Abstract:
An X-ray image diagnosing apparatus has a radiating unit, a placement unit, a detecting unit, a supporting unit, a moving control unit, an obtaining unit, a calculating unit, and a frame rate control unit. The placement unit is placeable an object. The supporting unit supports the radiating unit and the detecting unit in opposing relationship across the placement unit. The moving control unit relatively moves the supporting unit and the object on a longwise direction of the placement unit so as to perform an X-ray imaging at different imaging positions along the longwise direction. The obtaining unit obtains X-ray image by performing the X-ray imaging. The calculating unit calculates blood-vessel data on the basis of the X-ray image and calculates a frame rate on the basis of the blood-vessel data. The frame rate control unit configured to change the frame rate on the X-ray imaging.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an X-ray image diagnosing apparatus and a controlling method of that for displaying a plurality of X-ray images acquired in different positions. 
     2. Description of the Related Art 
     A known X-ray image diagnosing apparatus for acquiring an image of blood vessels in which contrast is enhanced using a contrast medium includes an X-ray source and an FPD or an I. I. equipped at both ends of a substantially C-shaped holder (C-arm), respectively, and an image processing unit. This X-ray image diagnosing apparatus is generally also referred to as an angiography apparatus, which allows diagnosis and treatment (medical treatment), such as insertion of a catheter into an object such as a patient by a doctor, and acquisition of an X-ray image. 
     One of examinations using the X-ray image diagnosing apparatus is a lower-extremity angiography examination. In the lower-extremity angiography examination, an image of the entire long and narrow image-acquisition region from the abdomen to the tiptoe is acquired while a contrast medium injected through a catheter proceeded to the abdominal aorta is traced. In the acquisition of an image of the entire image-acquisition region, the entire image cannot be acquired at a time, so that images of the entire image-acquisition region are acquired in several times. In this case, injecting the contrast medium every image-acquisition exerts a large burden on the patient. Therefore, a method for acquiring an image of the entire image-acquisition region from the abdomen to the tiptoe by one injection of the contrast medium was devised. When a proper quantity of contrast medium is injected, the part dyed with the contrast medium flows from the abdomen toward the tiptoe in the blood stream. The image-acquisition is repeated while the stream is traced. 
     There are two kinds of image-acquisition method, that is, bolus-chase angiography and stepping angiography. The mask images of the entire image-acquisition region are collected using either of the two kinds of image-acquisition method, and after a contrast medium is injected into the patient, the contrast images of the entire image-acquisition region are collected to execute a digital subtraction angiography (DSA). Then, the mask images and the contrast images are subjected to subtraction processing in which they are differentiated every image-acquisition position to generate difference images (DSA images). When the plurality of DSA images at the image-acquisition positions are bonded together, a long image that displays the entire image-acquisition region from the abdomen to the lower extremity in which all the blood vessels are drawn is generated. 
     As an art related to the present invention, Japanese Unexamined Patent Application Publication No. 2004-236910 is disclosed. 
     However, with this related art, if X-ray exposure is performed at a fixed frame rate, DSA images taken at a plurality of image-acquisition positions each include a portion that can be sufficiently checked (diagnosed) with one DSA image, which will increase the amount of X-ray exposure of the patient. 
     Moreover, in angiography of narrow blood vessels, such as those of a lower extremity, the narrow blood vessels are lost in the noise on the DSA images, thus sometimes making it difficult to view the running blood vessels. 
     Furthermore, it is necessary for the DSA to set (register) image-acquisition positions in advance, which is inefficient for the operator to execute X-ray diagnosis. 
     SUMMARY OF THE INVENTION 
     The present invention is made in consideration of the above-described circumstances. Accordingly, it is an object of the present invention to provide an X-ray image diagnosing apparatus and a controlling method of that in which X-ray exposure of a patient can be reduced and an optimum X-ray image diagnosing environment for the operator can be provided. 
     To solve the above-described problems, the present invention provides the X-ray image diagnosing apparatus comprising: a radiating unit configured to radiate X-rays; a placement unit which is placeable an object; a detecting unit configured to detect X-rays that passed through the object; a supporting unit configured to support the radiating unit and the detecting unit in opposing relationship across the placement unit; a moving control unit configured to relatively move the supporting unit and the object on a longwise direction of the placement unit so as to perform an X-ray imaging at different imaging positions along the longwise direction; an obtaining unit configured to obtain X-ray image by performing the X-ray imaging; a calculating unit configured to calculate blood-vessel data indicating at least one of diameters and concentrations of blood vessels on the basis of the X-ray image, and to calculate a frame rate on the basis of the blood-vessel data; and a frame rate control unit configured to change the frame rate on the X-ray imaging. 
