Title:
Dental X-ray photographic device
United States Patent 3906235
Abstract:
A device for use in the production of dental X-ray photographs comprises a hollow-anode X-ray tube projecting from a housing with the tube specially mounted to absorb shocks and stresses imposed on the anode tube. The anode tube which projects from the housing is preferably shielded when not in use by a projecting tube slidable relative to the housing. The device also includes a second X-ray tube for intra-oral and extra-oral photography with this second tube emitting X-rays at 90° to the axis of the hollow anode X-ray tube. Prefiltering material may be provided on the head of the anode tube or the head of the anode tube may be specially shaped so that uniform prefiltering of the radiation from the anode tube occurs over the beam angle necessary for full-mouth photography.
US Patent References:
Chi-ray method and means
Forde et al. - October 1932 - 1881448
Chi-ray tube with means to selectively deflect the electron beam to plural targets
Stanhope - November 1964 - 3158745
Panographic chi-ray tubehead with a projecting anode rod mounted for manual movement about two mutually perpendicular axes
Koerner et al. - December 1967 - 3359423
DENTAL X-RAY HEAD
Vandervelden - July 1972 - 3676683
Chi-ray method and means
Forde et al. - October 1932 - 1881448
Chi-ray tube with means to selectively deflect the electron beam to plural targets
Stanhope - November 1964 - 3158745
Panographic chi-ray tubehead with a projecting anode rod mounted for manual movement about two mutually perpendicular axes
Koerner et al. - December 1967 - 3359423
DENTAL X-RAY HEAD
Vandervelden - July 1972 - 3676683
Application Number:
05/509607
Publication Date:
09/16/1975
Filing Date:
09/26/1974
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
378/159, 378/193
International Classes:
A61B6/14; H01J35/32; H01J35/00; H01J35/00
Field of Search:
250/399,403,404,405,407,522,523 313/55,56
Primary Examiner:
Lawrence, James W.
Assistant Examiner:
Anderson B. C.
Attorney, Agent or Firm:
Sughrue, Rothwell, Mion, Zinn & Macpeak
Parent Case Data:
This is a Continuation, of application Ser. No. 365,372, filed May 30, 1973, which in turn is a Division of application Ser. No. 154,530, filed June 18, 1971., now U.S. Pat. No. 3,752,990, issued Aug. 14, 1973.
Claims:
Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is
1. A device for use in the production of dental X-ray photographs comprising two separate X-ray systems, one of which comprises a hollow-anode X-ray tube mounted in a housing and including an anode tube projecting from the housing for extra-oral photographs, and the other of which comprises an X-ray tube for intra-oral and extra-oral photographs provided in the housing, said other X-ray tube being mounted to direct its emitted X-rays at an angle of substantially 90° to the longitudinal axis of the hollow-anode X-ray tube.
2. A device as claimed in claim 1, in which the hollow-anode X-ray tube is mounted on the longitudinal axis of said housing or on an axis parallel thereto, and said other X-ray tube for intra-oral and extra-oral photography is offset laterally relative to the hollow-anode X-ray tube.
3. A device as claimed in claim 1, in which said other X-ray tube for intra-oral and extra-oral photography is arranged within said housing on the axis of said hollow-anode X-ray tube but positioned behind said latter tube.
4. A device as claimed in claim 1, in which the longitudinal axis of said other X-ray tube is at an angle to the longitudinal axis of the hollow-anode X-ray tube.
5. A device as claimed in claim 2, in which the cathode filament systems for the two X-ray tubes are mounted in a common casing.
6. A device as claimed in claim 5, in which said common casing is secured to mounting means which includes a target in alignment with the cathode filament for said second X-ray tube and a side window through which X-rays from said target are beamed.
7. A device as claimed in claim 6, which includes a protecting tube for the anode tube, said protecting tube being displaceable relative to the housing and in the axial direction of the anode tube in such manner that in a first, extended position it encloses the anode tube while in a second, withdrawn position the anode tube projects outwardly through an aperture provided in the protecting tube, and wherein windows for the outward transmission of X-rays from said target are provided in said housing and in said protecting tube at positions such that the windows are aligned with said side window when the protecting tube is in said position inclosing the anode tube, whereby the protecting tube only unmasks the radiation transmission aperture of that X-ray tube which is operational.
8. A device as claimed in claim 1, in which the cathode casing of said other X-ray tube is formed from a ceramic based material such as a ceramic oxide.
