Le roy j
US RE21964 E
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Description (OCR text may contain errors)
De 2I 2, 1941. vL E ROY J, LEISHMAN Re. 21,964
)IC-'RAY STEREOSCOPIC MEANS AND METHOD original Filed oct. 5, 1935 4 sheets-shea 1 95. my /00 /a 2! 1941- LE ROYJ. LElsHMAN Re. 21,964
XRAY STEREOSCOPI-G MEANS AND MTHOD original Filed oct. 5, 1935 4 Sheets-Sheet 3 /N VEN TOR:
. 2, 1941. LE ROY J. LEISHMAN Re? 21,954
X-RY STEREOSGOPIC MEANS AND METHOD Original Filed Oct. 5, 1955 4 Sheets-Sheet 4 Reissued Dec. 2, 1941 UNITED 21,964 x-RAY sTEaEoscorlo MEANS AND METHOD Le Roy J. Leishman, Los Angeles, Calif.
2,214,621, dated September 10, 1940,
43,688, October 5, 1935. Renewed February 13, 1940. Application for reissue September 10, 1941, Serial No. 410,320
The invention herein described relates to stereoscopic fluoroscopy and radiography. Some of its objects are: first, to provide practical means for varying the distance between the required two sources of X-rays; second, to afford simple means whereby the separate images produced by the X- rays from these two sources may each be made visible to a different eye; third, to make it possible to control the corresponding shutters for both X-ray tubes from a common control; fourth, to provide means foi*1 producing a second image in the space occupied by the grid lines that cross an X-ray picture or fluoroscopic shadowgraph; and iifth, to provide a simple stereoscope for viewing such stereoscopic pictures. Other objects will appear as the speciiication proceeds.
In the drawings:
Fig. 1 shows diagrammatically an arrangement whereby two fiuoroscopic images are produced in alternate strips by means of a grid opaque to X-rays and obscured each from a different eye by means of a second grid opaque to ordinary light.
Figs. 2 and 3 illustrate avmodication wherein a vibrating Bucky diaphragm or Lysholm grid causes the two X-ray images to fall in alternate strips during alternate halves of the cycle of the alternating `current operating the X-ray tubes and the grid vibrating mechanism.
Fig. 4 shows a transparent screen of alternate differently coloredr strips. In one modication of the invention, this colored screen replaces the grid that is opaque to ordinary light in Fig. 1.
Fig. 5 shows an assembly on which the two X- ray tubes may be mounted, together with the mechanism for operating the shutters and varying the distance between the tubes. v
Fig. 6 is a side elevation of Fig. 5, with certain parts omitted for the sake of clearness, and showing an X-ray tube mounted in its supports.
Fig. 7 shows part of the control mechanism for the moving parts illustrated in Fig. 5.
Fig. 8 is a plan view of part of the mechanism,
whereby the distance between the tubes is automatically varied in accordance with the position of the iiuoroscopic screen,- and, of a remote control for the tube shutters.
Fig. 9 is a front' elevation of the outer end of the control mechanism shown in Fig. 8.
Fig. 10 is a front elevation of the back end of the mechanism shown in Fig. 8, taken along line -6Bf, Fig. 8, and shows in addition the various elements whereby motion is transmitted to the movable parts illustrated in Figs. 5 and '1.
Fig. l1 shows diagrammatically a double Kerr cell assembly with additional parts whereby the right and left eyes may see through their associated optical systems during alternate halves of the cycle of the actuating current.
