JPH0473936B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a radiation image conversion panel (hereinafter simply referred to as an image conversion panel) having a photostimulable phosphor layer, which is subjected to image exposure using radiation. The present invention relates to a radiation image reading method in which the surface of a conversion panel is later scanned with photostimulable excitation light to cause the photostimulable phosphor to volatilize and read recorded image information.

[Conventional technology]

When a photostimulable phosphor is irradiated with radiation such as X-rays or ultraviolet rays, a portion of the energy is accumulated within the photostimulable phosphor depending on the amount of irradiation, and when it is irradiated with photostimulable excitation light, the accumulated energy is emitted as stimulated luminescence according to the amount of radiation applied earlier.
This phenomenon can be used to record images formed by various types of radiation, for example,
Publication No. 12144 discloses that a conversion panel having a photostimulable phosphor layer is subjected to imagewise exposure to radiation such as X-rays to absorb radiation energy and form a kind of latent image, and then the conversion panel has a photostimulable phosphor layer. A method is disclosed in which a radiation image is obtained by scanning the surface of a conversion panel with a beam and reading the stimulated luminescence intensity emitted by a phosphor. In these methods, a laser beam or the like is usually used as the stimulated excitation light, and a photodetector such as a photomultiplier tube is used to read the stimulated luminescence, and the stimulated luminescence intensity is extracted as an electrical signal and finally an image is generated. It can be used as a hard copy or played on a CRT.

These image recording methods have advantages such as an extremely wide recordable radiation exposure range, the ability to freely process image information obtained as electrical signals, and the ability to obtain images most suited to the purpose. However, there is a problem in that the energy stored in the photostimulable phosphor due to radiation irradiation decreases significantly over time.

Therefore, as shown in Figure 2, as the time from image exposure (t ₀ ) to radiation to scanning t ₁ by the stimulated excitation light increases, the intensity of the stimulated luminescence that is read decreases, resulting in a constant image tone. will not be obtained.

[Problem that the invention seeks to solve]

To deal with the above problem, for example, Japanese Patent Application Laid-Open No. 58-67242 performs pre-reading using weak stimulated excitation light prior to reading image information, and based on the output, the reading conditions for main reading, A reading device for setting image processing conditions is disclosed.

However, the decrease in stimulated luminescence intensity with time continues to progress from the start of reading (t ₁ ) to the end (t ₂ ), so from t ₀ to
Even if the attenuation during _t1 was corrected, it was not possible to prevent the occurrence of large density unevenness (shading) due to a difference in density between the beginning and end of the image reading screen.

The present invention aims to provide a radiation image recording apparatus capable of recording images without shedding due to the decrease in stimulated luminescence intensity between _t1 and _t2 .

[Means to solve the problem]

The above-mentioned problem is to provide image exposure with radiation to a radiation image conversion panel having a photostimulable phosphor layer,
In the radiation image reading method, the radiation image information is read by subsequently scanning the radiation image conversion panel with stimulated light and detecting the generated stimulated light, the radiation image conversion panel being exposed to radiation. An attenuation curve of the photostimulated light intensity is determined in advance according to the elapsed time, and based on the attenuation curve, the photostimulated light intensity is calculated from the start of reading of the radiation image information until the end of the reading. This could be achieved by a radiation image reading method characterized in that the attenuation of the image is corrected based on the time since the image was exposed to the radiation. Various methods can be used to correct the attenuation of the photostimulant intensity between the start and end of reading, but a preferred method is to correct the attenuation of the photostimulant intensity after radiation irradiation (t ₀ ). 2
(Figure) is _constant for an image conversion panel having a constant photostimulable phosphor layer. , and estimates the attenuation of the amount of stimulated luminescence after the reading start time t ₁ , and corrects the reading results accordingly. For example, a method is provided in which the amount of photostimulated light is read including the part, and the attenuation is detected from the amount of photostimulated light in that part, and the reading result of the image part is corrected. Correction of the reading result can be performed by controlling the amplification gain of the reading system, or it can also be performed by post-processing such as once storing the read value in a memory circuit and then multiplying it by a correction coefficient.

