JPH0577995B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] <Industrial Application Field> The present invention relates to a radiation detector that detects radiation, for example, X-rays, and an X-ray CT apparatus using the detector.

<Conventional technology> An X-ray CT device consists of an X-ray tube that emits fan beam X-rays (hereinafter referred to as X-rays) having a flat, fan-shaped spread angle θ, and a radiation detector that detects the X-rays. are opposed to each other with the subject in between, and these X-ray tubes and radiation detectors are rotated in the same direction and at the same angular velocity around the subject to perform X-ray projection in various directions on the cross section of the subject. After collecting data and collecting sufficient data, this data is analyzed to calculate the X-ray absorption rate corresponding to each position in the cross section of the object, and a gradation level corresponding to the absorption rate is given to the object. This method reconstructs image information in a cross section of a specimen.

FIG. 4 shows a radiation detector used in a conventional X-ray CT apparatus. This radiation detector 1
In this method, a large number of high-voltage application electrodes 2 and signal extraction electrodes 3 are arranged alternately in a high-pressure container 4, and
It is filled with high-pressure gas such as Xe (xenon).
Although a radiation detector generally has an arcuate outer shape, in FIG. 4 only a portion of the outer shape is cut out and approximated by a straight line.

The plurality of high voltage application electrodes 2 in the radiation detector 1 are connected to a common high voltage source 5, and the plurality of signal extraction electrodes 3 are connected to a data acquisition unit (DAS: Data Acquisition System) 6 in the X-ray CT apparatus. It is connected. The X-rays that have passed through the subject enter from the direction indicated by arrow 7 in the figure. Then,
This incident X-ray is detected by the main detector 1 as an ionizing current, which is sent as a detection signal to the data acquisition unit 6.
transmitted to.

FIG. 5 shows a detailed configuration of the data collection section 6. As shown in FIG.

Set the number of channels of radiation detector 1 to 512 (CH0 to
CH511), there are 32
Front ends 8 ₁ to 8 ₃₂ are provided.
Each front end ₈₁ to ₈₃₂ receives RESET and S/H from the DAS controller 15.
(sample hold) and CH-ADRS (channel address) are input, and each front end 8 ₁ to 8 ₃₂ controls the 16 of the X-ray detector 1 by this signal input.
Performs data collection processing for channels. However, the processing output of the front ends 8 ₁ to 8 ₃₂ is
BOARD-ADRS from DAS controller 15
(board address) signal
Buffer amplifier 10, sample hold circuit (S/H) 11, selected by BOARD MUX (board multiplexer) 9 and placed in the subsequent stage.
Data register 1 via A/D converter 12 in turn.
3, and after the timing is adjusted here, it is sent to an image reconstruction unit (not shown) via a data transmitter 14. Here, the above sample hold circuit 11, A/D
The operation of the converter 12, data register 13, and data transmitter 14 is controlled by the DAS controller 15.
controlled by. Therefore, the gantry of an X-ray CT device is equipped with a graticule system that outputs a predetermined pulse (GRATICULE pulse) according to the rotation of the gantry rotation system. DAS
The information is transmitted to the controller 15. Further, an enable signal is input to the DAS controller 15 from a scan controller (not shown), and when this enable signal is at H level, projection data collection is performed in the data collection unit 6. be exposed.

FIG. 6 shows details of the front end ₈₁ in FIG. 5. As shown in the figure, this front end ₈₁ includes an integrating circuit 3 that integrates the outputs of the detection channels CHO to CH15 of the radiation detector 1.
0 ₀ to 30 ₁₅ , sample and hold circuits 31 ₀ to 31 ₁₅ arranged after each integrating circuit, and a multiplexer (MUX) 32 that selects the sample and hold output of the sample and hold circuit. Each of the integrating circuits 30 ₀ to 30 ₁₅ is formed by connecting a capacitor 27 and a FET (field effect transistor) 28 between the inverting input terminal and the output terminal of an operational amplifier 26 . Integrating circuits 30 ₀ to 30 ₁₅ include
The RESET signal is inputted, and the S/H signal is further inputted to the sample and hold circuits 31 ₀ to 31 ₁₅ . CH-ADRS is 4 bits, and serves as a selection control signal for multiplexer 32. Note that the other front ends 8 ₂ to 8 ₃₂ are also configured in the same manner as described above. The input timing of each control signal is shown in FIGS. 7 and 8.