9. A device as claimed in claim 1 wherein the arrangement of prefiltering material on the head of the tube containing the anode is such that uniform prefiltering of the radiation occurs over the beam angle necessary for full-mouth photography.
10. A protecting tube for the anode tube of a device for use in the production of dental X-ray photographs comprising two separate X-ray systems, one of which comprises a hollow-anode X-ray tube mounted in a housing and including an anode tube projecting from the housing for extra-oral photographs and the other of which comprises an X-ray tube provided in the housing for intra-oral and extra-oral photographs, said other X-ray tube being mounted to direct its emitted X-rays at an angle of substantially 90° to the longitudinal axis of the hollow-anode X-ray tube, said protecting tube
1. A device for use in the production of dental X-ray photographs comprising two separate X-ray systems, one of which comprises a hollow-anode X-ray tube mounted in a housing and including an anode tube projecting from the housing for extra-oral photographs, and the other of which comprises an X-ray tube for intra-oral and extra-oral photographs provided in the housing, said other X-ray tube being mounted to direct its emitted X-rays at an angle of substantially 90° to the longitudinal axis of the hollow-anode X-ray tube.
2. A device as claimed in claim 1, in which the hollow-anode X-ray tube is mounted on the longitudinal axis of said housing or on an axis parallel thereto, and said other X-ray tube for intra-oral and extra-oral photography is offset laterally relative to the hollow-anode X-ray tube.
3. A device as claimed in claim 1, in which said other X-ray tube for intra-oral and extra-oral photography is arranged within said housing on the axis of said hollow-anode X-ray tube but positioned behind said latter tube.
4. A device as claimed in claim 1, in which the longitudinal axis of said other X-ray tube is at an angle to the longitudinal axis of the hollow-anode X-ray tube.
5. A device as claimed in claim 2, in which the cathode filament systems for the two X-ray tubes are mounted in a common casing.
6. A device as claimed in claim 5, in which said common casing is secured to mounting means which includes a target in alignment with the cathode filament for said second X-ray tube and a side window through which X-rays from said target are beamed.
7. A device as claimed in claim 6, which includes a protecting tube for the anode tube, said protecting tube being displaceable relative to the housing and in the axial direction of the anode tube in such manner that in a first, extended position it encloses the anode tube while in a second, withdrawn position the anode tube projects outwardly through an aperture provided in the protecting tube, and wherein windows for the outward transmission of X-rays from said target are provided in said housing and in said protecting tube at positions such that the windows are aligned with said side window when the protecting tube is in said position inclosing the anode tube, whereby the protecting tube only unmasks the radiation transmission aperture of that X-ray tube which is operational.
8. A device as claimed in claim 1, in which the cathode casing of said other X-ray tube is formed from a ceramic based material such as a ceramic oxide.
9. A device as claimed in claim 1 wherein the arrangement of prefiltering material on the head of the tube containing the anode is such that uniform prefiltering of the radiation occurs over the beam angle necessary for full-mouth photography.
10. A protecting tube for the anode tube of a device for use in the production of dental X-ray photographs comprising two separate X-ray systems, one of which comprises a hollow-anode X-ray tube mounted in a housing and including an anode tube projecting from the housing for extra-oral photographs and the other of which comprises an X-ray tube provided in the housing for intra-oral and extra-oral photographs, said other X-ray tube being mounted to direct its emitted X-rays at an angle of substantially 90° to the longitudinal axis of the hollow-anode X-ray tube, said protecting tube
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to devices for use in producing X-ray photographs, particularly dental X-ray photographs.
The invention is particularly concerned with devices for use in producing dental X-ray photographs which make use of special hollow-anode X-ray tubes which are quite distinct in construction and function from the usual diagnostic X-ray tubes.
2. Description of the Prior Art
In the presently known tubes of this hollow-anode type, the whole electrode system -- comprising a cathode emitting the electrons, a control electrode affecting the focussing, and a usually conical anode arranged in the anode tube with a collecting or focussing coil mounted on the anode tube and also affecting the focussing of the electron stream -- is so constructed that it is formed from two or three mechanically completely separate electrode units as far as adjustment of the system is concerned. In these hollow-anode X-ray tubes the focal spot is created at the end of a hollow-anode tube externally of the actual X-ray tube casing and with a conical anode it is at the cone tip pointing towards the cathode.
