JP4427282B2 - X-ray detector system for computed tomography apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray computed tomography apparatus and a detector and a DAS (data acquisition apparatus) mounted on the X-ray computed tomography apparatus, and in particular, a stable operation state relating to noise and operating voltage of the detector and DAS. Related to ensuring
[0002]
[Prior art]
An example of a computed tomography apparatus is an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus). This X-ray CT apparatus has been used for medical diagnosis or for various researches for a relatively long time, and has undergone a major change in history.
[0003]
In the early days, single-slice X-ray CT apparatuses were used. In the case of this single slice X-ray CT apparatus, an image of one slice of a subject is obtained, so it is difficult to capture a wide range of images in a short time, and a doctor or the like can obtain higher definition in unit time. There was a strong demand to capture images in a wide range (high resolution).
[0004]
In order to meet this demand, in recent years, multi-slice X-ray CT apparatuses have been developed and are quite popular. In this multi-slice X-ray CT apparatus, a detector row (one row) used in a single-slice X-ray CT device is arranged in a plurality of rows (for example, 4 rows, 8 rows, etc.) in a direction orthogonal to the row. A two-dimensional detector having a structure having detection elements of a total of M channels × N segments (M and N are positive integers) is used. A DAS (data acquisition device) is placed on the output side of the two-dimensional detector.
[0005]
The multi-slice X-ray CT apparatus includes an X-ray source that exposes a fan beam X-ray having a width spread in the slice direction, and the above-described two-dimensional detector, and has a conical X-ray beam (effective field of view). By detecting X-rays transmitted through the subject based on the diameter FOV) with a two-dimensional detector, multi-slice projection data of the subject can be collected at a time. Therefore, the multi-slice X-ray CT apparatus can collect a high-definition and wide-range image as compared with the single-slice X-ray CT apparatus.
[0006]
The two-dimensional detector described above includes a scintillator, a photodiode array, and a CMOS switch array. X-rays incident on the scintillator are converted into optical signals. This optical signal is incident on the photodiode array and converted into an electrical signal of an analog quantity for each segment of the two-dimensional array. This electrical signal is sent to the DAS at the subsequent stage via each element of the CMOS switch array for each segment. The CMOS switch array has a function of bundling electrical signals output from the photodiode array (signal synthesis) according to the designated number of detection element arrays in the slice direction.
[0007]
The DAS is an apparatus in which analog / digital conversion elements (DAS circuit components) are arranged in an array. As described above, a detection signal of an analog amount detected by a two-dimensional detector is input, and this signal is Amplify and convert to digital signal. This digital signal is then sent to the image reconstruction process.
[0008]
As for such a two-dimensional detector and a detector system having DAS as main elements, a structure in which most of the main elements are three-dimensionally mounted is known from Patent Document 1, for example. That is, a photodiode array and a CMOS switch are mounted on one surface of a substrate having both surfaces, and a DAS component is implemented on the other surface. The scintillator block is mounted on the photodiode array in a state optically connected to the array.
[0009]
This implementation is actually performed for each of a plurality of blocks obtained by dividing all channels into a plurality of blocks. In the case of an X-ray CT apparatus, the DAS usually has a circuit scale of about 500 to several tens of thousands of channels, so prepare the above-mentioned substrates every several tens to several hundreds of channels, and take charge of both sides of this substrate The detector block is formed by mounting the photodiode array, the CMOS switch, and the DAS component for the channels by the above-described three-dimensional mounting method. The plurality of detector blocks are arranged along an arcuate curved surface to constitute a detector system.
[0010]
In this detector system, the power required for each detector block is obtained from one power source via a cable (power line).
[0011]
Also, since DAS handles minute currents, the ground side of the DAS electrical circuit is usually mounted on the gantry (CT main unit) in order to prevent the minute currents from being affected by noise mixed through the ground circuit. Even if it is floating from the stand or connected to the pedestal, only one ground is used to prevent a strong ground connection with the pedestal. The entire DAS is operated in synchronism with one oscillator.
[0012]
[Patent Document 1]
JP 2001-215281 A
[0013]
[Problems to be solved by the invention]
However, the above-described conventional detector system has various unsolved problems as follows.
