Abstract:
A computer receives a plurality of two-dimensional fluoroscopy images of an examination object, capture time points and projection parameters and combines the images into image groups. Each image group contains all the images, the capture time point of which is between a minimum and a maximum time point specific to the respective image group. When the image groups are sorted by ascending minimum time points, the corresponding maximum time points form a strictly monotonously ascending order. The respective minimum and maximum time points are determined so that the computer reconstructs a three-dimensional object reconstruction of the examination object based on the images assigned to the respective image group. A respective two-dimensional reconstruction display is determined by the respective three-dimensional object reconstruction and outputted to a user in a coding specific to the respective image group by a display device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of German application No. 10 2008 023 053.7 filed May 9, 2008, which is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to an evaluation method for a plurality of two-dimensional fluoroscopy images of an examination object. 
     BACKGROUND OF THE INVENTION 
     The subject matter described above is generally known. It is used in particular to determine and display the blood flow in vascular systems. To this end a contrast agent is injected into the bloodstream and its propagation is captured and displayed. The displayed propagation of the contrast agent enables the user (generally a physician) to make an appropriate diagnosis. 
     The evaluation method of the prior art already operates well but is capable of improvement. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to create possibilities that allow improved and simpler diagnosis by the physician. In particular it should be possible to capture temporal assignment easily and intuitively. 
     The object is achieved for the evaluation method, based on an evaluation method of the type described above, in such a manner that the computer outputs each two-dimensional reconstruction display in a coding specific to the respective image group. For the computer program the object is achieved in that it is embodied correspondingly, so that it brings about the execution of such a further developed evaluation method. The same applies to the data medium and the computer. 
     Advantageous embodiments of the inventive evaluation method are described in the claims. The preferred embodiments also apply correspondingly to the computer program, the data medium and the computer. 
     The object is achieved by the evaluation method for a plurality of two-dimensional fluoroscopy images of an examination object,
         in which a computer receives the fluoroscopy images,   in which a capture time point at which the respective fluoroscopy image was captured and projection parameters subject to which the respective fluoroscopy image was captured are assigned to each fluoroscopy image,   in which the computer combines the fluoroscopy images into image groups in such a manner that
           the respective image group contains all the fluoroscopy images, the capture time point of which is between a minimum time point specific to the respective image group and a maximum time point specific to the respective image group and   when the image groups are sorted by ascending minimum time points, the corresponding maximum time points form a strictly monotonously ascending order,   
           in which the respective minimum time point and the respective maximum time point for each image group are defined in such a manner that the fluoroscopy images assigned to the respective image group can be used to determine a three-dimensional object reconstruction of the examination object,   in which the computer determines the respective object reconstruction for each image group based on the fluoroscopy images assigned to the respective image group,   in which the computer uses the respective three-dimensional object reconstruction to determine a respective two-dimensional reconstruction display,   in which the computer outputs the two-dimensional reconstruction displays to a user by way of a display device.       

     It is possible for the respective coding to be a color assigned to the respective image group. For example the temporally first reconstruction display can be coded red, the temporally second two-dimensional reconstruction display yellow, the temporally third reconstruction display green etc. Alternatively or additionally the respective coding can be a fill structure assigned to the respective image group. For example the temporally first reconstruction display can be display with a full structure, the temporally second reconstruction display checkered, the temporally third reconstruction display hatched, the temporally fourth reconstruction display dotted, etc. 
     It is possible for the computer to output the reconstruction displays simultaneously. Alternatively it is possible for the computer to output the reconstruction displays as a temporal sequence. 
     If the reconstruction displays are output as a temporal sequence, it is possible for the computer to display the reconstruction displays in full. In one preferred embodiment of the present invention however the computer only outputs the part of each reconstruction display that corresponds to none of the temporally preceding reconstruction displays. This last procedure can also be realized even if the computer outputs the reconstruction displays simultaneously. In this process, when outputting the respective part of the respective reconstruction display the computer can optionally also output the corresponding parts of the temporally preceding reconstruction displays. 
     It is possible for the examination object to be static; in other words it does not move when the fluoroscopy images are being captured. One example of such a static examination object is the human brain and the blood vessel system, which supplies the brain with blood. Alternatively the examination object can be a moving examination object. For example the person can move their head. There can also be respiration-induced or pulse-induced motion when capturing the lungs or abdomen. 
     It is possible to capture information about an inherent motion of the examination object while the fluoroscopy images are being captured and to supply this to the computer. In this instance the computer receives this information in addition to the fluoroscopy images. The computer is then able to carry out registration of the fluoroscopy images corresponding to the inherent motion of the examination object before determining the object reconstructions. Alternatively or additionally the computer can also carry out registration of the fluoroscopy images corresponding to the inherent motion of the examination object after determining the object reconstructions. 
