JPH0412970B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved simultaneous multilayer tomography apparatus.

2. Description of the Related Art Tomography is conventionally known as a method for obtaining an X-ray tomographic image of only a desired tomographic plane of an X-ray subject.

In this method, an X-ray tube and an X-ray photographic film are arranged with the X-ray object in between, and during X-ray irradiation, the X-ray tube and X-ray photographic film are moved using a straight line rule (X-ray tube) centered on the tomographic plane of the X-ray object. The focus of By moving the object relatively so as to satisfy the following conditions, only the desired tomographic plane is imaged on the X-ray photographic film, and the tomographic planes of other objects are blurred.
An X-ray image of only the desired tomographic plane of the object can be obtained.

Simultaneous multilayer tomography is also known as a method in which images of multiple tomographic planes of an X-ray object are obtained at once (simultaneously) by stacking multiple X-ray photographic films and performing the same imaging as described above. .

In the tomography method, it is sufficient that the above-mentioned linear law and geometric ratio law hold, and any method of moving the X-ray tube and the X-ray photographic film, such as linear, circular, elliptical, or spiral, can be used.

Such tomography techniques are described in detail in the "Radiation Technology Guide" published by the Tokyo Radiological Technologists Association.

The simultaneous multilayer tomography method will be explained below based on the accompanying drawings. Figure 1 shows the X-ray tube and
This is an example in which a horizontal linear motion method is adopted as a method of moving a line photographic film.

X-ray tube 1 and X-ray photographic films 2a, 2b, 2c
A cassette 3 containing a film laminate formed by laminating three films is placed with an X-ray subject 4 in between. X-ray photographic films 2a, 2b, 2c are usually
It is equipped with a line-intensifying screen, and care has been taken so that the lower the layer, the greater the sensitivity to X-rays.

When taking an image, move the X-ray tube 1 and cassette 3 in the directions of arrows 5 and 6, and move the
The X-ray object 4 is irradiated with rays. In this way, for example, the tomographic plane of the X-ray object formed on the X-ray photographic film 2a will be the X-rays 7a, 7 irradiated from the X-ray tube 1.
a' is an intersection portion 8a formed as the X-ray tube 1 is transported, and the tomographic plane of the X-ray object imaged on the X-ray photographic film 2c is the
Lines 7c and 7c' are an intersection 8c formed as the X-ray tube 1 is transported.

This simultaneous multilayer tomography method can obtain images of multiple tomographic planes of an X-ray object in a single scan, so for example, for moving organs such as the heart and lungs, tomographic images with exactly the same motion phase can be obtained. , even for other body parts, images of multiple tomographic planes can be obtained without any image shift due to the movement of the subject, which normally would be unavoidable between each tomographic image. It is convenient for diagnosis because it reduces the physical and mental burden.

However, in conventional simultaneous multilayer tomography, the X-rays transmitted through the X-ray object are transmitted through multiple X-rays.
As it passes through the X-ray photographic film, it attenuates, and the density is higher in the upper layers of the X-ray photographic film and lower in the lower layers, so the sensitivity of the X-ray photographic film and intensifying screen must be adjusted. Therefore, it is necessary to correct variations in the density of each layer, but it is generally extremely difficult to balance the sensitivity of such X-ray photographic films and intensifying screens depending on the X-ray subject. There is also a limit to increasing the sensitivity of the bottom layer of X-ray photographic film, and sufficient sensitivity could not be obtained even with the combination of an intensifying screen. Furthermore, lower energy X-rays are absorbed by the upper layer of X-ray photographic film, and higher energy X-rays are absorbed by the upper layer of X-ray photographic film.
Since the higher the line, the higher the contrast reaches the lower layer of the X-ray photographic film, the higher the contrast of the X-ray photographic film, the higher the contrast becomes, and the lower the contrast becomes lower: it is essential to adjust the gamma value of the X-ray photographic film for each layer. However, it has been extremely difficult to prepare an X-ray photographic film whose γ value is adjusted depending on the X-ray subject. For these reasons, with conventional simultaneous multilayer tomography, it is generally extremely difficult to obtain X-ray images with high diagnostic performance, and the number of stacked X-ray film-intensifying screens is only 4 at most. The limit is ~5 layers, and there is a drawback that imaging must be performed multiple times in order to obtain a large number of tomographic images.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the conventional multilayer tomography method and to provide a simultaneous multilayer tomography apparatus that can easily obtain X-ray tomographic images with high diagnostic performance.