[0014]
Ie There are unresolved issues due to the grounding of the DAS. As described above, since the ground side of the DAS electric circuit is almost lifted from the gantry, when the entire DAS is operated in synchronization with one oscillator as in the prior art, the ground level of the DAS itself fluctuates. Due to this fluctuation, there is a problem in that radiation noise is emitted from the ground circuit of the DAS and the image quality is deteriorated.
[0015]
Further, regarding the grounding method, there is a secondary problem that the fluctuation of the voltage level in the DAS due to the grounding state affects the operation by the analog signal.
[0017]
The present invention has been made in view of the above-described circumstances, and stabilizes the operation by reliably suppressing the fluctuation of the ground and the power supply voltage accompanying the clock synchronization operation of the DAS component in each of the plurality of detector blocks. Eyes Target.
[0019]
[Means for Solving the Problems]
Up Note In order to achieve the objective, the X-ray detector system of the computed tomography apparatus according to the present invention detects X-rays transmitted through the subject and outputs an analog amount of electrical signal corresponding to the X-rays for each channel. A detector, and a data acquisition device (DAS) that converts an analog electrical signal for each channel output from the detector into a digital electrical signal and outputs the electrical signal. A clock signal having a structure formed by dividing into a plurality (even number) of circuit blocks each having a number of channels, and in particular, the plurality of circuit blocks are grouped into two, and both groups have opposite phases. And anti-phase operation means for operating each of the circuit blocks in synchronization with each other.
[0020]
As an example, the anti-phase operation means supplies an oscillator that generates a reference clock signal and the clock signal generated by the oscillator to a circuit block belonging to one of the two groups as it is and the oscillator generates Means for inverting the polarity of the clock signal and supplying the clock signal to the circuit block belonging to the other of the two groups.
[0021]
Also, the above In order to achieve the object, as another aspect, the oscillators for generating the reference clock signals necessary for the plurality of circuit blocks are provided in the same number as the number of the circuit blocks, and the reference output from each of the plurality of oscillators is provided. A clock signal may be supplied to each of the plurality of circuit blocks independently and asynchronously.
[0022]
Further, as another example, it is provided with means for generating, separately for each circuit block, a reference clock signal having a different delay amount for each predetermined time between the plurality of circuit blocks, and each of the generated reference clock signals is provided for each circuit. You may make it supply to a block.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0026]
(First embodiment)
A first embodiment will be described with reference to FIGS.
[0027]
FIG. 1 shows the configuration of a multi-slice CT apparatus as an embodiment of an X-ray CT apparatus as a radiation CT apparatus according to this embodiment. This multi-slice CT apparatus can perform not only a multi-slice helical scan but also a conventional scan (single-slice scan and multi-slice scan).
[0028]
As shown in FIG. 1, the multi-slice CT apparatus 10 has a bed (not shown) on which a subject (for example, a patient) P is placed and a diagnostic opening OP for inserting the subject P to make a diagnosis. A gantry G that collects projection data of the subject P, and a data processing unit U that controls the overall operation of the gantry G and collects projection data and performs image reconstruction processing, image display, and the like. ing.
[0029]
The bed has a top plate that is slidable in the longitudinal direction by driving a bed driving unit (not shown). Usually, the subject P is placed so that the body axis direction coincides with the longitudinal direction.
[0030]
The gantry G includes an X-ray tube 11 as a radiation source disposed opposite to the subject P inserted into the diagnostic opening OP, and an X-ray detector 12 as a radiation detector, which will be described in detail later. And an X-ray detector system 14 including a data acquisition device (DAS 13), a non-contact data transmission device 15, a gantry drive unit 16, and a slip ring 17.
[0031]
The X-ray tube 11 and the X-ray detector system 14 (including the X-ray detector 12 and the DAS 13) are provided on a rotating ring 21 that can rotate within the gantry G, and are rotated by drive control from the gantry driving unit 16. The ring 21 rotates. As a result, the X-ray tube 11 and the X-ray detector system 14 can rotate together around a rotation center axis parallel to the body axis direction of the subject P inserted into the diagnostic opening OP of the gantry G. It has become. The rotating ring 21 is driven to rotate at a high speed of 1 second or less per rotation.
