Patent Publication Number: US-8542902-B2

Title: X-ray imaging apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-249456, filed on Oct. 29, 2009; and Japanese Patent Application No. 2010-222249, filed on Sep. 30, 2010, the entire contents of all of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an X-ray imaging apparatus. 
     BACKGROUND 
     According to an intervention treatment, which is one of treatment methods for an aneurysm, a doctor carries out insertion of a catheter or a guide wire while watching an X-ray fluoroscopic image displayed on a monitor. However, it is difficult to confirm visually a blood vessel on an X-ray fluoroscopic image unless injecting contrast media. On the other hand, if continuously injecting contrast media, a burden onto a patient becomes high. For this reason, conventionally, a roadmap function of displaying a composite image of a past image taken by injecting contrast media and an X-ray fluoroscopic image in real time onto a monitor has been used. 
     However, such roadmap function cannot cope with a displacement arising along with a state change in the X-ray imaging apparatus (for example, a movement of a bed, or a rotation of an arm), consequently, an image taken by injecting contrast media needs to be re-created each time. Re-creation leads to an increase in the quantity of contrast media to be used, and results in a burden onto the patient. Therefore, recently, a three-dimensional (3D) roadmap function has come into use, which includes preliminarily collecting a three-dimensional blood vessel image on which a blood vessel image is enhanced, and during a treatment, creating a three-dimensional projection image (hereinafter, “volume rendering image”) from the three-dimensional blood vessel image so as to reflect a state change in the X-ray imaging apparatus, and displaying a composite image of the created volume rendering image and an X-ray fluoroscopic image onto a monitor (for example, JP-A 2007-229473 (KOKAI)). 
     However, even if using the above 3D roadmap function, there is a problem that a displacement of an aneurysm arising along with insertion of a catheter or another tool cannot be coped with. 
     In other words, according to the 3D roadmap function, a volume rendering image is to be created from a preliminarily collected three-dimensional blood vessel image; however, the three-dimensional blood vessel image is collected in a state where catheter or other tool is not inserted (or is at a starting part of the blood vessel). On the other hand, for example, if a catheter is inserted up to the vicinity of an aneurysm, a bending force of the catheter along a blood vessel and a resilient force are generated, and the blood vessel deforms so as to reduce a bend of the blood vessel. Consequently, not only the position of the blood vessel, but also the position of the aneurysm is displaced from the position at the moment of collecting the three-dimensional blood-vessel image, resulting in that the position of the aneurysm is displayed on a monitor in a displaced state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram for explaining an overview of an X-ray imaging apparatus according to a first embodiment; 
         FIG. 2  is a functional block diagram of a configuration of the X-ray imaging apparatus according to the first embodiment; 
         FIG. 3  is a functional block diagram of a configuration of an image processing unit shown in  FIG. 2 ; 
         FIG. 4  is a flowchart for explaining three-dimensional (3D) blood-vessel image collecting processing; 
         FIG. 5  is a flowchart for explaining 3D roadmap image registration processing; 
         FIGS. 6A and 6B  are schematic diagrams for explaining determination of a displacement; 
         FIGS. 7A and 7B  are schematic diagrams for explaining determination of a displacement; 
         FIG. 8  is a schematic diagram for explaining determination from two directions; 
         FIGS. 9A to 9D  are schematic diagrams for explaining differences of areas of an aneurysm; 
         FIGS. 10A and 10B  are schematic diagrams for explaining an area of an aneurysm after positional and angular registration; 
         FIGS. 11A and 11B  are schematic diagrams for explaining determination according to a second embodiment; and 
         FIG. 12  is a schematic diagram for explaining a three-dimensional image acquiring unit. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of an X-ray imaging apparatus will be explained below in detail with reference to the accompanying drawings. 
     An X-ray imaging apparatus according to the embodiments includes a three-dimensional blood-vessel image collecting unit, an X-ray image collecting unit, a composite-image creating unit, a displacement determining unit, and a registration unit. The three-dimensional blood-vessel image collecting unit collects a three-dimensional blood vessel image on which a blood vessel image is enhanced. The X-ray image collecting unit collects an X-ray image. The composite-image creating unit creates a three-dimensional projection image projected based on a state of the X-ray imaging apparatus from a three-dimensional blood vessel image collected by the three-dimensional blood-vessel image collecting unit, and creates a composite image of the created three-dimensional projection image and the X-ray image collected by the X-ray image collecting unit. The displacement determining unit determines a displacement between an aneurysm on the three-dimensional projection image and the aneurysm on the X-ray image. The registration unit registers the composite image created by the composite-image creating unit by using the displacement determined by the displacement determining unit, and displays the registered composite image onto a display unit. 
     First of all, an overview of an X-ray imaging apparatus according to a first embodiment is explained below with reference to  FIG. 1 .  FIG. 1  is a schematic diagram for explaining an overview of the X-ray imaging apparatus according to the first embodiment. 
     As shown in  FIG. 1 , the X-ray imaging apparatus according to the first embodiment collects a three-dimensional blood vessel image on which a blood vessel image is enhanced. The X-ray imaging apparatus collects an X-ray fluoroscopic image. 
     The X-ray imaging apparatus then creates a three-dimensional projection image projected based on a state of the X-ray imaging apparatus from the collected three-dimensional blood vessel image, and creates a composite image of the created three-dimensional projection image and the X-ray fluoroscopic image. 