In the X-ray tubes used in dental medical diagnostic treatment for producing full-mouth or panoramic photographs, in which the anode tube is introduced into the mouth, the focal spot of the tube must be kept very small on account of the comparatively small focal length necessitated by these photographic techniques and on account of the lack of sharpness in the image which would otherwise arise, with the result that the electrode system of such a tube must be extremely accurately focussed and adjusted initially and must then remain so. The danger of the tube becoming out of adjustment is greater the smaller the diameter of the anode tube and the more sensitive the electrode system of the X-ray tube.
Since the wall thickness of the hollow-anode tube, which is barely the size of a finger in diameter, must be kept small and since the electron stream must be very accurately adjusted because of the comparatively small focal spot, the user of such tubes protects the very highly sensitive anode tube, which is formed from very soft annealed copper at those places where in the event of a mechanical stress the greatest bending moment is exerted, by placing a protective cap over the tube housing in the inactive position of the device to protect the anode tube from damage and defocussing. When preparing the instrument for use and when actually using the instrument the protective cap is removed in all cases.
In photographing the upper jaw, it is sometimes necessary in special cases to provide a cut-out in the film strip for the nose of the patient and to photograph the unphotographed nose part in the usual manner, i.e. with the film inside the mouth and with the X-ray tube outside the mouth. The presently known hollow-anode X-ray tubes cannot be used in this way. Photographic views of the whole jaw region are produced with the presently known hollow-anode X-ray tubes when inserted into the mouth for dental X-ray photographs, and these overall pictures obviously give information about the general status of the teeth. However, with these X-ray photographs one takes photographs of the whole of one or both jaws from one focal spot position, which automatically means that individual teeth or whole groups of teeth are shown heavily distorted on the X-ray film relative to their anatomically correct images or positions in the jaw. Because of this, for specific diagnosis of individual teeth it is necessary to take individual photographs of teeth or groups of teeth by the distortion free intra-oral or extra-oral techniques which are presently known. In order to carry out these two basically different photographic techniques the dental practitioner must have two different X-ray machines respectively adapted for the separate photographic techniques and with which one has to use X-ray tubes which are likewise different and adapted respectively for the differing photographic techniques.
SUMMARY OF THE INVENTION
It is therefore extremely desirable to provide a device equipped with a hollow-anode X-ray tube which is also such that distortion free photographs of individual objects can be achieved with it as with the known intra-oral and extra-oral photographic techniques. According to the present invention, this is achieved by providing a second X-ray tube for intra-oral and extra-oral photographs within the housing of the device and in addition to the hollow-anode X-ray tube, the direction of emission of radiation from the second tube being at an angle of substantially 90° to the longitudinal axis of the hollow-anode X-ray tube. A high voltage transformer for both tubes is preferably also mounted within the housing of the device so that in this case the device can be described as a one-piece instrument.
Instead of having two separate X-ray tubes it is alternatively possible to use a double X-ray tube suitable both for full-mouth photography and also for intra- and extra-oral photography, such double X-ray tube having two separate cathode filaments in a common casing. This results in a system which can be made extremely compact. On the other hand, a device using two separate X-ray tubes has the possible advantage that the X-ray tubes may be of a simpler and cheaper construction and that in the event of failure of one complete X-ray system or one X-ray tube the other X-ray system is still usable until replacement or repair of the failed system or tube. When using a common tube casing for both X-ray systems the casing may be secured to mounting means which includes an electron reflection target in alignment with the cathode filament for the said second X-ray tube and a side window through which X-rays from the target are beamed.
In order that the invention may be more fully understood, a number of embodiments in accordance therewith will now be described by way of example and with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view through a first embodiment in accordance with the invention, this device comprising a double X-ray tube adapted both for panoramic full-mouth photography and also for intra-oral and extra-oral photography, and with the device here shown in its operational position for the last-mentioned photographic technique;
FIG. 2 is a longitudinal sectional view through the head of the anode tube of a hollow-anode X-ray tube, the upper half (A) of the illustrated tube being of known form and the lower half (B) of the illustrated tube being of modified novel form;
FIG. 3 is a longitudinal sectional view through the head of the hollow-anode X-ray tube illustrating the radiation beamangle necessary for panoramic full-mouth examination and of interest in relation to prefiltering considerations;
FIG. 4 is a schematic longitudinal sectional view through a second embodiment in accordance with the invention, the device here comprising two separate X-ray tube systems;
FIG. 5 is a front end elevational view of the device of FIG. 4;
FIG. 6 is a schematic longitudinal sectional view through a third embodiment in accordance with the invention, again comprising two separate X-ray tube systems; and,
FIG. 7 is a front end elevational view of the device of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the embodiment of the device shown in FIG. 1, the X-ray apparatus comprises a casing 16 fitted with an anode tube 9 carrying a conical anode 17; a mount 1 at anode potential and rigidly connected to the tube casing 16; and a focussing unit 5 which is fixedly connected to the tube system. The mount 1 is connected to a housing 4 of the device by means of a resilient link 2, for example in the form of a spring element. A high voltage generator (not shown) for the X-ray tube is mounted in a suitable manner within the housing 4 of the device.
