US2204347A

US2204347A - Radiographic method and apparatus

Info

Publication number: US2204347A
Application number: US195183A
Authority: US
Inventors: Glenn W Files
Original assignee: General Electric X Ray Corp
Current assignee: General Electric X Ray Corp
Priority date: 1938-03-10
Filing date: 1938-03-10
Publication date: 1940-06-11
Anticipated expiration: 1957-06-11

Description

2 Sheats$heet 1 jy @fm @47 TIME mm B 5 e. w. I FILES RADIOGRAPHIC METHOD AND APPARATUS w June 11,1940.-

Filed March 10, 1938 Jlme 1940- ca. w. FILES 2,204,347

- RADIOGRAPHIO METHOD AND APPARATUS Filed March 10, 1938 .2 Shoots-Sheet 2 Patented June 11, 1940 UNITED STATES RADIOGRAPHIC METHOD AND APPARATUS.

Glenn W. Files, Oak Park, Ill., assignor to Gen-. eral Electric X-Ray Corporation, Chicago, Ill., a

corporation of New York Application March 10, 1938, Serial No. 195.183

18 Claims. (01. 250-62) be produced by short and very short, as well as This invention relates to X-ray radiography, and more particularly to a method and apparatus for taking X-ray photographs.

Heretofore, in the X-ray radiographic art,

5 Bucky diaphragms have been employed to reduce fogging of the film caused by secondary radiation emanating from the object being radiographed and from other objects in the path of the beam of X-rays. Such a diaphragm comprises alternate strips ofj'X-ray impervious and X-ray pervious materials,'the strips being disposed at an angle to one another, or radially to- Ward a common axis or focusing point which is substantially the center of the anode or target of 15 the X-ray tube. Such a diaphragm permits the primary X-ray radiation topass therethrough and expose the sensitized radiographic plate while reducing the exposure of the plate to the secondary radiation. These diaphragms have 59 not proved entirely satisfactory for all classes of radiography because the film or plate is frequently marked with a number of parallel, unexposed areas or lines produced by the radiographing of the X-ray impervious strips. It has heretofore been suggestedthat this defect could be overcome by bodily reciprocating the 'diaphragm during the exposure of the film or plate.

However, the diaphragm must be stoppedand.

restarted in the opposite direction at the] end of each of its movements and therefore the X-rays are periodically cut off from the portions of radiographic plate' lying beneath the opaque strips during this stopping and restarting of the diaphragm. This prevents the production of accurate, shadow-free radiographs.

X-ray radiographs of certain parts of the human body and certain objects cannot be made unless taken within a relatively short or very short period of exposure because an element 'of the part or object is in motion or because longer exposure detrimentally affects the part or object. In the case of such relatively short' and very short exposures, the stopping'and restartin'g'of the diaphragm at the end of each reciprocation 45 may require a large part ofthetotal permisisble exposure time and the consequent variation in the exposure density of the film or plate materially affects the clearness of the radiograph, makingthe same misleading and in many casessubstantially useless.

' It is accordingly an object of applicant's invention to provide a method and apparatus for making X-rayradiographs by means of Bucky diaphragms, by which these vi nsufiiciencies may be overcome and'by which clearradiographs may by relatively long periods of exposure.

A further object of applicants invention is to provide an X-ray radiograph method and apparatus which shall result in the production of line-free, shadowless radiographs regardless of the time of exposure.

Applicants invention further contemplates the provision of a method and apparatus in which, and by which," the diaphragm is moved' in synchronism with the energization of the 'X-ray tube, such energization being determined by the frequency of the voltage impulses applied to the X-ray tube.

Another and more specific object of applicants invention is to provide an 'X ray 'radicgraphi method and apparatus in which, and by which, the diaphragm is vibrated, as distinguished from reciprocated, at a relatively high speed and in synchronism with the energization of the X-ray tube.