The stimulable phosphor of the recording plate used in the present invention is
After the first light or high-energy radiation is irradiated, light corresponding to the irradiation amount of the first light or high-energy radiation is re-emitted by optical, thermal, mechanical, chemical, or electrical stimulation. , refers to a phosphor that exhibits so-called photostimulability. Here, light includes visible light, ultraviolet light, and infrared light among electromagnetic radiation, and high-energy radiation includes X-rays, gamma rays, beta rays, alpha rays, neutron rays, and the like.
This phosphor can be one that emits light with a wavelength of 300 to 500 nm when stimulated by excitation light. For example, it is described in JP-A-48-80487.
BaSO ₄ :fluorescent substance represented by Ax (where A is at least a species among Dy, Tb and Tm, and x is 0.001≦x<1 mol%), MgSO described in JP-A-48-80488 ₄ : Fluorescent substance represented by Ax (A is either Ho or Dy, and 0.001≦x<1 mol%), SrSO described in JP-A-48-80489 ₄ : Ax (However, A is at least one of Dy, Tb, and Tm, and x is 0.001≦
x<1 mol%. ), BeO, LiF, described in JP-A No. 52-30487,
Phosphors such as MgSO ₄ and CaF ₂ , US Pat. No. 3,859,527
SrS:Ce, Sm, SrS:Eu,
Sm, La ₂ O ₂ S: Eu, Sm and (Zn, Cd)S:
Examples include phosphors represented by Mn, X (where X is halogen). Also, the general formula is M〓O・
xSiO ₂ :A (However, M〓 is Mg, Ca, Sr, Zn, Cd or
Ba and A is Ce, Tb, Eu, Tm, Pb, Tl, Bi
and Mn, and x is 0.5≦
x≦2.5. ) are alkaline earth metal silicate-based phosphors. In addition, the general formula is (Ba ₁ −x−yMgxCay)FX:eEu ²⁺ (where X is at least one of Br and Cl, x, y, and e are each 0<x+y≦0.6,
This is a number that satisfies the following conditions: xy≠0 and 10 ^-5 ≦e≦5×10 ^-2 . ), the general formula of the alkaline earth fluorohalide phosphor described in JP-A-55-12144 is LnOX:xA (where Ln represents at least one of La, Y, Gd and Lu, X is Cl and/or Br, A is Ce and/or
or Tb, and x represents a number satisfying 0<x<0.1. ), the general formula described in JP-A-55-12145 is (Ba ₁ −xM〓 _x )FX:yA (where M〓 is Mg, Ca, Sr, Zn, and Cd). X is at least one of Cl, Br and I, A is Eu, Tb, Ce, Tm,
At least one of Dy, Pr, He, Nd, Yb and Er, x and y are 0≦x≦0.6 and 0≦y≦
Represents a number that satisfies the condition of 0.2. ), the general formula described in JP-A-55-84389 is BaFX:xCe,yA (where X is at least one of Cl, Br and I, and A is In, Tl). ,Gd,
at least one of Sm and Zr, and x and y are 0<x≦2×10 ^-1 and 0<y≦5, respectively
×10 ^-2 . ), Japanese Patent Application Laid-Open No. 1983-1983
The general formula described in -160078 is M〓FX・xA:yLn (where M〓 is at least one of Mg, Ca, Ba, Zn, and Cd, A is 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 ,
At least one of Nb ₂ O ₅ , Ta ₂ O ₅ and ThO ₂
Species, Ln are Eu, Tb, Ce, Tm, Dy, Pr, Ho,
At least one of Nd, Yb, Er, Sm and Gd
seeds, and x and y are each 5×10 ^-5 ≦x≦
This is a number that satisfies the conditions of 0.5 and 0<y≦0.2. )
A rare element-activated divalent metal fluorohalide phosphor represented by the general formula [] or [] described in JP-A-57-148285, the general formula [] xM ₃ (PO ₄ ) ₂ . NX: yA General formula [] M ₃ (PO ₄ ) ₂ : yA (In the formula, M and N are Mg, Ca, Sr,
At least one of Ba, Zn and Cd, X is F,
At least one of Cl, Br and I, A is Eu,
Tb, Ca, Tm, Dy, Pr, Ho, Nd, Yb, Er,
Represents at least one of Sb, Tl, Mn and Sn. Also, x and y are 0<x≦6, 0≦y≦1
This is a number that satisfies the condition. ), and the general formula [] or [], general formula [] nReX ₃・mAX′ ₂ :xEu general formula [] nReX ₃・mAX′ ₂ :xEu・ySm (in the formula, Re is La , Gd, Y, Lu, A is an alkaline earth metal, Ba, Sr, Ca
At least one of X and X' is F, Cl,
Represents at least one type of Br. Moreover, x and y are 1×10 ^-4 <x<3×10 ^-1 , 1×10 ^-4 <y
It is a number that satisfies the condition <1× ^-1 , and n/m is 1
The condition ×10 ^-3 <n/m<7×10 ^-1 is satisfied. )
_A phosphor represented _by at least one alkali metal,
M〓 is Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and
At least one divalent metal selected from Ni. M〓 is Sc, Y, La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Mb,
At least one trivalent metal selected from Lu, Al, Ga, and In. X, X′ and X″ are F, Cl,
At least one halogen selected from Br and I. A is Eu, Tb, Ce, Tm, Dy, Pr,
Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl,
At least one metal selected from Na, Ag, Cu, and Mg.

