US3908126A

US3908126A - X-ray apparatus for providing panoramic radiographic projections

Info

Publication number: US3908126A
Application number: US429482A
Authority: US
Inventors: Donald C Hudson; Charles R Morris; Horst G Fleck; Karl A Senghaas
Original assignee: Pennwalt Corp
Current assignee: KEYSTONE X-RAY Inc
Priority date: 1974-01-02
Filing date: 1974-01-02
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23
Also published as: BR7409990A; FI334474A; IT1023319B; FR2324023A1; GB1486991A; GB1486992A; FR2324023B1; JPS50102284A; SE7415962L; NL7415333A; DE2461441A1

Abstract

A radiographic apparatus is disclosed for providing continuous radiographs or x-rays of a selected portion of a subject lying in a horizontal position by simultaneously rotating an x-ray source and an x-ray film holder including an x-ray film about the subject. An x-ray film cassette is mounted in the film holder and while the film holder rotates about the subject, the film cassette is moved past an x-ray slit. The x-ray source and film holder are mounted for rotation with respect to a pivoted gimbal frame and apparatus is disclosed for shifting the frame a selected amount about its pivot point to shift the axis of rotation of the source and film holder with respect to the subject being x-rayed. The x-ray source and film holder are preferably mounted on a rotatable disc and novel drive apparatus is disclosed for rotating the disc. The film holder includes a novel drive mechanism for moving the cylindrical film cassette, in which an x-ray film is placed, at the proper rate of speed to provide the desired x-ray during rotation of the source and film holder. Also, a patient conveyor cart is disclosed for conveying a patient to the x-ray machine and permitting him to be easily and safely placed in position in the machine while in a horizontal position. The x-ray apparatus also includes apparatus for elevating and positioning the patient at a proper position in the machine, and a programming apparatus for automatically controlling the sequence of operation of the x-ray apparatus during selected modes of operation. Also, a slide rule profile projector is provided for selecting the required amount of shift of the gimbal frame for a desired x-raying operation.

Description

United States Patent [191 Hudson et al.

[ Sept. 23, 1975 [73] Assignee: Pennwalt Corporation, 8.8. White Dental Products Division, Philadelphia, Pa.

22 Filed Jan. 2, 1974 2| Appl.No.:429,482

OTHER PUBLICATIONS Planigraphy", American Jour. of Roentgenology and Radium Therapy, Vol. XXXVI, No. 5, Nov. 1936, Andrews, pp. 578 to 579.

Primary Examiner.lames W. Lawrence Assistant Examiner-B. C. Anderson Attorney, Agent, or Firm-Hubbard, Thurman, Turner & Tucker ABSTRACT A radiographic apparatus is disclosed for providing continuous radiographs or x-rays of a selected portion of a subject lying in a horizontal position by simultaneously rotating an x-ray source and an x-ray film holder including an x-ray film about the subject. An x-ray film cassette is mounted in the film holder and 7 while the film holder rotates about the subject, the

film cassette is moved past an x-ray slit. The x-ray source and film holder are mounted for rotation with respect to a pivoted gimbal frame and apparatus is disclosed for shifting the frame a selected amount about its pivot point to shift the axis of rotation of the source and film holder with respect to the subject being A" rayed. The x-ray source and film holder are preferably mounted on a rotatable disc and novel drive apparatus is disclosed for rotating the disc. The film holder includes a novel drive mechanism for moving the cylindrical film cassette, in which an x-ray film is placed, at the proper rate of speed to provide the desired x ray during rotation of the source and film holder. Also, a patient conveyor cart is disclosed for conveying a patient to the x-ray machine and permitting him to be easily and safely placed in position in the machine while in a horizontal position. The x-ray apparatus also includes apparatus for elevating and positioning the patient at a proper position in the machine, and a programming apparatus for automatically controlling the sequence of operation of the x-ray apparatus during selected modes of operation. Also, a slide rule profile projector is provided for selecting the required amount of shift of the gimbal frame for a desired xraying operation.

37 Claims, 31 Drawing Figures US Patent Sept. 23,1975 Sheet 1 0f 13 3,908,126

US Patent Sept. 23,1975 Sheet 2 of 13 3,908,126

US Patent Sept. 23,1975 Sheet 3 0f13 3,908,126

US Patent Sept. 23,1975 Sheet 4 of 13 3,908,126

US Patent Sept. 23,1975 Sheet 5 of 13 3,908,126

US Patfint Sept. 23,1975 Sheet 6 of 13 3,908,126

US Patent Sept. 23,1975 Sheet 7 of 13 3,908,126

US Patent Sept. 23,1975 Sheet 9 of 13 3,908,126

um bk u? NQQ Nu X 8+ (SEE N \AYW X Sheet 11 of 13 Sept. 23,1975

US Patent US Patent Sept. 23,1975 Sheet 12 of 13 3,908,126

F/RJT #AAF ACT/V5 Z/IJT H1411 ACTH/E US Patent Sept. 23,1975 Sheet 13 of 13 3,908,126

011 WWW X-RAY APPARATUS FOR PROVIDING PANORAMIC RADIOGRAPIIIC PROJECTIONS BACKGROUND OF THE INVENTION This invention relates to apparatus and methods for providing selected, continuous radiographs of a subject, particularly of the human body, and in one of its aspects to such apparatus and methods which provide for such radiographs of a subject lying horizontal. The principles of this invention apply to the production of panoramic radiographs, tomographs, laminographs and zone laminographs of the human body. The specific apparatus and methods described herein are particularly adapted to providing for full mouth dental radiographs using a film located outside of the mouth, and providing radiographs of other portions of the human skull.

Throughout this specification, the particular radiographic apparatus described utilizes x-rays to provide radiographs and is referred to as an Jr-ray apparatus without any intent to limit its application to just rays in the x-ray spectrum.

Panoramic radiographs can be obtained by directing an x-ray beam through an object to be x-rayed to a moving x-ray film, while rotating the source and film about the object. In obtaining panoramic radiographs of a human subject, for example of the dental arch or selected portions of the skull, compensation must be provided for the fact that the curvature of the desired area of focus is generally not a true circle. In U.S. Pat. NO. 2,798,958, apparatus is shown for obtaining radiographic projections of parts located internally of the human body, particularly full mouth dental radiographs using a single film outside the mouth. In the apparatus illustrated in that patent, the subject sits upright in a fixed position and an x-ray source and a single, extra oral, x-ray film are rotated about him. A cam mechanism is provided for varying the rate of film trave relative to the rate of travel of the x-ray source about the subject in order that the radiological projections occupy a distance on the film equal to the linear distance of a curved structure being x-rayed. To provide this, a plane-surfaced cam having a configuration correspond ing to the curvature of the object to be visualized, such as the dental arch, has its center of rotation coincident with the center of rotation ofa movable arm which supports the x-ray source and the x-ray film. The rotation of the cam is coupled to drive the film by a cable linkage.