     To solve the above-described problems, the present invention provides the X-ray image diagnosing apparatus comprising: a radiating unit configured to radiate X-rays; a placement unit which is placeable an object; a detecting unit configured to detect X-rays that passed through the object; a supporting unit configured to support the radiating unit and the detecting unit in opposing relationship across the placement unit; a moving control unit configured to relatively move the supporting unit and the object on a longwise direction of the placement unit so as to perform an X-ray imaging at different imaging positions along the longwise direction; a setting unit configured to preliminarily set an imaging condition that respective frame rates and the respective imaging positions are associated with each other; and an obtaining unit configured to obtain X-ray image by performing the X-ray imaging on the frame rates corresponding to the respective imaging positions in accordance with the imaging condition. 
     To solve the above-described problems, the present invention provides the controlling method of the X-ray image diagnosing apparatus including a radiating unit configured to radiate X-rays, a placement unit which is placeable an object, a detecting unit configured to detect X-rays that passed through the object, and a supporting unit configured to support the radiating unit and the detecting unit in opposing relationship across the placement unit, comprising; a moving control step of relatively moving the supporting unit and the object on a longwise direction of the placement unit so as to perform an X-ray imaging at different imaging positions along the longwise direction; an obtaining step of obtaining X-ray image by performing the X-ray imaging; a calculating step of calculating blood-vessel data indicating at least one of diameters and concentrations of blood vessels on the basis of the X-ray image, and calculating a frame rate on the basis of the blood-vessel data; and a frame rate control step of changing the frame rate on the X-ray imaging. 
     To solve the above-described problems, the present invention provides the controlling method of the X-ray image diagnosing apparatus including a radiating unit configured to radiate X-rays, a placement unit which is placeable an object, a detecting unit configured to detect X-rays that passed through the object, and a supporting unit configured to support the radiating unit and the detecting unit in opposing relationship across the placement unit, comprising: a moving control step of relatively moving the supporting unit and the object on a longwise direction of the placement unit so as to perform an X-ray imaging at different imaging positions along the longwise direction; a setting step of preliminarily setting an imaging condition that respective frame rates and the respective imaging positions are associated with each other; and an obtaining step of obtaining X-ray image by performing the X-ray imaging on the frame rates corresponding to the respective imaging positions in accordance with the imaging condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a schematic diagram showing an example of the hardware configuration of an X-ray image diagnosing apparatus of present embodiments; 
         FIG. 2  is a diagram showing an example of an arrangement of a display device that constitutes the X-ray image diagnosing apparatus of present embodiments; 
         FIG. 3  is a block diagram showing functions of the X-ray image diagnosing apparatus of a first embodiment; 
         FIG. 4  is a diagram showing average values at individual pixels in vicinity of branches of blood vessels; 
         FIG. 5  is a diagram showing luminance values at the individual pixels in the vicinity of the branches of the blood vessels after filtering; 
         FIG. 6  is a diagram showing a relationship between a long image and individual FOVs of the long image with a known single frame rate; 
         FIG. 7  is a diagram showing a relationship between a long image and the individual FOVs of the long image with the imaging by the image condition according to the first embodiment; 
         FIG. 8  is a block diagram showing functions of the X-ray image diagnosing apparatus of a second embodiment; 
         FIG. 9  a diagram showing a relationship between the long image and the FOVs of the long image by a pilot DSA angiography; 
         FIG. 10  is a block diagram showing functions of the X-ray image diagnosing apparatus of a third embodiment; 
         FIG. 11  is a schematic diagram for explaining a method for calculating blood-vessel data; 
         FIG. 12  is a diagram showing an example of plurality of correlation tables in graphical form; and 
         FIG. 13  is a flowchart showing an operation of the X-ray image diagnosing apparatus of the third embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     X-ray image diagnosing apparatuses and controlling methods of those according to embodiments of the present invention will be described with reference to the attached drawings. 
     An angiography apparatus, or an X-ray image diagnosing apparatus, includes a digital subtraction angiography (DSA) mode. In the DSA imaging mode, X-ray transmission images (mask images) that do not include an image of a contrast medium and 2-D X-ray transmission images (contrast images or live images) that include an image of a contrast medium are subjected to subtraction processing to generate difference images (DSA images), and the DSA images can be displayed or stored. 
