JPH0938075A - Radial rays exposure device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always obtain correct images by compensating deviation in a short time which occurs with time for each detection element of the line sensor. SOLUTION: A calibration radial ray source 8 is installed at the front of a radial ray detector 4 of the X-ray CT device, a calibration radial ray 11 from the calibration radial ray source 8 is irradiated to detection elements 7 during no exposure and sensitivity data is obtained and stored in a sensitivity data memory 22, and the calibration radial ray source 8 is stored in a shield box 12 during exposure. An output of an output detection circuit 21 is compensated by a compensator 23 based on sensitivity data memorized, so sensitivity deviation among the detection elements is eliminated, and a tomograpy image without arlifact can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation imaging apparatus such as an X-ray CT apparatus which is a medical image diagnostic apparatus, a digital imaging apparatus, and a gamma camera.

[0002]

2. Description of the Related Art Detection, which is composed of a combination of a fluorescent element that emits light upon incidence of radiation and a photoelectric conversion element that receives light from the fluorescent element and outputs an electric signal, as used in an X-ray CT apparatus A radiation detector composed of a large number of elements arranged in a one-dimensional array is not only an individual difference due to manufacturing variations of individual detection elements, but also the sensitivity of detection elements (especially fluorescent elements) depending on the radiation dose. However, there was a phenomenon that the For this reason, as the radiation imaging apparatus using this radiation detector is continuously used, the sensitivity of each detection element (each channel) decreases and the variation becomes large, and finally in an X-ray CT apparatus or the like. There is a problem that a virtual image is generated in the obtained tomographic image.
In the past, this problem was circumvented by performing a so-called calibration operation for correcting the output of the detection element to a predetermined value when there is no subject, so-called calibration, which has been performed. It took extra time to perform the operation, and the diagnosis was temporarily suspended, which was very inefficient.

[0003]

The present invention has been invented in view of the problems associated with the above-mentioned prior art, and the problem to be solved by the present invention is a solid state caused by variations in manufacturing of detection elements. Overcome differences and sensitivity changes of individual detection elements of the radiation detector that occur depending on the radiation dose, and always obtain good images without spending time for extra calibration during diagnosis It is to provide a radiation imaging apparatus capable of performing the above.

[0004]

In order to solve the above problems, the present invention provides a radiation imaging apparatus having a radiation detector in which a plurality of radiation detection elements are arranged one-dimensionally or two-dimensionally. A calibration radiation source installed on the front surface of the vessel so as to be scannable in the arrangement direction of the detection elements,
Storage means for storing the sensitivity data of each of the detection elements and correction means for correcting the output of each of the detection elements based on the sensitivity data are provided, and are obtained by scanning the calibration radiation source in front of the radiation detector. The output of each detection element in the imaging stage is corrected based on the sensitivity data of each detection element.

The sensitivity data of each detection element is stored in the sensitivity storage memory by measuring the output of each detection element while scanning the calibration radiation source with a stable radiation dose on the front surface of the radiation detector when the imaging is not performed. Is stored, and the output of each detection element is corrected based on the latest sensitivity data stored when imaging, so there is no virtual image without spending time for extra calibration that interrupts imaging. A good captured image can always be obtained.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an embodiment X of the present invention.
It is a schematic diagram of a line CT device. X emitted from the X-ray tube 1
The line 2 passes through the subject 3 and is detected by a radiation detector 4 which is an arc-shaped one-dimensional line sensor. The radiation detector 4 includes a fluorescent element 5 that emits light when exposed to X-rays.
And a plurality of detection elements 7, each of which is composed of a set of photoelectric conversion elements 6 such as photodiodes, for converting the light from the fluorescent element 5 into an electric signal, are arranged in an arc shape around the X-ray tube. It was formed. A calibration radiation source 8 is provided near the front surface of the radiation detector 4 (the surface on which the X-rays strike).
Is arranged, and the calibration radiation source 8 is configured to be scanned on the front surface of the radiation detector 4 along the direction in which the detection elements are arranged by a scanning mechanism including an arcuate rail 9 and a drive motor 10. There is. Further, near the end of the radiation detector 4, a calibration radiation source 8 can be housed, and a shielding box 12 surrounded by a lead plate or the like to prevent radiation from leaking is provided.

