Patent Number: 053894731
Section: description

DESCRIPTION OF PREFERRED EMBODIMENTS In accordance with the method of the present invention a monolithic panel is first produced from a photosensitive glass which has a differential of solubility not less than 25 and has side sizes and a thickness which corresponds to required sizes and ratio of the grid. For example, the glass can have the following content (mass %): SiO.sub.2 78-82; Al.sub.2 O.sub.3 3.2-4.8; Li.sub.2 CO.sub.3 11-14; Ca.sub.2 CO.sub.3 1.5-3.5; CeO.sub.2 0.20-0.40; SnO.sub.2 0.15-0.45; AgCl 0.01-0.035. The panel is then exposed by radiation beams for producing a hidden image of an X-ray to be produced, through the whole thickness of the panel. In order to ensure passage of the specifically shaped beams of radiation through the whole thickness of the monolithic panel without distortion of the formed image (in other words without refraction, reflection and dispersion of the rays) and also in order to prevent formation of semi-shadows at the borders of the image, the exposure is performed by a short wave electromagnetic radiation with a wavelength which is shorter than a wavelength of an ultraviolet radiation, for example, with X-ray radiation having a wavelength 0.6-0.03 A or gamma radiation having a wavelength 0.02-0.01 A. In order to provide the beams of the exposing radiation, which forms the three-dimensional grid image, with a desired three dimensional shape and also in order to prevent falling onto the panel of rays which extend not in the direction of shaping of the image, a volumetric tunnel-shaped mask-like device is utilized, such as for example the device disclosed in my patent application Ser. No. 08/009,976 filed on Jan. 27, 1993, now U.S. Pat. No. 5,307,394. The device is designed so that only those beams can pass through it and fall onto parts of the panel which have a shape and an angle providing the formation of a hidden image of openings (cells or lines), but the beams do not fall on the parts of the panel which must contain the image of partitions between the openings, and also semi-shadows at the borders of the images are not formed. This device can use a radiation source of any size and shape, and it can be located not in a focal point of the grid. After the exposure the panel is subjected to a thermal treatment to a temperature between 450.degree.-700.degree. C., for example 600.degree. C., in order to develop the hidden image of the grid. Then the panel is etched in a 10-20%, for example 15%, aqueous solution of hydrofluoric acid. Thereby a grid is produced in which directional throughgoing openings are located at the exposed parts of the panel and partitions between the openings are formed at the non-exposed parts of the panel. During the time corresponding to the etching of the opening (exposed part of the glass) over the length 2h (since the etching is performed from two sides simultaneously), the partition (non-irradiated part) is etched in direction of increase of the width of the opening d by the value 2.DELTA.d (since the etching is performed in direction of increase of the diameter in two directions in the longitudinal section simultaneously. The differential of solubility is a ratio of speeds of etching of exposed and not exposed parts, as follows: ##EQU1## wherein a is a differential of solubility, 2h=r.times.d in the case of a grid, r.gtoreq.5 is a ratio of the grid from requirements of radiology (ratio of r=5 of a cellular grid corresponds ro r=10 of a linear grid), d is a diameter of the opening; EQU .DELTA.d=0.01.delta..times.d .delta..ltoreq.10% is a maximum permissible relative error of geometrical sizes of the produced opening. Thus the mathematical expression of the differential of solubility for the grid is: ##EQU2## After the calculations ##EQU3## a.gtoreq.25. Then the openings are covered with a thin coating of an X-ray absorbing material, for example, lead or tungsten so as to provide a uniform coating of high density with a thickness of 0.050-0.040 mm over the whole length and width of the partitions, for example with an electrolythic or carbonilic coating. The coated partitions form strips of the grid, while the openings between the partitions form the cells of the grid, so as to form a monolithic grate of the grid. In order to increase the strength of the grid its sides are formed as a monolithic frame without openings, while its surfaces are provided with covers from an X-ray highly transparent material. The new methods increases the efficiency of manufacture and the quality of the grids since it makes possible the production of the grids with maximum X-ray transparency for primary radiation and especially for long wave X-ray radiation, with substantially increased absorbency of scattered radiation especially with the cellular grid so as to increase contrast, sharpness and resolution. This in turn improves the quality of X-ray pictures and reduces radiation action on patients and medical personnel. The present invention is not limited to the details shown since various modifications and structural changes are possible without departing in any way from the spirit of the present invention. What is desired to be protected by Letters Patent is set forth in the appended claims.