Another object of the present invention is to provide a multilayer tomography apparatus that obtains a larger number of X-ray tomographic images in one imaging operation, ie, without increasing the amount of radiation exposure, than in the past.

As a result of extensive research to achieve this objective, the present inventors placed a laminate consisting of a plurality of stimulable phosphor sheets on the opposite side of the X-ray tube through the X-ray object, and It has been found that the above object can be achieved by relatively moving the laminated body and the X-ray tube during irradiation so as to satisfy the linear law and the geometric ratio law, centering on the tomographic plane where the X-ray object is located.

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.

A sheet provided with a layer of such a stimulable phosphor is irradiated with radiation that has passed through the subject, and information about the subject is stored and recorded in the stimulable phosphor as radiation image information, and then laser light, etc. The stimulable phosphor sheet is scanned with excitation light to emit radiation image information as stimulated luminescent light, this stimulated luminescent light is read photoelectrically as an image signal, and the image signal is subjected to desired signal processing. The applicant has already proposed a radiation image system in which a visible image is output on a recording medium such as a photographic light-sensitive material or a display device such as a CRT. (Unexamined Japanese Patent Publication No. 55-12429
No. 56-11395, etc. ) This system has the very practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure changes considerably due to various imaging conditions, the amount of light emitted from the emitted light can be read by the light amount conversion means by setting the reading gain to an appropriate value and converted into an electrical signal, and this electrical signal can be converted into an electrical signal. By outputting a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure can be obtained.

In addition, according to this system, the radiation image information accumulated and recorded in the stimulable phosphor is converted into an electrical signal, then subjected to appropriate signal processing, and this electrical signal is used to produce recording materials such as photographic light-sensitive materials, CRTs, etc. By outputting the image as a visible image on a display device, a very large effect can be obtained in that a radiation image with excellent suitability for observation and interpretation (diagnosis) can be obtained.

In this way, in a radiation imaging system using a stimulable phosphor, by setting the reading gain to an appropriate value and reading the stimulated luminescence light photoelectrically,
X as required for each layer in conventional simultaneous multilayer tomography methods, since it is easily possible to correct deviations from the desired level of radiation energy stored in the storage fluorophore. It is not always necessary to balance the sensitivity of the line photographic film-intensifying screen; stimulable phosphors of the same sensitivity can be used in each layer, and the sensitivity of the stimulable phosphor in each layer can be adjusted. Even when changing the sensitivity, it is not necessarily required to maintain a strict sensitivity balance. In addition, in the past, there was a limit to the number of layers in the laminate due to limitations in the sensitivity of the X-ray photographic film and intensifying screen, but in this system, by appropriately setting the value of the reading gain, the accumulative fluorescence can be reduced. Since the sensitivity of the light body can be corrected, the number of layers in the laminate can be greatly increased. In other words, it becomes possible to obtain a tomographic image with a far greater number of layers than in the past with one imaging. Furthermore, by performing gradation processing on the photoelectrically read image signal, the contrast of the output radiation image can be easily corrected as desired. It is possible to obtain a large number of tomographic images with the same contrast without having to strictly adjust the γ value of the X-ray photographic film.

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-55-12492, it is preferable that the excitation light wavelength be 600 to 700 nm and the stimulated emission light wavelength be 300 to 500 nm.

