JP2011226902A - X-ray data acquisition device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray data acquisition device excellent in X-ray detection accuracy by overcoming difficulties in packaging and a problem of degradation of a feeble X-ray detection signal.SOLUTION: An X-ray data acquisition device includes: a detector substrate on a front surface of which an X-ray detection unit with an analogue-signal output terminal is mounted; an X-ray data acquisition element (DAS: data acquisition system) which is provided with an analogue-signal input terminal disposed on a back surface of the detector substrate; and an analogue-signal conductor which penetrates through the detector substrate to directly connect the analogue-signal output terminal and the analogue-signal input terminal.

Description

  The present invention relates to an X-ray data acquisition apparatus, and more particularly, to an integrated configuration of a detector as an X-ray detection unit and a data acquisition element in an X-ray computed tomography (CT) apparatus.

  In a known X-ray CT apparatus, an X-ray transmission data is collected by scanning a subject with an X-ray source and an X-ray detection unit facing each other, and an X-ray transmission image is reconstructed based on the data. As the X-ray detector, scintillator and photodiode cells are arranged in a two-dimensional array. The detection signal of the X-ray detection unit is amplified, analog-digital (AD) conversion, etc. for each cell of the two-dimensional array by a data acquisition element (hereinafter referred to as DAS), and is converted into digital data as an image reconstruction system. Forwarded to

  The X-ray CT two-dimensional detector disclosed in Patent Document 1 discloses a configuration in which an X-ray detector is mounted on the front surface side of a multilayer wiring board and a DAS is mounted on the back surface side of the multilayer wiring board. The analog signal output from the photodiode group of the X-ray detection unit is input to a switching element that bundles electric signals provided on the front surface side end of the multilayer wiring board, and passes through the multilayer wiring board to the DAS on the back surface side. Have been entered.

  In such an X-ray detector, an analog signal is input to the DAS via the switching element, so that the wiring length for the analog signal becomes long and the X-ray detection accuracy deteriorates. That is, since the level of the analog signal output from the photodiode is weak, the analog signal deteriorates as the analog signal wiring length increases.

  As means for shortening the wiring length for analog signals, Patent Documents 2 and 3 disclose a technique in which a DAS and an X-ray detection unit are stacked and integrally formed on the same substrate. That is, a plurality of DAS are mounted on the same substrate, and an X-ray detection unit including a photodiode group is stacked and mounted thereon.

JP2001-215281 (FIG. 4, paragraph numbers 42-53) JP-A-2008-73522 (FIGS. 6A and 6B, paragraph numbers 30-31) JP2008-145245 (FIGS. 10 and 11, paragraph numbers 35-45)

  In Patent Documents 2 and 3, the objective is to make the shortest connection between the photodiode and the DAS, and the photodiode group is mounted on the DAS. Therefore, stacking mounting is required. In order to reliably connect the photodiode group and the DAS and improve the connection reliability, it is necessary that all the DAS upper surfaces have flatness, but this requires an extremely advanced mounting technique.

  An object of the present invention is to provide an X-ray data acquisition apparatus with high X-ray detection accuracy that suppresses the deterioration of weak X-ray detection signals with a structure that reduces the difficulty of mounting and increases connection reliability.

  The X-ray data acquisition apparatus of the present invention includes a detector board on which an X-ray detector having an analog signal output terminal is mounted on the front side of the board, and an analog signal input terminal mounted on the back side of the detector board. An X-ray data acquisition element (DAS) and an analog signal conductor that penetrates through the front and back of the detector substrate and directly connects the analog signal output terminal and the analog signal input terminal are provided.

  According to the X-ray data acquisition apparatus of the present invention, low-cost and high-precision X-ray detection can be realized without using a special stacking technique.

1 is a schematic front view showing a configuration of an X-ray data acquisition apparatus according to a first embodiment of the present invention. The schematic perspective view which shows the structure of the X-ray data acquisition apparatus of the 2nd Embodiment of this invention. (A) The schematic sectional drawing which shows the analog signal wiring of the detector board | substrate by the 2nd Embodiment of this invention along the virtual plane I shown with a dashed-dotted line in FIG.