[0032]
The X-ray tube 11 generates a cone beam (quadrangular pyramid) shape or a fan beam shape X-ray with respect to the subject P placed in the effective visual field region FOV. The X-ray tube 11 is supplied with electric power (tube voltage, tube current) necessary for X-ray exposure from the high voltage generator 18 through the slip ring 17. As a result, the X-ray tube 11 can generate so-called cone beam X-rays or fan beam X-rays that spread in two directions: a slice direction parallel to the rotation center axis and a channel direction orthogonal to the slice direction. In normal diagnosis, the subject P is placed on the top plate along the longitudinal direction of the bed, so that the slice direction coincides with the body axis direction of the subject P.
[0033]
In addition, in the stand G In In this regard, between the X-ray tube 101 and the subject P, a cone-shaped or fan-shaped X-ray beam exposed from the X-ray focal point of the X-ray tube 101 is shaped to obtain an X-ray having a required size. A collimator 19 for forming a beam is provided.
[0034]
The data processing unit U is a preprocessing device 21 that performs preprocessing such as data correction with the host controller 20 as the center, a storage device 22, an auxiliary storage device 23, a data processing device 24, a reconstruction device 25, and an input device 26. , And a display device 27 are connected to each other via a data / control bus 28. Further, the bus 28 is connected to an external image processing device 30. The image processing device 30 includes an auxiliary storage device 31, a data processing device 32, a reconstruction device 33, an input device 34, and a display device 35.
[0035]
The pre-processing device 21 performs sensitivity correction, X-ray intensity correction, and the like on the projection data transmitted via the non-contact data transmission device 15. For example, 1000 sets (1000 views) of two-dimensional projection data for 360 ° subjected to sensitivity correction, X-ray intensity correction, and the like in the preprocessing device 21 are temporarily stored in the storage device 22.
[0036]
The reconstruction device 25 performs reconstruction processing of the fan beam reconstruction method or the cone beam reconstruction method on the projection data stored in the storage device 22 to generate (reconstruct) slice tomographic image data.
[0037]
Next, the X-ray detector system 14 according to the present embodiment will be described in detail with reference to FIGS.
[0038]
This X-ray detector system 14 is a device that detects X-rays that have passed through the subject P, and as a whole, the X-ray detector elements are arrayed in two directions (slice direction and channel direction) orthogonal to each other. A system in which a plurality of X-rays are detected in a two-dimensional manner.
[0039]
Specifically, the X-ray detector system 14 includes a plurality of (for example, 38) detector blocks 14 as shown in FIG. ₁ ~ 14 _n Is provided. This detector block 14 ₁ ~ 14 _n Are supplied with power from an external power supply device 38 via a cable 39.
[0040]
Each detector block 14n (represented by reference numeral 14n) has detection channels for each block out of all the detection channels provided for X-ray detection divided into a plurality of blocks. In the case of an X-ray CT apparatus, the DAS 13 normally has a circuit scale of about 500 to several tens of thousands of channels, and is therefore blocked every several tens to several hundreds of channels. The plurality of detection blocks 14 ₁ ~ 14 _n Are arranged so as to form an X-ray incident surface along one arc centered on the focal point of the X-ray tube 11 in the channel direction.
[0041]
3 and 4 show a plurality of detector blocks 14. ₁ ~ 14 _n A specific mounting structure of one arbitrarily selected detector block 14n is shown.
[0042]
Each detector block 14n has a single rigid double-sided mounting type printed circuit board 141. On one surface of the printed circuit board 141, a CMOS switch array (switch element array) 142, a photodiode array 143, and a scintillator block are provided. 144 are stacked in this order. Among these, the CMOS switch array 142 and the photodiode array 143 are electrically connected to each other, and the photodiode array 143 is optically coupled to the scintillator block 144.
[0043]
This all detector block 14 ₁ ~ 14 _n The CMOC switch array 142, the photodiode array 143, and the scintillator block 144 together constitute the X-ray detector 12 described above.
[0044]
On the other hand, DAS circuit components 13a,..., 13a constituting the DAS 13 of each detector block 14n are mounted on the other surface of the printed circuit board 141. The DAS circuit components 13a,..., 13a are electrically connected to the COS switch array 142 described above. As a result, the X-ray detector 12 and the DAS are mounted three-dimensionally via the printed board 141.