Variation of the rate of motion of the film by virtue of the cam in the film driving mechanism compensates for the fact that the portion of the skull being x-rayed, for example, a dental half-arch, is a complex curve and not a circle.

Also, during x-raying of certain portions of the head, particularly the dental arch, it is highly desirable to shift the center of rotation of the x-ray source and film so that each half-dental arch can be x-rayed without projecting x-rays through the spinal column of the patient. In U.S. Pat. No. 2,798,958, this is accomplished by manually moving the patient after the completion of one-half of an x-ray cycle, to relocate the center of the axis of rotation with respect to the head of the patient. In x-raying either half of the dental arch, the center of rotation is chosen so as to fall at the center of an imaginary circle whose circumference would pass through the crowns of the molar teeth ofthe side being x-rayed. The resulting radiograph is in two half-arch sections on a single film with an unexposed space in the center of approximately one inch wide. In U.S. Pat. No. 3,045,l l8, an improvement is provided in the apparatus described in U.S. Pat. No. 2,798,958, wherein after x-raying of one-half ofa dental arch, the apparatus automatically shifts the patient so that the line of sight between the x-ray source and the film bypasses the patients spinal column and permits x-raying of the other half of the dental arch.

While the x-ray apparatus of U.S. Pat. Nos. 2,798,958 and 3,045,] l8 have proven to be highly satisfactory, particularly for providing radiographs of the dental arch, they also have certain limitations. For example, there are many times when it is highly desirable to provide for radiographs of a patient lying in a horizontal position. This is particularly true where the patient finds difficulty in sitting upright such as when he is injured or is seriously ill. In the past, numerous devices have been suggested for providing such x-rays, including panoramic x-rays where an x-ray source and x-ray film are rotated about a portion of a patient being x-rayed to obtain radiographic projections of that portion. Examples of such apparatus is shown in U.S. Pat. Nos. 3,082,322; 3,484,604; 3,466,439; 3,432,657; 3,549,885; and 3,486,022. In some of the apparatus of those patents, it is required that the patient be rotated rather than the x-ray source and film. In U.S. Pat. No. 3,229,088, a complex apparatus is provided for rotating the head ofa patient (only partially) for taking radiographs of the dental arch.

Insofar as is known to applicants, none of the structures illustrated in these patents for providing x-rays of a subject in a horizontal position have resulted in a practical and economical x-ray apparatus which provides panoramic radiographic projections of selected portions of a subject lying horizontal, without undue discomfort or danger to the patient, and without relatively high cost. It is thus an object of this invention to provide such an apparatus.

A further limitation in the prior art referenced is that where a shift of the center of rotation is provided, either by shifting the patient or the x-ray apparatus, to position the line of sight of the x-ray apparatus with respect to the subject being x-rayed, the shift is fixed and the size and radius of the focal trough remains constant. However, by providing a variable shift within safe limits, and by being able to accurately adjust the position of the subject in the x-ray machine, the focal trough can be changed in size and location so that, for example. successive radiographs or tomographs can be made at selected, progressively deeper depths in a portion of the skull being examined to give, in effect, a three dimensional picture of the examined area. However, in order to provide this capability, suitable apparatus must be provided for providing the required shift, when selected. Also, once the shift is made variable, some means must be provided to ensure that the proper shift can be quickly selected for a desired operating condition and that the x-ray apparatus will automatically and accurately provide the selected operation, even when operated by a person with relatively little training in radiology.

Thus, another object of this invention is to provide an x-ray apparatus which is a substantial improvement over the prior art x-ray apparatus referenced, and provides for a variable shift which may be readily selected for a desired x-ray operation to greatly increase the range of practical usage of the x-ray apparatus. Further, presently available x-ray apparatus used in tomography generally costs several hundred thousands of dollars or more, thus limiting their availability and usage. and another object of this invention is to provide an x-ray apparatus which meets the previously stated objects, but which can produce tomographs and laminographs at a relatively lower cost for more general usage in medical and dental radiographic diagnosis. It is believed that the general availability of such an x-ray apparatus will greatly aid a large number of physicians and dentists in many of their diagnostic procedures.

Another object of this invention is to provide such an x-ray apparatus in which the center of rotation of the x-ray source and film can be shifted a variable amount without shifting the patient.

In the apparatus of US. Pat. No. 2,798,958, the x-ray film is loaded into a flat cassette having a center slit in the line of sight of the x-ray beam. The rotation of the cam mechanism utilized, which is mechanically driven by the motor causing the x-ray source and film holder to rotate, must be converted to a linear motion by a cable linkage connected to the rotating cam to move the x-ray film past the slit in the cassette. Unless the cable linkage is properly adjusted, it can introduce jitter into the movement of the x-ray film and distort the resulting radiograph. Also, the requirement for driving the cam directly from the motor rotating the x-ray source and film holder complicates the construction of the x-ray apparatus, and adds a further source of problems. Thus, another object of this invention is to provide a drive mechanism for moving the x-ray film during rotation of the x-ray source and film about an object being x-rayed without the need for a cable linkage, or for a direct connection to the x-ray excursion drive motor, while providing little or no jitter or other movement which would distort the resulting radiograph.

Another object of this invention is to provide such a drive mechanism which automatically adjusts the speed of movement of the film to compensate for variations in the curvature of the object being x-rayed.

A further object of this invention is to provide such a drive mechanism and film holder in which the x-ray film may be easily and rapidly loaded, orientated, and removed.

Another object of this invention is to provide such a drive mechanism in which the relative speed of rotation of the x-ray source and film holder, and the rate of movement of the x-ray film can be altered to permit panoramic radiographic projections to be taken of objects of different shapes while maintaining a substantially constant focus of the image. Because the apparatus of this invention readily provides for a selected variance in the amount of shift of the center of rotation of the x-ray source and film, and a selected variance in the shape of the focal trough during operation within preset limits, it can be used, for example, for providing successive tomographs of an area of examination so that each tomograph has a sufficient depth of focus to overlap with the next tomography and effectively provide a continuous, three dimensional picture of the examined area.

