JPS63189853A - Recording and reading method for radiation image - Google Patents

Abstract

PURPOSE:To attain clear drawing of the whole part of an object on an image by detecting a positional change in the radiation field of the object based upon the radiation of weak radiant rays, radiating strong radiant rays while modulating its intensity and recording and reading the image through a radiation image converting panel. CONSTITUTION:Weak radiant rays are projected from a radiant ray source 101 to the object 102, positional changes in a portion capable of easily transmitting radiant rays and a portion difficult to transmit radiant rays are detected by scanning based upon a line detector and the detected result is stored in an arithmetic recording part 105. Strong radiant rays are projected from the radiant ray source 101 to the object 102 while modulating its intensity through a controller 109 and a modulator 108 in accordance with the stored result. Consequently, a dynamic range is compressed and image information with a high SN and high contrast is recorded on the radiation image converting panel 103 consisting of a phosphor layer and read out. Thereby, the whole part of the object can be clearly drawn on an image.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention records radiation image information on a radiation Ss image conversion panel while modulating the intensity of radiation based on local changes in radiation passing through an object, and reads the radiation image information. The present invention relates to a method for recording and reading radiation image information that can clearly depict all parts of a subject.

[Background of the invention]

Radiographic images such as X-ray images are often used for medical purposes. One method for obtaining this radiographic image is the so-called radiographic method, in which radiation passing through the subject is irradiated onto a phosphor layer (phosphor screen), and this visible light is irradiated onto a film coated with a silver salt photosensitive material for development. be.

In recent years, with the advancement of radiation image diagnosis technology, methods have been devised to scan the radiograph, read the radiation image information recorded therein, convert it into a digital signal, and then reproduce it on a CRT or photosensitive material. It's here. As a result, more diagnostic information can be obtained from a single radiograph, resulting in improved diagnostic performance and reduced radiation dose. This method is also expected to improve the efficiency of storing and retrieving radiation image information.

In the radiation image information reading device using the photographic film, the photographic film on which the radiation image is recorded is exposed and scanned with reading light, and the reflected light or transmitted light is detected by a photodetector and converted into an electrical signal. It is being done.

On the other hand, methods for obtaining radiographic image information without using radiographic films made of silver salt photosensitive materials have been devised. In this method, the radiation passing through the object is absorbed by a certain type of phosphor, and then this phosphor is excited, for example, with light or thermal energy, so that the phosphor absorbs the radiation accumulated by the absorption. There are devices that emit energy as fluorescence and detect and image this fluorescence. Specifically, for example, U.S. Patent No. 3
, 859.527 or Japanese Patent Application Laid-open No. 12144/1983. These methods use a radiation image conversion method using a stimulable phosphor and visible light or infrared rays as stimulable excitation light, and use a radiation image conversion panel with a stimulable phosphor layer formed on a support. Then, the radiation that has passed through the object is applied to the photostimulable phosphor layer of this radiation image conversion panel, and radiation energy corresponding to the radiation transparency of each part of the object is accumulated to form a latent image. By scanning the stimulable phosphor layer with the stimulated excitation light, the radiation energy accumulated in each part of the radiation image conversion panel is emitted and converted into light. Radiation image information is obtained by detection with a photoelectric conversion element such as a multiplier tube or a photodiode.

Another method is to absorb the radiation that has passed through the object into a semiconductor panel having a uniformly charged photoconductor layer of selenium, silicon, etc. to form an electrostatic latent image.
There are devices that scan this semiconductor panel with light to electrically detect the electrostatic latent image on the panel and turn it into an image (
For example, JP-A-54-31219).

The radiographic image information thus obtained is either left as is or subjected to image processing such as spatial frequency processing and gradation processing in real time and output to a silver halide film, CRT, etc. for visualization, or is visualized on a semiconductor memory. device, magnetic storage device, optical disk storage device, etc., and then
If necessary, the images are taken out from these image storage devices and output to a silver halide film, CRT, etc. for visualization.

The various radiation image conversion panels described above generally have a wide dynamic range for radiation <(103 to 10").
), it is now possible to record image information from the low-signal region to the high-signal region of the subject, but the dynamic range of the image information obtained through the subject, that is, the minimum radiation transmission of the subject! (corresponding to the minimum signal value) and the maximum amount of radiation transmission (corresponding to the maximum signal value) is approximately 1
Since the contrast is about 0.02, the contrast is not sufficient.