       FIG. 1  is a schematic diagram showing an example of the hardware configuration of an X-ray image diagnosing apparatus of a first embodiment. 
     Referring to  FIG. 1 , the angiography apparatus  10 , or the X-ray image diagnosing apparatus, is broadly constituted of a holding system  11  and a DF system  12 . 
     The holding system  11  includes an X-ray source (tube)  21 , a X-ray detector  22 , a C-arm  23 , a table-top (catheter table)  25 , a high-voltage supply system  26 , a driving mechanism  27 , and an automatic contrast-medium injecting system (injector)  28 . Note that the holding system  11  in this case is of an under tube type in which the X-ray source  21  is located below the table-top  25 ; alternatively, the X-ray source  21  may be of an over tube type in which the X-ray source  21  is located above the table-top  25 . Furthermore, an X-ray radiation field aperture diaphragm composed of a plurality of lead blades and a compensating filter formed of silicon rubber or the like for attenuating a predetermined amount of X-rays may be equipped to prevent halation. 
     The X-ray source  21  is equipped at one end of the C-arm  23  and emits X-rays toward an object (patient) P on the table-top  25  depending on the condition of high-voltage electric power supplied from the high-voltage supply system  26 . 
     The X-ray detector  22  is equipped at the other end of the C-arm  23  and at the exiting side of the X-ray source  21  and detects X-rays passed through the patient P on the table-top  25 . The X-ray detector  22  is based on an image intensifier (I. I.)—TV system, and has an I. I.  22   a  and a TV camera  22   b.    
     The I. I.  22   a  converts X-rays that passed through the patient P to visible light and doubles the luminance in the course of light—electrons—light conversion to form highly sensitive projection data. The TV camera  22   b  converts the optical projection data to an electric signal using a charge coupled device (CCD) image sensor. 
     The C-arm  23  supports the X-ray source  21  at one end thereof and the X-ray detector  22  at the other end in opposing relationship about the patient P. The amount, timing, and speed of the movement of the C-arm  23  are controlled by the driving mechanism  27 . 
     The table-top  25  is used to place the patient P thereon. The high-voltage supply system  26  supplies high-voltage electric power to the X-ray source  21  under the control of the DF system  12 . 
     The driving mechanism  27  moves the C-arm  23  in a circular direction of the C-arm  23  (a left anterior oblique view (LAO) direction, or a right anterior oblique view (CRA) direction), and a swinging direction (a cranial view (CRA), or a caudal view (CAU) direction). 
     When performing a lower-extremity angiography examination using the angiography apparatus  10 , the operator takes images of the entire long and narrow image-acquisition region from the abdomen to the tiptoe in a plurality of times while tracing a contrast medium injected through a catheter proceeded to the abdominal aorta of the patient P on the table-top  25 , because the entire image-acquisition region is longer than the width of the I. I.  22   a  (the length of the table-top  25  in the longitudinal direction). Thus, the driving mechanism  27  can change the relative positions of the C-arm  23  and the table-top  25  in the longitudinal direction during image-acquisition in accordance with the control of the DF system  12 . For example, the driving mechanism  27  moves the C-arm  23  parallel to the table-top  25  along the length of the table-top  25  in accordance with the control of the DF system  12 . Alternatively, the driving mechanism  27  moves the table-top  25  parallel to the C-arm  23  along the length of the table-top  25  in accordance with the control of the DF system  12 . In this embodiment, the former one is adopted. 
     Furthermore, the driving mechanism  27  moves the C-arm  23  and the table-top  25  up and down together in accordance with the control of the DF system  12 . In addition, the driving mechanism  27  moves the table-top  25  vertically, horizontally, and longitudinally in accordance with the control of the DF system  12 . The driving mechanism  27  includes a sensor  27   a  for measuring the moving distance of the table-top  25  when translating the table-top  25  in the longitudinal direction. 
     The injector  28  is a unit for injecting a contrast medium into a catheter (catheter tube (not shown)) inserted into the abdominal aorta of the patient P under the control of the DF system  12 . 
     On the other hand, the DF system  12  is based on a computer, so that it can mutually communicate with a main network N, such as a local area network (LAN), of the hospital. The DF system  12  is broadly constituted of hardware, such as an analog to digital (A-D) converter  30 , an image generator/processer  31 , an image memory  32 , an image synthesizer  33 , a display device  34 , a central processing unit (CPU)  35  serving as a processor, a comprehensive memory  36 , a hard disc drive (HDD)  37 , an input device  38 , a communication controller  39 , and a system controller  40 . The CPU  35  is mutually connected to the individual hardware components that constitute the DF system  12  via a bus serving as a common signal transmission line. The DF system  12  may include a drive (not shown) for a recording medium. 
