Patent Publication Number: US-8542891-B2

Title: X-ray imaging apparatus that displays analysis image with taken image, X-ray imaging method, and image processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-176042, filed on Jul. 4, 2008; the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique of displaying an analysis image of a target region such as an angiostenosis part with an X-ray image being taken. 
     2. Description of the Related Art 
     Conventionally, there has been a treatment technique such that a linear structure such as a guide wire or a catheter is inserted into coronary arteries of a heart to expand a portion where the coronary arteries are narrow or blocked. This treatment technique is referred to as “Percutaneous Coronary Intervention (PCI) treatment”. In the PCI treatment, an X-ray imaging apparatus such as an X-ray angiography apparatus is used. The X-ray angiography apparatus displays an X-ray perspective projection image (hereinafter, “X-ray angiographic image”) as a guide image at the time of inserting a guide wire up to a lesioned part (a coronary artery stenosis site) during the PCI treatment. 
     Further, as means for diagnosing coronary arteries, clinical application software for an X-ray CT scanner referred to as “coronary artery analysis software” has been known (for example, see JP-A 2004-283373 (KOKAI)). This coronary artery analysis software has a function for obtaining a blood vessel core of the coronary arteries, an internal wall of a blood vessel, an estimated normal internal wall of a blood vessel, and the like as three-dimensional data using three-dimensional volume data of a heart area. 
     In PCI treatment, therefore, images of the internal wall of a blood vessel obtained by the coronary artery analysis software are displayed on an another apparatus separate from an X-ray angiography apparatus or developed on a film for reference, to support an operator. 
     Further, a technique for synthesizing and displaying analysis images showing an angiostenosis part and a running direction of a blood vessel obtained by coronary artery analysis software on an X-ray angiographic image has been developed. To generate the analysis images of the angiostenosis part and the running direction of a blood vessel, projection parameters (projection directions, positions, and enlargement ratios) need to be obtained. To obtain these projection parameters, therefore, a positioning process is performed in a following procedure. 
     (1) First, to match a projection direction, a user manually sets so that a projection direction of volume data becomes the same as that of the X-ray angiography apparatus. 
     (2) The volume data is projected from the direction set in procedure (1) to generate an MIP image, and the maximum intensity projection (MIP) image is binarized to an imaged blood area and other areas. 
     (3) An image showing only the blood area imaged by binarization is generated from the X-ray angiographic image. 
     (4) To perform positioning between binarized image f 1 (x, y) in procedure (2) and binarized image f 2 (x, y) in procedure (3), a parallel shifting amount (l, m) and an expansion ratio s are obtained by a correlation function shown in an equation (1). 
     
       
         
           
             
               
                 
                   
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     However, in the positioning process mentioned above, entire processing is performed after imaging by the X-ray angiography apparatus has started, and thus a longer processing time is required. During PCI treatment, an operator performs surgery, while appropriately changing the imaging direction and position of the X-ray angiography apparatus so that an observation target can be clearly seen on the displayed image. Therefore, every time the imaging direction of the X-ray angiography apparatus is changed, the positioning process needs to be performed from procedure (1), and thus the waiting time for positioning is required. As a result, the surgery time becomes longer, and strains on the patient increase. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, an X-ray imaging apparatus includes an imaging unit that irradiates X-rays on a subject and detects X-rays penetrating the subject to generate an X-ray projection image of the subject; a positioning-image creating unit that creates positioning images corresponding to a plurality of different projection conditions using volume data collected from the subject by a medical imaging apparatus; a projection-condition obtaining unit that selects an image most analogous to the X-ray projection image of the subject from the positioning images, and obtains a projection condition of the selected positioning image; a target-region storage unit that stores volume data of a target region, among the volume data collected, as target-region volume data; and an image display unit that creates and displays an image of the target region based on the target-region volume data stored in the target-region storage unit and the projection condition obtained by the projection-condition obtaining unit. 
     According to another aspect of the present invention, an X-ray imaging method includes irradiating X-rays on a subject; detecting X-rays penetrating the subject; generating an X-ray projection image of the subject; creating positioning images corresponding to a plurality of different projection conditions using volume data collected from the subject by a medical imaging apparatus; selecting an image most analogous to the X-ray projection image of the subject from the positioning images; obtaining a projection condition of the selected positioning image; storing volume data of a target region, among the volume data collected, as target-region volume data; and creating and displaying an image of the target region based on the target-region volume data and the projection condition. 
