1. Field of the Invention
This invention relates to a radiation image recording apparatus wherein a radiation image recording medium is exposed to radiation, which has passed through an object, and a radiation image of the object is thereby recorded on the radiation image recording medium. This invention particularly relates to a radiation image recording apparatus, which is of the slit exposure type and in which adverse effects of radiation scattered by an object are eliminated.
2. Description of the Prior Art
Radiation image recording apparatuses have heretofore been used wherein a sheet of X-ray photographic film intervening between two fluorescent intensifying screens is exposed to radiation, which has passed through an object, and a radiation image of the object is thereby recorded on the X-ray photographic film. Radiation image recording apparatuses have heretofore been used wherein a fluorescent plate is exposed to radiation, which has passed through an object, the fluorescence being thereby produced by the fluorescent plate, and the fluorescence is photoelectrically detected by an image intensifier, or the like, whereby an electric signal representing a radiation image of the object is obtained.
When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in obtaining electric signals representing radiation images of objects. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to radiation which has passed through an object, such as the human body. A radiation image of the object is thereby stored on the stimulable phosphor sheet. The stimulable phosphor sheet is then scanned two-dimensionally with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected by a photodetector and converted into an electric image signal.
In cases where a sheet of X-ray photographic film, a stimulable phosphor sheet, or the like, is exposed to radiation, which has passed through an object, a radiation image of the object being thereby recorded, or in cases where a radiation image of an object is formed and detected with an image intensifier, or the like, radiation which has been scattered by the object adversely affects the quality of the radiation image. Therefore, various attempts have heretofore been made to eliminate the scattered radiation during the operation for recording a radiation image.
For example, a slit exposure type of radiation image recording apparatus is disclosed in Japanese Unexamined Patent Publication No. 60(1985)-149043. With the disclosed radiation image recording apparatus, an object is scanned with linear radiation, which has passed through a slit. The linear radiation, which has passed through the object, is passed through a different slit and is then caused to impinge upon a radiation image storage means.
Also, multi-slit types of radiation image recording apparatuses are proposed in, for example, Japanese Unexamined Patent Publication No. 59(1984)-85650 and Med. Phy. 6(3), May/June 1979, pp. 197-204. With the proposed multi-slit types of radiation image recording apparatuses, a plurality of slits are utilized, and a radiation image is recorded with a plurality of streaks of linear radiation. Basically, the multi-slit type of radiation image recording apparatus comprises:
i) a radiation source for producing radiation, PA0 ii) a radiation image recording medium, which is located facing said radiation source, PA0 iii) a first slit plate composed of a radiation absorber and at least two slits, which are formed parallel to each other through said radiation absorber and through which said radiation passes, said first slit plate being located between said radiation source and an object, which object is placed between said radiation source and said radiation image recording medium, PA0 iv) a second slit plate composed of a radiation absorber and at least two slits, which are formed parallel to each other through said radiation absorber and through which said radiation passes, said second slit plate being located between said object and said radiation image recording medium such that at least two said slits of said second slit plate may be parallel to at least two said slits of said first slit plate, and PA0 v) a drive means for synchronously moving said first slit plate and said second slit plate in the direction, along which said slits stand side by side with each other, such that a plane, which passes through one of at least two said slits of said first slit plate and one of at least two said slits of said second slit plate, may pass through said radiation source. PA0 i) a radiation source for producing radiation, PA0 ii) a radiation image recording medium, which is located facing said radiation source, PA0 iii) a first slit plate composed of a radiation absorber and at least two slits, which are formed parallel to each other and through which said radiation passes, said first slit plate being located between said radiation source and an object, which object is placed between said radiation source and said radiation image recording medium, PA0 iv) a second slit plate composed of a radiation absorber and at least two slits, which are formed parallel to each other and through which said radiation passes, said second slit plate being located between said object and said radiation image recording medium such that at least two said slits of said second slit plate may be parallel to at least two said slits of said first slit plate, and PA0 v) a drive means for synchronously moving said first slit plate and said second slit plate in the direction, along which said slits stand side by side with each other, such that a plane, which passes through one of at least two said slits of said first slit plate and one of at least two said slits of said second slit plate, may pass through said radiation source, PA0 i) a radiation