In spite of the provision of a resilient supporting link 2 it is important to provide additional protection for the exposed comparatively slender anode tube 9 in its inactive position. For this purpose a protecting tube 15 is provided which is secured so as to be displaceable in the axial direction over the housing 4 of the device. In FIG. 1, this protecting tube 15 is shown in its operative protective position enclosing the anode tube 9. The tube 15 is provided with an aperture 18 in its end face to provide for passage of the anode tube 9 therethrough.
Additional springs 7 are provided between the housing 4 and the mount 1 on the tube casing 16 in order to adjust the flexibility and resiliency of the link 2 so that it will absorb forces arising as a result of impacts or pressures on the anode tube 9 and will return the tube system to its original setting as soon as such foreign external forces no longer act on the anode tube.
The embodiment of the invention which is shown in FIG. 1 comprises a double X-ray tube by means of which it is possible to use both the hollow-anode technique for panoramic full-mouth photography and also intra-oral and extra-oral photographic techniques for examination of individual teeth. In this embodiment, a tube side window 11 with an electron target disc 10 arranged adjacent thereto is provided in the mount 1 as a part of the tube casing 16, in addition to the anode tube 9 which has the anode 17 as an electron target point. A filament arrangement 13 acting as the cathode associated with the anode 17 and a filament arrangement 14 acting as the cathode associated with the electron target disc 10 are provided within the tube casing 16.
In this embodiment, the cathode filaments 13 and 14 which are necessary for the two electrode systems are mounted on a cathode support 12 and can be selectively switched on individually according to the desired type of photographic examination to be effected with the device.
In this embodiment, apertures are provided in the housing 4 and in the axially displaceable protecting tube 15 for the passage of the X-rays emitted through the tube side window 11. These apertures are so arranged that, when the device is used for hollow-anode photographic examination, the protecting tube 15 masks the aperture in the housing 4 in front of the side window 11 and uncovers the free end of the anode tube 9, while, when the device is used for intra-oral or extra-oral photographic examination the protecting tube 15 encloses the free end of the anode tube 9 and unmasks the side window 11.
The upper half of FIG. 2 of the drawings, designated as A, shows the head of a known form of hollow-anode X-ray tube in which the anode tube 9 is cylindrical and of uniform wall thickness in the radiating region. In such circumstances the X-rays coming from the anode 17 within a beam angle α and which do not pass through the wall of the anode tube at right-angles along the line S, for example rays passing along the lines S1 to S4, must penetrate larger amounts of the material of the anode tube. These rays are therefore prefiltered differentially and this has an extremely unfavourable effect on the quality of the image on the X-ray photograph.
In the lower half of FIG. 2, designated as B, there is there shown how this differential prefiltering of the X-rays is avoided by the use of a special configuration for the wall thickness of the head of the anode tube 9. With the wall thickness made non-uniform as shown, the same length of path S is traversed by all radiation from the anode 17 throughout the whole beam angle which is of interest.
FIG. 3 shows, in relation to an anode tube 9 with a conical anode 17 and fitted with an applicator 8 over the anode tube, the tube and applicator being shown inserted into a patient's mouth, that the beam angle α shown in FIG. 2 is in fact necessary for full-mouth photographic examination.
Alternatively, it is possible to provide additional prefiltering material on the head of the anode tube 9, preferably on its external surface, with such a distribution or gradation that the X-rays within the beam angle α which follow a shorter path through the wall of the head of the tube traverse a greater mass of prefiltering material than the X-rays which follow a longer path. In this case, the cylindrical wall of the anode tube, as is shown in the upper part A of FIG. 2, may have its thickness unchanged. Alternatively, this additional prefiltering material may be provided on the applicator 8 which is slidable over the anode tube 9, or it may be provided partially on this applicator and partially on the anode tube itself. By these means one can ensure in a simple manner that all the X-rays coming from the anode 17 are prefiltered to the same extent irrespective of their direction, and preferably to a degree equivalent to the case of the rays taking the longest path S4.