(B) The schematic sectional drawing which shows the digital signal wiring of the detector board | substrate by the 2nd Embodiment of this invention along the virtual plane II shown with a dashed-dotted line in FIG.
The schematic front view which shows the structure of the X-ray data acquisition apparatus provided with the electromagnetic wave shielding structure by the 3rd Embodiment of this invention. The schematic plan view which shows the electromagnetic wave shielding structure of the detector substrate surface layer by the 4th Embodiment of this invention. The block diagram for demonstrating operation | movement of the X-ray data acquisition apparatus of the 1st Embodiment of this invention.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a schematic front view of an X-ray data acquisition apparatus as a first embodiment of the present invention. This X-ray data acquisition apparatus includes a scintillator 2 that converts X-rays into light, a photodiode 3 that converts light into electricity, and an analog detection signal output from the photodiode 3 to each data collection element (DAS) 12. A detector board 13 for transmission, a plurality of DASs 12 for amplifying and digitizing an inputted analog signal, a transfer circuit 9 for outputting a digital detection signal outputted from each DAS 12 to a host system such as an image reconstruction system, and an X-ray The data communication path 10 connects the data acquisition device and the host system, and the control circuit 11 controls the X-ray data acquisition device. The scintillator 2 and the photodiode 3 are arranged as a two-dimensional array, and will be simply referred to as the scintillator 2 and the photodiode 3 below.

  The photodiode 3 and the DAS 12 are arranged at positions facing each other with the detector substrate 13 in between. The analog signal output terminal of the photodiode 3 and the analog signal input terminal of the DAS 12 are configured to be directly connected in the shortest manner through a conductor such as a through hole that penetrates and is conducted through the front and back of the detector substrate 13.

  By arranging and wiring the terminals of the photodiode 3 and the DAS 12 at positions facing each other through the detector substrate 13, the analog signal path can be shortened, and the X-ray detection accuracy can be improved.

  Next, the operation of the X-ray data acquisition apparatus will be described using the block diagram of the X-ray data acquisition apparatus shown in FIG. As a block diagram, there is almost no fundamental difference from the block diagram disclosed in Patent Document 3.

  In FIG. 6, a detector 20 as an X-ray detection unit includes a plurality of scintillators 2 and a plurality of photodiodes 3, and a data acquisition unit 21 includes a plurality of DASs 12, a transfer circuit 9, and a control circuit 11. When the plurality of scintillator arrays 2 receive X-rays 1 respectively, the X-rays are converted into light and applied to a plurality of pairs of photodiodes 3. The amount of light changes depending on the intensity of the X-ray.

  The photodiode 3 converts the received light into an analog signal 4 and transmits it to the DAS 12. At this time, since the analog signal 4 output from the photodiode 3 is weak, it is easily affected by the outside, and it is important to maintain the quality of the analog signal 4.

  In Patent Document 1, since the switching element is interposed, the wiring length of the analog signal 4 is long. However, in the present invention, the analog signal output terminal of the photodiode 3 and the analog signal input terminal of the DAS 12 are formed on the same substrate. Since the terminals can be shortened by directly connecting the terminals with an analog signal conductor penetrating the board, the structure is less susceptible to the influence from the outside.

  The DAS 12 that has received the analog signal 4 amplifies the analog signal 4 with the amplifier (A) 5, and then converts the analog signal 4 into a digital signal with the AD converter (AD) 6.

  In recent years, semiconductor technology has progressed, and some chips can process several hundred channels, and the information detected by the multiplexer (MX) 7 in the DAS is output as a time-division digital signal 8 to the outside. it can.

  Since DAS 12 also handles weak signals, it is a device that is easily affected by external noise. Nevertheless, the structure integrated with the detector 20 becomes closer to the X-ray tube and is strongly influenced by X-rays. Therefore, it is necessary to shield DAS 12 from X-rays, and in Patent Document 2, a shielding material such as tungsten is additionally used.