     Subsequently, the X-ray imaging apparatus determines a displacement between an aneurysm on the three-dimensional projection image and the aneurysm on the X-ray fluoroscopic image from the created composite image. 
     The X-ray imaging apparatus then registers the composite image based on the determined displacement, and displays the registered composite image onto a display unit. 
     In this way, the X-ray imaging apparatus according to the first embodiment registers the three-dimensional projection image and the X-ray fluoroscopic image based on information about the aneurysm that is an observation portion. As a result, the displacement of the aneurysm on the composite image can be registered, so that the position of the aneurysm on the three-dimensional projection image and the position of the aneurysm on the X-ray fluoroscopic image are matched with each other on the composite image. For example, according to a conventional three-dimensional (3D) roadmap function, a displacement of an aneurysm brings about difficulty in comparing total shapes of the aneurysm, thereby resulting in a situation that it is difficult to grasp loading of a coil; however, according to the X-ray imaging apparatus of the first embodiment can avoid such situation. 
     A configuration of the X-ray imaging apparatus according to the first embodiment is explained below with reference to  FIGS. 2 and 3 .  FIG. 2  is a functional block diagram of a configuration of the X-ray imaging apparatus according to the first embodiment. 
     As shown in  FIG. 2 , an X-ray imaging apparatus  100  according to the first embodiment includes an X-ray source device  1 , an X-ray detector  4 , an arm  5 , a couch  6 , a mechanism control unit  7 , a system control unit  8 , an X-ray high-voltage generating device  9 , an operation unit  12 , a display unit  13 , and an image processing device  20 . 
     The X-ray source device  1  includes an X-ray tube  2 , and an X-ray aperture device  3 . The X-ray tube  2  generates an X-ray by using a high voltage supplied by the X-ray high-voltage generating device  9 . The X-ray aperture device  3  controls a radiation field by blocking part of an X-ray generated by the X-ray tube  2 . 
     The X-ray detector  4  detects an X-ray having passed through a patient P by converting it into an electric charge. 
     The arm  5  supports the X-ray source device  1  and the X-ray detector  4 . The arm  5  in a C shape rotates around the patient P at high speed as like a propeller with a motor provided on a base. The couch  6  is configured for the patient P to lie on. The mechanism control unit  7  controls rotation of the arm  5  and movement of the couch  6 . 
     The system control unit  8  controls the whole of the X-ray imaging apparatus  100 , and includes a three-dimensional blood-vessel image reconstruction-data collecting unit  8   a , and an X-ray fluoroscopic/acquisition image collecting unit  8   b . The three-dimensional blood-vessel image reconstruction-data collecting unit  8   a  controls the whole of the X-ray imaging apparatus  100  so as to collect data for reconstructing a three-dimensional blood vessel image in accordance with, such as an operation by an operator received by the operation unit  12 , and stores the collected data into an image storage unit  22 . The X-ray fluoroscopic/acquisition image collecting unit  8   b  controls the whole of the X-ray imaging apparatus  100  so as to collect an X-ray fluoroscopic image or an X-ray acquisition image in accordance with, such as an operation by the operator received by the operation unit  12 , and stores the collected X-ray fluoroscopic image or the collected X-ray acquisition image into the image storage unit  22 . 
     The X-ray high-voltage generating device  9  includes an X-ray control unit  10 , and a high-voltage generating unit  11 . The X-ray control unit  10  controls an X-ray generated by the X-ray tube  2  by controlling the high-voltage generating unit  11 . The high-voltage generating unit  11  generates a high voltage to be supplied to the X-ray tube  2 . 
     The operation unit  12  receives an operation by the operator to the X-ray imaging apparatus  100 . The display unit  13  displays an image processed by the image processing device  20 . 
     The image processing device  20  includes an image processing unit  21  and the image storage unit  22 . The image processing unit  21  performs image processing on data detected by the X-ray detector  4  and stored by the image storage unit  22 . The image storage unit  22  stores data detected by the X-ray detector  4 , and an image processed by the image processing unit  21 . 
     The image processing device  20  is further explained below with reference to  FIG. 3 .  FIG. 3  is a functional block diagram of a configuration of the image processing unit. 
     As shown in  FIG. 3 , the image processing unit  21  includes a subtraction unit  21   a , a three-dimensional blood-vessel image reconstructing unit  21   b , a 3D roadmap unit  21   c , a displacement determining unit  21   d , and an registration unit  21   e.    
     The subtraction unit  21   a  performs subtraction processing by using data stored in the image storage unit  22 , and creates a Digital Subtraction Angiography (DSA) image. 
     The three-dimensional blood-vessel image reconstructing unit  21   b  creates a three-dimensional blood vessel image from the DSA image created by the subtraction unit  21   a.    
     The 3D roadmap unit  21   c  creates a volume rendering image that is projected based on a state of the X-ray imaging apparatus  100 , from the three-dimensional blood vessel image created by the three-dimensional blood-vessel image reconstructing unit  21   b , and creates a 3D roadmap image that the created volume rendering image and an X-ray fluoroscopic image are combined. 
     The displacement determining unit  21   d  determines a displacement between an aneurysm on the three-dimensional blood vessel image and the aneurysm on the X-ray fluoroscopic image, from the 3D roadmap image created by the 3D roadmap unit  21   c.    
     The registration unit  21   e  registers the 3D roadmap image by using the displacement determines by the displacement determining unit  21   d.    
     A process procedure by the X-ray imaging apparatus according to the first embodiment is explained below with reference to  FIGS. 4 to 6 .  FIG. 4  is a flowchart for explaining three-dimensional (3D) blood-vessel image collecting processing; and  FIG. 5  is a flowchart for explaining 3D roadmap image registration processing.  FIGS. 6A and 6B  and  FIGS. 7A and 7B  are schematic diagrams for explaining determination of a displacement.  FIG. 8  is a schematic diagram for explaining determination from two directions. The first embodiment assumes a case of performing an intervention treatment, which is one of treatment methods for an aneurysm. 
