JPH095445A - Radiological image pickup device - Google Patents

Abstract

PURPOSE: To suppress counting saturation and accurately discriminate energy in a high dose region by dividing multiple radiation detectors into multiple blocks every prescribed unit, and dividing and detecting one picture element of a radiological image with multiple radiation detectors. CONSTITUTION: Outputs of cells 1a, 1b are guided to charge-sensitive amplifiers 2a, 2b and converted into voltage pulses. The outputs of the amplifiers 2a, 2b are guided to comparators 3a, 3b. The comparators 3a, 3b compare the input voltage pulses with threshold Vth , they output H-level digital pulses while the input voltage pulses exceed the threshold Vth , and the outputs of the comparators 3a, 3b are inputted to counters 4a, 4b. Count values recorded by the counters 4a, 4b are digitally added 6, and the added values are stored in an image memory 5 as the data for one picture element of an X-ray image. The memory data of the image memory 5 are displayed on a screen such as a CRT as the variable-density image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image pickup apparatus such as an industrial nondestructive inspection apparatus and a medical X-ray image pickup apparatus (CT scanner).

[0002]

2. Description of the Related Art In recent years, a so-called photon counting system in which an incident photon signal is directly converted into an electric pulse using a semiconductor and the pulse signal is counted has been applied to a radiation image pickup apparatus.

An apparatus using the photon counting system basically has a charge output type X-ray sensor (for example, CdTe) 21, a charge sensitive amplifier 22, a comparator 23, a counter 24, and a charge output type X-ray sensor 21, as shown in FIG. It is configured by the image memory 25, and in such a circuit configuration, when an X-ray photon enters the X-ray sensor 21, the generated charge is converted into a voltage pulse by the charge sensitive amplifier 22. At this time, if the pulse wave height exceeds the threshold value Vth, the comparator 23 outputs a digital pulse and the value of the counter 24 is incremented by one.

Then, the count value finally recorded in the counter 24 is stored in a predetermined area of the image memory 5, and the stored data, that is, the value counted by one pixel of the X-ray sensor is displayed on the X-ray image. The grayscale information of one pixel is output and displayed on a screen such as a CRT.

[0005]

By the way, in the photon counting method, when the amount of incident radiation is low, the radiation can be accurately measured, but when the dose is large, it becomes impossible to separate the photons one by one. For,
There is a problem that the counting characteristic becomes non-linear (count counting down).

Further, the photon counting method has a feature that it is possible to perform energy discrimination counting. In this case as well, when the doses increase and the pulses overlap each other, the pulse wave height becomes not proportional to the incident energy. The point becomes a problem.

Particularly, in a CT scanner, strong X-rays are incident on a large light receiving area of about 1 mm × 30 mm, so that the above two problems are more serious. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a radiation image pickup device capable of detecting a wide range of radiation from low dose to high dose and having a wide dynamic range.

[0008]

In order to achieve the above object, the radiation image pickup apparatus of the present invention has a plurality of radiation detectors each of which generates a charge signal upon incidence of a radiation photon. An amplifier that converts the charge signal from the device into a voltage pulse, a voltage comparator that compares the output of this amplifier with a reference voltage and outputs a pulsed signal when it exceeds the reference voltage, and the output of this voltage comparator Is connected to a counter for counting, and the radiation detector group is divided into a plurality of blocks for each predetermined number of units,
It is characterized in that an adder for adding the count value of the counter is provided for each block, and the output of each adder is used as image data for one pixel of the radiation image.

[0009]

When a plurality of radiation detectors are divided into a plurality of blocks by a predetermined number of units and one pixel of the radiation image is divided and detected by the plurality of radiation detectors, one pixel is formed. The dose incident on each radiation detector becomes smaller in proportion to the number of pixel divisions, thereby suppressing counting saturation.

Here, in the photon counting method, since the pulse wave height based on the output of the radiation detector is compared with the threshold value Vth and counted, the obtained data contains no noise other than statistical noise. Therefore, even if the count values of the radiation detectors forming one pixel of the radiation image are simply digitally added, there is no problem of signal deterioration.