     The A-D converter  30  converts a time-series analog signal (video signal) output from the X-ray detector  22  to a digital signal. 
     The image generator/processer  31  performs a logarithmic conversion process (LOG process) on the digital signal of the projection data output from the A-D converter  30 , performs an adding operation as necessary to generate image data (a mask images and a contrast images) for each frame, and stores the image data in the image memory  32  under the control of the CPU  35 . The image generator/processer  31  performs image processing on the image data per frame and stores the processed image data in the image memory  32 . Examples of the image processing include image-data magnification/gradation/spatial filtering processes, a minimum value/maximum value tracing process on image data that is accumulated in time series, a subtraction process, and an adding operation for removing noise. Image data, such as difference images (DSA images), subjected to the subtraction process by the image generator/processer  31  is output to the image synthesizer  33  and is stored in a storage unit, such as the image memory  32 . 
     The image memory  32  stores image data output from the image generator/processer  31  under the control of the CPU  35 . The DSA images to be stored in the image memory  32  are given patient information, image-acquisition position information (table position and stage), image-acquisition-time information, etc. 
     The image synthesizer  33  combines the image data output from the image generator/processer  31  with character information, a scale, etc. of various parameters and outputs it as a video signal to the display device  34  under the control of the CPU  35 . Specifically, the image synthesizer  33  combines the DSA images from the image generator/processer  31  with character information, a scale, etc. of various parameters and outputs it as a video signal to the display device  34 . 
       FIG. 2  is a diagram showing an example of the arrangement of the display device  34  that constitutes the angiography apparatus  10 . 
     The display device  34  includes a fluoroscopic monitor  34   a , a reference monitor  34   b , and a system monitor  34   c . The fluoroscopic monitor  34   a , the reference monitor  34   b , and the system monitor  34   c  are each constituted of a liquid crystal display, a cathode ray tube (CRT), or the like. 
     The display device  34  shown in  FIG. 1  further includes a display image memory, such as a video random access memory (VRAM, not shown), a digital to analog (D-A) converter (not shown), and a display circuit. Image data to be displayed is displayed on the display device  34  in such manner that the image data is developed in the VRAM under the control of the CPU  35 . 
     The fluoroscopic monitor  34   a  displays a mask image, a contrast image, etc. output from the image synthesizer  33  as live images. 
     The reference monitor  34   b  displays the DSA image output from the image synthesizer  33  as a still image or displays DSA images as reproduced moving images. 
     The system monitor  34   c  mainly displays data for controlling the holding system  11 , such as data for switching a field of view (FOV). 
     The CPU  35  is a control unit having a large scale integration (LSI) configuration in which a semiconductor electronic circuit is sealed in a package having a plurality of terminals. When an instruction is input through an operation on the input device  38  by an operator, such as a doctor or a radiographer, the CPU  35  executes a program stored in the comprehensive memory  36 . Alternatively, the CPU  35  loads, in the comprehensive memory  36 , a program that is stored in the HDD  37 , a program transferred via the network N, received by the communication controller  39 , and installed in the HDD  37 , or a program that is read from a recording medium mounted in the recording-medium drive (not shown) and installed in the HDD  37  and executes the program. 
     The comprehensive memory  36  is a storage unit having storage elements, such as both a read only memory (ROM) and a random access memory (RAM). The comprehensive memory  36  is a storage unit that is used for an initial program loading (IPL), a basic input/output system (BIOS), storage of data, or temporary storage of the work memory of the CPU  35  and data. 
     The HDD  37  is a storage unit having a configuration in which a metal disk to which a magnetic substance is applied or evaporated is undetachably built. The HDD  37  stores programs (including application programs installed in the DF system  12  and also an operating system (OS)) and data. The OS may also be provided with a graphical user interface (GUI) that uses many graphics to display information for the user so that the user can perform basic operations with the input device  38 . 
     The input device  38  includes a keyboard, a mouse, or the like that is operable by the operator, through which an input signal according to an operation is transmitted to the CPU  35 . The input device  38  is broadly constituted of a main console or a system console. 
     The communication controller  39  performs communication control according to individual specifications. The communication controller  39  has a function capable of connecting to the network N. Thus, the angiography apparatus  10  can connect to the network N via the communication controller  39 . 