In Fig. 1, A and B are X-ray tubes placed side by side with unlike ends together. The anode of one tube is connected to the cathode of the other by wire l, which is in turn connected to the high potential wire 2. The opposite ends of these tubes, not shown in the figure, are also connected together and to the other side of the high voltage line. X-rays from these tubes fall on the fluorescent screen C through the grating D, the lines of which are so spaced with relation to the screen C andthe tubes A and B that the rays a from tube A pass between the strips of the grating D' and fall on the portions of screen C that are shielded by grid Dy from the rays b from tube B, as shown in the figure. E is a grating consisting of lines or strips alternately opaque and transparent to ordinary light. The spacing of these lines and the distance of grating E from screen C are such that the right eye R sees the portion of the screen C made iiuorescent by the rays a from tube A, and the left eye L sees the strips of screen C that are made to iiuoresce by rays b from tube B. Other details of Fig. 1 will be explained further on in thisspeciflcation.
If a patient to be examined iluoroscopically is placed between the tubes and grid D, the images produced by the X-rays on screen C will be slightly diierent, due to the distance between the targets where the X-rays originate. This difference is well known in stereoscopic X-ray work. Inasmuch as these images lie in alternate strips, the grating E hides one image from the right eye and the other image from the left eye, thus permitting each eye to see one image only. Due to the difference between these images, the eect is stereoscopic, and the shadows appear to be threedimensional objects. The observer thus has the sensation of looking right into the body. The
` grating D may consist of a self-supporting grid of lead or other substance opaque to X-rays, or of a sheet of Bakelite, aluminum or other material transparent to X-rays having grooves that are etched, engraved or pressed into the surface and then filled in with a material through which X- rays cannot pass, such as powdered lead in a suitable base. A satisfactory grid of this nature may also be made by Stringing wire between two parallel notched supports, as is done with the warp in certain kinds of weaving.
It is well known in radiography and fluoroscopy that the increased sharpness of an image pro- Cil similar strips of material with intervening spaces having a greater depth than width. F one of a series of magnets or solenoids for attracting the 'iron member G attached to the grid D2. H is one of a plurality of springs for resisting the action of the magnets or other similar electrically operated means. The current that energizes F is a rectified current originating in the same alternating current source as that which operates the X-ray tubes, as indicated in Fig. 2. When alternating current from wire 93a passes through wire 83 in the direction indicated by the arrow, it passes through the half-wave rectier 88, then through wire 3I, magnet F, and lwire 92, which connects to 82a, leading to the A. C. source. During the opposite half-cycle of the alternating current, no current will ilow through the circuit Just described, because it will be in the wrong direction to pass through rectifier 88. Alternating vcurrent from wires 92a and 93a is also used to operate the high voltage transformer IIIII, whose secondary |05 is connected by wires |06 and IIII to the X-ray tubes A and B. Because of the wellknown rectifying action of these tubes, they operate on opposite halves of the alternating current cycle. It will thus be evident that during one half oi' the alternating current cycle, F will be inoperative while the rays from one of the tubes pass between the lead strips of grid D2, leaving dark lines I beneath said strips on screen C as indicated in Fig. 2. During the next half cycle, F will be energized, thus causing grid D2 sil) to move to the position shown in Fig. 3, leaving the previously protected parts of the screen now exposed to the other X-ray tube which is now in operation while the ilrst tube remains inoperative on this half of the cycle.
'I'he tubes A and B are of course at some distance from screen C, as indicated in Fig. 1, but
they have been placed much closer in Fig. 2 merely to save space; and it should be understood that the electrical relationship between the tubes and the grid-actuating means, F, is vthe only feature of the tubes intended to be indicated by Fig. 2.
The necessity for rectifying the current to F can be obviated by polarizing F so that it operates only on alternate halves of the cycles oi an alter` nating current. Many other electrically operated means could be provided to vibrate the grid D2, such as a synchronous motor revolving an eccentric connected to the grid.
If an object to be X-rayed is placed between an assembly like that of Fig. 2 and a pair of X-ray tubes connected and positioned as shown in Fig. 1, and if the current to F is in phase with that which operates the tubes, it is obvious that two diterent shadows will occupy alternate strips on screen C. By placing a grid like that of E, Fig. 1, in front of screen C, Fig. 2 or 3, these images may be seen each by the proper eye only, and the ef fect will be sterescopic.
