Patent Number: 049820982
Section: description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Now, the present invention will be described more specifically below with reference to working examples. EXAMPLE 1 An intensifying screen (354 mm.times.354 mm in area) for X-ray radiography of the chest was produced by the following procedure, using calcium tungstate as phosphor and fixing the magnitudes of speed in the pattern of FIG. 1 so that when the magnitude of speed in the regions A' and B' was taken as 100, that of speed in the regions H and I would fall at 40. Preparation of light-absorbing layer FIG. 7 is a cross section illustrating the manner of absorbing manufacture of a photogravure plate used for the formation of a light-absorbing layer. With reference to this diagram, 30 stands for an intensifying screen used as a planar light source. A black paper pattern 32 provided with an opening 34 of the shape conforming to a desired pattern of speed correction and intended to intercept the light emanating from the planar light source was placed in close contact with one surface of the intensifying screen 30. This black paper pattern 32 and an X-ray film 36 disposed at a distance of about 10 mm downward from the lower side of the paper pattern 32 were enclosed in a cassette 38 and exposed to a beam of X-rays as indicated by the arrow z in the diagram. Then, the X-ray film was exposed to the scattered light from the planar light source. Consequently, there was obtained a photogravure plate having density smoothly and continuously varied across each of the borderline between the part corresponding to the black paper pattern 32 and the remaining part. In the present working example, two black paper patterns were prepared which contained openings shaped as illustated respectively in FIG. 8 and FIG. 9 as desired patterns of speed correction. An X-ray film was exposed to light first through the black paper pattern 32a possessing the opening 34a shown in FIG. 8 (as hatched) and subsequently through the black paper pattern 32b possessing the openings 34b shown in FIG. 9 (as hatched), to produce a photogravure plate. Then, a printing plate was produced from the photogravure plate. A yellow pigment capable of absorbing the light emitted from calcium tungstate was applied on a film of polyester 10 .mu.m in thickness by gravure printing, with the aid of the photogravure plate. Thus, a photo-absorbing layer was formed. Preparation of intensifying screen A slurry was prepared by mixing 20% by weight of calcium tungstate as phosphor with 2% by weight of polyvinyl butyral and 78% by weight of butyl acetate as a binder. As shown in FIG. 5 second layer 14b of phosphor about 75 .mu.m in thickness was formed by applying this phosphor slurry on a protective layer 18 made of polyester film about 10 .mu.m in thickness and drying the applied layer of the slurry. Subsequently, the light-absorbing layer 16 formed by the aforementioned procedure was superposed on the second layer 14b of phosphor. On this layer 16 a first layer 14a of phosphor 75 .mu.m in thickness was formed by applying a phosphor slurry of the same composition as mentioned above on the second layer 14b of phosphor and drying the applied layer of the slurry. Thereafter, a substrate 12 made of polyester film 250 .mu.m in thickness was attached fast to the upper surface of the aforementioned first layer 14a of phosphor, to produce an intensifying screen 10 for X-ray radiography of the chest. The intensifying screen thus obtained was superposed on an X-ray film and enclosed in a cassette. This X-ray film was exposed to a beam of X-ray film was tested for density distribution with a densitometer. When the X-ray film was examined with respect to speed distribution in the intensifying screen, this intensifying screen was found to possess a speed distribution as shown in FIG. 10. When the X-ray film was tested for change in speed along the line X--X in the diagram of FIG. 10, the intensifying screen was found to possess such a density distribution as shown in FIG. 11. As clearly noted from this diagram, the speed was smoothly and continuously changed across the borderlines between the regions of speed and within the regions speed. This fact clearly indicates that no visible line patterns were found in the produced X-ray radiograph. Then, the X-ray radiography of the chest was conducted on 50 subjects, using the intensifying screen possessing the speed distribution mentioned above. Consequently, in virtually all the cases, the lungfield, the trachea and the bronchus, and even the part of the bronchus overlapping the hilum of the left lung, were clearly radiographed in highly satisfactory contrast. The intensifying screen of the present case for the Xray radiography of the chest possessed a substantially continuous change in speed as shown in FIG. 10 because it was formed by using as the photogravure plate an X-ray radiograph having the light-absorbing layer blurred with the scattered beam of light from the planar light source. As a result, the pertinent internal organs could be radiographed clearly without entailing the occurrence of drawbacks detrimental to the diagnostic examination of the part such as line patterns in the image originating in the borderlines of change in density in the light-absorbing layer. Thus, it is evident that when the intensifying screen for the X-ray radiography of the chest possesses the speed distribution illustrated in FIG. 10 is highly effective in the diagnostic examination of the chest. EXAMPLE 2 A light-absorbing layer was prepared by the following procedure in the place of the light-absorbing layer of Example 1. Preparation of light-absorbing layer First, an X-ray radiograph of the chest of a person of standard body type was prepared and it was radiographed with the focal point moved to a certain distance. Then, the photograph of the chest taken at the aforementioned distance from the focal point was again radiographed with the focal point again moved to a certain distance. When a radiograph produced after repeating this procedure was found to show the minute details and the peripheries of bone in a perfectly blurred state, it was used as a photogravure plate. Then a printing plate was produced from the photogravure plate and a light-absorbing layer was formed using the printing plate by following the procedure of Example 1. Preparation of intensifying screen Subsequently, an intensifying screen for use in the X-ray radiography of the chest was produced using the lightabsorbing layer by following the procedure of Example 1. When the chest was actually X-ray radiographed by using the intensifying screen obtained as described above, the internal organs in the chest were clearly radiographed, indicating that the intensifying screen was as effective in producing an X-ray radiograph as the intensifying screen of Example 1. EXAMPLE 3 An intensifying screen for X-ray