area included in the X-ray image and specified by an input device includes a display area detector for detecting display area data representing the specified display area, and a control circuit for outputting a control signal to control a collimator drive circuit and/or a filter drive circuit on the basis of the display area data detected by the display area detector and x-ray image data supplied from the image processor, thereby controlling the position of a collimator and/or a filter so as to display the image of the display area optimally.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 08/398,808 filed on Mar. 6, 1995. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an X-ray image display apparatus for exposing a subject to an X-ray and thereby performing fluoroscopy and radiography on a subject region, and in particular to an X-ray image display apparatus in which a compensation filter and a collimator can be controlled so as to display an image satisfactorily on an image display device. 
     As shown in FIG. 1, a conventional X-ray image display apparatus of this kind includes a bed  2  for placing a subject  1  thereon, an X-ray tube  3  for exposing the subject  1  to an X-ray, an X-ray detector  4  disposed on the opposite side of the bed  2  from the X-ray tube  3  to convert an image of the X-ray transmitted through the subject  1  to a visible light image, a support  5  for supporting the X-ray tube  3  and the X-ray detector  4 , a television camera  6  for scanning the visible light image supplied from the X-ray detector  4  and outputting a video signal, an A/D converter  7  for converting the video signal supplied from the television camera  6  to a digital signal, a display processor  8  for processing the digital signal supplied from the A/D converter  7  and converting the processed image data to a video signal, an image display device  9  for displaying the video signal inputted from the display processor  8  as an image, a compensation filter  10  disposed between the X-ray tube  3  and the subject  1  to partially an X-ray exposure dose, a filter control circuit  11  for manually adjusting the position of the compensation filter  10 , a collimator  12  disposed on an output face of the X-ray tube  3  to partially interrupt the X-ray, and a collimator control circuit  13  for manually adjusting the collimator  12 . The display processor  8  includes an image processor  14  for conducting processing such as frequency emphasis and subtraction on the digital signal supplied from the A/D converter  7 , and a display circuit  15  for converting image data supplied from the image processor  14  to a video signal. In FIG. 1, numeral  16  denotes an X-ray controller for controlling the operation of the X-ray tube  3 , and numeral  17  denotes a support controller for controlling driving of the bed  2  and the support  5 . 
     In such an X-ray image display apparatus, an unnecessary part near the X-ray emitted from the X-ray tube  3  or a part where severe halation has occurred is interrupted by manually adjusting the collimator control circuit  13  while observing the image displayed on the image display device  9 . As for a part having brightness close to that of halation, the brightness is lowered by adjusting the filter control circuit  11 . 
     As an improvement to the conventional technique as shown in FIG. 1, a circuit for automatically controlling the filter control circuit  11  and the collimator control circuit  13  by using image data generated by the display processor  8  may occur to those skilled in the art. The circuit shown in FIG. 2 is a development of the conventional technique, and corresponds to an intermediate technique located between the conventional technique and the present invention. 
     In the X-ray image display apparatus shown in FIG. 2 with such an improvement added thereto, automatic control of the compensation filter  10  for removing unnecessary parts of the X-ray emitted from the X-ray tube  3  is exercised on the basis of a suitable control position calculated by the filter control circuit  11  by using image data taken in from the image processor included in the display processor  8 . Representive examples of such calculation and control will now be described by referring to FIG.  3 . FIG. 3 shows an output image region of the X-ray detector  4  including an X-ray image intensifier. The output image region is included in the scanning region of the television camera  6 . The output image region is circular in shape. Therefore, the inside of a circle denoted by numeral  4  becomes an effective image region. The circular region is divided into a plurality of region blocks a, b, c, . . . , u. A representative value included in each region block is compared with a reference value. On the basis thereof, the filter control circuit  11  makes a calculation to determine whether the compensation filter  10  should be used or not. In general, it is desirable to conduct weighting in the central part and the peripheral part in the circular region and exercise control so as to form a satisfactory image in the central part. In case the X-ray passes outside the subject  1 , i.e., the X-ray is directly incident upon the peripheral part of the X-ray detector  4 , or in case a large quantity of contrast medium gathers in one place in subject  1  and hence the place can be judged to be a dark portion, it is also possible to exercise such control as to disregard the representative value of the region block of that part. A control signal based upon calculation in the filter control circuit  11  is sent to the compensation filter  10  to control the position of the compensation filter  10 . By exercising such feedback control, a satisfactory image having reduced halation is obtained in fluoroscopy of a target part of the subject  1 . 