Fig. 4 shows a screen of alternate transparent strips of red and green or other suitable colors. Such a screen may be used as a substitute for screen E in the previous iigures. The colored lines are of such width that those of one color will register with the lines of one of the images on screen C, while the lines of the other image will lie behind the strips of the other color. If the strips ofthis alternately colored screen are red and green and the observer wears spectacles having one red and one green glass, the red strips of the screen will all appear black to the eye wearing. the green glass and therefore only the image lying behind the green strips can be seen by this eye. Similarly, the eye wearing the red glass will be able to se the other image only.
It will be obvious that stereoscopic X-ray pictures may be taken in alternate strips on the same plate by means of modifications of the apparatus just described, thus eliminating the necessity of using two plates with usual plate changers. In such stereoscopic radiography, screen C, Fig. 1 or 22, is replaced by the plate to be exposed.
Such pictures may be viewed by providing a view box with a grating like E, Fig. 1, or with a transparent screen having alternate strips of a dill'erent color, like that illustrated in Fig. 4. In using this latter arrangement, the two eyes must be provided with the colored spectacles described in a foregoing paragraph.
In Fig. 5, J is a supporting plate which may be A attached to the tube carriage by means of holes R. Rods K and L are attached to plate J by the supports M and MI respectively, having connecting screws Yl and YS, respectively. Plates Sl and S2 are suspended between rods K and L by means of rollers Q attached to these plates as shown in Figs. 5 and 6. Shaft N, having a righthand threaded portion 3, Fig. 5, and a left-hand threaded portion I, is journaled in the supports O and restrained from longitudinal movement by the collars T. Plates SI and S2 carry half nuts 5 and 6 respectively, which are adapted to engage threaded portions 3 and l respectively of 'the shaft N. 'I'he holes R and R2, Fig. 5, in plates SI and S2 respectively are for mounting X-ray tubes. This may be done by means of brackets V, Fig, 6, attached to these plates by means of screws or bolts Y. As shown in this drawing, the tube A is clamped between yoke W and support V by means of screws Y2. Plates SI and S2 have windows UI and U2 to permit the passage of X- rays. By turning shaft N, by means to be disclosed later, the threaded portions engage halfnuts 5 and 8, Figs. 5 and 6, causing the plates SI and S2, with X-ray tubes attached thereto, to move to or from a common center, depending upon whether shaft N is turned to the right or left. To limit Vthe lateral spread of the X-rays pass ing through windows UI and U2, Fig. 5, shutters ZI, Z2, Z3, and Z4 are movably attached to the plates SI and S2 by means of L-shaped members Il, I2, I3 and I4, attached to the plates, in the manner indicated in Fig. 6. Shutters ZI and Z2, Fig. 5, are provided with arms I5 and I6, respectively, extending toward the left; and Z4 and Z3 with arms I5a and IBa respectively, extending to theeright. Arms I5 and I6 carry pins I"I and I8 respectively, that ride in slots I9 and 2U respectively, in rocker 2| pivoted on pin 2.2 attached to plate Sl. Arms |5a and lia have pins Ila and |8a respectively, that slide in slots I9a and 20a in rocker 2Ia having a pivot 22a.
