US2813204A - X-ray apparatus - Google Patents

Description

Nov. 12, 1957 R. A. LEE 2,813,204

X-RAY APPARATUS Filed June 17, 1954 2 Sheets-Sheet l FIG-1 7 FIG-2 INVENTORQ ROBERT A. LEE

BY Mama-4%,

ATTORNEYS Nov. 12, 1957 R. A. LEE 2,813,204

X-RAY APPARATUS Filed June 17, 1954 2 Sheets-Sheet 2 FIG-4 FIG-5 IN VEN TOR.

ROBERT A. LEE BY ATTORNEYS United States Patent '0 X-RAY APPARATUS Robert A. Lee, Erlanger, Ohio, assignor to The Keleket X-Ray Corporation, Coviugton, Ky., a corporation of Ohio Application June 17, 1954, Serial No. 437,4ll8 9 Claims. (Cl. 250-239) This invention relates to X-ray apparatus and more particularly to the timing of exposures to X-ray radiation.

The invention has particular relation to the timing of X-ray exposures by means of photoelectric apparatus in which a fluorescent screen is positioned in the path of the X-ray beam after it has passed through the patient, and a phototube is mounted in position to receive the light from the screen and is connected in a control circuit which acts to terminate the exposure at the proper instant in accordance with the measured response of the phototube, photoelectric timing apparatus of this character being disclosed, for example, in Morgan and Hodges Patents No. 2,401,288 and ,No. 2,401,289 issued May 28, 1946. The control circuit in such photoelectric timing system is readily adjustable in accordance with the density of the tissues or parts of the body being exposed, which is particularly useful in radiography to assure that sufiicient radiation will pass through the body for adequate exposure of the film while preventing overexposure of either the patient or the film.

It is important in using the above 'phototiming systerm to assure that the response of the phototube accurately represents the actual exposure. This result is readily accomplished by positioning the phototube substantially directly in line with the center of the X-ray beam directed toward the fluorescent screen, but this requires a special mounting for the phototube when the system is used in conjunction with the fluorescent screen of a spot film tunnel or like X-ray apparatus. For example, the phototube may be mounted in a holder on a portion of the funnel body adjacent the fluorescent Screen thereon in such manner as to swing into line with the center of the .exposed area of the screen during radiography.

The present invention is especially related to an optical pickup device for use in a phototiming circuit which may be mounted in laterally spaced relation with a fluorescent screen such as the screen on a spot film tunnel for actuation by light directed laterally at an acute angle from the screen, and a primary object of the invention is to provide such a pickup device which will establish a highly accurate response by the phototube to the actual illumination of the screen during radiography 'by eliminating or compensating'for non-uniformity of the phototube due either to the inherent properties or sensitivity of the tube itself or to its position with respect to the fluorescent screen and the related geometry of its optical system.

Another object of the invention is to provide :such .a phototimer pickup device which is so constructed and arranged with respect to both the phototube and the fluorescent screen that it will efiect selective transmission of the light from the screen :to the tube in such propor tion with respect to the distance between the tube and the source points of the light on the screen as .to establish substantially uniformly effective overall illumination of the field of view to which the phototube is respons'ive.

It is also an object .of the invention ,to provide ;a phototimer pickup device as outlined above which incorporates a special control for preventing stray light from .affecting operation of the phototube and which may 'be quickly and easily adapted for use with exposed areas of the fluorescent screen of difierent sizes and shapes to assure uniformly high accuracy of timing of the X-ray exposures under all operating conditions.

Additional objects and advantages of the invention will be apparent from the followingdescription, {the no .cornpanying drawings and .the appended claims.