[0045]
FIG. 5 shows a schematic development view when each detector block 14n is viewed from the X-ray incident side. The detector block 14n includes a plurality of detection elements 1031 and 1032 formed by the scintillator block 144 and the photodiode array 143. The plurality of detection elements 1031 and 1032 are arranged in a matrix in two directions of the channel direction and the slice direction.
[0046]
Of the detection elements 1031 and 1032, one detection element 1031 has a sensitive area with a width of 1.0 mm in the slice direction and a width of 0.5 mm in the channel direction. The other detection element 1032 has a sensitive area with a width of 0.5 mm in the slice direction and a width of 0.5 mm in the channel direction.
[0047]
The width of the sensitive area of the photodiode is defined as a converted value on the rotation center axis of the X-ray tube 11. That is, “a photodiode having a sensitive area width of 1 mm” means “a photodiode having a sensitive area width corresponding to 1 mm on the rotation center axis of the X-ray tube”. For this reason, considering that X-rays diffuse radially, the width of the actual sensitive area of the photodiode is the distance between the X-ray focal point and the sensitive area of the photodiode with respect to the distance between the X-ray focal point and the rotation center axis. It is slightly wider than 1 mm according to the actual distance ratio.
[0048]
For example, 16 detection elements 1032 having a width of 0.5 mm are arranged in the slice direction. In addition, a plurality of, for example, 12 detection elements 1031 each having a width of 1 mm are arranged on each side of the group of detection elements 1032 having a width of 0.5 mm, which are smaller than the number of detection elements 1032 arranged.
[0049]
In the present embodiment, the number (for example, 16) of the detection elements 1032 arranged in the slice direction is larger than the number (for example, 12) of the detection elements 1031 arranged on both sides thereof, and the total number (for example, 24). Designed to be less than That is, the X-ray detector 12 according to this embodiment includes all the detection blocks 14. ₁ ~ 14 _n As an example, it is possible to provide a two-dimensional element structure in which 912 detection elements are arranged in the channel direction (row direction) and 40 detection elements are arranged in the slice direction (column direction).
[0050]
The X-ray detector 12 forms a two-dimensional detector having a non-uniform pitch with a detection element having a width of 0.5 mm and a detection element having a width of 1.0 mm. Two-dimensional detectors arranged in the column direction may be used, and the detection element size is not limited to 0.5 mm or 1.0 mm, but is not limited to this example such as a detection element having a width of 1.25 mm.
[0051]
The enormous analog amount of two-dimensional X-ray projections detected by the X detection elements 1031 and 1032 is temporarily collected in the DAS 13 formed as a chip via the CMOS switch array 142. Specifically, this X-ray projection data is transmitted via the CMOS switch 142, for example, for eight columns (912 rows × 8 columns) smaller than the X-ray detection device columns (912 rows × 40 columns of detection elements 1031 and 1032). ) Or 4 columns (912 rows × 4 columns) of data collection elements.
[0052]
In order to transfer the X-ray projection data to the DAS 13, the CMOS switch 142 receives a control signal from the host controller 20 and adds the X-ray projection data for each column in the slice direction (that is, the data is transferred to the column). Two-dimensional projection data of the required number of columns is generated (bundled every time).
[0053]
Similar to the X-ray detector 12, the DAS 13 has a chip structure in which DAS circuit components 13 a made up of A / D conversion elements as data collection elements are arranged in a two-dimensional array. For this reason, each data collection element of the DAS 13 performs amplification processing and A / D conversion processing on the transmitted X-ray projection data to generate projection data of a digital quantity. Since the signal bundling process (signal addition process between the columns in the slice direction) can be enjoyed as described above, the number of element columns in the slice direction of the data acquisition elements of the DAS 13 is usually larger than that of the X-ray detector 12. Less.
[0054]
The digital amount of two-dimensional projection data output from the DAS 13 is transmitted to the data processing unit U through the contactless data transmission device 15 that applies optical communication. In addition, although the non-contact-type apparatus which applied optical communication is illustrated as the data transmission apparatus 15 here, you may use contact-type data transmission apparatuses, such as a slip ring.
[0055]
The detection operation by the X-ray detector 12 is repeated, for example, about 1000 times during one rotation (about 1 second). As a result, an enormous amount of two-dimensional projection data for M × N channels is generated, for example, 1000 times per second (one rotation). Therefore, the operations of the DAS 13 and the non-contact data transmission device 15 are executed at an extremely high speed in order to transmit the enormous and high-speed generated two-dimensional projection data without time delay.