In this way, it emits stimulated luminescence light of 300 to 500 nm,
As the stimulable phosphor that can be preferably used in the present invention, for example, a rare earth element-activated alkaline earth metal fluorohalide phosphor [specifically, described in JP-A-55-12143] Ba _1x-y ,
Mg _x , Ca _y ) FX: aEu ²⁺ (However, X is at least one of Cl and Br, and x and y are 0<
x+y≦0.6 and xy≠0, and a is 10 ^-6 ≦a≦
5×10 ^-2 ), - (Ba _1-x , M〓 _x ) FX: 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, Dy, Pr, Ho,
at least one of Nd, Yb, and Er, x is 0≦x≦0.6, y is 0≦y≦0.2), etc.; ZnS described in Japanese Patent Application Laid-Open No. 12142/1982:
Cu, Pb, BaO.xAl ₂ O ₃ :Eu (however, 0.8≦x≦10)
and M〓O・xSiO ₂ :A (where M is M〓g, 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 LnOX:xA described in JP-A-55-12144 (however, Ln is La, Y,
at least one of Gd and Lu, X is at least one of Cl and Br, A is Ce and
at least one of Tb, x is 0<x<0.1); 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-56-74,175. 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.

In the present invention, the gradation processing used is JP-A No. 55-116339, JP-A No. 55-116340,
Examples include those disclosed in Publication No. -88740.

In the present invention, in addition to gradation processing, in order to improve the image quality of radiographic images and improve diagnostic performance,
JP-A-55-87970, JP-A-56-11038, JP-A-56-
Frequency processing disclosed in No. 75141, No. 56-104645, etc. can be used in combination.

In the present invention, the reading gain during reading is adjusted according to the radiation energy stored in the stimulable phosphor of each layer constituting the laminate.
Since it is necessary to perform gradation processing on the image signal after photoelectric conversion, it is necessary to know in advance the accumulated record information regarding the radiation energy accumulated and recorded in the stimulable phosphor. For this purpose,
JP-A No. 58-67240, No. 58-67241, No. 58-
67242, No. 58-67243, and No. 58-67244, the method and apparatus disclosed in No. 67242, No. 58-67243, and No. 58-67244 are used to obtain accumulated record information about radiation energy using excitation light with low energy. After performing the reading operation, the reading gain is set and the gradation processing conditions are set based on this accumulated recorded information, and the excitation light is irradiated onto the stimulable phosphor sheet again, and the resulting brightness is It is desirable to output a radiation image based on exhaustion light. however,
Methods for obtaining accumulated recorded information regarding radiation energy accumulated and recorded in a stimulable phosphor are not limited to such methods,
Of course, a method using so-called "instantaneous light emission" as disclosed in JP-A No. 55-50180, and other various methods can also be used.

Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. FIG. 2 is a schematic diagram of a simultaneous multilayer tomography apparatus showing an embodiment of the present invention. In FIG. 2, an X-ray tube 11 and a cassette 13 containing a stack of stimulable phosphor sheets 12a, 12b, 12c...12n are connected to an X-ray object 1.
It is arranged through 4.

During imaging, while moving the X-ray tube 11 and cassette 13 in the directions of arrows 15 and 16,
An X-ray object 14 is irradiated with X-rays from a ray tube 11 .
As a result, as in the case of Fig. 1, the X-ray object 14
The tomographic image of the tomographic plane 18a is the stimulable phosphor sheet 1.
2a, and the tomographic image of the tomographic plane 18n is stored and recorded on the stimulable phosphor sheet 12n.

In this way, the stimulable phosphors 12a, 12b,...1
X accumulated and recorded as X-ray energy in 2n
Multi-sectional planes 18a, 18b,...18 of line subject 14
Regarding the X-ray energy corresponding to the tomographic image of n, the upper layer of the stimulable phosphor sheet has higher density and contrast when it is made into a visible image.

In this way, the stimulable phosphor sheets 12a, 12b, . . . , 12n subjected to simultaneous multilayer tomography are sent to a reading device.

FIG. 3 shows stimulable phosphor sheets 12a, 12.
The pre-reading reading unit 21 is used to read the accumulated recorded information accumulated and recorded in the stimulable phosphor sheets 12a, 12b, ..., 12n to output the radiation image used for diagnosis. 2 is a schematic diagram of a reading device including a main reading reading section 32 that reads radiographic image information.