  In the present invention, the material of the detector substrate 13 and the mounting position of the DAS 12 are devised so that X-ray shielding can be performed without newly adding a shielding material.

  Specifically, a ceramic material is used as the material of the detector substrate 13 to serve as a shielding material in addition to the role as a substrate, and the DAS 12 is disposed on the back side of the detector substrate as viewed from the X-ray irradiation direction. Has been realized.

  The transfer circuit (TX) 9 plays a role of receiving the digital signal 8 from each DAS 12 and transferring the digital signal 8 to a higher-level image reconstruction system via the data communication path 10. The order in which the digital signal 8 is received, the timing of data transfer to the host system, and the like depend on instructions from the control circuit (CNT) 11. The transfer circuit 9 has options such as electrical communication, wireless communication, and optical communication according to the communication form. In particular, in a system in which an X-ray data acquisition apparatus is installed in a rotating body, wireless communication and optical communication that do not require electrical wiring are superior.

  In addition, by mounting DAS 12 on the back side of detector board 13, analog signals can be converted to digital signals and time-division multiplexed, so the interconnect with external systems is switched from analog signals to digital signals, and the number of interconnects with external systems is reduced. It can be greatly reduced.

  Further, assuming that the number of detector channels is increased, a system capable of changing the transfer rate to the external system is provided in the transfer circuit 9, thereby making it possible to change the number of channels without increasing the number of physical interconnects. it can.

  If the transfer circuit 9 has a wireless communication or optical communication function, the physical data communication path 10 can be eliminated. As a result, there is no physical connection between the X-ray data acquisition apparatus and the image reconstruction system that is the host system, so that the degree of freedom in system arrangement is improved. Further, since there are no physical restrictions on the connection, it is easy to increase the number of X-ray data acquisition apparatuses, and the number of sensor channels can be increased even after the installation and operation of the X-ray CT apparatus is started.

  Further, since the photodiode 3 and the DAS 12 are directly mounted on the front surface and the back surface of the detector substrate 13, respectively, low-cost and highly reliable mounting is possible without using a special stacking technique.

  Furthermore, since the mismatch in the terminal arrangement between the photodiode 3 and the DAS 12 can be adjusted by devising a multilayer wiring structure on the detector substrate 13, an X-ray data acquisition apparatus can be constructed even by combining a commercially available photodiode 3 or DAS 12. .

  FIG. 2 shows an X-ray data acquisition apparatus according to the second embodiment of the present invention, in which the array pattern of the analog signal output terminals 41 of the photodiode 3 and the array pattern of the analog signal input terminals 42 of the DAS 12 correspond one-to-one. It is a schematic perspective view which shows the case where it corresponds.

  3A and 3B, details of the multilayer wiring inside the detector substrate shown in FIG. 2 are shown. FIG. 3A shows a cross-sectional view of FIG. 2 cut along the virtual plane I. FIG. That is, a cross section of the detector substrate along a cross section including the analog signal output terminal 41 of the photodiode 3 and the analog signal input terminal 42 of the DAS 12 in common is shown, and the substrate thickness is enlarged for the sake of explanation. Yes. FIG. 3B shows a cross-sectional view of FIG. 2 cut along the virtual plane II. That is, the cross section of the detector substrate 13 along the cross section including the digital signal terminal 81 of the DAS 12 is shown.

  In FIG. 3A, the multilayer structure of the detector substrate 13 has the analog signal wiring region 400 in which only the analog signal conductor 40 is wired on the side where the photodiode 3 is mounted, and the DAS 12 mounted. And a digital signal wiring region 800 in which the digital signal wiring 80 is mainly wired. The digital signal wiring area 800 mainly accommodates a digital signal wiring 80 for transmitting a digital signal. However, since the analog signal conductor 40 also needs to pass through the digital signal wiring area 800, it is in contact with the digital signal wiring 80. The analog signal conductor 40 is wired so as not to occur. That is, the analog signal conductor 40 is wired so as to extend in the vertical direction (direction orthogonal to the main surface of the substrate) with respect to the analog signal input terminal 42 of the DAS 12.