Also, a is a numerical value in the range of 0≦a<0.5, and b
is a numerical value in the range of 0≦b<0.5, and c is a value in the range of 0<c
It is a numerical value in the range of ≦0.2. ), but the phosphor used in the present invention is not limited thereto. When the phosphor described above is irradiated with a certain amount of radiation and scanned with stimulated excitation light, the intensity of the stimulated luminescence that is read decreases with the passage of time after the irradiation, as shown in FIG. In FIG. 9, the phosphors and the phosphors are the phosphors represented by the general formula (1), but have different components. If a radiographic image is read using these phosphors without the correction of the present invention, a constant image quality cannot be obtained due to a decrease in the amount of stimulated luminescence between the start and end of reading.

In practice, the allowable range for fluctuations in the amount of light emitted during reading is about ±3%, and if the fluctuations exceed this range, shading will occur on the screen, causing problems. 9th
When using the phosphor shown in the figure, if reading is started 1 minute after radiation exposure and the reading is continued for 1 minute or more, the attenuation during that time will reach approximately 10%, significantly exceeding the above limit. become. The present invention is particularly effective in solving the problems of phosphors of this nature, and by using the method of the present invention, high quality radiographic images can be obtained.

The excitation light used to make these photostimulable phosphors emit light again is one that radiates the radiation energy accumulated in the photostimulable phosphors and converts them into light, such as visible light or infrared rays. However, it is particularly effective to use light in a wavelength range of 500 nm or more, and preferred are He--Ne laser, Ar laser, YAG laser, He--Cd laser, Kr laser, dye laser, semiconductor laser, etc. Furthermore, by using a filter on a light emitter that emits light in a broader band, it is possible to convert the light into light in a wavelength range of 500 nm or more.

As the support for the recording medium used in the present invention,
Any material can be used as long as it has the ability to support a generally known recording layer, such as paper, metal plates, synthetic resin plates, etc., polyethylene sheets with a thickness of 50 to 300 μm, plastic films, aluminum plates, and sheets with a thickness of 1 to 3 mm. Glass plates etc. are commonly used. The present invention will be specifically explained below using examples.