Other and further'advantages of the invention will be ,apparent from the following description when taken in connection with the accompanying drawings wherein: I

Fig. 1 is a viewin perspective of one preferred means for operating the diaphragm in accordance with the invention. I V

Fig. 2 is afragmentary, vertical section taken substantially along the line 2 2 of Fig.- 1.

Fig. 3 is a fragmentary,- vertical section taken along the line 3--3 of Fig. 1.

Fig. 4 is a diagrammatic view of a radiographic equipment including the diaphragm and operating means of Fig. 1.

Fig. 5 is a sketch illustrating the relation between the X-ray tube energizing impulses and the movements of the diaphragm."

Fig. 6 is a fragmentaryplan view'of a modified form of diaphragm operating means.

Fig. '7 is a further modified form of means for operating the diaphragm.

-' Fig. 8 is a perspective view of another'form ofdiaphragm operating means.

Fig. 9 is a view in elevation 'of still another form of diaphragm operating means.

To illustrate the invention,there is shown on the drawings in Fig. 4 a radiographic equipment comprising an X-ray .tube Hi from the anode of which emanates X-ray' beams l2 which pass throughthe X-ray transparent plate l4 forming the object supporting surface of an X-ray table or stand.

The X-ray table or stand comprises a base plate or shelf IS on which 'is' movably'supported in spaced relation thereto, a Bucky diaphragm l8. A cassette contains the radiographic plate or film and is adapted to be inserted between the diaphragm is and the base or shelf It. The X- rays, after passage through the supporting surface it of the table, pass through the grid of the diaphragm l8 and impinge upon the radiographic plate or film within the cassette The dia phragm cuts off the secondary radiation, as from the point 22 of the object illustrated diagrammatically at 2%. However, if the diaphragm remains stationary during the exposure of the plate or film, the lines of the grid are photographed upon the plate and, if the diaphragm is reciprocated during exposure of the plate, Shadow lines are developed thereon as an in-. cident to the stopping and reversing of the diaphragm.

Applicant has discovered that if the diaphragm be shifted or vibrated through a relatively small range or distance of movement and in synchronism with the energization of the X-ray tube or the impulses of electric voltage applied thereto, these undesirable lines will be eliminated. This will be understood from the sketch of Fig. 5 wherein the numeral 26 indicates the full-wave rectified alternating voltage impressed on the X-ray tube. Below the voltage value represented by the intersection of the horizontal line 28 with the voltage wave 25, substantial y no effective X-rays are produced by the X-ray tube iii. The voltage value represented by the line 28 is substantially one-half the peak value of the alternating voltage. Therefore, the time T which is required for the voltage to build up to the value represented by the line 28 is substantially one-sixth of the total time of a half cycle of the alternating current. Simiarly, the time Tl required for the alternating current voltage to decrease from the value'represented by the line 28 to zero is substantially one-sixth of the total time of a half cycle of the alternating current. The timeTl plus T--during which no effective Xrays are being projected upon the radiographic plate is therefore substantially onethird of the total time of a half cycle of the alternating current. In the case of sixty-cycle alternating current the total time of a half cycle of the alternating current is of a second, and the time'Il plus T-during which no exposure of the radiographic plate takes place is accordingly l of a second.

According to applicants method, the diaphragm is shifted or vibrated in synch'ronism with the impulse wave 26, the diaphragm being reversed in movement during the time-Tl plus T- and moving at a substantially uniform speed during the time T2 when the voltage value is suiiicient to produce effective X-rays. Since no X-rays are being produced during the time that the diaphragm is stopping, reversing and starting up in the opposite direction, the radiographic plate will be entirely free from grid lines, as has been found by actual test. Since the diaphragm is synchronized in its movement with the energization of the X-ray tube, the exposures may be made in as short a time as desired without any danger of having the radiographic plate exposed to the X-rays during the reversing movements of the diaphragm. On the other hand, the exposure may be extended for any desired length of time, however long, without any danger of having the plate blurred by the frequent reversing of the diaphragm.