     According to still another aspect of the present invention, an image processing apparatus includes an image obtaining unit that obtains an X-ray projection image of a subject; a positioning-image creating unit that creates positioning images corresponding to a plurality of different projection conditions using volume data collected from the subject by a medical imaging apparatus; a projection-condition obtaining unit that selects an image most analogous to the X-ray projection image of the subject from the positioning images, and obtains a projection condition of the selected positioning image; a target-region storage unit that stores volume data of a target region, among the volume data collected, as target-region volume data; and an image display unit that creates and displays an image of the target region based on the target-region volume data stored in the target-region storage unit and the projection condition obtained by the projection-condition obtaining unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of a configuration of an X-ray angiography apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a diagram illustrating examples of presets; 
         FIG. 3  is a diagram illustrating projection parameters; 
         FIG. 4  is a diagram illustrating an example of a range in which a subject center is changed when perspective projection images are created; 
         FIG. 5  is a diagram illustrating a search example of a perspective projection image by a positioning information calculating unit; 
         FIG. 6  is a diagram illustrating an example of a method of performing a search while narrowing a comparison range by dividing a region of an image group for positioning into smaller regions; 
         FIG. 7  is a diagram illustrating an example of a synthesized image; 
         FIG. 8  is a flowchart of a procedure performed by an X-ray angiography apparatus before imaging; 
         FIG. 9  is a flowchart of a procedure performed by the X-ray angiography apparatus after start of imaging; 
         FIG. 10  is a functional block diagram of a configuration of an X-ray angiography apparatus according to a second embodiment of the present invention; 
         FIG. 11  is a diagram illustrating an example of a synthesized image; 
         FIG. 12  is a functional block diagram of a configuration of an X-ray angiography apparatus according to a third embodiment of the present invention; 
         FIG. 13  is a diagram illustrating display examples of two types of images; 
         FIG. 14  is a functional block diagram of a configuration of an X-ray angiography apparatus according to a fourth embodiment of the present invention; and 
         FIG. 15  is a diagram illustrating display examples of synthesized images. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of an X-ray imaging apparatus, an X-ray imaging method, and an image processing apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings. 
     A configuration of an X-ray angiography apparatus according to a first embodiment of the present invention is explained first.  FIG. 1  is a functional block diagram of the configuration of the X-ray angiography apparatus according to the first embodiment. As shown in  FIG. 1 , an X-ray angiography apparatus  100  includes an X-ray angiography imaging unit  101 , an X-ray angiographic-apparatus preset storage unit  102 , a CT-volume-data storage unit  103 , a projection parameter converting unit  104 , a projection-image creating unit  105 , a projection-image storage unit  106 , a coronary artery analyzing unit  107 , an analysis-result storage unit  108 , an image extracting unit  109 , a positioning information calculating unit  110 , a positioning-information updating unit  111 , an analysis-image-for-synthesis creating unit  112 , and an analysis-image synthesizing and displaying unit  113 . 
     The X-ray angiography imaging unit  101  irradiates X-rays on a patient and detects the X-rays having penetrated the patient to generate images. The X-ray angiographic-apparatus preset storage unit  102  stores preset information of the X-ray angiography apparatus  100 . As shown in  FIG. 2 , a plurality of values are registered as preset information, for caudal view (CAU), cranial view (CRA), left anterior oblique view (LAO), and right anterior oblique view (RAO). However, only imaging directions having possibility to be used as an imaging direction at the time of starting treatment are stored in the X-ray angiographic-apparatus preset storage unit  102 . 
     The CAU, CRA, LAO, and RAO represent rotation directions of an isocenter, which is a center of rotation of X-ray beams. In the X-ray angiography apparatus  100 , patient&#39;s head is made to enter from a direction of arrow “A” (this angle is designated as 0 degree in γ angle in  FIG. 2 ), and the apparatus can be rotated in an α direction and a β direction, with the γ angle being fixed. That is, the X-ray angiography apparatus  100  can be moved in the CRA and CAU directions of the patient by sliding and rotating a C arm  60  that supports an X-ray tube  31  and an X-ray detector  32  in the α direction, and can be moved in the LAO and RAO directions by rotating the C arm  60  in the β direction. 
