Radiant energy – Source with recording detector – Using a stimulable phosphor
Patent
1993-10-13
1995-05-16
Hannaher, Constantine
Radiant energy
Source with recording detector
Using a stimulable phosphor
250585, 250586, G03B 4202
Patent
active
054163366
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a radiation image read-out apparatus which comprises an optical system for exposing a stimulable phosphor plate which contains a latent radiation image to a stimulating beam and for directing the stimulated light emitted from the phosphor plate of a light guide system to a photodetector, e.g. a photomultiplier tube.
There are materials having the capacity to become excited under the effect of radiation energy to which they are exposed, such as X-ray, ultraviolet, or gamma radiation. The absorbed radiation energy may contain information, for example a latent radiation image, which can be read out with the aid of stimulating radiation, such as a laser beam within the range of visible light, by recovering the light emitted from the material and by converting it into an image. One method based on this radiation image, i.e. RIM, technology is X-ray photography, in which radiation directed through the object to be photographed, modified by absorption into the object, is focussed on an excitable and later stimulable phosphor layer on the plate, and the plate thus exposed is read by means of a beam stimulating it, such as a laser beam, in order to produce an image on a photodetector, such as a photomultiplier tube.
The reading out of a radiation image thus takes place by exposing a stimulable phosphor plate which contains a latent radiation image to a stimulating beams and the stimulated light thus produced is collected into a photodetector by means of a light guide. The objective of the light collection is that a maximum amount of stimulated light extracted by the stimulating beam should be transferred to the light guide. The problem with this is that a large proportion of the stimulated light is emitted in directions in which it will not impinge against the light guide in such a way that it would become transferred to the photodetector.
The light guide is usually a member, such as a bent plate, formed from a material transparent to light, such as acrylic plastic, one end of the plate being connected to the photodetector and the other end being placed close to the point at which the stimulating beam impinges against the phosphor plate. The laser beam impinging against the surface of the phosphor plate stimulates light, which will be emitted in all directions. The objective is that as large a proportion as possible of the light emitted from the phosphor plate can be collected into the light guide. However, one single light guide is not capable of collecting more than a small proportion of the light emitted from the phosphor plate.
In U.S. Pat. No. 4,346,295, an effort has been made to solve the above-mentioned problem by placing a mirror surface close to the point at which the stimulating beam impinges against the phosphor plate, in such a manner that the mirror surface will reflect as much of the stimulated light as possible to the receiving end of the light guide. FIGS. 11 and 12 of the same publication depict an apparatus in which stimulated light is detected by using two photodetectors. The light is transmitted to the photodetectors by two light guides. In front of the photodetectors there are preferably arranged color filters which will prevent the access of stimulating light to the photodetectors and will allow the light emitted from the phosphor plate to pass through. However, the reflecting mirror also reflects stimulating light, which will weaken the image. Also, the use of two photodetectors is more expensive than the use of one.
Finnish patent application 903798 discloses a radiation image read-out apparatus in which the light guide system comprises two light guides or light-guide components the receiving ends of which have been arranged close to the point at which the stimulating beam impinges against the phosphor plate, and the output ends have been arranged in connection with the receiving end of one and the same photodetector. Thus the principle is that the light is collected on several guides but is directed to a common photodetector. Thereby the use of mirrors and extra ph
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Hannaher Constantine
Orion-yhtyma Oy
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