In the drawings--- Fig. 1 is a perspective view illustrating .a typical installation of a phototimer pickup device in accordance with the invention on a spotlfilm tunnel;

Fig. 2 is an assembly view taken :in section on the line 22 of Fig. 3 and illustrating a pickup device.c onstructed in accordance with the invention;

Fig- .3 is a pl n vi w of stheznickup device of Fig. 2. with portions of he housing brokenaway to illustrate details of internal construction;

Figs. 4 and 5 are detail views of the two light battles within the pickup device of Figs. and Stand Figs. 6, 7 :and 8 are optical diagrams illustrating the operation of the pickup :deviceof the invention and king respectively downwardly .and laterally.

Referring to the drawings, which illustrate a preferred embodiment of the invention, the spot ifilm tunnel 1 0 is shown in Fig. 1 as generally of athfi construction disclosed in the application .of jHaupt .et 211., Serial No. 310,524, .now Patent No. 2,109,221 filed September .19, 1952, and assigned to the same .assignee as this application. It includes a fluorescent screen-11 which is viewed directly by the operator during fluoroseopy ,and which is illuminated by that portion .of the X ray ibearn not absorbed by the .body of thepatient during radiography. The pickup device of the invention is indicated generally at 13, and it includesabasq-plate 15 supporting a bracket portion 16 forming the mounting for the socket 17 for a phototube 20 connected in the ,phototim-ing circuit, ,satisfactory results being obtained utilizing a Type IP21 Photom-ultiplier. All of these parts are shown as enclosed by a suitable cover .or housing 22.

The bracket 16 also supports a lens barrel .24 which extends through thefront .of the .housing 22 .at the desired angle for alignment the fluorescent screen 11, and at the forward end 10f this barrel is. an objective lens 25, shown as a .double lens in the mounting sleeve 26. The upper end of the barrel 24 ,is fl-attened horizontally .as shown, .and a translucent ,plate 30 .of .ditfusing material s h s .opal glass is mounted at the inner end of the barrel by means of tabs 31. The phototube 20 is so mounted with relation to the plate 3.0 that its cathode 33 is opposite ,and aligned horizontally with .the center of the plate 30 as indicated ,in Fig. 2. V

Figs. 6-8 illustrate diagrammatically the optical system of the invention as Well .as the conditions which tend to cause non-uniform response on the part of the phototube 20 .and which are compensated for .by means of the present invention. It is a common practice in spot film radiography to .make multiple exposures on a single film, with each exposure being limited to a ,different quadrant of the film and with each such quadrant being centered with respect to the X-ray beam during exposure. At the .same time, however, such .a tunnel is also commonly constructed so that at the option .of the operator, it will make tworadiographs each covering only one-half of the area or asingle radiograph occupying the entire film, with the exposed area in each case always being centered with respect to the .X-ray b am ini g exp sure. The present nvention make provision for accurate ,phototiming under all such conditions.

In Fig. 6, the rectangular outline 11a represents a central area of fluorescent screen 11, which conveniently may correspond to the portion of the screen which would be illuminated during exposure of one-fourth of the film within the tunnel, and it is desired in operation that the lens form an image of this area 11a which will illuminate the translucent plate 30. With the area 11a rectangular as shown, such image will be of inverted trapezoidal shape as a result of the angular relation of the lens and the screen 11 as well as the angular relation of the plate with respect to the lens. Similarly, if the area 11a is' circular, the'image thereof formed by lens 25 Will'be of flattened elliptical shape. A light baffie 40 is acco rdingly provided for transmitting to the plate 30 only the light incident on the lens 25 from the area 11a while blocking stray light from other sources, and this battle is located in substantially the plane in which the lens 25 will form the image of area 11a.

Referring'to Figs. 2 and 4, the baffle 40 is a plate of metal or other opaque material, preferably having a light absorbing surface such as dull black paint. The baffle 40 is mounted within the lens barrel 24 by means of a slot 41 closely adjacent the plate 30 in the wall of the barrel, and a tab 42 at the top of the baffle is bent to receive a mounting screw 43. The baflle 40 is proportioned to close the barrel 24 against the transmission of light there- -beyond except through a light window 44 which is aligned with the axis of lens 25 and is of inverted trapezoidal shape to conform with the actual shape of the image of the area 11a resulting from the geometry of the optical system. The shoulders 45 on bafile 40 are proportioned to fit in approximately the lower ends of the slot 41. Additional safety against stray light may also be provided by means of a light absorbing coating such as black paint on the surface of the translucent plate 30 along its edges outside and below the areas where the desired image of the area 11a is to be formed.