[0056]
The digital amount of projection data sent to the data processing device U is subjected to various types of preprocessing by the preprocessing device 21 and then stored in the auxiliary storage device 23 and is subjected to image reconstruction processing by the reconstruction device 25. . Thereby, a reconstructed image accompanying X-ray scanning can be obtained.
[0057]
FIG. 6 shows an electrical schematic block diagram of the X-ray detector system 14 configured as described above. Power is supplied to the chip circuit of the photodiode array 143 and the CMOS switch array 142 and the DAS circuit component 13a of the DAS 13 for each detector block.
[0058]
Since the X-ray detector system 12 is blocked as described above, the internal circuit of the DAS 13 is also blocked accordingly. FIG. 7 schematically shows the block formation of the DAS 13 and the detector block 14. ₁ ~ 14 _n A plurality of block DAS circuits 13 corresponding to each block of ₁ ~ 13 _n (Each consisting of DAS circuit components 13a... 13a) is formed. As a result, the DAS 13 can collect, for example, 1000 channels (number of data collection elements in the channel direction) as a whole, and is divided into 10 blocks. ₁ ~ 13 _n Each is assigned 100 channels of data collection.
[0059]
In the present embodiment, the plurality of DAS circuits 13 ₁ ~ 13 _n On the other hand, as shown in FIG. 8, the reference clock signal generated by one oscillator 51 is supplied through two paths. Specifically, the rectangular reference clock signal generated by the oscillator 51 is output as it is on one path A and output via the inverter 52 on the other path B. For this reason, as shown in FIG. 9, the reference clock signal of one path A and that of the other path B are generated in opposite phases.
[0060]
The oscillator 51 and the inverter 52 may be disposed in a housing (not shown) of the X-ray detector system 14 or may be provided separately from the main body of the X-ray detector system 14 (FIG. 2). Reference) may be provided.
[0061]
Multiple DAS circuits 13 ₁ ~ 13 _n Are further grouped, and the odd-numbered DAS circuits 13 in the arrangement order. ₁ , 13 ₃ ,... Commonly receive the reference clock signal supplied from one of the paths A described above, and perform an A / D conversion operation in synchronization with the reference clock signal. On the other hand, the even-numbered DAS circuit 13 ₂ , 13 ₄ ,... Commonly receive the reference clock signal supplied from one of the paths B described above, and perform an A / D conversion operation in synchronization with the reference clock signal.
[0062]
As described above, in the X-ray CT apparatus according to the present embodiment, the X-ray detector system 14 detects X-rays transmitted through the subject at the time of scanning, and the X-ray CT image is reproduced from the projection data obtained as a result. Composed. In this X-ray detection operation, in particular, the DAS 13 in the X-ray detector system 14 includes a plurality of DAS circuits 13. ₁ ~ 13 _n The plurality of DAS circuits 13 are ₁ ~ 13 _n Operate based on reference clock signals having opposite phases. Therefore, it is possible to almost surely cancel out radiation noise caused by fluctuations in the ground and the power supply between circuits, and to suppress the generation of such noise as a whole and provide a high-quality X-ray CT image. it can.
[0063]
It should be noted that the method of applying the reference clock signal to the DAS 13 according to the first embodiment can be implemented in various forms as follows.
[0064]
10 and 11 show a first modification. According to this embodiment, as shown in FIG. 10, the DAS circuit 13 of the blocked DAS 13 is formed. ₁ ~ 13 _n Oscillator 51 for a few minutes ₁ ~ 51 _n Prepare the oscillator 51 ₁ ~ 51 _n The reference clock signal that is the output of the DAS circuit 13 ₁ ~ 13 _n To be supplied separately. For this reason, as shown in FIG. ₁ ~ 13 _n Each of them can be operated in synchronism with independent reference clock signals and asynchronously among the circuits. Therefore, the DAS circuit 13 ₁ ~ 13 _n Most of the influence of the radiation noise caused by the fluctuation of the ground and the power supply voltage in each can be dispersed or offset, and the influence of the noise on the image quality can be reduced as in the first embodiment.