     To begin with, as a preliminary preparation for displaying a 3D roadmap image during a treatment, the X-ray imaging apparatus  100  according to the first embodiment collects a three-dimensional blood vessel image. 
     As shown in  FIG. 4 , under the operation by the operator, the three-dimensional blood-vessel image reconstruction-data collecting unit  8   a  of the system control unit  8  collects X-ray acquisition images for reconstructing a three-dimensional blood vessel image (Step S 101 ). 
     Specifically, the operator adjusts one of the position of the couch  6 , the height of the couch  6 , and the position of the arm  5 , or a combination of some of them, by operating the operation unit  12 , so as to capture a main blood vessel to be a treatment target, in the field of view in all directions. The operator confirms afterward that, for example, rotation of the arm  5  poses no danger to the patient P, and then starts to take an X-ray acquisition image. The three-dimensional blood-vessel image reconstruction-data collecting unit  8   a  then starts to collect X-ray acquisition images. 
     Collection of X-ray acquisition images is performed twice, namely, before an injection of contrast media and after the injection. Before the injection of contrast media, while rotating the arm  5  at high speed as like a propeller by 50 degrees per second, the three-dimensional blood-vessel image reconstruction-data collecting unit  8   a  takes images, for example, at every two degrees, and collects 100 frames of X-ray acquisition images (Step S 101 ). The collected 100 frames of the X-ray acquisition images are converted into digital signals by a not-shown analog-to-digital converter, and stored into the image storage unit  22 . The three-dimensional blood-vessel image reconstruction-data collecting unit  8   a  returns the arm  5  to the initial rotation-starting position quickly. 
     Contrast media are then injected by a contrast-media injector into the patient P, and after a lapse of a certain time, the three-dimensional blood-vessel image reconstruction-data collecting unit  8   a  again takes images, for example, at every two degrees, while rotating the arm  5  at high speed as like a propeller by 50 degrees per second, and collects 100 frames of X-ray acquisition images. Similarly to the X-ray acquisition images collected before the injection of the contrast media, the collected 100 frames of the X-ray acquisition images are converted into digital signals by the not-shown analog-to-digital converter, and stored into the image storage unit  22 . 
     Subsequently, the subtraction unit  21   a  of the image processing unit  21  creates a DSA image (Step S 102 ). 
     Specifically, the subtraction unit  21   a  performs subtraction processing on X-ray acquisition images of corresponding angles by using the X-ray acquisition images before the injection of the contrast media and the X-ray acquisition images after the injection of the contrast media stored in the image storage unit  22  at Step S 101 , thereby creating a DSA image. The subtraction unit  21   a  then sends the created DSA image to the three-dimensional blood-vessel image reconstructing unit  21   b.    
     The three-dimensional blood-vessel image reconstructing unit  21   b  of the image processing unit  21  then creates a three-dimensional blood vessel image (Step S 103 ). 
     Specifically, the three-dimensional blood-vessel image reconstructing unit  21   b  reconstructs a three-dimensional volume image by using the DSA image sent from the subtraction unit  21   a . As an example of reconstruction method, there are a Feldkamp method and ART (algebraic reconstruction technique). The former method is one of a filtered backprojection method, and latter method is one of iterative reconstruction method. The three-dimensional blood-vessel image reconstructing unit  21   b  for Feldkamp method performs appropriate convolution filtering processing, for example, Shepp &amp; Logan, or Ramachandran, on the 100 frames of DSA images. The three-dimensional blood-vessel image reconstructing unit  21   b  then creates a three-dimensional blood vessel image by performing backprojection computing processing, and stores the created three-dimensional blood vessel image into the image storage unit  22 . 
     A reconstruction region is defined as a cylinder that is inscribed in X-ray flux toward all directions of the X-ray tube. The inside of the cylinder needs to be three-dimensionally discreted at intervals of a length d in the center part of the reconstruction region to be projected to the width of one detecting element of the X-ray detector  4 , and a reconstruction image of discrete points needs to be obtained. Although an example of discrete intervals is described here, other discrete intervals defined for the apparatus can be used. 
     In this way, collection of the three-dimensional blood vessel image as a preliminary preparation for displaying a 3D roadmap image during a treatment is finished. 
     When the preliminary preparation is finished, subsequently a treatment is started. In other words, insertion of a catheter by the operator, such as a doctor, is started. At that moment, as the catheter is inserted up to the vicinity of an aneurysm, a bending force of the catheter along a blood vessel and a resilient force are generated, and the blood vessel deforms so as to reduce a bend of the blood vessel. Consequently, not only the position of the blood vessel, but also the position of the aneurysm is displaced from the position at the moment of collecting the three-dimensional blood-vessel image. 
     When the catheter is inserted up to the vicinity of an aneurysm, the operator starts to collect two-dimensional projection data while injecting contrast media in order to grasp the position of the aneurysm accurately. In other words, as shown in  FIG. 5  the X-ray imaging apparatus  100  receives a press of an X-ray acquisition image collection button (Yes at Step S 201 ). 
     The X-ray imaging apparatus  100  then collects an X-ray acquisition image (Step S 202 ). Specifically, the X-ray fluoroscopic/acquisition image collecting unit  8   b  of the system control unit  8  collects several frames before the injection of the contrast media, and a moving image to be collected at a certain rate after the injection of the contrast media, and stores the collected image data into the image storage unit  22 . The subtraction unit  21   a  of the image processing unit  21  then creates a mask image by averaging the several frames before the injection of the contrast media stored in the image storage unit  22 , and performs subtraction processing on the created mask image and the moving image after the injection of the contrast media with respect to each frame, thereby creating a DSA image. 