     The CT-volume-data storage unit  103  stores three-dimensional volume data of a heart area collected by taking images of the patient by an X-ray CT scanner. End-diastolic volume data are used here. 
     The projection parameter converting unit  104  obtains the preset information from the X-ray angiographic-apparatus preset storage unit  102  and converts the preset information to projection parameters. The projection parameters are required for creating a projection image from the volume data, and include a view angle  11 , a visual distance  12 , a visual direction  13 , and a subject center (X, Y, Z)  14  as shown in  FIG. 3 . The subject center  14  is a central position of X-ray photography, and the view angle  11  expresses a range of the X-ray photography by an angle centering on a focal point of the X-ray tube  31 . The visual distance  12  is a distance from the focal point of the X-ray tube  31  to the subject center  14 , and the visual direction  13  expresses a direction from the focal point of the X-ray tube  31  to the subject center  14 . An Up vector is a rotation angle of the X-ray tube  31 . 
     The view angle, the visual distance, and the visual direction can be converted from the preset information. However, because the subject center depends on an individual difference of physical constitution of the patient and a position of the patient on a bed, the subject center cannot be uniquely determined. Therefore, the projection parameter converting unit  104  obtains initial values of the subject center, for example, according to the following method. 
     (1) The position on a bed and a patient model are defined on the bed of the X-ray angiography apparatus. 
     (2) The positions of shoulders in the patient model and the volume data are matched with each other in an anteroposterior direction by referring to a region in which a direction of the patient can be easily specified, such as a collarbone and vertebra. 
     (3) Correction values are obtained from height and weight of the patient to obtain a deviation of a heart position between the patient model and the volume data. 
     If the initial values are obtained by this method, a plurality of examples need to be photographed beforehand for the patient model and the correction values. 
     The projection-image creating unit  105  creates perspective projection images with the subject center being changed within a certain range, from heart area volume data stored in the CT-volume-data storage unit  103 , centering on the initial values obtained for the subject center by the projection parameter converting unit  104 . The created perspective projection images are grouped for each preset, and stored in the projection-image storage unit  106  in association with the projection parameters. 
     The range in which the subject center is changed is, for example, under a condition that the point of view and projection plane shown in  FIG. 4  are fixed, ±3 centimeters centering on the initial values of the subject center and with 5 millimeter interval, and 13×13×13 perspective projection images are created. For projection, Ray-Summing (hereinafter, “RaySum”) is used, where an integral value of values present on a projection line is designated as a pixel value. 
     The range for creating the perspective projection images is not limited to this example, and the type of the perspective projection images is not limited to the RaySum, and can be changed according to a comparison method of images used by the positioning information calculating unit  110  described later. The perspective projection images for positioning are created here by changing the subject center. However, the perspective projection images for positioning can be created by changing the Up vector as well, for example, in a case that the shoulder positions are not matched with each other between the patient model and the volume data in the anteroposterior direction. The Up vector is changed, for example, in a range of ±5 degrees and with ±1 degree interval. Further, the perspective projection images for positioning can be created by changing the visual direction. Further, end-diastolic heart phase data are used here as the heart area volume data to be input. 
     The projection-image storage unit  106  groups and stores the perspective projection images created by the projection-image creating unit  105  for each preset in association with the projection parameters. When the X-ray angiography is started, the projection-image storage unit  106  sets a group corresponding to a preset imaging direction as an image group for positioning. 
     The coronary artery analyzing unit  107  performs coronary artery analysis to extract volume data of the angiostenosis part from the heart area volume data, and stores the extracted volume data in the analysis-result storage unit  108  as an analysis result. For example, a method described in Japanese Patent Application No. 2007-180761 can be used for the coronary artery analysis. The analysis-result storage unit  108  stores the analysis result, that is, the volume data of the angiostenosis part. 
     The image extracting unit  109  extracts the heart phase same as that of the heart area volume data, that is, an end-diastolic image from the X-ray angiographic images taken from the preset imaging direction. 
