Abstract:
An angiography system for angiographic examination of a patient is provided. The system has an x-ray emitter and an x-ray image detector attached to the ends of a C-arm, a patient support couch, a system control unit, an image system and a monitor. The system control unit generates a mask image that detects a reference image, effects a registration of the reference image to the C-arm, whereby if necessary a segmentation of the examination object is implemented in the reference image, contrasts image regions lying inside of the segmentation in order to generate a mask image, and subtracts the mask image from fluoroscopy live images acquired by the angiography system without contrast agent in order to form a roadmap image. The image system effects a reproduction of the roadmap images on the monitor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of German application No. 10 2011 005 777.3 filed Mar. 18, 2011, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The invention relates to an angiography system for the angiographic examination or intervention of an organ, vascular system or other body regions as an examination object of a patient using an x-ray emitter, an x-ray image detector, which are attached to the ends of a C-arm, a patient support couch with a couch plate for supporting the patient, a system control unit, an imaging system and a monitor as well as an angiographic examination method for the angiography system. 
       BACKGROUND OF INVENTION 
       [0003]    An angiography system of this type is known for instance from U.S. Pat. No. 7,500,784 B2 which is explained with the aid of  FIG. 1 . 
         [0004]      FIG. 1  shows a monoplanar x-ray system shown as an example having a C-arm  2  held by a stand  1  in the form of a six-axle industrial or articulated arm robot, to the ends of which an x-ray radiation source, for instance an x-ray emitter  3  having x-ray rubes and a collimator, and an x-ray image detector  4  as an image recording unit are attached. 
         [0005]    By means of the articulated arm robot known for instance from U.S. Pat. No. 7,500,784 B2, which preferably comprises six axes of rotation and thus six degrees of freedom, the C-arm  2  can be spatially adjusted in any way, for instance by being rotated about a center of rotation between the x-ray emitter  3  and the x-ray image detector  4 . The inventive angiographic x-ray system  1  to  4  can in particular be rotated about centers of rotation and axes of rotation in the C-arm plane of the x-ray image detector  4 , preferably about the center point of the x-ray image detector  4  and about the axes of rotation which intersect the center point of the x-ray image detector  4 . 
         [0006]    The known articulated arm robot comprises a base frame, which is fixedly mounted for instance on a floor. A carousel is rotatably fastened thereon about a first axis of rotation. A robot rocker is pivotably attached to the carousel about a second axis of rotation, to which a robot arm is rotatably fastened about a third axis of rotation. A robot hand is rotatably attached to the end of the robot arm about a fourth axis of rotation. The robot hand comprises a fastening element for the C-arm  2 , which can be pivoted about a fifth axis of rotation and can be rotated about a sixth axis of rotation which proceeds at right angles thereto. 
         [0007]    The realization of the x-ray diagnostics facility is not dependent on the industrial robot. Conventional C-arm devices can also be used. 
         [0008]    The x-ray image detector  4  may be a rectangular or square, flat semi-conductor detector, which is preferably created from amorphous silicon (a-Si). Integrated and possibly counting CMOS detectors can however also be used. 
         [0009]    A patient  6  to be examined as the examination object is located in the beam path of the x-ray emitter  3  on a couch plate  5  of a patient support couch. A system control unit  7  with an imaging system  8  is connected to the x-ray diagnostics facility, said imaging system receiving and processing the image signals of the x-ray image detector  4  (control elements are not shown for instance). The x-ray images can then be observed on displays of a monitor  9 . A known collision calculator  10  is further provided in the system control unit  7 , the function of which is described again in more detail. 
         [0010]    Instead of the x-ray system shown by way of example in  FIG. 1  having the supporting stand  1  in the fond of the six-axle industrial or articulated arm robot, as shown in simplified form in  FIG. 2 , the angiographic x-ray system can also comprise a normal ceiling or floor-mounted retaining bracket for the C-arm  2 . 
