JPH0731372B2 - Radiation image information reading method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention modulates the intensity of excitation light based on a spatial change of radiation passing through a subject when reading radiation image information recorded on a radiation image conversion panel. The present invention relates to a recording / reading method of radiographic image information capable of clearly depicting all parts of a subject.

[Background of the Invention]

Radiation images such as X-ray images are often used for medical purposes. As one method of obtaining this radiographic image, there is a so-called radiographic method in which the phosphor layer (fluorescent screen) is irradiated with the radiation that has passed through the subject and the visible light is irradiated to the film coated with the silver salt photosensitive material for development. is there.

In recent years, with the progress of radiological image diagnostic technology, a method of scanning the radiograph, reading the radiographic image information recorded therein, converting it into a digital signal, and then reproducing it on a CRT or a photosensitive material has come to be devised. Came. As a result, more diagnostic information can be obtained from one radiography, resulting in improved diagnostic performance and reduced exposure dose. This method is also expected to improve the efficiency of storage and retrieval of radiation image information.

In the radiation image information reading apparatus using the photographic film, the photographic film on which the radiation image is recorded is exposed and scanned by the reading light, and the reflected light or the transmitted light is detected by the photodetector and converted into an electric signal. Has been done.

On the other hand, a method of obtaining radiation image information without using a radiographic film made of a silver salt photosensitive material has been devised. As this method, the radiation that has passed through the subject is absorbed by a certain type of phosphor, and then this phosphor is excited by, for example, light or thermal energy, so that the radiation accumulated by the phosphor is absorbed. There is one in which energy is emitted as fluorescence and this fluorescence is detected and imaged. Specifically, for example, US Patent No.
3,859,527 or JP-A-55-12144.
These show a radiation image conversion method using a stimulable phosphor and using stimulable excitation light of visible light or infrared rays. A radiation image conversion panel having a stimulable phosphor layer formed on a support is used. Then, the radiation that has passed through the subject is applied to the stimulable phosphor layer of this radiation image conversion panel to accumulate the radiation energy corresponding to the radiation transmittance of each part of the subject 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 radiated, and this is converted into light. The radiation image information is obtained by detection with a photoelectric conversion element such as a double tube or a photodiode.

As another method, the radiation that has passed through the subject is absorbed by a semiconductor panel having a photoconductor layer such as selenium or silicon that is uniformly charged to form an electrostatic latent image,
There is one in which an electrostatic latent image on the semiconductor panel is electrically detected and imaged by scanning the semiconductor panel with light (for example, JP-A-54-31219).

The radiation image information thus obtained is either as it is or after being subjected to image processing such as spatial frequency processing or gradation processing in real time and output to a silver salt film, CRT or the like for visualization or semiconductor storage. It is stored in an image storage device such as a device, a magnetic storage device, an optical disk storage device, and then taken out from these image storage devices as necessary and output to a silver salt film, CRT or the like for visualization.

The various radiation image conversion panels generally have a wide dynamic range with respect to radiation (10 ³ to 10 ⁶ ), and it is possible to record image information from a low signal region portion to a high signal region portion of a subject. , The dynamic range of the image information obtained through the subject, that is, the ratio of the minimum radiation transmission amount (corresponding to the minimum signal value) and the maximum radiation transmission amount (corresponding to the maximum signal value) of the subject is about 10 ^2. The contrast is not enough.

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

However, since gradation processing is generally performed by setting the inclination of the line R on the right side of FIG. 7 so that the inclination is 1 to 2, the dynamic range of image information obtained through the subject is visible. It is enlarged 2-3 times on the image and 10 ⁴ to 10 ⁶
As a result, the optical density becomes 4 or more,
It disappears in black and disappears. That is, the dynamic range of image information obtained through a subject is 10 ² to 10 ³
Although the optical density is about 0 to 2.5, the area with the highest density resolution is as narrow as 0.8 to 1.5 on the optical density, and you can observe from a low signal area to a high signal area of the subject on one visible image. It becomes impossible to do. For example, in the case of a chest X-ray image, when trying to observe the lung field with the optimum optical density (0.8 to 1.5), the X-ray transmission amount in the mediastinum decreases,
In this part, the optical density becomes too low and it becomes blank and unobservable. Conversely, when the mediastinum part is set to the optimum optical density,
The amount of X-rays transmitted in the lung field increases, and the optical density becomes too high, resulting in blackening.