     Registration methods for registering the two-dimensional fluoroscopy images relative to one another—and also automatic registration methods—are known per se from the prior art. They are as such not the subject matter of the present invention. The same applies to registration methods used to register the three-dimensional object reconstructions relative to one another in some instances. 
     It is possible for the computer to determine the minimum time points and maximum time points of the image groups individually. In particular where there is continuous movement of the recording arrangement used to capture the fluoroscopy images it is however possible and also advantageous, if the computer determines the minimum time points and maximum time points of the image groups in such a manner that directly consecutive minimum time points have a uniform temporal setpoint interval for all the image groups and for each image group the difference between the respective maximum time point and the respective minimum time point is equal to a uniform setpoint time period for all the image groups. Continuous movement of the recording arrangement is in particular a continuous rotation of the recording arrangement of a CT system. C-arm systems can also bring this about in some instances. 
     The temporal setpoint interval is generally at least as long as half the setpoint time period. It is preferably even as long as the setpoint time period. 
     It is possible for the temporal setpoint interval to be permanently predetermined for the computer or to be determined by the computer based on otherwise predetermined variables. Alternatively the computer can receive the temporal setpoint interval from the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and details will emerge from the description which follows of exemplary embodiments in conjunction with the drawings of basic diagrams, in which: 
         FIG. 1  shows an x-ray system and an evaluation arrangement, 
         FIG. 2 to 4  show flow diagrams, 
         FIG. 5  shows an overall display, 
         FIG. 6  shows a flow diagram, 
         FIG. 7 to 9  show displacement operations of an x-ray source, 
         FIGS. 10 and 11  show flow diagrams and 
         FIG. 12  shows a displacement operation of an x-ray source. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to  FIG. 1  an x-ray source  1  has a recording arrangement  2 . The recording arrangement  2  comprises an x-ray source  3  and a flat panel detector  4 . The x-ray source  3  and flat panel detector  4  can be moved together. Generally they can be pivoted about a common pivot axis  5 , as shown by corresponding arrows in  FIG. 1 . Displacement of the x-ray source  3  and flat panel detector  4  is generally coordinated in this process, so that the pivot axis  5  is disposed between the x-ray source  3  and the flat panel detector  4  at any time point. 
     The x-ray system  1  is controlled by a control facility  6 . Further to corresponding activation by the control facility  6  the flat panel detector  4  captures a two-dimensional fluoroscopy image B of an examination object  7  disposed in the region of the pivot axis  5 , for example the brain of a human  7 , from a start time point at capture time points t respectively. The start time point here is selected as required. Generally it is defined in such a manner that it coincides with the start of the introduction of a contrast agent into the part of the blood vessel system of the examination object  7  under consideration. 
     The control facility  6  transmits the captured fluoroscopy images B to a computer  8 . Together with the fluoroscopy images B the control facility  6  transmits to the computer  8  the associated capture time point t for every fluoroscopy image B as well as the projection parameters P, subject to which the respective fluoroscopy image B was captured by means of the recording arrangement  2 . 
     The computer  8  can be a standard computer. The computer  8  is programmed using a computer program  9 . The computer program  9  can be stored in machine-readable form on a data medium  10  for example and be supplied to the computer  8  by way of the data medium  10 . A CD-ROM is shown as the data medium  10  in  FIG. 1  purely by way of example. The data medium  10  could however be configured differently, for example as a USB memory stick or as an SD memory card. 
     The computer program  9  has machine code  11 . The machine code  11  can be executed directly by the computer  8 . Execution of the machine code  11 —which naturally takes place during operation of the computer  8 —causes the computer  8  to execute an evaluation method, which is described in more detail below in conjunction with  FIG. 2 . 
     According to  FIG. 2  in a step S 1  the computer  8  receives the fluoroscopy images B. Each fluoroscopy image B is hereby assigned the corresponding capture time point t and the corresponding projection parameters P. The number of received fluoroscopy images B is generally very large. Generally significantly more than 100 fluoroscopy images B are received, for example 200, 300, 450 or yet more fluoroscopy images B. In the context of step S 1  the computer  8  can also preprocess the individual fluoroscopy images B, for example using DSA (=digital subtraction angiography) or contrast amplification. 
     In a step S 2  the computer  8  determines a minimum time point t i  and a maximum time point t′ i  respectively for a number n of image groups G i  (i=1 . . . , n). In this process the following equations apply irrespective of the value of the index i
 
 t   i+1   &gt;t   i  
 
 t′   i+1   &gt;t′   i  and
 
 t′   i   &gt;t   i .