[0011]

1 is a block diagram showing the configuration of an embodiment of the present invention. First, a plurality of one-dimensionally arrayed X-ray sensors 1 ... Is divided into two cells 1a and 1b, respectively, and these two cells 1a and 1b correspond to one pixel on an X-ray image. It corresponds to.

The outputs of the respective cells 1a and 1b are introduced into the charge sensitive amplifiers 2a and 2b provided corresponding to the respective outputs and converted into voltage pulses. The outputs of the charge sensitive amplifiers 2a and 2b are guided to the comparators 3a and 3b, which are also provided corresponding to the respective amplifiers.

Each of the comparators 3a and 3b compares the input voltage pulse with the threshold value Vth and outputs a digital pulse which is at H level while the input voltage pulse exceeds the threshold value Vth. Comparator 3a, 3
The outputs of b are input to the counters 4a and 4b, respectively.

The count values recorded in the respective counters 4a and 4b are digitally added by the adder 6, and the added value is stored in the image memory 5 as data for one pixel of the X-ray image and in each pixel thereof. Correspondingly, they are stored individually.

Then, an X-ray image is displayed on the screen of, for example, a CRT using the data stored in the image memory 5 as grayscale information. When displaying such an X-ray image, the data stored in the image memory 5 is not changed to CR.
T or the like may be output and displayed, or the stored data in the image memory 5 may be displayed after being subjected to image processing such as log conversion, smoothing, or edge processing.

As described above, in the embodiment of the present invention, the X-ray sensor 1 is divided into two cells 1a and 1b, and each cell 1
Since a counting circuit is provided for each of a and 1b,
Compared with the structure shown in Figure 1, even if the dose incident on one pixel is the same, the counting rate at the counters 4a and 4b becomes 1/2. Therefore, the counting down of counting that is a problem in this type of photon counting method Can be significantly reduced.

Although the X-ray sensor is divided into two cells in the above embodiments, the number of divisions is not limited to two, and the larger the number of divisions, the higher the effect. It goes without saying that you can get

Further, in the above embodiment, an example in which the X-ray sensor itself is divided into a plurality of cells has been described, but in addition to this, one pixel on the X-ray image is detected by a plurality of X-ray sensors, Connect a counter to each X-ray sensor,
A configuration may be adopted in which the added value of the count values of these counters is used as image data for one pixel.

Further, in the above example, one charge sensitive amplifier and one comparator and one counter are connected to one charge sensitive amplifier. However, when discriminating X-ray energy,
A plurality of comparators and counters may be connected in parallel to one charge sensitive amplifier according to the number of discriminations.

Here, it goes without saying that the present invention is also applicable to a radiation image pickup apparatus using a sensor array in which radiation sensors are arranged two-dimensionally (planarly).

[0021]

As described above, according to the present invention,
A charge-sensitive amplifier, voltage comparator, pulse counter, etc. are connected to each of the plurality of radiation detectors, and the radiation detector group is divided into a plurality of blocks for each predetermined number of units. Since an adder for adding the count value of the counter is provided for each block and the output of each adder is used as image data for one pixel of the radiation image, the count rate of the pulse counter is Can be kept low. As a result, it is possible to realize a radiation image pickup device having a wide dynamic range from low dose to high dose. In addition, since the counting saturation can be suppressed, it is possible to accurately perform energy discrimination in the high dose region.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of a conventional radiation image pickup device based on a photon counting method.

[Explanation of symbols]

 1 X-ray sensor 1a, 1b Cell 2a, 2b Charge sensitive amplifier 3a, 3b Comparator 4a, 4b Counter 5 Image memory 6 Adder

Claims (1)

[Claims] 1. An amplifier for converting a charge signal from the radiation detector into a voltage pulse for each of a plurality of radiation detectors that generate a charge signal by incidence of a radiation photon, and an output of the amplifier as a reference voltage. A voltage comparator that outputs a pulse signal when comparing and exceeds the reference voltage, and a counter that counts the output of this voltage comparator are connected, and the radiation detector group has a predetermined unit. Each block is divided into a plurality of blocks, and an adder for adding the count value of the counter is provided for each block, and the output of each adder is used as image data for one pixel of the radiation image. A radiation image pickup device configured.