     The positioning information calculating unit  110  compares the X-ray angiographic image extracted by the image extracting unit  109  with each perspective projection image in the image group set for positioning by the projection-image storage unit  106 , thereby searching for a perspective projection image whose position is matched best. The positioning information calculating unit  110  then sets projection parameters corresponding to the perspective projection image whose position is matched best as optimum positioning parameters. 
       FIG. 5  is a diagram illustrating a search example of the perspective projection image by the positioning information calculating unit  110 .  FIG. 5  depicts a case that the preset imaging direction of the X-ray angiography apparatus  100  is “preset  2 ” and the perspective projection images of an image group of “preset  2 ” are searched images. 
     An image search method includes a method of full-searching the image group for positioning, and a method of performing a search while narrowing a comparison range by dividing a region of an image group for positioning into smaller regions based on an amount of change of the projection parameters. The latter method can perform a search at a higher speed.  FIG. 6  is a diagram illustrating an example of the method of performing a search while narrowing the comparison range by dividing a region of an image group for positioning into smaller regions. In this example, a search is performed according to a following procedure. 
     (1) The perspective projection images are divided into images in regions A to H for each moving direction of the volume data, centering on the initial values of the subject center. 
     (2) A perspective projection image corresponding to the center of each region is compared with the X-ray angiographic image. 
     (3) It is assumed that an image whose position is accurate is present in a region including an image whose position is closest to the X-ray angiographic image, and the region is further divided (DA to DH). 
     (4) Procedures (2) and (3) are repeated, the search region is narrowed, and a full search is performed in a target region. 
     In this method, by dividing into regions overlapped on each other, selection of a region can be performed without error even if the image whose position is matched best is present near a boundary of the divided regions. 
     The correlation function shown in the equation (1) or mutual information I shown in an equation (2) below can be used for comparison of the images. In the equation (2), A and B are images, a and b are respectively a pixel in images A and B, P(A) and P(B) are respectively an entropy of the images A and B, P(A,B) is a total entropy, and p(a), p(b), and p(a, b) are probability distribution functions. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     The positioning-information updating unit  111  obtains amounts of changes of positioning parameters from a change amount of the imaging direction to update the positioning parameters, when the imaging direction of the X-ray angiography apparatus  100  is changed after setting of the positioning parameters. 
     The analysis-image-for-synthesis creating unit  112  creates a two-dimensional projection source image of the angiostenosis part as an analysis image for synthesis, using the volume data of the angiostenosis part stored in the analysis-result storage unit  108  and the positioning parameters. 
     The analysis-image synthesizing and displaying unit  113  synthesizes an image by overlapping the analysis image for synthesis created by the analysis-image-for-synthesis creating unit  112  on the X-ray angiographic image and displays the synthesized image.  FIG. 7  is a diagram illustrating an example of a synthesized image. 
     Procedures performed by the X-ray angiography apparatus  100  before imaging and after start of imaging in order to display the synthesized image are explained next with reference to  FIGS. 8 and 9 .  FIG. 8  is a flowchart of the procedure performed by the X-ray angiography apparatus  100  before imaging. As shown in  FIG. 8 , the projection parameter converting unit  104  obtains preset information from the X-ray angiographic-apparatus preset storage unit  102 , to create projection parameters for each preset (Step S 11 ). 
     The projection-image creating unit  105  creates perspective projection images while changing the subject center for each projection parameter (Step S 12 ), groups the perspective projection images for each preset, and stores the perspective projection images with the projection parameters in the projection-image storage unit  106 . 
     The coronary artery analyzing unit  107  analyzes the heart area volume data to detect an angiostenosis part, and stores the volume data of the angiostenosis part in the analysis-result storage unit  108  (Step S 13 ). 
     In this way, the projection-image creating unit  105  creates the perspective projection images while changing the subject center for each projection parameter, and stores the perspective projection images with the projection parameters in the projection-image storage unit  106 , thereby enabling to perform a positioning process at a high speed after imaging has been started. 
       FIG. 9  is a flowchart of the procedure performed by the X-ray angiography apparatus  100  after start of imaging. As shown in  FIG. 9 , when imaging is started, the image extracting unit  109  extracts an end-diastolic image (Step S 101 ), and the projection-image storage unit  106  sets an image group corresponding to a preset imaging direction as an image group for positioning (Step S 102 ). 