 
     The difference between directly consecutive minimum time points (i.e. t i+1 −t i ) is referred to below as the group interval. The group interval can be the same for all image groups G i . However this is not necessarily the case. 
     Similarly the difference between the maximum time point t′ i  and minimum time point t i  for each image group G i  is referred to below as the group time period. The group time period can—like the group time interval—be the same for all image groups G i . However this is also not necessarily the case. 
     In a step S 3  the computer  8  forms the image groups G i . Each image group G i  here comprises all the fluoroscopy images B, the capture time point t of which is between the minimum time point t i  and the maximum time point t′ i  of the respective image group G i . 
     The minimum time points t i  and the maximum time points t′ i  are defined in such a manner for all the image groups G i  that a respective three-dimensional object reconstruction R i  of the examination object  7  can be determined for each image group G i  based on the fluoroscopy images B assigned to the respective image group G i . The computer  8  carries out this determination in a step S 4 . If necessary in step S 4  the computer  8  can carry out a further evaluation of the object reconstructions R i , for example a segmentation of the blood vessel system of the examination object  7 , to the extent that contrast agent flows through it in the context of the object reconstruction R i  considered in each instance. 
     In a step S 5  the computer  8  determines a type of display in the same manner for all object reconstructions R i . For example the computer  8  can determine whether there should be a parallel projection, a perspective projection or a sectional display. Further display parameters (viewing direction, viewing angle, etc.) can also be determined in some instances. 
     Step S 5  is only optional. It is therefore shown with a broken line in  FIG. 2 . If it is not present, the type of display can be permanently predetermined for example. 
     Step S 5  can—if present—operate fully automatically. Alternatively the cooperation of a user  12  may be required. The cooperation of the user  12  can optionally be of an interactive nature, it then being possible for the input of the user  12  to be changed at any time. 
     In a step S 6  the computer  8  uses the respective three-dimensional object reconstruction R i  for the respective image group G i  to determine a respective two-dimensional reconstruction display D i . The respective reconstruction display D i  is determined here taking into account the type of display defined in step S 5  (or the otherwise known type of display). 
     In a step S 7  the computer  8  codes each two-dimensional reconstruction display D i  in a coding. The coding here is specific to the respective image group G i . The respective coding can be a color assigned to the respective image group G i  for example. Alternatively or additionally the respective coding can be a fill structure assigned to the respective image group G i . Both procedures are described in more detail below in conjunction with  FIG. 3 to 6 . 
     In a step S 8  the computer  8  outputs the coded reconstruction displays D i  to the user  12  by way of a display device  13 . 
       FIG. 3  shows a possible implementation of steps S 7  and S 8  in  FIG. 2 . 
     According to  FIG. 3  in a step S 11  the computer  8  selects the first reconstruction display D 1 . In a step S 12  the computer  8  assigns the first reconstruction display D 1  its corresponding coding. In a step S 13  the computer  8  outputs the currently selected reconstruction display D i  to the user  12  in the coding assigned to it by way of the display device  13 . 
     In a step S 14  the computer  8  checks whether it has already executed step S 13  for all the reconstruction displays D i . If not, the computer  8  passes on to a step S 15 . Otherwise the method in  FIG. 3  is terminated. 
     In step S 15  the computer  8  selects the temporally next reconstruction display D i . The computer  8  then goes back to step S 12 . 
     The procedure in  FIG. 3  results in the computer  8  outputting the individual reconstruction displays D i  one after the other, in other words as a temporal sequence, to the user  12  by way of the display device  13 . Each reconstruction display D i  is hereby output in its corresponding coding. 
     As described to date, with the procedure in  FIG. 3  the respective reconstruction display D i  is output in its entirety. Optionally however it is possible to assign a further step S 16  after step S 15 . Step S 16  is only shown with a broken line in  FIG. 3 , because it is optional. 
     If step S 16  is present, in step S 16  the computer  8  determines the components of the selected reconstruction display D i , which are also present in at least one of the temporally preceding reconstruction displays D j  (with j=1, . . . , i−1). As part of step S 16  the computer  8  removes these components from the selected reconstruction display D i . This modification means that for each reconstruction display D i  respectively the computer  8  only outputs the part which corresponds to none of the temporally preceding reconstruction displays D j . 
