GB1594499A

GB1594499A - Panoramic x-ray apparatus

Info

Publication number: GB1594499A
Application number: GB46455/77A
Authority: GB
Original assignee: PALOMEX Oy
Current assignee: PALOMEX Oy
Priority date: 1976-11-08
Filing date: 1977-11-08
Publication date: 1981-07-30
Also published as: FR2369824A1; FI67269B; IT1087434B; DE2749699C2; NL7712218A; FI763191A; DE2749699A1; FI67269C; JPS5358792A

Description

(54) PANORAMIC X-RAY APPARATUS (71) We, PALOMEX OY, a joint Stock Company organised under the laws of Finland, of Box 20, 04301 Hyryla, Finland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an apparatus for producing panoramic X-ray projections for example of a dental arch-shaped object on X-ray film, the apparatus comprising a relatively stationary frame, a relatively movable support arm to the opposite ends of which are secured the X-ray source and the film holder on opposite sides of the object to be radiographed, and means for producing relative rotation of the support arm around the object.

In panorama-tomographic X-ray techniques a layer of certain thickness of the object is radiographed on the film; the layer is called an image layer and its shape, position and thickness can be influenced by suitably planning the geometry associated with radiography of the object. In this technique as applied to dentistry, the X-ray tube and the film move relative to the patient who thus remains in a relatively fixed posture during the radiography.

The desired region of the object is radiographed accurately on the film if the film is given the same speed of travel as the speed of travel of the projection area of the object being radiographed, the projection area being received on the surface of the film.

In panorama-tomographic radiography techniques there are, among others, several variables affecting the final result: such as the position of the centre of rotation in relation to the object, the velocity of the film in relation to the velocity of the projection area on the film, the velocity of the X-ray beam in that layer of the object being radiographed, the width of the beam of X-ray radiation on the surface of the film, the distance of the layer that is radiographed from the centre of rotation, the distance between the focal spot and the centre of rotation, the size of the focal spot, the type of film used, the intensifying screens, the voltage and current of the X-ray tube, filtration of the X-rays and total exposure time. The effects of the above variables arc explained in more detail e.g. in the article by J. van Aken "Panoramic X-ray equipment", published in Reports of Councils and Bureaus/ Joda, Vol. 86, in May 1973.

Presently there are several panoramatomographic radiography machines available.

In one of the oldest known machines, the patient is standing up when radiographed and the X-ray tube and film move around the head of the patient who has been steadied in the required position. This machine is employed for radiographs of teeth and maxillary joints.

The shape of the layer that is radiographed consists of three different circular arcs, in other words the movement of the X-ray tube and the film has three different centres of rotation during radiography and change from one centre of rotation to another takes place through cycloidal movement.

In the apparatus of U.S. patent 3,045,118 the patient is in a sitting position and the radiographed layer consists of two circular arcs; change from one centre of rotation to the other takes place by moving the patient sideways over a suitable distance by lateral displacement of the chair.

In the German Patent specification DOS 1,955,294 is described a machine where the radiographed layer is elliptic. The movement of the centre of rotation of the X-ray tube and the film is based on a mechanism employing elliptical gear wheels, the function of which has been disclosed in German Patent specifications DOS 2,252,578 and 2,057,135.

Other corresponding machines are also available in the market but the mechanism producing their radiographic movement are generally similar to the above-mentioned basic types.

In designing the mechanisms of the machines currently available in the market, the basis has been a geometric curve close to the shape of jaw bone, the curve being either an ellipse or a combination of two or three circular arcs.

However, if the basis of design is the most common shape of jaw bone and there is an examination as to which would be the best possible movement of the centre of rotation of the rotational movement of the X-ray tube and the film, it will be noticed that it does not accurately follow any specific and simple geometric form.

A consequence of this is that the movement used in the available radiographic machines is always a somewhat inaccurate approximation as compared to ideal movement.

The purpose of the present invention is to overcome the above drawbacks of the prior art machines and to provide a panoramic X-ray device for a dental arch shaped object, in which the movements of the source of X-ray radiation and the film correspond as closely as possible to the shape of the object being radiographed.

According to the invention, there is provided a panoramic X-ray apparatus comprising a relatively stationary frame member supporting a fixed guide pin or stud, said frame member slidably supporting a carrier plate which is reciprocable with respect to the frame member, the carrier plate having a bearing means by which a guide plate is rotatably mounted on the carrier plate, the guide plate having an arm member extending on each side of the axis of rotation of said bearing, one end of the arm supporting a source of X-rays and the other end of the arm supporting an X-ray film holder, the apparatus including means mounted on said arm for producing rotary movement of the arm around said bearing, the rotatable guide plate being adapted to cooperate with guide pin or stud to follow a predetermined track during said rotary movement of the guide plate, with which the arm also rotates, whereby the carrier plate and the centre of the arm are caused to reciprocate rectilinearly with respect to the frame member during said rotation such that the centre of rotation of the arm moves along a path corresponding to the simultaneous rectilinear movement of the carrier plate with respect to the frame member, the ends of said arm following the track determined by said guide plate. The essential nature of the invention is thus that a rotational movement and a linear movement occur in synchronism with each other, the linear movement taking place along the axis of symmetry of the dental arch or a corresponding object to be radiographed.

