JPS5944339B2 - Radiographic image conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation image conversion method, and more particularly to a radiation image conversion method using a photostimulable phosphor.

Conventionally, so-called radiography using silver salts has been used to obtain radiographic images, but in recent years, due to problems such as depletion of silver resources on a global scale, methods of imaging radiographic images without using silver salts have been developed. I became desired. As an alternative to the radiographic method described above, the radiation transmitted through the object is absorbed by a phosphor, and then this phosphor is excited with a certain type of energy to release the radiation energy stored in the phosphor. A method has been considered in which the fluorescent light is emitted and the fluorescent light is detected and imaged.

As a specific method, a method has been proposed in which a thermally fluorescent phosphor is used as the phosphor and thermal energy is used as the excitation energy to convert a radiation image (UK Patent No. 1462).
No. 769 and JP-A-51-29889).

This conversion method uses a panel with a thermofluorescent phosphor layer formed on a support, and the thermofluorescent phosphor layer of this panel absorbs the radiation that has passed through the subject, responding to the intensity of the radiation. By accumulating radiation energy and then heating this thermofluorescent phosphor layer, the accumulated radiation energy is extracted as a light signal, and an image is obtained by varying the intensity of this light. However, since this method heats the accumulated radiation energy when converting it into a light signal, it is absolutely necessary that the panel be heat resistant and not deformed or altered by heat. There are major restrictions on the materials of the thermally fluorescent phosphor layer and the support. As described above, the radiation image conversion method using a thermofluorescent phosphor as a phosphor and using thermal energy as excitation energy has major drawbacks in terms of application. On the other hand, a radiation image conversion method using one or both of visible light and infrared rays as excitation energy is also known (US Pat. No. 3,859,527).

This method does not require heating when converting the accumulated radiation energy into optical signals, unlike the method described by Dojo, and therefore the panel does not need to be heat resistant, which makes it more preferable. It can be said to be a radiation image conversion method. However, the phosphors used in this method are only cerium and samarium activated strontium sulfide phosphors (SrS).
:Ce, Sm), europium and samarium activated strontium sulfide phosphor (SrS:Eu,.Sm), europium and samarium activated lanthanum oxysulfide phosphor (La2O2S:Eu.Sm), manganese and halogen activated sulfide Zinc/cadmium phosphor [(Zn,.Cd)
S:Mn. X, where X is a halogen], and the sensitivity of methods using these fluorophores is extremely low, and improvements in sensitivity are desired from a practical standpoint. It is rare. In the present invention, radiation transmitted through an object is absorbed by a phosphor, and then this phosphor is excited with electromagnetic waves, which are either visible light or infrared rays, or both, so that the radiation energy stored in the phosphor is absorbed. It is an object of the present invention to provide a practical radiation image conversion method that has extremely high sensitivity and detects the fluorescence.

In order to achieve the above object, the present inventors have been searching for phosphors that can be used in the above method.

As a result, the general formula where Ln is LasY, . Gd and L
at least one of u, X is C1 and/or Br
, A represents Ce and/or Tb, and X represents a number satisfying O<x<0.1.

It was discovered that the above method can be extremely sensitive if one or more of the fluorescers contained in the rare earth-activated lanthanum oxyhalide phosphor represented by is used, and the present invention has been completed. I came to the conclusion.

In the radiation image conversion method of the present invention, the radiation that has passed through the object is absorbed by a phosphor that is one or more of the phosphors included in the LnOX:XA phosphor, and then this phosphor is Exciting with electromagnetic waves that are one or both of long-wavelength visible light of 500 nm or more and infrared rays, the radiation energy accumulated in this phosphor is released as fluorescence,
It is characterized by detecting this fluorescent light.

In the general formula, Ln is particularly preferably La. The radiation image conversion method of the present invention will be specifically explained using schematic diagrams.

In FIG. 1, 11 is a radiation generating device, 12 is a subject,
13 is a radiation image conversion panel having a visible to infrared stimulable phosphor layer; 14 is a light source as an excitation source for emitting a latent radiation image of the radiation image conversion panel as fluorescent light; 15
16 is a device for reproducing the photoelectric conversion signal detected by 15 as an image; 17 is a device for displaying the reproduced image; 18 is a light source 14 This is a filter for cutting reflected light from the radiation image conversion panel 13 and transmitting only light emitted from the radiation image conversion panel 13. From 15 onwards, it is sufficient that the optical information from 13 can be reproduced as an image in some form, and is not limited to the above.