     The subtraction unit  21   a  then displays the created DSA image onto the display unit  13  (Step S 203 ). The DSA image displayed on the display unit  13  is an image after the subtraction processing, on which a blood vessel image is enhanced. 
     The 3D roadmap unit  21   c  of the image processing unit  21  then determines whether a press of a 3D roadmap button is received, and waits until receiving the press (Step S 204 ). At that moment, the final acquisition image of the DSA image is displayed on the display unit  13 . 
     When the 3D roadmap unit  21   c  then determines that the 3D roadmap button is pressed as the operator presses the 3D roadmap button (Yes at Step S 204 ), the 3D roadmap unit  21   c  creates a volume rendering image (Step S 205 ). 
     Specifically, the 3D roadmap unit  21   c  reads a three-dimensional blood vessel image stored in the image storage unit  22 , and creates a volume rendering image from the read three-dimensional blood vessel image. If there is a plurality of three-dimensional blood vessel images, for example, when a plurality of aneurysms is a treatment target, the 3D roadmap unit  21   c  displays the plurality of three-dimensional blood vessel images onto the display unit  13  in thumbnail, and receives selection by the operator. 
     The 3D roadmap unit  21   c  then receives information indicating a state of the X-ray imaging apparatus  100  from the system control unit  8 , for example, an observation angle, an observation field of view, an observation magnification, and an observation position, and creates a volume rendering image so as to be matched with the state indicated by those information. 
     The 3D roadmap unit  21   c  then creates a 3D roadmap image, and displays it onto the display unit  13  (Step S 206 ). 
     Specifically, the 3D roadmap unit  21   c  combines the volume rendering image created at Step S 205  and the DSA image displayed on the display unit  13  at Step S 203 , and displays it onto the display unit  13 . 
     Here, suppose a displacement occurs between the position of the aneurysm on the volume rendering image and the position of the aneurysm on the DSA image. For example, suppose a displacement shown in  FIG. 6A  occurs. 
     According to the first embodiment, when the displacement determining unit  21   d  of the image processing unit  21  receives a press of a registration switch (Yes at Step S 207 ); the displacement determining unit  21   d  determines a displacement between the position of the aneurysm on the volume rendering image and the position of the aneurysm on the DSA image by using input afterward by the operator (Step S 208 ). 
     For example, suppose after the operator presses a not-shown registration switch, the operator clicks the center of the aneurysm on the volume rendering image displayed on the display unit  13  by using an input device, such as a mouse, moves the volume rendering image through a drag operation so as to match the position of the aneurysm on the volume rendering image with the position of the aneurysm on the DSA image, and then releases the registration switch where the displacement is corrected. For example, suppose it is released at a position as shown in  FIG. 6B . The displacement determining unit  21   d  then determines a displacement by using the operation information by the operator. 
     Subsequently, the displacement determining unit  21   d  associates the determined displacement with observation angle information at this moment, and stores it into the image storage unit  22  (Step S 209 ). 
     The X-ray imaging apparatus  100  according to the first embodiment then stores registration information with respect to the observation angles in two directions. In other words, by repeating processing at Steps S 201  to S 209  except Step S 204 , registration information with respect to the observation angles in two directions is stored. 
     For example, it is assumed that insertion of a coil by the operator, such as a doctor, is started. A coil inserted at first is called a first coil, which is inserted so as to wrap around an aneurysm with a basket. For this reason, the shape of the coil precisely expresses outer contours of the aneurysm, so that the position of the aneurysm can be determined without injecting contrast media. 
     The operator starts to collect an X-ray fluoroscopic image while inserting a coil in order to grasp the position of the aneurysm accurately. In other words, shown in  FIG. 5 , the X-ray imaging apparatus  100  receives a press of an X-ray fluoroscopic image collection button (Yes at Step S 201 ); and collects an X-ray fluoroscopic image (Step S 202 ). 
     At this moment, the 3D roadmap button is in a pressed state, and a 3D roadmap image that the volume rendering image and the X-ray fluoroscopic image are combined is displayed on the display unit  13 . 
     Here, suppose the observation angle is changed. The 3D roadmap unit  21   c  then receives information indicating a state of the X-ray imaging apparatus  100  from the system control unit  8 , for example, an observation angle, an observation field of view, an observation magnification, and an observation position, and creates a volume rendering image so as to be matched with the state indicated by those information. 
     By receiving a press of the X-ray fluoroscopic image collection button, the 3D roadmap unit  21   c  then creates a 3D roadmap image, and displays it onto the display unit  13  (Step S 206 ). 
     Here, suppose a displacement occurs again between the position of the aneurysm on the volume rendering image and the position of the aneurysm (coil) on the X-ray fluoroscopic image. For example, suppose a displacement as shown in  FIG. 7A  occurs. 
     When the displacement determining unit  21   d  of the image processing unit  21  receives a press of the registration switch (Yes at Step S 207 ); the displacement determining unit  21   d  determines again a displacement between the position of the aneurysm on the volume rendering image and the position of the coil on the X-ray fluoroscopic image by using input afterward by the operator (Step S 208 ). 