' The outward projections of rockers 2| and 2Ia are pivotally attached to levers 23 and 23a respectively by pins 24 and 24a. As will be seen in Fig. 7, levers 23 and 23a are pivotally joined by pin 25, which slides vertically in slot 26 in the upwardly extending part of plate J. l A cord 21 attached to pin 25, passes over pulleys P1 and P6 and also around pulley P3, which latter pulley ls attached to shaft 28 journaled in the lateral extension of plate J. If shaft 26 is turned to the right, cord 21 will pull up on pin 25, causing levers 23 and 23a to raise the outward arm of rockers 2| and 2Ia respectively, Fig. 5. This will move the upper arms of theseV rockers inwardly, along with pins I1 and |1a and the associated shutters Z| and Z4. This same movement of the rockers will cause the lower pins I6 and |811 to move outward, thus pulling shutters Z2 and Z3 against the respectively associated shutters ZI and'Z4. Itv
I dlcated by the relative position of these windows with respect to the holes for mounting the tubes, which holes are assumed to be symmetrically arranged in relation to the tubes. More accurate- 1y, the center of the opening between shutters ZI and Z2 must be slightly to the right of the focal spot on the target in the 4left tube; and the center of the opening between shutters Z3 and Z4 must be somewhat to the left of the focal spot 0n the target in the right tube. This difference is indicated in Fig. 1, in which |0| and ||||a indicate the positions of the focal spots on the targets of the left and right tubes respectively. The distance |02 from the centerof the opening between shutters ZI and Z2, and the center of the opening between the other pair of shutters Z3 and Z4, is less than the distance ID3 between th focal spots l||I| and IIIIa.
Shutters 23 and 30 operate vertically, and are long enough vto cross both windows U|and U2. Shutter 29 is attached to cord 3| at 32 and 32a.
Beginning at point 32, cord 3| passes downward and around pulley PI then up and around pulley P2, thence to the right and around pulley 34, Fig. 7, which turns freely on shaft 28. From pulley 34, cord 3| goes to the left to pulley P3`, and then downward, as shown in Fig. 5, around pulleyA P4, thence up and around P5, and finallyvaround pulley P6, and back to 32. 'Ihe lower shutter 33 is attached to cord 3| at points 33 and 33a, Fig. 5. If pulley 34 is turned to the right, shutters 29 and 36 will close; and they may be opened by turning 34 to the left.
If the frame J is opaque to X- rays, it is necessary to provide it with a window, U3, Fig. 6, to permit'the passage of the rays that emerge between the shutters. 'I'his window may be wide enough to accommodate the rays from both tubes, or individual windows may be used. To avoid confusion with other lines, no window of this type is shown in Fig. 5.
Figures 8, 9, and 10 illustrate, among other things, an automatic mechanism for increasing the distance between the two X-ray tubes as the iiuoroscopic screen is moved away. To plate J is attached two supporting rods, the uppermost of which, 35, is shown in the plan view, Fig. 8. Rod 35 passes through holes in arms 36 and 31, which are adapted to move along 35. Beneath arm 36,
there is another arm '38, shown in Fig. 9. which is a front elevation of the parts that lie behind line 33-40, Fig. 8 To these arms is attached a plate 4|, which is fastened to arm 36 by means of bolts 42, passing through 36 and tightened in place by nuts 43, Figs. 8 and 9. Plate 4I is fastenedto lower arm 38 by bolts 44 and nuts 45, Fig. 9. 46 is the hole in arm 36 which slides along rod 35, Fig. 8, and 41, Fig. 9, is the corresponding hole in arm 38 which slides along a rod like 35, not shown in Fig. 8 because it lies directly beneath 35.
A shaft 48 passes through arms 36 and 38, Fig. 9, and is held in place by collars 43 and 50. Beginning at the lower end, this shaft 46 supports,- in the order named, one end of lever 5I, spacer 52, pulley 53, spacer 54, pulley 55, spacer 56, pulley 51, spacer 58, pulley 59 and spacer 60. These pulleys and lever 5| are all free to turn on shaft 48. Lever 5| is attached to lever 6I, Fig. 8, by pin 62. 'Ihe other end of lever 6| is attached to shaft 63, Fig. 10, to which shaft is also attached gear 64. Referring to Fig. 10, which is a front elevation of the parts lying behind line 65-66,
Fig. 8, together with additional parts not Ypractical to include in the plan view, it will be seen that shaft 63 is journaled insupports 61 and 68 and held in place by collars 69, 69. As the outer end of lever 6| approaches plate J, shaft 63 and gear 64 turn in the direction indicated by the arrow on gear 64, causing gear 10, shaft 3 and gear 1 to turn in the direction indicated by the arrow on gear 1, which in turn rotates gear 6 in the direction of the arrow shown thereon, thus turning shaft N and bringing the X-ray tubes closer together in the manner previously explained. As the assembly attached to arm 36, Fig. 8, moves away from plate J, the outward end of lever 6| is pulled away from -plate J by means of lever 5|, thus causing the X-ray tubes to nove further apart by means of the mechanism illustrated in Figs. 5 and 10.
