JPH08116435A - Shading correction method in radiation image reading - Google Patents

Abstract

PURPOSE: To easily and excellently attain shading correction in double side reading for obtaining an image signal representing a radiation image from both sides of a stimulable phosphor sheet. CONSTITUTION: Reference output signals DA, DB are obtained from both sides of the stimulable phosphor sheet uniformly irradiated with radioactive rays and a correction value arithmetic circuit 20 obtains shading correction data based on the signals. Image signals SA, SB representing the radiation image are obtained from both sides of the stimulable phosphor sheet on which the radiation image is stored and recorded, and the image signals SA, SB are added to apply shading correction based on shading correction data when the sum signal is obtained. Thus, it is not required to provide plural shading correction data and shading is corrected with high accuracy and simple configuration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a stimulable phosphor sheet on which a radiation image is stored and recorded with excitation light, thereby obtaining an image signal emitted from the sheet, and shading the obtained image signal. The present invention relates to a shading correction method for correcting a radiation image when reading the image.

[0002]

2. Description of the Related Art An image signal is obtained by reading a recorded radiation image, and after subjecting this image signal to appropriate image processing,
Image reproduction and recording are performed in various fields.
For example, an X-ray image is recorded using a film having a low gamma value designed to be suitable for later image processing, and the X-ray image is read from the film on which the X-ray image is recorded and converted into an electric signal. By performing image processing on this electric signal (image signal) and reproducing it as a visible image on a copy photograph or the like, there is provided a system capable of obtaining a reproduced image having good image quality performance such as contrast, sharpness, and graininess. It has been developed (see Japanese Patent Publication No. 61-5193).

In addition, the applicant of the present invention has proposed radiation (X-ray, α
Radiation, β rays, γ rays, electron rays, ultraviolet rays, etc.), a part of this radiation energy is accumulated, and when excitation light such as visible light is then irradiated, the stimulated emission light of a light amount corresponding to the accumulated energy is emitted. Stimulable phosphor that emits light (stimulable phosphor)
Using, the radiographic image of a subject such as a human body is once photographed and recorded on a sheet-shaped stimulable phosphor, and the stimulable phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light.
A radiation recording / reproducing system that photoelectrically reads the obtained stimulated emission light to obtain an image signal, and outputs a radiation image of a subject as a visible image on a recording material such as a photographic light-sensitive material or a CRT based on the image signal. Have already been proposed (JP-A-55-12429, etc.).

In the system as described above, in order to read an image, a scanning surface on which image information is recorded is scanned with a light beam, and reflected light, transmitted light or emitted light from the scanning surface is detected. Image information reading devices that read image information by doing so have been conventionally used in, for example, an image input unit of a computer or an image reading unit of a facsimile. In such an image information reading device, a light beam emitted from a laser light source or the like is deflected by an optical deflector to scan a surface to be scanned, and light carrying image information from the surface to be scanned is detected by photoelectric reading means. By doing so, an image signal is obtained. The photoelectric reading means includes a relatively small photomultiplier tube (photomultiplier) and an optical guide formed so that one end is arranged along the main scanning line and the other end is joined to the photomultiplier. A long photomultiplier directly arranged along the main scanning line, or a line sensor arranged along the main scanning line, which is disclosed in JP-A-62-16666, is used. .

However, in the above-mentioned image information reading apparatus, the unevenness of the scanning light beam intensity due to the unevenness of the reflectance of the reflecting surface of the optical deflector, the unevenness of the scanning speed of the light beam due to the variation of the deflection speed of the optical deflector, or The image signal obtained from the photoelectric reading unit may fluctuate due to unevenness of light-condensation of the light guide in the main scanning direction, uneven detection of the photoelectric reading unit due to uneven sensitivity of the long photomultiplier in the main scanning direction, and the like. If the light detection efficiency is partially reduced (shading) due to such unevenness,
Naturally, it becomes impossible to correctly detect the image information recorded on the surface to be scanned.

Therefore, the present applicant avoids the influence of shading by detecting the shading state in advance and correcting the image signal and the sensitivity of the photomultiplier according to the main scanning position of the light beam. A shading correction device of this kind has already been proposed (Japanese Patent Laid-Open No. 61-18976).
No. 3, No. 62-47259, No. 62-47261, No. 64-86759, and JP-A-2-58973).

On the other hand, as a method for photoelectrically reading the stimulated emission light described above, the photoelectric reading means described above is arranged on both sides of the stimulable phosphor sheet so that excitation light is emitted only on both sides or one side of the stimulable phosphor sheet. And a double-sided condensing reading method for photoelectrically reading the stimulated emission light emitted by this excitation light scanning from both sides of the stimulable phosphor sheet (for example, JP-A-55-87970). . In such a double-sided condensing reading method, one radiation image is accumulated and recorded on the stimulable phosphor sheet, and the stimulated emission light is condensed from both sides of the stimulable phosphor sheet. The light collection efficiency is improved and the S / N ratio is further improved.

