Abstract:
An X-ray CT apparatus comprises an X-ray tube for irradiating X-ray onto a target object, a xenon gas type detector for detecting the X-ray passing through the target object and for outputting an analog electric signal corresponding to an amount of the X-ray, a data acquisition system, a substrate for supporting the detector and the data acquisition system, which has a high rigidity and a surface where a wiring portion for transmitting an analog signal outputted from the detector to the data acquisition system is formed, and a rotation mechanism for rotating the X-ray source and the substrate for supporting the detector and the data acquisition system around the body axis of the target object as the rotation center.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an X-ray detection apparatus used for an X-ray computed tomography apparatus. 
     2. Description of the Related Art 
     As for an X-ray detection apparatus, a scintillation detection apparatus and a xenon gas type detection apparatus have been put into practice. Each of these apparatus comprises an X-ray detector for detecting an X-ray which has passed through a target object and for converting a transmitted X-ray into a charge signal, and a data acquisition system (which will be abbreviated as a DAS hereinafter) for converting a detected charge signal outputted from this X-ray detector into a digital signal and for supplying a digital signal to a data reconstruction computer. The DAS comprises a front-end-processing section including an integrating circuit for processing an analog detection signal, a low-pass filter, a multiplexer, and the like, and an A/D converter for converting an analog signal outputted from the front-end-processing section, into a digital signal. 
     In a conventional X-ray detection apparatus, the X-ray detector and the DAS have large sizes and are respectively contained in different boxes. 
     FIG. 1 shows the structure of an X-ray detection apparatus used in a conventional X-ray CT apparatus. The detection apparatus comprises an X-ray detector 101 and a DAS 100, as has been described above. The DAS comprises, for example, a front-end section 106 comprising an integrating circuit and a low-pass filter, an A/D converter 104, and a control circuit 105 for controlling the front-end section 106 and the A/D converter 104. The DAS 100 is formed on one circuit board or on a plurality of circuit boards, and the circuit board or boards are contained in one box, constituting an independent apparatus. 
     In order to transmit a detection signal outputted from the X-ray detector 101 to the DAS 100, the X-ray detector 101 and the DAS 100 (e.g., the front end section 106 thereof) are connected with each other by a cable (such as a coaxial cable) or a vinyl-sheet type circuit board (or a flexible circuit board). 
     Another example of a conventional apparatus will be an apparatus in which a part of the DAS 100 is included in the X-ray detector 101. The front-end section 106 of the DAS 100 is included in the X-ray detector 101, or the front-end section 106 is divided into a first stage 102 and a second stage 103 of the front-end section. Only the first stage 102 of the front end section 106 is included in the X-ray detector 101, and the DAS 100 includes the A/D converter 104 and the controller 105 for controlling the A/D converter 104 on the basis of a timing signal used for taking in a signal outputted from the X-ray detector 101. 
     In this example, the first stage 102 and the second stage 103 of the front-end section or the second stage 103 and the A/D converter 104 are connected with each other by a cable or by a vinyl-sheet-like circuit board. 
     In any of the above examples, the X-ray detector 101 and the DAS 100 are respectively constructed as separate devices, and are electrically connected with each other by a cable or by a vinyl-sheet-like circuit board after the X-ray detector 101 and the DAS 100 are installed on a rotation gantry of the X-ray CT apparatus. In case where an X-ray detector and a DAS are constructed as separate devices, connection between both of these devices leads to the following drawback. In an X-ray CT apparatus, data is collected while rotating an X-ray tube and a detector. The rotation of the detector and the X-ray tube causes vibration of a cable or vinyl-sheet-like circuit board connected between the X-ray detector and the DAS. When the cable or the flexible circuit board for transmitting a signal vibrates, the coating film (made of resin) of the cable and the core wire (made of metal) thereof rub each other, or the circuit board (made of resin) and the printed wiring (made of metal) rub each other, thereby generating static electricity. This results in a problem that the static electricity enters as noise into an analog signal outputted from the X-ray detector 101, or into an analog signal processed by the front-end section 106. If a noise signal thus enters, there is a drawback that the image quality of a tomographic image finally reconstructed is deteriorated. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an X-ray detection apparatus which comprises an X-ray detector and a data processing section for converting an analog output of the X-ray detector into a digital signal and which prevents a noise signal caused by vibration of the X-ray detector from entering into the analog output signal from the X-ray detector. 