In the operation of any x-ray apparatus of the type contemplated by the present invention, particularly where relatively small selected areas are being examined, it is highly desirable that as little operator intervention as possible be required, and that the operator be required to make as few initial adjustments or settings as possible, to lessen the chance of operator error or misjudgment.

Thus, a further object of this invention is to provide automatic control apparatus for controlling the sequence of operation of an x-ray apparatus of the type provided by this invention, permitting selection by the operator of desired modes of operation and desired degrees of shift of the center or rotation of the x-ray source, which the apparatus will then automatically provide.

A further object of this invention is to provide improved patient conveying and elevating apparatus for rapidly and safely moving a patient who may be ill or injured into proper position in an x-ray apparatus with little or no physical handling of the patient during this procedure. Furthermore, another object of the present invention is to provide safety features which automatically prevent interference between the patient and the x-ray apparatus while the patient is being moved in and out of the machine, or while the x-ray apparatus is being operated. By use of the positioning apparatus of this invention, the patient can be safely and relatively precisely positioned in the x-ray apparatus within adjustable limits and this feature further adds to the flexibility of the present apparatus.

A further object of this invention is to provide a single x-ray apparatus which satisfies all of the above stated objects regarding radiographic capability, cost and availability, patient safety, and operator convenience.

These and other objects of this invention, which will be apparent upon consideration of the following detailed description of the drawings and of the appended claims and drawings, are accomplished in accordance with this invention by providing an x-ray apparatus for taking panoramic radiograph projections wherein an x-ray. source and x-ray film holder are mounted in an upright frame to rotate in a vertical plane with respect to the frame, and about an object being .t-rayed, while the film is moved past a lens or slit, and the center of rotation of the x-ray source and film holder can be shifted a selected amount by causing the frame to move with respect to the object being x-rayed. In the preferred embodiment of this invention illustrated, the upright frame is pivoted gimbal frame mounted in turn on a fixed frame at a lower pivot point and means for causing the frame to pivot about its lower pivot point a se lected amount to shift the center of rotation of the x-ray source and film holder a selected amount. The x-ray source and film holder are preferably mounted on opposite sides of a centerless disc supported for rotation on the gimbal frame, and the disc is driven along its outer edge, which is beveled, by an electric motor through a novel arrangement of drive wheels so that the circumferential speed of the mating faces of the drive wheels and disc are equal at substantially the center of contact, and a smooth, precise movement of the disc is provided.

In the preferred embodiment illustrated, the means for causing a selected amount of shift includes a switch acutator for providing stepped increments of shift of the gimbal frame on either side of the vertical centerline of the frame. In this manner, the disc supporting the x-ray source and film holder for rotation can be rotated about one center of rotation when one-half of the x-ray scan is taken, and a second center of rotation when the other half x-ray scan is taken. so that. for example, a full dental arch can be x-rayed without projecting x-rays through the patients spinal column.

Also, means is provided for controlling the rate of movement of the x-ray film passing the x-ray slit. In the preferred embodiment of this invention, the x-ray film is placed in a cylindrical cassette which is mounted for rotation in the film holder. A constant speed electric motor is provided for rotating the cassette at substantially the speed of rotation of the disc supporting the x-ray source and film holder, except that the speed of rotation of the cassette is varied as required to compensate for variations in the shape of the area being xrayed. The housing of the film drive motor is mounted to float with respect to the film holder and a sloped cam mechanism is connected directly between the rotating shaft of the motor and the floating housing so that the differential speed of rotation of the shaft with respect to the housing is a function of the shape of the cam. The shape of the sloped cam for particular xray operation can be determined by translating the change in radius of a basic cam as described herein which would provide the required change in the rate of movement of the film.

In accordance with this invention. a slide rule profile projector is provided to aid in determining the required shift for a particular x-ray operation. The profile projector includes curved faces corresponding to the best line of focus of the x-ray apparatus for a particular sloped cam. The curved faces are movable towards and away from each other and by overlapping the curved faces on an outline of the object to be x-rayed (each curved face representing one-halfofthe x-ray) and noting the spacing between the faces, the required amount of shift can be determined. An important feature of the preferred embodiment of this invention illustrated is that the stepped increments of gimbal shift can be numbered on a switch selector so that the same shift will be provided each time the same number is selected by the operator. and a scale of numbers can be provided on the profile projector corresponding to the shift selector numbers. Thus. if the shift reading on the profile projector for the best line of focus of a particular area to be .r-rayed is, for example, 5, then the operator need only select shift position 5 on the shift selector of the x-ray apparatus and the required shift will be provided.

The preferred form of x-ray apparatus of this invention illustrated also includes a patient conveyor cart having a movable conveyor belt to aid in movement of the patient to and placement ofthe patient in the apparatus, and hydraulically operated patient elevator apparatus for properly positioning the patient in the apparatus. Safety limit switches are suitably located to automatically control the operation of the hydraulic elevator apparatus to avoid interference between the patient and the .r-ray apparatus while the patient or the .r-ray apparatus is being moved with respect to each other.

Other features of this invention are described in the following detailed description of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS In the drawings. wherein like reference numerals are used throughout to designate like parts. and wherein preferred embodiments of the present invention are disclosed.

FIG. I is a perspective view in elevation of the preferred form oferay apparatus of the present invention;

FIG. 2 is a frontal view in elevation of the apparatus of FIG. I with the elevator pedestal and front panel removed;

FIG. 3 is a view in elevation showing the switching mechanism for setting the shift of the center of rotation of the apparatus in FIG. 2;

FIG. 4 is a sectional view through 4-4 in FIG. 3; FIG. 5 is a front elevation taken generally at 5 in FIG. 4;

FIG. 6 is a sectional view taken at 66 in FIG. 2;

FIG. 7 is a perspective view of the elevator pedestal of the apparatus of FIG. I and of a portion of a patient conveyor cart prior to connection with the pedestal;

FIG. 8 is a view taken at 88 in FIG. 7, except that the cart has been moved in position prior to elevation of the cart and the patient;

FIG. 9 is a sectional view similar to FIG. 8, extended through the line 9-9 in FIG. 2, and showing the patient in position in the apparatus of FIG. I with the pedestal and belt conveyor raised;

FIG. 10 is a view taken at I010 in FIG. 9;