Embodiments of the invention will be described in more detail by way of example and with reference to the accompanying. drawings in which: Figure 1 is a schematic side view of one embodiment of a panoramic X-ray apparatus in accordance with the invention, Figure 2 is a plan view of the apparatus shown in Figure 1, Figure 3 is a side view of another embodiment of the apparatus, and Figure 4 is a plan view of the apparatus shown in Figure 3.

In the drawings, some parts, particularly those associated with the supporting frame, have not been depicted for the sake of clarity.

The frame member 1 with a flange is fixedly secured to the main flame of the apparatus (not shown) and together with the guide stud or pin 2 provided thereon is actually the only relatively stationary part shown in the drawings.

In the frame member 1 there is slidably fitted a carrier plate 3 which is longitudinally reciprocable between the side flanges of the frame member 1, (in the vertical direction in Figure 2). The carrier plate 3 supports the entire movable assembly. On the carrier plate 3 there is fixedly mounted an axle bushing 4 on which a rotatable guide plate 6 is rotatably mounted by means of a bearing 5. The stud 2 is located in a shaped eccentric groove or slot in the guide plate 6 as the plate rotates relative to the plate 3. The shape of the groove or slot is such that the distance of the groove or slot from the centre of the bearing 5 is variable and stud 2 is fixed in the stationary frame, the carrier plate 3 is constrained to move linearly relative to the frame member 1 while the carrier plate 6 rotates relative to the plate 3.

An arm 8 is fixed to the carrier plate 6, on one end of which arm there is fitted a source of X-ray radiation 31 and on the other end of which a curved X-ray film holder 30 is mounted on a support axis 29. The patient's head (not shown) is placed between the source 31 and the film 30, below the frame member 1 in Figure 1.

The rotatable guide plate 6 bearing the arm 8 is rotated by an electric motor 13 by means of pulleys 7 and 10 and a toothed belt 9.

Pulley 7 is attached to the bushing 4 and thus the motor, whose frame is attached to the arm 8, also moves around the centre of rotation.

The curved film carried in the holder 30 is synchronously transported with the rotation of arm 8 so that the beam of X-rays coming from the X-ray source 31 sweeps over the film 30 during transport. The synchronised movement of the film is accomplished, in Figures 1 and 2, by means of an eccentric pulley 12 mounted on the shaft 11 of the motor 13, driving belt 14, wheels 15 and 17 mounted on the shaft 16, and by means of the wheel 27 mounted on the film holder support axis 29.

The shape of the eccentric pulley 12 is designed to correspond to the combined rotational/ translational movement produced by the guide plate and the carrier plate.

A requirement for the mechanism to be realised was that the layer which it radiographs, as to its shape and size, accurately corresponds to the layer having the correct anatomical shape and size. Earlier studies have already established the shape and size of the anatomically proper image layer. The invention is based on the fundamental observation that the movement of the centre of rota tion that is common to the X-ray tube 31 and to the film in the holder 30 can be accom plished by mere reciprocating linear movement occuring during the radiography. Thus, the movement of the X-ray tube and the film is the combination of continuous rotational move- ment (4, 6) and reciprocating linear movement (1, 3). The linear movement (1, 3) is accomplished by means of the shaped slot or groove in the guide plate 6, the shape of which is chosen so that the combination of the rotational (4, 6) and translational (1, 3) movements defines the above-mentioned object layer of anatomically proper shape and size so that the beam of X-ray radiation strikes as perpendicularly as possible relative to the layer being radiographed. Thus, the object is radiographed on the film in a perpendicular projection whereby the image is accurate as to its dimensions and thus also diagnostically clearer and more readily readable.

The above-mentioned desired combination of reciprocating linear movement and rotational movement is also in practice easy to realize by a reliable and simple mechanism whereby also mechanical accuracy of velocities and accelerations of radiographic movements necessary in panorama-tomographic illustrations is obtained in a relatively easy manner.

in the panorama-tomographic radiography technique the essential point is that the film movement and the rotational (4, 6) and translational (1, 3) movements are accurately synchronized relative to each other. Since the rotational movement (4, 6) of the X-ray tube 31 was synchronized by means of said mechanism relative to its linear movement (1, 3), the film movement must further be synchronized relative to said movements so that all movements of the mechanism would be synchronized relative to each other.