     The system controller  40  includes a CPU and a memory (not shown). The system controller  40  controls the operations of the high-voltage supply system  26 , the driving mechanism  27 , the injector  28 , etc. of the holding system  11  in accordance with an instruction from the CPU  35 . 
       FIG. 3  is a block diagram showing the functions of the angiography apparatus  10  of the first embodiment. 
     When the CPU  35  of the DF system  12  in the angiography apparatus  10  shown in  FIG. 1  executes programs, the angiography apparatus  10  functions as an image condition setting unit  51 , a DSA image acquiring unit  52 , and a long-image generating unit  53 . Although the components  51  to  53  are described as the functions of the CPU  35 , the present invention is not limited thereto; the components  51  to  53  may be provided as hardware in the DF system  12 . 
     The image condition setting unit  51  has the function of setting an image condition including a plurality of different frame rates (image-acquisition intervals) in advance in executing DSA imaging by moving the table-top  25  (patient P) along the length of the table-top  25  with respect to the C-arm  23 . For example, the image condition setting unit  51  sets the image condition including the frame rates so that the frame rates from the abdomen (upper body) to the tiptoe (lower body) of the entire image-acquisition region including the lower extremity gradually increase. 
     The DSA image acquiring unit  52  has the function of controlling the system controller  40  in accordance with the image condition set by the image condition setting unit  51  to execute the DSA imaging of the entire image-acquisition region and the function of acquiring DSA images, or contrast images, at a plurality of image-acquisition positions from the image memory  32 . The DSA image acquiring unit  52  performs the DSA imaging for collecting mask images of the entire image-acquisition region by stepping angiography, and after a contrast medium is injected into the patient P, collecting contrast images of the entire image-acquisition region by stepping angiography. The DSA image acquiring unit  52  then performs a subtraction process whereby the mask images and the contrast images are differentiated for the individual image-acquisition positions to generate difference images (DSA images). The DSA images generated by the DSA image acquiring unit  52  are stored in a storage unit, such as the image memory  32 , together with the positional information of the table-top  25  acquired from the sensor  27   a , image-acquisition-time information, etc. 
     In the stepping angiography, the table-top  25  is moved to an image-acquisition position earlier than the arrival of the contrast medium in accordance with a first frame rate of the frame rates included in the image condition that is set by the image condition setting unit  51  and is stopped there, and an image is acquired, with the table-top  25  stopped. After the image-acquisition at the image-acquisition position is completed, the table-top  25  is moved and stopped in accordance with a second frame rate of the frame rates included in the image condition, and an image is acquired, with the table-top  25  stopped again. That is, the stepping angiography is a method for image-acquisition in which the table-top  25  is intermittently move in accordance with various frame rates to cover the entire image-acquisition region with the intermittent movement of the table-top  25 . In the stepping angiography, the DSA image acquiring unit  52  controls the system controller  40  in accordance with various frame rates to give an instruction to repeat the movement and stop of the table-top  25  and image-acquisition. 
     The long-image generating unit  53  has the function of generating a long image indicating the entire image of the lower extremity on the basis of the DSA images acquired by the long-image generating unit  53 . The long image generated by the long-image generating unit  53  is displayed (longitudinally displayed) on the reference monitor  34   b  of the display device  34  via the image synthesizer  33 . 
     For example, the long-image generating unit  53  executes a partially overlapping process in accordance with stage information on the basis of DSA images acquired in different positions by the long-image generating unit  53  to generate a long image indicating the entire low extremity. For example, the long-image generating unit  53  extracts the edges of blood vessels on the basis of a difference in luminance on the DSA images and executes the partially overlapping process to connect the blood vessels to generate a long image indicating the entire low extremity. 
     Note that a signal to noise (S/N) ratio can be improved when the long-image generating unit  53  takes the luminance value of a portion at which DSA images coincide as the average value of luminance values corresponding to the portion, determines that luminance values lower than a certain level is noise, and filters them. Since there may be branches of the blood vessels in the vicinity of the edges thereof, the long-image generating unit  53  performs the filtering not by comparing the average value with a fixed noise detecting threshold value (gain) but by comparing the average value with a weighted noise detecting threshold value. 
       FIG. 4  is a diagram showing the average values at individual pixels in the vicinity of the branches of blood vessels.  FIG. 5  is a diagram showing luminance values at the individual pixels in the vicinity of the branches of the blood vessels after filtering. 
