Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2001-11-15
2004-08-24
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S581000, C250S590000
Reexamination Certificate
active
06781144
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a radiation image radiographing cassette housing therein a stimulable phosphor sheet and to a radiation image reading apparatus that reads radiation image information accumulated in the stimulable phosphor sheet.
For digitizing radiation image information generated in a hospital and thereby for storing and transmitting it, there has become popular a radiation image reading apparatus which outputs image data as digital data. As a radiation image reading apparatus of this kind outputting digital data, a radiation image reading apparatus employing a stimulable phosphor sheet is known well.
The stimulable phosphor sheet can detect a part of radiation energy transmitted through a subject and can accumulate radiation energy thus detected in the stimulable phosphor sheet. Further, it is possible to take out the radiation energy accumulated in the stimulable phosphor sheet as stimulated light, by exciting it with a laser beam having a prescribed wavelength. This stimulated light can be taken out as an electric signal by a photoelectric transfer element such as a photomultiplier.
In general, the stimulable phosphor sheet is housed in a casing that is a portable thin box called a cassette, to be used. The form of usage of this type makes it possible for a user to carry the stimulable phosphor sheet easily together with a cassette, thus, radiographing can be conducted through the same handling as for a screen/film type cassette which has been used in the past.
As a method for handling a stimulable phosphor sheet, there is known well a contact conveyance method wherein a flexible stimulable phosphor sheet is taken out by a sucker from a cassette, and the stimulable phosphor sheet thus taken out is interposed between rollers to be conveyed, as disclosed in TOKKAIHEI No. 1-237636. Since a stimulable phosphor surface is pressed by rollers in the contact conveyance method, when rollers are contaminated with dirt or dust, the phosphor surface is contaminated or scratched and a life of a stimulable phosphor sheet is shortened, which is a fatal weak point. Further, a scratch or dirt on the stimulable phosphor surface appears as a noise in the image read, and it makes it impossible to provide quality images as diagnostic images.
As a method to solve the weak point of the contact conveyance method, there is proposed a method shown in TOKKAIHEI No. 11-160821. In this method, a stimulable phosphor sheet is stuck on a rigid sheet member, and the stimulable phosphor sheet and the rigid sheet member are conveyed through the method wherein only the rigid sheet member comes in contact (the stimulable phosphor surface does not come in contact). The method to convey the stimulable phosphor sheet without touching the stimulable phosphor surface is called a non-contact conveyance method.
In this non-contact conveyance method, the stimulable phosphor surface is neither contaminated nor scratched, because conveyance under the condition of non-contact with the stimulable phosphor surface is assured. Therefore, the non-contact conveyance method is observed as a new conveyance method for stimulable phosphor sheets because it has a merit that a noise caused by dirt or a scratch on the stimulable phosphor surface does not appear on the image read, and a life of the stimulable phosphor sheet is long.
However, in the case of the non-contact conveyance method, it is difficult to convey a stimulable phosphor plate under the condition that it is curved to a certain extent as in a contact conveyance method, because the stimulable phosphor sheet is generally required to be conveyed under the condition that it is stuck on a rigid sheet member. Namely, what is conducted by the contact conveyance method is only a linear conveyance at all times.
In the non-contact conveyance method, there is considered a method to read image information while drawing out a stimulable phosphor plate from a cassette. This method, however, has a weak point that a vibration caused by contact is transferred to a stimulable phosphor plate that is in process of reading operation if a user comes in contact with a cassette in the course of reading, and thereby, a noise is generated in the image read. In the non-contact conveyance method, in particular, the stimulable phosphor surface is easily subjected to vibration compared with the contact conveyance method because it is impossible to control vibration by interposing the surface of the stimulable phosphor sheet with rollers. In particular, a rigid sheet member on which a stimulable phosphor sheet is stuck propagates vibrations well, which is more undesirable. In the non-contact conveyance method, therefore, it is necessary to read image information after a stimulable phosphor plate has been taken out of a cassette completely.
A size of a stimulable phosphor sheet amounts to 354×430 mm in the case of a size of 14×17 in. A non-contact conveyance method has a weak point that an apparatus needs to be large in size, because a sheet in the aforesaid size is required to be conveyed without being curved after it has been taken out of a cassette completely. For example, in the case of a cassette in a size of 14×17 in., when there is assumed an occasion wherein a stimulable phosphor sheet is drawn out of a cassette linearly, and then, image information is read while the linear conveyance of the sheet is maintained, a distance from the rear end of the cassette to the front end of the stimulable phosphor sheet needs to be a length equivalent to three cassettes each being in a size of 14×17 in. (430 mm×3=1290 mm), and if an area for parts and a space which are necessary for constituting an apparatus are further taken into consideration, the apparatus turns out to be considerably large in size.
Therefore, there has been proposed a method wherein a stimulable phosphor sheet is drawn out downward, and then, is subjected to parallel displacement in the horizontal direction (direction perpendicular to the surface of the stimulable phosphor sheet), as in TOKKAIHEI No. 11-160821. However, a mechanism for accurate parallel displacement for the large-sized sheet is extremely complicated, and it results in a cost increase. Further, there is a weak point that reliability and stability are lowered fundamentally, because accurate parallel displacement for the large-sized sheet itself is an unreasonable demand.
There are two types of the radiation image reading apparatuses; one is the large sized apparatus that can accept a plurality of cassettes at a time, and the other is small sized apparatus that can accept only one cassette. The large type has demerits of occupying a large space and high cost, on the contrary, the small type has a poor efficiency due to that only one cassette can be accepted. Generally, in one radiographing examination 1 to 5 cassettes, 1.8 cassettes in average, are used, therefore, unless 2 cassettes in minimum can be accepted at a time by the radiographing apparatus, working efficiency will be remarkably decreased.
Further, in order to read the radiation image information from the stimulable phosphor sheet, a conveyance of the stimulable phosphor sheet, the cassette holding the stimulable phosphor sheet, or a part of the cassette holding the stimulable phosphor sheet is necessary. However, if an abnormality in the conveyance such as a jam occurs in the process of conveying the stimulable phosphor sheet, the cassette holding the stimulable phosphor sheet, or a part of the cassette holding the stimulable sheet, there may be a case where the conveyance cannot be continued and the apparatus have to be stopped.
Regarding the apparatus used at the medical service site, when the apparatus stopped due to abnormal conveyance, it is required not only notifying the user of the occurrence of the conveyance abnormality, but also immediately clearing the abnormality to return to be usable again. If the apparatus is kept stopped, a radiographing diagnosis for an emergent patient cannot be conducted and the following med
Frishauf Holtz Goodman & Chick P.C.
Hannaher Constantine
Konica Corporation
Moran Timothy
LandOfFree
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