In the mechanism according to the invention, the movement of the film 30 is derived from the same drive shaft 11 as the common rotational movement (4, 6) of the X-ray tube 31.

In this way both the movement of the film and the rotational movement (4, 6) are synchronized relative to each other. Since the shaft 11 is attached with bearings to the common support arm 8 of the X-ray tube and film axis, the distance of the shaft 11 in the arm from the linearly reciprocating parts 3 and 4 remains constant during the rotational movement and the drive of the rotational movement can thus be arranged between the shaft 11 and the linearly moving part by means of a belt 9, gear wheels or in some other similar manner. The radius and shape of the eccentric pulley or drive wheel 12 varies in such a way with respect to the drive direction of the belt 14 that the velocity of the film is correctly variable during radiography in order to accurately radiograph the desired area.

Thus, the linear movement of the centre of rotation according to the invention provides the additional feature that the transport mechanism of the film can be arranged in a very advantageous manner.

In addition, the belt transmissions, which the invention has made possible, are advantageous in absorbing possible variations, since an even more important variable than the accuracy of the path of movement is the uni formity or smoothness of the movement.

Since the shaft 11 can be rotated at considerably higher (e.g. triple) velocity than the support arm the film movement can also be made satisfactory regarding the accuracy and the desired velocity changes.

The device according to the invention can, in addition, just as well be used for a reclining patient in which case the frame part is mounted in a vertical position and suitably lifted and lowered on a vertical pillar.

By changing the transmission ratio between the drive shaft 11 and film holder support axis 29, the radiographic device can be used to produce such shapes of the layer to be radiographed which would be better suitable for radiographs of face bones and cheek and forehead sinuses than the layer intended for radiographs of teeth and jaws. In fact, this is an additional advantage which is partly an accidental consequence of the movement mechanism according to the invention.

One embodiment allowing the change of transmission ratio is depicted in Figures 3 and 4. The device is similar to that shown in Figures 1 and 2 with the exception of the transmission from the pulley to the film holder support axis 29. A three-armed member 18 is mounted on bearings on the shaft 16, this member being pivotable into two different positions by means of a linkage 25 of a solenoid 26 or some other similar actuating means. The Y-shaped member 18 supports stub axes 19 and 22, with gear wheels 20 and 21 being mounted on the former, and gear wheels 23 and 24 on the latter. In the position of Figure 4, the rotational movement is transmitted to the shaft 29 of the film holder from the gear wheel 17 via gear wheels 20, 21 and 27 while in the other position the movement should be transmitted from the pulley 17 through gear wheels 23, 24 and 27.

The dislosed embodiments can be modified.

By means of two sets of wheels, however, there is obtained an inexpensive, very stable and, at the same time, sufficiently accurate movement mechanism. When the frame part 1 is in a vertical position, the guide plate may comprise only a guiding rib instead of a slot or groove, since the guide stud or pin 2, mounted on the frame member 1, rests on the guiding rib under the influence of gravity acting on the movable part of the apparatus.

WHAT WE CLAIM IS: 1. A panoramic X-ray apparatus comprising a relatively stationary frame member supporting a fixed guide pin or stud, said frame member slidably supporting a carrier plate which

