US2605427A - Diffusion-preventing device for x-rays - Google Patents

Description

y 29, 1952 R. A. DELHU MEAU 2,605,427

I DIFFUSION-PREVENTING DEVICE FOR X-RAYS Filed. Ndv. 18, 1949 In van for Patented July 29, 1952 DIFFUSION-PREVENTING DEVICE FOR X-RAYS Roger Andr Delhumeau, Saint-Maude, France Application November 18, 1949, Serial No. 128,057 In France November 25, 1948 4 Claims. (Cl. 250-453) It is known that X-rays upon emerging from a body traversed by them undergo irregular deviations which result in diffusion detrimentalto the clearness of the observed or radiographed images. To prevent such diifusion it has been suggested to interpose between the body and the screen or plate a diffusion-preventing grid adaptedto absorb the deviated rays.

In the early construction of such gridsit was first attempted to make use of the absorptive capacity of lead for X-rays. Accordingly the grids were constructed in the form of laminated sheets of a substance having a lowv absorption rate forX-rays interspersed with fine laminations or layers of lead.

V The earlier grids of such construction coinprised rather heavy intercalated absorptive laminations, and the pattern formed by the layers or laminations of lead interfered with the image.

-To eliminate this, devices were used for imparting to'the grid a translatory movement in a direction parallel to the plane of the laminations. The production of such movement requires the provision of a rather complicated and cumber- 'ome' mechanism which substantially increases 'the'cost of the X-ray outfit. Moreover, it retempted to bring the absorptive laminations closer together and a thinner grid was used, in which the intercalated laminations were made of resin, cardboard, aluminiuimand similar substances. Such grids provide a fine pattern, which is not very troublesome both for X-ray observation and X-ray photography. Certain types of such grids are focalized, that is to say their laminations throughout the width of the plate have an inclination parallel to that of thecentral rays to make allowance for'the fact that the X-rays areemitted in'the form of a conical beam.

Whether or not a'focali zed grid is used, the construction of the above-described laminated 2 cardboard or wood for example. Still further constructional difficulty is encountered when it becomes necessary, in order to provide focalization, to form said permeable intermediate layers 1 with a nonuniform thickness in order to allow for the correct inclination of the various lambnations of lead across the grid. Indeed, in some forms of construction in the case of grids with intercalated laminations made of aluminium, focalization cannot be achieved. I Focalized grids in which the intermediate laminations aremade of materials other than aluminium have the grave shortcoming of beingjweaker and are apt to crack or split easily whereupon they are liable to overlap in partsand become immediately unserviceable.

This invention has for its object to provide a diffusionipreventing grid for X-ray practice which, ascompared with known grids, ofie rs the advantages of being much more simpler to fabricate, allowing very accurate focalization andbeing much stronger than grids composed-of laminated strips.

The gridof the invention is characterized in that it comprises a plate made of a substance permeable to X-rays, formed with narrow closelyspaced grooves extending to only part offi ts depth, said grooves being filled with a substance impermeable to X-rays.

In simple laminated grids formin a lineate pattern; the diffusionpreventing function is performed only in a direction perpendicular to the direction of thelamellae; in a direction parallel with the laminations on the other hand, difiusion is not prevented, whereby such grids only I imperfectely fulfil the diffusion-preventing func tion which is assigned to them.

' To'avoid this drawback, it has been suggested to superimpose two laminated grids in crossed relationship over each other, but this has other and important drawbacks in that a dotted pattern becomes superimposed overthe lineate patternsat the intersections of the lead laminations, since at such points the absorptive thickness is twice as great than elsewhere. Moreover, and

[this is the gravest defect, the total depth of the grids of prior art is a delicate process because of 5b the very small thickness or depth (in the order of.

about 5 mm.) which the laminations or layers of lead have to have, and also the comparatively 7 m be e yqble iibn b egrid isdou'b1ed, since two equal depths of intermediate laminationsare superimposed, so that substantially longer times of exposurehave to be used unless one is'willing' to accept a substantially reduced degree of screen; illumination, which the invention, accordinglif i "stancebermeabie tax-ra s formed,

rbs 1 atteinedfgrid comprising ja make the pattern lines fade out merely by impart 1 ing movement to the grid in adirectionpparallel to its length.

The accompanying drawings illustrate by way of example, in isometric perspective view, pr.eferred embodiments of grids according to the invention.

Fig. 1 is a fragmentary perspective of a lineate grid according to the invention.

Fig. 2 is a fragmentary perspective of a crisscross grid according to the invention.

- Fig. 3 is a, fragmentarysectional view taken onthe line III-III of .Fig. '1 when the grooves have been filled with a .material nonpermeable to X-rays.

Fig. 4 isa similar view .ofamodification.

Fig. 5 is a diagrammatic view showing the focalization of the grooves .of agrid according'to Fig. 1.