     As shown in  FIG. 4 , the average values of the individual pixels are classified into a high average value (apparent blood vessel images), an intermediate average value (unclear whether it is a blood vessel image or noise), and a low average value (apparent noise). Pixels corresponding to the intermediate average value are determined whether they are the edges of blood vessels from the average values of surrounding pixels (the noise detecting threshold value is changed). For example, pixels in region A with the intermediate average value, in which surrounding pixels have a fixed luminance level or higher, are subjected to filtering using a larger noise detecting threshold value in consideration of the possibility that the pixels are branches of the blood vessels. For pixels in region B whose surrounding pixels have a fixed luminance level or lower shown in  FIG. 4 , a smaller noise detecting threshold is used. 
     To improve the S/N ratio, the long-image generating unit  53  may set the luminance value of a portion at which DSA images overlap as the most numerous value of the plurality of luminance values corresponding to the portion. 
       FIG. 6  is a diagram showing a relationship between the long image and the individual FOVs of the long image with a known single frame rate.  FIG. 7  is a diagram showing a relationship between the long image and the individual FOVs of the long image with the imaging by the image condition according to the first embodiment. 
     As shown in  FIG. 6 , when the DSA imaging is performed using the known single frame rate, the region from the abdomen to the inguinal region that can be sufficiently checked (diagnosed) using one DSA image is also exposed several times, which increases an exposure amount of the patient P. Moreover, images of narrow blood vessels, such as peripheral blood vessels, are lost in noise, sometimes making it difficult to view the running blood vessels. 
     On the other hand, as shown in  FIG. 7 , when the DSA imaging is performed using the imaging condition of the first embodiment, the exposure of the patient P can be decreased by reducing the number of image-acquisitions for the region from the abdomen to the inguinal region by decreasing the frame rate because the region from the abdomen to the inguinal region has so thick blood vessels that it is easy to view. On the other hand, the number of image-acquisitions is increased for the peripheral blood vessels by increasing the frame rate because the peripheral blood vessels are sometimes lost in noise. 
     With the angiography apparatus  10  of the first embodiment, the number of image-acquisitions of thick blood vessels can be decreased, so that X-ray exposure of the patient P can be reduced. Moreover, with the angiography apparatus  10 , image-acquisition positions are automatically set depending on the frame rates that constitute the image condition, so that there is no need for the operator to set image-acquisition positions in advance. Thus, an optimum X-ray diagnosis environment for the operator can be provided. 
       FIG. 8  is a block diagram showing the functions of an angiography apparatus  10 A of a second embodiment. Since the hardware configuration of the angiography apparatus  10 A of the second embodiment is the same as that of the angiography apparatus  10  of the first embodiment shown in  FIGS. 1 and 2 , a description thereof will be omitted. 
     When the CPU  35  shown in  FIG. 1  executes programs, the angiography apparatus  10 A functions as the DSA image acquiring unit  52 , the long-image generating unit  53 , a pre-DSA image acquiring unit  54 , a blood-vessel data calculating unit  55 , and an image condition setting unit  56 . Although the components  52  to  56  are described as the functions of the CPU  35 , the present invention is not limited thereto; the components  52  to  56  may be provided as hardware in the DF system  12 . The same functions of the angiography apparatus  10 A shown in  FIG. 8  as those of the angiography apparatus  10  shown in  FIG. 3  are given the same reference numerals, and descriptions thereof will be omitted. 
     The pre-DSA image acquiring unit  54  has the function of controlling the system controller  40  in accordance with a relatively low fixed frame rate for pilot angiography to execute the DSA imaging of the entire image-acquisition region including the extremity of the patient P and the function of acquiring a plurality of DSA images (contrast images) at individual image-acquisition positions from the image memory  32 .  FIG. 9  shows the relationship between a long image and the FOVs of the long image by the pilot DSA angiography. 
     The blood-vessel data calculating unit  55  has the function of extracting blood vessels using the luminance of the pre-DSA images acquired by the pre-DSA image acquiring unit  54  and calculating at least one of the diameters of the blood vessels and the luminance values of the blood vessels (the concentration of the contrast medium) as blood-vessel data. A method for calculating the blood-vessel data will be described later with reference to  FIG. 11 . 
     The image condition setting unit  56  has the function of setting a image condition including different frame rates in advance for executing the DSA imaging while moving the table-top  25  in the longitudinal direction with respect to the C-arm  23 . For example, if the blood vessel diameters calculated by the blood-vessel data calculating unit  55  are greater than or equal to a threshold value, the image condition setting unit  56  sets a low frame rate, and if the blood vessel diameters are smaller than the threshold value, the image condition setting unit  56  sets a high frame rate. The DSA image acquiring unit  52  controls the system controller  40  in accordance with the image condition set by the image condition setting unit  56  to execute the DSA imaging of the extremity of the patient P. 
