JPH0238215B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a computerized tomography apparatus, and more specifically, to a computerized tomography apparatus, and more specifically, to a computerized tomography apparatus, an X-ray image obtained by irradiating an intended cross-section of an X-ray object with X-rays from a plurality of different directions. After the ray projection distribution image is once accumulated and recorded on a stimulable phosphor sheet, the intensity corresponding to the accumulated and recorded X-ray projection distribution image is obtained by scanning the stimulable phosphor sheet with excitation light. This invention relates to a computerized tomography apparatus that generates stimulated luminescence light and reconstructs a tomographic image of the X-ray object using electrical signals obtained by photoelectrically converting the stimulated luminescence light. be.

A tomographic image of an X-ray object is reconstructed from multiple X-ray projection distribution images obtained by irradiating X-rays from multiple different directions to a certain intended cross section of the object. A computerized tomography device (hereinafter referred to as the "CT device") was developed by Hounsfield and colleagues. It is attracting attention as an innovative technology in the field of medical diagnosis.

FIG. 1 shows a typical example of a CT device used today.

An X-ray tube 3 that emits fan-shaped X-rays 2 (usually with a spread angle of 30° to 40°) that encompasses the imaging area 1 where the X-ray subject is located, and is formed in an arc shape to be equidistant from the X-ray tube 3. Fan-shaped X-rays 2 transmitted through the X-ray inspected object
The imaging unit of the CT apparatus is composed of the detector 4 that detects the . The detector 4 is composed of hundreds of densely arranged detection elements, and the detection elements used include a photomultiplier having a scintillator on its light-receiving surface, a high-pressure xenon gas detector, a semiconductor detector, and the like. The X-ray tube 3 and the detector 4 are integrally rotatable around the X-ray subject in the directions of arrows 5 and 6, respectively. Furthermore, the CT apparatus has a computer for processing an X-ray projection distribution image obtained by transmitting X-rays through the object to be inspected using the detector 4.

When photographing, the X-ray tube 3 and detector 4 are
X-ray tube 3 is set at a certain angle to the object to be inspected.
A fan-shaped X-ray 2 is irradiated in a pulsed manner. The fan-shaped X-rays 2 that have passed through the X-ray inspection object are detected by the detector 4 as an X-ray projection distribution image. This detected X
The line projection distribution image is stored in the computer memory. After imaging for one angle is completed, the X-ray tube 3 and detector 4 are rotated by a small constant angle in the directions of arrows 5 and 6, respectively, relative to the X-ray object, and then the Photographing is performed to obtain an X-ray projection distribution image, and the obtained X-ray projection distribution image is stored in a computer. By repeating the above-mentioned operations, X-ray projection distribution images are sequentially obtained at fixed angles to the X-ray inspected object, and when the X-ray tube 3 and detector 4 have made one rotation (360 degrees) around the X-ray inspected object. Imaging to obtain a tomographic image of the X-ray object is completed. By using a computer to process the X-ray projection distribution images at various angles for the X-ray subject stored in the memory of the computer, a tomographic image of a certain part of the X-ray subject can be obtained. can.

In addition to the above-mentioned CT device, a detector consisting of an X-ray tube and a relatively small number of detection elements performs linear scanning at a certain angle with respect to the X-ray object, and after performing this linear scanning. , after rotating the X-ray tube and detector by a small fixed angle relative to the X-ray object, linear scanning is performed again, and after that, the rotation and linear scanning are repeated alternately until the One is a system in which the imaging ends when the X-ray object is rotated 180 degrees, and the other is one in which the detectors are arranged in a 360 degree ring shape around the X-ray object, as shown in Figure 1, and only the X-ray tube is used. There is a method that rotates 360 degrees.

Generally, in order for a tomographic image to have good diagnostic suitability, it is desirable to have a high spatial resolution so that even fine tissue can be distinguished.
In any of the above-mentioned methods, the spatial resolution of the finally obtained tomographic image is determined by how many detection elements the detector includes per unit space. However, if a photomultiplier with a scintillator on the light-receiving surface is used as a detection element,
Since the shape of the photomul is large, sufficient spatial resolution cannot be obtained. If a high-pressure xenon gas detector or semiconductor detector is used, it is possible to arrange the detection elements more densely than when using a photomultiplier, but even in this case, a spatial resolution of only about 1 line/mm can be obtained. However, high-pressure xenon gas or semiconductor detectors have the disadvantage of lower sensitivity than photomultipliers, which have a scintillator on the light-receiving surface. In order to obtain accurate tomographic images, it is necessary to increase the amount of X-ray exposure that the subject receives. In addition, when a detector is configured with multiple detection elements, it is a necessary condition that each detection element has the same sensitivity, but it is technically impossible to make the sensitivity of each detection element exactly the same. It was extremely difficult.