       FIG. 4  shows a similar procedure to the procedure described just above in conjunction with  FIG. 3  and the optional step S 16 . The procedure in  FIG. 4  essentially differs from the last described procedure in  FIG. 3  in that step S 13  in  FIG. 3  is replaced by steps S 21  and S 22 . In step S 21  the computer  8  adds the part of the currently selected reconstruction display D i , which corresponds to none of the temporally preceding reconstruction displays D j , to an overall display D. The overall display D is displayed in step S 22 . 
     The procedure according to  FIG. 4  means that during the first iteration the first reconstruction display D 1  is output by way of the display device  13  in the coding assigned to the first reconstruction display D 1 , during the second iteration the part of the second reconstruction display D 2  in the coding assigned to the second reconstruction display D 2 , which was not already displayed in the context of the first reconstruction display D 1 , is also displayed, etc. During the last iteration each part of the reconstruction displays D i  is displayed in the coding in which it first comes up. The progression of the propagation of the contrast agent is thus visualized.  FIG. 5  shows this procedure. 
     As mentioned above, the coding can be a color assigned to the respective image group G i . For example the first reconstruction display D 1  can be displayed in red, the second reconstruction display D 2  in orange, the third reconstruction display D 3  in yellow, etc. It is likewise possible to assign the color red for example to the first reconstruction display D 1  and the color yellow to the last reconstruction display D n . Transition colors from red to yellow are then assigned gradually to the other reconstruction displays D 2  to D n−1 . It is pointed out here for the sake of completeness only that the specified colors are purely exemplary. 
     As an alternative or in addition to the assignment of colors, a respective fill structure can be assigned to the respective reconstruction displays D i . For example the first reconstruction display D 1  can be displayed completely filled in, the second reconstruction display D 2  with large checkering, the third reconstruction display D 3  with fine checkering, the fourth reconstruction display D 4  hatched, the hatching running from bottom left to top right, etc. It is likewise possible for example to assign a relatively large number of fill elements to the first reconstruction display D 1 , so that a background is 80% or more covered, and to assign a fill structure, with which only a relatively small proportion of the background is filled, for example 20% or less, to the last reconstruction display D n . In this instance the other reconstruction displays D 2  to D n−1  can show a gradual reduction in the degree of cover from (purely by way of example) 90% to 10%. 
       FIG. 6  shows a slight modification of the procedure in  FIG. 4 . The difference is that step S 22  is not executed in the context of the loop between steps S 12  and S 16 , but only after leaving the loop, in other words if the check in step S 14  is positive. This modification means that in the context of the overall display D the computer  8  outputs the reconstruction displays D i  to the user  12  simultaneously by way of the display device  13 . 
     The x-ray system  1  used to capture the fluoroscopy images B can be a CT system for example. In this instance the recording arrangement  2  rotates continuously about the pivot axis  5 . It therefore executes a number of complete circuits continuously about the pivot axis  5  according to the diagrams in  FIG. 7  to  FIG. 9 . The circuits are shown here as spirals in  FIG. 7 to 9 , in order to be able to differentiate the individual circuits in  FIG. 7 to 9  from one another. In reality the circuits are of course circular. Also only the path of the x-ray source  3  is shown in  FIG. 7 to 9 . At every time point the flat panel detector  4  lies diametrically opposite the x-ray source  3  relative to the pivot axis  5 . 
     The group time periods are selected as required in  FIG. 7 to 9 . Generally they are selected to be as short as possible, to keep time-related reconstruction artifacts as small as possible. Generally the group time periods are the same for all the image groups G i . They are generally selected so that the recording arrangement  2  (or the x-ray source  3 ) passes through a pivot angle α, which is 180° plus the fan angle β of the recording arrangement  2 , relative to the pivot axis  5  during the group time period Δt i . This procedure allows the so-called Feldkamp algorithm, which is generally known to those skilled in the art, to be used to determine the object reconstructions R i . However it is possible and sometimes also expedient in individual instances to determine the pivot angle α differently. For example it is possible to select the pivot angle α to be smaller and only to carry out a so-called tomosynthesis. 
     Generally the user  12  will predetermine the pivot angle α, to be passed through by the recording arrangement  2  during the respective group time period, for the computer  8 . In this instance the computer  8  uses the predetermined pivot angle α and the rotation speed of the recording arrangement  2  known to it to determine the corresponding group time periods automatically. In this instance in particular the group time periods for all the image groups G i  are all identical to a setpoint time period Δt. 
     As mentioned above, the group intervals can likewise have the same value for all the image groups G i , hereafter referred to as the temporal setpoint interval δt. The temporal setpoint interval δt here—see FIG.  7 —can be longer than the setpoint time period Δt. The temporal setpoint interval δt can however also be identical to the setpoint time period Δt according to  FIG. 8 . The temporal setpoint interval δt according to  FIG. 9  can (again alternatively) be shorter than the setpoint time period Δt. The temporal setpoint interval δt should however be at least as long as half the setpoint time period Δt. 