[0065]
FIG. 12 shows a second modification. In the case of this modification, as shown in the figure, one oscillator 51 is provided, and a reference clock signal output from the oscillator 51 is sequentially supplied to a delay circuit 53 having a fixed delay time. ₁ ~ 53 _n-1 Each is delayed by a certain time. DAS circuit 13 of DAS 13 ₁ ~ 13 _n Also, the delay circuit 53 ₁ ~ 53 _n-1 The DAS circuit of each group includes an oscillator 51 and a delay circuit 53. ₁ ~ 53 _n-1 Each outputs a reference clock signal. As a result, the number of oscillators 51 can be reduced to one, and the use of the reference clock signal delayed by a predetermined time can cause a large influence of radiation noise due to fluctuations in the ground and the power supply voltage as described above. The portions can be dispersed or offset, and the influence of noise on the image quality can be reduced as in the first embodiment described above.
[0066]
(Second Embodiment)
Next, a second embodiment according to the present invention will be described with reference to FIGS.
[0067]
The X-ray CT apparatus according to this embodiment relates to voltage adjustment in each detector block 14 n of the X-ray detector system 14. Since the overall configuration of the X-ray CT apparatus is the same as that of the first embodiment described above, the same components are denoted by the same reference numerals and description thereof is omitted or simplified.
[0068]
In each detector block 14n according to this embodiment, a power connector 61 and a voltage regulator 62 are mounted on a part of the DAS side surface of the printed circuit board 141, as shown in FIG. Accordingly, as shown in FIG. 14, the output terminal of the power source 63 is connected to the power connector 61 of each detector block 14 n via the cable 64, and reaches the voltage regulator 62 via the power connector 61. ing.
[0069]
The voltage regulator 62 has a function of adjusting its input voltage to a predetermined voltage value, and its output terminal is the DAS circuit 13 of each detector block 14n. ₁ ~ 13 _n Connected in parallel. At this time, the output voltage V of the power source 63 ₀ As shown in FIG. 14, even if the cable 64 is the longest, that is, the voltage drop is the longest in the detector block 14n, the input voltage of the voltage regulator 62 is the specified voltage V required by the DAS circuit component 13a. ₁ It is set to be higher than (for example, 5 (V)).
[0070]
For this reason, in each detector block 14n, the voltage regulator 62 has a specified voltage V ₁ Higher input voltage (for example, 6 (V)), and the input voltage is set to the specified voltage V ₁ The voltage is adjusted (stepped down) to a value (for example, 6 (V)).
[0071]
Thus, in the X-ray detector system 14 according to the present embodiment, although the amount of voltage drop due to the cable 64 to each detector block 14n differs between the blocks (for example, 0.1 to 0.5 ( V) and so on, in order to absorb this fluctuation, the power supply voltage is reliably set to the specified value V in all detector blocks. ₁ Can be adapted to
[0072]
Therefore, in all the detector blocks, the DAS circuit component 13a can operate with the same voltage. As a result, the influence of fluctuations in A / D conversion characteristics due to the difference in power supply voltage between detector blocks can be reliably prevented or suppressed, the X-ray detection characteristics can be further stabilized, and the reliability of the apparatus can be improved. Can be planned.
[0073]
(Third embodiment)
Next, a third embodiment according to the present invention will be described with reference to FIGS.
[0074]
The X-ray CT apparatus according to this embodiment relates to the structure of the power supply line in each detector block 14 n of the X-ray detector system 14. The overall configuration of the X-ray CT apparatus is the same as that of the first embodiment described above.
[0075]
In this X-ray detector system 14, as shown in FIG. 16, a metal bar 71 as a plate-like conductor is used for the power supply (+ side) supplied to each detector block 14n. Specifically, the power supply device 72 and the X-ray detector system 14 are connected by a cable 73, and the metal bar 71 supplies power inside the X-ray detector system 14. As shown in FIG. 17, the metal bar 71 is electrically connected to a predetermined position of each detector block 14n via a branch portion 71a by screwing or connector connection.
[0076]
By using the metal bar 71 as a power supply line in this way, fluctuations (differences) in the voltage drop amount on the power supply side depending on the installation position of each detector block 14n can be suppressed. The voltage difference can be suppressed to an extremely small value. As a result, the detection operation can be stabilized and the image quality can be improved. On the other hand, since measures such as thickening the cable are not necessary, the mounting space in the X-ray detector system 14 can be saved, and the system 14 can be made compact.