Furthermore, in conventional CT equipment, at least
The X-ray projection distribution image is obtained by rotating the ray tube intermittently at a fixed angle around the X-ray inspection object, stopping the X-ray tube once at each angle, and irradiating the X-ray inspection object with X-rays. However, in order to change the angle at which the X-rays are irradiated onto the X-ray object, there is a dead time during which the X-ray tube is transferred, which increases the imaging time by the dead time. This long imaging time is a serious drawback for CT devices. In other words, when photographing still images of the head or skeleton, there is relatively no problem even if the photographing time is long, but when photographing internal organs, if the photographing time is prolonged, muscular movements, respiratory movements, peristalsis, etc. This causes the X-ray subject to move during imaging, reducing the contrast and spatial resolution of the finally obtained tomographic image, and causing noise called artifacts, making it difficult to obtain tomographic images suitable for diagnosis. become unable.

Therefore, an object of the present invention is to provide a CT system that has high spatial resolution and high sensitivity compared to conventional CT equipment.
The object of the present invention is to provide a CT device, and further, to provide a CT device that can shorten the imaging time compared to conventional CT devices.

As a result of extensive research to achieve this objective, the inventor of the present invention accumulated and recorded the X-ray projection distribution images obtained for each X-ray irradiation at different positions on a stimulable phosphor sheet, Thereafter, the stimulable phosphor sheet is scanned with excitation light, and the stimulated luminescent light emitted from the stimulable phosphor sheet is read photoelectrically. It has been found that the above object can be achieved by reconstructing a tomographic image of the body.

That is, the computerized tomography apparatus of the present invention calculates the X-ray exposure from a plurality of X-ray projection distribution images obtained by irradiating a certain cross section of an X-ray object with X-rays from a plurality of different directions. In a computerized tomography system that reconstructs a tomographic image of an object to be examined, an
Sheet arrangement means in which a stimulable phosphor sheet on which an X-ray projection distribution image is recorded is arranged at a position facing the ray tube, and the X-ray projection distribution image obtained for each X-ray irradiation is a stimulable fluorophore sheet. sheet moving means for moving a stimulable phosphor sheet placed in the sheet placement means relative to the X-ray tube and the X-ray inspection object so that the sheet is stored and recorded at different positions on the body sheet; scanning the stimulable phosphor sheet on which the X-ray projection distribution image has been accumulated and recorded with excitation light;
A reading means for photoelectrically reading the stimulated luminescent light emitted from the stimulable phosphor sheet to obtain an electrical signal, and a reconstruction for reconstructing a tomographic image of the X-ray subject using the obtained electrical signal. It is characterized by having means.

In the present invention, a storage phosphor is a material that, when irradiated with radiation (X-rays, alpha-rays, beta-rays, gamma-rays, ultraviolet rays, etc.), accumulates a portion of this radiation energy internally, and then emits visible light. When irradiated with excitation light such as, it has the property of emitting stimulated luminescence light in an amount corresponding to the accumulated energy.

Using such a stimulable phosphor, radiation image information of a human body, etc. is once recorded on a stimulable phosphor sheet, and this phosphor sheet is scanned with excitation light such as a laser beam to produce stimulated luminescence. , the obtained stimulated luminescence light is read photoelectrically to obtain an electrical signal, and this electrical signal is subjected to signal processing, and is then processed into a recording material such as a photographic light-sensitive material,
The applicant has already proposed a method for reading radiation image information that is output as a visible image on a display device such as a CRT. (Unexamined Japanese Patent Publication No. 55-12429, No. 56-
No. 11395 etc. ) In such a method, the stimulable phosphor sheet is
Generates electrons or holes proportional to the intensity of X-rays transmitted through the X-ray inspection object, and traps the generated electrons or holes at the trap level of the stimulable phosphor;
When the X-ray transmitted image of the X-ray inspected object is stored and recorded as radiographic image information, and then the excitation light is irradiated onto this stimulable phosphor sheet, the electrons or holes trapped at the trap level are expelled. It has the property of emitting stimulated luminescence light. It has been found that the intensity of the stimulated luminescence light emitted in this way is proportional to the number of trapped electrons or holes, that is, the intensity of the X-rays transmitted through the X-ray inspection object. By efficiently condensing this stimulated luminescence light and photoelectrically converting it with a highly sensitive photodetector such as a photodetector, an X-ray transmission image can be extracted with high sensitivity in the form of an electrical signal. Furthermore, it is recognized that such a stimulable phosphor can provide a high spatial resolution of 10 lines/mm or more.

