JPS628157B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a CT scanner equipped with a multi-channel radiation detector used in X-ray CT and the like.

FIG. 1 is a diagram showing the basic configuration of a conventionally known continuous rotation type CT scanner used for X-ray CT. In the figure, 1 is radiation (here X-ray)
The radiation source rotates around a rotation center 0 located at the center of the field of view 2 where the subject is placed. This radiation source 1 generates a pulsed fan beam with sufficient spread to encompass a field of view 2. 3 is a radiation detector that detects X-rays and obtains an electrical signal corresponding to the radiation dose. More specifically, the detectors 3 are a type of ionization chamber, and are arranged in an arc shape on the circumference with the radiation source 1 at the center. FIG. 2 is a perspective view showing an example of such an ionization chamber. That is, high-voltage electrodes 33a and signal electrodes 33b are arranged alternately at intervals of, for example, 0.5 mm to 1.0 mm between the insulator supports 31 and 32, and these are filled with high-pressure xenon gas (Xe gas at 10 to 25 atmospheres). The ionization chamber is housed in an arcuate container (not shown) to form an arcuate ionization chamber. Each electrode plate has a gap of 1.0 between the electrodes.
Because it needs to be small, about mm or less,
Tungsten material is used, which is about 0.1 mm thin and difficult to see through X-rays.

However, CT scanners that use an ionization chamber with such a configuration have many problems as described below. In other words, the lifespan of the detector is short, about one year, because the sealed Xe gas leaks from the container.
Sensitivity also decreases gradually. In addition, the manufacturing process involves a large number of man-hours and difficulties in arranging a large number of electrode plates in a fixed direction, and during use, noise due to vibration of the electrode plates becomes a problem, which creates restrictions on mounting methods, etc. However, there are problems in that the X-rays are absorbed by the Al material of the container, resulting in the subject being exposed to unnecessary radiation. Furthermore, although it is said that the ionization chamber has good directivity and can reduce noise caused by scattered radiation, in reality,
Movement of the focal point of the radiation source (for example, movement due to thermal expansion) occurs as apparent X-ray distribution fluctuation noise due to the sharpness of the directivity. This noise is larger than the noise caused by scattered radiation, and the fact is that good directivity places very strict conditions on the X-ray source.

In order to solve these problems, the present invention provides a CT scanner that uses a simple structured omnidirectional solid-state detector array in place of the conventional ionization chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 3 is a diagram showing the basic configuration of an embodiment of the CT scanner according to the present invention. In FIG. 3, reference numeral 4 denotes a non-directional solid-state detector array, which detects the X-rays from the X-ray source 1. This array 4 is arranged to face the radiation source in a chord relationship with the radiation source 1 as the center of the circle. FIG. 4 is an enlarged view of this array. In Figure 4, 5 is for example
It is a single crystal substrate of a high atomic number compound semiconductor such as CdTe. This CdTe single crystal substrate is composed of Cd and Te.
The mixture is vacuum sealed in a quartz glass ampoule, heated and crystallized in a Bridgeman furnace, etc., and the resulting single crystal ingot is cut and processed. An example of the dimensions and shape of the single crystal substrate 5 is as shown in FIG. 4, which has a comb shape, and has residual portions 51, 52, 53 with a width of 0.9 to 0.8 mm.
...and have cut portions 61, 62, 63... having a width of 0.1 to 0.2 mm and a depth of 0.8 to 1.0 mm at regular intervals. An ohmic junction electrode 70 made of, for example, Pt is formed on the back surface of the substrate 5 (the back surface on the side where the substrate is continuous), and an ohmic contact electrode 70 made of, for example, Pt is formed on the apex portion of the remaining portion (the tip portion of the comb-shaped teeth). , for example, shot key barrier junction electrodes 81, 82, 8 made of Al.
3... is formed. These electrodes are formed on the single crystal substrate 5 by, for example, a vapor deposition method or a sputtering method.

In the multichannel radiation detector configured in this way, the radiation to be measured enters from the Schottky barrier junction electrodes 81, 82, 83, . . . .

FIG. 5 is a diagram of the operating principle of the radiation detector according to the present invention, in which A is a sectional view of one remaining portion (tooth portion), and B is a potential distribution diagram inside the element corresponding to A.

When the CdTe single crystal substrate and the electrode metal form a Schottky barrier junction, a potential distribution occurs from the electrode 81 side as shown in FIG _. A depletion layer is created. When radiation enters here from the Schottky barrier junction electrode 81 side, energy is lost within it and free carriers are generated. Electrons serve as majority carriers in the N-type element, and holes serve as majority carriers in the P-type element.
This carrier is generated within the depletion layer W _eff on the Schottky barrier side and is taken out as an ionization current I. This ionization current I can be expressed by equation (1), where E is the incident radiation energy.

I=η・A・N・q/εion ・{E・μ _E /μ _T (1−e ^- 〓 ^t

Claims (1)

[Claims] 1. A radiation source that can rotate continuously and generate a pulsed fan beam, and that rotates integrally with the radiation source and detects radiation over the entire width of the pulsed fan beam. The invention is characterized by comprising non-directional solid state detectors arranged in a straight line.
CT Sukyana. 2. Using a high atomic number compound semiconductor single crystal as a substrate, sandwiching the substrates and forming a Schottky barrier junction electrode on one side, and forming an ohmic junction electrode on the other side, the Schottky barrier junction is formed. A multichannel radiation detector in which a plurality of comb-shaped residual portions are formed by providing cut portions at predetermined intervals from the electrode side, and radiation to be measured is incident from the shot key barrier junction electrode side. 2. The CT scanner according to claim 1, wherein a CT scanner is used as the non-directional solid state detector.