FIG. 11 is a view taken at 11-11 in FIG. 9, showing the underside of the conveyor cart;

FIG. 11 is an enlarged view taken at 12 in FIG. 12;

FIG. 13 is an elevation view of a preferred form of cy- Iindrical film cassette utilized with the present invention;

FIG. MA is a schematic view of a basic cam defining the desired rate of movement of the x-ray film during an x-ray scan;

FIG. 14B is a schematic view of a modified cam of the present invention defining this rate of movement;

FIG. 15 is a front view in elevation of the film drive mechanism of the present invention shown without the film holder in place;

FIG. 16 is a view taken at 16l6 in FIG. 15;

FIG. 17 is a sectional view taken at I717 in FIG. 16;

FIG. 18 is an overall schematic of a preferred form of electrical control system, and programmer apparatus for the x-ray apparatus of FIG. 1;

FIG. 19 is a schematic view of a preferred form of a hydraulic system for the x-ray apparatus of FIG. I;

FIG. 20 is an electrical schematic of the switching apparatus for the hydraulic system of 19, and for the shift selector switch mechanism of FIG. 3;

FIG. 21 is an electrical schematic of the switching apparatus for controlling the excursion of the x-ray source;

FIG. 22 is an electrical schematic of the switching apparatus for controlling the motion of the film cassette;

FIGS. 23A and 238 show the positions of the apparatus of FIG. 2 during mode 1 operation;

FIGS. 24A and 24B show the positions of the apparatus of FIG. 2 during mode 2 operation;

FIG. 25 is a pictorial representation of a sample x-ray provided by the present apparatus in the dental mode;

FIG. 26 is a view in elevation ofa slide rule type profile projector for use with the present invention;

FIG. 27 is a schematic view showing an imaginary outline of a section through a patients head to illustrate the application of this invention in x-raying the dental arch; and

FIG. 28 is a view similar to FIG. 27, except that a lower skull projection is taken to illustrate the application of the present invention in x-raying through the base of the skull.

GENERAL DESCRIPTION Referring now to the drawings, in FIG. I, a preferred form of x-ray apparatus of this invention is illustrated as including an upright frame and housing 31 and base frame 31a forming a box-like structure, and a box-like patient elevator pedestal 32 mounted in front of housing 31. Elevator pedestal 32 includes an elevator apparatus 33 movable in and out (i.e., towards and away from housing 31) as indicated by the arrow 34, and a patient support platform 35 mounted on elevator apparatus 33 for movement up and down as indicated by the arrow 36. As shown in FIG. 9, platform 35 is in the form of a hollow box and includes a top plate 35a pivotally mounted on a bottom plate 35b by brackets 35c mounted on each side of bottom plate 35b (only one bracket 350 is shown in FIG. 8). A slotted block 37 is mounted on platform 35, and includes an elongated slot 38 therein for controlling the movement of a belt on a patient conveyor cart as illustrated in FIGS. 7 12. Block 37 is movable towards and away from housing 31 as indicated by arrow 39. Platform 35 also includes an elongated slot 40 for interconnection with a bar on the front of a patient conveyor cart as hereinafter described. Extending from platform 35 and towards housing 31 is a patient headrest 41 which is also movable to adjust the tilt of the patients head as hereinafter described. The apparatus for raising and lowering the respective members of pedestal 32 described is illustrated in FIGS. 7 l2 and will hereinafter be described in detail. Elevating apparatus 33 on pedestal 32 functions to support the patient at the proper elevation and in the proper position within the x-ray apparatus for the xraying operation.

A rotatable disc 42, defining a generally circular opening 43, is mounted in x-ray apparatus 30 as hereinafter described. A cylindrical member 42a extends from the edge of disc 42 defining opening 43 into apparatus 30. As illustrated in FIG. 1, an x-ray source 44 and an x-ray film holder or housing 45 including a cylindrical film cassette 46 are mounted on the opposite sides of disc 42 adjacent opening 43 so that they face each other, and are spaced apart a sufficient distance to permit the head of a patient to be inserted between them. The mounting and operation of disc 42 and source 44 are shown in FIGS. 2, 6, 23A, 2313, 24A and 24B, and the configuration and operation of the film holder 45 is illustrated in FIGS. 13 17. A retractable tape measurement 47 may be mounted on the inside of housing 45 for measuring the correct patient heat to film distance during operation of apparatus 30.

Disc 42 is mounted to rotate in an opening in a front plate 48 which is, in turn, mounted on a suitable frame which is illustrated in detail in FIG. 2. During operation, the head of a patient to be x-rayed is supported on headrest 41 between x-ray source 44 and film housing 45 so that as disc 42 rotates, it carried x-ray source 44 and film housing 45 about the head of a patient in a manner similar to the apparatus in US. Pat. Nos. 2,798,953 and 3,045,] 18, except that the patient is upright in those patents instead of horizontal. Also, while the shift required to provide a panoramic x-ray through certain areas to be x-rayed in those patents is provided by shifting the position of the patient with respect to the center of rotation of the x-ray source and film. this shift, when required, is provided in the present invention by shifting the center of rotation of disc 42, and providing for variations in the degree of this shift.

Suitable control apparatus 49 for providing the required electrical switching and control functions to operate the elements described of x-ray apparatus 30 is shown as being mounted in the upper righthand portion of housing 31, as, for example, a removable sub-panel. Details of this apparatus are illustrated in FIGS. 3 5 and 18 22.

Of course, an x-ray apparatus constructed in accordance with the principles of this invention may take many different forms. other than the general arrangement described with respect to apparatus 30.

GIMBAL SHIFT AND DISC DRIVE APPARATUS As noted, an important feature of the present invention is the provision for shifting the center of rotation of disc 42 during operation rather than shifting the patient.