The X-ray tube casing, including the part of the anode tube adjacent to the cathode, is preferably made from a ceramic-based material having high resistance to bending stresses. Among the best materials are ceramic oxides, particularly beryllium oxide, which can absorb large bending moments and which at the same time are permeable to the magnetic field necessary for focussing the electron stream.
In each of the embodiments described above in which the mounting of the X-ray tube within the housing of the device is accomplished by means of an intermediate element such as the resilient link 2, this resilient supporting link need not necessarily consist of a spring element, but for example can alternatively be in the form of resilient membranes, or in the form of ball and socket joints in association with individual springs spaced on a circle around the tube. In each case the arrangement is such that the reaction to bending stresses of the resilient link due to forces acting from externally on the anode tube 9 is smaller than the reaction to deformation of the anode tube 9 due to the external forces acting thereon.
The focussing unit 5 shown in FIG. 1 may be an electromagnetic unit or a permanent magnet system. It will further be appreciated that an electrostatic focussing unit could alternatively be used.
In the embodiment shown in FIGS. 4 and 5 there is provided a hollow-anode X-ray tube suitable for full-mouth or panoral photographic examination and comprising the X-ray tube casing 16, the anode tube 9, and an associated transformer 6 mounted on an axis 19 which is parallel to but displaced upwardly relative to the longitudinal axis 20 of the housing 4 of the device. Parallel to this tube 9, 16 is provided an intra-oral tube 21 having its longitudinal axis 22 displaced downwardly relative to the longitudinal axis 20 of the housing 4 of the device. The direction 23 of the emitted radiation from the intra-oral X-ray tube 21 is at 90° to the longitudinal axis 19 of the hollow-anode X-ray tube 9, 16.
In this embodiment, the hollow-anode X-ray tube 9, 16 is resiliently mounted in the housing 4 by means of springs or a spring bellows or a membrane 2. A protecting tube 15 is provided to protect the anode tube 9. The protecting tube 15 is displaceable along the axis of the X-ray tube such that its cylindrical wall is displaceably positioned within the housing 4 and only its forward end wall portion provided with an aperture 25 for the anode tube 9 lies outside the housing 4. A window 24 for the passage of radiation from the intra-oral tube 21 is provided in the cylindrical wall portion of the protecting tube 15. This window 24 is only aligned with the output from the intra-oral tube 21 when the hollow-anode X-ray tube 9, 16 is not operational and is enclosed by the protecting tube 15. However, the window 24 is not in alignment with the axis 23 of the radiation from the tube 21 when the protecting tube 15 is displaced inwardly and the hollow-anode X-ray tube 9 extends in its operative position.
The embodiment illustrated in FIGS. 6 and 7 only differs from that shown in FIGS. 4 and 5 in that the two X-ray tubes 9, 16 and 21 are not arranged one below the other but are positioned on a common axis 22 one behind the other within the housing 3. In this embodiment the housing 3 is not cylindrical but has an inverted teardrop shape cross-section. The hollow-anode X-ray tube is mounted within the housing 3 in almost the same way as in the embodiment shown in FIGS. 4 and 5 but below the pivot axis 20 of the housing, while the second X-ray tube 21 lies on the axis 22 behind the hollow-anode X-ray tube 9, 16. The two transformers 6 and 17 of these two X-ray systems are provided as a one-piece unit positioned within the upper portion of the housing which is of larger cross-section.
In both the embodiments shown in FIGS. 4 to 7 the direction 23 of the emitted radiation from the intra-oral tube 21 makes an angle of 90° with the longitudinal axis 19 of the hollow-anode X-ray tube 9, 16.
The casing of the intra-oral or extra-oral X-ray tube 21 preferably consists of a ceramic oxide with the tube side window being formed from sintered beryllium oxide.
Since certain other obvious changes may be made in the device without departing from the scope thereof, it is intended that the above description of certain embodiments of the invention be interpreted in an illustrative and not a limiting sense.
1. Field of the Invention
This invention relates to devices for use in producing X-ray photographs, particularly dental X-ray photographs.
The invention is particularly concerned with devices for use in producing dental X-ray photographs which make use of special hollow-anode X-ray tubes which are quite distinct in construction and function from the usual diagnostic X-ray tubes.