Therefore, when visualizing the radiation image information obtained in this way, gradation processing is performed to enhance the contrast and increase the density resolution.

However, since gradation processing is generally performed so that the slope of the line R on the right side of Figure 8 (the slope in the figure is 1) is 2 to 3, the dynamic range of image information obtained through the subject is limited to the visible range. On the image, it is expanded 2-3 times and is 10'~
10', and as a result, the optical density is 4 or more.
As a result, it becomes completely black and nothing is visible.In other words, the dynamic range of image information obtained through the subject is
102 to 103 (approximately O to 2.5 in optical density),
The region with the highest concentration resolution has an optical density of 0.8 to 1.5.
It is so narrow that it is impossible to observe from a low-signal region to a high-signal region of the subject on a single visible image. For example, in the case of a chest X-ray image, if you try to observe the lung field at the optimal optical density (0.8 to 1.5), the amount of X-rays transmitted through the mediastinum will decrease, and the optical density will decrease in this area. If it becomes too low, it will become white and cannot be observed. Conversely, if the optimal optical density is set in the mediastinum area, the amount of X-rays transmitted through the lung area will increase, and the optical density will become too high, resulting in a black image. As a result, it becomes unobservable.

[Purpose of the invention]

In view of the above-mentioned points, it is an object of the present invention to provide a method for recording and reading radiographic images that can clearly depict all parts of a subject on a single image.

[Structure of the invention]

In order to achieve the above object, the present invention accumulates and records radiation image information by irradiating a storage type radiation image conversion panel with radiation that has passed through a subject, and the radiation image information stored and recorded on the storage type radiation image conversion panel. In a method for recording and reading radiographic images in which information is read using excitation light, the dynamic range of the image information is compressed when the radiographic image information is stored and recorded, so that the image information can be read with an improved signal-to-noise ratio. . Specifically, first, a subject is irradiated with weak radiation, local changes in the radiation are detected, and then the strong radiation that passes through the subject is modulated in intensity based on the detected information. This is done by simultaneously irradiating the area.

In this invention, a stimulable phosphor is preferably used as the radiation image conversion panel. This stimulable phosphor is a stimulable phosphor that is irradiated with the first light or high-energy radiation and then stimulated by thermal, mechanical, chemical, electrical, etc. (stimulable excitation). It is a phosphor that exhibits stimulated luminescence corresponding to the amount of radiation irradiated, but from a practical standpoint, it is preferably a phosphor that exhibits stimulated luminescence with excitation light of 500 rv or more, and in particular, it is a phosphor that exhibits stimulated luminescence in response to excitation light. It is a phosphor with high response speed. It is more preferable to use a phosphor that efficiently exhibits stimulated luminescence with respect to light in the oscillation wavelength range of a semiconductor laser. Such stimulable phosphors include, for example, SrS:Ce, 5Il1%SrS described in U.S. Pat. No. 3,859,527.
: Eu, Sl1% LagOzS : Eu+S
Examples include phosphors represented by s+ and (Zn, Cd)s: Mr5sX (where X is a halogen). Moreover, the general formula described in JP-A-55-12143 is (Ba, -x-yMgxCay)FX: el! u”
(However, X is at least one of Br and CZO, and x, y, and e are each Q<x+y≦0.6゜xy#
Q and 10-6≦e≦5X10-''), the general formula of the alkaline earth fluorohalide phosphor described in JP-A-55-12144 is LnOX: xA (However, Ln represents at least one of Lap Y+ Gd and Lu, X represents CI and/or Br, A represents Ce and/or Tb, and X represents a number satisfying Q < X < 0.1 .) Phosphor expressed by JP-A-55-1
The general formula described in No. 2145 is (Ba+-xMI
x) FX: yA (However, Ml is Mg
+ Ca+ Sr+ at least one of Zn and Cd; X is at least one of CIl, Br and ■; A is Eu+ Tb+ Ce, Tm, Dy, Pr.

At least one of Ha, Nd, Yb, and Er, and X and y represent numbers satisfying the following conditions: 0≦X≦0.6 and O≦y≦0.2. ), the general formula described in JP-A-55-84389 is BaP
X: xCe+ yA (However, X is at least one of Cj', Br, and ■, A is at least one of In+ Tl, Gd, S+++, and Zr, and x and y are each 0<x≦2 X 10-' and Q<y≦5X1
A phosphor represented by 0-”), JP-A-55-1
The general formula described in No. 60078 is MI FX -xA: yLn (however, M
l is at least one of Mg+ Ca+ Ba+ Sr+ Zn and Cd, A is Bean MgO, CaO
, SrO.