As shown in FIG. 1, when a subject 12 is placed between the radiation generating device 11 and the radiation image conversion panel 13 and irradiated with radiation, the radiation passes through each part of the subject 12 as the radiation transmittance changes. , the transmitted image (that is, the image of the intensity of the radiation) is incident on the radiation image conversion panel 13.

This incident transmitted image is absorbed by the phosphor layer of the radiation image conversion panel 13, thereby generating a number of electrons or holes proportional to the amount of radiation absorbed in the phosphor layer. Accumulated at the trap level of the body. That is, an accumulated radiographic image (a kind of latent image) is formed. This latent image is then excited with light energy to become visible. i.e. 50
The phosphorescent layer is irradiated with electromagnetic waves, which are long-wavelength visible light of 0 nm or more and/or infrared rays, by the light source 14 to expel the electrons or holes accumulated at the trap level, and the accumulated image is emitted as fluorescent light. The intensity of this emitted fluorescent light is proportional to the number of accumulated electrons or holes, that is, the intensity of the radiation energy absorbed by the phosphor layer of the radiation image conversion panel 13, and this optical signal is Convert it into an electrical signal with a Q photoelectric conversion device 15 such as a multiplier tube,
The image reproduction device 16 reproduces the image as an image, and the image display device 17 displays this image. Next, the radiation image conversion panel used in the radiation image conversion method of the present invention and the excitation light source for emitting the accumulated image as fluorescence will be explained in detail.

The structure of the radiation image storage panel is comprised of a support 21 and a phosphor layer 22 formed on one side of the support 21, as shown in FIG. 2-a.

It goes without saying that this phosphor layer 22 is made of one or more phosphors included in the LnOX:XA phosphor. LnOX: The matrix of phosphor (LnO
approximately 10-6 to 10-1, especially 10-6 to X)
When the concentration is 5×10 −3 gram atoms, the stimulation intensity becomes extremely strong, and particularly efficient radiation image conversion can be achieved by using the phosphor layer of these radiation image conversion panels. Next, an example of a method for manufacturing a radiation image conversion panel will be shown below. First, 8 parts by weight of the phosphor and 1 part by weight of nitrified cotton were mixed in a solvent (acetone,
mixture of ethyl acetate and butyl acetate),
A coating solution having a viscosity of approximately 50 centistokes is prepared. Next, this coating solution was uniformly applied onto a horizontally placed polyethylene terephthalate film (support) and allowed to stand overnight to air dry to form a phosphor layer of approximately 300 μm, which was then used as a radiation image conversion panel. do. For example, a transparent glass plate or a thin metal plate made of aluminum or the like may be used as the support. The radiation image conversion panel is made of two transparent substrates 23, 2 such as glass plates as shown in FIG. 2-b.
A phosphor layer 22 having an arbitrary thickness may be obtained by sandwiching a phosphor between the two layers, and the periphery of the phosphor layer 22 may be sealed.

In the radiation image conversion method of the present invention, the light source for the light energy that excites the phosphor layer of the radiation image conversion panel described above has a band spectral distribution in one or both of the long wavelength visible region of 500 nm or more and the infrared region. In addition to the light source that emits light, He-Ne laser light (633 nm)
, YAG laser light (1064 nm), ruby laser light (694 nm), etc., are used.

Especially when using laser light, high excitation energy can be obtained. Among laser beams, it is particularly preferable to use He--Ne laser beam. FIG. 3 shows LaOBr:Ce(10-4) and Tb(10-4) used in the phosphor layer of the radiation image conversion panel in the radiation image conversion method of the present invention.
4) After irradiating the phosphor with X-rays at a tube voltage of 80K, it shows the change in the intensity of the fluorescent light emitted when optical energy of different wavelengths is applied (so-called excitation spectrum).
As is clear from FIG. 3, LaOBr:Ce. In the case of Tb fluorophores, the excitable wavelength range is in the range of 500 to 900 nm, with the optimum excitation wavelength range being particularly 500 to 700 nm.

