JPS6215746A - Radiation detector - Google Patents

Abstract

PURPOSE:To make a good image without an artifact, by emplacing band-shaped grounded protective electrode plates at the front and rear ends of signal electrode plates and electrically disconnecting the protective electrode plates from the signal electrode plates, to suppress the electric field distortion in each cell. CONSTITUTION:Band-shaped grounded protective electrode plates 16 are emplaced at the front and rear ends of signal electrode plates 13 and electrically disconnected therefrom so that the protective electrode plates act as dummy electrodes against a high-voltage electrode plate 12 at the front and rear ends of the signal electrode plates. As a result, the signal electrode plates 13 for handling an ionization current are not affected by the distortion of an electric field. The protective electrode plates 16 are thus provided to suppress the electric field distortion which would result from an X-ray incidence windoew 11 and the curvature of the front ends of the electrodes. Therefore, the electric field distortion in each cell is suppressed to prevent the difference between the characteristics of the cells. This results in making a good image without an artifact.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to X-ray CT (Computerized To
The present invention relates to improvements in radiation detectors used in (mography) devices.

[Technical background of the invention and its problems]

As shown in FIG. 3, the X-ray CT apparatus is comprised of an X-ray source 1 that emits flat fan-beam X-rays in a Norse-like manner, and a plurality of radiation detection cells that detect these X-rays arranged in parallel. The X-ray source 1 and the radiation detector 2 are opposed to each other with the subject 3 in between, and the X-ray source 1 and the radiation detector 2 are rotated in the same direction and at the same speed around the subject 3, and X-ray absorption data is collected in the data collection section 4, and this data is analyzed by a computer (not shown) to calculate the X-ray absorption rate for each position in the cross section of the subject and calculate the floor according to the absorption rate. The cross section of the subject is reconstructed as an image.

In order to finally obtain a high-quality image with an X fiICT device, that is, an image with good spatial resolution, density resolution, and S/N, a radiation detector with high sensitivity, high resolution, and uniform characteristics among cells is required. is necessary.

This type of radiation detector has conventionally been constructed as shown in FIG. That is, high-voltage electrode plates 12 and signal electrode plates 13 are arranged alternately behind an X-ray entrance window 11 (ground potential) inside a box (not shown) filled with gas that ionizes X-rays (radiation). A DC positive potential of 100 V to 400 V is applied to the electrode plate 12 from a high voltage power supply 14. The electrolytic vector moves from the high-voltage electrode plate 12 to the signal electrode plate 13, and the
Electrons and Xe (xenon) ions ionized by the wire move and reach the signal electrode plate 13 to become an ionization current, which is amplified by the amplifier 15 and output as a signal.

In this case, the electric field vector is uniform near the center of the electrode, but becomes distorted toward the tip/end of the electrode. This is X
This is because the line entrance window 11 is at ground potential and electric field distortion occurs due to the influence of the curved surface of the electrode tip. Therefore, in this type of radiation detector in which 500 to 700 unit cells are configured by the high-voltage electrode plate 12 and the signal electrode plate 13, artifacts (particularly ring artifacts) occur due to uneven characteristics due to the electric field distortion of each cell. This caused the problem that high-quality reconstructed images could not be obtained.

[Purpose of the invention]

The present invention has been made based on the above-mentioned aspects, and its purpose is to provide a radiation detector that suppresses electric field distortion in each cell and thereby obtains high-quality images without artifacts. .

[Summary of the invention]

In order to achieve such an object, the present invention detects the energy of X-rays transmitted through the f-plane of a subject in an X-ray CT apparatus as an ionization current, and outputs this as a signal as X-ray absorption data. In a Xe gas detection type radiation detector in which high-voltage electrode plates and signal electrode plates are alternately arranged inside a box sealed with a gas that ionizes the wire (radiation),
The present invention is characterized in that band-shaped guard electrodes electrically separated from the signal electrode and having a ground potential are arranged at the front and rear ends of the signal electrode plate.

[Embodiments of the invention]

An embodiment of the radiation detector according to the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 3 are given the same reference numerals, and FIG. 2, which is a perspective view thereof.

In this embodiment, a band-shaped guard electrode 16 electrically separated from the signal electrode plate 13 and having a ground potential is arranged at the front and rear ends of each signal electrode plate 13. In this case, the end of the guard electrode plate 16 is arranged to be approximately aligned with the end of the high voltage electrode plate 12.

With such a configuration, the guard electrode plate 16 connects the dummy voltage t of the high voltage 'lK electrode plate 12 at the tip and rear end of the signal electrode plate 13.
The signal electric shuttle slope 13, which acts as M and handles ionization, is not affected by electric field distortion. The electric field distortion En/Eo as shown in the figure is approximately 1 in this embodiment.

As described above, in this embodiment, by providing the guard electrode plate 16, the curved surface portion of the X-ray entrance window 11 and the tip of the electrode can be
Since the electric field distortion caused by 41 can be suppressed, the electric field distortion for each cell is suppressed, and the unevenness of characteristics for each cell is also suppressed, so that a high-quality reconstructed image without artifacts can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, electric field distortion for each cell is suppressed by arranging band-shaped guard electrodes electrically separated from the signal electrode and at ground potential at the front and rear ends of the signal electrode plate. However, it is possible to provide a radiation detector that can obtain high-quality images without artifacts.

[Brief explanation of drawings]

1 and 2 are diagrams showing one embodiment of the X-ray detector according to the present invention, FIG. 3 is a schematic diagram for explaining the outline of the X-ray CT device, and FIG. 4 is a diagram showing a conventional example. It is a diagram. 11... X-ray entrance window, 12... High voltage electrode plate, 13...
...Signal electrode plate, 14...High voltage power supply, 15...Amplifier, 16...Guard electrode plate.

Claims (1)

[Claims] A box body filled with gas that ionizes X-rays (radiation), which detects the energy of X-rays that have passed through the cross section of a subject in an X-ray CT device as an ionizing current and outputs this as a signal as X-ray absorption data. In a Xe gas detection type radiation detector in which high-voltage electrode plates and signal electrode plates are arranged alternately inside, a ground potential is provided at the front and rear ends of the signal electrode plate, electrically separated from the signal electrode. A radiation detector characterized in that a band-shaped guard electrode is arranged.