A grout pulse is generated every minute rotation of the X-ray tube, and projection data is collected for each pulse in the sequence shown in FIGS. 7 and 8. The projection data thus obtained is transmitted to an image reconstruction unit (not shown) and used to form a tomographic image of the subject.

(Problem to be Solved by the Invention) Incidentally, the sampling pitch of the projection data is determined by the arrangement pitch of the signal extraction electrodes 3, as shown in FIG. The section that contributes to the detection output of one channel is up to the high voltage application electrode 2 adjacent to the signal extraction electrode 3. The thickness of the signal extraction electrode 3 and the high voltage application electrode 2 is a dead space and is insensitive to X-rays.

In order to improve the spatial resolution, it is desirable to reduce the sampling pitch, and for this purpose, the arrangement pitch of the signal extraction electrodes 3 must be reduced. However, even if the arrangement pitch of the signal extraction electrodes 3 is set to 0.8 mm, considering that each electrode needs to have a thickness of 0.15 to 0.2 mm to prevent adverse effects caused by vibration and deflection, Since a dead space of 0.3 to 0.4 mm is created and the X-ray detection efficiency is reduced, there is a limit to improving the spatial resolution by reducing the arrangement pitch of the signal extraction electrodes 3.

Therefore, the present invention aims to eliminate the above-mentioned drawbacks.
The purpose is to provide a radiation detector that can easily reduce the sampling pitch of projection data even when the arrangement pitch of the signal extraction electrodes 3 is the same as conventional ones, and by using this detector. An object of the present invention is to provide an X-ray CT device that can obtain reconstructed images with excellent spatial resolution.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the present invention, a plurality of signal extraction electrodes and high voltage application electrodes are arranged alternately, and a signal is transmitted from each signal extraction electrode. 1st for taking out
In a radiation detector having lead wires drawn out, the high voltage application electrodes can be used for both high voltage application and signal extraction by individually drawing out second lead wires from each of the high voltage application electrodes. I'm trying to get it. Furthermore, a plurality of signal extraction electrodes and high voltage application electrodes are arranged alternately, a first lead wire for signal extraction is drawn out from each signal extraction electrode, and a second lead wire is individually connected from each high voltage application electrode. A radiation detector is formed by drawing out a lead wire, and a high voltage is applied to the high voltage application electrode through the second lead wire, and a high voltage is applied to the subject through the first and second lead wires. The X-ray CT apparatus is configured to include a data collection section that collects X-ray projection data and an image reconstruction section that performs image reconstruction processing based on the obtained X-ray projection data. Further, the data collection unit includes a first integrating circuit group that integrates the X-ray detection signal obtained via the first lead wire;
and a second integrating circuit group that integrates the X-ray detection signal obtained through the second lead wire, and applies a high voltage to the high voltage application electrode via the second integrating circuit group. I try to do that.

(Function) By individually drawing out the second lead wires from each of the high voltage application electrodes, the high voltage application electrodes can be used for both high voltage application and signal extraction. Even if the original arrangement pitch of the signal extraction electrodes is equal to that of the conventional detector, the sampling pitch of the X-ray projection data can be reduced to 1/2 of that of the conventional detector.

Furthermore, in the X-ray CT apparatus, the data collection unit collects X-ray projection data using the radiation detector described above, and performs image reconstruction processing based on the obtained X-ray projection data, thereby improving spatial resolution. It is possible to obtain excellent reconstructed images.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 1a shows an embodiment of a radiation detector according to the invention.

This radiation detector 35 is constructed by alternately arranging a plurality of high voltage application electrodes 2 and signal extraction electrodes 3, and filling a container with Xe gas. Lead wires 37 are individually led out from each signal extraction electrode 3. This lead wire 37 is called a first lead wire. Further, lead wires 38 are individually drawn out from each high voltage applying electrode 2. This lead wire 38 is referred to as a second lead wire. As is clear from a comparison of FIG. 1a and FIG. 4, this radiation detector 35 is significantly different from the conventional detector 1 because:
The point is that the second lead wires 38 are individually drawn out from each of the plurality of high voltage application electrodes 2. By drawing out the second lead wire 38 in this manner, the plurality of high voltage application electrodes 2 can be used for both high voltage application and signal extraction. Since high-pressure Xe gas is sealed in the high-pressure container 36, the first and second lead wire lead-out portions are hermetically sealed.