It will be seen, therefore, that applicant has devised a method for taking X-ray radiographs by means of a diaphragm which consists in shifting or vibrating the diaphragm in synchronism with the energization of the X ray tube, or the impulses of alternating current supplied to the tube, and in stopping, reversing and restarting the diaphragm during the time at which the value of the alternating voltage is below that required to produce X-rays eiTec-tive in exposing the film.

One preferred form of apparatus by which the above described method may be performed is shown in Figs. 1 to 3. The diaphragm i l, as shown in these figures, may be of any desired construction comprising X-ray transparent plates and 32 between which is mounted a ..:id structure 34 comprising alternate Iii-ray opaque and transparent strips 343 and. 33, respectively. The plates 38 and 3.2 with the grid l -i interposed therebetween are mounted in a preferably rectangular frame t! comprising bars or blocks d2 surrounding the grid 34% and clamping the strips thereof in proper position and a sheet metal shell 44 preferably of aluminum and of U-shaped cross section enclosing the blocks or bars 42. The diaphragm. M is mounted on the base or shelf It? by brackets 45 of such resilient material and so shaped as to permit the diaphragm to have the requisite degree of movc-- ment. rubber and each comprises a longitudinal portion E8 securely fastened to the frame of the dia-- phragm as by belts or the like 50. bracket or support 46 is further provided with depending legs 52 extending between the diaphragm and the base or shelf l5 and is securely fastened to said base or shelfby belts or the like 54 passing through inwardly turned feet 5t. One of the brackets 46 is disposed at each corner of the diaphragm and the longitudinal axis of each bracket extends at right angles to the axis of movement or vibration of the diaphragm, Thus, while the diaphragm is substantially supported, the brackets 46 offer little, if any, interference to the movement of the diaphragm. The brackets also prevent transmission of the vibrations of the diaphragm to the base or shelf it of the table.

In the form of the invention shown in Figs. 1. and 2, the diaphragm is operated in synchronism with the energization of the X-ray tube, or the impulses of alternating voltage applied to the tube, by a synchronous motor 58. This motor is mounted upon the base or shelf it of the X-ray table or stand and is of a size suificient to fit with-- in the space between the object supporting surface l4 and said base or shelf. The shaft 66 of the motor carries a gear 62 which meshes with a, gear 64 carried by a stud or shaft 66 mounted o the frame of the motor 53. The gears 52 and are preferably of fibre or other sound deadcning material.

Where the alternating current supplied is of BO-cycle frequency and the motor 58 is a synchronous motor operating at 1800 R. P. M., the ratio between the

gears

52 and 64 is two to one in order that the gear 64 may have a speed of 3600 R. P. M. Of course synchronous motors of other speeds may be employed and the ratio between the

gears

62 and 64 varies correspondingly to obtain this desired speed of rotation for the gear 64. The gear 64 is connected to the diaphragm Us by a link 68 pivoted eccentrically to the gear 64 and to a cross head Hi bolted to one side of the frame 40 centrally thereof. The

The brackets are preferably of semi-soft conventional means may be provided, if necessary or desirable, to maintain the motor 58 in synchronism with the supply voltage. I

In the form of the invention shown in Fig. 6, the shaft 60 of the synchronous motor has secured thereto a cam 14 engaging a pair of cam rollers or followers 16 journaled on pins 18 carried by a plate 80 bolted to one side of the frame 40 and centrally thereof. If the speed of rotation of the shaft 60 is 1800 R. P. M., the cam 14 will be provided with

alternate quadrants

82 and 84 having cam surfaces of progressively increasing radii in the direction of rotation and

alternate quadrants

86 and 88 of progressively decreasing radii in the direction of rotation.

The cam followers 16 may be maintained in constant engagement with the surface of the cam 14 by the natural resiliency of the rubber mountings or brackets 46. Additional resilient means for maintaining the cam followers or rollers 16 in engagement with the cam 14 may be provided if desired. This means may comprise-a pair of coil springs 90 interposed between the opposite side of the frame 40 and a flange or bar 92 secured to, or-formed integrally with, the base or shelf l6 of the X-ray stand'or table.