[Object of the Invention]

In view of the above points, an object of the present invention is to provide a radiographic image recording / reading method capable of clearly depicting all portions of a subject on one image.

[Structure of Invention]

In order to achieve the above-mentioned object, the present invention is a method of reading radiation image information, which is read as an electric signal by irradiating radiation image information which is transmitted through a subject and is recorded on a radiation image conversion panel with a laser beam. In the second aspect, the intensity of the laser light is modulated based on the spatial change of the radiation intensity applied to the radiation image conversion panel to compress the dynamic range. As an example, prior to the main reading, a weak excitation light is applied to the conversion panel in which the image information is stored and recorded to detect a spatial change during recording of the radiation passing through the subject, and when the main reading is performed with a strong excitation light, The intensity of the excitation light is modulated based on the detection information.

In this invention, a stimulable phosphor is preferably used as the radiation image conversion panel. This stimulable phosphor is the first light or high energy that is stimulated by light, heat, mechanical, chemical or electrical (stimulation excitation) after the first light or high energy radiation is irradiated. Although it is a phosphor showing stimulated emission corresponding to the dose of radiation,
From a practical point of view, it is preferably a phosphor that shows stimulated emission by excitation light of 500 nm or more, and particularly a phosphor having a high response speed of stimulated emission to excitation light. It is more preferable that the phosphor efficiently emits stimulated emission for light in the oscillation wavelength region of the semiconductor laser. Examples of such stimulable phosphors include SrS: Ce, Sm, SrS: Eu, Sm, La ₂ O ₂ S: Eu, Sm and (Zn, C described in U.S. Pat.No. 3,859,527.
d) A phosphor represented by S: Mn, X (where X is a halogen) can be mentioned. Further, the general formula described in JP-A-55-12143 is (Ba ₁ -x-yMgxCay) FX: eEu ²⁺ (where X is at least one of Br and Cl, x,
y and e are 0 <x + y ≦ 0.6, xy ≠ 0 and 10 ⁻⁶ ≦, respectively
It is a number that satisfies the condition of e ≦ 5 × 10 ^-2 . ) Alkaline earth fluorohalide phosphor represented by JP-A-55-121
The general formula described in No. 44 is LnOX: xA (where Ln is at least one of La, Y, Gd and Lu, and X is C
l and / or Br, A is Ce and / or Tb, and x is 0 <x <
Represents a number that satisfies 0.1. ), The general formula described in JP-A-55-12145 is (Ba ₁ -xM ^II x) FX: yA (where M ^II is Mg, Ca, Sr, Zn or Cd). At least one of X, at least one of Cl, Br and I, and A of E
At least one of u, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, and Er, and x and y represent numbers satisfying the conditions of 0 ≦ x ≦ 0.6 and 0 ≦ y ≦ 0.2. ), A phosphor represented by
The general formula described in 55-84389 is BaFX: xCe, yA (where X is at least one of Cl, Br and I, and A is I
It is at least one of n, Tl, Gd, Sm, and Zr, and x and y are 0 <x ≦ 2 × 10 ⁻¹ and 0 <y ≦ 5 × 10 ^{−2, respectively.}
Is. ), The general formula described in JP-A-55-160078 is M ^II FX xA: yLn (where M ^II is at least Mg, Ca, Ba, Sr, Zn and Cd). A, BeO, MgO, CaO, SrO, BaO, ZnO, Al ₂ O ₃ , Y ₂ O ₃ , La ₂
O ₃ , In ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , GeO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and T
At least one of hO ₂ , Ln is Eu, Tb, Ce, Tm, Dy, Pr, H
o, Nd, Yb, Er, Sm and at least one of Gd, X is at least one of Cl, Br and I,
x and y are 5 × 10 ⁻⁵ ≦ x ≦ 0.5 and 0 <y ≦ 0.2, respectively.
Is a number that satisfies the following condition. ) Rare earth element activated divalent metal fluorohalide phosphor, JP-A-57-148285
General formula xM ₃ (PO ₄ ) ₂ · NX ₂ : yA M ₃ (PO ₄ ) ₂ : yA (where M and N are respectively Mg, Ca, Sr, Ba, At least one of Zn and Cd, X is at least one of F, Cl, Br and I, A is Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Sb, Tl,
Represents at least one of Mn and Sn. Further, x and y are numbers satisfying the conditions of 0 <x ≦ 6 and 0 <y ≦ 1. ), A phosphor represented by the general formula nReX ₃ · mAX ′ ₂ : xEu nReX ₃ · mAX ′ ₂ : xEu, ySm (wherein Re is at least one of La, Gd, Y and Lu, A Is an alkaline earth metal, at least one of Ba, Sr and Ca, and X and X ′ are at least one of F, Cl and Br. X and y are 1 × 10 ⁻⁴ <x <3 × 10. ^-1 , 1 x 10 ^-4 <y
It is a number that satisfies the condition <1 × 10 ^-1 , and n / m is 1 × 10 ^-3
The condition <n / m <7 × 10 ^{-1 is} satisfied. Phosphor represented by), and the following general formula ^{M I X · aM II X '} 2 · bM III X "3: cA ( where, M ^I at least one alkali is that Li, Na, K, selected from Rb and Cs Metal, M ^II is Be, Mg, Ca, Sr, Ba, Zn, C
It is at least one divalent metal selected from d, Cu and Ni. M ^III is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
It is at least one trivalent metal selected from r, Tm, Yd, Lu, Al, Ga and In. X, X'and X "are at least one halogen selected from F, Cl, Br and I. A is Eu, Tb,
Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and
It is at least one metal selected from Mg.