An additional source of possible non-uniform response by phototube 20 is illustrated in Figs. 7 and 8, which show that with the pickup unit 13 mounted as indicated 'in Fig. 1 so as to align the axis of the lens 25 with the center of the screen 11, the device will be responsive primarily to the light directed laterally and at a relatively acute angle from the screen area 11a. It will therefore be apparent that the point A closest thereto will appear substantially brighter than the point B lying in the center of the far side of the area 11a, while the points C in the two far corners of the illuminated area of the screen will appear to have the lowest relative illumination and the points D and B will appear of different brightness intermediate that of point A and point B. In accordance with the invention, it is recognized that the geometry of this system will normally have the effect of preventing the phototube 20 from responding to the overall illumination of the screen, both because of the inverse square law of illumination and also because of the common inherent tendency of phototubes to have hot spots along their cathodes which are more sensitive than the rest of the cathodes and produce a response in excess of the proper value. Accordingly the pickup device of the invention incorporates special means for eliminating and compensating for such non-uniform effective illumination of the field with respect to the phototube.

A light bafile is mounted within the lens barrel 24 in spaced relation forward of the plate 30, and this bafile is constructed to transmit to the plate 30 substantially all of the light rays directed to the lens 25 from the most remote portions of the screen area 11a while proportionately blocking these light rays from the nearer areas of the screen in such manner as to establish a substantially uniformly illuminated image of the area 11a on the plate 30. As shown in Fig. 5, the b'afile 50 is a plate of metal or other opaque material, preferably having a light absorbing surface such as dull black paint. The bafile 50 is mounted within the lens barrel between the bafile 40 and the lens by means of a slot 51 in the wall of the barrel and a tab 52 at the top of the baffle which is bent over to receive a mounting screw 53. Substantially the entire upper half of the baffle 50 is solid as shown except for a small hole 55. Along its lower edge is a dependent portion 56 of convex curvature and relatively small radius, while on each side of this part56 is a scalloped or concave portion 57 each of greater diameter than the part 56 and proportioned to extend to the adjacent inner wall of the lens barrel.

The operation of the baflle 50 is best illustrated in Figs. 7 and 8 in conjunction with certain of the light rays directed toward the lens 25 from a plurality of points within the screen area 11a. As shown, the proportions and positioning of the baffle 50 are such that all of the light represented by the rays 60, 61 and 62 which establish the position of the point B in the image on plate 30 is allowed to travel from the lens 25 to the plate 30 in order to form an image of the point B of maximum brightness. The same is true of the rays from all of the marginal portions of the area 11a along its side CC, and since the corners of this area are more remote from the lens than the point B, provision is made for transmission of all of the light from substantial portions of these corners, by way of the scalloped portions 57 along the lower edge of baffle 50. It will of course be apparent that with the lens tilted with respect to the screen, the image of the area 11a will actually be formed in a slightly curved surface, but for practical purposes this image will lie approximately in the plane of the bafile 40 as shown.

The light rays from nearer portions of the area 11a, however, are proportionately cut off by the bafile 50. Referring to Fig. 8, it will be noted that while the light from the point D directed toward the lower portion of lens 25 is transmitted to the plate 30, as indicated by the rays 63 and 64, a substantial portion of the other light traveling'from the point D to the lens is blocked by the baffle 50, as indicated by the ray 65. The same is proportionately true for the light emanating from portions of the area 11a adjacent the point D. The light from still nearer portions of the screen, represented by the point E, is substantially entirely blocked, as shown by the rays 66, 67 and 68-.

