JPH0572345A - Radiation image pickup device - Google Patents

Abstract

(57) [Summary] [Object] To provide a structure for obtaining an energy-discriminated image in a photon counting type radiation image pickup device without increasing the number of circuits below a comparator. [Configuration] For detectors adjacent to each other in the array,
Circuit means is provided for introducing both outputs into only one amplifier, guiding the output of this amplifier to both of the two comparators, and differentiating the reference voltages of the two comparators from each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image capturing apparatus such as an X-ray image used for medical diagnosis and the like, and more particularly to a radiation image capturing apparatus using a photon counting method.

[0002]

2. Description of the Related Art In radiation image pickup based on a photon counting method, in principle, the radiation dose is measured by counting the pulse signals generated by the radiation incident on the detector, and one detector is used as a pixel. Image is formed. In a radiographic image pickup apparatus of such a system, generally, while scanning a detector array in which a large number of detectors are arranged in a row and one row or a plurality of rows are collected,
Each detector is connected to a measuring circuit consisting of an amplifier, a comparator and a counter, the output from each detector is converted into a voltage pulse, and the pulses exceeding the threshold value are counted by the counter and sent to each detector. The incident dose is obtained, and an image in which the count value (dose) is used as the pixel density is obtained.

[0003] By using such a radiation imaging apparatus, the energy of radiation is discriminated and an energy-specific image is created for the purpose of more accurately imaging the tissue of a living body or the like and performing advanced image diagnosis. The method is already known. As a method of performing such energy discrimination, conventionally, a plurality of comparators and counters are connected in parallel to an amplifier connected to each detector and the reference voltages of the comparators are made different from each other, so that different energy from each comparator is obtained. A method for obtaining a radiation dose has been proposed (for example, Japanese Patent Laid-Open No. 60-80746).

[0004]

By the way, in this type of detector array, the detectors are arranged as densely as possible in order to make the pixels smaller and improve the spatial resolution. When the detectors are arranged in a high density, the amplifiers, comparators and counters connected to the detectors also need to be mounted in a higher density. For example, when such a photon counting method is used for the detection part of a tomographic imaging apparatus such as a CT scanner, a compact structure is required. Connecting a comparator and a counter in parallel in
Not only is it a hindrance to device miniaturization, but there are many difficulties in terms of mounting technology.

The present invention has been made in view of the above circumstances, and the radiation energy can be changed as needed in a compact structure without increasing the number of measuring circuits below the comparator as in the conventional case. It is an object of the present invention to provide a radiation image pickup apparatus capable of discriminating and constructing an image.

[0006]

A configuration for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. According to the present invention, each detector (1
a (1a, 1b ...) One for each amplifier (2a, 2b)
..), comparators (3a, 3b ...) And counters (4a, 4b ...) Connected in series, and for both detectors (1a, 1b) adjacent to each other, both outputs Of the first switching means (switches 51, 52) for introducing one of the amplifiers (2b) into the other (2a) and disconnecting the other (2a), and the amplifier (2b) into which this output is introduced.
The second switching means (61, 62) for guiding the output of the above to both the two comparators (3a, 3b) and the circuit means (7) for changing at least one of the reference voltages of these two comparators are provided. ..

[0007]

[Operation] In the normal mode without energy discrimination,
As shown in FIG. 2, measurement based on a conventional normal photon counting method is performed in a state where one amplifier, one comparator, and one counter are connected to one detector. When performing energy discrimination, the first and second switching means are driven to introduce the outputs of the two detectors 1a and 1b into one amplifier 2b as shown in FIG. Two output pulse comparators 3
If the reference voltage of one of the comparators 3a is made higher than in the normal state while being led to both a and 3b,
Regarding the radiation incident on the detectors 1a and 1b, the counter 4a counts the radiation having the energy equal to or higher than the threshold value similar to the normal mode, and the counter 4b counts the radiation having the energy equal to or higher than a certain value. That is, it is possible to obtain an image for each energy in which the two detectors 1a and 1b are regarded as one pixel.

[0008]

Embodiment FIG. 1 is a partial circuit configuration diagram of an embodiment of the present invention. A large number of semiconductor radiation detectors 1a, 1b, ...
The detector array A is formed by arranging them in a row or a matrix of a plurality of rows. Each detector 1a, 1b, ... Has one pre-main amplifier 2a, 2b ,.
..., and one comparator 3a, 3b, ... And one counter 4a, 4b ...

With respect to a large number of detectors constituting the detector array A, two adjacent detectors are one.
Switching devices as shown in FIG. 1 are inserted in the measurement circuit that forms a set and that follows them. That is, a switch 51 is inserted between one of the two detectors 1a and 1b adjacent to each other and the pre-main amplifier 2a. The input terminal of the pre-main amplifier 2b for the detector 1b is connected via the switch 52.