     In recent years, advancements in image processing techniques have made it possible to expand and display moving pictures in real time and perform filtering on images in a video processing circuit. Expansion display been conventionally performed by changing the size of the image intensifier functioning as the X-ray detector  4 . In angiography of the subject  1 , however, a catheter and a guide wire have become very thin. In case expansion is performed only by stepwise changing the pickup range of the display screen of the image intensifier, the display area becomes narrower as the expansion ratio is increased. When the image is expanded, therefore, the catheter or wire might depart from the display range and be lost. Or even if the subject moves or the bed is slightly moved during display of an expanded image, the catheter or wire might depart from the display range and be lost. Thus, such expansion display has become uncapable of coping with such disadvantages. Therefore, expansion display using the display circuit  15  shown in FIG.  2  and digital processing has been put to use. In this case, an arbitrary area can be expanded or compressed at an arbitrary magnification owing to digital processing. In FIG. 4, the picked-up image area is represented by a square region E. FIG. 5 shows the display image area of the image display device  9 . If, as an example, region blocks e, f, g, j, k,  1 , o, p and q in the area included in the square region E shown in FIG. 4 are expanded by the display circuit  15 , only the portion including the region blocks e, f, g, j, k, l, o, p and q is expanded and displayed on the screen of the image display device  9  as shown in FIG.  5 . By using the image thus expanded and displayed, even a fine cathether can be easily manipulated. 
     In case expansion display using the display circuit  15  and digital processing is made in the image display in such an X-ray image diagnostic apparatus, the image in the area included in the square region E shown in FIG. 4 is taken in and the compensation filter  10  is controlled by the filter control circuit  11  by using representative values of respective region blocks e, f, g, j, k, l, o, p and q. Therefore, a satisfactory image is obtained as the entire image in the region  4 . As for the expanded and displayed image portion shown in FIG. 5, however, a satisfactory display image is not obtained. The peripheral region shown in FIG. 4 is an area which is not observed. In the portion including the region blocks a, b, c, h, m, r, d, i, n, s, t and u, the subject  1  is thus subjected to unnecessary X-ray exposure. Therefore, the subject  1  is subjected to unnecessary exposure to the X-ray. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an X-ray image display apparatus in which the position of a compensation filter or a collimator is controlled on the basis of display image data so as to display an image most satisfactorily. 
     Another object of the present invention is to provide an X-ray image display apparatus in which the position of a collimator is controlled on the basis of display image data so as to reduce exposure of a portion of the subject which is not displayed on the image to the X-ray. 
     In X-ray image display apparatuses, an X-ray image obtained by an X-ray detector is picked up by a television camera and the X-ray image thus picked up is subjected to image processing in a display processor and displayed on an image display device. However, the image actually displayed on the image display device is different from the X-ray image obtained by the X-ray detector. Even if an adjustment is made so as to optimize the X-ray image, therefore, it does not necessarily follow that the image displayed on the image  10  display device is optimized. 
     In accordance with the present invention, therefore, the apparatus includes a display area detector for detecting, on the basis of display image data processed by a display processor, a display area included in an X-ray image obtained by an X-ray detector and displayed on an image display device, and the position of a compensation filter or a collimator is controlled so as to optimize the X-ray image in the display area detected by the display area detector. 
