US2631244A - Optical system for x-ray screen image intensifiers - Google Patents

Description

ZQ L/ 'y w 4 2 I 9'57 March 10, R L. LQNG|N| OPTICAL SYSTEM FOR mm SCREEN IMAGE INTENSIF'IEIRS y 3 go Filed July 14, 1948 WITNESSES: INVENTOR' Ezchard L. Lonyznz. v BY 7 ATTOR A Q n 1 3 c Q Patented Mar. 10, 195

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IMAGE 1N TENSIFIERS' Richard L. Longinl, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 14, 1948, Serial No. 38,586

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My invention relates to optical systems and, in particular, relates to an improved type of optical system for viewing images produced on screens such as the fluorescent screens employed in X-ray apparatus.

For many purposes'in which images are produced by X-rays and the like, it is desirable to be able to view the image instantly on a fluorescent screen. Fo example, in medical work, it would be desirable for many diagnostic purposes to be able to view on a fluorescent screen an imag of the internal organs of a patient during their normal activities. However, it is well known that where the X-ray radiation is kept within limits which the patient may safely tolerate, the image produced on a fluorescent screen is undesirably faint and cannot be viewed by the diagnosti'cian' in" *aetair"evenarter remainmg in a darkened room for a period of the order of half an hour to accustom his eyes to the low luminous intensities on the screen.

An arrangement in which the image on the fluorescent screen of such an X-ray equipment can be reproduced instantaneously with an enormous increase of intensity is described in Longini and Hunter Patent 2,555,545 issued June 5, 1951, for an Imag Intensifier, filed August 28, 1947, and assigned to the assignee of the present application which claims certain subject matter herein disclosed. Briefly, the above-mentioned image intensifier produces on a photo-electric screen closely adjacent the fluorescent screen an electron image which is a replica of the luminous image, and produces a second luminous image of greatly enhanced intensity but smaller dimensions on a second fluorescent screen which is viewed by the diagnostician through a suitable magnifying optical system. The present invention constitutes an improvement on the optical system described in the above-mentioned Longini and Hunter application.

The photo-electric and fluorescent screens of the above-mentioned application are disposed in a light-optical system which will erect the image. This latter requirement lengthens the distance between the diagnostician and the patient.

One object of my invention is, accordingly, to provide a novel type of optical system in which the diagnostician is able to take a position suitably close to the patient during observation.

Another object of my invention is to provide a novel type of optical system which at once reduces the separation between the diagnostician and the patient and produces an erect image for observation. 7

Another object of my invention is to provide an improved type of image intensifier system for viewing images on screens produced by radiant energy.

Still another object of my invention is to provide an improved "arrangement "for observing X-ray patterns of objects opaque to visible radiation.

Still another object of my invention is to provide an improved apparatus for X-radiation of patients for medical purposes.

A still further object of my invention is to provide an improved optical system for viewing images on fluorescent screens.

Other objects of my invention .will become apparent upon reading the following description, taken in connection with the drawing, in which:

Figure 1 is a general plan view of an X-ray apparatus being employed by a diagnostician for observation of a patient, which apparatus embodies the principles of my invention;

Fig. 2 is a perspective view of a novel type of reflecting prism forming a part of the optical system embodied in my invention;

a highly evaculated electron tube, and since the which makes it inconvenient for him to aid in properly positioning and manipulating the 1atter to obtain theview which he desires. Furthermore. the electron lenses employed in the vacuum tube produce an inverted or reversed image on the fluorescent screen which the diagnostician is to view, and it is necessary to provide Fig. 3 is a sectional view in the plane III- -III Referring in detail to Fig. Lian X-ray tube of conventional type is used to irradiate a patient or other object 2 and throw an X-ray image thereof on a fluorescent screen 3 in a manner too wellknown in the radiographic art to require further description. The fluorescent screen 3 forms an end wall in a high-vacuum tube 4 of the general type described in the Longini and Hunter patent already referred to. The vacuum tube 4 may be of cylindrical form having one transparent end wall on which the fluorescent screen 3 is positioned and having a second end wall 5 of glass supporting a screen comprising finely divlded particles of an electron-phosphor, such as zinc cadmium sulphide, also described in the first of these planes and the dot above-mentioned Longini and Hunter applicais positioned a photo-emissive layer which may be separated from the fluorescent screen 3 by a thin layer of glass or the like. The tube 4 is provided with an electrostatic field electron optieal system (not shown).

The arrangement so far described is disclosed in more detail in the above-mentioned Longinl and Hunter patent and operates in the following way: The X-ray image of the patient produced 'phor screen 5. The electrostatic field above mentioned is arranged to converge the paths of the electrons within the tube 4 and to produce on the screen 5 a luminousimage which is a replica of that on the screen 3, except that it is prefer- 'ably of substantially smaller diameter and is of a brightness which is of the order of 500 times that of the image on the screen 3.

