Abstract:
A detector for an X-ray computed tomography apparatus has a number of detector elements b 1  . . . b 10  separated from one another by septa. In order to fashion the detector especially universally, the widths of the detector elements are selected such that a channel occupancy combination from the following group can be realized: [20×b 1  or 20×b 2  or 16×b 4 ], [16×b 1  or 16×b 2  or 12×b 4 ], [8×b 1  or 8×b 2  or 8×b 4  or 8×b 6 ], [4×b 1  or 4×b 2  or 4×b 4,  4×b 8,  4×b 12 ], [8×b 1  or 8×b 2  or 8×b 5 ], [4×b 1,  4×b 2,  4×b 4,  4×b 10].

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed to a detector for an X-ray computed tomography apparatus of the type having a number of detector elements of different widths separated from one another by septa, forming a detector line arranged in a direction of a rotational axis of the tomography apparatus, with a number of such detector lines being arranged next to each other, and wherein a predetermined number of channels are provided for acquiring signals generated by the detector elements, with one or more of the detector elements being selectively connectable to respective ones of the channels for acquiring the signals.  
           [0003]    2. Description of the Prior Art  
           [0004]    Detectors of the above general type are disclosed in German OS 195 02 574 and PCT Application WO 98/05980. They have a number of parallel detector lines that proceed in the direction of the axis of a subject to be transirradiated, for example a patient. Each detector line is composed of a number of detector elements that, for example, are manufactured of a scintillator ceramic.  
           [0005]    For readout of the signals generated by the detector elements, usually four, currently at most eight, channels are available dependent on the computing power of the computer. Dependent on the demands regarding the desired image information, a number of detector elements lying next to one another in a detector line can be respectively connected to one channel. When, for example, two or more detector elements of a detector line are connected to one channel, information about a relatively large volume excerpt of the transirradiated subject is obtained. Such an information is especially well-suited for producing high-contrast images with which, for example, it is possible to differentiate soft parts in the brain.  
           [0006]    When, in contrast, only one detector element from each line is respectively connected to each of the channels, the transirradiated volume is small. The information thus obtained is especially well-suited for the resolution of fine structures, for example in the inner ear region.  
           [0007]    For gating the required, fan-shaped X-ray beam, a diaphragm precedes the known detector. The provision of such a diaphragm causes increased manufacturing outlay. Moreover, the detector has a number of detector elements with a number of septa separating them. The efficiency of such a detector is not especially high. The multitude of provided detector elements further increases the manufacturing outlay of the detector.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the invention is provide a simply constructed, universal detector with enhanced efficiency for an X-ray computed tomography apparatus.  
           [0009]    This object is achieved in accordance with the invention in a detector of the type initially described wherein the widths of the detector elements are selected such that a channel occupancy combination selected from the following group can be realized: [20×b 1  or 20×b 2  or 16×b 4 ], [16×b 1  or 16×b 2  or 12×b 4 ], [8×b 1  or 8×b 2  or 8×b 4  or 8×b 6 ], [4×b 1  or 4×b 2  or 4×b 4 , 4×b 8 , 4×b 12 ], [8×b 1  or 8×b 2  or 8×b 5 ], [4×b 1 , 4×b 2 , 4×b 4 , 4×b 10 ], wherein the detector elements are designated b 1  . . . b 10 .  
           [0010]    In terms in the above, such as 20×b 1  or 12×b 4 , for example, b 1  designates a slice having a thickness equal 1 times the thickness of a detector element referenced b 1 , and b 4  designates a slice having a thickness equal to 4 times the thickness of the detector element referenced b 1 . Slice combination 20×b 1  can be scanned if 20 electronics channels are available, while 12 electronics channels are sufficient to stand the slice combination 12×b 4 .  
           [0011]    A detector that enables the inventive channel combination can have a minimized number of septa with respect to the selected channel occupancy combination. The efficiency, particularly the quantum efficiency, of such a detector is enhanced. A diaphragm preceding the detector can be foregone. This, in particular, reduces the cost outlay for the manufacture of the X-ray computer tomograph.  