     For example, suppose after the operator presses the not-shown registration switch, the operator clicks the center of the aneurysm on the volume rendering image displayed on the display unit  13  by using the input device, such as a mouse, moves the volume rendering image through a drag operation so as to match the position of the aneurysm on the volume rendering image with the coil on the X-ray fluoroscopic image, and then releases the registration switch where the displacement is corrected. For example, suppose it is released at a position as shown in  FIG. 7B . The displacement determining unit  21   d  then determines a displacement by using the operation information by the operator. 
     Subsequently, the displacement determining unit  21   d  associates the determined displacement with observation angle information at this moment, and stores it into the image storage unit  22  (Step S 209 ). In this way, the X-ray imaging apparatus  100  according to the first embodiment stores registration information with respect to the observation angles in two directions. 
     As shown in  FIG. 8 , the aneurysm center position on the three-dimensional blood vessel image can be determined from the aneurysm center coordinates in two directions, and the present aneurysm center position can be determined from the coordinates of the displacement destination; accordingly, registration information for registering with respect to the observation angles in the two directions can be collected. The position at the moment of collecting the three-dimensional blood vessel image and the present position of the aneurysm in the three-dimensional space can be determined, and subsequent displacements can be automated. In other words, as the aneurysm center position on the three-dimensional blood vessel image is corrected so as to match with the present aneurysm center position, when the observation angle is changed afterward, the X-ray imaging apparatus  100  according to the first embodiment can display the registered 3D roadmap image onto the display unit  13 . 
     As described above, the X-ray imaging apparatus  100  according to the first embodiment creates a volume rendering image that is projected based on a state of the X-ray imaging apparatus  100 , and creates a 3D roadmap image of the created volume rendering image and an X-ray fluoroscopic image. The X-ray imaging apparatus  100  determines a displacement between an aneurysm on the volume rendering image and the aneurysm on the X-ray fluoroscopic image. The X-ray imaging apparatus  100  then registers the 3D roadmap image by using the determined displacement, and displays the registered 3D roadmap image onto the display unit  13 . 
     Accordingly, the X-ray imaging apparatus  100  according to the first embodiment can correct a displacement of an aneurysm. In other words, the X-ray imaging apparatus  100  according to the first embodiment registers the volume rendering image and the X-ray fluoroscopic image based on information about the aneurysm that is an observation portion. 
     As a result, the displacement of the aneurysm can be corrected, so that the position of the aneurysm on the volume rendering image and the position of the aneurysm on the X-ray fluoroscopic image are matched with each other on the 3D roadmap image. For example, according to the conventional 3D roadmap function, a displacement of the aneurysm brings about difficulty in comparing a total shape of an aneurysm, thereby resulting in a situation that it is difficult to grasp loading of a coil; however, according to the X-ray imaging apparatus  100  of the first embodiment can avoid such situation. 
     The X-ray imaging apparatus  100  according to the first embodiment can use a method of collecting X-ray images from observation angles in at least two directions, and determining the position of an aneurysm in a three-dimensional space by using the X-ray images collected from the observation angles in at least two directions. In such case, the X-ray imaging apparatus  100  determines the position of an aneurysm in the three-dimensional space also from the three-dimensional blood vessel image, thereby determining the position of the aneurysm in the three-dimensional space at the moment of collecting the three-dimensional blood vessel image and the present position of the aneurysm in the three-dimensional space. The X-ray imaging apparatus  100  then corrects the aneurysm center position on the three-dimensional blood vessel image so as to match with the present aneurysm center position, thereby automatically correcting displacement even when the observation angle is changed. In such case, registration of the 3D roadmap image can be automated by using already collected information. 
     A second embodiment is explained below. Although the first embodiment has explained above the method of correcting only positional displacement of an aneurysm, the second embodiment explains below a method of correcting the angle of an aneurysm.  FIGS. 9A to 9D  are schematic diagrams for explaining differences of areas of an aneurysm. 
     Sometimes, a position at which an aneurysm is produced is in a part with a large curvature, for example, as shown in  FIG. 9A , in some cases. However, if a catheter is inserted up to the vicinity of the aneurysm for treating the aneurysm, the catheter tries to rebound to a straight line, so that the catheter deforms to a direction to have a smaller curvature as shown in  FIG. 9B . As a result, a displacement occurs as described above. 
     However, when change in the curvature is large, if only positional displacement is corrected, a difference still occurs in the area of the aneurysm, as shown in  FIG. 9C . Specifically, an enlarged view of the aneurysm and its peripheral part are shown in  FIG. 9D , in which shaded portions indicate differences in the area of the aneurysm between the moment of taking the three-dimensional blood vessel image and the moment of the 3D roadmap. 
     In order to correct the differences, the X-ray imaging apparatus  100  according to the second embodiment corrects not only the position of the aneurysm, but also the angle with a parent vessel, thereby being capable to match the area of the aneurysm completely between the moment of taking the three-dimensional blood vessel image and the moment of the 3D roadmap, as shown in  FIGS. 10A and 10B .  FIGS. 10A and 10B  are schematic diagrams for explaining an area of an aneurysm after positional and angular registrations. 