As described in the above-mentioned Longini and Hunter patent, an optical system is arranged which projects along the line of the central axis of the tube 4 and permits an observer to see an 4 line -23 would lie in the second of these planes.

The prism likewise would consist of two other planes. one comprising the points 22-23-25-21 and the other comprising the points 23-24-28- 26, these planes intersecting each other in the line 26-23 and being positioned at right angles to each other. The intersection 23-26 is perpendicular to the intersection 21-25 and makes an angle of 45 degrees with each of the planes 2 l-22-23-24-25 and 2l-25-28-26-2'l. The edge 2l-25 would similarly make an angle of 45 degrees with each of the planes 22-23-26-21 and 24-23-26-28. The planes so far described would normally form peaks similar to those at 23 and 26 above the triangle 2l-22-21 and belowtriangle 24-25-28 in Fig. 2; but for convenience in supporting the prism these peaks are ...removed .by...the .two. .plane faces so, numbered enlarged image of the visible picture on the screen screen 5, and altogether it substantially lengthens the distance from the object 2 along the axis of the tube 4 to the eye of the observer. many cases is an inconvenience, inasmuch a the observer is'not within easy reach of the object 2. In accordance with my invention, I provide an improved type of optical system in which a roof-prism l I, not only inverts the image appearing on the screen 5, but turns the light rays emanating from it through a 90-degree angle so that they may be observed by a diagnostician positioned at one side of the axis of the tube 4 and within easy arms len th of the irradiated object 2.. An ancillary optical system l2 may, if desired, be positioned between the observer and the face of the roof-prism I I.

One meansof doing this is to be described. .This particular arrangement of elements should not be construed as limiting my idea.

Turning to Figs. 2, 3 and 4, the form of the roof-prism will be described in more detail. Referring to Fig. 2, the prism, for reasons about to be discussed in more detail, preferablyhas faces which are not plane but spherical; but for purposes of clarity, it will first be discussed as though it comprises plane surfaces, and the reasons and functions of the curvature imparted to the surfaces will then be discussed.

The prism may be considered to comprise one plane surface containing the points 2 l-22-23- 24-25 which intersects another plane surface 2l-25-28-26-2'I, said two planes being at right angles to each other. 2l-25 would be the intersection of these planes; .and in Fig. 4, the line 23-25 wol ie in the 1 straight This in which are perpendicular to the intersection Fig. 3 represents a section of the prism made by passing a plane through the line 2l-25 normal to the line 26-23. Fig. 4 is the section resulting from passing a plane through line 23-26 normal to the line 2 l-25.

The prism H is positioned in the optical system of Fig. 1 with the plane 2l-22-23-24-25 flat against the screen 5. The surfaces 22-23- 25-2'! and 24-23-26-28 may be coated with silver to make them highly reflective, and if this is done, it will be found that a ray of light starting from the image on the screen 5 will enter the prism at the point 3| and be reflected from the surface 24-23-26-28 along such a line as 32-33. Upon striking the silvered surface 22- 23-26-21, it will again be reflected along the line 33 34 "to emerge frorrrthe *prism II in a In Fig. 3, the line direction at right angles to that at which it entered at the point 3i. The optical properties of such a prism are such that light rays from an image on the screen 5 will, after traversing the prism with the successive reflections above mentioned, form a reversed image of the view onthe screen 5 which is projected in a direction at right angles to the axis of the tube 4. An observer may, accordingly, view such an image in a direction at right angles to said axis.

While the foregoing describes the properties of a true prism with plane surfaces, such an image as has just been described would be of the same size as that on the screen 5, and it is desirable for present purposes to considerably magnify'the dimensions of the observed image. In order to accomplish this result, the surfaces 22-23- 26-21 and 24-23-26-28 are altered from true planes to make them constitute concave spherical mirrors having the radius of curvature necessary to produce the desired magnification of the image. The degree of curvature of spherical reflectors required to produce the desired magnification may, of course, be calculated by well known optical laws. For most purposes, the curvature of the two spherical surfaces should be the same and distortion will be minimized by making it not too great. H In order to further magnify the observed image, the surface erably ground to fit the external surface ofthe electron-phosphor screen 5, and is cemented to that end of the tube 4.

In certain instances, it will be found that the electron optical system comprised within the tube of the combined optical system in which distor-.

tion would individually exist.

- The arrangement of Fig. 1 may be provided with a suitable casing l3 in a manner well known "in *the art to exclude undesired-rl-ight -strom .the

optical system.

In Fig. 3, the point 35 is the mid-point of the intersection 23-26; the line 3538 is the intersection of section-plane III with the surface 21-23-28-21, and the line 35-31 is the intersection of that section-plane with the surface 23--24-28--26.

In Fig. 4, 23-;25is the intersection of sectionplane IV line 2H 26 is the intersection of that sectionplane with surface 2l-25--28-26 -21.