           [0012]    Expediently, the septa are symmetrically arranged with reference to a symmetry plane of the detector line that proceeds perpendicular to the rotational axis. This further facilitates manufacture.  
           [0013]    The detector elements have respective widths B 1  . . . B 10 . A smallest, first width B 1  can have a value selected from the following group: 0.375 mm, 0.5 mm, 0.625 mm, 0.75 mm, 1.0 mm. A tenth width B 10  can amount to ten times, an eighth width B 8  to eight time, a sixth width B 6  to six times, a fifth width B 5  to five times, a fourth width B 4  to four times and a second width B 2  to twice the first width B 1 . According to a further feature, the overall width of the detector line is 40 times, 48 times or 64 times the first width B 1 . 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 shows the schematic structure of a known X-ray computed tomography apparatus;  
         [0015]    [0015]FIG. 2 is a schematic illustration of a first detector line in accordance with the invention;  
         [0016]    [0016]FIG. 3 is a schematic illustration of a second detector line in accordance with the invention;  
         [0017]    [0017]FIG. 4 is a schematic illustration of a third detector line in accordance with the invention;  
         [0018]    [0018]FIG. 5 is a schematic illustration of a fourth detector line in accordance with the invention;  
         [0019]    [0019]FIG. 6 is a schematic illustration of a fifth detector line in accordance with the invention;  
         [0020]    [0020]FIG. 7 is a schematic illustration of a sixth detector line in accordance with the invention;  
         [0021]    [0021]FIG. 8 is a schematic illustration of a seventh detector line in accordance with the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    [0022]FIG. 1 shows a focus  1  of an X-ray source from which a fan-shaped X-ray beam  2  gated by a diaphragm (not shown) emanates. The beam  2  penetrates a subject  3  and strikes a detector  4 . The detector  4  is formed by a number of parallel detector lines D, each thereof being formed by a row of detector elements b. The detector elements b are respectively separated from one another by septa s.  
         [0023]    The measuring system  1 ,  4  is rotatable around a rotational axis  5 , so that the subject  3  is transirradiated from different projections during which the detector lines D are read out by a signed acquisition system  8 . A computer  6  calculates an image of the subject  3  from the detector signals that are thereby formed, said image being reproduced on a monitor  7 .  
         [0024]    In FIGS. 2 through 8, examples of detector lines D in accordance with the invention, formed of a number of detector elements b that are in turn separated from one another by septa s, are shown. Each of the detector elements b, for example, is manufactured of a scintillator ceramic facing toward the incident X-radiation that is connected to a light sensitive resistor (not shown here) at its side facing away from the radiation entry side. The light-sensitive resistor can in turn be optionally connected to one or more available electronics channels.  
         [0025]    Given the first detector line D shown in FIG. 2, twenty first detector elements b 1  each having a first width B 1  are provided in a symmetrical arrangement, B 1  being the minimum width. The first width B 1  can, for example, amount to 0.375 mm, 0.5 mm, 0.625 mm, 0.75 mm or 1.0 mm. Five second detector elements b 2  with the width B 2  respectively adjoin in a symmetrical arrangement at both sides of the first detector elements b 1 . The width B 2  is twice as wide as the width B 1 . Four fourth detector elements b 4  adjoin at each of the sides of the detector elements b 2 , the fourth width B 4  thereof corresponding to four times the first width B 1 . The proposed structuring has 64 times the first width B 1 . In particular, the following slice combinations thus can be activated: 20×b 1 , 20×b 2 , 16×b 4 .  
         [0026]    Given the detector line D shown in FIG. 3, four second detector elements b 2  at each side adjoin sixteen first detector elements b 1 , and two fourth detector elements b 4  adjoin each of the groups of second detector elements b 2 . The arrangement is symmetrical. The overall length of this detector line D amounts to  48  times the first width B 1 . The following slice combinations can be activated on, for example, the 16 electronics channels that are available: 20×b 1 , 20×b 2 , 16×b 4 .  
