JPS60108836A - Radiation image reading method - Google Patents

Abstract

PURPOSE:To lessen the influence by the attenuation of the image recorded on a phosphor and to increase an SN ratio by using the 2nd higher harmonic of an Nd<3+>: YAG laser as excitation light and detecting the light having a specific wavelength region out of the light emitted from the phosphor with a photodetector thereby increasing the speed for reading the image. CONSTITUTION:The laser light of 1,064nm radiated from a YAG laser light source 14 is made incident via a filter 15 to cut light on a short wavelength side to a non-linear optical crystal 16 such as KDP or the like. The resultant 2nd higher harmonic of 532nm is made incident through a half mirror 17 to a panel 10. The excitation light scans a phosphor layer 12 as a flying spot. The excited phosphor radiates the radiation energy accumulated imagewise thereon in the form of accelerated fluorescence of 300-500nm. The accelerated fluorescence is reflected by the mirror 17 and after the mixed light or stray light out of the region is cut from said light by a filter 19, the fluorescence enters a photodetector 20, by which the fluorescence is detected and measured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading method in a radiation imaging system.
This invention relates to an image reading method in a radiographic imaging system in which a radiographic image is recorded on a fluorescent material (referred to as a "phosphor"), a radiographic image is read out and reproduced, and it is recorded as an R-ray image on a recording material. .

(Prior art) Conventionally, so-called radiography using silver salt has been used to obtain radiographic images, but in recent years, due to problems such as the depletion of silver resources on a global scale, radiographic images have been developed without using silver salt. A method of imaging has become desirable.

As an alternative to the above-mentioned radiographic method, the radiation transmitted through the object is absorbed by a phosphor, and the phosphor is then excited with a certain energy to extract the radiation accumulated in the phosphor. A method has been considered in which energy is emitted as fluorescent light, and this fluorescent light is detected and imaged. As a specific method, for example, British Patent No. 1,462,769 and Japanese Patent Application Laid-Open No. 51-29889 disclose a method of converting a radiation image by using a thermal phosphor as a phosphor and using thermal energy as excitation energy. It has been proposed. This conversion method uses a panel formed with a thermal phosphor layer χ on a support.
The thermal phosphor layer of this panel absorbs the radiation that has passed through the subject and accumulates radiation energy corresponding to the intensity of the radiation.Then, by heating this thermal phosphor layer, the accumulated radiation energy is released into the light. The image is obtained by extracting the light as a signal and depending on the intensity of this light.

On the other hand, for example, US Pat. No. 3,859,527 and Japanese Patent Application Laid-Open No. 12144/1983 propose a radiation image conversion method using electromagnetic radiation selected from visible light and infrared rays as excitation energy.

Furthermore, in connection with this, JP-A-355-12429 discloses a method for improving the S/N ratio, in which a phosphor is excited using light in a wavelength range of 600 to 700 nm as the excitation light, and the fluorophore is emitted. A 51C method has been proposed in which a photodetector receives light in the wavelength range of 300 to 500 nm of the body's emitted light. This method does not require heating when converting the accumulated radiation energy into a light signal unlike the method using a thermal phosphor flame described above, so the panel does not need to be heat resistant (this method does not require heating). From this point of view, it can be said that this method is a more preferable radiation image conversion method.

However, as excitation energy, 600-700 nm
The method using light in the wavelength range uses He-N as an excitation light source.
Even when e-laser light is used, the excitation energy is insufficient, and high-speed scanning is difficult when scanning a panel (hereinafter simply referred to as a panel) in which a stimulable phosphor layer is formed on a support with excitation light. Not only that, but furthermore, the reduction of the radiation m, it to the subject when radiation energy is applied imagewise to the panel cannot be said to be sufficient. Also 600-7
The traps in the region excited by 00 nm are relatively shallow and are greatly affected by the fading phenomenon, making it difficult to preserve clear iat for a long period of time. Another 600~
When using light in the wavelength range of 700 nm as excitation light,
The rise and fall of the excited fluorescent light lag behind the rise and fall of the excitation light. This is also one of the reasons that prevents an increase in the scanning speed when scanning with a panel excitation light.