Referring now to FIG. 2, preferred apparatus for providing this shift is shown as including a pivoted gimbal or operating frame 50 mounted inside housing 31 for supporting disc 42 for rotation. As illustrated. frame 50, which may be made of lightweight aluminum tubing, has its lower end 50a in the form of an apex of a triangle and this end is provided by a tubular sleeve 51a mounted by spaced bearings 51b (see FIG. 9) to pivot on a rigid pivot pin 510 which is, in turn, mounted in base frame 31a of apparatus 30. By this arrangement, frame 50 can pivot about pin 51c to shift between the dotted line positions 50b and 500 inside the housing 31, which are on either side of the center shift position illustrated by the solid line position of frame 50 in FIG. 2. As illustrated in FIG. 2, single, V-grooved

rollers

52 and 53 are rotatably mounted on the upper portion of the frame 50 and on opposite sides thereof by arms 54a and 550, respectively, and each of arms 54a and 550 are respectively pivotally supported on frame 50 by brackets 54b and 55b. Also, opposed pairs of V- grooved

rollers

56 and 57 are rotatably mounted on opposite sides of frame 50, below

rollers

52 and 53, on opposed plates 58a and 590, respectively, and

plates

58a and 59a are in turn respectively pivotally mounted on brackets 58b and 59b connected to gimbal frame 50. Rotatable disc 42, which may be made of a piece of flat aluminum with opening 43 in the center, includes a beveled outer edge 60 having converging beveled surfaces 60a and 60b, and disc 42 is mounted between and supported on

rollers

52, 53, 56 and S7 with edge 60 supported in the grooves of the rollers as shown in FIG. 6. An adjustable rod 61, which may be adjusted in length by a turnbuckle 62, may be connected between

arms

54a and 55a to adjust the force with which

rollers

52 and 53 engage beveled edge 60 of disc 42. A pulley may be rigidly connected to each of rollers 57, and mounted to rotate with the roller, and pulleys 65 may be driven by a constant speed motor 63 through an endless belt 64 connected to pulleys 65 (see FIG. 6). Of course, if desired, rollers 56 can be driven instead of rollers 57. As illustrated in FIG. 6, the V-groove of each of rollers 57 includes converging surfaces 570 and 57b, so that these surfaces are engaged with a corresponding surface of edge 60 of disc 42 to provide a ripple free, precision drive which is highly responsive and capable of withstanding continuous directional changes during rotation of the disc and the structures mounted on it. To accomplish this, the relationship between V- groove surfaces 57a and 57b of rollers 57 and beveled edge 60 of disc 42 is such that the circumferential speed of the mating members agrees at a center line 66 representing the true pitch diameter of the disc. On either side of line 66, the circumferential speed of the mating members is in conflict, but of opposing character so that the direction of their components of motion cancel each other. Thus, in the area represented by the arrows 69, the circumferential speed of disc 42 exceeds that of rollers 57, and in the area represented by the arrow 68 the opposite is true. As a result, although disc 42 supports a relativeely heavy stationary load, driving rollers 57 are not subject to compression so that relatively small rollers, which can be made of phenolic or similar material, can effectively and efficiently rotate a relatively large disc carrying a relatively heavy weight, for example, in the order of 120 pounds, at a constant speed of, for example, 2 rpm.

Referring again to FIG. 2, the preferred apparatus illustrated for shifting the position of gimbal frame 50 within housing 31 includes a double acting hydraulic cylinder 70, which is controlled by a four-way, threeposition solenoid valve 71, illustrated in detail in FIG. 19. A shift control means is preferably mounted in the lower portion of housing 31 for responding to the shift in position of frame 50 to control the extent of the shift. A preferred form of this means is illustrated as including a lever arm 72 pivotally mounted at one end 72a to a linkage rod 73, and pivotally mounted at its other end 72b to an upwardly extending rod 74. Linkage rod 73 is also pivotally mounted at its lower end to the base frame 31a of housing 31. At a point 76, intermediate its ends, arm 72 is pivotally connected to an actuator rod 75 which is connected to frame 50 so that the motion of frame 50 between its respective shift positions is identically tracked at intermediate pivot point 76. Intermediate pivot point 76 is located so that the dis ance between the

end pivot points

72a and 72b of lever 72 is four times the distance between pivot point 76 and the end pivot point connected to linkage 73, so that the motion of rod 74 in a vertical direction is four times the motion of arm 75 in response to the shift of frame 50. As shown in FIGS. 3 and 4, rod 74 is connected at its upper end, in the upper portion of housing 3|, to operate a shift selector mechanism generally designated by the numeral 77. A preferred form of such a selector mechanism is illustrated as including a switch actuator 78 which is mounted in an elongated slot 780 in the center of a plate 79, and switch actuator 78 is connected to the upper end of rod 74 to follow the movement thereof.

Elongated slots

80, and 81 are also located in plate 79 on either side of slot 780 and function as guides for microswitches 8 2 and 83, respectively, which are mounted to be actuated by actuator 78 and to move back and forth in the slots to different positions representing different desired shifts of gimbal frame 50, with switch 82 representing the left limit of i shift and switch 83 representing the right limit of shift.

A third microswitch 78b is mounted to be actuated by actuator 78 on the back of plate 79, adjacent the center of slot 78a, and switch 7817 represents the center position of shift of frame 50. As illustrated in FIG. 3, an endless cable 84 is connected between spaced

pulleys

85 and 86 mounted, respectively, on the upper and lower ends of plate 79, and each of

switches

82 and 83 is rigidly connected to cable 84 to move in its respec tive guide slot under control of cable 84. Pulley 85 is mounted on a shaft 87 which is, in turn, connected to operate a rotary switch 88, and shaft 87 extends through housing 31 to be actuated by a pointer knob 89 as illustrated in FIGS. 4 and 5. By adjusting the rotary position of shaft 87 by knob 89, switches 82 and 83 can be moved from a position representing the maximum shift of frame 50 in one direction, wherein switch 82 is adjacent to the upper end of slot and switch 83 is adjacent the lower end of slot 81, to a central position in which switches 82 and 83 are located in their respective slots directly across from each other, and to a position representing the maximum shift of frame 50 in the opposite direction, wherein switch 82 is located adjacent the lower end of slot 80 and switch 83 is located adjacent the upper end of slot 81.

Of course, switches 82 and 83 may be set at positions between the described extreme positions, and center position. As indicated in FIG. 5, the extreme positions of

switches

82 and 83 may be represented by

positions

1 and 15 indicated for pointer knob 89, the center position by knob position 8, with intermediate positions represented by knob positions 2 7 and 9 l4. Referring to the area marked generally by the numeral 90 in the top of FIG. 2, maximum shift positions of the axis of rotation of disc 42 are indicated, along with intermediate positions corresponding to the numbers 1 I5 as in FIG. 5. In the illustration given, numeral 8, which would represent a position wherein

switch

82 and 83 are located near the center of

slot

80 and 81 and are across from each other, represents zero or no shift. Thus, during operation of the apparatus of FIG. 2, knob 89 can be set to provide a desired degree of shift within the limits described. Also, pulleys 85 and 86 can be sized so that each of positions 1 I5 is a 20' step of shaft 87 and causes a one centimeter movement of each of

switches

82 and 83, which in turn causes a onehalf centimeter shift of the center of rotation of disc 42. Thus, the amount of shift of frame 50 can be accurately controlled.