Further, a is a numerical value in the range of 0 ≦ a <0.5, and b is 0 ≦
The value is in the range of b <0.5, and the value of c is in the range of 0 <c <0.2. ) Alkali halide phosphors represented by). In particular, among the stimulable phosphors, the alkaline earth fluorohalide-based phosphor and the alkali halide-based phosphor have a high response speed of stimulated emission to excitation light, and the oscillation wavelength region of the semiconductor laser is also high. Matching with is preferable.

However, the stimulable phosphor used in the radiation image conversion panel is not limited to the above-mentioned phosphor, and a phosphor that exhibits stimulated emission when irradiated with stimulated excitation light after irradiation with radiation. Any phosphor may be used as long as it is a phosphor.

〔Example〕

 Next, the method of the present invention will be described in detail with reference to Examples.

The radiation image information recording apparatus includes a radiation source 10 as shown in FIG.
The radiation image information is accumulated and recorded in the conversion panel 103 by irradiating the radiation image information conversion panel (hereinafter referred to as the conversion panel) 103 with the radiation emitted from 1 through the subject 102. The radiation image information stored and recorded in the conversion panel 103 is read by the radiation image reading device. The radiation image reading apparatus includes a light source 201 for generating excitation light as shown in FIG. 2, and the light source 201 is driven by a driver circuit 202. The beam generated from the light source 201 reaches the deflector 207 via the filter 203, the split mirror 204, the beam optical system 205, and the mirror 206. The deflector 207 comprises a galvanometer mirror driven by a deflector driver 208 to deflect the beam into the scan area at a constant angle. The deflected beam is adjusted by the fθ lens 209 so as to have a constant speed on the scanning line, and the conversion panel 103 in which the image information passing through the subject 102 through the mirror 210 is accumulated and recorded.
Scan the top in the direction of arrow a. At the same time, the conversion panel 103 is moved in the sub-scanning direction (direction of arrow b) by an appropriate moving means, and the entire surface is scanned. The stimulated emission emitted from the image conversion panel 103, which is scanned by the beam, is condensed by a condenser 212, passes through a filter 213, and reaches a photoelectric converter 214 such as a photomultiplier tube, where an analog electric signal is output. (Image signal)
Is converted to. A power source 215 supplies a high voltage to the photomultiplier tube. The image signal output as a current from the photomultiplier tube is voltage-amplified through the current-voltage conversion amplifier 216, and further the emission intensity signal is converted into an image density signal Log
After passing through the converter 217 and the sample hold circuit 218, it is converted into a digital signal by the A / D converter 219 and stored in the memory 220. This memory 220 is a CPU 22 that performs digital calculation.
1, the CPU 221 can be connected via an interface 222 to an external device, such as a large computer for storing and processing data, a mini computer, a CRT display device for outputting an image, various hard copy creation devices, etc. The data stored in the memory 220 can be calculated and transferred. 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, He-Ne laser, He-Cd. Laser, Ar
Various lasers such as ion laser, Kr ion laser, N laser, YAG laser and its second harmonic, ruby laser can be used. Therefore, when reading the radiation image information, the subject
Compress the dynamic range of the image information passing through 102.
This dynamic range compression is performed by first applying weak excitation light to the conversion panel 103 in which the image information is stored and recorded, before the main reading, to locally change the intensity of radiation at the time of recording, that is, a portion that is easily transmitted and is difficult to be transmitted. The part is detected and stored in the calculation storage unit 105. After that, light source 2
The output of 01 is increased to irradiate the conversion panel 103 with strong excitation light, and the driver 202 of the light source 201 is driven through the controller 109 based on the information from the arithmetic storage unit 105 to modulate the intensity of excitation light. Done by. For example, if the data when reading the recorded image by applying weak excitation light to the conversion panel 103 as shown by the line aa 'in FIG. 3 (I) shows the curve b as shown in FIG. By modulating the excitation light intensity at this time as shown by the curve b ′ in FIG. 3 (III), the dynamic range of the image information is compressed as shown by the curve b ″ in FIG. 4 (IV).