     The positioning information calculating unit  110  then compares the image extracted by the image extracting unit  109  with respective perspective projection images in the image group for positioning, to calculate positioning information, that is, positioning parameters (Step S 103 ). Thereafter, when the imaging direction is changed, the positioning-information updating unit  111  updates the positioning parameters (Step S 104 ). 
     The analysis-image-for-synthesis creating unit  112  creates an analysis image of the angiostenosis part using the positioning parameters and the volume data stored in the analysis-result storage unit  108  as an image for synthesis (Step S 105 ), and the analysis-image synthesizing and displaying unit  113  overlaps the analysis image of the angiostenosis part on a live image and displays the live image overlapped by the analysis image (Step S 106 ). 
     As described above, in the first embodiment, the projection-image creating unit  105  creates positioning images before imaging, and the projection-image storage unit  106  groups the positioning images for each preset and stores the images. When imaging is started, the positioning information calculating unit  110  calculates the positioning parameters, using the positioning images stored in the projection-image storage unit  106 . Therefore, positioning can be performed at a high speed during imaging, and a synthesized image can be displayed on a real-time basis. 
     Furthermore, in the first embodiment, when the imaging direction of the X-ray angiography apparatus  100  is changed, the positioning-information updating unit  111  updates the positioning parameters directly based on the change amount of the imaging direction. Accordingly, when the imaging direction of the X-ray angiography apparatus  100  is changed, synthesis and display can be performed on a real-time basis. 
     As a result, the coronary artery analysis information such as the running direction of the blood vessel and the angiostenosis part can be confirmed on the X-ray angiographic image. Accordingly, confirmation of an advancing direction at the time of inserting a catheter and position adjustment of a treatment tool such as a balloon or a stent can be easily performed, thereby enabling to reduce the operation time. Further, it leads to reduction of usage of a contrast agent and exposure, thereby enabling to reduce strains on the patient. 
     In the first embodiment, a case that the image for synthesis of the angiostenosis part is created, and displayed, overlapped on the live image has been explained. However, not only the angiostenosis part but also an analysis image for synthesis expressing other target regions and noteworthy information in the PCI treatment such as a running direction of a blood vessel, a blood flow rate, plaque characteristics, and a rate of stenosis can be overlapped on the live image and displayed. In a second embodiment of the present invention, therefore, an X-ray angiography apparatus that selectively overlaps an analysis image for synthesis relating to a plurality of target regions and the noteworthy information on the live image and displays the live image overlapped by the analysis image is explained. 
       FIG. 10  is a functional block diagram of a configuration of an X-ray angiography apparatus according to the second embodiment. For convenience&#39; sake, like reference number refers to like functional unit that functions in the same way with each unit shown in  FIG. 1 , and explanations thereof will be omitted. 
     As shown in  FIG. 10 , an X-ray angiography apparatus  200  includes a coronary artery analyzing unit  207 , an analysis-result storage unit  208 , and an analysis-image-for-synthesis creating unit  212  instead of the coronary artery analyzing unit  107 , the analysis-result storage unit  108 , and the analysis-image-for-synthesis creating unit  112  in the X-ray angiography apparatus  100 . The X-ray angiography apparatus  200  additionally includes an analysis-result-for-synthesis selecting unit  214  and an analysis-result-for-synthesis switching unit  215 . 
     The coronary artery analyzing unit  207  performs coronary artery analysis for a plurality of items such as a running direction of a blood vessel, a blood flow rate, plaque characteristics, and a rate of stenosis other than the angiostenosis part. The analysis-result storage unit  208  stores coronary artery analysis results for the items such as the running direction of the blood vessel, the blood flow rate, the plaque characteristics, and the rate of stenosis, other than the angiostenosis part. 
     The analysis-result-for-synthesis selecting unit  214  sets which item of the analysis results stored in the analysis-result storage unit  208  is to be synthesized and displayed on an X-ray angiographic image. When the analysis-result-for-synthesis selecting unit  214  sets a plurality of analysis results to be synthesized and displayed, all the set analysis results are simultaneously synthesized and displayed. Alternatively, in this setting, setting can be divided into each phase being treated, and an analysis content can be individually set, for example, an image of the running direction of the blood vessel at the time of inserting the guide wire, and an image of the angiostenosis part at the time of positioning of a treatment tool such as a stent with respect to a target to be treated. 