         [0011]    Instead of the C-arm  2  shown by way of example, the angiographic x-ray system can also comprise separate ceiling and/or floor-mounted retaining brackets for the x-ray emitter  3  and x-ray image detector  4 , which are fixedly electronically coupled for instance. 
         [0012]    By means of the articulated arm robot known from the afore-cited U.S. Pat. No. 7,500,784, B2, rotation angiographs, so-called DynaCTs, can be created in order to generate 3D image recordings of an aneurysm for instance. 
         [0013]    Angiography systems of this type are used in the field of fluoroscopy-controlled, interventional repairs of abdominal aortic aneurysms. 
         [0014]    An abdominal aortic aneurysm (AAA) is an aneurysm on the abdominal aorta. This is treated by inserting a stent graft. Guide wires and catheters are introduced into the aorta by way of the two strips, by way of which one or several stent grafts, otherwise known as composite stent-graft devices, are introduced (see  FIG. 3 ), such as are shown for instance in Cardiology today, January 2011, page 36. The aim when inserting these stent grafts is to position the “landing zone” of the vascular prosthesis as far as possible in the healthy vascular wall, but in the process not to cover any important vessel outlets. The outlets of the renal arteries, the superior mesenteric artery (arteria mesenterica superior), the truncus coeliacus, and the internal pelvic arteries (arteria iliaca interna) are to be kept free. One sensitive point is the disposal of the “main stent” in the aorta, whereby the said vessel outlets are not permitted to be closed. With complex stents which include the leg arteries, the final stent must sometimes be composed of “partial stents” (for instance an aortic stent to which stents for leg arteries are attached). 
         [0015]    The so-called “roadmapping” technology is frequently used for the precise positioning of the stents, such as is described again by way of example for instance with the aid of  FIGS. 4 to 9 . The idea here is provide the physician with a type of “map” to navigate the instrument by continuously displaying the vessels. A mask image is herewith initially generated by administering contrast agent. The subsequently recorded fluoroscopy live images are now captured without contrast agent, nevertheless with an introduced instrument. If the mask image is deduced from the live images, the roadmap images are obtained, on which the anatomical background was “subtracted” and the vessels appear to be light-colored and the introduced instrument appears to be dark. The problem is that a new mask image has to be created for each new angulation. 
         [0016]    In order, for monitoring purposes, not to have to inject contrast agent for a constant vessel representation during the complex stent positioning, a reference image can also be correctly anatomically overlaid which shows the vessels, in the case of the aorta and the outgoing vessels. This reference image may either be a 2D angiography (DSA—digital subtraction angiography) or, more expediently, a previously captured 3D image data record, for instance a CT angiography, of the aneurysm. These show more details and can be overlaid at any angulation of the C-arm (see  FIGS. 4 to 9 ). Occasionally such a reference volume or image is also presegmented (see  FIGS. 10 and 11 ). 
         [0017]    This representation may however be unfamiliar to the physician. Furthermore, the overlaid reference image may possibly cover important details of the fluoroscopy image. 
         [0018]    In summary, common knowledge is:
       The manual or automatic segmentation of AAAs and the corresponding calculation of centerlines,   The (flexible) 2D/3D or 3D/3D registration, for instance of 2D and 3D angiographs,   The roadmap technology and   The adaptive 2D reference overlay, such as is described for instance in DE 10 2008 023 918 A1.       
 
       SUMMARY OF INVENTION 
       [0023]    The invention assumes the object of embodying an angiography system for the angiographic examination of a patient and angiographic examination method for examining the patient of the type cited in the introduction such that mask images of this type are also generated from any angulations without the repeated administration of contrast agents, so that the physician is able to achieve his/her usual roadmap representation. 
         [0024]    The object is achieved in accordance with the invention for an angiography system of the type cited in the introduction by the features cited in the independent claim. Advantageous embodiments are specified in the dependent claims. 