radiography of the head (300 mm.times.250 mm) was prepared by the following procedure, using calcium tungstate as a phosphor and fixing the speed distribution such that the speed in the region L would fall at 40 where the speed in the region J was taken as 100 in the diagram of FIG. 2. Preparation of light-absorbing layer A black light-shielding plate provided in the central part thereof with a substantially elliptical opening measuring 150 mm in major diameter and 100 mm in minor diameter. An X-ray film was disposed at a distance of about 10 mm downward from the light-shielding plate and was exposed to light in the same manner as in Example 1. A printing plate was produced by using this X-ray film as a photogravure plate. Then, on a polyester film 10 .mu.m in thickness, a light-absorbing layer was formed with yellow pigment by following the procedure of Example 1. Preparation of intensifying screen Similarly to the intensifying screen of the construction illustrated in FIG. 5, the same calcium tungstate-containing slurry as used in Example 1 was applied on a protective film 18 of polyester about 10 .mu.m in thickness and the applied layer of the slurry was dried, to give rise to a second layer 14b of phosphor about 50 .mu.m in thickness. Then, the light-absorbing layer 16 formed by the method described above was superposed on the second layer 14b of phosphor. Further the phosphor slurry of the aformentioned percentage composition was applied on the light-absorbing layer 16 and the applied layer of the slurry was dried, to give rise to a first layer 14a of phosphor 50 um in thickness. Thereafter, a substrate 12 of polyester film 250 .mu.m in thickness was attached fast to the upper side of the layer 14a of phosphor, to complete an intensifying screen 10. The intensifying screen thus obtained was placed on top of an X-ray film, enclosed in a cassette, exposed to a beam of X-rays, and tested for speed distribution in the same manner as in Example 1. The produced X-ray radiograph was found to possess a speed distribution illustrated in FIG. 12. As concerns the continuity of the change in speed, the X-ray radiograph showed no discernible line pattern, indicating that the speed was changed with sufficient continuity. Then, 50 persons were subjected to clinical test by the "Mr. Towne's method" of the head using the intensifying screen possessing this speed distribution. In virtually all the X-ray radiographs produced in the test, not merely the backbone and the occipital bone but also the portion near the scalp were clearly radiographed with highly satisfactory contrast. The intensifying screen obtained in this working example for use in X-ray radiography of the head possessed a substantially continuous change in speed as illustrated in FIG. 12 and, therefore, enabled the head to be clearly radiographed even to the peripheral part such as the portion near the scalp. It did not give rise to any such detriment to the diagnostic examination as line patterns which would possibly be produced because of the borderlines in change of density in the light-absorbing layer. The intensifying screen for the X-ray radiography of the head possessing the speed distribution illustrated in FIG. 12, as obvious from the clinical results mentioned above, permits acquisition of such information concerning the portion near the scalp as has never been utilized for diagnostic examination. Thus, it is highly effective in the diagnostic examination of the head. EXAMPLE 4 An intensifying screen (300 mm.times.200 mm) for X-ray radiography of the upper and lower jaws and the peripheries thereof was prepared by the following procedure, using calcium tungstate as a phosphor and fixing the speed distribution so that the speed in the region N would fall at 65 where that of the region M was taken as 100 in FIG. 3. Preparation of light-absorbing layer A black light-shielding plate provided in the central part thereof with an opening of the shape to give a shadow as illustrated in FIG. 3 was prepared. An X-ray film was disposed at a distance of about 10 mm downward from the light-shielding plate and exposed to light in the same manner as in Example 1. A printing plate was produced by using this X-ray film as a photogravure plate. Then, a light-absorbing layer was formed on a film of polyester 10 .mu.m in thickness by depositing carbon black by following the procedure of Example 1. In this light-absorbing layer, the portions for starting speed change toward the portion corresponding to the strip of region M of high speed were located each at a distance of about 30 mm to the left and right from the center. The light-absorbing layer possessed a density change corresponding to Type 2 illustrated in FIG. 4. Preparation of intensifying screen Similarly to the intensifying screen of the construction shown in FIG. 5, the same calcium tungstate-containing slurry as used in Example 1 was applied on a protective layer 18 of polyester about 10 .mu.m in thickness and the applied layer of the slurry was dried, to give rise to a second layer 14b of phosphor about 50 .mu.m in thickness. The light absorbing layer 16 formed by the method described above was superposed on the second layer 14b of phosphor. Then, the phosphor slurry of the aforementioned composition was applied on the layer 16 and the applied layer of the slurry was dried, to give rise to a first layer 14a of phosphor 100 .mu.m in thickness. Thereafter, a substrate 12 of polyester film incorporating therein titanium oxide or carbon black and having a thickness of 250 .mu.m was attached fast on the first layer 14a of phosphor, to give rise to an intensifying screen 10 for X-ray radiography of the upper and lower jaws and the peripheries thereof. Then, 50 persons were subjected to diagnostic examination by the X-ray radiography of the upper and lower jaws and the peripheries thereof, using the intensifying screen obtained as described above. In all the X-ray radiographs thus obtained, the parts were radiographed with substantially uniform density without suffering the shadow of the backbone to impair the distribution of radiographic density. In accordance with present working example, since the light-absorbing layer was incorporated in the layer of phosphor in such a manner as to form a strip of region of high speed at the position practically corresponding to the backbone, the amount of light emitted in the portion corresponding to the backbone was increased enough to permit production of a highly desirable X-ray radiograph of the upper and lower jaws and the peripheries thereof without giving rise to a portion of uneven-density due to the difference in X-ray absorption between the backbone and the other parts. In the category of dentistry and surgery specializing in oral cavity, therefore, this invention enables diagnostic examination of the pertinent parts of the human body to be effected accurately with one X-ray radiography.