     Further, when a plurality of analysis results are superposed at the same position in the image, a priority level of superposition of the analysis results and transparent superposition are set so that information is not lost due to superposition. The setting can be changed by an operator before or during an operation. 
     The analysis-result-for-synthesis switching unit  215  switches the analysis image set by the analysis-result-for-synthesis selecting unit  214  with a progress of a treatment phase. The analysis image can be manually switched by the operator or can be automatically switched according to an approaching position of the catheter. 
     The analysis-image-for-synthesis creating unit  212  creates analysis images for synthesis based on switching by the analysis-result-for-synthesis switching unit  215 .  FIG. 11  is a diagram illustrating an example of the synthesized image displayed by the analysis-image synthesizing and displaying unit  113 . In  FIG. 11 , a running of a blood vessel and a stenosis part  21  are displayed superposed on an X-ray angiographic image. 
     In the second embodiment, the analysis-result storage unit  208  stores the coronary artery analysis results for the items analyzed by the coronary artery analyzing unit  207 . The analysis-result-for-synthesis switching unit  215  switches an item to be synthesized to the item set by the analysis-result-for-synthesis selecting unit  214  among the coronary artery analysis results stored in the analysis-result storage unit  208 . Accordingly, various coronary artery analysis results can be switched, synthesized, and displayed, with the progress of the treatment phase. 
     In the first and second embodiments, a case that one synthesized image is displayed on one display device has been explained. However, a plurality of images can be displayed on one display device or the images can be displayed on a plurality of display devices. In a third embodiment of the present invention, a case of displaying the images using a plurality of display devices is explained. 
       FIG. 12  is a functional block diagram of a configuration of the X-ray angiography apparatus according to the third embodiment. For convenience&#39; sake, like reference number refers to like functional unit that functions in the same way with each unit shown in  FIG. 10 , and explanations thereof will be omitted. 
     As shown in  FIG. 12 , an X-ray angiography apparatus  300  includes a synthesis display setting unit  316 , an image synthesizing unit  317 , and an image displaying unit  318  instead of the analysis-image synthesizing and displaying unit  113  in the X-ray angiography apparatus  300 . 
     The synthesis display setting unit  316  sets which image is displayed at which position. The setting can be changed by an operator before and during an operation. For example, as a type of the image, the synthesis display setting unit  316  sets any one of: 
     only an unsynthesized X-ray angiographic image; 
     only a synthesized image of the X-ray angiographic image and the analysis result; 
     two types of images, that is, the unsynthesized X-ray angiographic image and the synthesized image of the X-ray angiographic image and the analysis result; 
     two types of images, that is, the unsynthesized X-ray angiographic image and a synthesized image of a heart shape image of the heart area volume data and the analysis result; and 
     two types of images, that is, the synthesized image of the X-ray angiographic image and the analysis result, and the synthesized image of the heart shape image of the heart area volume data and the analysis result. 
     As display positions, for example, in the case of two types of display images, the synthesis display setting unit  316  sets any one of: 
     display images on separate display devices; 
     display images in parallel on one display device; and 
     display an image superposed on a part of the unsynthesized X-ray angiographic image. 
     The image synthesizing unit  317  creates a synthesized image based on the setting performed by the synthesis display setting unit  316 . The image displaying unit  318  displays the X-ray angiographic image or the synthesized image based on the setting performed by the synthesis display setting unit  316 . 
       FIG. 13  is a diagram illustrating display examples of two types of images. In  FIG. 13 , a case that two types of images, that is, the unsynthesized X-ray angiographic image and the synthesized image of the X-ray angiographic image and the analysis result are displayed in parallel and a case that the synthesized image is displayed superposed on a part of the unsynthesized X-ray angiographic image are shown. 
     As described above, in the third embodiment, a plurality of types of images are displayed on a plurality of display devices based on the setting performed by the synthesis display setting unit  316 . Therefore, the operator can appropriately position and display the images, which are considered to be useful. 
     In the first to third embodiments, a case that the coronary artery analysis is performed using the three-dimensional volume data has been explained; however, the coronary artery analysis can be performed using four-dimensional volume data. In a fourth embodiment of the present invention, an X-ray angiography apparatus that uses four-dimensional volume data is explained. 