         [0025]    The object is achieved in accordance with the invention for an angiography system, such that an apparatus for generating a mask image is provided in the system control unit, which is embodied such that,
       it captures a reference image adapted to different or changed imaging geometries of the angiography system,   it effects a registration of the reference image to the C-arm, whereby a segmentation of the examination object is if necessary implemented in the reference image,   it contrasts image regions lying within the segmentation in order to generate a mask image, and   it subtracts this mask image from fluoroscopy live images acquired by the angiography system without contrast agent to form a roadmap image, and
 
that the image system effects a reproduction of the roadmap images on the monitor. As a result, a creation of a mask image for a roadmap is achieved without the renewed or repeated administration of contrast agent for changing angulations, couch positions etc.
       
 
         [0030]    If pre-interventional, segmented 3D data is used, no segmentation of the examination object needs to be implemented in the reference image. On the other hand, after registering the reference image to the C-arm, the examination object has to be segmented in the reference image. 
         [0031]    An adaptive reference image is an anatomically correct overlay (2D/3D), which adjusts to changed imaging geometry (in other words C-arm angle, zoom etc. and/or couch positions). The registration of the reference image to the C-arm is known for instance from “Imaging Systems for Medical Diagnostics”, edited by Arnulf Oppelt, 2005, pp. 65-66. 
         [0032]    It has proven advantageous if the image regions lying within the segmentation are contrasted such that they are set to black in order to darken or homogenously color a specific offset value according to the local thickness of the vessel. Alternatively, the local thickness of the vessel can be calculated from the distances of the vessel edges detected by means of the segmentation or can be replaced, colored and/or darkened according to a mathematical forward projection of the segmentation (DRR). 
         [0033]    The adaptive reference image which is registered to the C-arm may advantageously be a 2D reference image which adjusts to different settings of the angiography system, whereby the different settings may be changes to the zoom, the SID and/or couch settings. 
         [0034]    According to the invention, the adaptive reference image which is registered to the C-arm may be a 3D data record of a CT angiography implemented prior to an intervention or a C-arm CT angiography recorded during the intervention. 
         [0035]    It has proven advantageous for the apparatus for generating a mask image to effect a display of additional information, whereby this additional information can be displayed through recesses of mask parts. 
         [0036]    The additional information may be inventive information relating to vascular courses, vascular occlusions, orifices and/or thrombi. 
         [0037]    The object is inventively achieved for an angiographic examination method for examining an organ, vascular system or other body regions of a patient with an afore-cited apparatus by means of the following steps:
   S1) Detecting a reference image   S2) Registering the reference image to the C-arm, whereby a segmentation of the examination object is if necessary implemented in the reference image,   S3) Creating a mask image from the reference image for a roadmap image with different alignments of the C-arm, without administering contrast agent,   S4) Creating a mask image from the reference image for a roadmap image with different alignments of the C-arm without administering contrast agent,   S5) Generating fluoroscopy live images,   S6) Subtracting the mask image from the fluoroscopy live images in order to generate roadmap images and   S7) Reproducing the roadmap images.   
 
         [0045]    If pre-interventional 3D data of a computed tomography for instance is used to detect a reference image, these may already be segmented. It is only then that a registration of the reference image to the C-arm takes place. The segmentation can therefore also take place as a first step prior to registration. 
         [0046]    If by contrast a 3D data record is created by means of DynaCT, it is only then that a registration of the reference image to the C-arm takes place and then the segmentation of the examination object in the reference image. 
         [0047]    The generation of a mask is simplified if in order to create a mask image from the reference image according to step S4, the image regions lying within the segmentation of the aneurysm are contrasted. This may be inventively achieved if they are set to black or they are “darkened” according to the local thickness of the vessel. 
         [0048]    An aneurysm of a patient can advantageously be segmented for segmentation purposes according to step 3). 