The electrical schematic of switch 88 is shown in FIG. 20, and the hydraulic schematic of the valve 71 for controlling shift cylinder 70 is shown in FIG. 19.

PATIENT CONVEYOR AND ELEVATOR MECHANISM Referring now to FIGS. 7 12, a patient conveyor cart 100, supported on wheels for portability, is illustrated as including a patient P lying on a belt conveyor 10] on top of the cart. In FIG. 7, elevator apparatus 33 is shown extended away from x-ray apparatus 30 and in its lower position for receipt of cart 100. Cart also includes a guide bar 102 located underneath the front end of the cart, and the cart also includes a second bar I03 spaced towards the rear of the cart from bar 102, which, as described in FIG. 11, operates a mechanism for moving belt conveyor I01 to shift the patient from the position shown in FIGS. 7 and 8 to a position such as shown in FIG. 9.

As shown in FIGS. 8 and 9, patient elevator apparatus 33 includes apparatus for moving belt conveyor 101 in and out to move the patient from a position on cart 100, to the position wherein his head is lying on headrest 41; apparatus for moving cart I00 and the patient to the correct elevation for movement of the patient into machine 30; apparatus for moving patient P and cart I00 inwardly and outwardly from machine 30 when the patient is at the proper elevation; and apparatus for tilting headrest 41 for proper positioning of the patients head.

As illustrated in FIG. 8, the apparatus for moving belt conveyor 101 includes block 37 which is connected through piston rods 104 (only one shown) to spaced hydraulic cylinders 105 mounted inside of platform 35. As shown in FIG. 8, cart 100 is lifted to insert bar 102 in slot 40 of platform 35 and bar 103 in slot 38 of movable block 37, with cylinders 105 retracted as shown in FIG. 7.

As shown in FIG. 10, platform 35 is supported by parallel arms 106 which telescope into tubular members 107 mounted on a generally rectangular platform 108 which is, in turn, pivotally mounted at their lower ends to the lower frame of pedestal 32 so that arms 109 supporting platform 35 form a parallelogram movable between the positions shown in FIGS. 8 and 9. A hydraulic cylinder 110 is vertically mounted on platform 108 in the approximate center thereof, and includes a piston rod 111 standing upwardly and secured to lower plate 35b of platform 35 for moving it up and down between the lower position shown in FIG. 8 to the upper position shown in FIG. 9. Thus, when patient conveyor cart 100 has been supported on extendable block 37 and platform 35, as shown in FIG. 8, cylinder 110 can be actuated to raise the platform 35 to a position in which a patient can be moved inwardly towards machine 30, and this operation will raise cart 100 off the ground so that it is no longer supported by its front wheels.

The apparatus for moving elevator mechanism 33, and thus patient P, towards and away from machine 30 includes a hydraulic cylinder 112 mounted inside of pedestal 32 and connected to a cross member 112a connected between the lower end of tubular members 107. As shown in FIG. 8 when cylinder 112 is extended, apparatus 33 is in its outward position and when cylinder 112 is retracted, as shown in FIG. 9, apparatus 33 is in its inward position wherein the patient is located with his head between x-ray source 44 and film housing 45.

Headrest 41 is mounted on an angled plate 41a which is pivotally supported by parallel plates 113 on the back wall of platform 35 (see FIG. 1). Plate 41a is pivotally connected at a pivot point 114 to parallel plates 113 and extends from pivot point 114 to the piston rod of a hydraulic cylinder 115 mounted inside of platform 35, so that as piston rod is extended or retracted, headrest 41 pivots to provide different positions of tilt for a patients head.

As previously noted, top plate 35a of platform 35 and block 37 is pivotally mounted with respect to bottom plate 35b to follow the horizontal level of cart 100 when elevated off of its front wheels.

The electrical control and hydraulic control apparatus for controlling the operation of hydraulic cylinders 105, I10, 112 and 115 are illustrated in FIGS. 19 and 20 and their operation is hereafter described in detail.

Referring now to FIG. 11, a preferred form of a patient conveyor mechanism for cart 100 is illustrated for driving belt conveyor 101 which may be an endless belt made of a flexible material preferably with a low coefficient of friction mounted for rotation about rollers (not shown) on the opposite ends of cart 100. The conveyor mechanism includes a slide mechanism 120 having bar 103 at one end connected to parallel spaced apart

rods

120a and 120b, which are in turn slidably mounted inside slotted, parallel guides 121a and 12112 mounted on each side of conveyor belt 101 and adjacent its longitudinal edges. The other ends of rods a and 120b are connected to a cross member 122, parallel with and spaced from bar 103, so that as bar 102 is moved in the direction of arrow 123, cross member 122 follows the movement of bar 103. Means is also provided which is connected to conveyor belt 101 and amplifies the motion of bar 103 while causing movement of conveyor 101 in the desired direction. As illustrated, this means includes a closed linkage mechanism 124 including opposed parallel members pivotally connected with their ends to form a closed diamond. Mechanism 124 is pivotally connected at one apex 125 to a cross member 126 which is rigidly connected to cart 100, and is pivotally connected at the opposite apex 127 to conveyor belt 101. A cross member 128 is pivotally connected between opposite members of linkage mechanism 124, and cross member 128 is pivotally connected at an intermediate point 129 to cross member 122 at approximately its center. Thus, as cross member 122 is moved in conjunction with bar 103, moving pivot point 129 in the direction shown, linkage mechanism 124 is caused to move apex pivot point 127 with respect to apex pivot point 125, thus moving conveyor 101 with respect to cart 100.1n FIG. 11, mechanism 124 is shown extended as it would be with the patient loaded in machine 30, and mechanism 124 is retracted with cross member 122 adjacent cross member 126 as shown in dotted lines when the patient is lying fully on cart 100. In the arrangement described, the relative movement of apex pivot point 127 with respect to apex pivot point 125 is greater than the movement of pivot point 129, for example 3-4 times depending on the relationship of the elements described, thus providing significant amplification of the movement of bar 103 in response to bydraulic cylinders 105, and reducing the stroke length requirement for the cylinders. The amount of amplification provided can be increased or decreased as desired by varying the size of linking mechanism 124, although it is desirable that linkage mechanism 124 not be so large that it extends beyond the sides of cart 100 when retracted. Conveyor belt 101 can be marked with the proper patient position so that full travel of piston rods 104 will carry him from the position of FIG. 8 to the position of FIG. 9.