The excitable wavelength range of the LnOX:XA phosphor used in the method of the present invention varies slightly depending on the composition of the phosphor, but is approximately between 500 and 900 nm, and the optimum excitation wavelength range is between 500 and 700 nm. It is. In the method of the present invention, one or both of long-wavelength visible light of 500 nm or more and infrared rays can be used as an excitation light source for emitting the radiation energy accumulated in the phosphor layer as fluorescent light. The area trap is shallow, the fading phenomenon is significant, and therefore the information storage period is short, which is not very desirable in practice. For example, in order to obtain an image, the phosphor layer of the panel is often scanned and excited with infrared rays, and the emitted light is electrically processed. Because it takes time, there is a risk that there will be a difference between the first read value and the last read value even if the same radiation dose is irradiated. For these reasons, it is more desirable for the phosphor used in the radiation image conversion method of the present invention to have a deep trap and be efficiently excited by higher energy light, that is, the shortest wavelength Q light possible. LnOX used in the method of the present invention:
The XA phosphor has an optimal excitation wavelength range in the visible light region of 500 to 700 nm, and therefore has little fading and a high ability to store the radiation latent image accumulated in the phosphor layer. In addition, when exciting with light energy in the method of the present invention, it is necessary to separate the reflected light of the excitation light and the fluorescent light emitted from the phosphor layer, and the fact that the fluorescent light emitted from the phosphor layer is received. Because photoelectric converters generally have high sensitivity to light energy with a short wavelength of 600 nm or less, it is desirable that the fluorescent light emitted from the phosphor layer has a spectral distribution in the short wavelength region as much as possible. , the phosphor used in the method of the present invention also satisfies this condition. That is, LnOX used in the method of the present invention:
All XA phosphors emit light with a main peak at 500 nm or less, which makes it easy to separate from the excitation light and closely matches the spectral sensitivity of the photoreceiver, allowing efficient light reception and increasing the sensitivity of the image receiving system. I can do it. Figure 4 shows LaO
Br: Ce. As an example, an emission spectrum is shown when a Tb phosphor is irradiated with X-rays at a tube voltage of 80 K and then excited with a single beam of light from a He-Ne laser.

Table 1 shows the sensitivity of the radiation image conversion method of the present invention in SrS:E
u. This figure shows a comparison with the sensitivity of a conventionally known radiation image conversion method using an Sm phosphor.

In Table 1, the sensitivity is 80% for the tube voltage on the radiation image conversion panel.
KVf) After irradiating X-rays, this is excited with He-Nep laser light, and the fluorescence emitted from the phosphor layer is received by a photoreceiver (photomultiplier tube with spectral sensitivity S-5). It is expressed as the emission intensity of SrS:Eu. The sensitivity is expressed as a relative value with the sensitivity of a conventionally known method using an Sm phosphor being set to 1.

As is clear from Table 1 above, the radiation image conversion method (washing 2 to 5) of the present invention is different from the conventional radiation image conversion method (washing 1).
) is significantly more sensitive than

As explained above, the present invention provides a radiation image conversion method with extremely high sensitivity, and has great industrial utility value as a method that replaces conventional radiographic methods.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of the radiation image conversion method of the present invention. 11...Radiation generator, 12...Subject, 13...Radiation image conversion panel, 14...
...Light source, 15...Photoelectric conversion device, 16.
...Image reproduction device, 17...Image display device, 18...Filter 1. FIGS. 2-a and 2-b are cross-sectional views of a radiation image conversion panel used in the radiation image conversion method of the present invention. 21...
... Support, 22 ... Fluorescent layer, 23, 24
...Transparent support plate. Figure 3 shows LaO used in the radiation image conversion method of the present invention.
Br: Ce, . This is an excitation spectrum of Tb phosphor.

Claims (1)

[Claims] 1. The radiation transmitted through the object is absorbed by at least one of the phosphors represented by the following general formula, and then this phosphor is selected from long wavelength visible light of 500 nm or more and infrared rays. 1. A radiation image conversion method characterized in that a phosphor is excited by electromagnetic waves to cause a phosphor to emit accumulated radiation energy as fluorescence, and detect this fluorescence. General formula LnOX:xA where Ln is at least one of La, Y, Gd and Lu, X is Cl and/or Br, A is Ce and/or Tb
, x represents a number satisfying 0<x<0.1. 2. The radiation image conversion method according to claim 1, wherein the wavelength of the electromagnetic wave is 900 nm or less. 3. The radiation image conversion method according to claim 2, wherein the electromagnetic wave is a laser beam. 4. The radiation image conversion method according to claim 3, wherein the laser beam is a He-Ne laser beam.