In the double-sided condensing reading method disclosed in the above-mentioned JP-A-55-87970, a stimulable phosphor sheet is formed by laminating a stimulable phosphor sheet on the surface of a transparent support to form a transparent stimulable phosphor sheet. A stimulable phosphor sheet on which a radiation image is stored and recorded is mounted on a holder, and photoelectric reading means are arranged above and below the stimulable phosphor sheet. That is, in the photoelectric reading means arranged above the holder, the stimulated emission light emitted from the surface of the stimulable phosphor sheet is read, and in the photoelectric reading means arranged below the holder, the back surface of the stimulable phosphor sheet is read. The stimulated emission light emitted from the device is read.

[0009]

As described above, it is considered variously to perform shading correction on the image signal obtained from only one side of the sheet. However, when performing the shading correction in the double-sided reading method, the following is performed. There are some problems to mention. That is, since the image signals obtained from both sides of the sheet have different shading characteristics, when the shading correction data obtained from only one side of the sheet is used, accurate shading correction is performed when the image signals obtained from both sides of the sheet are added. Can't do.

In view of the above circumstances, it is an object of the present invention to provide a shading correction method in radiographic image reading, which is capable of favorably performing shading correction with a simple configuration even when performing the above-mentioned double-sided reading. To do.

[0011]

A shading correction method in radiographic image reading according to the present invention is the above-described shading correction method in double-sided reading, in which shading correction data for correcting shading of the added image signal is obtained in advance, and It is characterized in that the fluctuation of the added image signal due to the shading is corrected based on the shading correction data.

Further, the stimulable phosphor sheet uniformly irradiated with radiation is irradiated with the excitation light, and the stimulated emission light emitted from both sides of the sheet by the irradiation of the excitation light is photoelectrically converted. It is preferable to obtain two signals representing the shading data by detecting and obtain the shading correction data based on the data obtained by adding the respective signals.

[0013]

According to the shading correction method for reading a radiation image according to the present invention, for example, a stimulable phosphor sheet uniformly irradiated with radiation is irradiated with exciting light, and the exciting light is irradiated on both sides of the sheet. The two signals representing the shading data are obtained by photoelectrically detecting the stimulated emission light emitted from each of them, and the shading correction data is obtained based on the data obtained by adding the respective signals. The shading correction data obtained in advance The shading correction is performed according to. That is, each image signal obtained from both sides of the sheet always has constant shading, and therefore, the addition signal always has constant shading. Therefore, when the added image signal is obtained, for example, two signals representing the shading correction data are obtained as described above, and the shading correction is performed by the shading correction data obtained by adding the respective signals to obtain the added image. Optimal shading correction is performed on the signal. As a result, even when performing double-sided reading, it is only necessary to have a single shading correction data, and it is not necessary to have shading correction data corresponding to each surface. The memory can be miniaturized and therefore
The configuration of the device for carrying out the present invention can be simplified.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a radiation image reading apparatus including an apparatus for carrying out a shading correction method in a radiation image reading method according to the present invention.
As shown in FIG. 1, in the radiation image reading apparatus, the stimulable phosphor sheet 1 is arranged on endless belts 9a and 9b which are rotated by a motor (not shown). Above the sheet 1, a laser light source 10 that emits a light beam 11 that is excitation light, a rotary polygon mirror 12 that reflects and deflects the light beam 11 and is rotated by a motor (not shown) that main-scans the sheet 1 and the reflection. A scanning lens 19 is provided for converging the deflected light beam 11 on the sheet 1 and scanning the sheet 1 at a constant speed. Furthermore, above the position where the light beam 11 is scanned, a light collecting guide 14a that collects the stimulated emission light emitted by the scanning of the light beam 11 from above is arranged in the vicinity, and below the position. Has a light collecting guide 14b for collecting the stimulated emission light from below, which is arranged vertically to the sheet 1. Photomultipliers (photomultiplier tubes) 15a and 15b for photoelectrically detecting the stimulated emission light are connected to the light collecting guides 14a and 14b, respectively. The photomultipliers 15a and 15b are connected to logarithmic amplifiers 16a and 16b as shown in FIG. 2 described later, and shading correction is performed on the obtained image signals.