In addition, excitation of gas lasers such as He-Ne lasers is caused by discharge, but when the discharge light is detected by a photodetector, it is difficult to separate it from the emitted light from the phosphor, resulting in an SN. This is one cause of lowering the ratio.

(Object of the Invention) In view of the above-mentioned problems, the present invention provides a high-speed pulse I12+ of excitation light.
It is an object of the present invention to provide a practical radiation image reading method that is less affected by image decay and has a high 13N ratio.

(Structure of the Invention) The purpose of the present invention is to read the radiographic image recorded on the phosphor by scanning the phosphor with excitation light and detecting the emitted light from each point with a photodetector. In the method, the excitation light is 532 nm (7) s, s+ :Y
A phosphor is excited using the second harmonic of YAG laser (hereinafter referred to as a single YAG laser), and light in the wavelength range of 300 to 500 nrn is emitted from the phosphor. We have discovered what can be achieved by a radiation image reading method characterized by receiving light with a photodetector.

Here, the above-mentioned YAG laser refers to Y, A, and A as base material crystals.
This is a laser that uses IBO, (yttrium aluminum garnet) and contains it as trivalent Na3+Y active ions. Originally, YAG laser was 1064
Although it is a laser with an oscillation wavelength (fundamental wave) of nm,
A second harmonic is generated by a nonlinear optical effect, and green light of 532 nm can be obtained. A typical nonlinear optical crystal for obtaining this second harmonic is KDP (K)T! P
04 ), or BNN (BF12NaNb601
5) etc.

In the present invention, a phosphor refers to a phosphor that, after being irradiated with the first light or high-energy radiation, is stimulated by photogravitational, thermal, mechanical, chemical, or electrical stimulation. A phosphor that exhibits %1F and %1F, which re-emits light corresponding to the amount of irradiation. Light here includes visible light, ultraviolet light, and infrared light among electromagnetic radiation, and high-energy radiation includes X-rays, gamma rays,
Beta ill'! , 7 Lua Includes y-rays, neutron beams, etc.

Next, the present invention will be explained in more detail.

Figure 1 shows the excitation light power and the emission from the phosphor)'(: )Y
; It shows the relationship between jUI and the light intensity of excited stimulated fluorescence. As you can see from this same example, fIi71+ notes-
It can be seen that there is a proportional relationship between - and phosphorescence.

That is, in such a phosphor, the emission intensity increases by increasing the laser power. For this reason, for example, when reading a radiation image on a panel, it is necessary to
If you need faster scanning speed, double the laser power and you'll get IIi! It is possible to achieve a scanning speed of J element 5 μsec, which doubles the readout speed, ie, halves the time required to obtain an actual image from a latent image.

The output of a YAG laser is highly stable and extremely large. For example, when continuous oscillation is used, if a rod with a diameter of about 1OcIrL is used, it will produce an ioo
An output of w'f or more can be obtained. For this reason YA
Approximately 4 for the fundamental wave (1064 am) output of the G laser
The second harmonic output obtained with ~10% efficiency is also He-
Even when compared with No laser (maximum output of about 50 mW) VC, it is sufficiently large. Therefore, the photostimulation fluorescence when a YAG laser is used as the excitation light is stronger than when a H@-N@ laser is used. For example, when the 200 mW second harmonic of a YAG laser is used as the excitation light 2) mW He
The intensity of light emitted from the phosphor is approximately 6 times higher than when a -Ne laser is used as excitation light.

In other words, the maximum power of the YAG laser is He-Ne
It is much larger than a laser, and the stimulated fluorescence from the panel can be obtained to a very intense range. Therefore, high-speed scanning is possible when scanning the panel with excitation light.

Furthermore, since the power of the excitation light and the emission intensity are in a proportional relationship, it is possible to reduce the radiation dose by increasing the laser power. Being able to reduce the amount of radiation that irradiates the human body with n<+ is extremely useful for reducing radiation damage to the human body.