Bad, Zn(L Al 203+ Y!0
3+ LazOs+ InzOi+5iOt+Ti
0t* Zr0t+ Ge0t+ 5nor, NbgO
s+ Tag's and Th0z (both are one type, Ln is f!u, Tb, Ce, Ts, Dy+Pr,
At least one of Ha, Nd, Yb, Er, Ss, and Gd, X is at least one of CIl, Br, and I, and X and y are 5×104≦X≦0.5 and Q, respectively. This is a number that satisfies the condition <y≦0.2. ) A rare earth element activated divalent metal fluorohalide phosphor represented by any of the following general formulas described in JP-A No. 57-148285: (wherein M and N are each Mg + ca , Sr+
A small amount of Ba, Zn and Cd (both are one kind, X is F,
At least one of C6゜Br and ■, A is Eu, T
b+ Ce.

Tta, Dy+ Pr, Ho, Nd, Yb,
Er, Sb+ T1. Represents at least one of F'In and Sn. Also, X and y are O<x≦6.0
This is a number that satisfies the condition ≦y≦1. ), a phosphor represented by any of the following general formulas (% formula % (in the formula, Re is at least one of Lal, Gdly, Lu, A is an alkaline earth metal, Ban S
r, at least one of Ca, X and X' are p, C
It represents at least -1 of I and Br. Also, X and y are l x 10-'< X < 3 xlO-', 1 x
It is a number that satisfies the condition lQ-'< y < I Xl0-', and n7m is 1
The condition l0-' is satisfied. ), and the following general formula % formula %: (However, Ml is Li, Nat K+ Rh and C
At least one alkali metal selected from s,
Ml is Ban Mg, Ca+ Sr, Ban Zn
, cd, Cu, and 'li. Ml is Sc+ y, La, C
e, Pr, Nd, Pm+ Sm, Eu+ Gd
,Tb.

Dy+ Ho, Hr, Tm, Yd, Lu,
Aj! +At least one trivalent metal selected from Ga and In. X.

X' and X# are at least one type of halogen selected from F, C1, Br and I. A is Eu, Tb.

Ce, Tm, o, Prl HQI NatY
b, Erl Gdl Lul 5atl
Y.

At least one metal selected from TJI Nat Ag, Cu, and M.

Also, a is a numerical value in the range of 0≦a<0.5, and b is O
It is a numerical value in the range of ≦b<0.5, and C is 0<c<0.2
is a numerical value in the range of . ) and the like can be mentioned. In particular, among the above-mentioned stimulable phosphors, alkaline earth fluorohalide-based phosphors and alkali halide-based phosphors have a high response speed of stimulated luminescence to excitation light, and also have a high stimulable luminescence response speed in the oscillation wavelength range of semiconductor lasers. A good match is preferred.

However, the stimulable phosphor used in the radiation image conversion panel is not limited to the above-mentioned phosphor, but is a phosphor that exhibits stimulated luminescence when irradiated with radiation and then irradiated with stimulable excitation light. Any phosphor may be used.

〔Example〕

Next, the method of the present invention will be explained in detail using examples.

1 to 4 show a first example of a radiation image information recording device suitable for carrying out this method. In FIG. 0, 101 is a radiation source, 102 is a subject, and 103 is the subject 102. This is a radiation image conversion panel (hereinafter referred to as a conversion panel) that accumulates and records radiation image information by irradiating radiation (X-rays) that has passed through it. When the radiation image information is stored and recorded on this conversion panel 103, the dynamic range of the image information obtained through the subject 102 is compressed and stored and recorded. In this compressed recording, first,
■The radiation source 101 applies weak radiation to the subject 102,
It detects local changes in the radiation, that is, areas where it is easy to penetrate and areas where it is difficult to penetrate. After that, (2) the storage type radiation image conversion panel 103 is irradiated with strong radiation that has passed through the subject 102 while modulating the intensity based on the detection information;

The above-mentioned detection (■) is performed by scanning the line detector 104 on the opposite side of the subject 102 as shown in FIG. It is stored in the calculation recording unit 105. In this case, when a radiation fan beam generating device is used as the radiation source 101 as shown in FIG. 3(n), the line detector 104 may be scanned in synchronization (interlocking) with the fan beam emitted from the fan beam generating device. In addition, as shown in the same figure (I[I), an image intensifier 106 is used in place of the line detector 104, and the image information of the subject 102 is amplified by this, and the image information of the subject 102 is focused on the most visible area by the television camera 107. and the weak part is calculated and recorded by the recording unit 10.
5 may be stored. The radiation for this recording may be weak as described above, and the line detector 104
And the spatial resolution of the television camera 10.7 may be low.