     In accordance with another aspect of the present invention, the position of the collimator is controlled so as to expose only the part of the subject associated with the display area to the X-ray without exposing parts of the subject other than the display area detected by the display area detector to the X-ray. 
     In accordance with still another aspect of the present invention, a compensation filter for decreasing X-ray exposure dose is inserted for a portion brought to a halation state or a near-halation state and included in a display area detected by the display area detector, and the position of the compensation filter is controlled so as to make an image displayed on an image display device satisfactory. In particular, the X-ray directed to portions other than the display area is interrupted by a collimator to prevent the subject from being exposed to the X-ray. When an especially severe halation portion included in the display area cannot be sufficiently reduced by a compensation filter alone, the X-ray directed to that portion may be interrupted by inserting a collimator. 
     Operation of the X-ray image display apparatus thus configured will now be described. An image signal supplied from a display processor is inputted to a display area detector connected to the display processor. An image display area is detected by the display area detector. An image signal of the detected display area is sent to a filter control circuit. The compensation filter or collimator of the X-ray tube is controlled on the basis of the image signal of the display area by operation of this filter control circuit. As a result, the compensation filter or collimator can be controlled optimally. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a conventional X-ray image display apparatus; 
     FIG. 2 is a block diagram showing an X-ray image display apparatus obtained by partially improving the apparatus illustrated in FIG.  1  and situated midway in technical level between the conventional technique and the present invention; 
     FIG. 3 is a diagram for explaining an example of feature value extraction of an image picked up in the apparatus shown in FIG. 2; 
     FIGS. 4 and 5 are diagrams showing the range of a display image area of a display device in the apparatus shown in FIG. 2; 
     FIG. 6 is a block diagram showing an embodiment of the present invention; 
     FIG. 7 is a block diagram showing a detailed configuration of a principal part of FIG. 6; 
     FIG. 8 is a flow chart showing an example of operation in the embodiment illustrated in FIGS. 6 and 7; 
     FIGS. 9 through 13 are diagrams for explaining functions of the present invention; 
     FIG. 14 is a flow chart showing another example of operation in the embodiment illustrated in FIGS. 6 and 7; 
     FIG. 15 is a diagram for explaining another example of operation of the present invention; and 
     FIG. 16 is a flow chart showing another example of operation of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, embodiments of the present invention will be described in detail by referring to the attached drawings. 
     FIG. 6 is a block diagram showing an embodiment of an X-ray image display apparatus according to the present invention. Components corresponding to those of FIG. 2 are denoted by like numerals. This X-ray image display apparatus is used to expose a subject  1  to the X-ray and perform fluoroscopy and radiography on a target part. As shown in FIG. 6, the X-ray image display apparatus includes a bed  2 , a support  5  for supporting an X-ray tube  3  and an X-ray detector  4 , a television camera  6 , an A/D converter  7 , a display processor  8 , an image display device  9 , a compensation filter  10 , a filter drive circuit  11 , a collimator  12 , a collimator drive circuit  13 , a control circuit  19 , and a display area detector  18 . 
     A subject  1  is laid down on the upper face of the bed  2 . The bed  2  is raised up or tilted to assume various positions such as a horizontal position, an oblique position and an upright position. The X-ray tube  3  emits an X-ray onto the subject  1  laid down on the bed  2 . The X-ray irradiation is controlled by a control signal outputted from an X-ray controller  16  which will be described later. An image of the X-ray emitted from the X-ray tube  3  and transmitted through the subject  1  is incident upon the X-ray detector  4 . The X-ray detector  4  converts the X-ray image to a visible light image. The X-ray detector  4  includes an X-ray image intensifier, for example. Furthermore, the X-ray tube  3  is disposed on the opposite side of the bed  2  from the X-ray detector  4 . The X-ray tube  3  and the X-ray detector  4  are supported on opposite ends of the support  5  called C-arm, for example. The support  5  is controlled so as to conduct a movement such as rotation by a control signal outputted from a support controller  17  which will be described later. 