PATIENT ELEVATOR LIMIT SWITCHES During elevation and positioning of a patient in apparatus 30, care must be taken to avoid hitting the patients head or headrest 41 against x-ray source 44. Also, care must be taken to ensure that the patients head is properly positioned between source 44 and film holder 45 so that the patient is not struck by either of these objects when disc 42 is rotated. Further, it is highly desirable that the patient be fully withdrawn from apparatus 30 and fully on cart 100 before the cart is fully lowered to where it can be removed from elevator apparatus 33. In view of these requirements, it is preferred that certain limit switches be provided in association with elevator apparatus 33 and patient conveyor cart 100 to automatically limit the movement of the patient or disc 42 when the danger of interference is present. Examples of such limit switches which have been established to be desirable for this purpose are shown in FIGS. 9, 10, and 12. Of course, the number and location of such switches can vary depending on

Claims

1. An x-ray apparatus for providing substantially continuous panoramic radiographic projections of an object on an x-ray film, comprising, in combination: a fixed frame; an x-ray source mounted for rotation with respect to said frame; a film holder including an x-ray slit and means for supporting an x-ray film for movement past said slit, said film holder mounted for rotation with said x-ray source to permit panoramic radiographic projections to be taken of an object placed between said x-ray source and film holder; means for rotating said x-ray source and film holder about said object; means for shifting the center of rotation of said x-ray source and film holder with respect to said object and in substantially the plane of rotation of said x-ray source and film holder to permit portions of a single panoramic radiograph to be taken from different centers of rotation for providing a focal trough of predetermined shape; and means for providing selective variations in the amount of said shift.

2. The x-ray apparatus of claim 1 wherein said means for shifting the center of rotation of x-ray source and film holder includes: a gimbal frame mounted to pivot about a point on said fixed frame; means for mounting said x-ray source and said film holder at opposed positions on said gimbal frame for rotation with respect to said gimbal frame; and means for shifting said gimbal frame with respect to said fixed frame.

3. The x-ray apparatus of claim 2 wherein said means for providing selective variations in the amount of said shift includes means responsive to the movement of said gimbal frame with respect to sAid fixed frame to control the extent of said movement.

4. The x-ray apparatus of claim 3 wherein said last mentioned means includes a selector switch having a plurality of positions corresponding to shift positions of said gimbal frame, a left shift limit switch and a right shift limit switch, each switch connected to said selector switch to be positioned at a plurality of different positions corresponding to different shift positions, said limit switches electrically connected to stop said shifting means when actuated, and actuator means connected to said gimbal frame and movable in response thereto to actuate one of said limit switches during shifting of said gimbal frame to determine the extent of said shift.

5. The x-ray apparatus of claim 4 further including means for amplifying the motion of said actuator means in response to said shift of said gimbal frame.

6. The x-ray apparatus of claim 2 wherein said means for mounting said x-ray source and film holder on said gimbal frame is a centerless disc supported for rotation on said gimbal frame, and includes means for supporting said disc on said gimbal frame for rotation with respect thereto.

7. The x-ray apparatus of claim 6 wherein the outer edge of the disc is beveled and includes two outwardly extending and converging faces, and said last mentioned means includes a plurality of V-grooved rollers mounted on and spaced about said gimbal frame for supporting said disc, said rollers including converging faces for mating with the faces of the outer edge of said disc, said mated faces providing two contact friction areas of opposing character.

8. The x-ray apparatus of claim 7 wherein each of said rollers is resiliently mounted on said gimbal frame.

9. The x-ray apparatus of claim 1 further including a cylindrical film cassette removably mounted in said film holder for supporting the x-ray film for movement past said x-ray slit.

10. The x-ray apparatus of claim 1 further including a film drive mechanism for moving an x-ray film past the x-ray slit at a variable rate of speed as a function of the shape of a desired focal trough, said film drive mechanism including a movable film cassette for mounting said film in said film holder, said film cassette adapted to support and move an x-ray film past said slit; motor means connected to drive said film cassette, said motor means including a rotatable shaft and a housing; and means coupled between said shaft and housing to vary the speed of rotation of said shaft with respect to said housing by selectively rotating said housing with respect to said shaft as a function of the shape of a desired focal trough.

11. The x-ray apparatus of claim 10 wherein said last mentioned means includes means for mounting said housing to float with respect to said shaft, and a sloped cam connected to rotate with said shaft and to cause selected movement of said housing with respect to said shaft during rotation of said shaft.

12. The x-ray apparatus of claim 1 wherein the object to be x-rayed is a portion of a human subject lying horizontal.

13. The x-ray apparatus of claim 12 further including conveying and positioning means for positioning the subject in the x-ray apparatus for an x-raying operation.

14. The apparatus of claim 13 wherein a portion of the head of the subject is to be x-rayed, and wherein said conveying and positioning means includes a headrest, an elevator mechanism for moving said headrest vertically and horizontally with respect to said x-ray source and film holder, and a conveyor cart for engaging said elevator mechanism whereby when the subject''s head is supported on said headrest, the remainder of his body is supported on said conveyor cart.

15. The i x-ray apparatus of claim 14 wherein said conveyor cart is mobile and includes: a frame; a conveyor belt mounted to move a subject thereOn from a first position on said cart to a second position thereon wherein he can be positioned in said x-ray apparatus with his head on said headrest; and means connected to said belt and adapted to be actuated by a movable element in said elevator mechanism for moving said belt.

16. The conveyor cart of claim 15 wherein said last mentioned means includes means for amplifying the motion of said movable element to cause a greater movement of said belt in response thereto.

17. The x-ray apparatus of claim 14 further including a plurality of safety limit switches for preventing interference between the movement of said subject and said x-ray source.

18. The x-ray apparatus of claim 17 wherein said headrest is adapted to be tilted to tile the subject''s head, and one of said limit switches is responsive to the amount of tilt of the headrest and the vertical height of said elevator mechanism to prevent horizontal movement of said headrest towards said x-ray source when such movement would result in interference.

19. The x-ray apparatus of claim 18 further including switch means responsive to said one of said limit switches to automatically cause vertical movement of said elevator mechanism when horizontal movement thereof will cause interference between said headrest and said x-ray source.