Furthermore, when the same panel is used repeatedly, if the intensity of the excitation light used to release the accumulated radiation energy as fluorescence is weak, or if the wavelength of the excitation light is inappropriate, the radiation energy will be completely absorbed by the panel. It is not deleted from the list, and some of it remains. This residual radiation energy is added as noise in subsequent radiation image conversion, and the image quality of the obtained image is significantly deteriorated. Therefore, before the step of irradiating the panel with radiation #I, it is necessary to remove the radiation energy remaining in the panel and causing noise with light included in the excitation light wavelength range. However, when using a high-power excitation light such as a YAG laser, even if the panel is used repeatedly, the radiation energy that causes noise is already sufficiently erased and does not remain. Therefore, it is not necessary to irradiate excitation light before irradiating radiation, and image quality can be maintained at a good pressure.

Figure 2 shows how the amount of decay (1)eea7) of the extractable energy accumulated in the phosphor changes depending on the wavelength of excitation light. Based on the stimulated fluorescence that is excited and emitted immediately after irradiation with radiation, the luminescence intensity declines when the product is left in the dark for several hours and then excited and emitted with excitation light of a predetermined wavelength. I'll show you how things are going. 532 as excitation light
Surprisingly, when using the second harmonic of a YAG laser with a wavelength of 600 to 800 nm, the apparent decrease in the emission intensity is smaller than when using light in the wavelength range of 600 to 800 nm.
The decline almost disappears in about 3 hours. In other words, the efficiency of extracting the energy stored in the phosphor is high, and the degenerative phenomenon is greatly improved in practical use. Therefore, if the second harmonic of a YAG laser is used as the excitation light, the recording on the phosphor can be stored for a long period of time in practice.

In addition, the decrease in the amount of energy decline means that Y
The second harmonic of the AG laser is on the shorter wavelength side, that is, on the higher energy side, than that of the lie-Ne laser, etc., and the H@-N
This is related to the fact that long-wavelength light such as e-laser excites traps that are difficult to excite.
The total amount of light emitted when excited by the second high n wave of a YAG laser is greater than when excited by light with a longer wavelength such as a He-Ne laser. Therefore, the sensitivity is brighter than using the second high frequency wave of the YAG laser,
This is also useful for reducing the amount of X-rays irradiated to the human body.

FIG. 3 shows the response when excitation light whose intensity changes in a rectangular waveform indicated by a dotted line is compared.

Curve 1iA shown by the solid line shows the emission intensity when the phosphor is excited with He-Ne laser light, and curve B shows the emission intensity when the same phosphor is excited with the second harmonic of a YAG laser. shows. As can be seen from this graph, when irradiating He-No laser light with a pulse width of about 8 μ8 as excitation light,
The rise and fall of phosphorescence is about 5 to 6 microns. However, when the second harmonic of a YAG laser is used as the excitation light, the rise and fall times are about 1 μ8, which deteriorates the responsiveness. For this reason, for example, a panel with a spot diameter of 10
When scanning with a laser beam of about 0 μm, H@-Ne
With a laser, it is difficult to scan at a scanning speed of 5 μ6 or less per pixel, but this is possible with a YAG laser.

Regarding the distribution of the reflected light of the excitation light and the stimulated fluorescence, we set the stimulated fluorescence to the armored wavelength side and the excitation light to the long wavelength side, and only the wavelength range of the stimulated fluorescence is placed in front of the photodetector. By providing a filter that allows the light to pass through, it is possible to prevent the S/N ratio from decreasing.

The wavelength of photostimulated light of 300 to 500 nm can be obtained by selecting a phosphor that emits light in this wavelength range or by using a phosphor having a peak in this wavelength range. However, even if the phosphor emits light in the above wavelength range, if the photodetector also measures light outside the wavelength range, the SIN ratio will be extremely reduced.

For this purpose, a photodetector with sensitivity at least in the wavelength range of 300 to 500 nm is used, and σ) a luminous film is placed in front of the photodetector.
It is necessary to provide a filter that passes only the fluorescent wavelength range.