[0077]
As an aspect related to the noise mixing countermeasure described in the first embodiment, there is a wiring structure in the DAS 13 of the detector block 14n. As shown in FIG. 18, detector blocks 14 n adjacent to each other in the channel direction are coupled to each other by an inter-block connector 81. For this reason, depending on the type of the X-ray detector system 14, each detector block 14n includes a DAM chip which is an IC for A / D conversion (for example, 16 channels), and data collection for running each block. It may be necessary to implement wiring.
[0078]
In the case of such a wiring structure, in the DAS circuit 13n of each detector block 14n, as shown in FIG. 18, a DAM chip 82 that handles analog signals and a wiring pattern 83 for collecting data after digital conversion are arranged separately. It is desirable. In the example of FIG. 18, the wiring pattern 83 is arranged at the center in the slice direction in each detector block 14n, while the DAM chips 82 are arranged on both ends of the wiring pattern 83 in the slice direction. As a result, it is possible to reduce noise from the wiring pattern 83 that handles digital signals in the DAM chip 82 that handles analog signals. As a result, it is possible to prevent the deterioration of SD (Standard Deviation) that is an index of image noise. In addition, by placing the DAM chip 82 that handles analog signals on both sides in the slice direction, the DAM chip 82 can be disposed avoiding X-rays and the wiring to the DAM chip 82 can be shortened.
[0079]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention when it is practiced.
[0080]
For example, in the above-described embodiment, as the X-ray CT apparatus, the rotation / rotation (ROTATE / ROTATE) type in which the current mainstream X-ray tube and the radiation detector integrally rotate around the subject has been described as an example. Further, the present invention may be applied to various types such as a fixed / rotated (STATIONARY / ROTATE) type in which a large number of detection elements are arrayed in a ring shape and only the X-ray tube rotates around the subject.
[0081]
Furthermore, in the above-described embodiment, as a mechanism for converting incident X-rays into electric charges, indirect conversion in which X-rays are converted into light by a phosphor such as a scintillator and the light is further converted into electric charges by a photoelectric conversion element such as a photodiode. Although the shape has been described, the direct conversion type utilizing the generation of electron-hole pairs in the semiconductor by X-rays and the movement to the electrodes, that is, the photoconductive phenomenon, may be employed.
[0082]
Further, in the above-described embodiment, the single-tube type X-ray CT apparatus has been described. However, a so-called multi-tube type X-ray CT in which a plurality of pairs of an X-ray tube and an X-ray detector are mounted on a rotating ring. You may apply to an apparatus.
[0083]
【The invention's effect】
As described above, according to the X-ray detector system of the computed tomography apparatus according to the present invention, the X-ray detector system includes a countermeasure for preventing radiation noise caused by ground potential fluctuations in a plurality of detector blocks. As a result of taking measures against inconsistencies in operating characteristics due to differences in power supply voltage between detector blocks and detector blocks, it is possible to improve the image quality by improving the stability and uniformity of the X-ray detection operation and improving the system structure. Can also contribute to downsizing.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a schematic configuration of an X-ray detector system employed in the X-ray CT apparatus according to the embodiment.
FIG. 3 is a schematic perspective view showing one of a plurality of detector blocks offset by the X-ray detector system from the X-ray incident side thereof.
FIG. 4 is a schematic perspective view showing one of a plurality of detector blocks from the back side.
FIG. 5 is a diagram schematically illustrating the arrangement of X-ray detection elements in one detector block in an X-ray detector system employed in the X-ray CT apparatus according to the embodiment.
FIG. 6 is a block diagram showing an electrical function of a detector block portion in the X-ray detector system.
FIG. 7 is a conceptual diagram for explaining DAS blocking.
FIG. 8 is a diagram for explaining how to supply a reference clock signal used in the X-ray detector system of the X-ray CT apparatus according to the first embodiment.
FIG. 9 is a timing chart for explaining the dephasing of the reference clock signal in the first embodiment.
FIG. 10 is a diagram for explaining how to supply a reference clock signal according to a first modification of the first embodiment.
FIG. 11 is a timing chart illustrating phase dispersion of the reference clock signal according to the first modification.
FIG. 12 is a diagram for explaining how to supply a reference clock signal according to a second modification of the first embodiment.