When this radiation detector 35 is used in an X-ray CT apparatus, the other ends of the first and second lead wires 37 and 38 are connected to a data acquisition section (DAS) 39. This data collection section 39 includes a first integrating circuit group 40 that integrates the X-ray detection signal obtained via the first lead wire 37 and an X-ray detection signal obtained via the second lead wire 38. Second integration circuit group 4 for integration
1. The positive electrode side of the high voltage source 5 is connected to the non-inverting input terminal of each operational amplifier 26 forming the second integrating circuit group 41, and by doing so, a high voltage is applied to each high voltage application electrode 2. can do. Note that the configuration of this data collection section 39 will be described in detail later.

Figure 1b shows the X
A line CT device is shown.

The X-ray tube 43, the X-ray CT device 35, and the data acquisition unit 39 belong to a rotating system of a galint (also referred to as a gantry), and rotate in the same direction around the subject P.
The galint has a photographing hole, and the subject P is placed in this photographing hole. The X-ray tube 43 includes a high pressure generating section 46
X-rays are emitted toward the subject P by applying a high voltage generated by the The radiation detector 39 detects the component of X-rays transmitted through the object, and has a plurality of (for example, 512) detection channels. The detailed configuration of this radiation detector 39 is similar to that shown in FIG. 1a. The data collection unit 39 receives the detection output of the radiation detector 35 and collects X-ray projection data of the subject P. This data collection section 39 is under the control of the scan controller 5. scan controller 45
is responsible for controlling the execution of CT scans using X-rays.

The bed controller 48 controls the operation (mainly movement of the top plate) of the bed on which the subject P is placed, and the bed controller 48, the high pressure generator 46, and the Galint controller 47 are connected to the scan controller 45. is under the control of.

The image reconstruction unit 44 forms a tomographic image of the subject P by executing image reconstruction processing based on the X-ray projection data collected by the data collection unit 39. In addition, CPU (central processing unit) 5
A memory 53, a disk 52, a display console 51, an image reconstruction unit 44, and a scan controller 45 are connected to this unit via a CPU bus 55.
It is coupled to the CPU 54. The data of the tomographic image formed in the image reconstruction section 44 is then transferred to the display console 5 under the control of the CPU 54.
1 and is visualized on a CRT display 50. A keyboard 49 is connected to the display console 51,
This keyboard 49 is used to set photographing conditions and image data processing conditions.

Next, the detailed configuration of the data collection section 39 will be explained based on FIG. 2.

In FIG. 2, parts having the same functions as those shown in FIG. 5 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

The main difference between this data collection section 39 and the one shown in FIG. 5 is that it uses an optical coupler (OPC).
circuits 61, 62, front ends 8 ₁ ′ to 8 ₃₂ ′,
Board multiplexer (BOARD MUX) 9′,
Buffer amplifier 10', sample hold (S/
H) The provision of the circuit 11', the A/D converter 12', and the output register 13', the expansion of the control function of the DAS controller 60, and the high voltage via the front ends ₈₁ ' to ₈₃₂ '. The high voltage of the source 5 is connected to the high voltage application electrode 2 of the radiation detector 35 (Fig. 1a).
(see).

Second lead wires 38 drawn out from each high voltage application electrode 2 of the radiation detector 35 are connected to the front ends 8 ₁ ′ to 8 ₃₂ ′. Each front end 8
₁ ′ to T ₃₂ ′ are the outputs of channels (CH0′ to CH511′) newly formed by the high voltage application electrode 2 of the radiation detector 35, and each front end 8 ₁ ′ to 8 ₃₂ ' performs processing for 16 channels each.