Embodiment FIG. 1 is a block diagram showing an example of a radiation image reading apparatus suitable for carrying out the method of the present invention. Reference numeral 1 denotes a laser for generating stimulated excitation light, which is driven by a laser driver circuit 2. The laser beam LB generated by the laser 1 passes through a monochromatic light filter 3, a mirror 4, a beam shaping optical system 5, and a mirror 6.
and reaches the deflector 7. The deflector 7 includes a carbano mirror driven by a deflector driver and deflects the laser beam LB into the scanning area at a constant angular velocity. The deflected laser beam LB passes through a mirror 10 adjusted by an fΘ lens 9 so as to have a constant speed on a scanning line, and scans an image conversion panel 11 in the direction of arrow a. The image conversion panel 11 simultaneously moves in the sub-scanning direction (arrow b) and the entire surface is scanned. Stimulated light generated from the image conversion panel 11 after being scanned by the laser beam LB is focused by an optical fiber condenser 12, and passes through a filter 13 that passes only the wavelength region of the stimulated light, and is then sent to a photomultiplier tube or the like. /electrical converter, the signal reaches the light receiving section 14 and is converted into an analog electrical signal. 15 is a photo/electrical conversion power source that supplies high voltage to the photomultiplier tube. The image signal output as a current from the photomultiplier tube is voltage amplified through a current-voltage conversion amplifier 16, and a Log converter 17 that converts the emission intensity signal into an image density signal.
After passing through a sample hold circuit 18 that maintains the signal for a certain period of time in synchronization with the image clock signal, the A/D
After being converted into a digital signal by a converter 19, it is stored in a memory. The memory is connected to a CPU 20 that performs digital calculations and the like. CPU20
can be connected via the interface 21 to external devices such as large-sized computers and mini-computers for storing and processing data, CRT display devices for outputting images, various hard copy production devices, etc., and data can be stored in memory. calculation of data,
Perform the transfer.

Reference numeral 22 denotes an attenuation correction control circuit for correcting the attenuation of the stimulated emission intensity during the period from the start to the end of reading of the stimulated emission, which reads a control signal corresponding to a signal from the correction amount detection means described later. The signals sent and read to the required blocks of the system are corrected. Correction of the read signal can be carried out in various blocks of the readout system.

For example, Laser: Adjustment of the output by controlling the laser driver 2 Scanning section: Adjustment of the scanning speed of the light beam by controlling the deflection driver 8 Light receiving section: Adjustment of the optical/electrical conversion gain by controlling the power supply 15 of the photomultiplier tube Current-voltage Conversion amplifier: Control of amplification gain Log converter: Control of conversion gain Sample hold: Control of internal gain A/D converter: Control of A/D conversion dynamic resin In addition, a correction signal is input to the CPU 20 and temporarily stored in memory. It is also possible to perform a correction operation on the data and output it to the memory input interface again. Control for correction may be performed at any one of the above-mentioned processing steps, or may be performed at multiple locations in parallel. The output mode of the attenuation correction control circuit may correspond to the stage of control.

When the read value is corrected based on the time from the time of radiation exposure to the image conversion panel to the start of reading, the attenuation correction control circuit is provided with a storage section, and the attenuation correction control circuit is provided with a storage section that stores the pre-measured stimulated luminescence intensity and time of the image conversion panel to be used. Input the relationship (Figure 2) in advance,
In the calculation section, the stimulated luminescence intensity I(t ₁ ) at the scanning start time t ₁ and the stimulated luminescence corresponding to the scanning time tn of the scanning line to be corrected are determined according to the elapsed time input from the time detection means until the start of reading. I(t ₁ )/I(tn) may be calculated from the intensity I(tn) and output to the reading system to control its reading gain, or the data once stored in the reading memory may be corrected.

As the time detection means, various known electronic or mechanical timer units can be used.
These time detection means are, for example, (1) provided on the radiation exposure apparatus side and activated in conjunction with the radiation exposure switch to display the elapsed time, so that a person can read the displayed value and correct the attenuation of the reading apparatus. Manual input to control circuit.