While I have described the foregoing arrange- 6 a spherical reflecting surfaces substantially at right angles to eachother and having a line of intersection forming substantially equal angles t its points of intersection with said output screen, and optical magnifying means in the path of light reflected fronfsald'l'eflecting surfaces.

4. An image intensifier comprising an electron optical system producing a luminous image on a screen forming a wall portion thereof and a roof-prism traversed by the light from said image comprising one surface contiguous to saidscreen, a second surface of spherical contour substantially at right angles to said screen, said prism also comprising two reflecting spherical'surfaces substantially at right angles to each other intersecting each other in a line which makes substantially equal angles at its intersection with each of the first two surfaces mentioned, and

,. ..optical. magnifying,means in thepath of light ith surface 2i-22-23--24-25; and

ment as utilized for observation of X-ray images V any by non visible radiations 'or otherwise.

I claim as m invention: 1. In combination with an electronic imageintensifler having an output screen on which a reflec d from said reflecting surfaces.

5. A X-ray apparatus comprising means for formingyan X-ray image of an irradiated object on a fluorescentscreen, an electron optical image intensifier comprising a substantially cylindrical high vacuum tube having its axis normal to said screen and having an output screen substantially normal to said axisf"ai bof-prism traversed by light from said output screen comprising two surfaces substantially at right angles ot each other. one said surface being positioned adjacent to said output screen. and the other said surface being spherical; said prism also comprising two other spherical-reflecting surfaces substantially at right angles to each other and having a line of intersection forming equal angles with each of the two surfaces first mentioned.

6. A roof-prism comprising two surfaces sub- "stantially atmightangles-"to :each other, one of luminous image appears, a roof-prism traversed 1 by the light from said, luminous image for permitting said image to be viewed from-a position at one side of theaxis of said image intensifier, said roof-prism having two reflecting surfaces, and a third surface of spherical contour traversed by the light reflected from one of said reflecting surfaces.

2. An X-ray apparatus comprising means for forming an X-ray image of an irradiated object on a fluorescent screen, an electron optical image intensifier comprising a substantially cylindrical high vacuum tube having its axis normal to said sgejefinpand having an output screen substantially no al to said axis, a roof-prism traversed by light from said outputscreen comprising two surfaces substantially at right angles to each other. one said surface being positioned adjacent to said oultfput screen, said prism also comprising two sp erica reflecting surfaces substantially at right angles to each other and having a line of intersection forming equal angles with each of the two surfaces first mentioned.

3. An X-ray apparatus comprising means for forming an X-ray image of an irradiated object on a fluorescent sgeen, an electron optical image intensifier comprising a substantially cylindrical higfiVaEuum tube having its axis normal to said screen and having an oi t put scr een substantially normal to said axis, a roof-prism traversed by light from said output screen comprising two surfaces substantially at right angles to each other, .one surface being positioned adjacent to said l put screen, said prismalso comprising two said surfaces constituting the entrance face of said roof-prism being optically cemented to an electrgi phosphor screenand the other of said surfaces constituting the exit face of said roofprism being curved, said prism comprising also two other surfaces substantially at right angles to each other, said other-surfaces being light reflecting and each having slight spherical curvature with the concave surfaces toward each other,

and having a curve of intersection forming substantially equal angles with the normal to said first surface and with the optical axis of said second surface whereby said reflecting surfaces form the roof of said roof -prism.

7. An optical transmission element comprising a prism having a phosphor screen optically continuous with one of its surfaces which constitutes the entrance face of said-prism. a second surface of curved form having its optical axis substantially parallel to said screen and constituting the exit face of said prism, said prism also comprising two spherical surfaces having central axes substantially at right angles to each other and having a line of intersection forming an angle of substantially 45 with said screen, said two' an electron optical image intensifier comprising means for projecting into incidence with an output sgeen positioned in the path of said beam an electron image which is a reversed replica to small scale of that on said fluorescentscreen.

' a reflector for said output screen comprising two surfaces substantially at right angles to each '-'section with said outputscreen'toweilect the' light other and having a line of intersection forming substantially a 45 angle at its point of intertherefrom in a beam substantially parallel to said output screen and withinless than arms length. distance of said object, and optical rnag-z nifying means in the path of the last mentioned beam,

RICHARD L. LONGINI.

Number Number f s REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Moller Mar. 14, 1911 Roach Feb. 10, 1925 Wappler ---a Sept. 22, 1936 Ogloblinsky Sept. 14, 1937 Coolidge May 16, 1939 Loebell July 16, 1940 Gardner July 7, 1942 Bertele June 29, 1943 Konigsberg Dec. 28, 1943 Kallmann Mar. 14, 1944 -=Young 'Apr. 18, 1944 Lawlor Nov. 28, 1944 FOREIGN PATENTS 1 Country Date Great Britain July 31, 1919 France NOV. 10, 1942

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