Although I prefer the above-described automatic means for varying the distance between the X-ray tubes, it is possible by a, modification to ,attach a flexible shaft directlyto shaft N so that the distance between the X-ray tubes may be controlled at the will of the operator from any,
remote point by means of a knob on theopposite end of the flexible shaft.
The shutters for the tubes may be controlled from the assembly attached to arm 36, Figs. 8 and 9. Knob 1|, Fig. 8, and pulley 12 are both attached to shaft 13, journaled in plate 4|. Shaft 13 passes through knob 14 and tube 15, which is attached to knob 14. Tube 15 passes through plate 16 and is attached to pulley 11. Plate 16 is attached to arm 31 and to another arm directly below 31 which therefore does not'show in the l Figs. 8 and il,y
drawing. Knobs 1| and 14 control the shutters by means of the cords 21 and 3|, which in this case are long enough to extend over a. system of pulleys, (similar to those used on dental drills)v to pulleys 12 and 11 respectively, which are shown in Figs. 8 and 9. In' this modification. pulleys P9 and 34, Fig. '7, are omitted, and the following 12, pulleys 53 .and5:3a, Flg.'9, 53h and 53e, Fig; 10,
from whence it passes to pulley P3, Fig. 7. From here back to pulley P8a, cord 21. follows the course originally described. It will thus be evident that shutters ZI, Z2, Z3, and Z4, Fig. 5, can be controlled by knob 1|, Fig. s, which is attached to pulley 12 by shaft 13. When pulley 34, Fig. '1, is eliminated to permit the remote operation of shutters 28 and 30, cord 3|, after leaving pulle'y P2, passes over pulley 34a, Fig. 10, around pulley 51h, Fig. 10, then around 51a, Figs. 8 and 9, pulleys 51., 11, 55, and 55a, Fig. 9, and 55h, Fig. 10, from whence it follows the course originally described. Inasmuch as pulley 1,1, is connected to knob 14, by tube 15, as shown in Fig. 8, it follows that shutters 29 and 3l) may be controlled by knob 14.
If it is not desired to control the vertical and lateral shutters from a remote point, pulley 34, Fig. 7, may instead be connected to a tube and knob like 15 and 14 respectively, Fig. 8, and pulley P8, Fig. '1, may be connected to shaft 28, which may be extended through the tube and connected to a knob like 1|. Fig. 8, in a manner well known in the art.