Since a high voltage is applied to the front ends ₈₁ ' to ₈₃₂ ', the board multiplexer 9', the buffer amplifier 10', the sample and hold circuit 11', the A/D converter 12', and the output register 13', Electrical insulation by the OPC circuits 61 and 72 prevents high voltage from being applied to other circuits. The basic operation of this high voltage side circuit group is the same as the conventional circuit group (8 ₁ to 8 ₃₂ , 9, 10, 11,
12, 13; hereinafter referred to as [low-voltage side circuit group] for convenience), but since the signal current flows in opposite directions in the high-voltage side circuit group and the low-voltage side circuit group,
There are some restrictions in circuit design. For example, when the integrator circuits in the front ends 8 ₁ to 8 ₃₂ (corresponding to the first integrator circuit group ₄₀ in FIG. to 8 ₃₂ ' integration circuit group (first
(corresponds to the second integrating circuit group 41 in Figure a)
must be operated at a positive voltage (for example, 0 to +10V). The sample and hold circuit is a buffer amplifier,
Similarly, the A/D converter and the like are operated so that the high voltage side and the low voltage side have opposite polarities. However, if a signal inversion circuit is placed at the first stage of each of the high-voltage side front ends 8 ₁ ′ to 8 ₃₂ ′, the above restriction can be avoided. That is, by providing the signal inversion circuit, the high voltage side circuit group can be formed in the same way as the low voltage side circuit group.

The operation of the high voltage side circuit group is via the OPC circuit 61.
It is controlled by the DAS controller 60, and the X-ray projection data obtained under this control is transmitted to the OPC circuit 6.
2 to the data transmitter 14, and is sent to the image reconstruction unit 44 together with the X-ray projection data in the output register 13.

Next, the operation of the above configuration will be explained.

Every minute rotation of the X-ray tube 43, the
X-rays are emitted, and the X-rays that have passed through the subject P are incident on the radiation detector 35. A high voltage is applied to the high voltage application electrode 2 of the radiation detector 35 via the second integrating circuit group 41 in the data acquisition unit 39,
The high voltage side circuit group including this second integrating circuit group 41 operates with the high voltage as a reference potential.

Each signal extraction electrode 3 in the radiation detector 35
Detection signal by (CHn, CH _o+1 , CH _o+2 ,…)
are processed by the front ends 8 ₁ to 8 ₃₂ , and the processed output is taken into the A/D converter 12 via the board multiplexer 10 and sample hold circuit 11 , where it is A/D converted and then output. It is held in the output register 13.

On the other hand, the detection signals (CHn′, CH _o ′ ₊₁ ,
CH _o ′ ₊₂ ,...) are processed by the front ends 8 ₁ ′ to 8 ₃₂ ′, and the processed output is taken into the A/D converter 12 ′ via the board multiplexer 9 ′ and the buffer amplifier 10 ′. Here, after being A/D converted, it is held in the output register 13'. The projection data in this register 13' is stored in the OPC circuit 62.
transmitted to the data transmitter 14 via
It is transmitted to the image reconstruction unit 44 together with the projection data in the output register 13.

The above data collection operation is controlled by various control signals output from the DAS controller 60 at the timing shown in FIG. As is clear from the figure, the projection data acquisition timing is exactly the same on the high pressure side and the low pressure side. According to such projection data collection, the sampling pitch of the projection data obtained for one graticule pulse (that is, one X-ray exposure) is different from the conventional one by combining the high-pressure side data and the low-pressure side data. It is 1/2 compared to that of the device. In other words, as shown in Fig. 3, the sampling pitches on the high-pressure side and the low-pressure side are the same as in the conventional case (see Fig. 10), but since there is a pitch shift of 0.5 channels in the X direction, By combining these, the sampling pitch is 1/2 that of the conventional one. In other words, the number of channels (density) is doubled without sacrificing geometric efficiency (or increasing dead space). Note that the sampling frequency is a little less than twice the cutoff frequency of the aperture response of the radiation detector 35, so that the sampling theorem is satisfied in an almost ideal state.

The image reconstruction process in the image reconstruction unit 44 uses the convolution/back projection method similar to the conventional method, but as mentioned above, the sampling pitch of the projection data is 1/2 that of the conventional method. ,
Images with excellent spatial resolution can be formed. The regenerated image data obtained through the processing of the image reconstruction unit 44 is transferred to the display console 51 under the control of the CPU 54, visualized on the CRT display 50, and stored in the memory 13 and disk as necessary. 12.