20. An x-ray apparatus comprising, in combination: a fixed frame; a gimbal frame mounted to pivot about a point on said fixed frame; an x-ray source; an x-ray film holder for supporting an x-ray film; means for mounting said x-ray source and said film holder at opposed positions on said gimbal frame for rotation with respect to said gimbal frame; means for supporting an object to be x-rayed between said x-ray source and film holder; means for rotating said x-ray source and film holder about said object to provide a panoramic radiographic projection of a selected area of said object; and means for shifting said gimbal frame with respect to said fixed frame in substantially the plane of rotation of said x-ray source and film holder to permit rotation of said x-ray source and film holder about said object from a plurality of different centers of rotation for providing a focal trough of predetermined shape.

21. The x-ray apparatus of claim 20 further including means for providing selective variations in the amount of said shift, said means being responsive to the movement of said gimbal frame with respect to said fixed frame to control the extent of said movement.

22. The x-ray apparatus of claim 21 wherein said last mentioned means includes a selector switch having a plurality of positions corresponding to shift positions of said gimbal frame, a left shift limit switch and a right shift limit switch, each switch connected to said selector switch to be positioned at a plurality of different positions corresponding to different shift positions, said limit switches electrically connected to stop said shifting means when actuated, and actuator means connected to said gimbal frame and movable in response thereto to actuate one of said limit switches during shifting of said gimbal frame to determine the extent of said shift.

23. The x-ray apparatus of claim 22 further including means for amplifying the motion of said actuator means in response to said shift of said gimbal frame.

24. A method of providing a panoramic radiographic projection of a selected portion of the body of a subject comprising the steps of: moving the subject in position in an x-ray apparatus between a rotatable x-ray source and an x-ray film holder including an x-ray film so that the selected portion will be positioned in the line of sight between said source and film when they are rotated about the subject; rotating the x-ray source and x-ray film holder about the subject and about a first center of rotation, while simultaneously continuously exposing a first section of said x-ray film to an x-ray beam to provide a continuous radiographic projection of a first part of said selected portion on said film; automatically shifting the center of rotation of said x-ray source and x-ray film to a second center of rotation upon completion of said last mentioned step; and rotating said x-ray source and x-ray film about said subject and about said second center of rotation while simultaneously continuously exposing a second section of said x-ray film to said x-ray beam to provide a continuous radiographic projection of a second part of said selected portion on said film.

25. The method of claim 24 wherein said selected portion of the body is in the frontal part of the head, and further including the steps of: placing the head of the subject between said x-ray source and x-ray film while said source and film holder are located on the vertical center line of said x-ray apparatus; shifting the center of rotation of said x-ray source and film holder to said first position and moving said source and holder to a position wherein rotation about said first part of said selected portion with the subject facing said film holder can begin; and performing the last three steps of claim 24.

26. The method of claim 24 where in the selected portion is in the back of the head, and further including the step of initially positioning the x-ray apparatus so that the back of the head may be positioned in the x-ray apparatus adjacent the film holder, and the x-ray source rotated about the front of the head without interference.

27. X-ray apparatus comprising, in combination: an x-ray source; a power supply for providing operating voltages to said x-ray source; an x-ray film housing for supporting an x-ray film; means for rotating and means for selectively shifting the center of rotation of said x-ray source and film holder about an object to be x-rayed to provide substantially continuous panoramic radiographic projections of the object; means for moving the x-ray film to continuously expose it to an x-ray beam during rotation of said x-ray source and x-ray film holder; and a programming apparatus including a plurality of sequential programmer step positions and a plurality of programmer switches, means for sequentially moving said programmer through its step positions, and means for selectively actuating any of said programmer switches, selected ones of said programmer switches being connected to control the sequence of operation of said power supply, rotating means, shifting means, and means for moving said x-ray film to provide said radiographic projection.

28. The x-ray apparatus of claim 27 wherein said x-ray source and said film holder are rotated about said object on the same axis of rotation, and said means for selectively shifting the center of rotation of said axis with respect to said object being connected to at least one of said programmer switches for control of its sequence of operation.

29. An x-ray apparatus for providing panoramic radiographic projections of an object comprising, in combination: x-ray means for providing a rotational x-ray scan about the object; to provide said panoramic radiographic projections means for automatically shifting the center of rotation of said x-ray means from a first center of rotation to a second center of rotation during an x-ray scan; and means for selectively varying the amount of said shift to provide a focal trough of predetermined shape.

30. The x-ray apparatus of claim 29 wherein said means for automatically shifting center of rotation of said x-ray means includes a programmer means for controlling the sequence of operation of said x-ray apparatus.

31. The apparatus of claim 30 wherein said means for selectively varying the amount of said shift includes switch means for selectively setting the limits of said shift.

32. The x-ray apparatus of claim 29 wherein said x-ray means includes an x-ray film holder having an x-ray slit and including an x-ray film and means for moving the x-ray film past said x-ray slit during an x-ray scan, and further including means for varying the movement of said film past said x-ray slit as a function of the shape of the object being x-rayed.

33. The x-ray apparatus of claim 32 wherein said last mentioned means includes a motor having a housing and a shaft rotatable with respect thereto, and means for selectively rotating said housing with respect to said shaft during rotation of the shaft to vary the speed of rotation of the shaft with respect to the housing.

34. The x-ray apparatus of claim 33 wherein said means for automatically shifting the center of rotation of said x-ray means includes a programmer means for controlling the sequence of operation of said x-ray apparatus.

35. The x-ray apparatus of claim 29 further including means for positioning a human subject in the apparatus for an x-ray operation.

36. The x-ray apparatus of claim 34 further including means for positioning a human subject in the apparatus for an x-ray operation.

37. An x-ray apparatus for providing panoramic radiographic projections of an object on an x-ray film, comprising, in combination: a fixed frame; an x-ray source mounted for rotation with respect to said frame; a film holder including an x-ray slit and means for supporting an x-ray film for movement past said slit, said film holder mounted for rotation with said x-ray source to permit panoramic radiographic projections to be taken of an object placed between said x-ray source and film holder; means for rotating said x-ray source and film holder about said object and about a vertical axis; means for laterally shifting said vertical axis to shift the center of rotation of said x-ray source and film holder with respect to said object to permit portions of a single panoramic radiograph to be taken from different centers of rotation; and means for providing selective variations in the amount of said shift.