Examples of the above-mentioned phosphor that emits light in the wavelength range of 300 to 500 nm include 1, for example, BaSO4:Ax (where A is DF,
At least one of Tb and Tm, and X is 0.0
A phosphor represented by 01≦x (1 mol%), MgSO4:Ax (
However, A is either Ho or Say, and 0.
001≦χ×1 mol%. ), SrSO described in JP-A-48-80489
4: Fluorescent substance represented by Ax (where A is at least one of Dy, 'rb and Tm, and X is o, ooi≦X<1 mol%), JP-A-52-30487
Phosphors such as BaO, LiF, MgSO4 and CaFx described in US Pat. No. 3,859,527, SrS:Ce*8m, 8
r8: Eu r Sms La1OtS: Eu
, 8m and t(zn,ca)s :Mn,X (however, X
Examples include fluorophores represented by (herogen). Also,
The general formula is -OLlxslOt: A (where Ml is M
g, Ca.

Sr, Zn, Cd or Ba and A is Co
, 'rb t Eu # Tm HPb l Tl
, BI and Nagi, and X is 0
．． 5≦X≦2.5. ) is an alkaline earth gold silicate-based phosphor. In addition, the general formula is (Bal-1-yBal-1-y FX: eEu”
(However, X is at least one of Br and CI,
! , 7 and e are respectively 0 (x+y≦Q, 6, xy
〆0 and 10-6≦e≦5Xl0-'' is a number that satisfies the following conditions. General formula % Formula %: (Ln is at least one of La, Y, Gd and Lu, X is C7 and/or Br, A is Cs and/or Tb'a?, X is 0(x( A phosphor represented by 0, 1), JP-A-55-1214
The general formula C described in No. 5 is (Bal -XM"X) FX: yA (However, MI
I represents at least one of Mg, Ca, Sr*Zn, and Cd;
A is Ku, Tb, Co
rTm, Dy*Pr, HorNd
, Yb, and Er, and X and y represent values satisfying the conditions of 0≦X≦0.6 and O≦y≦0.2. ), JP-A-55-8
The general formula described in No. 4389 is B milk FX: x
ce.

7A (where X is C), at least one of Br and I, A is In p TI HGd HSm and Z
a phosphor, at least one of The general formula is MlIFX * xA : yLn (where MTl is Mg t Ca I Bal Zn
and at least one of Cd, A is BeOHMg
O* CaOp SrOr BaO#ZnO, Al2O
5r Yt03 r La10s e ItltOs
r 5lot r TIO! +Zr011 G302
At least 1 of r 5nO1l Nb, o, 17112QB and The. Ln is Eu, T
b, Cm r Tm + D)'.

Pr, Ho, Nd, YbtEr,
8m and Gd (both are one type, X and y are 5X10''-1l≦X≦0.5 and 0<y
This is a number that satisfies the condition of ≦0.2. ) Rare earth element-active divalent metal fluorohalide phosphor, general formula [I] or [■) described in JP-A-57-148285, general formula CI) xis (PO4)t'
NX: yA general formula [I[) Ms(PO+)*
: yA (where M and N are Mg, Cm, and Sr, respectively)
, Ba+Zn, and Cd, and X is F, CJ.

Br and 5 of ■ are also at least one type, A is Bu, T
b.

Co, Tml Dy, Pr, Ho,
Nd, Yb, Kr l Sb #TJ,
Represents at least one of Mn and Sn. Also, X
and y is a number that satisfies the conditions x≦6, O≦y≦1.
to).

General formula ([1nR5X5 a mAX2 : xEu General formula (IV) nR@X1 a mAX4 : xEu
@ysm (in the formula, Re is La l Gd l Y +
At least one of Lu, A is an alkaline earth metal,
At least one of Ba, Sr*Ca, X
and X' represents at least one of F, C11, and Br. Also, X and y are 1×io-'<X<3X10
-', I Xl0-'<y< I Xl0-', and n/m is I
(n/m (satisfying the condition 7X10-')) may be used, but the phosphor used in the present invention is not limited thereto.