     With the angiography apparatus  10 A of the second embodiment, the number of image-acquisitions of thick blood vessels can be decreased, so that W-ray exposure of the patient P can be reduced. Moreover, with the angiography apparatus  10 A, image-acquisition positions are automatically set depending on the frame rates that constitute the image condition, so that there is no need for the operator to set image-acquisition positions in advance. Thus, an optimum X-ray diagnosis environment for the operator can be provided. 
       FIG. 10  is a block diagram showing the functions of an angiography apparatus  10 B of a third embodiment. Since the hardware configuration of the angiography apparatus  10 B of the third embodiment is the same as that of the angiography apparatus  10  of the first embodiment shown in  FIGS. 1 and 2 , a description thereof will be omitted. 
     When the CPU  35  shown in  FIG. 1  executes programs, the angiography apparatus  10 B functions as the long-image generating unit  53 , a digital angiography (DA) image acquiring unit  57 , a blood-vessel data calculating unit  58 , and a frame rate calculating unit  59 . Although the components  53  and  57  to  59  are described as the functions of the CPU  35 , the present invention is not limited thereto; the components  53  and  57  to  59  may be provided as hardware in the DF apparatus  12 . The functions of the angiography apparatus  10 B shown in  FIG. 10  are given the same reference numerals as those of the angiography apparatus  10  shown in  FIG. 3 , and descriptions thereof will be omitted. 
     The DA image acquiring unit  57  has the function of controlling the system controller  40  in accordance with a frame rate that is appropriately calculated by the frame rate calculating unit  59  to execute the DA imaging of the entire image-acquisition region and the function of acquiring DA images (contrast images) from the image memory  32 . The DA image acquiring unit  57  performs DA imaging for collecting DA images of the entire image-acquisition region by stepping angiography after a contrast medium is injected into the patient P. The DA images generated by the DA image acquiring unit  57  are stored in a storage unit, such as the image memory  32 , together with the positional information of the table-top  25  acquired from the sensor  27   a , image-acquisition-time information, etc. The DA images acquired by the DA image acquiring unit  57  are displayed on the fluoroscopic monitor  34   a  substantially in real time. 
     The blood-vessel data calculating unit  58  has the function of extracting blood vessels using the luminance of the DA images that are appropriately acquired by the DA image acquiring unit  57  and calculating at least one of the diameters of the blood vessels and the luminance values of the blood vessels (the concentration of the contrast medium) as blood-vessel data. 
       FIG. 11  is a schematic diagram for explaining a method for calculating the blood-vessel data. 
       FIG. 11  shows a blood vessel in the FOV of a DA image acquired by the DA image acquiring unit  57 . As shown in  FIG. 11 , the blood-vessel data calculating unit  58  extracts a blood vessel in a region of interest (ROI) of the DA image acquired by the DA image acquiring unit  57  and calculates at least one of the average value of the diameters of the extracted blood vessels and the average value of the luminance values of the blood vessels as the blood-vessel data. Although not shown, the blood-vessel data calculating unit  58  extracts a blood vessel in the vicinity of the center of the DA image acquired by the DA image acquiring unit  57  and calculates at least one of the average value of the diameters of the extracted blood vessel and the average value of the luminance values of the blood vessel as the blood-vessel data. 
     The frame rate calculating unit  59  has the function of calculating the next frame rate on the basis of the blood-vessel data that is appropriately calculated by the blood-vessel data calculating unit  58  while moving the table-top  25  in the longitudinal direction with respect to the C-arm  23 . For example, for an image-acquisition position at which the blood vessel diameter calculated by the blood-vessel data calculating unit  58  is greater than or equal to a threshold value, the frame rate calculating unit  59  sets a low frame rate, and for an image-acquisition position at which the blood vessel diameter is smaller than the threshold value, the frame rate calculating unit  59  sets a high frame rate. Alternatively, for an image-acquisition position at which the luminance value of the blood vessel calculated by the blood-vessel data calculating unit  58  is greater than or equal to a threshold value, the frame rate calculating unit  59  sets a low frame rate, and for an image-acquisition position at which the luminance value of the blood vessel is smaller than the threshold value, the frame rate calculating unit  59  sets a high frame rate. The DA image acquiring unit  57  controls the system controller  40  in accordance with a frame rate that is appropriately calculated by the frame rate calculating unit  59  to execute the DA imaging of the extremity of the patient P. 