The calibration radiation source 8 is composed of a radioactive isotope such as Cs137 and has a constant intensity.
Is always radiated. The calibration radiation source 8 is scanned along the front surface of the radiation detector 4 during the period when the imaging is not performed, so that the calibration radiation 11 is sequentially incident on each detection element constituting the radiation detector 4. The output from each detection element at that time is measured. Since the intensity of the applied radiation is constant, the output from the radiation detector 4 (or the value standardized with its maximum value being 1) represents the variation in the sensitivity of each detection element. These outputs are stored in the sensitivity data memory 22 via the output detection circuit 21 and the switch S1. Here, the output detection circuit 21 amplifies and digitizes the analog output from each detection element of the radiation detector 4 and outputs it as digital data.

When performing an actual image pickup, the calibration radiation source 8 is housed in a shielding box 12 arranged beside the radiation detector 4. By doing so, the calibration radiation 11
Does not leak from the shielding box 12, so that the radiation detector 4 is not irradiated with extra radiation that becomes the background during measurement, and no extra noise is included in the measurement data. However, the shielding box 12 is not always necessary, and the radiation emitting port of the container for the calibration radiation source 8 that has been retracted from the front of the radiation detector 4 may be covered.

During imaging, the output of the radiation detector 4 is connected to the corrector 33 via the output detection circuit 21 and the switch S1. The obtained imaging data is corrected by being divided by the calibration sensitivity data stored in the sensitivity data memory 22 by the compensator 33 to be corrected, and becomes data which is not affected by the characteristic variation among the detection elements. This data is reconstructed as tomographic image data by the controller 24, and the image is displayed on the display 25 such as a CRT. Here, the controller 24 also performs an operation of controlling the sensitivity data memory 22, the compensator 23, the switch S1 and the like so as to play their respective roles. The controller 24,
The functions of the compensator 23, the sensitivity data memory 22, the switch S1 and the like can be collectively processed by one computer as software.

The present invention includes the following configurations. X-ray C having a radiation detector formed by arranging a plurality of detection elements each including a combination of a fluorescent element and a photoelectric conversion element
In the T apparatus, a calibration radiation source installed on the front surface of the radiation detector so as to be able to scan in the parallel direction of the detection elements, a radiation shielding box housing the calibration radiation source, and sensitivity data of each of the detection elements. And a calculation means for correcting the output of each detection element based on this sensitivity data, and while scanning the calibration radiation source on the front surface of the radiation detector in the preparation stage of imaging, Sensitivity data of each detection element is stored in the storage means by measuring the output, the calibration radiation source is housed in the shielding box at the time of imaging, and the output of each detection element obtained at the time of imaging is described above. An X-ray CT apparatus characterized in that it is corrected by the calculation means based on sensitivity data.

[0011]

According to the present invention, the calibration radiation source and its scanning mechanism make it possible to easily correct variations in the characteristics of the detection elements of the radiation detector and a reduction in sensitivity during the imaging or during the preparation stage. Therefore, a good image can always be obtained without interrupting photographing for diagnosis or spending extra time.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an X-ray CT apparatus showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... X-ray tube 2 ... X-ray 3 ... Test object 4 ... Radiation detector 5 ... Fluorescent element 6 ... Photoelectric conversion element 7 ... Detection element 8 ... Calibration radiation source 9 ... Rail 10 ... Motor 11 ... Calibration radiation 12 ... Shield box 21 ... Output detection circuit 22 ... Sensitivity data memory 23 ... Corrector 24 ... Controller 25 ... Indicator

Claims (1)

[Claims] 1. A radiation imaging apparatus having a radiation detector in which a plurality of radiation detection elements are arranged one-dimensionally or two-dimensionally, and is installed on the front surface of the radiation detector so as to be scannable in the arrangement direction of the detection elements. A calibration radiation source,
Storage means for storing the sensitivity data of each of the detection elements and correction means for correcting the output of each of the detection elements based on the sensitivity data are provided, and are obtained by scanning the calibration radiation source in front of the radiation detector. A radiation imaging apparatus characterized by correcting the output of each detection element in the imaging stage based on the sensitivity data of each detection element.