     It is possible for the temporal setpoint interval δt to be permanently predetermined for the computer  8 . It is likewise possible for the computer  8  to determine the temporal setpoint interval δt automatically based on the setpoint time period Δt. Again alternatively according to  FIG. 10  it is possible for the computer  8  to receive the temporal setpoint interval δt from the user  12 . In this instance a step S 31  is inserted between the steps S 1  and S 2  according to  FIG. 10 . In step S 31  the computer  8  receives the temporal setpoint interval δt from the user  12 . 
     Additionally according to  FIG. 10  a step S 32  can also be present. If step S 32  is present, the computer  8  can receive the setpoint time period Δt or the corresponding pivot angle α in step S 32 . As an alternative or in addition to predetermination of the setpoint time period Δt or the corresponding pivot angle α, it is possible for the computer  8  to receive a value for the minimum time point t 1  of the first image group G 1  in the context of step S 32 . 
     According to  FIG. 10  step S 2  is also modified compared with the procedure in  FIG. 2 . In the context of step S 2  in  FIG. 10  the computer  8  determines the minimum time points t i  and the maximum time points t′ i  according to the equations
 
 t′   i   =t   i   +Δt  
 
 t   i+1   =t   i   +δt.  
 
     If the examination object  7  does not move while the fluoroscopy images B are being captured, excellent results can be achieved with the procedures described above. If however the examination object  7  moves while the fluoroscopy images B are being captured, it is possible for motion-induced artifacts to occur to a significant extent. In this instance the procedure in  FIG. 2  is preferably modified according to  FIG. 11 . The procedure in  FIG. 11  is possible here as an alternative or in addition to the procedure in  FIG. 10 . 
     According to  FIG. 11  step S 1  in  FIG. 2  is modified in such a manner that in addition to the fluoroscopy images B the computer  8  also receives information I about an inherent motion of the examination object  7  while the fluoroscopy images B are being captured. For example, if the examination object  7  corresponds to the human abdomen or pulmonary chamber, a chest strap may be used to capture a respiratory state of the examination object  7  and transmit it to the computer  8 . 
     According to  FIG. 11  a step S 41  can be assigned in front of step S 4  in  FIG. 2 . In step S 41  the computer  8  carries out registration of the fluoroscopy images B. Registration of the fluoroscopy images B naturally corresponds here to the inherent motion of the examination object  7 . Registration in step S 41  can be rigid or elastic. The corresponding registration methods are known to those skilled in the art. They are as such not the subject matter of the present invention. 
     As an alternative or in addition to step S 41  a step S 42  can be assigned after step S 4 . In step S 42  the computer  8  carries out registration of the object reconstructions R i . Registration of the object reconstructions R i  naturally also corresponds to the inherent motion of the examination object  7 . Registration in step S 42  can—as with registration in step S 41 —alternatively be rigid or elastic. The corresponding registration methods are also known to those skilled in the art in respect of step S 42 . They are as such not the subject matter of the present invention. 
     The present invention has been described above in conjunction with fluoroscopy images B, with the fluoroscopy images B being captured using an x-ray system  1 , which is configured as a CT system. However the present invention can also be used if the fluoroscopy images B are captured by means of a differently configured x-ray system  1 , for example a C-arm x-ray system. 
     If the recording arrangement  2  of the differently configured x-ray system  1  is able, in a similar manner to a CT system, to execute a number of complete circuits about the pivot axis  5 , this is immediately evident without further ado. However the present invention can also be applied, if the x-ray source  3  and flat panel detector  3  can only be pivoted over an overall angle γ of maximum 360°, for example 270° or 220° or 200°, according to  FIG. 12 . The recording arrangement  2  must then be pivoted back to its original position A after every forward displacement operation V by means of a backward displacement operation V′. The fluoroscopy images B are captured here at least during the forward displacement operations V. Alternatively fluoroscopy images B can be captured or not captured during the backward displacement operations V′. Generally all the fluoroscopy images B captured during a single displacement operation V, V′ form an image group G i . This is shown schematically in  FIG. 12  for three displacement operations V, V′. The number (“three”) of displacement operations V, V′ shown here is of course purely exemplary. 
     The present invention has many advantages. In particular intuitive assignment of the blood flow to time is possible. A diagnosis based on the assignment of blood flow to time is therefore facilitated for the user (physician)  12 . 
     The above description serves exclusively to describe the present invention. The scope of protection of the present invention should however be defined exclusively by the accompanying claims.