2. Description of the Prior Art
In the presently known tubes of this hollow-anode type, the whole electrode system -- comprising a cathode emitting the electrons, a control electrode affecting the focussing, and a usually conical anode arranged in the anode tube with a collecting or focussing coil mounted on the anode tube and also affecting the focussing of the electron stream -- is so constructed that it is formed from two or three mechanically completely separate electrode units as far as adjustment of the system is concerned. In these hollow-anode X-ray tubes the focal spot is created at the end of a hollow-anode tube externally of the actual X-ray tube casing and with a conical anode it is at the cone tip pointing towards the cathode.
In the X-ray tubes used in dental medical diagnostic treatment for producing full-mouth or panoramic photographs, in which the anode tube is introduced into the mouth, the focal spot of the tube must be kept very small on account of the comparatively small focal length necessitated by these photographic techniques and on account of the lack of sharpness in the image which would otherwise arise, with the result that the electrode system of such a tube must be extremely accurately focussed and adjusted initially and must then remain so. The danger of the tube becoming out of adjustment is greater the smaller the diameter of the anode tube and the more sensitive the electrode system of the X-ray tube.
Since the wall thickness of the hollow-anode tube, which is barely the size of a finger in diameter, must be kept small and since the electron stream must be very accurately adjusted because of the comparatively small focal spot, the user of such tubes protects the very highly sensitive anode tube, which is formed from very soft annealed copper at those places where in the event of a mechanical stress the greatest bending moment is exerted, by placing a protective cap over the tube housing in the inactive position of the device to protect the anode tube from damage and defocussing. When preparing the instrument for use and when actually using the instrument the protective cap is removed in all cases.
In photographing the upper jaw, it is sometimes necessary in special cases to provide a cut-out in the film strip for the nose of the patient and to photograph the unphotographed nose part in the usual manner, i.e. with the film inside the mouth and with the X-ray tube outside the mouth. The presently known hollow-anode X-ray tubes cannot be used in this way. Photographic views of the whole jaw region are produced with the presently known hollow-anode X-ray tubes when inserted into the mouth for dental X-ray photographs, and these overall pictures obviously give information about the general status of the teeth. However, with these X-ray photographs one takes photographs of the whole of one or both jaws from one focal spot position, which automatically means that individual teeth or whole groups of teeth are shown heavily distorted on the X-ray film relative to their anatomically correct images or positions in the jaw. Because of this, for specific diagnosis of individual teeth it is necessary to take individual photographs of teeth or groups of teeth by the distortion free intra-oral or extra-oral techniques which are presently known. In order to carry out these two basically different photographic techniques the dental practitioner must have two different X-ray machines respectively adapted for the separate photographic techniques and with which one has to use X-ray tubes which are likewise different and adapted respectively for the differing photographic techniques.
SUMMARY OF THE INVENTION
It is therefore extremely desirable to provide a device equipped with a hollow-anode X-ray tube which is also such that distortion free photographs of individual objects can be achieved with it as with the known intra-oral and extra-oral photographic techniques. According to the present invention, this is achieved by providing a second X-ray tube for intra-oral and extra-oral photographs within the housing of the device and in addition to the hollow-anode X-ray tube, the direction of emission of radiation from the second tube being at an angle of substantially 90° to the longitudinal axis of the hollow-anode X-ray tube. A high voltage transformer for both tubes is preferably also mounted within the housing of the device so that in this case the device can be described as a one-piece instrument.
Instead of having two separate X-ray tubes it is alternatively possible to use a double X-ray tube suitable both for full-mouth photography and also for intra- and extra-oral photography, such double X-ray tube having two separate cathode filaments in a common casing. This results in a system which can be made extremely compact. On the other hand, a device using two separate X-ray tubes has the possible advantage that the X-ray tubes may be of a simpler and cheaper construction and that in the event of failure of one complete X-ray system or one X-ray tube the other X-ray system is still usable until replacement or repair of the failed system or tube. When using a common tube casing for both X-ray systems the casing may be secured to mounting means which includes an electron reflection target in alignment with the cathode filament for the said second X-ray tube and a side window through which X-rays from the target are beamed.
