JPS63221277A - Radiation detector for energy subtraction - Google Patents

Abstract

PURPOSE:To remove scattered rays generated by a filter for energy subtraction and to improve picture quality by arranging a filter equipped with a grid function between a 1st radiation detection plate and a 2nd radiation detection plate. CONSTITUTION:Radiant rays which are transmitted through a subject and enters an Al or synthetic resin cassette 16 in a radiation input direction is absorbed by a 1st radiation detection plate made of a phosphor which emits accumulative type stimulated phosphorescence and stored in the plate 17 so as to have low energy and high contrast in X-ray image data. An X-ray spectrum transmitted through the plate 17 is made incident on the filter 18 for energy subtraction. A grid 20 is arranged between the filter 18 and 2nd radiation detection plate 19 and the grid 20 removes the scattered rays generated when the filter 20 extracts the X-ray spectrum of a high energy component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an improvement of a radiation detector for energy subtraction used in a radiographic apparatus used in the field of medical diagnosis.

(Prior Art) As an aid to understanding the present invention, typical conventional examples of radiographic systems, particularly CR (computed radiography) systems, are shown in FIGS. 3 to 3. This will be explained with reference to FIG.

In Fig. 3, this X-ray photography system
an X-ray imaging device @1 that receives X-rays that have passed through the object while irradiating the object onto a phosphor plate (hereinafter abbreviated as IP), and stores the X-rays as energy for an X-ray image;
P is scanned with excitation light having a wavelength of 500 to soon nm, and the energy stored in the IP is excited from the trap to emit light with a wavelength of 300 to 500 nm, and this emitted light is An X-ray image reading device 2 configured to measure with a photodetector (for example, a photomultiplier or a photodiode) set to receive only light in the wavelength range, and an X-ray image reading device 2 After reading the image, the output signal of the photodetector is non-linearly amplified, roughly converted to a digital signal by an A/D converter, and then this signal is subjected to frequency emphasis processing and, if necessary, gradation processing, An image processing device (also referred to as HO8T IPC) 3 that stores this result in a storage means such as an image memory.
Then, the image data stored in the image memo 1, etc. is sequentially read out, converted into an analog signal by a D/A converter, and amplified by a scanner, and then input to a recording light source to produce an X-ray image. X-ray image reproducing device e4 that converts data into optical signals
and an X-ray image recorder B device 5 which inputs the optical signal through a lens system and irradiates it onto a recording material such as a photographic film to form an X-ray image on the material. The X-ray image formed on the recording material is observed and used for diagnosing the subject (patient).

Conventionally, when performing energy subtraction image projection in the X-ray image mirroring device 1 in the X-ray photography system explained using FIG. 3, a radiation detector for energy subtraction as shown in FIG. 4 is used. 6 was used. This detector uses a cassette 6A made of materials such as Al or synthetic resin.
From the radiation input direction, there is a radiation detection plate 6B that detects image data of radiation, such as X-rays, at the first incident energy (that which has passed through the subject), and then the energy characteristics of the radiation that has passed through the plate 6B. A filter (for example, Cu) that changes the 60. Furthermore, the filter 6C@
It is composed of a second radiation detection plate 6D that detects X-ray image data using transmitted energy. Next, using FIG. 5, it will be explained how the X-ray spectrum of a tube voltage of 80 KV at each detection plate changes as energy. The X-ray spectrum a from the X-ray tube of the tungsten target that passes through the object and enters the first radiation detection plate 6B is transmitted by the first radiation detection plate (
For example, barium fluoride halide BaFX:X is C1
), Br or ■Capacitive stimulable luminescent phosphor, commonly known as imaging plate or IP>6B, absorbs it and creates contrast at low energy in X-ray image data.
Stored in P6B. Since this IP6B contains 8a (barium), the X-ray spectrum transmitted through the first radiation detection plate is deformed as shown in b with an X-ray absorption edge near K<32 K e V, and the energy subtraction filter is incident on the This filter is used to separate the effective energy of the X-ray spectrum incident on the first radiation detection plate 6B, and is generally made of Cu (copper) and has a thickness of 1# or less. The X-ray spectrum transmitted through this filter is deformed as shown in C, and the second
The radiation is incident on the radiation detection plate 6D. As can be seen from the X-ray spectrum of C, it contains almost only high energy, and this second radiation detection plate 6D stores data that provides contrast with the high-energy effective energy.

As explained above, the data obtained by the first radiation detection plate 6B and the second radiation detection plate 6D is
Image reproduction processing is performed using the X-ray photography system shown in the figure, and between two images (low energy image and high energy image) based on the following formula.
So-called energy subtraction can be performed.