In the prefetch reading unit 21, a laser light source 22
The laser beam 23 emitted from this laser beam 23
After passing through a filter 24 that cuts out the wavelength range of the stimulated luminescent light emitted from the stimulable phosphor sheet 20 by excitation of The light is incident on the light sheet 20 while being deflected one-dimensionally. Here, the laser light source 22 is selected so that the wavelength range of the laser light 23 does not overlap with the wavelength range of the stimulated luminescence light from the stimulable phosphor 20. On the other hand,
The phosphor sheet 20 is conveyed in the direction of the arrow 27 for sub-scanning, and as a result, the entire surface of the phosphor sheet 20 is irradiated with laser light. Here, the power of the laser light source 22, the beam diameter of the laser light 23, the scanning speed of the laser light 23, and the transport speed of the phosphor sheet 20 are different from the pre-read laser light 2.
The energy of 3 is chosen to be smaller than that of the main reading. When the laser beam 23 is irradiated in this manner, the stimulable phosphor sheet 20 emits stimulated luminescent light with an amount proportional to the accumulated and recorded X-ray energy, and this emitted light is transmitted to the pre-reading light guide sheet. 28. This light guide sheet 28
does not have a straight line on its incident surface, and is arranged adjacent to and opposite to the scanning line on the stimulable phosphor sheet 20, and has an annular exit surface, and is placed on the light receiving surface of the photodetector 29, such as a photomultiplier. They are held in close contact. This light guide sheet 28 is made by processing a transparent thermoplastic resin sheet such as acrylic resin.
The structure is such that the light incident from the incident surface is transmitted to the exit surface while being totally reflected inside, and the stimulated luminescent light from the stimulable phosphor sheet 20 is guided through the light guide sheet 28. , is emitted from the exit surface and is received by the photodetector 29. Preferred shapes, materials, etc. of the light guiding sheet are disclosed in Japanese Patent Application Laid-open Nos. 55-87970 and 56.
-Disclosed in Publication No. 11397, etc.

A filter is attached to the light receiving surface of the photodetector 29, which transmits only light in the wavelength range of stimulated luminescence light and cuts out light in the wavelength range of excitation light, and detects only stimulated luminescence light. It's getting wet. Photodetector 2
The stimulated luminescent light detected by 9 is converted into an electrical signal and further amplified by amplifier 30. The accumulated recording information of the X-ray image information output from the amplifier 30 is input to the control circuit 31 of the main reading reading section 32. The control circuit 31 sets the amplification factor setting value a and the recording scale factor so that a tomographic image with the same density and contrast in each tomographic plane and with good diagnostic performance is obtained according to the obtained accumulated record information. The setting value b and the reproduction image processing condition setting value c are output. The stimulable phosphor sheet 20 on which the pre-reading has been completed is transferred to the reading section 32 for main reading.