         [0049]    The navigation of instruments is simplified by improved visibility in the vessel, if additional information is displayed in the mask image and/or the roadmap image. These can be displayed in accordance with the invention through recesses of mask parts, whereby the additional information is information relating to vascular courses, vascular occlusions, orifices and/or thrombi. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0050]    The invention is described in more detail below with the aid of exemplary embodiments shown in the drawing, in which; 
           [0051]      FIG. 1  shows a known C-arm angiography system having a industrial robot as a carrying apparatus, 
           [0052]      FIG. 2  shows an abdominal aorta with an aortic aneurysm, 
           [0053]      FIG. 3  shows the aorta according to  FIG. 2  with an inserted stent graft, 
           [0054]      FIGS. 4 to 6  show schematic representations to explain the road mappings, 
           [0055]      FIGS. 7 to 9  show road mapping as an example of an abdominal aortic aneurysm, 
           [0056]      FIG. 10  shows a principle of a 2D/2D overlay, 
           [0057]      FIG. 11  shows a principle of a 2D/3D overlay, 
           [0058]      FIG. 12  shows a segmentation for a “virtual roadmap mask”, 
           [0059]      FIG. 13  shows a generation of a “virtual roadmap mask”, 
           [0060]      FIG. 14  shows a “virtual roadmap mask” with additional information, 
           [0061]      FIGS. 15 and 16  show roadmaps with additional information, 
           [0062]      FIG. 17  shows a segmentation for a “virtual roadmap mask” 
           [0063]      FIG. 18  shows a generation of a “virtual roadmap mask”, and 
           [0064]      FIG. 19  shows an inventive roadmap having a plurality of additional information. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0065]    An abdominal aorta  11  is shown in  FIG. 2 , which comprises an abdominal aortic aneurysm (AAA). An abdominal aortic aneurysm (AAA)  12  is an aneurysm on the abdominal aorta  11 . 
         [0066]    The aortic aneurysm  12  is treated by inserting a stent graft, in other words a composite stent graft device, such as is shown in  FIG. 3 . To this end, guide wires  14  and catheters  15  are introduced into the aorta  11  by way of the two strips through the leg arteries  13 , by way of which the stent grafts  16  are introduced. 
         [0067]    With complex stent grafts  16 , which include the leg arteries  13 , the final stent must sometimes be composed of “partial stents”, whereby a partial stent  18  for the other leg artery  13  is “flanged” on an aortic stent  17  for instance, which protrudes through the AAA into one of the leg arteries  13 , through a so-called window. 
         [0068]    The principle behind road mapping technology is now indicated in  FIGS. 4 to 6  with the aid of a schematic representation. The basic idea behind the road mapping technology is to provide the physician with a type of “map” for navigating instruments during the examination and intervention above all in body regions which are subjected to less movement, such as the aorta or the cranium, by constantly displaying the vessels. A mask image  20  ( FIG. 4 ) is herewith initially generated by administering contrast agent, which for instance indicates an anatomical background  21  with a contrast agent-filled aorta  22 . Subsequently acquired fluoroscopy live images  23  ( FIG. 5 ) are now recorded without contrast agent but with an introduced instrument  24 . If the mask image  20  according to  FIG. 4  is taken from these fluoroscopy live images  23 , a roadmap image  25  ( FIG. 6 ) is obtained, from which the anatomical background  21  was “subtracted”. The vessels  26  appear to be light-colored, the introduced instrument  24  appears to be dark and the subtracted anatomical background  27  appears to be gray. 
         [0069]    With the aid of  FIGS. 7 to 9 , the principle behind the road mapping technology according to  FIGS. 4 to 6  is now shown in real x-ray images in the example of an aortic aneurysm  28 , which can be seen in the mask image  20  ( FIG. 7 ) on account of the contrast agent administration in front of the anatomical background  21 . In the subsequently recorded fluoroscopy live images  23  according to  FIG. 8 , the introduced instrument  24  is now additionally visible; the aortic aneurysm  28  is however only very unclearly visible, if at all, on account of the missing contrast agent. 