In order that the invention may be more fully understood, a number of embodiments in accordance therewith will now be described by way of example and with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view through a first embodiment in accordance with the invention, this device comprising a double X-ray tube adapted both for panoramic full-mouth photography and also for intra-oral and extra-oral photography, and with the device here shown in its operational position for the last-mentioned photographic technique;
FIG. 2 is a longitudinal sectional view through the head of the anode tube of a hollow-anode X-ray tube, the upper half (A) of the illustrated tube being of known form and the lower half (B) of the illustrated tube being of modified novel form;
FIG. 3 is a longitudinal sectional view through the head of the hollow-anode X-ray tube illustrating the radiation beamangle necessary for panoramic full-mouth examination and of interest in relation to prefiltering considerations;
FIG. 4 is a schematic longitudinal sectional view through a second embodiment in accordance with the invention, the device here comprising two separate X-ray tube systems;
FIG. 5 is a front end elevational view of the device of FIG. 4;
FIG. 6 is a schematic longitudinal sectional view through a third embodiment in accordance with the invention, again comprising two separate X-ray tube systems; and,
FIG. 7 is a front end elevational view of the device of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the embodiment of the device shown in FIG. 1, the X-ray apparatus comprises a casing 16 fitted with an anode tube 9 carrying a conical anode 17; a mount 1 at anode potential and rigidly connected to the tube casing 16; and a focussing unit 5 which is fixedly connected to the tube system. The mount 1 is connected to a housing 4 of the device by means of a resilient link 2, for example in the form of a spring element. A high voltage generator (not shown) for the X-ray tube is mounted in a suitable manner within the housing 4 of the device.
In spite of the provision of a resilient supporting link 2 it is important to provide additional protection for the exposed comparatively slender anode tube 9 in its inactive position. For this purpose a protecting tube 15 is provided which is secured so as to be displaceable in the axial direction over the housing 4 of the device. In FIG. 1, this protecting tube 15 is shown in its operative protective position enclosing the anode tube 9. The tube 15 is provided with an aperture 18 in its end face to provide for passage of the anode tube 9 therethrough.
Additional springs 7 are provided between the housing 4 and the mount 1 on the tube casing 16 in order to adjust the flexibility and resiliency of the link 2 so that it will absorb forces arising as a result of impacts or pressures on the anode tube 9 and will return the tube system to its original setting as soon as such foreign external forces no longer act on the anode tube.
The embodiment of the invention which is shown in FIG. 1 comprises a double X-ray tube by means of which it is possible to use both the hollow-anode technique for panoramic full-mouth photography and also intra-oral and extra-oral photographic techniques for examination of individual teeth. In this embodiment, a tube side window 11 with an electron target disc 10 arranged adjacent thereto is provided in the mount 1 as a part of the tube casing 16, in addition to the anode tube 9 which has the anode 17 as an electron target point. A filament arrangement 13 acting as the cathode associated with the anode 17 and a filament arrangement 14 acting as the cathode associated with the electron target disc 10 are provided within the tube casing 16.
In this embodiment, the cathode filaments 13 and 14 which are necessary for the two electrode systems are mounted on a cathode support 12 and can be selectively switched on individually according to the desired type of photographic examination to be effected with the device.
In this embodiment, apertures are provided in the housing 4 and in the axially displaceable protecting tube 15 for the passage of the X-rays emitted through the tube side window 11. These apertures are so arranged that, when the device is used for hollow-anode photographic examination, the protecting tube 15 masks the aperture in the housing 4 in front of the side window 11 and uncovers the free end of the anode tube 9, while, when the device is used for intra-oral or extra-oral photographic examination the protecting tube 15 encloses the free end of the anode tube 9 and unmasks the side window 11.
The upper half of FIG. 2 of the drawings, designated as A, shows the head of a known form of hollow-anode X-ray tube in which the anode tube 9 is cylindrical and of uniform wall thickness in the radiating region. In such circumstances the X-rays coming from the anode 17 within a beam angle α and which do not pass through the wall of the anode tube at right-angles along the line S, for example rays passing along the lines S1 to S4, must penetrate larger amounts of the material of the anode tube. These rays are therefore prefiltered differentially and this has an extremely unfavourable effect on the quality of the image on the X-ray photograph.
In the lower half of FIG. 2, designated as B, there is there shown how this differential prefiltering of the X-rays is avoided by the use of a special configuration for the wall thickness of the head of the anode tube 9. With the wall thickness made non-uniform as shown, the same length of path S is traversed by all radiation from the anode 17 throughout the whole beam angle which is of interest.
FIG. 3 shows, in relation to an anode tube 9 with a conical anode 17 and fitted with an applicator 8 over the anode tube, the tube and applicator being shown inserted into a patient's mouth, that the beam angle α shown in FIG. 2 is in fact necessary for full-mouth photographic examination.