       FIGS. 11A and 11B  are schematic diagrams for explaining determination according to the second embodiment. For example, the displacement determining unit  21   d  of the image processing unit  21  determines the center of a parent vessel at proximal and distal positions of an aneurysm, as shown in  FIGS. 11A and 11B . Here, it is assumed that the center of the aneurysm and the center positions of the parent vessel at proximal and distal positions of an aneurysm at the moment of taking the three-dimensional blood vessel image are denoted by A c , A p , and A d , respectively. Furthermore, the center of the aneurysm and the center positions of the parent vessel in front and back of the aneurysm at the moment of 3D roadmap are denoted by B c , B p , and B d , respectively. 
     The displacement determining unit  21   d  then registers the position and the angle so as to match A c  and B c , and so as to parallelize a straight line A connecting A p  and A d , and a straight line B connecting B p  and B d . The displacement determining unit  21   d  can directly determine three-dimensional coordinates of three points from the three-dimensional blood vessel image, can further determine three-dimensional coordinates by determining the present three points from two directions, and can automate positional and angular registrations afterward (in the third direction and afterward). 
     As described above, the X-ray imaging apparatus  100  according to the second embodiment determines the amount of inclination of a parent vessel in the vicinity of an aneurysm on a three-dimensional blood vessel image, and determines the amount of inclination of the parent vessel in the vicinity of the aneurysm on an X-ray image. The X-ray imaging apparatus  100  then registers a 3D roadmap image by using the determined displacement and the determined amount of inclination, and displays the registered 3D roadmap image onto the display unit  13 . 
     Accordingly, the X-ray imaging apparatus  100  according to the second embodiment can correct an angular displacement of an aneurysm as well as a positional displacement. In other words, the X-ray imaging apparatus  100  according to the second embodiment corrects an angular displacement based on the amount of inclination of a parent vessel in the vicinity of the aneurysm. As a result, the angular displacement of the aneurysm can be corrected as veil as the positional displacement, so that the position of the aneurysm on the volume rendering image and the position of the aneurysm on the X-ray fluoroscopic image are more accurately matched with each other on the 3D roadmap image. 
     The X-ray imaging apparatus  100  according to the second embodiment can use a method of collecting X-ray images from observation angles in at least two directions, and determining the position of three points in the vicinity of an aneurysm in a three-dimensional space by using the X-ray images collected from the observation angles in at least two directions. In such case, the X-ray imaging apparatus  100  determines the position of the three points in the vicinity of the aneurysm in the three-dimensional space also from the three-dimensional blood vessel image, thereby determining the position of the three points in the vicinity of the aneurysm in the three-dimensional space at the moment of collecting the three-dimensional blood vessel image and the present position of the three points in the vicinity of the aneurysm in the three-dimensional space. The X-ray imaging apparatus  100  then registers the three-dimensional blood vessel image so as to match the aneurysm center position on the three-dimensional blood vessel image with the present aneurysm center position, and to match the parent vessel angle on the three-dimensional blood vessel image with the present parent vessel angle. Accordingly, even when the observation angle is changed, positional displacement and angular displacement can be automatically corrected. 
     Moreover, by combining it with the method of determining the position of the aneurysm in the three-dimensional space at the moment of collecting the three-dimensional blood vessel image and the present position of the aneurysm in the three-dimensional space, when the observation angle is changed afterward, the X-ray imaging apparatus  100  can automate registration of a 3D roadmap image against positional displacement and angular displacement by using already collected information. 
     Although the first embodiment and the second embodiment are explained above, an embodiment can be implemented by various different forms in addition to the embodiments described above. 
     Although the first embodiment explains above the method by which the X-ray imaging apparatus determines a displacement by using operation information by the operator (such as a drag operation), an embodiment is not limited to this. For example, it can be a method by which the operator is led to click the center of an aneurysm on a volume rendering image and to click the center of the aneurysm on an X-ray fluoroscopic image, and then a displacement is determined by using those operation information. 
     Moreover, for example, it can be a method by which the X-ray imaging apparatus determines an aneurysm by performing analysis processing on each of a volume rendering image and a DSA image/an X-ray fluoroscopic image, and determines displacement between aneurysms. 
     Various methods of analysis processing are conceivable. For example, a method can be used by which respective positions of the aneurysm on a volume rendering image and a DSA image are determined by continuously performing trace processing on boundaries between a blood vessel region and the other regions, detecting a discontinuous point during the trace processing, and determining that the point is a neck of the aneurysm, so that displacement is determined from the respective determined positions of the aneurysm. 
     Moreover, a method can be used by which the position of an aneurysm is determined from an X-ray fluoroscopic image by extracting the shape of a coil inserted into the aneurysm through threshold processing, and then displacement is determined by using the position of the aneurysm and a position of the aneurysm determined from a volume rendering image. A material having a high X-ray absorption coefficient, such as platinum, is used in a coil in the greater number of cases. Therefore, it can be configured to extract a coil through image processing in accordance with a threshold, and to determine that a portion extracted as the most outer coil is the boundary of an aneurysm. 
     Furthermore, for example, a method of determining displacement by performing correlation computing processing between a volume rendering image and a DSA image/an X-ray fluoroscopic image can be used. 
     It is specifically explained below. Between a volume rendering image and an X-ray fluoroscopic image, the displacement determining unit  21   d  performs correlation computing processing expressed by Expression (1) as follows:
 