FIG. 4 shows a filter used in the present invention, for example BG-3.
(manufactured by Spectrofilm) An example of the transmittance spectrum is shown. This filter hardly transmits excitation light of 532 nm, and the emission of stimulated fluorescence and excitation light can be achieved by using this filter. That is,
In the reading stage, the excitation light is not included in the photostimulated fluorescence as 8A1 noise, ・', ゛, and the wavelength range of the excitation light is 8/N compared to the case where the wavelength range is 600 nm or more.
The ratio will not decrease (X,).

Further, excitation of a gas laser such as a He-Ne laser is by discharge, whereas excitation of a solid state laser such as a YAG laser is by light from a xenon lamp or the like. For this reason, He-Ne
When a laser is used as excitation light, this discharge light is mixed into the excitation light in addition to the light oscillated by the laser. This discharge light becomes noise when the photostimulated fluorescence from the phosphor is detected by a photodetector.

In comparison, a YAG laser does not contain this discharge light. Furthermore, when obtaining the second harmonic of a YAG laser, it is possible to cut wavelengths shorter than 1064 nm before entering the laser beam into the nonlinear optical crystal such as the KDP. In this case, the photodetector used to detect the lack of photostimulated fluorescence from the phosphor does not contain light at a sensitive wavelength. Therefore, using the second skin wave of the YAG laser as excitation light also prevents the S/N ratio from decreasing from this point of view.

Furthermore, when a YAG laser is used as pulsed light, it is possible to obtain pulsed light with higher efficiency and a larger output than when using continuous light. The excitation light used in the present invention may be continuous light or pulsed light. .

When using the aforementioned pulsed light, it can also be synchronized with the scan time on the panel.

At this time, the phosphorescence from the phosphor was detected! , ), the above-mentioned filter may be used to separate the excitation light from the reflected light, but a separation method using the delay in light emission as described in Japanese Patent Application No. 57-124744 VC; is particularly effective when synchronized with the time of the excitation light pulse.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 5 shows the radiographic image reproduction/recording step -4'. When X-rays are emitted from a radiation source, such as an X-ray tube, and irradiated onto a human body, the X-rays enter the panel in an imagewise weak pattern. The panel imagewise stores the energy of radiation (X?J) at the trap level of the phosphor (radiation imaging).

Next, the second harmonic spot of the 532 ntn YAG laser scans the panel in which the radiation energy has been accumulated imagewise, and the energy trap is excited to emit light in the wavelength range of 300 to 500 nm. The emitted stimulated fluorescence is detected and measured by a photodetector, such as a photomultiplier tube or a photodiode, which is adjusted to selectively receive light in this wavelength range (radiation image reading).

The output signal from the photodetector is then amplified, filtered and level converted. In order to remove noise and obtain a predetermined resolution through the filtering, signals in a predetermined band or above are cathode-coded.

For example, if a 40 x 40 cr& panel is scanned in about 5 minutes with a 100 μm diameter spot, m per pixel.
Since the time is microseconds, it is sufficient for the increased S band to be 50 kHz, and bands beyond that are cut off.

Further, as a means of reducing noise, a method of integrating the output signal for each pixel or a method of logarithmically converting the output signal to reduce the signal range is used.

The output signal amplified in this way is level-converted (image processing) in order to give good contrast to the observed image portion or improve sharpness.

The output signal (electrical signal) from the photodetector subjected to the above 5VcM control is sent to an optical scanning device such as a drop tube for observation (radiation S image reproduction). Alternatively, the reproduced image is further recorded on a suitable recording material (radiation image recording).

FIG. 6 shows an example of a tank bottom of a panel used in the present invention.

10 is a panel, 11 is a support, and 12 is a phosphor layer coated on the support 11. The panel 10 is generally cut into four or half pieces.

As the support, a synthetic resin sheet such as polyethylene, a thin metal plate such as aluminum, a glass plate, etc. are used, and the thickness can be determined from a practical standpoint. Furthermore, whether it is transparent or opaque, it can be used freely by changing the measurement position of stimulated fluorescence.

As the phosphor to be coated, the above-mentioned phosphor having a stimulated fluorescence wavelength range of 300 to 500 nm is used.