       FIG. 14  is a functional block diagram of a configuration of the X-ray angiography apparatus according to the fourth embodiment. For convenience&#39; sake, like reference number refers to like functional unit that functions in the same way with each unit shown in  FIG. 10 , and explanations thereof will be omitted. 
     As shown in  FIG. 14 , an X-ray angiography apparatus  400  includes a CT4D volume-data storage unit  403 , a coronary artery analyzing unit  407 , an analysis-result storage unit  408 , and an analysis-image-for-synthesis creating unit  412  instead of the CT-volume-data storage unit  103 , the coronary artery analyzing unit  207 , the analysis-result storage unit  208 , and the analysis-image-for-synthesis creating unit  212  in the X-ray angiography apparatus  200 . The X-ray angiography apparatus  400  additionally includes an end-diastolic data extracting unit  419  and a synthesis-timing setting unit  420 . 
     The CT4D volume-data storage unit  403  stores four-dimensional volume data of the heart area collected by taking images of a patient by an X-ray CT scanner. The coronary artery analyzing unit  407  performs the coronary artery analysis with respect to the four-dimensional volume data, and the analysis-result storage unit  408  stores the coronary artery analysis result performed with respect to the four-dimensional volume data. The end-diastolic data extracting unit  419  extracts end-diastolic volume data from the four-dimensional data based on electrocardiogram information registered simultaneously at the time of obtaining the four-dimensional data. 
     In the fourth embodiment, the data used for synthesis is four-dimensional, different from the first to third embodiments, and thus one time phase data in the data are selected to obtain the positioning parameters. Analysis images of all the time phases are created by the obtained positioning parameters. The end-diastolic volume data having relatively less heart fluctuation is used here for positioning. 
     The synthesis-timing setting unit  420  sets timing of a heartbeat phase for creating, synthesizing, and displaying the analysis image. The analysis image for synthesis can be created only after determining the imaging direction of the X-ray angiography apparatus  400 . Therefore, a rendering load is reduced according to the following setting. 
     Rendering of the image is performed only for one cycle of heartbeat and repeatedly displayed. 
     An analysis image is not updated in the time phase of heartbeat having no (or less) fluctuation of the heart. 
     The synthesis display is suspended until the imaging direction is determined while the angiographic imaging direction is being changed, and creation and display of the analysis image to be synthesized is started after determination of the imaging direction. 
     The analysis-image-for-synthesis creating unit  412  creates the analysis image at a timing set by the synthesis-timing setting unit  420 .  FIG. 15  is a diagram illustrating a display example of a synthesized image. In this example, a case that the analysis image is not updated in the time phase of heartbeat having no (or less) fluctuation of the heart is shown. 
     As described above, in the fourth embodiment, because the analysis image is created using the four-dimensional volume data of the heart area, the analysis images can be superposed and displayed, according to a movement of the heart in the X-ray angiographic image. 
     In the first to fourth embodiments, a case that the analysis image is synthesized with the X-ray angiographic image of the coronary arteries and displayed has been explained. However, the present invention is not limited thereto, and is similarly applicable to a case that only an analysis image is displayed. 
     In the first to fourth embodiments, a case that the analysis image is synthesized with the X-ray angiographic image of the coronary arteries and displayed has been explained. However, the present invention is not limited thereto, and is similarly applicable to a case that the analysis image is synthesized with other X-ray images of a brain or the like and displayed. 
     In the first to fourth embodiments, a case of using the X-ray angiography apparatus has been explained. However, the present invention is not limited thereto, and is similarly applicable to other X-ray imaging apparatuses and an image processing apparatus that receives image data from the X-ray imaging apparatus, and synthesizes and displays the analysis image. 
     In the first to fourth embodiments, a case of using the CT volume data collected by an X-ray CT scanner has been explained. However, the present invention is not limited thereto, and is similarly applicable to a case of using the volume data collected by other medical imaging apparatuses. 
     In the first to fourth embodiments, a case that the projection-image creating unit  105  creates positioning images before imaging and the projection-image storage unit  106  groups and stores the positioning images for each preset has been explained. However, the present invention is not limited thereto, and is similarly applicable to a case that the positioning image is created after start of imaging. Further, the coronary artery analyzing unit  107  can be configured to detect a stenosis part after start of imaging. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.