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. plished by mere reciprocating linear movement occuring during the radiography. Thus, the movement of the X-ray tube and the film is the combination of continuous rotational move- ment (4, 6) and reciprocating linear movement (1, 3). The linear movement (1, 3) is accomplished by means of the shaped slot or groove in the guide plate 6, the shape of which is chosen so that the combination of the rotational (4, 6) and translational (1, 3) movements defines the above-mentioned object layer of anatomically proper shape and size so that the beam of X-ray radiation strikes as perpendicularly as possible relative to the layer being radiographed. Thus, the object is radiographed on the film in a perpendicular projection whereby the image is accurate as to its dimensions and thus also diagnostically clearer and more readily readable. The above-mentioned desired combination of reciprocating linear movement and rotational movement is also in practice easy to realize by a reliable and simple mechanism whereby also mechanical accuracy of velocities and accelerations of radiographic movements necessary in panorama-tomographic illustrations is obtained in a relatively easy manner. in the panorama-tomographic radiography technique the essential point is that the film movement and the rotational (4, 6) and translational (1, 3) movements are accurately synchronized relative to each other. Since the rotational movement (4, 6) of the X-ray tube 31 was synchronized by means of said mechanism relative to its linear movement (1, 3), the film movement must further be synchronized relative to said movements so that all movements of the mechanism would be synchronized relative to each other. In the mechanism according to the invention, the movement of the film 30 is derived from the same drive shaft 11 as the common rotational movement (4, 6) of the X-ray tube 31. In this way both the movement of the film and the rotational movement (4, 6) are synchronized relative to each other. Since the shaft 11 is attached with bearings to the common support arm 8 of the X-ray tube and film axis, the distance of the shaft 11 in the arm from the linearly reciprocating parts 3 and 4 remains constant during the rotational movement and the drive of the rotational movement can thus be arranged between the shaft 11 and the linearly moving part by means of a belt 9, gear wheels or in some other similar manner. The radius and shape of the eccentric pulley or drive wheel 12 varies in such a way with respect to the drive direction of the belt 14 that the velocity of the film is correctly variable during radiography in order to accurately radiograph the desired area. Thus, the linear movement of the centre of rotation according to the invention provides the additional feature that the transport mechanism of the film can be arranged in a very advantageous manner. In addition, the belt transmissions, which the invention has made possible, are advantageous in absorbing possible variations, since an even more important variable than the accuracy of the path of movement is the uni formity or smoothness of the movement. Since the shaft 11 can be rotated at considerably higher (e.g. triple) velocity than the support arm the film movement can also be made satisfactory regarding the accuracy and the desired velocity changes. The device according to the invention can, in addition, just as well be used for a reclining patient in which case the frame part is mounted in a vertical position and suitably lifted and lowered on a vertical pillar. By changing the transmission ratio between the drive shaft 11 and film holder support axis 29, the radiographic device can be used to produce such shapes of the layer to be radiographed which would be better suitable for radiographs of face bones and cheek and forehead sinuses than the layer intended for radiographs of teeth and jaws. In fact, this is an additional advantage which is partly an accidental consequence of the movement mechanism according to the invention. One embodiment allowing the change of transmission ratio is depicted in Figures 3 and 4. The device is similar to that shown in Figures 1 and 2 with the exception of the transmission from the pulley to the film holder support axis 29. A three-armed member 18 is mounted on bearings on the shaft 16, this member being pivotable into two different positions by means of a linkage 25 of a solenoid 26 or some other similar actuating means. The Y-shaped member 18 supports stub axes 19 and 22, with gear wheels 20 and 21 being mounted on the former, and gear wheels 23 and 24 on the latter. In the position of Figure 4, the rotational movement is transmitted to the shaft 29 of the film holder from the gear wheel 17 via gear wheels 20, 21 and 27 while in the other position the movement should be transmitted from the pulley 17 through gear wheels 23, 24 and 27. The dislosed embodiments can be modified. By means of two sets of wheels, however, there is obtained an inexpensive, very stable and, at the same time, sufficiently accurate movement mechanism. When the frame part 1 is in a vertical position, the guide plate may comprise only a guiding rib instead of a slot or groove, since the guide stud or pin 2, mounted on the frame member 1, rests on the guiding rib under the influence of gravity acting on the movable part of the apparatus. WHAT WE CLAIM IS:

1. A panoramic X-ray apparatus comprising a relatively stationary frame member supporting a fixed guide pin or stud, said frame member slidably supporting a carrier plate which

is reciprocable with respect to the frame member, the carrier plate having a bearing means by which a guide plate is rotatably mounted on the carrier plate, the guide plate having an arm member extending on each side of the axis of rotation of said bearing, one end of the arm supporting a source of X-rays and the other end of the arm supporting an X-ray film holder, the apparatus including means mounted on said arm for producing rotary movement of the arm around said bearing, the rotatable guide plate being adapted to cooperate with the guide pin or stud to follow a predetermined track during said rotary movement of the guide plate, with which the arm also rotates, whereby the carrier plate and the centre of the arm are caused to reciprocate rectilinearly with respect to the frame member during said rotation such that the centre of rotation of the arm moves along a path corresponding to the simultaneous rectilinear movement of the carrier plate with respect to the frame member, the ends of said arm following the track determined by said guide plate.

2. An apparatus according to claim 1 wherein a transmission means is provided to produce the rotation and relative reciprocation of the arm and the guide plate with respect to the carrier plate.

3. An apparatus according to claim 2 wherein the transmission means for producing the rotary and reciprocal movements of the arm and the carrier plate include an electric drive motor mounted on the arm.

4. An apparatus according to claim 2 or claim 3 wherein the transmission means includes a driving belt and pulley arrangement.

5. An apparatus according to any one of claims 1 to 4, wherein means are provided for rotating the X-ray film holder about an axis in synchronism with the movements of the arm.

6. An apparatus according to claim 5 wherein means for producing the rotary and rectilinear movements of the arm and the rotatable guide plate is also connected by a further transmission means to the means for rotating the X-ray film holder.

7. An apparatus according to claim 6 wherein the transmission ratio between the two transmission means is variable

8. A panoramic X-ray apparatus substantially as hereinbefore described and with reference to the accompanying drawings.