-As shown in Fig. .1, thegrid is. simplyformed by. a, plate I :formedat closely spaced intervals,

which in thecaseof fixed grids may be of about 0.4 mm with channels or grooves 2 about 1.5 mm.

in depthand about 0.1 mm. in width, and these grooves .are filled with an X-ray absorbentsubstance 3 '(Fig. 3). The pattern effect of such a grid when maintained stationary is quite acceptable. .In the caseo'f a grid to be used with .a Potter (movable, grid) alarger spacing between 'thegrooves may sufiice, said grooves being ;provided, in a manner known per se, with a reater depth. 7

A grid formed as just described is strong, since it is an integral structure rather than being a laminated assembly. Moreover, it-ispossible to achieve 'focalization by progressively inclining the grooves, from the central one to the outermost grooves. Such a .focalization is clearly shown in Fig. 5 where 4 designates an X.-,.ra y lamp located above agrid according toFig. 1. This grid is diagrammaticallyshown in sectionand it may be seen that the central. groove ,2m'is located in a vertical plane, passing through the center of, lamp 4 while on either side the grooves 2n are inclined, with the angle .of inclination increasing progressively with the distance ,from the center of the plate so that the projected planes of said grooves converge at the focal point at-which the.center of the lamp-4 is situated.

Obviously, any suitable materials may .be .used in .such construction, the permeable substance formingthe plate being for instancea suitable resin while the.X-ray absorbing substance filling the. grooves comprises lead .or equivalent mate- -rials.. r

.The grooved plates of the invention may be produced by a variety of means, as by printing, engraving, cutting; constriction of. wider grooves, and the like, and the desired focalization may be secured by suitable adjustment of the tools used inf forming the individual grooves, or bybodily distortion of the plate as a whole.v .One way of producing a focaliz edjfgrikzl. according to-the ,in- [vention isjto cut theg'rooves therein;with;a milling'j machine the .cutterofwhicli is progressively pattern in the image.

tilted to produce the desired focalization efiect.

To fill the grooves with the X-ray absorbent substance, thin sheets of lead foil may be inserted, or the grid may be filled in with the absorbent substance in powder form, or even with a liquid absorbent substance, in which case the grid is surrounded with a frame. One example of such a liquid absorbent substance is mercury, possibly in amalgam form,.for instance a silver amalgam which will harden with time. When a .liquid is used, the filling step may be carried out in vacuo, by placing an auxiliary plate over the grooved face and sucking in the liquid through the ends of the ducts thus formed.

Figure 2 illustrates a. grid according to the invention provided with a criss-cross grooved pattern, wherein, as shown, said grooves 211 and 2b extend perpendicularly to each other, diagonally with respect to the sides 5 and 6 of the grid, whereby, on imparting a displacement to the grid in a direction parallel to the length of the plate,-it will be possible to cause a displacement of .both sets of lines .therein effective to erase'th'e Obviously, the angles of both sets of parallel lines could differ and the directions thereof could differ. Thus, there would be no objection to forming them parallel with the sides of the plate in the case of a stationary grid.

Moreover, by forming the groovesat sufficiently close intervals, the resulting criss-cross pattern on the image maybe made to be in the same order of magnitude as the grain of the plateor paper used, so that its presence will be .unimportant. It should be understood that with .a focalized criss-cross grid according to theinvention theimage pattern appearsin the form of a fine regularchequer-work, in which the points of intersection do not stand outas they do inthe case of a superimposed pair of grids. According to the modification shown in Fig.4, thegrooved face of the plate I may be covered with another, plate I having a thickness similar to the solid bottom, said other plate beingsecured in place by any suitable means such as by a solvent for the nonabsorbent substance. Thishas the advantage, in addition of protecting the absorbent substance of balancing any strains and stresses which might be developed in the formation of the grooves.

What I claim is:

1. A diffusion-preventing grid :for X-raypracticecomprising a plane plate .of uniform thick- .ness .of a substance permeable to X-rays, said plate having formed in one face thereof:a .series of parallel, uniformly-spaced finegrooves ofuniform depth which is substantially less than the thickness of said plate, the-spacing of saidgrooves being less than 0.4mm the width of the grooves being substantially less than said spacing and the depth of the grooves being greater than the spacing of saidgrooves and less than 1.5 mm., the side walls ofeach groove being parallel with one another and at least one groove in the central portion ofthe plate being substantially perpen- Ldicular to the face of the plate while grooves .andabsorptive of X-rays filling said-grooves.

T2. A..difiusion-.preventinggrid for X-ray practicelaccordingtoclaim ,1, for use as a fixed grid ROGER ANDRE DELI-IUMEAU.

REFERENCES CITED The following references are or record inthe file of this patent:

8 UNITED STATES PATENTS Number Re. 23,179

Number Name Date Files Dec. 6, 1949 Bucky Dec. 21, 1915 Richardson Mar. 6, 1923 Gunther Mar. 24, 1925 Tichy et a1 Dec. 15. 1925 Meyer Sept. 21, 1926 Lindstedt et a1. Nov. 7, 1939 Millenaar Dec. 7, 1943 FOREIGN PATENTS Country Date Great Britain Feb. '7, 1929 France Mar. 25, 1935

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