JPH0258179A - Shading correction method for radiographic information reader - Google Patents

Abstract

PURPOSE:To easily and accurately correct shading by leaving a stimulative phosphor sheet for inspection containing radioactive isotopes for a prescribed time as it is and irradiating it with stimulating light and detecting the stimulated phosphorescent light emitted from the sheet to detect the state of shading. CONSTITUTION:Before reading, a stimulative phosphor sheet 1 for inspection which contains radioactive isotopes uniformly throughout the surface and is left for a prescribed time as it is irradiated with stimulating light 3a. The emitting light emitted from the stimulative phosphor sheet 1 is detected by a photoelectric reading means 6 to detect the characteristic of shading due to the variance in intensity of the stimulating light 3a, the variance in sensitivity of the photoelectric reading means 6, or the like. This characteristic of shading is stored in a storage means 13, and the variance of a picture signal due to shading is corrected in accordance with the output of the storage means 13 at the time of reading the stimulative phosphor sheet 1. Thus, the state of shading of the device is easily and accurately corrected.

Description

Detailed Description of the Invention (Field of the Invention) The present invention relates to a radiation image information reading device that photoelectrically reads radiation image information stored and recorded on a stimulable phosphor sheet using excitation light to obtain an image signal. uneven strength,
The present invention relates to a method for correcting fluctuations in image signals due to uneven detection of photoelectric reading means.

(Conventional technology) Certain phosphors are exposed to radiation (X-rays, α-rays, β-rays.

When irradiated with γ-rays, ultraviolet rays, electron beams, etc., a portion of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor increases depending on the accumulated energy. is known to exhibit stimulated luminescence, and phosphors that exhibit this property are called stimulable phosphors.

Using this stimulable phosphor, radiation image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet, and the stimulable phosphor sheet is irradiated with excitation light such as a laser beam to emit stimulated light. Generate light, photoelectrically read the resulting stimulated luminescent light to obtain an image signal, and based on this image signal, a radiation image of the subject is displayed as a visible image on a recording material such as a photographic light-sensitive material or a display device such as a CRT. The present applicant has already proposed a radiographic image information recording and reproducing system that reproduces the information as follows. (JP-A-55-12429, JP-A-5B-11395, etc.) The radiation image information reading device that reads radiation image information in the above system uses a laser beam, etc. Excitation light is irradiated to produce stimulated luminescence light, and this stimulated luminescence light is detected photoelectrically.

That is, the excitation light is light in a wavelength range that produces stimulated luminescence light indicating image information from the stimulable phosphor sheet,
This excitation light is caused to main-scan on the stimulable phosphor sheet by an optical deflector and is irradiated onto the sheet. At the same time, the stimulable phosphor sheet is sub-scanned in a direction substantially perpendicular to the irradiation direction of the excitation light, and the entire surface of the stimulable phosphor sheet is irradiated with the excitation light. The stimulated luminescence light emitted from the excitation light irradiation part of the stimulable phosphor sheet is detected by a photodetector such as a photomultiplier via a light guide usually made of a light-guiding material, and is converted into an electrical signal indicating image information. is converted to

However, in the above-mentioned reading device, there may be unevenness in the intensity of the excitation light due to uneven reflectance of the reflecting surface of the optical deflector, uneven scanning speed of the excitation light due to variations in the deflection speed of the optical deflector, or uneven focusing of the light guide. (In other words, for example, parts with poor light guiding efficiency occur at the end of the light guide, etc.)
The output of the photodetector may change. In addition, the above-mentioned photodetectors such as photomultipliers often have sensitivity unevenness (sensitivity differs depending on the position of the light-receiving surface). When - is used, sensitivity unevenness tends to occur in the main scanning direction. If such various unevenness causes a partial decrease in photodetection efficiency (shading), it will naturally become impossible to correctly detect the stimulated luminescence from the stimulable phosphor sheet.

Therefore, the applicant has devised a method to avoid the influence of shading by detecting the shading state in advance and correcting the image tS signal and the sensitivity of the photomultiplier according to the irradiation position of the excitation light. have already proposed a shading correction device (Japanese Patent Application Laid-Open No. 12-47259,
G2-472tif, etc.).

In addition, in order to detect the above shading state,
The entire surface of a stimulable phosphor sheet for regular testing is irradiated with radiation of uniform intensity, and prior to reading image information, the stimulable phosphor sheet for testing is exposed to solid light as described above. A method is used in which a phosphor sheet is irradiated with excitation light and stimulated luminescence light emitted from the stimulable phosphor sheet is detected. In other words, if there is no shading at all in the reading device, the stimulated luminescence light emitted from the solidly exposed sheet should always be detected as a constant value, so the solidly exposed stimulable phosphor sheet The state of change in the detected value of stimulated luminescence light emitted from
Once it cools down, you can know the shading status.