     The television camera  6  scans the visible light image converted and outputted by the X-ray detector  4  and outputs a video signal. The A/D converter  7  is supplied with the video signal outputted from the television camera  6 . The A/D converter converts the video signal to a digital signal. The display processor  8  processes the digital signal supplied from the A/D converter  7  and converts image data thus processed to a video signal. The display processor  8  includes an image processor  14  and a display circuit  15 . The image processor  14  conducts processing such as frequency emphasis processing (processing for amplifying a high-frequency component included in the video signal and emphasizing contours of the image) and subtraction processing (processing for subtracting an image obtained before injection of a contrast medium into a blood vessel from an image obtained after injection of the contrast medium and displaying only the image of the blood vessel) on the digital signal supplied from the A/D converter  7 . A display area to be displayed on the image display device  9  is inputted to the display circuit  15  to select the display area by a console  20 . The display circuit  15  extracts image data associated with the selected display area from image data supplied from the image processor  14  and converts the extracted image data to a video signal. The image display device  9  is supplied with the video signal from the display circuit  15  and displays the video signal as an image. For example, a television monitor is used as the image display device  9 . 
     The compensation filter  10  functions to decrease the quantity of the X-ray irradiated upon a part of the subject and included in the X-ray emitted from the X-ray tube  3  toward the subject  1 . For example, the compensation filter  10  is formed by a plurality of plate members including aluminum or copper. The compensation filter  10  is disposed so as to be movable parallel to a face of the X-ray tube  3  opposed to the subject  1 . The control circuit  19  is supplied with image data processed by the image processor  14  in the display processor  8  as described below. On the basis of the image data, the control circuit  19  calculates control positions of the filter and collimator and controls the compensation filter  10  and the collimator  12  via the filter drive circuit  11  and the collimator drive circuit  13 , respectively. The control circuit  19  sends control signals S 1  and S 2  based upon the result of calculation to the filter drive circuit  11  and the collimator drive circuit  13 , respectively. The collimator  12  partially interrupts the X-ray emitted from the X-ray tube  3  toward the subject  1 . The collimator  12  includes a plurality of plate members formed by an X-ray absorbing material such as lead. The collimator  12  is disposed so as to be movable between the output face of the X-ray tube  3  and the compensation filter  10 . The control circuit  19  is supplied with image data processed by the image processor  14 . The control circuit  19  functions to calculate the control position of the collimator and controls the collimator  12 . Via the collimator drive circuit  13 , the control circuit  19  sends a control signal S 2  based upon the result of calculation to the collimator drive circuit  13 . 
     In FIG. 6, the X-ray controller  16  is provided to control the operation of the X-ray tube  3 . The X-ray controller  16  sets X-ray conditions such as tube voltage, tube current and exposure time. The support controller  17  is provided to control driving of the bed  2  and the support  5 . The support controller  17  raises or tilts the bed  2  so as to attain a position such as a horizontal, oblique or upright position, and rotates the support  5  suitably. Thus, the support controller  17  exercises movement control. A combination of movements of the bed  2  and the support  5  allows positioning in a large number of positions in fluoroscopy and radiography. 
     In accordance with the present invention, the display area detector  18  is connected to the display circuit  15  included in the display processor  8  and a detection signal S 3  of the display area detector  18  is sent to the control circuit  19 . This display area detector  18  is supplied with a video signal from the display circuit  15  to detect the display area of an image displayed on the image display device  9 . For example, the display area detector  18  detects an image signal of the display area in expansion or compression display and sends the image signal as the detection signal S 3 . By using both the image data processed by the image processor  14  and the image signal of the display area of the image display device  9  detected by the display area detector  18 , therefore, the control circuit  19  calculates the control position of the filter and controls the position of the compensation filter  10 . 
     With reference to FIG. 7, mutual relations of the image processor  14 , the display circuit  15 , the control circuit  19  and the display area detector  18  and internal configurations of them will now be described in more detail. 