     According to the present invention, there is provided an X-ray detection apparatus comprising an X-ray detector for detecting X-ray and for outputting an analog signal corresponding to an amount of the X-ray detected, a data processor for converting the analog signal outputted from the X-ray detector into a digital signal, a substrate having a high rigidity, for supporting the X-ray detector and the data processor, and connection means formed on the substrate, for transmitting a signal outputted from the X-ray detector to the data processor. 
     According to the present invention, there is provided another X-ray computer tomography apparatus comprising irradiation means for irradiating X-ray onto a target object, detection means for detecting the X-ray passing through the target object, and for outputting an electric signal corresponding to an amount of the X-ray detected, and rotation means for rotating the irradiation means and the detection means around a body axis of the target object as a rotation center, wherein the detection means comprises an X-ray detector for detecting the X-ray and for outputting an analog signal corresponding to an amount of the X-ray detected, a data processor for converting the analog signal outputted from the X-ray detector into a digital signal, and a substrate for supporting the X-ray detector and the data processor, the substrate having a high rigidity and having a surface on which a wiring section for transmitting the signal outputted from the X-ray detector to the data processor is formed. 
     According to the X-ray detection apparatus of the present invention, the X-ray detector and the data processor are formed on the substrate having a high rigidity, and both of the detector and the data processor are formed to be integral with each other. Signal transmission from the detector to the data processor is achieved by a wiring formed on the substrate having the high rigidity. Therefore, the substrate does not vibrate even when the detection apparatus is rotated. As a result, static electricity which will be caused by a friction between a metal portion of a signal transmission line and a coating portion thereof does not enter into an analog signal of the detector. 
     Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. 
     The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the present invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the present invention in which: 
     FIG. 1 is a block diagram showing a structure of an X-ray detection apparatus of a conventional X-ray CT apparatus; 
     FIG. 2 is a view schematically showing the X-ray CT apparatus in which an X-ray detection according to an embodiment of the present invention is used; 
     FIG. 3 is a side cross-sectional view showing the inner structure of the X-ray detection apparatus according to the embodiment of the present invention; 
     FIG. 4 is a front view showing the inner structure of the X-ray detection apparatus according to the embodiment of the present invention; 
     FIG. 5 is a rear view showing the inner structure of the X-ray detection apparatus according to the embodiment of the present invention; and 
     FIG. 6 is a rear view showing the inner structure of another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of an X-ray detection apparatus according to the present invention will now be described with reference to the accompanying drawings. FIG. 2 schematically shows the entire X-ray CT apparatus of a third generation using an X-ray detection apparatus according to the present embodiment. An X-ray fan beam emitted from the X-ray tube 10 with a predetermined fan angle passes through a patient 14 laid on a bed 12 and enters into an X-ray detection apparatus 16. Projection data is thereby collected. The projection data outputted from the detection apparatus 16 is supplied to a reconstruction device 18 through a signal transmitting member such as a slip-ring or the like. The X-ray tube 10 and the X-ray detection apparatus 16 are integrally rotated by a support/rotate mechanism not shown. In this manner, projection data projected to a certain slice of the patient 14 from all directions of 360 degrees is collected, and the reconstruction device 18 reconstructs a tomographic image of one slice on the basis of the projection data, to display the tomographic image on a display device 20. In recent years, helical scanning has been put into practical use, for the purpose of reducing the scanning time. In the helical scanning, a bed 12 is moved at the same time when the X-ray tube 10 and the X-ray detection apparatus 16 are rotated, and data of a plurality of slices is sequentially collected. 
     The details of the X-ray detection apparatus 16 will be explained. FIG. 3 is a cross-sectional view of the X-ray detection apparatus 16, taken from the side surface (in the lateral direction of FIG. 2). FIG. 4 is a front view of the inside, taken from the left side of FIG. 3. Each of the components of the detection apparatus 16 is installed on a circuit board 32 having a shape as shown in FIG. 4. This circuit board 32 is made of material (or synthetic resin) having a high rigidity and is a so-called printed circuit board, unlike the flexible circuit board used in a conventional apparatus. As a detector, a xenon gas type detector is used in which electrode plates are disposed at a predetermined interval. The electrode plates 36i (i=1 to n) are disposed in an arc-like arrangement, such that the directions of the surfaces of the plates coincide with the center of the X-ray tube 10. At a corner portion of each electrode plate 36i, a projecting portion 34i as a signal extraction electrode. Both sides of each electrode plates 36i are fixed by resin plates 38 and 40, thus constituting a detector. Adjacent two electrode plates constituted a detector of one-channel. 
