Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2000-02-22
2002-02-05
Mack, Ricky (Department: 2873)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S581000
Reexamination Certificate
active
06344657
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a stimulable phosphor sheet employed in a process for radiation image recording and reproducing method including a double-side reading system.
BACKGROUND OF THE INVENTION
As a method replacing a conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor was proposed, and has been practically employed.
A representative radiation image recording and reproducing method comprises the steps of:
irradiating one surface of a stimulable phosphor sheet (or radiation image storage panel) with radiation having passed through an object or having been emitted by an object to record a radiation energy image of the object on the stimulable phosphor sheet:
sequentially exciting said surface of the stimulable phosphor sheet with stimulating rays to release the radiation energy recorded in the phosphor as stimulated emission;
photoelectrically detecting the stimulated emission from the excited surface and, optionally, from the opposite surface of the stimulable phosphor sheet to obtain electric signals;
reproducing the radiation image of the object as a visible image from the electric signals; and
applying erasing light onto at least the front side surface of the already excited stimulable phosphor sheet to release radiation energy remaining in the phosphor sheet.
Thus, the stimulable phosphor sheet can be repeatedly employed.
In this method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to the object at a considerably smaller dose, as compared with a conventional radiography using a combination of a radiographic film and radiographic intensifying screen.
The stimulable phosphor sheet has a basic structure comprising a support and a stimulable phosphor layer provided thereon. However, if the phosphor layer is self-supporting, the support may be omitted. On the free surface (surface not facing the support) of the phosphor layer, a transparent protective film is generally placed to keep the phosphor layer from chemical deterioration or physical shock.
The phosphor layer usually comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor without binder. The phosphor layer containing no binder can be formed by deposition process or firing process. Further, the layer comprising agglomerated phosphor soaked with a polymer is also known. In any type of phosphor layer, the stimulable phosphor emits stimulated emission when excited with stimulating rays after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or radiated from an object is absorbed,by the phosphor layer of the phosphor sheet in proportion to the applied radiation dose, and a radiation image of the object is produced in the phosphor sheet in the form of a radiation energy-stored image. The radiation energy-stored image can be released as stimulated emission by sequentially irradiating the phosphor sheet with stimulating rays. The stimulated emission is then photoelectrically detected to give electric signals, so as to reproduce a visible image from the electric signals.
The radiation image recorded in the phosphor sheet is generally read by the steps of applying stimulating rays onto the front surface side (phosphor layer side) of the phosphor sheet, collecting light emitted by the phosphor particles by means of a light-collecting means from the same side, and photoelectrically converting the light into image signals. A system for reading the image from one side of the phosphor sheet in this manner is referred to as “single-side reading system”. However, there is a case that the light emitted by the phosphor particles should be collected from both sides (i.e., the front and the back surface sides) of the phosphor sheet. For instance, there is a case that the emitted light is wanted to be collected as much as possible. There is also a case that the radiation image recorded in the phosphor layer varies along the depth of the layer, and that the variation is wanted to be detected. A system for reading the image from both sides of the phosphor sheet is referred to as “double-side reading system”. A stimulable phosphor sheet employed in the double-side reading system, as well as a phosphor sheet employed in the single-side reading system, is wanted to be as sensitive as possible and to provide an image of high quality (e.g., high sharpness, high resolution, high graininess, etc.).
For not only erasing a remaining radiation image but also removing other stored radiation energy given by environmental radiation or radioactive isotope contaminated in the phosphor sheet, the phosphor sheet for double-side reading system (as well as that for single-side reading system) is subjected to the aforementioned erasing step after the stored image is read out or before the next recording procedure. In this erasing step, light for erasing (hereinafter referred to as “erasing light”) is applied onto the front surface or both of the front and the back surfaces of the phosphor sheet.
A radiation image remaining in the phosphor sheet for double-side reading system is more effectively erased by applying the erasing light onto both surfaces, as compared with applying the light onto one surface. Further, in that case, if the erasing light is applied onto the front surface more than onto the back surface, the erasing efficiency is much improved. However, the total amount of the erasing light is restricted by the employed reading apparatus, and hence if the amount of the erasing light applied onto the front surface side is increased, the amount of the light applied onto the back surface side is decreased. Accordingly, the radiation energy remaining on the back surface side is relatively increased. In consideration of this problem, a stimulable phosphor sheet (as well as an erasing system) giving excellent erasing efficiency is required.
The inventors studied about stimulable phosphors from various viewpoints, and found that improvement of the erasing property is generally incompatible with improving the stimulated emission property. Therefore, if the erasing property of the phosphor in a stimulable phosphor sheet is improved, the emission produced by stimulation is impaired, and consequently the radiation image given by the stimulable phosphor sheet is liable to have poor quality.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a stimulable phosphor sheet giving both improved erasing efficiency and a reproduced radiation image with high quality in a double-side reading system.
For solving the aforementioned incompatible problems (namely, for improving the erasing efficiency without impairing the image quality), the inventors have further studied and finally achieved the present invention.
The present invention resides in a stimulable phosphor sheet comprising a stimulable phosphor which is employed in a radiation image double-side reading system, in which radiation energy image erasability on a front side surface onto which stimulating rays are to be applied being lower than that on a back side surface in such manner that a ratio of a difference of an erasing value to a lower erasing value determined on the front side surface or on the back side surface is less than 10%; said erasing value being determined under the following conditions:
each surface of the stimulable phosphor sheet is submitted to an erasing procedure in which a ratio of an energy of erasing light applied to the front side surface and an energy of erasing light applied to the back side surface is adjusted to 6:4, 7:3, or 8:2; and
the erasing value is calculated on each surface by dividing a quantity of stimulated emission after the erasing procedure by a quantity of stimulated emission before the erasing procedure.
The invention further resides in a radiation image recording and reproducing method which comprises the steps of:
irradiating one surface of the stimulable phosphor sheet of the invention with
Matsumoto Hiroshi
Suzuki Hideki
Fuji Photo Film Co. , Ltd.
Mack Ricky
LandOfFree
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