In the above, when compensating for the portion of the subject 102 having a low radiation transmittance, the necessary image information will be lost if it is corrected in all the spatial frequency regions, so 0.2 lp / mm
Below, it is necessary to compensate only in the region of preferably 0.1 lp / mm or less. That is, since the radiation image is formed by a slight difference in the amount of transmission between the part of the subject 102 where the radiation easily passes and the part where the radiation does not easily pass, the radiation image is compensated in all spatial frequency regions and the difference in the amount of transmission is eliminated. Since it becomes impossible to create an image, it is necessary to make compensation between large structures such as the heart and lungs and the spine and lungs. As a method for detecting only signals in such a low spatial frequency region, the detectors may be arranged roughly from the beginning and the spatial resolution may be set low, but the detectors may be arranged finely and averaged once for the detected signal. It can be said that the method of applying the conversion processing (filtering) is more preferable.

In addition, this invention (a) irradiates the subject 102 with radiation,
After detecting the spatial change of the radiation, (b) conversion panel
Take the main shot at 103. Thereafter, when the image information stored and recorded in the conversion panel (c) is read, the radiation image information may be read while modulating the excitation light intensity based on the information (a). In this case, (a)
Is detected by scanning the line detector 104 on the opposite side of the subject 102 which is irradiated with the radiation from the radiation source 101 as shown in FIG. 4 (I), and the detection result is stored in the arithmetic storage unit 105. When the radiation fan beam generator is used as the radiation source 101 as shown in FIG. 2 (II), the scan of the line detector 104 is synchronized with the fan beam emitted from this. Also,
As shown in (III) of the figure, a radiation image intensifier 106 is used in place of the line detector 104, by which the image information of the subject 102 is amplified and photographed by the television camera 107 to detect a strong portion and a weak portion of the image information. Then, it may be stored in the calculation storage unit 105. The radiation for this detection may be weak, and the line detector 104 and the television camera 107 may have low spatial resolution.

FIG. 5 shows the case where the conversion panel 103 is irradiated with the radiation passing through the subject 102 and the image information thereof is recorded, and at the same time, the image information is read. The intensity of the excitation light is modulated simultaneously based on the detection information. That is, the subject 102 is erected on the front surface of the conversion panel 103 from the beginning, and the conversion panel 103 is scanned together with the subject 102 by the slit-shaped fan beam generated by the radiation source 101. Simultaneously with this, a line detector 104 similar to those shown in FIGS. 4 (I) and (II) installed behind the conversion panel 103 is interlocked to detect a spatial change in radiation (a site that easily transmits and a site that does not easily transmit). This is immediately fed back to the arithmetic storage unit 105, the driver 202 of the light source 201 is driven via the controller 109, the excitation light intensity is modulated, and the image information can be read.