Error(Δ x,Δy )=∫∫{Fluoro( x−Δx,y−Δy )−RM( x,y )} 2   dx,dy   (1)
 
     where, “Δx” denotes a displacement in the x axis direction between an aneurysm on the volume rendering image and the aneurysm on the X-ray fluoroscopic image. Moreover, “Δy” denotes a displacement in the y axis direction between the aneurysm on the volume rendering image and the aneurysm on the X-ray fluoroscopic image. 
     Furthermore, “Fluoro” stands for “fluorography”, and corresponds to the X-ray fluoroscopic image in this case. Moreover, “RM” stands for “Roadmap”, and corresponds to the volume rendering image on a 3D roadmap image in this case. 
     In other words, the right side of Expression (1) is a subtraction between the X-ray fluoroscopic image that is moved by “Δx” in the x axis direction and by “Δy” in the y axis direction, and the volume rendering image on the 3D roadmap image, so that as the higher the degree of matching between the both images becomes, the smaller the value of the left side, “Error(Δx, Δy)”, turns. 
     Therefore, the displacement determining unit  21   d  obtains “Δx” and “Δy” that bring “Error(Δx, Δy)” to the minimum value by calculating. 
     The registration unit  21   e  then registers the 3D roadmap image in accordance with “Δx” and “Δy” calculated by the displacement determining unit  21   d  as registration information. For example, the registration unit  21   e  moves the position of the volume rendering image to be combined to the 3D roadmap image by “Δx” in the x axis direction and by “Δy” in the y axis direction, and combines anew the moved volume rendering image with the X-ray fluoroscopic image, thereby registering the 3D roadmap image. 
     When performing the correlation computing processing, a method can be used according to which the farther it is from the position of an aneurysm, the smaller weight is assigned to the correlation coefficient. In other words, suppose an aneurysm is relatively small in relation to the size of a blood vessel. Consequently, if only the correlation computing processing between the images is simply performed, there is a possibility that when a displacement of the blood vessel is corrected, it may be determined that “the displacement of the aneurysm is corrected”. However, if the correlation coefficient is assigned with a weight, for example, the position of an aneurysm is determined from one of the images, and the farther it is from the position of the determined aneurysm, the smaller correlation coefficient is applied; registration by placing emphasis on displacement of the aneurysm can be performed in the correlation computing processing. 
     It is specifically explained below. Between a volume rendering image and an X-ray fluoroscopic image, the displacement determining unit  21   d  performs correlation computing processing expressed by Expression (2) as follows: 
     