Therefore, according to the present invention, since the X-ray projection distribution image is once accumulated and recorded on the stimulable phosphor sheet, there is no need to use a detector consisting of a large number of detection elements arranged densely. This not only makes it possible to perform imaging with high spatial resolution and high sensitivity, but also eliminates the problem of variations in sensitivity between detection elements. Furthermore, X
If the stimulable phosphor sheet is continuously transported during imaging in a direction almost perpendicular to the plane formed by the rotation of the X-ray tube, it is possible to continuously irradiate X-rays from the X-ray tube. Since it is possible to continuously rotate the X-ray tube, the dead time in the conventional CT apparatus described above can be eliminated, and the imaging time can also be shortened.

In order to improve the S/N ratio, the stimulable phosphor used in the present invention is one in which the wavelength range of the stimulated luminescence light emitted by excitation light irradiation does not overlap with the wavelength range of the excitation light. desirable. Specifically, as disclosed in JP-A-55-12429, it is preferable to use one in which the excitation light wavelength is 600 to 700 nm and the stimulated emission light wavelength is 300 to 500 nm.

As described above, examples of stimulable phosphors that emit stimulated luminescent light of 300 to 500 nm and can be preferably used in the present invention include rare earth element-activated alkaline earth metal fluorohalide phosphors [specifically, ,
(Ba _1-xy , Mg _x , Ca _y )FX described in JP-A-55-12143: aEu ²⁺ (However,
and Br, x and y are 0<x+y≦0.6 and xy≠0, and a
is 10 ^-6 ≦ a ≦ 5 × 10 ^-2 ), JP-A-55-12145
(Ba _1-x , M〓x) FX described in the publication:
yA (However, M〓 is at least one of Mg, Ca, Sr, Zn and Cd, X is at least one of Cl, Br and I, A is Eu, Tb, Ce, Tm,
At least one of Dy, Pr, Ho, Nd, Yb and Er, x is 0≦x≦0.6, y is 0≦y≦0.2), etc.; ZnS: Cu, Pb, BaO・xAl ₂ O ₃ : Eu (however, 0.8
≦x≦10) and M〓・xSiO ₂ :A (however, M〓 is
Mg, Ca, Sr, Zn, Cd or Ba, A is
Ce, Tb, Eu, Tm, Pb, Tl, Bi or Mn, and x is 0.5≦x≦2.5); and JP-A-55
−LnOX described in Publication No. 12144: xA (However, Ln
is at least one of La, Y, Gd and Lu
1, X is at least one of Cl and Br,
A is at least one of Ce and Tb, x is 0<x<0.1); and the like. Among these, rare earth element-activated alkaline earth metal fluorohalide phosphors are preferred, and among these, barium fluorohalides shown as specific examples are particularly preferred because of their excellent stimulable luminescence.

Furthermore, metal fluorides are added to barium fluorohalide phosphors as disclosed in JP-A-56-2385 and JP-A-56-2386, or as disclosed in JP-A-54-150873. As described above, the addition of at least one of a metal chloride, a metal bromide, and a metal iodide is preferable because the stimulated luminescence is further improved.

Further, as disclosed in JP-A-55-163500, when the phosphor layer of a stimulable phosphor plate prepared using the above-mentioned stimulable phosphor is colored with a pigment or dye, This is preferable because the sharpness of the finally obtained image is improved.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a CT that is a preferred embodiment of the present invention.
FIG. 2 is a schematic diagram of the device.