FIG. 13 is a schematic perspective view showing each detector block mounted on the X-ray detector system of the X-ray CT apparatus according to the second embodiment of the present invention.
FIG. 14 is a block diagram illustrating power supply to each detector block in the second embodiment.
FIG. 15 is a diagram for explaining voltage adjustment for each detector block for explaining power supply in the second embodiment;
FIG. 16 is a schematic perspective view showing an X-ray detector system of an X-ray CT apparatus according to a third embodiment of the present invention.
FIG. 17 is a diagram illustrating power supply using a metal bar according to the third embodiment.
FIG. 18 is a diagram for explaining a modification relating to the wiring form of each detector block;
[Explanation of symbols]
12 X-ray detector
13 DAS (data collection device)
13 ₁ ~ 13 _N DAS circuit
13a DAS circuit parts
14 X-ray detector system
14n (14 ₁ ~ 14 _N ) Detector block
51, 51 ₁ ~ 51 _N Oscillator
53 ₁ , 53 _N ... delay circuit
52 Inverter
61 Power connector
62 Voltage regulator
63 Power supply
71 metal bar
141 Printed circuit board
142 CMOS switch
143 photodiode array
144 Scintillator block

Claims (6)

A detector that detects X-rays transmitted through the subject and outputs an analog electric signal corresponding to the X-ray for each channel, and an analog electric signal for each channel output by the detector An X-ray detector for a computer tomography apparatus comprising: a data acquisition device that converts an electrical signal into an output; and at least the data acquisition device is divided into a plurality of circuit blocks each including a predetermined number of channels In the system,
Computational tomography characterized by comprising anti-phase operation means for grouping the plurality of circuit blocks into two and operating each of the circuit blocks in synchronization with clock signals having opposite phases between the groups. X-ray detector system of the device.   The anti-phase operation means supplies an oscillator that generates a reference clock signal, and supplies the clock signal generated by the oscillator to a circuit block belonging to one of the two groups as it is, and the clock signal generated by the oscillator 2. An X-ray detector for a computed tomography apparatus according to claim 1, further comprising: means for inverting the polarity of the first clock and supplying the clock signal to a circuit block belonging to the other of the two groups. system. A detector that detects X-rays transmitted through the subject and outputs an analog electric signal corresponding to the X-ray for each channel, and an analog electric signal for each channel output by the detector An X-ray detector for a computer tomography apparatus comprising: a data acquisition device that converts an electrical signal into an output; and at least the data acquisition device is divided into a plurality of circuit blocks each including a predetermined number of channels In the system,
A plurality of oscillators for generating the reference clock signals necessary for the plurality of circuit blocks are provided in the same number as the number of the circuit blocks, and the plurality of circuits independently and asynchronously output the reference clock signals output from the plurality of oscillators. An X-ray detector system for a computed tomography apparatus, wherein the X-ray detector system is supplied to each of the blocks. A detector that detects X-rays transmitted through the subject and outputs an analog electric signal corresponding to the X-ray for each channel, and an analog electric signal for each channel output by the detector An X-ray detector for a computer tomography apparatus comprising: a data acquisition device that converts an electrical signal into an output; and at least the data acquisition device is divided into a plurality of circuit blocks each including a predetermined number of channels In the system,
Means for generating a reference clock signal having a different delay amount for each predetermined time between the plurality of circuit blocks is provided for each circuit block, and each of the generated reference clock signals is supplied to each circuit block. An X-ray detector system for a computed tomography apparatus. The detector is a two-dimensional detector in which a detector row having detector elements for a plurality of predetermined channels in a channel direction is arranged with a predetermined number of detector rows in a slice direction orthogonal to the channel direction,
A scintillator block that converts the X-rays into optical signals for each detection element, and a photo that is optically coupled to the scintillator block and that outputs optical signals output from the scintillator block to the detection elements into analog electrical signals. a diode array, an electric signal output from the photodiode for each detection element, claim 1-4, characterized in that a switch element array for synthesizing every specified number of columns of said slice direction An X-ray detector system for a computed tomography apparatus according to one item.   6. The X-ray detector system for a computed tomography apparatus according to claim 5, wherein the photodiode array, the switch element array, and the data collection device have a structure in which each circuit block is three-dimensionally mounted via a substrate.

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