In this form, of the invention the cam 14. constitutes ,a means for controlling the move-- ments of the diaphragm and for moving the diaphragm in one direction, and the rubber mountings or brackets 46 or the springs 90 r both brackets and springs constitute a means for maintaining the cam followers 16 in engagement with the cam and a means for moving the diaphragm in the opposite direction.

Where the motor shaft '60 rotates at a speed other than 1800 R. P. M., the cam surface of the cam 14 will be suitably modified to cause the diaphragm l4 to complete its cycle of movement in A of a second and in synchronism with the alternating current supply voltage; By providing a single small cam roller and providing a cam whose surface has small but sudden drops or depressions-between the

portions

82 and 86 and the

portions

84 and 88, and a sudden rise or elevation between the

portions

88 and 82 and between the

portions

86 and 84, the time required to effect a stopping, reversing and restarting of the diaphragm at the end of each half cycle of its movement may be as small as desired. However, a cam having a smoothly varying cam surface, as disclosed in Fig; 6, will accomplish the stopping, reversing and restarting of the diaphragm well within the-allotted time of of a second. 1

In the form of the invention shown in Fig. 7, the motor shaft 60 has secured thereto, and eccentrically with respect to its axis, an eccentric disk 94. The disk 94 drives or vibrates the dial phragm I4 by means-of an eccentric strap 96.

having an integral arm 98' pivotally connected as at I00 to the cross head 10 secured to the.

frame 40 of the diaphragm. This form of the invention has an operating advantage over the form of the invention shown in Fig. 1 in respect to the quietness of operation but requires that the motor shaft 60 have a speed of rotation of 3600 R; P. M.

102 may be connected to the frame 40 of the diaphragm in any desired manner and interposed between the diaphragm and an upstanding lug I84 secured to, or formed integrally with, the base or shelf l6 of the X-ray table or stand. A solenoid I06 having an armature I08 secured to one side of the frame 48 is provided to initiate the vibration of the diaphragm. The energizing circuit for this solenoid may be interlocked inany desire and conventional manner (not shown) with the X-ray tube energizing circuit to thatupon closure of the energizing circuit the vibration of the diaphragm will be initiated, it being understood that the solenoid I06 is only momentarily energized upon the energization of the X-ray tube. 1

In order to maintain the vibrations of the spring I02 or other vibratory means in syn- I chronism with the: alternating current supply voltage over an extended period of exposure,

secured to, and extending laterally from, one

side of the diaphragm frame 48. In this form of the invention, reliance is had upon the inherent vibration of the motor III) to effect a vibration of the diaphragm 14. Adjustablephase control means such as an adjustable capacity I I4 and an adjustable inductance I l 8 may be provided for the purpose of maintaining the inherent vibrations of the motor in'synchronism with the alternating current supply voltage.

It will be seen from the above description that applicant has provided a method and means for tion and arrangement of the parts without .de-

parting from the spirit of the invention or sacrificing any of its attendant advantages, and the right is hereby reserved to make all such changes as fairly fall within the scope of the following claims.

The inventionis hereby claimed as follows:

1. A method of making short exposure Xray radiographs which comprises energizing an X- ray tube by pulsating current and vibrating a diaphragm of alternate X-ray opaque and X-ray transparent strips transversely of the produced beam of X-rays in synchronism with the pulsating current, the reversal of the diaphragm at each of its limits of movement beingaccom plished within the time interval that the magnitude of the pulsating current impulse is below the value required to produce X-rays.

2. A method ofmaking short exposure X-ra radiographs which comprises'energizing an X- ray tube with pulsating, full-wave, rectified impulses of alternating current, vibrating a diaphragm of. alternate X-ray opaque and X'-ray transparent strips "across the beam of X-rays in synchronism with the'energi zing impulses, the

reversal of the diaphragm at the limit of its movement being accomplished in the time interval that successive impulses of the energizing current are below the value required to produce X-rays.