50 pieces of phosphor selected from these together with a binder
Coat to a thickness of ~1000 μm.

Next, the seventh rEI shows the radiation IIH image reading device v. A YAG laser is used as an excitation light source.

A laser beam of 1064 nm emitted from a YAG laser light source 14 enters a nonlinear optical crystal 16 such as KDP through a filter 15 that cuts off light with wavelengths shorter than 1064 nm. The obtained second harmonic of 532 nm passes through the bar 7mi 9-17 and enters the panel 10.

The excitation light scans the phosphor layer 12 as a flying spot, but with current technology it is difficult to make the spot diameter less than 50 μm, and resolution deteriorates if it exceeds 300 pm, so the spot diameter is 50 to 300 μm. It is preferable.

The phosphor excited by the excitation light emits an image @ tr (accumulated radiation energy vaoo~500 nm as a photostimule fluorescence.
The light is reflected by a filter 19 to 300 to cut off any stray light or mixed light outside the 500 nm wavelength range, and enters the original detector to be detected and measured.

The phosphor layer 12 reflects a portion of the excitation light, and since the excitation light is considerably stronger than the stimulated fluorescence, particular care must be taken to completely cut out the reflected light and maintain a good S/N ratio. There must be. In the present invention, by selecting the above-mentioned phosphor 1, it is possible to avoid the overlap of the wavelength spectra of stimulated fluorescence and excitation light, and by using a filter having the above-mentioned transmission wavelength range, the disturbance caused by the excitation light can be reduced. It completely prevents this.

(Effect of the invention) As explained above, in the present invention, as excitation light, 5
The use of the second harmonic of a 32 nm YAG laser has the following effects.

(1) Since the YAG laser has high power, when scanning the panel with excitation light, it can scan at high speed, improving readout speed.

(2) Since the YAG laser has high power, the amount of radiation irradiated can be reduced.

(3) The degradation of the energy accumulated in the phosphor over time (7 Adeinda) is less likely to occur, and the image recorded on the panel can be taken out and used for a long period of time with high stimulated fluorescence intensity. .

(4) Is the second harmonic (532 nm) of the YAG laser rji? 'Since it is A light, is it normal q vision? An optical transponder for Th can be used. In addition, it is easy to adjust the equipment.

(5) Since the YAG laser is a solid laser, there is no mixing of discharge light, and a decrease in the 8N ratio can be prevented.

(Example) By utilizing the five effects described above, the object of the present invention can be completely achieved.

Next, the present invention will be explained using Examples and Comparative Examples.

Example I 8 parts by weight of a phosphor consisting of BaFBr:Eu was dispersed in lffi parts of polyvinyl butyral (binder) using a solvent containing equal parts of acetone and ethyl acetate, and this was dispersed on a polyethylene terephthalate substrate using a wire perforator. The panel was created by applying the same material.

The dry film thickness of the phosphor layer of this panel was approximately 300 μm.

After irradiating this panel with a tube voltage of 80 KVP O) X M, the stimulated fluorescence emitted from the phosphor layer was detected using the apparatus shown in FIG. In other words, 1 as excitation light
The second harmonic (532 nm) of a 0 mW YAG laser was used to excite the phosphor over a 4μ exposure. FIG. 8 shows the spectrum of stimulated fluorescence at this time.

As is clear from FIG. 8, the emission spectrum of this phosphor has a K peak of approximately 390 nm. This makes it easy to separate the excitation light and photostimulated fluorescence using an excitation light cut filter having the transmission spectrum shown in Figure 4 on the front side of the photomultiplier tube, and allows photostimulation to be produced with a high SIN ratio. I was able to detect it.

Furthermore, when scanning the panel with the second harmonic of the YAG laser 1 of lO@W, a panel with a size of 40 m was scanned at about 20 SeC, and a good image could be obtained.