In this way, the apparatus of this embodiment is equipped with the radiation detector 35, collects X-ray projection data at half the sampling pitch of the conventional method, and uses this data to reconstruct a tomographic image of the subject P. This makes it possible to obtain images with excellent spatial resolution. In addition, by improving the geometric efficiency of X-ray detection, it has advantages such as improving the S/N ratio of reconstructed images and reducing the amount of X-ray irradiation.
For the same reason, the X-ray dose (mAs) is not insufficient even during short-time scans, and high-speed scans are possible, resulting in excellent effects.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various modifications are possible.

In the above embodiment, a radiation detector filled with Xe gas and an X-ray CT device using the detector have been described. The present invention can also be applied to general detectors in which high voltage application electrodes and signal extraction electrodes are alternately arranged. In addition, instead of using all high-voltage application electrodes for signal extraction, detection signals are also extracted from the high-voltage application electrodes only in the central area of the CT field of view, and other areas are left with their original state as before. The detection signal may be extracted only from the signal extraction electrode.

Furthermore, in the above embodiment, a high voltage is applied to the high voltage application electrode 2 via the second integrating circuit group 41, but it is also possible to apply a high voltage via a circuit other than the integrating circuit group in the data collection section. You may go.
Note that the high voltage polarity on the high voltage application electrode 2 side may be either positive or negative.

[Effects of the Invention] As detailed above, according to the present invention, the arrangement pitch of the signal extraction electrodes can be reduced by enabling the high voltage application electrodes to be used both for high voltage application and signal extraction. A radiation detector that can easily reduce the sampling pitch of projection data even in the same case as before, and an X-ray CT that can obtain reconstructed images with excellent spatial resolution by using the detector equipment can be provided.

[Brief explanation of drawings]

FIG. 1a is an explanatory diagram of an embodiment of the radiation detector according to the present invention, and FIG. 1b is an X-ray CT using the detector.
2 is a detailed configuration block diagram of the main parts of FIG. 1b, FIG. 3 is an explanatory diagram of the sampling pitch in the radiation detector of FIG. 1a, and FIG. 4 is a diagram of conventional radiation detection. Illustration of the vessel, No. 5
The figure shows a detailed configuration block diagram of the main parts of a conventional X-ray CT device, FIG. 6 shows a detailed configuration block diagram of the main parts of FIG. 5, and FIGS. 7 and 8 show various control signals in the conventional device. FIG. 9 is a timing diagram of various control signals in the apparatus of this embodiment, and FIG. 10 is a diagram illustrating the sampling pitch of the radiation detector of FIG. 4. 2... Electrode for high voltage application, 3... Electrode for signal extraction, 35... Radiation detector, 37... First lead wire, 38... Second lead wire, 39... Data collection unit, 40 . . . first integration circuit group, 41 . . . second integration circuit group, 44 . . . image reconstruction unit.

Claims (1)

[Scope of Claims] 1. A radiation detector in which a plurality of signal extraction electrodes and high voltage application electrodes are arranged alternately, and a first lead wire for signal extraction is drawn out from each signal extraction electrode, A radiation detector characterized in that a second lead wire is individually drawn out from each high voltage application electrode so that the high voltage application electrode can be used for both high voltage application and signal extraction. 2 Arrange a plurality of signal extraction electrodes and high voltage application electrodes alternately, draw out the first lead wire for signal extraction from each signal extraction electrode, and individually connect the second lead wire from each high voltage application electrode. Consisting of a lead wire drawn out,
A radiation detector capable of detecting X-rays transmitted through the subject, and applying a high voltage to the high voltage application electrode through the second lead wire, and applying a high voltage to the high voltage application electrode through the first and second lead wires. An X-ray CT apparatus comprising: a data collection section that collects X-ray projection data of the subject; and an image reconstruction section that performs image reconstruction processing based on the obtained X-ray projection data. 3. The data collection unit includes a first integrating circuit group that integrates an X-ray detection signal obtained through the first lead wire, and a first integration circuit group that integrates an X-ray detection signal obtained through the second lead wire. 3. The X-ray according to claim 2, further comprising a second integrating circuit group, and applying a high voltage to the high voltage applying electrode via the second integrating circuit group.
CT device.