(Problem to be solved by the invention) However, when implementing the above method,
There is a problem in that it is difficult to properly perform solid exposure itself. In other words, the radiation g often causes shading, and it is difficult to obtain a radiation source that evenly irradiates the scanned sheet, and the radiation UA 10 is not a homogeneous radiation. Even if the radiation source is placed too close to the sheet to be scanned, the distribution of radiation will be uneven, and if it is placed too far from the sheet to be scanned, the radiation will still be irradiated unevenly due to diffusion. The disadvantage is that it is very difficult to set up. Furthermore, since the shading characteristics of a reading device change over time, even if the shading characteristics are detected by solid exposure during device manufacturing, the shading characteristics must be re-detected while the user is using the device. In this case, there is a problem that the shading characteristics cannot be redetected unless the user has a radiation source for solid exposure.

The present invention has been made in view of the above-mentioned problems, and provides a shading correction method for a radiation image information reading device that can always easily and accurately detect the shading state of the device without performing solid exposure. The purpose is to provide the following.

(Means for Solving the Problems) The shading correction method of the present invention is characterized in that, prior to reading radiation image information on a stimulable phosphor sheet, the entire surface of the stimulable phosphor sheet contains a radioactive isotope evenly and is left for a predetermined period of time. The stimulable phosphor sheet is irradiated with excitation light,
By detecting the emitted light emitted from the stimulable phosphor sheet for inspection with a photoelectric reading means, shading characteristics due to uneven intensity of excitation light, uneven sensitivity of the photoelectric reading means, etc. are detected, and the characteristics of this shading are stored in a storage means. The image signal is stored in the stimulable phosphor sheet, and the variation in the image signal due to the shading is corrected in accordance with the output of the storage means when reading the stimulable phosphor sheet.

Note that the radioisotope is evenly contained over the entire surface of the stimulable phosphor sheet 4 for inspection, meaning that the radioisotope is evenly contained to the extent that the radiation energy from the radioisotope is evenly accumulated in the sheet. It means that it is nailed.

(Function) If a test stimulable phosphor sheet containing a radioisotope is left for a predetermined period of time as described above, this sheet will emit radiation emitted from its own radioisotope uniformly over its entire surface. Radiation energy is stored in the Therefore, this stimulable phosphor sheet for inspection is exposed to light without using a radiation source, and stimulated luminescence is emitted from the stimulable phosphor sheet by irradiating the stimulable phosphor sheet for inspection with excitation light. The shading state can be detected by detecting . Note that the specific method of shading correction performed in accordance with the detected shading state may be any of the well-known 1. I- Any method can be used.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a radiation image information reading apparatus in which shading correction is performed according to an embodiment of the present invention.

A stimulable phosphor sheet 1 on which radiation image information is stored and recorded
is transported in the direction of arrow Y for sub-scanning by a sheet transport means 2 such as an endless belt. Further, the excitation light 3a emitted from the laser light source 3 is deflected by the reflected color 4a of the galvanometer mirror 4, which is a light deflector, and moves the stimulable phosphor sheet 1 in a direction X approximately perpendicular to the sub-scanning direction Y.
main scan. In this way, from the part of the sheet 1 irradiated with the excitation light 3a, stimulated luminescence light is emitted in an amount corresponding to the radiographic image information stored and recorded, and this stimulated luminescence light is mainly transmitted through the condensing guide 5. It is photoelectrically detected by a long photomultiplier 6 arranged along the scanning line.

The analog output signal S output from the photomultiplier 6 is amplified by a log amplifier 7, then passed through an analog calculation section 8, which will be described later, and then digitized by an A/D converter. The digital read image signal Sd obtained in this way is sent to the image processing circuit 10, where it undergoes processing such as gradation processing and frequency processing, and is then input to an image reproduction device 11 such as a CRT or optical scanning recording device. be done. Since the above-mentioned read image signal Sd carries the light intensity of the above-mentioned stimulated luminescence light, by using this read image signal Sd, the radiation image stored and recorded on the stimulable phosphor sheet 1 can be transferred to the above-mentioned image reproducing device. 11, it is reproduced as a visible image. The read image signal Sd may be directly input manually to the image reproducing device 11 as described above, or may be temporarily recorded on a recording medium such as a magnetic disk or a magnetic tape.

In the radiographic image reading apparatus described above, shading may occur due to uneven intensity of the light beam, uneven scanning speed, uneven sensitivity of the long photomultiplier in the main scanning direction, etc., as described above. When aging occurs due to unevenness, the photomultiplier
The output signal S changes depending on the beam scanning position even for image portions having the same amount of stored energy, making it impossible to read image information accurately. A method for correcting this shading will be described below.