The light traveling from the nearest point A toward the lens 25 is similarly directed toward the baflle 50, as indicated by the rays 7072, and it would all be blocked if the upper half of the baffle were entirely solid. It has been found, however, that a more accurately uniform average illumination of the image of the screen is obtained if a small percentage of such light is transmitted to the plate. It is for this purpose that the small hole 55 is provided in the baffle, and satisfactory results have been obtained with this hole located slightly above the rays from the point A traveling through the center of the lens 25, and represented by the ray 70 in Fig. 7, in order to transmit a portion of the rays from point A.

The particular proportioning of the baflle 50 is dependent upon a variety of factors, including the shape of the area of the screen scanned by the device, the inverse attenuation of light from different points within the screened area, the difference in solid angle to the lens opening from different points within the scanned area, the shape of the lens aperture, and the angular relationship between the planes of baffle 50 and the fluorescent screen. The illustrated configuration of baffie 50 has been found satisfactory for use with the device constructed for mounting at the edge of a 12-inch screen and with the axis of the lens aligned with a point approximately 4 inches from the front of the housing 22 in order to lower the image in the lens barrel and consequently to decrease the overall height of the device. More specifically, with the inner diameter of the lens barrel approximately 1.5 inches and with the portion of the baffle 50 lying above a line connecting the shoulders 75 occupying the upper half of the lens barrel, satisfactory results have been obtained with the portions 56 and 57 of the baffle curved as shown and with the hole 55 having a diameter of inch and located with its center approximately 0.11 inch above the line connecting the shoulders 75;

It should also be noted that the difiusing plate 30 has a compound function in the operation of the device. With theparts arranged as described so that the image of the area 1111 is "focused inthe plane of the baffle 40, the image formed on the plate 30 is out of focus. This minimizes bright spots in the image to which the cathode of the tube 20 is responsive, and the further diffusion of light in the image by the material of the plate 30 results'in the cathode receiving in effect a sample of light integrated over the area of the baflie 40. This in turn minimizes sensitivity of the device both to minor variations in cathode position and also to hot spots in the cathode.

It will accordingly be seen that this pickup device accomplishes the desired objectives of the invention while retaining outstanding advantages of simplicity of construction. Since the bafile 40 is designed to transmit only the light emanating from a limited central area of the fluorescent screen, it will operate with equal efiectiveness whether the radiograph being taken occupies the entire film or only a desired centered fraction thereof. For similar reasons, the baifle 50 will operate to establish uniform overall apparent illumination of the image of the desired screen area on the translucent plate 30, and the diflusing effect of this plate otters further assurance that the phototube will respond to such overall illumination and thus establish the desired accurate timing.

While the form of device herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of device, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. An optical pickup device for mounting in laterally spaced relation with a fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the X-ray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said screen, means in said housing for supporting said phototube in position for actuation by light rays directed thereto from said screen at an acute angle, means carried by said housing defining a passage for transmitting said angularly directed light rays to said phototube, a light baflie mounted within said passage and constructed to transmit to said phototube substantially all said angularly directedlight rays from the most remote areas of said screen while proportionately blocking said light rays from less remote areas of said screen, and means in said passage for optically difiusing said transmitted light rays to effect integration thereof and thereby to establish substantially uniform response of said phototube to the illumination of said screen.

2. An optical pickup device for mounting in laterally spaced relation with a fluorescent screen in combination withthe phototube in a phototiming system for an X-ray tube to time the transmission of the X-ray beam to said screen, comprising a housing for said phototube con structed for mounting in said laterally spaced relation with said fluorescentscreen, a lens carried by said housing for receiving light rays directed to said housing from said screen at an acute angle, a translucent plate supported within said housing in position for illumination by light transmitted by said lens, means in said housing for supporting said phototube in position for actuation in response to illumination of said plate, and a light baflle mounted between said lens and said plate and constructed to transwit to said plate substantially all said angularly directed light rays from the most remote points of said screen while blocking the major portion of said light rays emanating from the nearest point on said screen and proportionally transmitting such light rays from the areas on said screen intermediate said nearest point and said most remote points to establish substantially uniform illumination of said plate, said baflie being located in such relation with the focal plane of said lens that the image thereof on said plate is out of focus to provide a difiused such image reducing the sensitivity of said device to variation in the position of the cathode of said phototube and to hot spots in said cathode.