         [0070]    By subtracting the mask image  20  according to  FIG. 7  and these fluoroscopy live images  23  according to  FIG. 8 , only the roadmap images  25  shown in  FIG. 9  are obtained, on which the anatomical background  21  was almost completely eliminated. The vessels  26  formerly filled with contrast agent and the aortic aneurysm  28  appear to be lighter colored than the gray subtracted anatomical background  27  and the reproduced dark instrument  24 . The physician is now able to see where he/she has to navigate the instrument  24 . 
         [0071]    The principle of the 2D/2D and 2D/3D overlay is now explained in more detail with the aid of  FIGS. 10 and 11 . 
         [0072]    In order already nowadays to provide the physician with additional information when positioning the AAA stent, a previously recorded reference image is anatomically correctly overlaid onto the fluoroscopy image. This reference image may either be a 2D angiography  30  (DSA) of the abdominal aortic aneurysm  31  according to  FIG. 10  or more expediently a 3D data record, for instance computed tomography, of the aortic aneurysm  31  according to  FIG. 11 , such as indicated symbolically. 
         [0073]    In  FIG. 11 , a 3D segmentation of the aorta with the abdominal aortic aneurysm  31  from the pre-interventionally generated 3D data record was implemented as a prerequisite, which can be calculated for instance as a 3D grid model  32 , such as is shown by way of example in the cube. The 3D grid model  32  is projected into the fluoroscopy image as segmentation  33 , such as is symbolized by the dotted lines  34 , and a 2D/3D overlay image  35  or reference image is obtained. 
         [0074]    A pre-segmented, pre-operative computed tomography is used for instance for this 3D overlay. No additional contrast agent is therefore actually also needed here. 
         [0075]    By contrast, in  FIG. 10 , there is no 3D grid model  32 , but instead only the 2D angiography  30 . The abdominal aortic aneurysm  31  in the 2D angiography  30  is segmented and this 2D segmentation  36  is projected into the fluoroscopy image (if also only precisely from this view) and a 2D/2D overlay image  37  or reference image is obtained. 
         [0076]    For this 2D overlay by means of a DSA, a single contrast agent administration is however needed, the advantage of a “normal” roadmap is however that certain changes to the C-arm  2  such as zoom, SID and/or small couch movements can be included. 
         [0077]    In the case of the two  FIGS. 10 and 11 , it is always only the outline of the 2D projection and not the full model which is shown. 
         [0078]    Resulting from the 2D angiography  30  to the 2D overlay image  35  are the steps
       segmentation of the aorta with the abdominal aortic aneurysm  31  in the 2D angiography  30  and   displaying the outlines of the segmented aorta as a 2D segmentation  36  in the native fluoroscopy image.       
 
         [0081]    The main prerequisite for the inventive representation is an adaptive reference image registered to the C-arm, as is explained further with the aid of  FIGS. 10 and 11 , this may be either
       a 3D data record which is registered to the C-arm, for instance a previously implemented CT angiography or a C-arm CT recorded during the intervention or   a 2D reference image registered to the C-arm (for instance a DSA), which adjusts to the different zoom, SID, couch settings etc.   (see DE 10 2008 023 918 A1)       
 
         [0000]      SID=Source Image Distance/x-ray emitter-x-ray detector distance 
         [0085]    To simplify matters, the principle of the inventive generation of virtual roadmap mask images is described below with the aid of an aortic aneurysm. Further exemplary embodiments or examples of use are found below. 
         [0086]    The 3D data record registered to the C-arm is expediently pre-segmented. It is insignificant here how this happens, in other words whether the aorta
       was automatically segmented by means of a mathematical method or   was “cut out” manually by means of a user for instance.       
 
         [0089]    It is also insignificant for the inventive apparatus and the inventive method how this segmentation is represented, in other words for instance
       as a mask which displays the regions which do not belong the segmentation,   as a surface grid, which spans the wall of the segmented aorta for instance or as   a mathematical model, such as for instance an encoding of the centerlines and surfaces of the segmentation as a 2D spline or non-uniform rational B-spline (NURBS).       