Member 18, Figs. 8 and 9, is fastened between plates 4I and 16 by screws 18. Shaft 88 passes through member 18, and to this shaft are attached arms 8l and 82, by means of screws 83 and 84, respectively. To the other end of arms `ill and 82, the holder for the uoroscoplc screen has made it possible, in the past, to use synchronous shutters to block the vision of the right and left eyes alternately to prevent them from seeing the images intended for the opposite eyes. In addition to new means already described for attaining this same end Without the use of moving parts, another novel method is to provide each eye with a Kerr cell and associated members and energize the Kerr cells alternately by an A. C. current in phase with that which operates the X-ray tubes. Such an arrangement is illustrated in Fig. 11, in which 85 and 85a are Kerr cells, 88 and 88a are polarizers for polarizing the incident light rays, and 81 and 81a are analyzers each capable of adjustment with respect to its cooperating polarizer either to transmit or reject the light polarized by the associated polarizer. 'I'hese cooperative functions of polarizers and analyzers are well-known in the construction of polariscopes, which are widely used, and in the Kerr cell units as employed n television and telephotography. 88 and 88a are rectifying means whereby cells 85 and 85a are operated on alternate halves of the cycle f the same A, C. current. Current from transformer |88, passing through lwire 88, in the direction of the arrow, will pass through wire 98 and rectifier 88, but will be in the wrong direction to pass through 88a. After leaving rectier 88, said current passes through wire 9|, cell 85, wire 92 and wire 93 back to theA transformer. During the other half of the cycle, the current from wire 93 will pass through wire 82a, (in the direction of the arrow) cell 85a, wire 8Ia, rectifier 88a, wire 98a. and then through wire 88 back to the transformer in an opposite direction to that during the half of the cycle when 85 was energized through the rectifying action of cell 88. Members 84 and 85, and 84a and 85a support the Kerr cell assemblies, which are paired together by means of brackets 96 and 91, attached to members 95 and 85a by screws 98 and, 98a respectively. L and R are the right and left eyes respectively, looking through the cells along lines 98 and 99a respectively.
It is possible, with such Kerr cell assemblies, to arrange the analyzers so that light passes only when the cells are electrically energized, or when they are not energized. In the arrangement shown in Fig. 1l, it is immaterial which adjustment of the analyzers is used, providing both analyzers are adjusted the same-that is, so that light passes through whichever cell receives the charge, or fails to pass through whichever one is energized. It will be assumed, however, that the adjustments have been xed so that light will pass through the charged cell. When current passes through rectifier 88, as is the case during half of the cycle of the A. C. current, the left assembly represented by 81, and 88 becomes transparent, and the left eye L is able to see through the assembly along line 99; and during the opposite half of the cycle the right eye sees through assembly 81a, 85a and 88a along line 89a. Inasmuch as these cells are operated by alternating current in phase with that operating the X-ray tubes, the polarity is adjusted so that the right and left eyes see when the left and right tubes, respectively, are operating, thereby carrying out the same objective as that achieved by grating D and E in Fig. l.
It is obvious that various modifications may be made from the embodiments of the invention herein described without departing from the spirit of the invention.
My claims are:
1. In X-ray apparatus,` a combination including a supporting element; two members movably mounted on said element, each member carrying an X-ray tube and a pair of laterally movable shutters; means for moving said members in opposite directions simultaneously; and means for moving the shutters in each pair simultaneously in opposite directions simultaneous with the corresponding movement of the shutters in the other pair.
2. In X-ray apparatus, a combination including two X-ray-tube-carrying members; means for moving said tube-carrying members in opposite directions simultaneously; a. pair of shutters movably mounted on each tube-carrying member; means for moving the shutters in each pair simultaneously in opposite directions simultaneous with the corresponding movement of the shutters in the other pair; the distance from the adjoining edges of one pair of shutters when closed to the adjoining edges of the other pair of shutters when closed being less than the distance from the focal spot on the target of one tube to the focal spot on the target of the other tube.
3. In X-ray apparatus, a combination including a supporting member; two supported members each carrying an X-ray tube and a pair of laterally movable shutters;y manually controllable means for moving said supported members in opposite directions simultaneously; means for moving the shutters in each pair simultaneously in opposite directions simultaneous with the corresponding movement of the shutters in the other pair; the distance from the adjoining edges of one pair of shutters when closed to the adjoining edges of the other pair of shutters when closed being less than the distance from the focal spot on the target of one tube to the focal spot on the target of the other tube.
4. In X-ray apparatus, a combination including: a source of alternating current; two X-ray tubes adapted `to operate on opposite halves of the cycle of said alternating current; a surface that luoresces when exposed to X-rays; a grid of X-ray resistant strips interposed between said surface and said tubes; and electrical means for vibrating said grid in synchronism with thei operation of said tubes; said grid consisting of parallel strips opaque to X-rays, said strips having a spacing substantially equal to their width.