3. In an X-ray radiographic apparatus for short exposures, an X-ray tube, means for energizing said tube with pulsating current, a diaphragm comprising alternate X-ray opaque and X-ray transparent strips and means for cyclically shifting said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X-rays.

4. In an X-ray radiographic apparatus for ,hort exposures, an X-ray tube, means for energizing said tube with pulsating current, a sensitized film, a support, a diaphragm comprising alternate X-ray opaque and X-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting the diaphragm on said support, means for vibrating said diaphragm in synchronism with i the pulsating current and for reversing the movement of the diaphragm at each of its limits of movement in the time interval that the pulsating current is below the value required to produce X-rays.

5. In an X-ray radiographic apparatus for short exposures, means for supplying full-wave, rectified, pulsating impulses of alternating current to said X-ray tube, a sensitized film, a support, a diaphragm comprising alternate X-ray opaque and A-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting the diaphragm on said support, means for vibrating said diaphragm in synchronism with the pulsating our- 2 rent and for reversing the movement of said tized film, a support, a diaphragm comprising a I frame and a grid, said grid having alternate ray opaque and X-ray transparent strips and said diaphragm being interposed in the path of the beam of. X-rays and between the Xray tube and the film, a plurality of brackets of flexible material secured to said frame and to said support, and means for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X rays.

'7. In an X-ray radiographic apparatus for short exposures, an X-ray tube, a source of pulsating current, means for energizing said tube from said source, a sensitized film, a support, a diaphragm comprising alternate X-ray opaque and X-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting the diaphragm-on said support, and means for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X-rays, said means for vibrating the diaphragm in synchronism with the pulsating current comprising a synchronous motor adapted to be energized from said source of pulsating current, and means connecting the shaft of the motor to said diaphragm.

8. In an X-ray radiographic apparatus for short exposures, an X-ray tube, a source of pulsating current, means for energizing said tube from said source, a sensitized film, a support, a diaphragm comprising alternate X-ray opaque and X-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting the diaphragm on said support, and means for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X-rays, said means for vibrating the diaphragm in synchronism with the pulsating current comprising a synchronous motor adapted to be energized from said source of pulsating current, a shaft driven by said motor, a bracket secured to said diaphragm and a link pivotally connected to said bracket and to said shaft eccentrically with respect to the axis of. rotation of said shaft.

9. In an X-ray radiographic apparatus for short exposures, an X-ray tube, a source of pulsating current, means for energizing said tube from said source, a sensitized film, a support, a diaphragm comprising alternate X-ray opaque and X-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting the diaphragm on said support, and means for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X-rays, said means for vibrating the diaphragm in synchronism with the pulsating current comprising a synchronous motor adapted to be energized from said source of pulsating current, a disk eccentrically mounted on the motor shaft and an eccentric strap pivotally connected to the frame of the diaphragm and enclosing said disk.

10. In an X-ray radiographic apparatus for short exposures, an X-ray tube, a source of pulsating current, means for energizing said tube from said source, a sensitized film, a support, a diaphragm comprising alternate X-ray opaque and X-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting the diaphragm on said support, and means for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X-rays, said means for vibrating the diaphragm in synchronism with the pulsating current comprising a synchronous motor adapted to be energized from said source of pulsating current and mounted on said support, a cam driven by the motor shaft, a cam follower secured to the diaphragm, and resilient means for maintaining said follower in engagement with said cam.

11. In an X-ray radiographic apparatus for short exposures, an X-ray tube, means for energizing said tube with pulsating current, a sensitized film, a diaphragm comprising alternate X- ray opaque and X-ray transparent strips interposed between said X-ray tube and said film, and means for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X-rays, said means for vibrat- I the diaphragm on said support, and means for ing the diaphragm in synchronism with the pulsating current comprising resilient means having a natural period of vibration conforming to the frequency of the pulsating current.