As a means for photographing while modulating the intensity of the radiation described above, a position intensity modulator 108 is interposed between the radiation source 101 and the subject 102 as shown in FIG. This is performed by being driven by a controller 109 connected to the recording unit 105. For example, the chest of the subject 102 may be photographed using a fan beam as shown in FIG.
In the case of recording on the conversion panel 103 by irradiating it like a" line, the position intensity modulator 108 is connected to the calculation recording section 10.
Based on the image information on the line stored in 5, the controller 109 is controlled to compress the intensity of the radiation in the lung parts A, A' and the spine part B, as shown in the third modified figure. The structure of the position intensity modulator 108 shown here is not particularly limited, but for example, as shown in FIG. It is sufficient that the number of the draft plates 110 is the same as the number of pixels of the detector, which can be inserted into and removed from the fan beam path a-a' as shown in FIG. 2 (II). For example, if the detector has 2,000,000 pixels, the maximum number of images is 2,000.
As will be described later, when the spatial frequency region is limited by averaging processing, the number of images that can respond to the spatial frequency, for example, when averaging to 100 pixels, 100 images is sufficient.

When compensating for a portion with a low transmittance of radiation transmitted through the subject 102 by the position intensity modulator 108, if compensation is performed in all spatial frequency regions, necessary image information will also be lost, so 0.21p/lan is used. Below, preferably 0
．． It is necessary to compensate only in the region below 111p/mvi. That is, since a radiation image is formed by subtle differences in the amount of transmission between parts of the subject 102 that allow radiation to easily pass through and parts that do not allow it to pass through, compensation is performed in all spatial frequency regions.
If the difference in the amount of transmission is eliminated, an image cannot be created, so it is necessary to compensate for large structures such as the heart and lungs, or the spine and lungs, for example.

As a method of detecting only signals in such a low spatial frequency region, it is possible to arrange the detectors coarsely from the beginning and set the spatial resolution low, but it is also possible to arrange the detectors finely and then average the detected signals. It can be said that a method of performing processing (filtering) is more preferable.

FIG. 5 shows a second example of a radiation image information recording apparatus suitable for implementing the present method. In this case, when the conversion panel 103 is irradiated with radiation that has passed through the subject 102, detection of a local change in the radiation and modulation of the intensity of the radiation based on the detected information are simultaneously performed. That is, the subject 102 is placed in front of the conversion panel 103 from the beginning, and the slit-shaped fan beam generated by the radiation source 101 is used to cover the conversion panel 103 together with the subject 102.
scan. At the same time, a line detector 104 similar to that shown in Fig. 2 (1) and (■) installed behind the conversion panel 103 is linked to detect local changes in radiation (areas that are easy to penetrate and areas that are difficult to penetrate). Then, this is immediately fed back to the position intensity modulator 108 via the arithmetic storage unit 105 and the controller 109, and the image is imaged on the conversion panel 103 in one scan while modulating the intensity of the radiation to the part of the subject 102 that is difficult to penetrate. Shows how. Furthermore, when implementing this method, a pencil beam may be used instead of the slit-shaped fan beam. Moreover, these slit-shaped fan beams and pencil beams can also be generated by a method of moving a slit as shown in FIG.

Further, by inserting a slit member (not shown) between the subject 102 and the conversion panel 103 to remove scattered radiation, the sharpness of the image can be further improved.

FIG. 7 is an explanatory diagram showing an example of a radiation image reading device. In the figure, 201 is a light source for generating excitation light, and the light source 201 is driven by a driver circuit 202.