source for producing radiation, PA0 ii) a radiation image recording medium, which is located facing said radiation source, PA0 iii) a first group of a plurality of cylindrical radiation absorbers, which are located between said radiation source and an object, which object is placed between said radiation source and said radiation image recording medium, such that the first group of the plurality of said cylindrical radiation absorbers may stand side by side with each other with small gaps intervening therebetween, each of the first group of the plurality of said cylindrical radiation absorbers being supported such that each said cylindrical radiation absorber can rotate around an eccentric shaft, which is shifted from a center axis of each said cylindrical radiation absorber, PA0 iv) a second group of a plurality of cylindrical radiation absorbers, which are located between said object and said radiation image recording medium such that the second group of the plurality of said cylindrical radiation absorbers may stand side by side with each other with small gaps intervening therebetween, each of the second group of the plurality of said cylindrical radiation absorbers being supported such that each said cylindrical radiation absorber can rotate around an eccentric shaft, which is shifted from a center axis of each said cylindrical radiation absorber, and PA0 v) a drive means for synchronously rotating the first group of the plurality of said cylindrical radiation absorbers and the second group of the plurality of said cylindrical radiation absorbers such that a plane, which passes through one of the small gaps intervening between the first group of the plurality of said cylindrical radiation absorbers and through one of the small gaps intervening between the second group of the plurality of said cylindrical radiation absorbers, may pass through said radiation source. PA0 i) a radiation source for producing radiation, PA0 ii) a radiation image recording medium, which is located facing said radiation source, PA0 iii) a first slit belt composed of a flexible, long strip-shaped, radiation-permeable substrate and a plurality of radiation absorbers, which are supported on said radiation-permeable substrate such that slit-like gaps may intervene between the plurality of said radiation absorbers, said first slit belt being located between said radiation source and an object, which object is placed between said radiation source and said radiation image recording medium, PA0 iv) a second slit belt composed of a flexible, long strip-shaped, radiation-permeable substrate and a plurality of radiation absorbers, which are supported on said radiation-permeable substrate such that slit-like gaps may intervene between the plurality of said radiation absorbers, said second slit belt being located between said object and said radiation image recording medium such that said slit-like gaps on said second slit belt may be parallel to said slit-like gaps on said first slit belt, PA0 v) a first belt moving means provided with rotatable members, which are engaged with said first slit belt and move said first slit belt in the direction, which is normal to the direction along which each said slit-like gap on said first slit belt extends, PA0 vi) a second belt moving means provided with rotatable members, which are engaged with said second slit belt and move said second slit belt in the direction, which is normal to the direction along which each said slit-like gap on said second slit belt extends, and PA0 vii) a control means for controlling said first belt moving means and said second belt moving means and synchronously moving said first slit belt and said second slit belt such that a plane, which passes through one of said slit-like gaps on said first slit belt and through one of said slit-like gaps on said second slit belt, may pass through said radiation source.
However, with the radiation image recording apparatus disclosed in Japanese Unexamined Patent Publication No. 60(1985)-149043, the two slit plate located parallel to each other are linearly moved over the whole recording area of the radiation image recording medium. Therefore, the slits cannot be moved quickly. Accordingly, with this conventional radiation image recording apparatus, a long time is required for a single radiation image to be recorded, and the recording capacity cannot be kept high. Also, there is the risk that the object moves during the operation for recording a radiation image of the object and an artifact occurs easily. Additionally, the problem occurs in that the load of the radiation source cannot be kept low.
With the multi-slit type of radiation image recording apparatus, radiation images can be recorded quickly. However, if the distance, by which each slit moves within the time during which the radiation is irradiated, is not exactly equal to the intervals between the slits, some regions of the radiation image recording medium are scanned n times with the linear radiation, and the other regions of the radiation image recording medium are scanned n+1 times with the linear radiation. Therefore, the problem occurs in that artifacts occur at the boundaries between the regions scanned n times with the linear radiation and the regions scanned n+1 times with the linear radiation.
Also, for the radiation image recording apparatus wherein a plurality of slits are utilized, it is desired for a radiation image to be recorded quickly such that an artifact due to movement of an object during the operation for recording the radiation image of the object may be prevented from occurring. Additionally, the conventional radiation image recording apparatus, wherein a plurality of slits are utilized, has the drawbacks in that the apparatus cannot be kept small in size.