A stimulable phosphor sheet 1 on which a radiation image of a subject is stored and recorded is set on the endless belts 9a and 9b. The stimulable phosphor sheet 1 set at this predetermined position is conveyed (sub-scanned) in the arrow Y direction by the endless belts 9a and 9b. On the other hand, the light beam 11 emitted from the laser light source 10 is reflected and deflected by a rotary polygon mirror 12 driven by a motor (not shown) and rotating at a high speed in the arrow direction, and is incident on the sheet 1 and is substantially in the sub-scanning direction (arrow Y direction). The main scanning is performed in the vertical arrow X direction. From the position of the sheet 1 irradiated with the light beam 11, stimulated emission lights 13a and 13b (here, the stimulated emission lights 13a and 13b are emitted from the sheet 1 respectively) in a quantity of light according to the stored and recorded radiation image information. Above,
Shown as divergent from below) is diverged. The stimulated emission light 13a is guided by a light collecting guide 14a and photoelectrically detected by a photomultiplier (photomultiplier tube) 15a. The stimulated emission light 13a that has entered the focusing guide 14a from the entrance end face advances through the inside of the focusing guide 14a by repeating total reflection, is emitted from the exit end face, is received by the photomultiplier 15a, and represents a radiation image. Bright emission light 13a
Is converted into an electric signal by the photomultiplier 15a. Similarly, the stimulated emission light 13b is collected by the focusing guide 14b.
And is photoelectrically detected by a photomultiplier (photomultiplier tube) 15b.

The analog output signals S _A and S _B output from the photomultiplier 15a are subjected to shading correction as described below.

In the image reading apparatus as described above,
As described above, shading may occur due to unevenness of the intensity of the light beam, uneven scanning speed, uneven sensitivity in the main scanning direction of the long photomultiplier, and the like. The output signals S _A and S _B of the pliers 15a and 15b are
Even for an image portion having the same amount of accumulated energy, it changes depending on the beam scanning position, and accurate image information cannot be read.

A method of correcting this shading will be described below.

FIG. 2 is a schematic diagram of an apparatus for carrying out the shading correction method according to the present invention. Before reading the radiation image information as described above, the stimulable phosphor sheet 1 is irradiated with radiation such as X-rays of uniform intensity. The stimulable phosphor sheet 1 thus subjected to so-called solid exposure is subjected to image reading in the same manner as described above. The stimulable phosphor sheet 1 scanned by the light beam 11 emits stimulated emission light of uniform intensity, and the stimulated emission light is photomultiplier 15 through the light guides 14a and 14b.
detected by a and 15b.

The reference output signals D _A and D _B output from the photomultipliers 15a and 15b are logarithmic amplifiers 16, respectively.
Amplified by a and 16b, the analog operation unit 30 described later
And digitized in the A / D converter 17. The digitalized reference output signal D is temporarily stored in the memory 18
After being stored in, the correction value calculation circuit 20 is input. In the correction value calculation circuit 20, the difference between the reference output signals (this is caused by the above-mentioned shading and shows the shading characteristic) is obtained.

That is, as shown in FIG.
The sheet 1 has X along the main scanning direction X.₁, X₂, X₃,
...... X_JIf the pixels in the Jth column are arranged,
Average value D of the reference output signals D for m pixels₁Seeking
In addition, several pixels in the main scanning direction (for example, 8
Pixel) reference output signal average value D₁Is the average value of
The average value of these values is used as the representative signal value R₁, R₂,
R₃, …… R_kAnd Next, the representative signal value R₁, R₂,
R₃, …… R_kAverage value R₀And each representative signal value R₁, R
₂, R₃, …… R_kShading correction day which is the difference of
Ta U₁, U₂, U ₃, …… U_kAnd calculate these values as
Store in memory 22.

The shading correction data U ₁ ... U _J obtained in this way becomes data as shown in FIG. 4, for example.

When the radiation image information stored and recorded in the stimulable phosphor sheet 1 is read as described above, the memory 22 is used.
The shading correction data U ₁ ... U _J are sequentially called from the image data, and the image signal read from the stimulable phosphor sheet 1 is corrected. That is, a scanning start detector (not shown) is provided on the optical path of the main scanning start position of the light beam, and when the reading of the image information is started, the scanning start detector detects the clock every time the light beam is detected. Generator 21
To the memory 22, and a pulse signal is oscillated from the clock generator 21 toward the memory 22 by this signal.

Shading correction data U ₁ ... U _J is output from the memory 22 in response to the pulse signal input. At the same time, a synchronization signal synchronized with the main scanning of the light beam is input to the memory 22, and the correction value U _k is output when the pixels in the main scanning direction are read. These correction values are converted into analog in the D / A converter 23, and then sent to the analog operation unit 30 as a correction signal together with an image signal obtained by photoelectrically reading the stimulated emission light.

The image signal is affected by shading. By adding shading correction data to this image signal, fluctuations in the image signal due to shading are corrected and accurate image information is read. be able to.

In the analog operation section 30, the logarithmically amplified image signals S _A and S _B and the shading correction data are added to perform shading correction, and an added image signal Sadd subjected to shading correction is obtained. The added image signal Sadd is converted into a digital added image signal by the A / D converter 17, is temporarily stored in the memory 18, and is finally subjected to shading correction.
Is output as a visible image by a reproducing device such as a CRT or a laser printer.