3. An optical pickup device for mounting in laterally spaced relation with a rectangular fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the Xray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said screen, means in said housing for supporting said phototube in position for actuation by light rays directed thereto from said screen at an acute angle, means carried by said housing defining a passage for transmitting said angularly directed light rays to said phototube, a light bathe mounted within said passage and constructed to transmit to said phototube substantially all said angularly directed light rays from the most remote areas of said screen while proportionately blocking said light rays from less remote areas of said screen to establish substantially uniform response of said phototube to the illumination of said screen, and an additional light baifle mounted in said housing between said first baflie and said phototube and having therein a light transmitting window of trapezoidal configuration proportioned with respect to said angularly directed light rays to transmit to said phototube only such light'rays emanating from said fluorescent screen.

4. An optical pickup device for mounting in laterally spaced relation with a rectangular fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the X-ray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said screen, means in said housing for supporting said phototube in position to receive light rays directed at an acute angle from said screen, means carried by said housing defining a passage for transmitting said angularly directed light rays to said phototube, means for aligning said passage with the centerline across said screen,.and a light baifle mounted within said passage and constructed to transmit through said passage substantially all said angularly directed light rays from an area extending along the far side of said fluorescent screen while blocking the major portion of said light rays emanating from the nearest point of said screen and proportionally transmitting such light rays from the areas on said screen intermediate said nearest point and said far side to establish substantially uniform response of said phototube to the illumination of said screen.

5. An optical pickup device for mounting in laterally spaced relation with a fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the Xray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said fluorescent screen, a lens carried by said housing for receiving light rays directed to said housing from said screen at an acute angle, a translucent plate supported within said housing in position for illumination by light transmitted 'by said lens, means in said housing for supporting said phototube in position for actuation in response to illumination of said plate, a first light bafll-e mounted in said 'passage adjacent said plate and having therein a light transmitting window of trapezoidal configuration proportioned with respect to said angularly directed light rays to transmit to said plate only such light rays emanatingfr'om a predetermined limited rectangular area on said fluorescent screen, a second light baffle mounted between said first baflie and said lens and constructed to transmit to said plate substantially all said angularly directed light rays from the far side of said screen area while blocking an increasing proportion of the light rays directed thereto from successively nearer parts of said screen area to establish substantially uniform response of said phototube to the illumination of said screen.

6. An optical pickup device for mounting in laterally spaced relation with a fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the X-ray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said fluorescent screen, a lens carried by said housing for receiving light rays directed to said housing from said screen at an acute angle, a lens barrel supporting said lens in a position to focus said light rays within said housing, a translucent plate supported at the inner end of said lens barrel for illumination by the light transmitted by said lens, means in said housing for supporting said phototube in position for actuation in response to illumination of said plate, and a light baffle mounted within said lens barrel between said lens and said plate and constructed to block substantially the upper one-half of said barrel to minimize transmission of light to said plate from the nearest portions of said fluorescent screen while leaving a substantial portion of the remainder of said barrel open for transmission of light therethrough, said baflie having along the lower edge thereof a depending portion of convex curvature terminating slightly below the axis of said lens to limit transmission of light to said plate from the corresponding areas of said screen to the portions of said screen beyond the center thereof, the portions of said baflie edge on either side of said depending portion being of concave curvature to increase the transmission of light to said plate from the opposite corner portions of said screen.