Further, a switch 61 is inserted between the pre-main amplifier 2a for the detector 1a and the comparator 3a for inputting its output, and the latter stage portion of the switch 61 and the other detector 1b. Is connected to the input terminal of the comparator 3b via the switch 62. The above switches 51, 52, 61 and 62 are switched in a pattern to be described later by a command from the control circuit 7 placed outside, and the reference voltage of the comparator 3b for the detector 1b is controlled by the control circuit 7. It is configured so that it can be changed by a command.

Next, the operation of the above embodiment of the present invention will be described together with the method of use. First, when imaging is performed in a normal measurement mode in which energy discrimination is not performed, each switch in all the groups is set to the state shown in FIG. 2 and the reference voltages of all the comparators 3a, 3b, ... Are set. In both cases, the detector array A is scanned with the threshold voltage V _TH set.

As a result, the output from each of the detectors 1a, 1b, ... Is such that all of the voltage pulses having a peak value exceeding the threshold voltage V _TH are output by the respective counters 4a, 4b ,. .. are counted as one pixel, and a normal radiation image in which the dose of radiation exceeding a certain energy is used as the pixel density is obtained.

When performing energy discrimination, each switch is set to the state shown in FIG. 1, and the reference voltage of one comparator 3b of the pair of comparators is set to
For example, the detector array A is scanned by setting it to a predetermined voltage V _B higher than V _TH . As a result, the outputs of the pair of detectors 1a and 1b are both input to the pre-main amplifier 2b, and the output of the pre-main amplifier 2b is input to both comparators 3a and 3b. Compared to _TH or V _B. As a result, the counter 4a counts the voltage pulses having the peak value exceeding V _TH , while the counter 4b counts the voltage pulses having the peak value exceeding V _B higher than that.

In this state, when an image is constructed with a value obtained by subtracting the counting result of the counter 4b from the counting result of the counter 4a, the image is composed of two detectors (1a and 1b, ...
.) Is set as one pixel, and a radiation image in which the dose of the radiation having the energy level corresponding to the range of V _{TH to} V _B is set as the pixel density is obtained. Further, when an image is constructed by the counting result of the counter 4b, the image is also divided into two pieces.
A radiation image is obtained in which each detector in the set has one pixel, and the pixel concentration is the dose of radiation exceeding the energy level corresponding to V _B.

In the above embodiment, in performing the energy discrimination, the reference voltage of one comparator 4b is increased and the counter 4b counts the voltage pulse having the peak value higher than V _B. It is also possible to reverse the output condition of the comparator 4b and generate an output when a voltage pulse lower than V _B is input, only in this case.
An image of radiation corresponding to an energy level of V _B or less is obtained from the counting result of the counter 4b, and the counter 4a
An image by radiation corresponding to an energy level exceeding V _B can be obtained from a value obtained by subtracting the result of counting by the counter 4b from the result of counting.

Further, in the present invention, as the two detectors adjacent to each other, either one adjacent to the detector row in the column direction or one adjacent to the detector row in the direction orthogonal to the detector row can be adopted. .. Further, it goes without saying that the reference voltages of both the pair of comparators can be arbitrarily changed.

[0017]

As described above, according to the present invention, the number of comparators and counters can be increased without increasing the number of comparators and counters.
An amplifier, a comparator and a counter are provided for each of the detectors, and the detectors adjacent to each other are set as one set to discriminate the energy of the radiation incident on these detectors by simply operating the switching means as necessary. Therefore, it is possible to obtain a radiation image having different energies under a compact structure without increasing the size of the apparatus. Further, since the image pickup apparatus of this type has a digital output and is made compact according to the present invention, it can be incorporated in a detection portion of a CT scanner and is also applied as a tomographic image apparatus having an energy discrimination capability. It has become possible.

[Brief description of drawings]

FIG. 1 is a partial circuit configuration diagram of an embodiment of the present invention, showing a state in which energy discrimination is performed.

FIG. 2 is a partial circuit configuration diagram of the embodiment of the present invention, showing a state without energy discrimination.

[Explanation of symbols]

 1a, 1b ... Semiconductor radiation detector 2a, 2b ... Pre-main amplifier 3a, 3b ... Comparator 4a, 4b ... Counter 51, 52, 61, 62 ... Switch 7 ... Control circuit A ... Detector array

Claims (1)

[Claims] 1. A detector array having one or a plurality of detector rows formed by arranging a plurality of semiconductor radiation detectors in a row and a scanning means for the detector array, wherein each of the detectors has a detector. An amplifier that converts and amplifies the output into a voltage pulse, a comparator that compares the output of this amplifier with a reference voltage, and a counter that counts the output from this comparator are connected, and the output of each counter is associated with each pixel In the device for forming the above-mentioned detector, the first switching means for introducing both outputs of the detectors adjacent to each other in the detector array into one of the amplifiers and disconnecting the other, and the amplifier to which the output is introduced. Second, which directs the output of both to both comparators
And a circuit means for changing at least one of the reference voltages of the two comparators.