  If the arrangement pattern of the analog signal output terminal 41 of the photodiode 3 and the arrangement pattern of the analog signal input terminal 42 of the DAS 12 are in one-to-one correspondence, all the analog signal conductors 40 have the same length. And it can be wired at the shortest distance. When a commercially available DAS 12 is used, the terminal arrangement pattern is generally different as shown in FIG. 1, and the difference in that case is appropriately determined in the analog signal wiring region 400 in the analog signal conductor 40. This can be done by changing and adjusting the wiring pattern.

  In the multilayer substrate layer configuration of the detector substrate 13, the cross-talk between the analog signal and the digital signal is suppressed by arranging the photodiode 3 side as an analog signal wiring region 400 and the DAS 12 side as a digital signal wiring region 800. And stable X-ray detection can be realized.

  FIG. 3B shows a cross section of the detector substrate 13 along the cross section including the digital signal terminal 81 of the DAS 12, so that the analog signal conductor 40 shown in FIG. As a result, the analog signal conductor 40 is not drawn. For the sake of explanation, the figure also shows an enlarged substrate thickness. FIG. 3B shows a case where the digital signal wiring 80 for digital signals is wired only in the digital signal wiring region 800. Regarding the arrangement of the digital signal wiring 80, it is desirable to arrange the digital signal wiring 80 so as to avoid crosstalk with the analog signal conductor 40 by arranging (lowering the layer) on the lower layer side of the detector substrate 13.

  Referring to FIGS. 4 and 5, there is shown an electromagnetic wave shielding method when the X-ray data acquisition apparatus shown in FIG. 1 is affected by electromagnetic waves.

  FIG. 4 shows a method of shielding the DAS 12 from electromagnetic waves in the X-ray data acquisition apparatus according to the third embodiment of the present invention. The electromagnetic shielding can be realized by covering the periphery of the DAS 12 with the detector substrate 13 and the electromagnetic shielding sheet 16.

  The detector substrate 13 and the electromagnetic wave shielding sheet 16 are electrically coupled to each other. This electrical coupling is performed on the surface of the detector substrate 13. As long as the surface is a surface, the mounting surface of the photodiode 3 or the mounting surface of the DAS 12 can be used. For the electromagnetic wave shielding sheet 16, copper or iron of a conductive material can be used.

  In FIG. 4, the data communication path 10 can be taken out from the direction orthogonal to the longitudinal direction of the detector substrate 13 so as not to cross the electromagnetic wave shielding sheet 16.

  FIG. 5 shows the structure of the surface layer (substrate surface and back surface) of the detector substrate 13 in the X-ray data acquisition apparatus according to the fourth embodiment of the present invention. By covering the surface layers of the front and back surfaces of the detector substrate 13 with the ground layer 15 so as not to contact the analog signal or digital signal conductors 40 or 80 exposed on the surface surface of the detector substrate 13, The internal wiring can have a role of shielding electromagnetic waves. All portions where wiring for analog signals and digital signals is not provided are covered with the ground layer 15 and the ground layer on the front surface side and the ground layer on the back surface side are made conductive by a through hole or the like formed in the substrate.

  In the present invention, the photodiode on the substrate surface and the DAS on the substrate back surface are directly connected. Therefore, if a dedicated DAS or photodiode is designed, an analog signal is transmitted from the substrate surface to the substrate back surface as shown in FIG. The length of the analog signal is only the thickness of the substrate. Furthermore, the lengths of all analog signals are uniform and can be wired at equal distances. Furthermore, separation from a digital signal becomes easy. Even if a general-purpose photodiode and DAS are used, the wiring shown in FIG. 3 can be made as close as possible by arranging both devices at positions facing the center of the same substrate. This makes it possible to create an X-ray data acquisition device that can obtain uniform characteristics in all photodiode cells, and an X-ray detector that can suppress the degradation of weak X-ray detection signals requires advanced mounting technology. Without getting.

