Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2000-02-22
2001-12-25
Mack, Ricky (Department: 2873)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S584000
Reexamination Certificate
active
06333513
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for processing electric signals of a radiographic image recorded in a stimulable phosphor sheet, which is favorably employed for reproduction of a radiographic image in a radiographic image recording and reproducing method.
BACKGROUND OF THE INVENTION
As a method replacing a conventional radiography using a combination of a radiographic film and radiographic intensifying screen, a radiation image recording and reproducing method utilizing a stimulable phosphor is practically employed. This method employs a stimulable phosphor sheet (i.e., radiation image storage panel) comprising a stimulable phosphor, and comprises the steps of causing the stimulable phosphor to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as “stimulating rays”) to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals. The phosphor sheet thus processed is then subjected to a step for erasing a radiation image remaining therein, and then stored for the next radiation image recording and reproducing procedure. Thus, the stimulable phosphor sheet can be repeatedly employed.
In general, a support and a protective film are provided on the top and bottom surfaces of the stimulable phosphor sheet, respectively. The stimulable phosphor sheet usually comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor without binder. The stimulable phosphor sheet containing no binder can be formed by deposition process or firing process. Further, the stimulable phosphor sheet comprising agglomerated phosphor soaked with a polymer is also known.
The radiation image recording and reproducing method is often used as X-ray radiography for medical diagnosis. In that case, it is especially desired to obtain a radiation image of high quality (particularly, high sharpness for high resolution) by applying a small dose of radiation. Therefore, the stimulable phosphor sheet is required to have a high sensitivity and to provide an image of high quality.
The sharpness of radiation image is mainly affected by diffusion or scattering of the stimulating rays in the stimulable phosphor sheet in the case that the reading process is performed by the steps of sequentially scanning the stimulating rays to divide the plane of the phosphor sheet into plural pixels, and detecting the stimulated emission by a photodetector. In this process, the procedure for reading the latent image comprises the steps of sequentially applying a light beam of the stimulating rays onto the surface of the phosphor sheet to induce the stimulated emission, and successively collecting and detecting the emission. If the stimulating rays diffuse or scatter on the place of the phosphor sheet, the stimulating rays excite the stimulable phosphor not only at the target pixel but also in its adjacent pixels. Consequently, the stimulated emission emitted from the target pixel is contaminated with that from the adjacent pixels. The contamination of the emission impairs the sharpness of the reproduced radiographic image.
For avoiding the diffusion or scattering of the stimulating ray in the stimulable phosphor sheet, it has been proposed to divide a plane of the stimulable phosphor sheet into small physically divided sections (microcells) with a partition reflecting or absorbing the stimulating rays.
Japanese Patent Provisional Publication No. 59-202100 discloses a stimulable phosphor sheet having a honey-comb structure consisting of a great number of microcells filled with stimulable phosphor. This phosphor sheet comprises a substrate and a stimulable phosphor layer provided thereon, and the honey-comb structure sectioned with a partition is further provided on the phosphor layer.
Japanese Patent Provisional Publication No. 9-15396 describes a stimulable phosphor sheet which comprises a grid having openings with a size larger than a beam spot of stimulating rays to define an emitting area of one pixel by the grid opening so that the resulting radiation image can have a high space resolution.
According to the study of the present inventor, the stimulable phosphor sheet comprising a grid and plural microcells surrounded by the grid in its stimulable phosphor layer generally has nonuniformity in the sensitivity on the respective microcells. The nonuniformity of sensitivity is caused by nonuniformity of the phosphor layer which is prepared by coating a stimulable phosphor-containing solution on a plane having a grid thereon.
The stimulable phosphor sheet having non-uniform sensitivity gives a reproduced radiation image of low quality because it has a structure noise due to nonuniformity of the sensitive material. Moreover, if the scanning space (space between one scanning line and next scanning line) is not identical to the sizes of microcells, a moire (i.e., a pattern of interfering stripes) is observed on the reproduced radiation image, to reduce the quality of the radiation image.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for processing electric signals of a radiographic image recorded in a stimulable phosphor sheet having microcells, to reproduce the radiographic image with high image quality.
The present invention resides in a method for processing electric signals of a radiographic image which are obtained by the steps of scanning a stimulating light beam on a stimulable phosphor sheet comprising a stimulating light-reflective or light-absorbent grid and stimulable phosphor-containing microcells surrounded by the grid and having a radiographic image recorded therein in a direction along the grid and photoelectrically collecting in sequence stimulated emissions emitting from the stimulable phosphor-containing microcells, which comprises the steps of:
(1) detecting a signal of a grid surrounding a microcell and a signal strength I corresponding to the microcell surrounded by the grid, so as to determine a signal strength I(x,y) in a microcell residing in a position (x,y) which is determined from a size information of the stimulable phosphor sheet and an order of the detected signal corresponding to the grid;
(2) determining a correcting value for the signal strength I(x,y) according to the following formula:
correcting value=
I
(
x,y
)
/I
0
(
x,y
)
wherein I
0
(x,y) is a base sensitivity strength which is predetermined in the microcell residing in the position (x,y);
and
(3) processing each signal strength detected in each microcell using each correcting value determined in each microcell, in consideration of a predetermined pixel size of the radiographic image, to obtain a corrected radiographic image data.
In the above-described method of the invention, the step (3) for processing each signal strength detected in each microcell comprises, if the pixel size is larger than the size of microcell and the pixel comprises plural microcells, obtaining an average of correcting values of the microcells and using the average correcting value for the pixel comprising plural microcells.
Otherwise, if the pixel size is equal to or smaller than the size of microcell, the step (3) for processing each signal strength detected in each microcell is performed using a correcting value which is determined from the correcting value of the microcell, in consideration with correcting values of its adjacent microcells.
REFERENCES:
patent: 4944026 (1990-07-01), Arakawa et al.
patent: 2000-241919-A (2000-09-01), None
Fuji Photo Film Co. , Ltd.
Mack Ricky
Sughrue & Mion, PLLC
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