(2) Install it in either the radiation exposure device or the reading device, connect it electrically to both devices, start it up in conjunction with the radiation exposure switch, and measure the passage of time _.
is read and automatically input into the attenuation correction control circuit at the start.

(3) Attached to the image conversion panel, when attached to a radiation exposure device, it connects to the device, starts up in conjunction with the exposure switch, and when attached to the reading device for reading, connects to the device and starts reading. At the same time, the elapsed time is input to the attenuation correction control circuit. It can be used in various ways.

The embodiment shown in FIG. 1 uses the method (3) above,
The gain of the photomultiplier tube power supply 15 in the light receiving section is controlled to correct the photostimulated light attenuation of the image conversion panel. 23 in the figure is a timer unit provided in the image conversion panel 11.

FIG. 3 is a flowchart showing the photostimulation band decay correction operation in the apparatus.

Also, in Figure 4, after the read data is temporarily stored in the memory as it is, a correction coefficient corresponding to t for each line is generated from the attenuation correction circuit, and the data is called from the memory to the CPU and the two are multiplied to perform correction. This is the procedure in case.

In addition, when correcting the stimulated luminescence of the image conversion panel by actually measuring it, for example, as shown in FIG. A photostimulated light intensity measurement area 51 is provided, and this area is also scanned during reading. The stimulated luminescence intensity in the same region also decreases during the reading operation, but if the gain of the reading system is controlled so that the reading value is always the same as at the start of reading, or if the reading value is multiplied by a correction coefficient, The attenuation of stimulated luminescence intensity between the start and end of reading is corrected.

The curve in Figure 5 is a schematic drawing of the stimulated luminescence intensity Io at the start of reading and the stimulated luminescence intensity In obtained by the n-th scanning of the image area. In this case, it is sufficient to perform a reading gain correction of Io/In or to multiply the read data by this correction coefficient.

FIG. 6 shows an example of a reading device suitable for implementing this method. Here, the signal of the stimulated luminescence intensity measurement area is separated from the signal read by the photodetector 13 by a measurement area signal separation circuit. The signal is input to the attenuation correction control circuit 61 to calculate Io/In and control the reading system.

Even in this case, the read value correction control can be performed at each stage of the reading device as described above.

FIG. 7 is a flowchart showing the procedure for reading data using this method, and FIG. 8 is a flowchart for reading data without correction, storing it in memory, and then performing correction calculations.

〔Effect of the invention〕

As described above, by the method of the present invention, it is possible to completely correct the temporal attenuation of the luminescence intensity of the photostimulable phosphor from the start to the end of image reading, and to read image information accurately without shedding. Summer. The method of the present invention can also be carried out in parallel with other corrections, such as correction of stimulated luminescence intensity from the time of radiation exposure (t ₀ in FIG. 2) to the start of reading (t ₁ ).

[Brief explanation of the drawing]

1 and 6 are block diagrams of a radiation image reading device suitable for carrying out the method of the present invention, and FIGS. 2 and 9 are graphs showing attenuation of stimulated luminescence intensity.
3, 4, 7, and 8 are flowcharts showing image reading and correction procedures according to the method of the present invention, and FIG. 5 shows an image conversion panel provided with a stimulated luminescence intensity measurement area and It is a schematic diagram showing the scanning result. 1... Laser, 11... Image conversion panel, 14
... Light receiving part, 51 ... Stimulated luminescence intensity measurement area, 5
2... Image area.

Claims (1)

[Scope of Claims] 1 Image exposure is applied to a radiation image conversion panel having a stimulable phosphor layer using radiation, and then the radiation image conversion panel is scanned with photostimulation excitation light to excite the generated photostimulation light. In a radiation image reading method for reading radiation image information by detecting radiation image information, a decay curve of photostimulated light intensity is determined in advance according to elapsed time after radiation exposure of the radiation image conversion panel, and the attenuation curve is determined in advance. Based on the curve, the attenuation of the photostimulated light intensity from the start of reading of the radiation image information to the end of reading is corrected by the time from image exposure with the radiation. Characteristic radiation image reading method.