In the reading unit 32 for main reading, the laser beam 34 emitted from the laser light source 33 for main reading is excited by the laser beam 34, and the stimulable phosphor sheet 20 is
After passing through a filter 35 that cuts out the wavelength range of the stimulated luminescence light emitted from the stimulable luminescent light, the beam diameter is strictly adjusted by a beam expander 36, and then the beam diameter is precisely adjusted by a light deflector 37 such as a galvanometer mirror. The light is deflected and incident on the stimulable phosphor sheet 20 through the stimulable phosphor sheet 20. An fθ lens 39 is arranged between the optical deflector 37 and the plane reflecting mirror 38,
Even when the laser beam 34 scans the phosphor sheet 20, it always has a uniform beam diameter. On the other hand, the phosphor sheet 20 is moved in the direction of the arrow 40 to perform sub-scanning, and as a result, the entire surface of the phosphor sheet 20 is irradiated with laser light. When the laser beam 34 is irradiated in this way, the stimulable phosphor sheet 20 emits stimulated luminescent light with an amount proportional to the accumulated and recorded X-ray energy, and this emitted light is transmitted to the light guide sheet for book reading. 41. The light guide sheet 41 for main reading has the same material and structure as the light guide sheet 28 for prereading. Stimulated luminescent light guided through the light guiding sheet 41 for main reading while undergoing repeated total reflection is emitted from its exit surface and is received by the photodetector 42. A filter that selectively transmits only the wave region of the stimulated luminescent light is attached to the light receiving surface of the photodetector 42, so that the photodetector 42 detects only the stimulated luminescent light. The stimulated luminescence light detected by the photodetector 42 is converted into an electrical signal, and after being amplified to an electrical signal of an appropriate level by the amplifier 43 whose sensitivity is set by the amplification factor setting value a, the stimulated luminescence light is converted to an electrical signal. 44. The A/D converter 44 converts the signal into a digital signal using a scale factor suitable for the signal fluctuation range by setting a recording scale factor b, and inputs the digital signal to the signal processing circuit 45. In the signal processing circuit, signal processing is performed based on the reproduction image processing condition setting value c to obtain an X-ray image that has the same density and contrast of the tomographic image of each tomographic plane and is suitable for observation and interpretation, and transmits it to the recording device. be done. Recording devices include those that optically record by scanning a photosensitive material with a laser beam or the like;
Various methods can be used, including those that display electronically on a CRT, etc., those that record the X-ray image displayed on a CRT, etc. using a video printer, etc., and those that record on a heat-sensitive recording material using heat rays. .

It goes without saying that the present invention is not limited to the above-described embodiments, and that various modifications can be made.

For example, as a method for making the contrast and density of the tomographic image of each tomographic plane the same, instead of amplifying the output of the photodetector 42 to an appropriate level signal with the amplifier 43, When using a multiplier tube, the applied voltage may be changed depending on the amplification factor setting value a, or the A/
Instead of converting to a digital signal using a scale factor suitable for the signal fluctuation width in the D converter 44, the signal fluctuation width is optimized using an analog amplifier according to the recording scale factor setting value b, and then the A/D converter converts the signal into a digital signal.
It may be converted into a digital signal by a converter 44.

In addition, as mentioned above, the X-ray tube 11 and the cassette 13
The relative movement method is not limited to linear motion, but also circular,
It may be oval, spiral, etc.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram illustrating a conventional simultaneous multilayer tomography method, FIG. 2 is a schematic diagram illustrating a simultaneous multilayer tomography apparatus of the present invention, and FIG. 3 is a preferred reading device used in the present invention. FIG. 1, 11...X-ray tube, 2a, 2b, 2c, 12
a, 12b, 12c, 12n, 20... stimulable phosphor sheet, 3, 13... cassette, 4, 14...
...X-ray object, 7a, 7a', 7c, 7c', 17
a, 17a', 17n, 17n'...X-ray, 8a, 8
c, 18a, 18b, 18c, 18n...tomographic plane, 21...reading unit for pre-reading, 22...laser light source for pre-reading, 23...laser light, 24...filter, 25...light polarizer, 26... ...Flat reflector, 2
8...Light guide sheet for pre-reading, 2a...Photodetector, 30...Amplifier, 31...Control circuit, 32...
... Reading section for main reading, 33 ... Laser light source for main reading, 34 ... Laser light, 35 ... Filter, 36
...beam expander, 37...optical deflector,
38...Flat reflecting mirror, 39...fθ lens, 41...
...Light guide sheet for book reading, 42...Photodetector, 4
3...Amplifier, 44...A/D converter, 25...Signal processing circuit.

Claims (1)

[Claims] 1. A laminate consisting of a plurality of stimulable phosphor sheets and an X-ray tube placed on opposite sides of the X-ray object, the laminate and the X-ray tube being placed on the opposite side of the X-ray object. It is characterized by mainly comprising a means for relative movement so as to satisfy the linear law and the geometric law, and a means for obtaining accumulated record information about the radiation energy accumulated and recorded in the stimulable phosphor sheet. Simultaneous multilayer tomography device.