The beam generated from the light source 201 is passed through a monochromatic light filter 2.
03, sprint mirror 204, beam shaping optical system 20
5 and a mirror 206 to reach a deflector 207. This deflector 207 includes a galvanometer mirror driven by a deflector driver 208 and deflects the beam at a constant angle into the scanning area. The deflected beam is adjusted to have a constant speed on the scanning line by the fθ lens 209, passes through the mirror 210, and is stored on the conversion panel 103 where the dynamic range of the image information transmitted through the object 102 is stored and recorded in a compressed state as described above. is scanned in the direction of arrow a. At the same time, the conversion panel 103 is moved in the sub-scanning direction (in the direction of the arrow) by an appropriate means, and the entire surface is scanned. Stimulated luminescence scanned by the beam and generated from the image conversion panel 103 is collected by a condenser 212, and passed through a filter 113 that passes only the wavelength range of stimulated luminescence to a photoelectric converter such as a photomultiplier tube. The light reaches a light receiving section 214 equipped with a light receiving section 214, where it is converted into an analog electrical signal (image signal).

215 is a power source that supplies high voltage to the photomultiplier tube. The image signal output as a current from the photomultiplier tube is the current −
A Log converter 21 which is voltage amplified through a voltage conversion amplifier 216 and further converts the emission intensity signal into an image density signal.
7. After passing through the sample and hold circuit 218, it is converted into a digital signal by an A/D converter 219 and stored in the memory 2.
20. This memory 220 is connected to a CPU 221 that performs digital calculations, etc., and the CPU 221 connects to external devices via an interface 122, such as a large computer for storing and processing data, a minicomputer, a CR7 display device for outputting images, and various hardware. The memory 22 can be connected to a copy making device, etc.
It is designed to perform calculations and transfer of data stored in 0.

Note that the light source 201 for generating the excitation light is not particularly limited as long as it radiates the radiation energy accumulated in the conversion panel 103 and converts it into light, but a semiconductor laser, a He-Ne laser, a He-Cd laser, etc. , Ar ion laser, Kr ion laser, N laser, YAG laser and its second harmonic, ruby laser, and various other lasers can be used.

Further, in the above embodiment, an example was shown in which a photostimulable phosphor was used as the conversion panel 103, but the invention is not limited to this.
For example, it goes without saying that the present invention can also be applied to recording an electrostatic latent image on a photoconductor.

〔Effect of the invention〕

As explained above, the present invention accumulates and records radiation image information by irradiating a storage type radiation image conversion panel with radiation that has passed through a subject, and records the radiation image information stored and recorded in the storage type radiation image conversion panel. The method for recording and reading radiation images read with excitation light is characterized in that the dynamic range of the image information is compressed when the radiation image information is stored and recorded, so that it can be read with an improved signal-to-noise ratio. At the same time, it has the excellent effect of being able to clearly depict all parts of the subject during reading.

[Brief explanation of the drawing]

1 to 4 show a first example of a recording apparatus for implementing the method of the present invention, in which FIG. 1 is a schematic perspective view, and FIG.
I) to (Ill) are explanatory diagrams showing means for detecting local changes in radiation passing through the subject, Fig. 3 is an explanatory diagram showing the compression state of the dynamic range, and Fig. 4 (1) and (II) are explanatory diagrams showing the means for detecting local changes in radiation passing through the subject. A perspective view of a modulator and an explanatory diagram of the modulation state, FIG. 5 is a schematic perspective view showing a second example of a recording device, FIG. 6 is a perspective view of a slit moving system, and FIG. 7 is an example of a reading device. The schematic perspective view shown in FIG. 8 is a diagram showing the relationship between the dynamic range of the panel and object, the signal strength, and the image density. 101... Radiation source 102... Subject 103... Storage type radiation image conversion panel 104...
Line detector 105 --- Calculation recording section Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7

Claims (3)

[Claims] (1) A radiation image in which radiation image information is accumulated and recorded by irradiating a storage type radiation image conversion panel with radiation that has passed through the subject, and the radiation image information stored and recorded in the storage type radiation image conversion panel is read with excitation light. A method for recording and reading radiographic images, characterized in that the dynamic range of the image information is compressed when the radiographic image information is stored and recorded. (2) After the compression of the dynamic range irradiates the subject with weak radiation and detects local changes in the radiation,
2. A method for recording and reading a radiographic image according to claim 1, which is carried out by irradiating a storage type radiographic image conversion panel with intense radiation that has passed through a subject while modulating the intensity based on the detected information. (3) Recording and reading of a radiation image according to claim 2, which simultaneously detects a local change in radiation passing through the object and modulates the intensity of the radiation based on the detected information. Method.