     With reference to FIG. 7, the digital signal supplied from the A/D converter  7  is subjected to image data processing in the image processor  14  and then stored in a field memory  22  included in the display circuit  15 . Therefore, image data stored in this field memory  22  are data of the entire image picked up by the television camera  6 . On the basis of a display area specifying command supplied by an operator via the console  20 , a digital signal processor  23  generates image data of the specified display area from image data stored in the field memory  22  by using a conventionally known method and stores the generated image data into a display memory  24 . A D/A converter  25  successively reads out image data stored in the display memory  24 , performs D/A conversion on the image data thus read out, and transmits the D/A converted image data to the image display device  9  as a video signal. 
     A field memory  26  and a display memory  27  included in the display area detector  18  regularly take in image data stored in the field memory  22  and the display memory  24  included in the display circuit  8 , respectively. A digital signal processor  28  compares and collates image data stored in the field memory  26  with image data stored in the display memory  27 , calculates data representing coordinates of the display area, and stores the calculated data into a register  30  included in the control circuit  19 . Another register  31  stores image data successively subjected to signal processing in the image processor  14 . 
     On the basis of data stored in the registers  30  and  31 , a CPU (central processing unit)  32  operates according to a flow chart shown in FIG.  8 . The CPU  32  sends control signals to the filter drive circuit  11  and the collimator drive circuit  13  via an interface  33  to control positions of the compensation filter  10  and the collimator  12 , respectively. The concept of this control operation will hereafter be described. 
     In FIG. 9, a picked-up image area for expansion display included in the output image region of the X-ray detector  4  is represented by a square region E in the same way as FIG.  4 . As an example, the case where region blocks d, e, f, i, j, k, n, o and p included in the region E are expanded and displayed is illustrated. FIG. 11 shows an expanded display of region blocks d, c, f, i, j, k, n, o and p of a display image area on the image display device  9 . 
     FIG. 12 shows the case where region blocks of the whole image are weighted and displayed in the output image region of the X-ray detector  4 . That is to say, a circular output image region is divided into three concentric circle regions A 1 , A 2  and A 3 , for example. The region block k located at the center of the innermost region A 1  is provided with the largest weight. Each of the region blocks e, f, g, j, l, o, p and q included in the second region A 2  located outside of the region A 1  is provided with the second largest weight. Furthermore, each of the region blocks a, b, c, d, h, i, m, n, r, s, t and u included in the third region A 3  located outside of the second region A 2  is provided with the third largest weight. Thereby, the innermost region Al is given priority. As shown in FIG. 13, for example, four filter blades  10   a  through  10   d  of the compensation filter  10  according to the intermediate technique shown in FIG. 2 can move from the periphery toward the center. And the four filter blades  10   a  through  10   d  are set so as to limit the irradiation X-ray on the outside of the second region A 2 . 
     However, weighting of display regions and control of the compensation filter  10  in the example of the technique shown in FIGS. 12 and 13 have the following drawback. In case the square region E shown in FIG. 9 is desired to be expanded and displayed, the difference in weight between the region blocks i and k is large and suitable control of the compensation filter  10  cannot be expected if weighting as shown in FIG. 12 is used. In case of FIG. 9, therefore, the region block j located at the center of the square region E should be provided with the largest weight, and region blocks d, e, f, i, k, n, o and p located outside the region block j should be provided with the second largest weight. Thereby, the region block j located at the center of the square region E is given priority. As shown in FIG. 10, for example, four filter blades  10   a  through  10   d  (where  10   d  is not illustrated) of the compensation filter  10  according to the present invention shown in FIG. 6 can move from the periphery toward the center of the square region E. And the four filter blades  10   a  through  10   d  are set so as to limit the irradiation X-ray on the outside of the region E. In case the expansion region E shown in FIG. 9 has moved to another location, the above described operation should be executed again for a new region block located at the destination of the movement. Owing to such operation, control of the compensation filter  10  suitable for the expanded and displayed image can be exercised. 