[H-Dh(x,y)] -[L-DJ(x,y)]
+C However, Dh (x, y)... Image data at high energy Dffl (X, V)... Image data at low energy H, L... Weighting coefficient C of each energy data
... Correction factor 1, that is, the weight or correction value of each H, L, and C as described above, using the low energy image data obtained in (a> in FIG. 5) and the high energy image data obtained in C. By appropriately adding , and subtracting the high energy component data (those with high subject contrast), it is possible to extract only the low energy component data (those with low subject contrast) as image data.

Conversely, the low-energy image data obtained in a using only the low-energy components are also designated H and L.

By subtracting with an excessive value of C, it is possible to create an image containing only data of high energy components.

(Problems to be Solved by the Invention) As explained above, an energy subtraction image is created. For example, the low-energy image data obtained in a of FIG. 5 is subtracted with the high-energy image data obtained in c. When only image data of low-energy components are created, the subtraction image becomes very grainy due to the influence of scattered radiation, and if the original diagnostic information cannot be identified, the image will inevitably result in a misdiagnosis. The set X-ray tube voltage at the time of imaging is, for example, 80KV, 100KV, 120KV.
This tendency increases markedly as KVt increases.

Before using the cassette 6A shown in FIG. 4, attempts to remove scattered radiation from the subject, such as using a grid or a Butsky kidney, are ineffective.

Therefore, as a result of various experiments, it was found that the cause of the above problem was strongly influenced by scattered rays generated when extracting the X-ray spectrum of high energy components with an energy subtraction filter (for example, CU). .

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a radiation detector for energy nabtraction that eliminates the adverse effects of scattered radiation.

[Configuration of the Invention] (Means for Solving Problems) The present invention has a configuration in which a filter with a grid function is disposed between the first radiation detection plate and the second radiation detection plate.

(Function) Since scattered radiation is removed by the filter section with a grid function, it is possible to obtain a high-quality image.

(Buying Side Example) The present invention will be described in detail below with reference to FIGS. 1 and 2.

FIG. 1 shows a radiation detector according to the present invention.

This includes first and second radiation detection plates 17 and 19 that have the same functions as conventional ones, an energy subtraction filter 18, and a grid arranged between the filter 18 and the second radiation detection plate 19, which is the key point of the present invention. 20, and is installed in a cassette 16 that can be closed and opened to bring the inside into a state. Of course, this grid 20 may be an integrated filter in which the grid 20 is adhered to the back surface of the filter 18. Furthermore, this cassette 1
Everything installed inside the camera may be in close contact with each other, and even if there is some arr 5pace ffi, there is no problem as long as the internal components do not move during shooting.

The configuration shown in FIGS. 2(a> and 2b) is basically the same as that in FIG. An open 5pace is provided in the storage section 16Ai6B, and the butkey grid 20 can be installed in this open 5pace, and the energy subtraction filter 18 is installed in the first radiation detection plate storage section 16A.
The radiation detection plate 17 is provided between the first radiation detection plate 17 and the grid 20 as a part of the radiation detection plate 17 . Further, each storage section can be opened individually to allow the first and second radiation detection plates 17 to be opened.
．． 19 can be set independently.

The grid 20 shown in each of the above figures can be a grid that does not change the characteristics of the X-ray spectrum characteristic C shown in Fig. 5 by using a grid or a grid that has a scattered ray removal effect. preferable.

According to the X'-ray detector having the above configuration, the grid 2
Since scattered rays can be removed by zero, image data of high energy components can be formed using only one second radiation detector plate.

[Effects of the Invention] According to the present invention described above, during energy subtraction, it is possible to form high-energy single-shot image data that is free from the influence of scattered rays in the filter, so that the subtraction image does not have any graininess. There will be many high-quality diagnostic reports.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the structure of one embodiment of the radiation detector of the present invention, Fig. 2 (a> and (b> are perspective views and AA sectional views thereof showing other embodiments of the present invention); Figure 3 is a block diagram of a radiation imaging system using a conventional radiation detector.
FIG. 4 is a sectional view of a conventional radiation detector, and FIG. 5 is a radiation spectrum characteristic diagram. 16...Cassette, ]7...First radiation fA ray detection plate, 18...Energy subtraction filter, one...Second radiation detection plate, 20...Grid. (Figure 1 A CG) Figure 2 Figure 3 A Figure 4

Claims (1)

[Claims] In energy subtraction imaging using radiography equipment, the first
A radiation detector for energy subtraction, characterized in that a radiation detection plate, a second radiation detection plate, and a filter having a grid function are arranged between the two plates.