SU1402870A1 - Method of detecting shadow x-ray projections - Google Patents

Abstract

The invention relates to the field of X-ray technology and can be used in scanning systems with scintillation radiation detectors. The purpose of the invention is to increase the accuracy of registration of shadow projections of objects with a continuous change in thickness from minimum to maximum and from maximum to minimum. This method is carried out by scanning the object 9 in opposite directions under screening conditions with an absorbing screen 7 in each direction of scanning the object area 9, the thickness of which varies from maximum to minimum. 2 Il. i (L

Description

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The invention relates to X-ray technology and can be used in scanning systems with multiple sciens of radiation detectors.

The purpose of the invention is to improve the accuracy of registration of shadow projections of objects with a continuous change in the thickness from the minimum to maximum and from maximum to minimum.

Fig. 1 shows the dynamic nonlinearity curves of various detector types when scanning a cylindrical phantom in Fig. 2, a linear scanning tomograph for carrying out the proposed method.

The method is based on the dependence of the dynamic nonlinearity of the scintillation detector on the change in the object thickness during scanning, FIG. Figure 1 shows the time dependences of the dynamic nonlinearity jf (t) for various types of radiation detectors, obtained by registering the shadow projection of a cylindrical water phantom in a line-scan tomography. (CslCTl) t photodiode), curve 3 - to a semiconductor detector (CdTe single crystal), J (t) value is determined by the formula

5 (t) () Wo / w,

where WP and 1d are the intensities of the x-ray radiation and the output signal of the detector on the direct beam;

W and I are the intensity of X-ray radiation and the output signal of the detector at an arbitrary scanning time t when the radiation is absorbed in the object.

The plot of the dependence J (t) to the left of point A corresponds to the transition from the minimum phantom thickness to the maximum, and the section to the right from point A corresponds to the transition from the maximum phantom thickness to the minimum. As can be seen from FIG. 1, the magnitude of the dynamic nonlinearity of a cirr detector (curve 1) in the region to the left of point A: minimal. Thus,

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Q l double scanning of an object in opposite directions, provided that the area of the object shielding in each direction decreases from maximum to minimum, can be achieved by using a scintillation detector to obtain minimal dynamic nonlinearity over the entire shadow projection.

A linear scanning tomograph (FIG. 2) for implementing the proposed method includes an X-ray emitter 4, an extra-object collimator 5j, an after-object collimator 6, a set of scintillation detectors 7, a platform 8 for accommodating the object under study 8, an absorbing screen 10 and a scanning mechanism 11.

The extreme rays of the x-ray beam are shown by arrows 12 and 13, and the scanning directions are shown by arrows 14 and 15,

The method is carried out as follows.

In the initial position, the X-ray emitter 4, the collimators 5 and 6, and the detector set 7 are in the extreme left position. The absorbing screen 10 is placed between the emitter

4 and the object 9 being irradiated, protecting the object area 9 from the back in the direction of scanning (arrow 14) from its geometrical center from the radiation. The position of the geometric center of the object 9 relative to the edge of the screen 10 is estimated approximately, for example, using a light marker projected onto the object.

9 from the radiator 4,

In the process of scanning in the direction of the arrow 14, the system of X-ray emitter 4, collimator ro.v

5 and 6 and the set of detectors 7 is moved to the position shown in Fig. 2 by a dotted line. In this case, each of the detectors 7 measures the intensity of the X-ray radiation. The analog signals of the detectors are converted to digital and are entered into the computer memory. The sampling rate of the detector counts is determined by the sensors of the position of the X-ray emitter 4 or a set of detectors 7. The last counting is performed in the dark zone behind the absorbing screen 10 and is used to determine the level of dark current. During scanning, the signal of each detector 7 varies from maximum

the value of the direct beam to the minimum when the radiation passes through the zone of the geometric center of the object 9. At the same time, the local deviations of the dense, in the object 9 from the average value do not have a significant effect on the main tendency to decrease the signal. Thus, for the scanning conditions considered, the angular scanning of the studied sample is provided.

cue to monotonous transition from the maximum x-ray intensity to the minimum, i.e. The dynamic nonlinearity of scintillation detectors is minimal. After the first 15 scan, the absorbing screen 10 is moved to the position shown in FIG. 2 by a dotted line, and scanning is performed in the opposite direction along arrow 15. At the same time (like 20 during the first scan in arrow 1A), the basic tendency of the x-ray intensity to change from maximum to minimum is retained.

For the convenience of cross-linking the data of the first and second halves of the shadow X-ray projection, the end is absorbing. the screen 10 when changing its position is shifted by some distance

(for example, 1/20 of the average size of the section of the object 9 from its geometric center).

Claims (1)

Invention Formula The way to register shadow x-ray projections by linear or an object with an x-ray beam and detecting radiation transmitted through the object by at least one single scintillation detector, characterized in that, in order to improve the accuracy of recording shadow projections of objects with continuous thickness changes from minimum to maximum and from maximum to minimum, measure twice the object under study in opposite directions in the shielding conditions in each scanning direction of the area of the object whose thickness changes Tc from maximum to minimum, and the shadow x-ray projection is formed from the totality of the results obtained in each scanning direction. thirty and A (pue.i 0.5 t, c