 
         [0093]    The aim of the inventive method is to generate a mask image for a roadmap without the renewed or repeated administration of contrast agent for changing angulations, couch positions etc. If this mask image is subtracted from the fluoroscopy live images such as with the conventional roadmap, then the usual roadmap representation is produced again. The subsequent description therefore concentrates on the generation of the mask image. 
         [0094]    The registered and superimposed reference image, in this case in other words the 3D segmentation projected into the fluoroscopy image (see  FIG. 12 ) is used for the generation of the reference image. Above all with segmented reference images, the precise projection of the vessel outline on the 2D image is known. The mask image  25  is now easily generated such that the image regions of the initial fluoroscopy image lying inside of the segmentation are “artificially” contrasted ( FIG. 13 ). There are several options here. The pixel ranges within the vessel outline may for instance
       be simply set to black,   be darkened by a specific “offset” (for instance 100 gray-scale values in a 256 stage image),   be “darkened” according to the local thickness of the vessels (known by the segmentation) or   replaced, colored and/or darkened in accordance with a mathematical forward projection of the segmentation (DRR).       
 
         [0099]    The result in all instances is a mask image  25 , the subtraction of which from the fluoroscopy live images  23  once again results in the roadmap image shown in  FIGS. 10 and 11 , nevertheless without having to provide any contrast agent. 
         [0100]    The principle behind generating a “virtual roadmap mask” is now explained in more detail on the basis of the 2D/3D and/or 2D/2D overlay with the aid of  FIGS. 12 and 13 . 
         [0101]    A mask image for a roadmap is generated by the inventive apparatus without administering contrast agent, as is illustrated with the aid of  FIGS. 12 and 13 . One of the overlay images  35  or  37  is used here as a reference image. The aorta and aneurysm  38  are segmented from this since the precise projection of the vessel outline on the 2D image is above all known in the case of segmented reference images  39 . A mask image  40  is now easily generated such that the image regions lying inside the segmentation of the aneurysm are artificially contrasted as a mask  41 , in other words set to black, as apparent in  FIG. 13 . 
         [0102]    A subtraction of this mask image once again produces the roadmap image shown in  FIGS. 10 and 11 , nevertheless without having to administer contrast agent. 
         [0103]    While the contrasted vessels can only be shown in a planar fashion in “normal” mask images, additional information can be displayed in the “virtual” mask images  40 . 
         [0104]    Therefore vascular occlusions  42  can be produced for instance in the mask  41  through recesses of the mask parts for instance, as shown with the aid of  FIG. 14 , so that a virtually plastic impression is produced. The vascular occlusions  42  are only marked by circles in the Figures for the purpose of demonstrating improved visibility. They do not need to be present in the mask image  40  as shown in  FIG. 19 . 
         [0105]    In the corresponding roadmap image  43  shown in  FIG. 15 , the vessel courses  44  are then clearly apparent, which significantly simplifies the navigation of the instrument  24  for instance. 
         [0106]    Furthermore, orifices  45  can be produced in the mask  41  for instance (simply through recesses of mask parts). In the associated roadmap image  43 , the orifices  45  are then clearly visible, as a result of which the navigation is noticeably simplified, as is shown clearly with the aid of  FIG. 16 . The orifices  45  are likewise marked by circles for better visibility in the Figure. 
         [0107]    A thrombus can be highlighted in the “virtual roadmap mask” for instance as further additional information.  FIG. 17  shows how a thrombus  46  is displayed in the segmented reference image  39 . This segmented thrombus  46  is then clearly visible in the corresponding roadmap image  40  according to  FIG. 18 , which significantly simplifies the navigation. 
         [0108]    In  FIG. 19 , the completely inventive mask image  43  is then reproduced with the additional information relating to the vascular courses  44 , vascular occlusions  42 , orifices  45  and the segmented thrombus  46 . The instrument  24  can then be reliably navigated for instance in the clearly visible vascular courses  44 . 
         [0109]    By means of the inventive apparatus and the inventive method, the physician is provided with the roadmap representation to which he/she is accustomed for a complex intervention, without contrast agent having to be repeatedly injected for instance during angulations changes. 