     After a detector is thus constructed, the resin plate 40 is fixed to one surface of the circuit board 32 by an adhesion or mechanically by a screw. The electrodes 34i penetrate through a through hole formed in the circuit board 32 and project from the opposite surface (or the pattern formation surface). These electrodes are electrically connected to a wiring pattern formed on the pattern formation surface, by soldering. A DAS 42 is provided on the pattern formation surface, and the wiring pattern connects the electrodes 34i with input terminals of channels of the DAS 42, respectively. 
     The circuit board 32 comprises an upper section of a sectorial shape for fixing the X-ray detector (e.g., the resin plate 40) and a lower section for fixing the DAS 42, as shown in FIG. 4. The detector is contained in a casing 44, and is sealed by a cover 46 with the circuit board 32 interposed therebetween, in order to fill the detector with a xenon gas. Note that the side of the casing 44 facing the X-ray tube 10 is thin, and serves as an X-ray entrance port. 
     The DAS 42 includes a front-end section including an integration circuit and a low-pass filter, an A/D (analog/digital) converter, and the like, as shown in FIG. 1. The DAS 42 is contained in a casing different from the detector. As shown in the rear view of FIG. 5, a circuit pattern 48 for the DAS 42 is formed at a lower portion of the pattern formation surface of the circuit board 32, and is electrically connected through a connector or the like, with the wiring pattern 50 connected to the electrodes 34i of the X-ray detector. Circuits (or electric components) of the DAS are directly installed on the circuit pattern 48. 
     Thus, according to the X-ray detection apparatus of the present embodiment, the X-ray detector and the DAS 48 are fixed onto the circuit board 32 having a high rigidity so that the X-ray detector and the DAS 48 are integrated with each other. Therefore, when the X-ray detection apparatus 16 is rotated together with the X-ray tube 10 are rotated around the body axis of a target object to collect projection data, the X-ray detector, the circuit board 32, and the DAS 42 integrally vibrate. Therefore, connecting portions between the X-ray detector 16 and the printed wiring pattern on the circuit board 32 and between the DAS 42 and this printed wiring pattern are not broken due to vibration, but a high reliability is ensured. Further, since the wiring pattern is formed on a circuit board having a high rigidity, the circuit board (made of resin) and the printed wiring (made of metal) do not rub each other, so that there is no static electricity caused by friction. As a result, the X-ray detection apparatus according to the present embodiment overcomes the drawback of a conventional apparatus that static electricity enters as noise into an analog electric signal outputted from the X-ray detector or an analog electric signal processed by the DAS. Accordingly, the image quality of a tomographic image finally reconstructed is not damaged. 
     Note that a digital output of the DAS 42 is fed to the slip ring through a cable, a flexible circuit board, or the like, and is supplied to the reconstruction device 18 shown in FIG. 2. Since the signal which is transmitted through the cable is a digital signal, electrostatic noise does not enter into the digital signal. 
     As has been described above, according to the present embodiment, there is provided an X-ray detection apparatus into which electrostatic noise does not enter even when vibration occurs. 
     Another embodiment of the present invention will be explained. In the following embodiment, the same portions as used in the first embodiment will be denoted by the same reference numerals, and detailed explanation of those portions will be omitted therefrom. 
     In the first embodiment, the circuit pattern 48 for the DAS 42 is formed directly on the circuit board 32. However, if the circuit pattern is of a large scale, the circuit board 32 must undesirably be of a large scale. In this case, the DAS 42 may be divided into several sections, which may respectively be formed on circuit boards 50j (j=1 to m). These circuit boards 50j may be fixed vertically on the circuit board 32 and may be connected to a connector provided on the wiring pattern formed on the circuit board, as shown in FIG. 6. In this manner, the area of the circuit board 32 can be reduced and the size of the entire apparatus is reduced. 
     As has been explained above, according to the present invention, there is provided an X-ray detection apparatus which prevents electrostatic noise caused by vibration of the X-ray detector from entering into an analog electric signal outputted from the X-ray detector. 
     The present invention is not limited to the embodiment described above, but may be variously modified in practice. For example, the DAS which is provided on the circuit board opposite to the detector may be provided in the same side as the detector is provided. In this case, an end of the wiring pattern formed on the pattern formation surface is connected through a through-hole to the side of the DAS opposite to the pattern formation surface. In the above description, the xenon gas type detector is explained as an detector. The detector is not limited to the above type but any type of detector, e.g., a solid-state detector may be used.