FIGS. 6 (I) to (III) show an example in which the detection of the recording state of the conversion panel 103 and the scan during the main reading are alternately performed. In the case of FIG. 1I, first, the conversion panel 103 in which the image information is stored and recorded is subjected to a sub-scan S ₁ with weak excitation light,
After detecting a spatial change in the intensity of the radiation passing through the subject 102, that is, a part that is easily transmitted and a part that is not easily transmitted, the main scan S _{2 is performed} while changing the excitation light intensity on the same line with strong excitation light based on the information. Then, the image information is read, and this is repeated. In the case of (II) in the figure, the sub-scan S ₁ is inserted between the main scan S ₂ and the main scan S ₂ .
A spatial change in the intensity of radiation passing through the subject 102 is detected during the sub-scan S _1, and image information is read while changing the excitation light intensity during the main scan S ₂ based on that information, and this is repeated. is there. In the case of (III) in the figure, the sub scan S ₁ is performed after the main scan S ₂
This is a method of detecting a spatial change in the radiation intensity at S ₁ and reading the radiation image information while changing the excitation light intensity at the main scan S ₂ based on the information, and repeating this. All of these (I) to (III) are sub-scan S ₁
The excitation light intensity of is preferably weaker than that of the main scan S ₂ . Further, the sub-scan S ₁ may have a higher scan speed than the main scan S ₂ .

Although not particularly shown in the drawing, (a) after digitizing once and storing in a memory, a region where radiation is difficult to pass through is detected from this image information, and (b) image information data is corrected based on the information. It is also possible to do so.

Further, although an example in which the stimulable phosphor is used as the conversion panel 103 has been shown in the above-mentioned embodiment, the present invention is not limited to this. For example, it is needless to say that it can be applied when a photoconductor is used and an electrostatic latent image is recorded on the photoconductor. [Effects of the Invention] According to the configuration of the present invention, even if there is a site where radiation is easily transmitted and a site where radiation is difficult to be mixed in one image, the dynamic range is compressed by each region, It became possible to clearly describe all parts. Therefore, it is possible to eliminate problems such as white spots that occur when the optical density becomes too low and black that occurs when the optical density becomes too high depending on the part. In addition, it can be read in the state where the S / N ratio is improved, and it has an excellent effect that a clear depiction can be made over the entire surface of the subject.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an example of a recording apparatus for carrying out the method of the present invention, FIG. 2 is a schematic perspective view of a reading apparatus, and FIGS. 3 (I) to (IV) are image information. Explanatory diagram showing the compression process of the dynamic range, FIGS. 4 (I) to (III) are explanatory diagrams showing the means for detecting the spatial change of the radiation of the subject, and FIG.
The figure shows a schematic perspective view of an example in which recording and reading are simultaneously performed,
FIG. 7 is an explanatory diagram in the case where the main scan and the sub-scan are performed alternately, and FIG. 7 is a diagram showing the relationship between the dynamic range of the panel and the subject, the signal intensity, and the image density. 101 …… Radiation source 102 …… Subject 103 …… Storage type radiation image conversion panel 104 …… Line detector 105 …… Computing and recording unit 109 …… Controller 201 …… Excitation light source 202 …… Driver circuit 212 …… Concentrator 214 …… Photoelectric converter such as photomultiplier tube 216 …… Current-voltage conversion amplifier 219 …… A / D converter 220 …… Memory 221 …… CPU 222 …… Interface

Claims (4)

[Claims] 1. A method of reading radiation image information, which is read as an electric signal by irradiating a laser beam with radiation image information recorded on a radiation image conversion panel by being irradiated with radiation transmitted through an object, wherein the radiation image conversion is performed. A method of reading radiation image information, characterized in that the intensity of the laser light is modulated to compress the dynamic range on the basis of the spatial change of the radiation intensity applied to the panel. 2. The position change of the radiation intensity is detected by shining a weak laser beam on the conversion panel on which the image information is recorded prior to the main reading. A method for reading the described radiation image information. 3. A method for reading radiation image information according to claim 1, wherein the detecting means for detecting the radiation that has passed through the subject detects the spatial change in the radiation intensity. 4. The method according to claim 1, wherein the spatial change of the radiation intensity transmitted through the object and the modulation of the laser light intensity based on the detected information are simultaneously performed. The method for reading radiation image information according to item 1 or 2.