7. An optical pickup device for mounting in laterally spaced relation with a fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the X-ray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said fluorescent screen, a lens carried by said housing for receiving light rays directed to said housing from said screen at an acute angle, a lens barrel supporting said lens in a position to focus said light rays within said housing, a translucent plate supported at the inner end of said lens barrel for illumination by the light transmitted by said lens, means in said housing for supporting said phototube in position for actuation in response to illumination of said plate, a light baflie mounted within said lens barrel between said lens and said plate and constructed to block substantially the upper one-half of said barrel to minimize transmission of light to said plate from the nearest portions of said fluorescent screen while leaving a substantial portion of the remainder of said barrel open for transmission of light therethrough, said baffle having along the lower edge thereof a depending portion of convex curvature terminating slightly below the axis of said lens to limit transmission of light to said plate from the corresponding areas of said screen to the portions of said screen beyond the center thereof, the portions of said baflie edge on either side of said depending portion being of concave curvature to increase the transmission of light to said plate from the opposite corner portions of said screernand said baffle having a small light window therethrough above said depending portion thereof and coinciding with a portion of the light rays from the nearest point on the screen to transmit a correspondingly small portion of said light to said plate.

8." An optical pickup device for mounting in laterally spaced relation with a fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the X-ray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said fluorescent screen, a lens carried by said housing for receiving light rays directed to said housing from said screen at an acute angle, a translucent plate supported within said housing in position for illumination by light transmitted by said lens, means in said housing for supporting said phototube in position for actuation in response to illumination of said plate, a first light baflle mounted in said passage adjacent said plate and having therein a light transmitting window of trapezoidal configuration proportioned with respect to said angularly directed light rays to transmit to said plate only such light rays emanating from a predetermined limited rectangular area on said, fluorescent screen, and a second light baffle mounted between said lens and said first baflie and constructed to block a substantial portion of the beam transmitted from said lens to said first baffle, said second bafile having along the lower edge thereof a depending portion of convex curvature terminating slightly below the axis of said lens to limit trans mission of light to said plate from the corresponding areas of said screen to the portions of said screen be yond the center of said rectangular area, the portions of said baffle edge on either side of said depending portion being of concave curvature to increase the transmission of light to said plate from the opposite corner portions of said area.

9. An optical pickup device for mounting in laterally spaced relation with a fluorescent screen in combination with the phototube in a phototiming system for an X-ray tube to time the transmission of the X-ray beam to said screen, comprising a housing for said phototube constructed for mounting in said laterally spaced relation with said fluorescent screen, a lens carried by said housing for receiving light rays directed to said housing from said screen at an acute angle, aetranslucent plate supported within said housing in position for illumination by light transmitted by said lens, means in said housing for supporting said phototube in position for actuation in response to illumination of said plate, a first light baflle mounted in said passage adjacent said plate and having therein a light transmitting window of trapezoidal configuration proportioned with respect to said angularly directed light rays to transmit to said plate only such light rays emanating from a predetermined limited rectangular area on said fluorescent screen, and a second light baflie mounted between said lens and said first baflie and constructed to block a substantial portion of the beam transmitted from said lens to said first baflie, said second baflle having along the lower edge thereof a depending portion of convex curvature terminating slightly below the axis of said lens to limit transmission of light to said plate from the corresponding areas of said screen to the portions of said screen beyond the center of said rectangular area, the portions of said baffle edge on either side of said depending portion being of concave curvature to increase the transmission of light to said plate from the opposite corner portions of said area, and said baffle having a small light window therethrough above said depending portion thereof and coinciding with a portion of the light rays from the nearest point on the screen area to transmit a correspondingly small portion of said light to said plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,207,097 Logan July 9, 1940 2,561,085 Zavales et al. July 17, 1951 2,631,243 Weber et al Mar. 10, 1953 -2,654,858 Feller Oct. 6, 1953 2,668,913 Goldfield et al. Feb. 9, 1954

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