     Note that the frame rate calculating unit  59  may have a correlation table in advance in which blood-vessel data, for example, blood-vessel diameters and frame rates are associated with each other, and may calculate a frame rate with reference to a blood-vessel diameter calculated by the blood-vessel data calculating unit  58  on the correlation table. The frame rate calculating unit  59  may further have a plurality of correlation tables so that, after selecting a desired correlation table, the frame rate calculating unit  59  can calculate a frame rate with reference to a blood-vessel diameter calculated by the blood-vessel data calculating unit  58  on the desired correlation table. 
       FIG. 12  is a diagram showing an example of the plurality of correlation tables in graphical form. 
       FIG. 12  shows the relationship between blood-vessel data, for example, blood-vessel diameters, and frame rates with three correlation curves (correlation curves C 1 , C 2 , and C 3 ). If the angiography apparatus  10 B stores the correlation curves C 1 , C 2 , and C 3  in advance, the frame rate calculating unit  59  can set the next frame rate on the basis of the correlation curve C selected by the operator and blood-vessel data calculated by the blood-vessel data calculating unit  58 . 
     Next, the operation of the angiography apparatus  10 B of the third embodiment will be described with reference to a flowchart shown in  FIG. 13 . 
     The angiography apparatus  10 B executes DA imaging at an initial image-acquisition position in the entire image-acquisition region to generate a DA image at the initial image-acquisition position (step ST 1 ). 
     The angiography apparatus  10 B extracts blood vessels using the luminance of the DA image generated in step ST 1  and calculates at least one of the diameters of the blood vessels and the luminance values of the blood vessels (concentration of a contrast medium) as blood-vessel data (step ST 2 ). In step ST 2 , for example, the blood-vessel diameters, or the blood-vessel data, are calculated. 
     The angiography apparatus  10 B calculates the next frame rate for DA imaging, with the table-top  25  moved in the longitudinal direction with respect to the C-arm  23 , on the basis of the blood-vessel diameters calculated in step ST 2  (step ST 3 ). 
     The angiography apparatus  10 B moves the table-top  25  to the next image-acquisition position (stop position) and stops it in accordance with the frame rate calculated in step ST 3  or step ST 8 , to be described later (step ST 4 ). Next, the angiography apparatus  10 B executes DA imaging at the image-acquisition position at which the table-top  25  is stopped in step ST 4  to generate a DA image at the image-acquisition position (step ST 5 ). The DA image generated in step ST 5  is displayed on the fluoroscopic monitor  34   a  substantially in real time. 
     The angiography apparatus  10 B determines whether to execute DA imaging of the next frame in the image-acquisition region (step ST 6 ). If the determination in step ST 6  is YES, that is, if the angiography apparatus  10 B determines to execute the DA imaging of the next frame in the image-acquisition region, the angiography apparatus  10 B extracts blood vessels on the basis of the luminance of the DA image generated in step ST 5  and calculates the diameters of the blood vessels as blood-vessel data (step ST 7 ). 
     The angiography apparatus  10 B calculates the next frame rate for DA imaging, with the table-top  25  moved in the longitudinal direction with respect to the C-arm  23 , on the basis of the blood-vessel diameters calculated in step ST 7  (step ST 8 ). 
     On the other hand, if the determination in step ST 6  is NO, that is, if the angiography apparatus  10 B determines not to execute the DA imaging of the next frame in the image-acquisition region, the angiography apparatus  10 B concludes the DA imaging. 
     Although the angiography apparatus  10 B is described when applied to stepping the DA imaging of the entire image-acquisition region, the present invention is not limited thereto. For example, the angiography apparatus  10 B takes angiograms in accordance with an appropriately calculated frame rate while moving the table-top  25  in the longitudinal direction at a fixed speed. That is, the angiography apparatus  10 B may adopt an image-acquisition method of covering the entire image-acquisition region while continuously moving the table-top  25  irrespective of the frame rate. With this image-acquisition method, the DA image acquiring unit  57  controls the system controller  40  in accordance with a calculated frame rate to repeat image-acquisition during the movement of the table-top  25 . 
     With the angiography apparatus  10 B according to the third embodiment, the number of image-acquisitions of thick blood vessels can be decreased, X-ray exposure of the patient P can be reduced. Moreover, with the angiography apparatus  10 B, the image-acquisition position is automatically determined depending on an appropriately calculated frame rate, so that there is no need for the operator to set the image-acquisition position in advance, which provides the operator with an optimum X-ray image diagnosing environment.