12. In an X-ray radiographic apparatus for short exposures, an X-ray tube, means for energizing said tube with pulsating current, a sensitized film, a support, a diaphragm comprising alternate X-ray opaqueand X-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting vibrating said diaphragm in synchrcnism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required j to produce Y-rays, said means for vibrating the diaphragm in synchronism with the pulsating current comprising resilient means having a natural period of vibration, conforming to the fre quency of the pulsating current, and means for initiating themovement of, the diaphragm.

13. In an X-ray radiographic apparatus for short exposures, an X-ray tube, means for ener-,

gizing said tube with pulsating current, a sensitized film, a support, a diaphragm comprising alternate. X-ray opaque and X-ray transparent strips interposed between said X-ray' tube and said film, flexible supporting means for mounting the diaphragm on said support, resilient means having a natural period of vibration conforming to the frequency of the pulsating current for vibrating said diaphragm in synchronism with said pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required I to produce X-rays, and means comprising a solenoid adapted to be connected to the source of pulsating current for initiating the movement of the diaphragm upon energization of. the -X-ray tube.

14. In an X-ray radiographic apparatus for short exposures, an X-ray tube, a source of pulsating current, means for energizing said tube from said source, a sensitized film, a support; a

-diaphragm comprising alternate X-ray opaque and X-ray transparent stripsinterposed between said X-ray tube and said film, flexible supporting X-ray' tube, and for retensioning said resilient means whereby to maintain the .movements of the diaphragm in synchronism with the pulsating current.

15. In an X-ray radiographic apparatus for short exposures, an X-ray tube, means for enere gizing said tube with pulsating current, a sensiproduce efiective X-raystized film, a support, a diaphragm comprising alternate X-ray opaque and X-ray transparent strips interposed between said X-ray tube, and

said film, flexible supporting means for mounting the diaphragm on said support, and means for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required toproduce X-rays, said means comprising electric motor means having a period of mechanical vibration conforming to the frequency of the pulsating current, and means for mounting said electric motor means on said diaphragm;

16. In an X-ray radiographic apparatusfor short exposures, an X-ray tube, a source of pulsating current, means for energizing said tube from said source, a sensitized film, a support, a

diaphragm comprising alternate X-ray opaque and X-ray transparent strips interposed between said X-ray tube and said film, flexible supporting means for mounting the diaphragm on said support, and means [for vibrating said diaphragm in synchronism with the pulsating current and reversing the movement of the diaphragm in the time interval that the pulsating current is below the value required to produce X-rays, said means comprising electric motor means adapted to be energized from the source of pulsating current and having a period of mechanical vibration con- 7 forming to the frequency of the pulsating current,

means for mounting said electric motor means on said diaphragm whereby said diaphragm is vibrated in synchronism with'the pulsating cur-' rent, and phase control means for maintaining the vibrations of the motor in synchronism with the pulsating current.

17. InX-ray radiographic apparatus, a shiftable diaphragm having a frame and a grid, said grid comprising alternate X-ray opaque and X- ray transparent strips, a support for said diaphragm and a plurality ofv spaced,iflexible brackets secured to'said frame and to said support for permitting substantially free shifting of said diaphragm at right angles to the grid stripswhile preventing movement of the same in a direction longitudinally of the grid strips.

18. A method of making short exposure X-ray radiographs which comprises energizing an X- ray tube by current pulsating'inmagnitude at a substantially constant frequency from a value below that required to produce effective X-rays to a value sufficient toproduce effective X-rays, and shifting a diaphragm of alternate X-ray opaque and X-ray transparent strips back and forth across the beam of X-rays and between the X-ray tube and a radiographic film at a speed such that a complete movement in one direction is wholly accomplished duringthe time that the magnitude of the energizing impulse is sufficient toproduce effective X-rays and the direction of movement of the diaphragm is reversed during the time interval when'the magnitude of the energizing impulse is below the value required to GLENN w. FILES.