In the method of this embodiment, prior to reading the stimulable phosphor sheet 1 on which image information has been stored and recorded as described above, the stimulable phosphor sheet 20 for inspection made of aRL containing a radioactive isotope is prepared as described above. Storable phosphor sheet 1
It is read in the same way. That is, the test stimulable phosphor sheet 20 [for example, BaFx:Eu2+ phosphor (X is CQ,

Use of at least one of Br and I] is the first
As shown in the figure, it has the same shape as the above-mentioned stimulable phosphor sheet, and contains, for example, 226Ra in the phosphor or 14(in the binder). The above 22IIRa114
C is evenly distributed over the entire surface of the stimulable phosphor sheet for inspection, and the stimulable phosphor sheet 20 for inspection has a time period during which the 22sRa and 14C allow sufficient radiation energy to be accumulated in the sheet. After being placed on standby for a period of time, the sheet is placed on the sheet conveying means 2. Note that the waiting time does not need to be set as a specific time or more, and if it is not desirable for the stimulable phosphor sheet for inspection to be exposed excessively, the stimulable phosphor sheet for inspection After the sheet is once irradiated with erasing light to emit radiation energy from the sheet, the sheet may be left on standby for a certain period of time and then loaded into the reading device.

The test stimulable phosphor sheet 20 loaded in the reading device in the same way as the stimulable phosphor sheet 1 emits stimulated luminescence light of uniform intensity by being scanned by the excitation light 3a. is detected by a photomultiplier 6 via a light guide 5.

At this time, the reference output signal So output from the photomultiplier 6 is amplified by the log amplifier 7 in the same manner as described above, and passed through the analog calculation section 8, which will be described later.
/D converter 9 digitizes the data. Digitized reference output signal Sd. is input to the correction value calculation circuit 12. In this correction value calculation circuit 12, the difference between the reference output signals (this is caused by the shading and indicates the shading characteristics) is determined for each pixel in the main scanning direction.

That is, as shown in FIG. 2, the stimulable phosphor sheet for inspection 20 has Xl, Xl, X3, .・
. . . X, one column of pixels are lined up, and the correction value calculation circuit 12 calculates each column
．． Xl, X3. ......X, reference output signal Sdo
The average values of these average values are determined as representative signal values R1, R2+ R3+ . . . R, respectively.

shall be. Then, the arithmetic circuit 12 calculates the average value Ro of all the representative signal values R1, R2, R3, .
. . . Correction values U, , U2, which are the differences between R1. U3. ...
...Determine UJ and store these values in the memory 13.

When reading the radiation image information stored and recorded on the stimulable phosphor sheet 1 as described above, the correction values U, U2 . U3. . . . U are called out in order, and the image signal read from the stimulable phosphor sheet is corrected. That is, a synchronizing signal T synchronized with the main scanning of the excitation light is input to the memory 13, and when the nth column of pixels in the main scanning direction is read, the correction value Un regarding the nth column is output. ing. These correction values are converted into analogs by the D/A converter 14, and then sent to the analog calculation unit 8 as correction signals together with the image signal obtained by photoelectrically reading the stimulated luminescence light. The above image signal is affected by shading, but by adding a correction signal to this image signal, it is possible to correct the fluctuations in the image signal due to shading and read the image information accurately. .

The radioactive isotope to be dispersed in the above-mentioned stimulable phosphor sheet for inspection is not limited to the above-mentioned "C% Ra", but can be selected from those with an appropriate half-life and radiation intensity. Alternatively, it is preferable to use a radioactive isotope of the same element or homologous element as the binder component, since the substance can be completely dissolved in solid solution and uniform dispersion can be obtained.

Note that the shading correction using the correction value described above may be performed in any specific manner as long as the image signal finally obtained from the reading device can be made free from the influence of shading. Instead of directly changing the image signal as in , the sensitivity of the photomultiplier or the power of the excitation light may be changed depending on the shading state. In addition to the above-mentioned long photomultiplier, the photoelectric reading means may include a combination of a conventionally known large light guide and a small photomultiplier,
A line sensor or the like may also be used.

(Effects of the Invention) As explained above in detail, according to the shading correction method of the present invention, the shading state can be detected well without performing solid exposure before reading.
Radiography for shading correction is no longer required,
Shading correction can be easily and accurately performed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a radiation image information reading apparatus that performs shading correction according to an embodiment of the present invention, and FIG. 2 is a schematic diagram illustrating shading correction according to the method according to the present invention. l...Stormative phosphor sheet 3a...Excitation light 6...
Photomultiplier 8...Analog calculation unit 12...Correction value calculation circuit 13...Memory 20...Stormative phosphor sheet for inspection

Claims (1)

[Claims] A stimulable phosphor sheet on which radiation image information has been stored and recorded is irradiated with excitation light to generate stimulated luminescent light from the stimulable phosphor sheet, and the stimulated luminescent light is detected by a photoelectric reading means to generate an image signal. In a radiation image information reading device that obtains
Prior to reading the radiation image information on the stimulable phosphor sheet, the excitation light is irradiated onto the stimulable phosphor sheet for inspection, which contains a radioisotope evenly over the entire surface and has been left for a predetermined period of time. , detecting the shading characteristics due to intensity unevenness of the excitation light, sensitivity unevenness of the photoelectric reading means, etc. by detecting the light emitted from the stimulable phosphor sheet for inspection with the photoelectric reading means;
A shading correction method for a radiation image information reading device, wherein the shading characteristics are stored in a storage means, and fluctuations in the image signal due to the shading are corrected according to the output of the storage means when reading the stimulable phosphor sheet.