     Operation of the CPU  32  included in the control circuit  19  in the embodiment of the present invention heretofore described will now be described by referring to a flow chart shown in FIG.  8 . 
     In FIG. 8, processing begins at “START”. At step  35 , image data of respective pixels stored in the register  31  are read out for all region blocks a through u shown in FIG. 9, and the arithmetic mean, maximum and minimum of magnitude values of all pixel data are calculated for each of the region blocks and stored in a memory included in the CPU  32 . 
     At step  36 , coordinates of a display area to be subjected to expansion display are read out from the register  30  and a region block j located at the center of the display area is determined. This block j is provided with the largest weight, and region blocks located outside the region block j are provided with the second largest weight. Region blocks located outside region blocks provided with the second largest weight are provided with the third largest weight. The larger a weight a region has, the harder a filter makes it. 
     At step  37 , a representative value of each region block is determined on the basis of the value calculated at step  35 . As this representative value, the arithmetic mean value is typically used. Alternatively, the maximum value may be used. At step  38 , the representative value of each region block is compared with a predetermined value giving a reference of halation. Depending upon whether the representative value exceeds the predetermined value, it is determined whether halation exists. When halation exists, it is determined which coordinate values the region block wherein halation exists has. 
     If it is found at step  38  that no halation exists for every region block, processing proceeds to “END.” If halation exists, however, a filter located nearest to a coordinate position of a region block involving halation is inserted as far as that position at step  39 . It is checked at step  40  whether halation has disappeared as a result. If halation is judged to have disappeared at step  40 , processing proceeds to “END.” If halation still exists, it is determined at step  41  whether an adjacent filter can be inserted as far as the position of the halation. If it is possible, that adjacent filter is inserted at step  42 . Furthermore, it is checked at step  43  whether halation has disappeared. If halation is judged to have disappeared at step  43 , processing proceeds to “END.” If halation still exists, processing proceeds to step  44 . It is determined at step  44  whether the region block involving halation is within the display area. 
     Also, when it is determined at step  41  that the adjacent filter cannot be inserted, processing skips to step  44 . 
     When the region block involving halation is judged at step  44  to be on the outside of the display area, the display picture is not affected even if the X-ray is interrupted and hence the collimator is inserted as far as that region block at step  47  and processing proceeds to “END.” When the region block involving halation is judged at step  44  to be within the display area, it is determined at step  45  whether the region block involving halation is located in such a position that a bad influence is not exerted upon the displayed image even if the collimator is inserted. If the result of judgment is “YES,” the collimator is inserted as far as that region block and processing proceeds to “END.” If the result of judgment is “NO,” there is no further way to cope with the halation and hence processing directly proceeds to “END.” 
     Operation of the circuit configuration shown in FIG. 6 has heretofore been described by referring to the flow chart of FIG.  8 . Another example of operation will now be described by referring to FIG. 14. A region calculation processing step  101  and a filter insertion processing step  102  shown in FIG. 14 correspond to steps  35  through  37  and steps  38  through  43  shown in FIG. 8, respectively. 
     With reference to FIG. 14, processing begins at “START.” started. At step  101 , the same operation as steps  35  through  37  of FIG. 8 is conducted. Processing then proceeds to step  50 . At step  50 , it is determined whether halation exists. If the result of judgment at step  50  is “NO,” processing proceeds directly to “END.” If the result of judgment at step  50  is “YES,” it is determined at step  51  whether the position of halation is within the display area. If the result of judgment at step  51  is “NO,” the position of halation is located outside the display area and hence the X-ray is desired to be interrupted. At step  52 , therefore, a collimator is inserted as far as the existence position of halation and processing proceeds to “END.” 