In the above embodiment, the image signals S _A and S _B are added before A / D conversion by the A / D converter 17, but, for example, as shown in FIG. By providing two A / D converters 17a and 17b, the image signal S
_A and S _B are converted to A / D by A / D converters 17a and 17b, respectively.
Shading correction may be performed when the D-converted and A / D-converted image signals S _A and S _B are added. Note that in FIG. 5, the same components as those in FIG. 2 are denoted by the same reference numerals as those in FIG. 2, and detailed description thereof will be omitted.

In the double-sided reading embodiment described above,
The stimulable phosphor sheet 1 is scanned by the laser light emitted from one laser light source 10. However, the present invention is not limited to this, and the surface of the stimulable phosphor sheet 1 is shown in FIG. Light source 10a on each side
, 10b, rotary polygon mirrors 12a, 12b, scanning lenses 19a, 19b
Alternatively, the two surfaces of the stimulable phosphor sheet 1 may be scanned with the light beams 11a and 11b to read the stimulated emission light to obtain two image signals.

Further, in the above-described embodiment, the reference light to be received by the photomultipliers 15a and 15b for obtaining the shading correction data is emitted from the stimulable phosphor sheet 1 which is solidly exposed by radiation such as X-rays. Although stimulated emission light is used, the reference light for obtaining the shading correction data is not limited to this. For example, a stimulable phosphor sheet that has the same size as the stimulable phosphor sheet 1 and can store visible light energy is uniformly irradiated with visible light, and then the stimulable phosphor sheet is irradiated with a laser beam. At that time, stimulated emission light emitted from this stimulable phosphor sheet can also be used as reference light. In this case, an erasing light source (which emits visible light as erasing light) that is usually incorporated in a reading device to remove the image remaining on the already-read stimulable phosphor sheet is used to obtain the shading correction data. It is available and convenient.

Even without using the reference light as described above,
It is possible to obtain the shading correction data to be stored in the memory 22. That is, when the sensitivity unevenness characteristics of the photomultiplier are obtained in advance, the shading correction data can be determined according to the characteristics. However, as shown in the above-described embodiment, if the correction value calculation circuit 20 is provided, the correction value can be appropriately calculated after the image information reading device is actually operated. It is preferable because it can cope with changes with time.

Further, the shading correction based on the shading correction data described above may be carried out in any concrete manner as long as the image signal finally obtained from the reading device can be made unaffected by the shading. Instead of directly changing the image signal as in the above-mentioned embodiment, the sensitivity of the photomultiplier is changed between the front surface side and the back surface side of the sheet or the power of the light beam is changed according to the shading state. May be. As the photoelectric reading means, a combination of the above-mentioned large-sized light guide and a small-sized photomultiplier (see Japanese Patent Laid-Open No. 55-87970, etc.), a long photomultiplier, a line sensor, etc. It can also be used.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a radiation image double-sided reading device.

FIG. 2 is a schematic diagram of an apparatus for performing a shading correction method according to the present invention.

FIG. 3 is a diagram for explaining shading correction according to the present invention.

FIG. 4 is a diagram illustrating an example of shading correction data.

FIG. 5 is a schematic diagram of another apparatus for implementing the shading correction method according to the present invention.

FIG. 6 is a diagram showing another embodiment of the radiation image double-sided reading device.

[Explanation of symbols]

 1 Storage phosphor sheet 10, 10a, 10b Laser light source 11, 11a, 11b Light beam 12, 12a, 12b Mirror 13a, 13b Photostimulated emission light 14a, 14b Light guide 15a, 15b Photomultiplier 16a, 16b Logarithmic converter 17, 17a, 17b A / D converter 18 Memory 19, 19a, 19b Scan lens 20 Correction value calculation circuit 21 Clock generator 22 Memory 23 D / A converter 24 Switch

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area H04N 1/04 H04N 1/04 E

Claims (2)

[Claims] 1. A stimulable phosphor sheet on which a radiation image is stored and recorded is irradiated with excitation light, and the stimulated emission light emitted from both sides of the sheet by irradiation of the excitation light is photoelectrically detected. A shading correction method in reading a radiation image, wherein two image signals representing the radiation image are obtained, and the respective image signals are added to obtain an addition image signal representing the radiation image, the shading of the addition image signal being corrected. The shading correction method is characterized in that the shading correction data to be obtained is obtained in advance, and the variation of the added image signal due to the shading is corrected based on the shading correction data. 2. The stimulable phosphor sheet that is uniformly irradiated with radiation is irradiated with the excitation light, and the stimulated emission light emitted from both sides of the sheet by the irradiation of the excitation light is photoelectrically converted. The shading correction method according to claim 1, wherein two signals representing the shading data are obtained by detection, and the shading correction data is obtained based on the data obtained by adding the respective signals.