US 2827571 A
Description (OCR text may contain errors)
March 18, 1958 H. A. KLASENS ET AL INTENSIFYING SCREEN FOR MAKING X-RAY REGISTRATIONS Filed May 8, 1956 l 2 3 FIG..2
N NTOR N K A KLASENS l HANNES OOSI'ERKAMP AGENT United States Patent i INTENSIFYING SCREEN FOR MAKING X-RAY REGISTRATIONS Hendrik Anne Klasens and Wijbe Johannes Oosterkamp,
Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc New York, N. Y., a corporation of Delaware Application May 8, 1956, Serial No. 583,457
Claims priority, application Netherlands May 23, 1955 3 Claims. (Cl. 250-80) It is well known that in making X-ray registrations the lack of definition of the image on the photographic plate or film can be reduced by using intensifying screens, in which the light produced by the X-rays is scattered very slightly. The intensifying screens serve to amplify the brightness of the image registered on the photographic plate. The light scattering can be very slight, when the screens comprise a honeycomb-shaped grid, the walls of which are made of a metal which highly reflects light, for example silver. The apertures of the grid are filled with a suitable fluorescent substance which is sensitive to X-rays.
The desired slight extent of light-scattering would require the manufacture of grids, the apertures of which are not more than 0.1 mm. in width, whilst the thickness of the walls does not exceed 0.01 mm. Even if the grids were made less fine-meshed, so that one would content oneself with a lower image definition, the manufacture of such screens has a limitation in that the known methods which can be used for this purpose, are complicated and take up much time, so that the screens become expensive.
It has been found in practice that the lack of definition of the X-ray image, if it does not exceed 0.5 mm., is not very inconvenient. When using the normal intensifying screens, which are provided with a layer of luminescent substance, which is not divided by a grid, this limit need not be exceeded. Consequently, usually no use is made of the special grid-shaped screens.
According to a certain development of the art of making X-ray registrations, the X-ray tube is loaded by anode voltages which are higher than is usual. This is of advantage in that a larger amount of X-rays penetrate through the object and this permits of shorter exposure times and requires a smaller dose of radiation. In addition, the use of a higher anode voltage is of advantage, when the image is clouded by parts showing a high radiation absorption, as is the case, for example, in making radiographs of the lungs. Thus, the inconvenient action of the picture of the thorax is considerably reduced.
However, the greater hardness of the X-rays produced results in a reduced absorption by the intensifying screens and by the photographic film or plate. This phenomenon is the reason why the registrations fall short of expectations.
A method of compensating for the reduction in absorption in the material which is sensitive to the X-rays, consists in increasing the thickness of the sensitive layer. In photographic plates or films this measure cannot be used, since a greater thickness of the emulsion layer considerably raises the price of the registration material and, in addition, the layer cannot readily be developed completely. A thicker layer of fluorescent material for the intensifying screens increases the lack of definition, so that the permissible lack of definition of 0.5 mm. would be exceeded.
The invention relates to an intensifying screen for X-ray registrations of the kind in which diffusion of the light produced in the luminescent substance is counteracted and to a construction which can be manufactured readily and cheaply. According to the invention, the grid-shaped structure of such a screen consists of photographically sensitive glass, in which the apertures are separated by narrow partitions the surfaces of which are coated with a metal which highly reflects the light, for example, with silver.
The term photographically sensitive glass relates to certain known silicate-containing glasses in which use is made of substances which produce the formation of resistant photographic images in the glass under the action of actinic rays (X-rays or ultraviolet rays) and of a heat treatment. As a result of the 'heat treatment, the particles of the substances which have been added as a fine powder, such as, for example, gold, silver or copper, in the exposed region become crystallisation cores for the non-metallic substances. These crystals have the property of being dissolved more rapidly in hydrofluoric acid than the material which has not been exposed to radiation.