     If the result of judgment at step  51  is “YES,” filter insertion processing is conducted at step  102 . This processing is identical with steps  38 - 43  of FIG.  8 . If the result of judgment at step  38 ,  40  or  43  included in this processing is “NO,” processing proceeds to “END.” If halation still exists, it is determined at step  53  whether the collimator can be inserted as far as the position of the collimator. If the result of judgment at step  53  is “YES,” the collimator is inserted at step  52  and processing proceeds to “END.”If the result of judgment at step  53  is “NO,” processing proceeds directly to “END.” 
     In case the expansion display region E shown in FIG. 9 is small, weights of region blocks d, e, f, i, j, k, n, o and p in the region E may have the same magnitude. In the embodiment of FIG. 6, information supplied from the image processor  14  included in the display processor  8  and information supplied from the display area detector  18  are inputted to the control circuit  19  to control the compensation filter  10 . However, this is not restrictive. Instead of providing the display area detector  18  and the control circuit  19 , weighting of region blocks and calculation of the representative values in all display images including the expansion image may be executed in the display circuit  15  included in the display processor  8 . 
     The concept of another embodiment of the present invention will now be described by referring to FIG.  15 . FIG. 15 shows the case where region blocks d, e, f, i, j, k, n, o and p included in the output image region of the X-ray detector  4  are expanded and displayed in the same way as in FIG.  9 . In this case, four X-ray blocking members  12   a ,  12   b ,  12   c  and  12   d  (where  12   d  is not illustrated) of the collimator  12  are inserted from the periphery by control operation of the collimator drive circuit  13 , and the region outside of the region blocks d, e, f, i, o, k, n, o and p is completely covered to interrupt the irradiation X-ray. At this time, the compensation filter  10  is also moved simultaneously by control operation of the filter drive circuit  11 . Positions of the filter blades  10   a  through  10   c  are thus set as shown in FIG.  10 . By the way, even if only the X-ray interruption performed by position control of the collimator  12  is used, there is an effect of preventing X-ray exposure. Control of the compensation filter  10  is exercised for the purpose of preventing halation in the display area. 
     This embodiment is implemented by the circuit configuration shown in FIGS. 6 and 7. The CPU  32  included in the circuit configuration executes operation of this embodiment according to a flow shown in FIG.  16 . In FIG. 16, steps corresponding to those of FIG. 14 are denoted by like numerals. 
     With reference to FIG. 16, region calculation processing similar to that described before is first conducted at step  101 . Then, at step  55 , the collimator is inserted so as to leave the display area as shown in FIG.  15 . Thus, the subject is not exposed to unnecessary X-ray irradication. At step  102 , the position of the compensation filter  10  is controlled in processing for eliminating halation existing in the display area similar to that described before. Thereafter, operation completely identical with that of FIG. 14 is conducted. 
     In the above described embodiment, the display area detector  18  takes in an image signal from the display circuit  15  included in the display processor  8 . The present invention is not limited to this. Alternatively, a signal may be taken in directly from the image processor  14  which is also included in the display processor  8 . 
     Owing to the configuration of the present invention heretofore described, an image signal from a display processor is inputted to a display area detector connected to the display processor. The display area of the image is detected in the display area detector. The image signal of the detected display area is sent to a filter drive circuit. Owing to operation of this filter drive circuit, a compensation filter and a collimator of an X-ray tube can be controlled by using the image signal of the display area as well. Therefore, even if collected images are expanded and displayed, for example, therefore, positions of the compensation filter and the collimator can be controlled and set so as to optimize the image of the area of expansion display. 
     Furthermore, the image signal of the display area detected by the display area detector is sent to the filter drive circuit and the collimator drive circuit. The compensation filter is controlled by operation of the filter drive circuit, and the collimator is controlled by operation of the collimator drive circuit. The X-ray irradiation of the portion except the display area can thus be interrupted. As a result, the compensation filter and the collimator can be controlled optimally. In this case, undesired exposure of the suject to the X-ray can be prevented more efficiently.