5. In X-ray apparatus, a combination including: two alternately operative sources of X-rays; a surface that fluoresces when exposed to X-rays; a grid comprising parallel strips that are opaque to X-rays, said grid interposed between said sources and said surface; electrical means for vibrating said grid; and a grating comprising strips that are transparent to at least part of the rays ofthe visible spectrum alternating with strips that are substantially opaque to said latter rays; said latter strips adaptedv to register f between said grid and said grating.
6. InX-ray apparatus, a combination including: a source of alternating current; two X-ray tubes adapted to operate on opposite halves of the cycle of said alternating current; a-surface that fluo'resces when exposed to X-rays, said surface positioned to receive X-rays from said tubes; and two Kerr cell 4assemblies each comprising a polarizer and an analyzer; said assemblies adapted to pass light on opposite halves of the cycle of said alternating current so that thedluorescence on said surface that is caused by the X-rays from one tube may be seen through one of said assemblies only, and the fluorescence caused by the X-rays from the other of said tubesmay be seen through the other assembly only.
7. In X-ray apparatus, a combination includ- 4ing two members, each carrying an X-ray tube and a pair 'of laterally movable shutters; a fluoroscopic screen; a movably mounted support for said screen adapted to move in a direction perpendicular to said shutters; and means for moving said members in opposite directions simultaneously, said means operated by the movement of said support. i
8. In X-ray apparatus, a combination including a. supporting element; two members movably supported on said element,'each of said members carrying an X-ray tube and a pair of laterally movable shutters; a. supporting structure adapted to move toward and from said shutters; a ilu- `oroscopic screen carried by said structure; means for moving said members in opposite directions simultaneously, said means operated by the movement of said structure; means for varying the opening between each of the two pairs of shutters simultaneously, said shutter-controlling means operable from a manual control carried by said structure.
9. In X-ray apparatus, a combination including a supporting element; two members movably supported on said element, each of said members carrying an X-ray tube; a structure adapted to move in a direction at right angles to the direction of movement of said members; a fluorescent screen mounted on said structure; and automatic means for moving said members in opposite directions simultaneously, said automatic means operated by the movement of said structure.
10. In X-ray apparatus, a combination including two X-ray tubes mounted for relative movement therebetween; two sets of shutters, each set individual to one of said tubes, said sets mounted for relative movement therebetween; and means for moving the individual shutters in both sets simultaneously irrespective of the distance between the sets. l
1l. In X-ray apparatus, a combination including: a source of alternating current; two X-ray tubes adapted to operate on opposite halves of the cycle of said alternating current; a surface that fiuoresces when exposed to X-rays, said surface positioned to receive X-rays from said tubes; two devices individual respectively to the right and left eyes and each constructed and arranged to transmit light that has been polarized substantially in a given plane; and means interposed between "said screen and said devices for polarizing the light from said screen and transmitting it to said devices on opposite halves of the cycle of .saidvalternating current so thatthe fluorescence on said surface that is caused by the X-rays from one tube may be seen through one of said devices only, and the iluorescence caused by the X-rays from the other tube may be seen through the other device only.
12. In X-ray apparatus, a combination includ- I ing two4 X-ray tubes; a structure movable with i ing two X-ray tubes; means individual to each tube for limiting the spread of the X-rays emitted thereby; a structure movable with respect to said tubes; a uorescent screen mounted on said structure; and means operable by the movement of said structure for varyingwthe distance between said tubes and between said rst mentioned means.
14. In X-ray apparatus, a combination including two movably mounted X-ray tubes; two sets ofshutters, each set individual to one of said tubes; a structure movable with respect to said tubes and shutters; a iiuorescent screen mounted on said structure; and means operable by the movement of said structure for moving said tubes in opposite directions simultaneously and for varying the distance between said sets.
LE ROY- J .LEISHMAN