         [0110]    The present invention proposes the generation of mask images from the overlaid reference images, so that the physician is able to keep his/her familiar roadmap representation (also from any angulations) without repeatedly administering contrast agents. 
         [0111]    Furthermore, this “virtual” roadmap representation enables the introduction of additional information, which cannot be reproduced in “normal” roadmap representations. 
         [0112]    In other embodiments and/or extensions, additional information can also be inventively encoded in this “virtual” roadmap, which does not offer a normal roadmap representation. 
         [0113]    Anatomical reference: 
         [0114]    On account of the segmentation information, the mask image can be configured such that following subtraction, the regions outside of the aorta are not “subtracted”, but are instead also represented. This is thus advantageous in that the roadmap representation applies within the aorta, while outside thereof the complete anatomical reference with vertebrae, pelvis, bowel etc. is visible. 
         [0115]    Vessel coverages ( FIGS. 14 and 15 ): 
         [0116]    While in “normal” mask images, the contrasted vessels can only be shown 2-dimensionally, more information can be shown in the “virtual”. Thus vascular occlusions can therefore be produced in the mask for instance (simply through recesses of mask parts) ( FIG. 14 ). In the corresponding roadmap image ( FIG. 15 ), the vessel courses are then clearly apparent which significantly simplifies the navigation. 
         [0117]    Vessel outlets (orifices,  FIG. 16 ): 
         [0118]    Vessel outlets or orifices can also be produced in the mask for instance. In the corresponding roadmap image, the orifices are then clearly apparent, which significantly simplifies navigation. 
         [0119]    Further additional information, for instance aorta thrombus ( FIG. 19 ): 
         [0120]    Whereas in “normal” mask images only the actually contrasted vessels can be shown, in the “virtual” mask image, additional information can also be shown. If a segmentation of a thrombus exists for instance, then the corresponding outline can be produced in the mask ( FIG. 17 ). In the corresponding roadmap image ( FIG. 18 ), the thrombus course is then clearly apparent which can significantly simplify the navigation and positioning of a stent. 
         [0121]    The method can in principle be extended to all procedures, which profit from the overlay of (presegmented) reference images, and in which the roadmap technology is used for representation purposes, these are for instance
       the exchange of aortic valves,   interventions in neuroradiology,   interventions in the periphery (arms, legs) and   interventions in the thoracic aorta.       
 
         [0126]    The “roadmap” representation in the angiography in principle refers to the following procedure:
       A: creating a 2D mask image WITH contrast agent (shows vascular system and anatomical background)   B: recording live images WITHOUT contrast agent, but possibly with instruments (shows this instrument and the anatomical background)   Representation as a subtraction image B−A, ONLY shows the contrasted vascular system and the instrument, the anatomical background is subtracted.       
 
         [0130]    Alternatively, the mask image can also be recorded without contrast agent, then only the instrument, and not the vascular system are shown in the subtraction image, which is therefore not desirable. 
         [0131]    The DISADVANTAGES of this known method are: 
         [0132]    If the C-arm  2  moves, the mask image A no longer passes to the live image B and the technology cannot be used and/or a new mask image A must be created. 
         [0133]    The inventive approach (as an example with a segmented 3D volume) is:
       with a volume registered to the C-arm  2 , which indicates the vascular system, the volume can be anatomically correctly displayed into a 2D image recorded by the C-arm  2  for all angulations of the C-arm  2  etc.   then a mask image A 1  is created WITHOUT contrast agent, on which the vascular system is NEVERTHELESS visible, in which the 3D display of the vessel on the 2D image A 1  is to be colored black accordingly as a “virtual contrast”.   live images are then recorded again and B−A 1  is shown as a roadmap with vessels, without having administered contrast agent.       
 
         [0137]    Advantage: 
         [0138]    This process can be repeated any number of times without having provided contrast means each time. With each new angulation, the first image with the displayed vessels is easily used as a mask and is detached from the rest.