In addition, in FIG. 9, the tube voltage of 80 KVP is also
This shows the relationship between the emission intensity due to photostimulation and the excitation (C) wavelength when irradiation with source energy of a different wavelength is performed after irradiation with a radiation, that is, the excitation spectrum of photostimulation. In this way, the peak of the photostimulated excitation spectrum appears to exist around 500 nm1 [in the case of phosphor, 532 nm C1
) The use of the YAG laser as the second high ali wave pumping light is effective in terms of pumping efficiency of 11"tVC.

Comparative Example 1 Using the same panel as Example 1, the tube voltage was 80 KVP
After irradiating ll1I, 5 mw of He-No laser light (
632,8 am) to excite the fluorophore for 4 μset. Emitted light was detected using an excitation light cut filter in front of the photomultiplier tube, and the emitted light intensity was about % of that in Example 1.

Further, the phosphor'%: 5 mW He-Ne laser light (
632,8i+m), 40 x 40
It took about 1-1 to scan a cIIL-sized panel and obtain an image of similar quality to that of Example 1.

Example 2 A panel was prepared in the same manner as in Example 1, and the panel was irradiated with X-rays at a tube voltage of 80 KVP and 10 iRO. Using the apparatus shown in FIG.
) Using the second harmonic (532 nm) of a YAG laser, this panel was irradiated for 4 μset, and stimulated fluorescence was detected.

In addition, the second harmonic (532
nm) was irradiated onto the diffuser plate for 4 μset, and the detected signal was used as noise.

As a result, the relative intensity ratio between the detected photostimulated fluorescence intensity and noise was 1:1O.

Comparative Example 2 A panel was produced in the same manner as in Example 1, and this spring k V
C80KVP, after irradiation with 10 mR xg #
I￥7 Filter 15 in the apparatus shown in the figure, and
The nonlinear optical crystal 16 was removed, the YAG laser 14 was replaced with an Its-No laser, and this device was used to generate a 10 mW H@-Ne laser beam (633 nm).
'FW? The panel was irradiated for 4 .mu.set, and stimulated fluorescence was detected.

In addition, a white diffuser plate was used instead of the panel, and 10 mW He-Ne laser light (633 nm
) was irradiated onto a 4 μ(6) open diffuser plate, and the detected signal was used as noise. The relative intensity ratio of the detected stimulated fluorescence intensity and noise was [10-''.

From the results of Example 2 and Comparative Example 2, it can be seen that when using the [2-high n wave of the YAG laser, the noise is reduced by about one order of magnitude and the S/N ratio is improved compared to when using the H@-No laser. I found out that it does.

[Brief explanation of the drawing]

Figure 1 is a graph showing the excitation light laser power and emission light intensity, Figure 2 is a graph showing the excitation light wavelength and fading rate, Figure 3 is a graph showing the response of the photochromic body, and Figure 4 is the excitation light intensity. Characteristic diagram showing the transmittance spectrum of the light cut filter,
FIG. 5 is a flowchart showing the radiation silver photography method of the present invention;
Figure 6 is a cross-sectional view of the phosphor (panel), Figure 7 is a side view of the reading device, #I\8 is a graph showing the characteristics of the stimulated emission spectrum of BaFBr:Eu, and Figure 9 is BaFBr.
: It is a graph which shows the photostimulation excitation spectrum of Bu. 10...Storage phosphor plate, 11...Support, 12
... Accumulative firefly) N-body layer, 14... YAG laser light source, 15... Filter, 16... Nonlinear optical crystal, 17... Half mirror 119... Filter,
Addition: Photodetector. Agent Yoshimi Kuwahara Figure 1 Rede Power (mw) 120 □-” Haruaki (hy) Figure 5 0 50 o'clock! ;l (JIJsec) ) 4 figure expert (1 → ru 5 figure muscle 60 1 Figure 7

Claims (1)

[Claims] In a method for reading a radiation image recorded on a stimulable phosphor material by scanning the stimulable phosphor material with excitation light and detecting the emitted light from each point with a photodetector, the excitation light is , Nd": Excite the stimulable phosphor material using the second harmonic of a YAG laser, and photodetect the light in the wavelength range of 300 to 500 nm among the light emitted from the stimulable phosphor material. A radiation image reading method characterized by receiving light with a device.