An X-ray tube 13 that emits fan-shaped X-rays 12 (spread angle of approximately 30° to 40°) that encompasses the imaging area 11 where the X-ray subject is located, and a fan-shaped X that passes through the X-ray subject.
A stimulable phosphor sheet 17 for accumulating and recording the rays 12 is arranged in an arc shape so as to be equidistant from the X-ray tube 13. The X-ray tube 13 and the stimulable phosphor sheet 17 are integrally rotatable around the X-ray subject in the directions of arrows 15 and 18, respectively. Further, the stimulable phosphor sheet 17 is attached to the X-ray tube 1
3 and the stimulable phosphor sheet 17 can be transported in the direction of an arrow 19 substantially perpendicular to a plane formed by rotation of the stimulable phosphor sheet 17. In this embodiment, X
As the ray tube 13, one that can continuously irradiate X-rays is used.

During imaging, X-rays are continuously transmitted from the X-ray tube 13.
The X-ray tube 13 and the stimulable phosphor sheet 17 are rotated in the directions of arrows 15 and 18, respectively, while irradiating the radiation. At that time, the stimulable phosphor sheet 17 is
Since the X-rays are also transferred in different directions, multiple X-ray projection distribution images obtained by irradiating X-rays from multiple different directions to a certain intended cross section of the X-ray inspected object are The information is stored and recorded sequentially at different positions on the sheet. When the X-ray projection distribution image from the 360° direction of the X-ray inspected object is accumulated and recorded on the stimulable phosphor sheet 17, the imaging ends. After photographing, take out the stimulable phosphor sheet 17 from the photographing section,
The X-ray projection distribution image having each angle with respect to the X-ray inspected object stored and recorded on the stimulable phosphor sheet 17 is read by the reading device. As this reading device, for example, the same device as that disclosed in Japanese Patent Application Laid-open No. 11395/1983 can be used.
That is, a stimulable phosphor sheet is scanned two-dimensionally with excitation light such as a laser beam, and the stimulated luminescent light generated at that time is detected by photoelectric conversion using a photodetector such as a photomultiplier. Reconstructing a tomographic image of an X-ray object by processing the generated electrical signals using a computer is exactly the same as in conventional CT apparatuses.

In the embodiment described above, in order to eliminate dead time and shorten imaging time, X-rays are continuously irradiated from the X-ray tube and the X-ray tube and stimulable phosphor sheet are continuously transported. As with the conventional CT apparatus described with reference to FIG. 1, the X-ray object may be imaged intermittently at each angle.

As explained above in detail, the CT device of the present invention installs a stimulable phosphor sheet in place of the detector used in conventional CT devices, and once a radiation projection image is transferred to the stimulable phosphor sheet. Since the sensor is stored and recorded, it is possible to obtain images with higher spatial resolution and higher sensitivity compared to the case where a large number of detection elements are densely arranged.
This eliminates the problem of variations in sensitivity between detection elements, and uses a stimulable phosphor sheet that is extremely lightweight and easy to handle instead of a detector consisting of multiple X-ray detection elements in conventional CT equipment. Not only can the imaging device be made compact, lightweight, and simple, but there is no dead time, so the imaging time is shortened, and even when organs with muscle movement, breathing movement, peristalsis, etc. The object to be examined does not move, so contrast and spatial resolution do not deteriorate, and artifacts do not occur, making it possible to obtain tomographic images with good diagnostic suitability.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a conventional CT device. FIG. 2 is a schematic diagram showing a preferred embodiment of the CT device of the present invention. 1, 11... Shooting area, 2, 12... Fan-shaped X
Ray, 3, 13...X-ray tube, 4...Detector, 5,
6, 15, 18, 19... transport direction, 17... stimulable phosphor sheet.

Claims (1)

[Scope of Claims] 1. A method for determining the X-ray inspection object from a plurality of X-ray projection distribution images obtained by irradiating a certain cross section of the X-ray inspection object with X-rays from a plurality of different directions. In a computerized tomography system that reconstructs tomographic images,
Sheet arrangement means in which a stimulable phosphor sheet on which an X-ray projection distribution image is recorded is arranged at a position facing the ray tube, and the X-ray projection distribution image obtained for each X-ray irradiation is a stimulable fluorophore sheet. sheet moving means for moving a stimulable phosphor sheet placed in the sheet placement means relative to the X-ray tube and the X-ray inspection object so that the sheet is stored and recorded at different positions on the body sheet; scanning the stimulable phosphor sheet on which the X-ray projection distribution image has been accumulated and recorded with excitation light;
A reading means for photoelectrically reading the stimulated luminescent light emitted from the stimulable phosphor sheet to obtain an electrical signal, and a reconstruction for reconstructing a tomographic image of the X-ray subject using the obtained electrical signal. A computerized tomography apparatus characterized by comprising: means.