The invention uses the known technique of Working photographically sensitive glass. Due to the difference between the rate of speed of the process of etching exposed material and that of etching non-exposed glass, grids can be manufactured by forming an image of a pattern corresponding to the grid-shape on the thin glass-plate after which the material of the exposed parts, in which the apertures must be produced, is removed by etching.
By using a grid, in which the size of the apertures is chosen in a suitable ratio to the thickness of the partitions, the lack of definition of the image can be limited to the desired degree. The use of the glass etching process permits of producing a grid having smaller apertures, however, since a small portion of the non-exposed material is also removed by the etching, the thickness of the partitions cannot be reduced. The rates of speed at which the non-exposed material and the exposed material are removed by etching, are in the ratio of about 1:10. When use is made of a glass-plate 1 mm. thick, the apertures must be spaced apart by a distance of at least 0.1 mm. Because of the comparatively high value of the thickness of the partitions, the size of the apertures should preferably be made not too small, so that a favourable ratio is produced between the total surface area of the apertures and of the screen. By using a screen of thickness 1 mm., which absorbs a considerably higher amount of X-rays, the lack of definition can be limited to that of a screen not provided with a reflecting grid and having a luminescent layer 0.3 mm. thick.
In order that the invention may readily be carried into effect, an embodiment will now be described in detail with reference to the accompanying drawing, in which:
Fig. l is a plan view and Fig. 2 a cross-sectional view of a screen in accordance with the invention.
Fig. 1 shows the frame of an intensifying screen for X-ray registrations which is made of a photographically sensitive glass. As initial material use is made of a thin glass plate of thickness, for example, 1 mm., on which a grid is arranged which is perforated so as to be shaped into a form corresponding to that of the screen. This grid must be made from a material which does not pass the radiation by which it is exposed. After the exposure, a photographic print of the grid is produced in the glass, which print is made resistant by heating. The material which has been exposed to light is subsequently removed by etching in a bath of hydrofluoric acid, so that a perforated plate is left, a cross-section of which is shown in Fig. 2. In the case shown, use is made of a screen having square apertures 1, however, the apertures may Patented Mar. 18, 1958.
be shaped into the form of "another polygon or they may be circular; The partitibns'f'are considrablyfnarrower' than the width of the apertures 1 and in determining the thickness allowance is made for. any rednction in thickness dile tb'the fact-f t h 'at mat'rialwliich h asrndt been eiipbsed t'bfiiie: rays from the Vradiatibn: source is remoyed' in 'the'etchin'g-pr'eces's, 'A swill b'e rseenf fi'or n Fig. 2f; the partitions Zare slightly..- tapered onboth'Psi'desl- This is (if 'ady'aiitag'e fer preventingftliefilling fiom dropping outfof the apertures; v r
The perfbratedglassplate is then coated by silveringv with a thin-layer 3 of light-refiectingemetala: Finally. the apertures "are filled 'with 'luminescent 'material' 4.
Such a'screen permitsofrestricting the lack-of definition able amount of light passes reflected, in the directibn ofthc film or photographic plate, the image of the screen produced on the registering material will not be inconvenient.
What is claimed is: i 1 1. 7 An intensifyingscreen v for X-ray, registrations-c0mpn'sing'a 'honeycoi'nb shaped' grii 'thewalls of which are light-reflecting and the apertii'res of'which are filled with a luminescent substance;- said aperturesibeingzfbrmedzinz a-glass plate made ofiphvtngrapliically 'sensitive g'lass and thepartitions are 'coatedwith'a-lighbreflectingimetal layer. 2. An intensifyingscreen' a"s"clai rned"in'claim'dj in which the'partitions are tapered on bOflLSidfiS- 3, An intensifying screen as claimed in claim l in which to areasbnably'satisfactry valne. The maximum thick- 15 thc lighfl efi g layel'iysilvel" ness' of the partitions maybe ()Il'mm. In the-present casetheilacli'of definition israboutioj mm. Since a consider- N6 refren'cescite'cl.
by the inclined walls and is