  The idea of making analog signals the shortest and uniform is also disclosed in Patent Documents 2 and 3, but in Patent Documents 2 and 3, there is a special dedicated in which the flatness of all DAS upper surfaces is uniform. Since it is necessary to make DAS without fail, it is unavoidable that it is a very expensive device including development costs. On the other hand, in the present invention, it is not always necessary to create such a dedicated DAS, so that development costs are not incurred.

  Furthermore, there are also differences in assembly difficulty and connection reliability. As shown in Patent Documents 2 and 3, when adopting a structure in which a plurality of DAS are mounted on a substrate and one photodiode module is mounted thereon, in order to securely connect the photodiode and the DAS, Although it is necessary that the flatness of all DAS upper surfaces is obtained, it is extremely difficult to obtain such flatness. Considering that the X-ray detector is installed while the centrifugal force is working, in such a stack structure, the connection between the photodiode and the DAS is likely to be stressed, and it becomes difficult to maintain the connection reliability. On the other hand, according to the embodiment of the present invention, all the components can be mounted on a substrate having a flatness, so that there is an advantage that it is easy to mount and maintain connection reliability.

  An application example of the present invention is an X-ray CT apparatus.

DESCRIPTION OF SYMBOLS 1 X-ray 2 Scintillator 3 Photodiode 4 Analog signal 5 Amplifier 6 AD converter 7 Multiplexer 8 Digital signal 9 Transfer circuit 10 Data communication path 11 Control circuit 12 Data acquisition element (DAS)
DESCRIPTION OF SYMBOLS 13 Detector board | substrate 15 Grounding layer 16 Electromagnetic wave shielding sheet 20 Detector 21 Data acquisition part 40 Analog signal conductor 41 Analog signal output terminal 42 Analog signal input terminal 80 Digital signal wiring 81 Digital signal terminal 400 Analog signal wiring area 800 Digital signal wiring area

Claims (9)

  A detector board having an X-ray detector having an analog signal output terminal mounted on the front side of the board, and an X-ray data acquisition element (DAS) having an analog signal input terminal mounted on the back side of the detector board. And an analog signal conductor that directly connects the analog signal output terminal and the analog signal input terminal through the front and back of the detector substrate.   The X-ray detection unit includes, as components, a scintillator that converts X-rays into light, and a photodiode that converts the light into the analog signal and outputs the analog signal to the analog signal output terminal. Includes an analog-to-digital converter that converts an analog signal input to the analog signal input terminal into a digital signal, and a digital signal output from the DAS near the back side of the detector board. The X-ray data acquisition apparatus according to claim 1, further comprising a multi-layer wiring structure for digital signals for connecting a signal to a host system.   3. The X-ray according to claim 2, wherein an array pattern of the analog signal output terminals matches an array pattern of the analog signal input terminals, and all the analog signal conductors have the same length. Data acquisition device.   4. The X-ray data acquisition apparatus according to claim 1, wherein the conductor extends in a direction orthogonal to a main surface of the detector substrate. 5.   5. The X-ray data acquisition apparatus according to claim 2, wherein the analog signal conductor penetrates the detector substrate so as not to contact the digital signal multilayer wiring. 6.   2. The X-ray data acquisition apparatus according to claim 1, wherein the DAS includes a circuit for time-division multiplexing the digital signal as a component.   The X-ray data acquisition apparatus according to claim 6, further comprising a control circuit that controls system operation on a back side of the detector substrate.   The X-ray data acquisition apparatus according to claim 1, wherein a substrate material of the detector substrate is a ceramic material.   A transfer circuit for transferring a digital signal output from the DAS to a host system is provided on the back surface of the detector substrate, and the transfer circuit is configured to perform telecommunication, optical communication according to the environment in which the X-ray data acquisition device is installed. The X-ray data acquisition apparatus according to claim 2, wherein communication means such as communication and wireless communication can be selected.

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