         [0027]    Given the third detector line D shown in FIG. 4, seven second detector elements b 2  at each side adjoin eight centrally disposed first detector elements b 1 , and a sixth detector element b 6  adjoins each of the groups of second detector elements b 2 . The sixth detector element b 6  exhibits six times the width of the first width B 1 . The overall length of this detector line D again amounts to 48 times the first width B 1 . The following slice combinations can be activated on, for example, the eight electronics channels that are available: 8×b1, 8×b2, 8×b4, 8×b6.  
         [0028]    Given the fourth detector line D shown in FIG. 5, two second detector elements b 2  at each side adjoin eight centrally disposed first detector elements b 1 , two fourth detector elements b 4  in turn adjoin the groups of second detector elements b 2  at each side, a second detector element b 2  in turn following thereupon at each side and a sixth detector element b 6  in turn following thereupon at each side. In this embodiment, the width B of the detector elements b does not increase steadily toward ends the of the detector line. The overall length of this detector line D amounts to 48 times the first width B 1 . The following slice combinations can thus be activated on, for example, the eight electronics channels that are available: 8×b 1 , 8×b 2 , 8×b 4 , 8×b 6 .  
         [0029]    Given the fifth detector line D shown in FIG. 6, one second detector element b 2  at each side adjoins four first detector elements b 1 , three fourth detector elements b 4  adjoin each second detector element b 2 , and an eighth detector element b 8  following thereupon at each side. An eighth width of the eighth detector element b 8  amounts to eight times the first width B 1 . The overall length of this detector line D amounts to 48 times the width of the detector element b 1 . The following slice combinations can thus be activated on, for example, the four electronics channels that are available: 4×b 1 , 4×b 2 , 4×b 4 , 4×b 8 , 4×b 12  .  
         [0030]    The slice combination 4×b 12  set forth above means that one can combine a total of two detector elements b 8 , six detector elements b 4 , two detector elements b 2 , four detector elements b 1 , from left to right in the figure, with one of four electronics channels respectively, as follows:  
         [0031]    1. One detector element b 8  and one detector element b 4  to a slice having 12 times the thickness of a detector element referenced b 1 ;  
         [0032]    2. Two detector elements b 4 , one detector element b 2  and two detector elements b 1  to a slice having 12 times the thickness of a detector element referenced b 1 ;  
         [0033]    3. Two detector elements b 1 , one detector element b 2  and two detector elements b 2  to a slice having 12 times the thickness of a detector element referenced b 1 ; and/or  
         [0034]    4. One detector element b 4  and one detector element b 8  to a slice having 12 times the thickness of a detector element referenced b 1 .  
         [0035]    This results in a slice combination of  4 ×b 12  which can be scanned with 4 electronics channels without the necessity of actually having detector elements of a width equal to 12 times the width of a detector element referenced b 1 .  
         [0036]    Given the sixth detector line D shown in FIG. 7, two second detector elements b 2  at each side adjoins twelve first detector elements b 1 , and two fifth detector elements b 5  in turn adjoin the second detector elements b 2  at each side. The overall length of this detector line D corresponds to 40 times the first width B 1 . The following slice combinations can thus be activated on, for example, the eight electronics channels that are available: 8×b 1 , 8×b 2 , 8×b 5 .  
         [0037]    Given the seventh detector line D shown in FIG. 8, one second detector element b 2  at each side adjoins four first detector elements b 1 , a fourth detector element b 4  follows thereupon at each side, a second detector element b 2  follows thereupon at each side, and a tenth detector element b 10  follows thereupon at each side. A tenth width B 10  of the tenth detector element b 10  amounts to ten times the first width B 1 . The overall length of this detector line D again amounts to 40 times the first width B 1 . The following slice combinations can thus be activated on, for example, the four electronics channels that are available: 4×b 1 , 4×b 2 , 4×b 4 , and 4×b 10 .  
         [0038]    All of the inventive detector lines D are symmetrical relative to a symmetry plane proceeding parallel to the z-axis. The structures of the detector lines D enable a minimization of the septa s, and thus an increase in the quantum efficiency. Detector arrays for X-ray computed tomography systems to be universally operated can be manufactured with the inventive detector lines D. Such X-ray computed tomography systems do not require the provision of a diaphragm inserted into the beam path.  
         [0039]    Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.