       
         
           
             
               
                 
                   
                     
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     in addition,
 
 r =sqrt{( x−x   0 ) 2 +( y−y   0 ) 2 }  (3)
 
     It is assumed that “x 0 ” and “y 0 ” denote coordinates indicating the position of the aneurysm (for example, the center of the aneurysm) on the volume rendering image before registration. Consequently, “r” in Expression (3) denotes a distance from the position of the aneurysm (for example, the center of the aneurysm). 
     In other words, Expression (2) is an expression that Expression (1) is multiplied by “1/r+1” such that the farther it is from the position of the aneurysm, the smaller weight is assigned to the correlation coefficient. For example, when it is close to the center of the aneurysm, the value of “r” is small, so that a result of the subtraction between the volume rendering image and the X-ray fluoroscopic image is calculated with a weight close to “1”. By contrast, when it is far from the center of the aneurysm, the value of “r” is large, so that a result of the subtraction between the volume rendering image and the X-ray fluoroscopic image is calculated with a weight much less than “1”. 
     Therefore, the displacement determining unit  21   d  obtains “Δx” and “Δy” that bring “Error(Δx, Δy)” to the minimum value by calculating, according to Expression (2). The registration unit  21   e  then registers the 3D roadmap image in accordance with “Δx” and “Δy” calculated by the displacement determining unit  21   d  as registration information. 
     The method of determining displacement by performing correlation computing processing can be combined with the trace processing or the threshold processing described above. In other words, the correlation computing processing performed by the displacement determining unit  21   d  can be processing to be performed on a volume rendering image itself and an X-ray fluoroscopic image itself, or can be correlation computing processing to be performed between aneurysms extracted from respective images through the trace processing or the threshold processing. 
     The second embodiment explains above the example of performing registration of angular displacement in addition to positional displacement by determining the amount of inclination of a parent vessel in the vicinity of an aneurysm, and furthermore, correlation computing processing can be used for the registration. 
     It is specifically explained below. Between a volume rendering image and an X-ray fluoroscopic image, the displacement determining unit  21   d  performs correlation computing processing expressed by Expression (4) as follows:
 
Error(Δ x,Δy,Δθ )=∫∫{Fluoro( X−ΔX   0   ,Y−ΔY   0 )−RM( x,y )} 2   dx,dy   (4)
 
where,
 
 X=x  cos θ− y  sin θ  (5)
 
 Y=x  sin θ+ y  cos θ  (6)
 
Δ X   0   =Δx  cos θ−Δ y  sin θ  (7)
 
Δ Y   0   =Δx  sin θ+Δ y  cos θ  (8)
 
     Precisely, “Δθ” denotes a rotational angle between an aneurysm on the volume rendering image and the aneurysm on the X-ray fluoroscopic image. Moreover, “X”, “Y”, “ΔX 0 ”, and “ΔY 0 ” are expressed by Expressions (5) to (8) described above. In this way, Expressions (4) to (8) express that the x coordinate and the y coordinate (the coordinate system of the x axis and the y axis) are converted into the coordinate system of the X axis and the Y axis, which the x axis and the y axis are rotated by θ degree, respectively; so that as the higher the degree of matching between the volume rendering image and the X-ray fluoroscopic image becomes, the smaller the value of the left side of Expression (4), “Error(Δx, Δy, Δθ)”, turns. 
     Therefore, the displacement determining unit  21   d  obtains “Δx”, “Δy”, and “Δθ” that bring “Error(Δx, Δy, Δθ)” to the minimum value by calculating. 
     The registration unit  21   e  then registers the 3D roadmap image in accordance with “Δx”, “Δy”, and “Δθ” calculated by the displacement determining unit  21   d  as registration information. For example, the registration unit  21   e  moves the position of the volume rendering image to be combined to the 3D roadmap image by “Δx” in the x axis direction and by “Δy” in the y axis direction, and rotates it by “−Δθ”, then combines anew the moved and rotated volume rendering image with the X-ray fluoroscopic image, thereby registering the 3D roadmap image. 
     Moreover, for example, a method of determining three-dimensional coordinates indicating the center of an aneurysm by performing ray trace processing on the aneurysm on a volume rendering image can be used. Furthermore, for example, a method of determining an aneurysm and determining a displacement by performing image processing of detecting a round shape from each of a volume rendering image and an X-ray fluoroscopic image can be used. 
     Although the first embodiment explains above the method of using a three-dimensional blood vessel image that is created based on two-dimensional projection data collected by the X-ray imaging apparatus as a three-dimensional blood vessel image, an embodiment is not limited to this. For example, image data of Computed Tomography Angiography (CTA), Magnetic Resonance Angiography (MRA), no-contrast enhancement Magnetic Resonance Imaging (MRI), or the like, can be used. In such case, as shown in  FIG. 12 , the X-ray imaging apparatus can include a three-dimensional image acquiring unit, and the three-dimensional image acquiring unit can acquire those image data from another device via a network, for example, Ethernet (registered trademark). When the image data include human body information other than blood vessel information, blood vessel information can be additionally extracted by using a method of threshold processing, a method of specifying the range of pixel value, or a method of region growing, or a combination of some of them, and a three-dimensional blood vessel image can be created. 
     Moreover, the methods described above are not limited to the 3D roadmap function, and can be applied to a two-dimensional roadmap. 
     The first embodiment and the second embodiment explain above the methods according to which the X-ray imaging apparatus  100  uses as an X-ray image an X-ray acquisition image (DSA image) that is taken while injecting contrast media in the first time direction, and uses an X-ray fluoroscopic image in the second time direction. However, an embodiment is not limited to this. For example, it can be a method of using an X-ray fluoroscopic image that is taken while injecting contrast media in the first time direction, or a method of using an X-ray acquisition image in the second time direction. In other words, which of an X-ray acquisition image and an X-ray fluoroscopic image to be used as an X-ray image, and in what way to combine them to use are arbitrarily selectable. In the above description, “X-ray fluoroscopic image” is used as the meaning of an X-ray image that is taken with, for example, X-rays of a low radiation dose; on the other hand, “X-ray acquisition image” is used as the meaning of an X-ray image that is taken with, for example, X-rays of a high radiation dose. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.