Alternatively, it is possible to provide additional prefiltering material on the head of the anode tube 9, preferably on its external surface, with such a distribution or gradation that the X-rays within the beam angle α which follow a shorter path through the wall of the head of the tube traverse a greater mass of prefiltering material than the X-rays which follow a longer path. In this case, the cylindrical wall of the anode tube, as is shown in the upper part A of FIG. 2, may have its thickness unchanged. Alternatively, this additional prefiltering material may be provided on the applicator 8 which is slidable over the anode tube 9, or it may be provided partially on this applicator and partially on the anode tube itself. By these means one can ensure in a simple manner that all the X-rays coming from the anode 17 are prefiltered to the same extent irrespective of their direction, and preferably to a degree equivalent to the case of the rays taking the longest path S4.
The X-ray tube casing, including the part of the anode tube adjacent to the cathode, is preferably made from a ceramic-based material having high resistance to bending stresses. Among the best materials are ceramic oxides, particularly beryllium oxide, which can absorb large bending moments and which at the same time are permeable to the magnetic field necessary for focussing the electron stream.
In each of the embodiments described above in which the mounting of the X-ray tube within the housing of the device is accomplished by means of an intermediate element such as the resilient link 2, this resilient supporting link need not necessarily consist of a spring element, but for example can alternatively be in the form of resilient membranes, or in the form of ball and socket joints in association with individual springs spaced on a circle around the tube. In each case the arrangement is such that the reaction to bending stresses of the resilient link due to forces acting from externally on the anode tube 9 is smaller than the reaction to deformation of the anode tube 9 due to the external forces acting thereon.
The focussing unit 5 shown in FIG. 1 may be an electromagnetic unit or a permanent magnet system. It will further be appreciated that an electrostatic focussing unit could alternatively be used.
In the embodiment shown in FIGS. 4 and 5 there is provided a hollow-anode X-ray tube suitable for full-mouth or panoral photographic examination and comprising the X-ray tube casing 16, the anode tube 9, and an associated transformer 6 mounted on an axis 19 which is parallel to but displaced upwardly relative to the longitudinal axis 20 of the housing 4 of the device. Parallel to this tube 9, 16 is provided an intra-oral tube 21 having its longitudinal axis 22 displaced downwardly relative to the longitudinal axis 20 of the housing 4 of the device. The direction 23 of the emitted radiation from the intra-oral X-ray tube 21 is at 90° to the longitudinal axis 19 of the hollow-anode X-ray tube 9, 16.
In this embodiment, the hollow-anode X-ray tube 9, 16 is resiliently mounted in the housing 4 by means of springs or a spring bellows or a membrane 2. A protecting tube 15 is provided to protect the anode tube 9. The protecting tube 15 is displaceable along the axis of the X-ray tube such that its cylindrical wall is displaceably positioned within the housing 4 and only its forward end wall portion provided with an aperture 25 for the anode tube 9 lies outside the housing 4. A window 24 for the passage of radiation from the intra-oral tube 21 is provided in the cylindrical wall portion of the protecting tube 15. This window 24 is only aligned with the output from the intra-oral tube 21 when the hollow-anode X-ray tube 9, 16 is not operational and is enclosed by the protecting tube 15. However, the window 24 is not in alignment with the axis 23 of the radiation from the tube 21 when the protecting tube 15 is displaced inwardly and the hollow-anode X-ray tube 9 extends in its operative position.
The embodiment illustrated in FIGS. 6 and 7 only differs from that shown in FIGS. 4 and 5 in that the two X-ray tubes 9, 16 and 21 are not arranged one below the other but are positioned on a common axis 22 one behind the other within the housing 3. In this embodiment the housing 3 is not cylindrical but has an inverted teardrop shape cross-section. The hollow-anode X-ray tube is mounted within the housing 3 in almost the same way as in the embodiment shown in FIGS. 4 and 5 but below the pivot axis 20 of the housing, while the second X-ray tube 21 lies on the axis 22 behind the hollow-anode X-ray tube 9, 16. The two transformers 6 and 17 of these two X-ray systems are provided as a one-piece unit positioned within the upper portion of the housing which is of larger cross-section.
In both the embodiments shown in FIGS. 4 to 7 the direction 23 of the emitted radiation from the intra-oral tube 21 makes an angle of 90° with the longitudinal axis 19 of the hollow-anode X-ray tube 9, 16.
The casing of the intra-oral or extra-oral X-ray tube 21 preferably consists of a ceramic oxide with the tube side window being formed from sintered beryllium oxide.
Since certain other obvious changes may be made in the device without departing from the scope thereof, it is intended that the above description of certain embodiments of the invention be interpreted in an illustrative and not a limiting sense.