Panoramic tomography X-ray apparatus particularly for dental photography.

Panorama tomography X-ray machine especially for dental imaging

Panoramatomografiröntgenanordnlng för speclellt tandfotografering

The invention relates to a panoramic tomography X-ray device, in particular for dental imaging, which device comprises a body part pivotally mounted on a second body part with an X-ray tube attached to one end and a film cassette device inside which an X-ray film can be placed. the object to be photographed is positionable and which device comprises a traction device, rotating said pivotable body portion in a plane, preferably horizontally, for taking a panoramic X-ray image.

Most panoramic X-ray devices for dental imaging are designed and constructed to rotate the X-ray around the patient's head, thereby imaging the dental arch applied to a moving film when applied to a plane.

In order for an object to be sharply imaged on film when the radial structure at the front or rear of the object is blurred invisible, the transverse velocity of the film relative to the beam must be equal to the scanning speed of the beam at the object multiplied by the magnification ratio. Magnification is determined by the ratio of the distance between the focus film plane to the distance between the focus and the subject.

The thickness of the sharply described layer is directly proportional to the distance of the instantaneous center of rotation from the film plane and inversely proportional to the magnification and the width of the beam. Only the relative position of the Focus, the subject, and the film plane is relevant to the image. The momentary center of rotation is only relevant through the sweep speed.

With reference to the above, the following is a basic equation for panoramic photography:

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I ^ / L v = (or, where o ίθ = distance from foco F to the current location of the image layer

- distance from focus F to film plane ω = angular velocity of rotational motion around the center r = distance of the imaging point from the instantaneous center of rotational motion = velocity of the pixel in the image or film plane.

In a panoramic tomography device for dental imaging, the main subject is the dental arch and jaw joints (other important objects also exist). In order for the projection produced by the device on the object to be as usable as possible, the most mechanically problem-free solution, i.e. a fixed center of rotation, must be abandoned. The way in which the position of the momentary center of rotation is changed during shooting depends on e.g. the following factors:

- orthogonality, the purpose of which is that the adjacent teeth do not overlap at any point in the dental arch, and thus the beam must be wiped as perpendicularly as possible to the object, i.e. orthogonally against the dental arch;

- a constant magnification, i.e. that the magnification over the entire area of ​​the dental arch is kept the same, in order to achieve which the distance from the imaging layer to the film plane is kept constant throughout the rotation;

- the smoothness of the movement, which has been caused by problems because the instantaneous center of rotation has to be moved during shooting. The projection must be such that the momentary shift of the center of rotation can take place without points of discontinuity which would cause excessive accelerations and thus problems with the image quality;

- minimization of the patient's radiation exposure, for which purpose the projection must be such that the patient is not exposed to more than one radiation exposure at one point.

In addition to the projection mechanism of the device's X-ray source and film cassette producing a projection that meets the above projection requirements, it should be fabricated at a reasonable cost without any play clearances and other inaccuracies. Thus, in order to produce the desired projection, said mechanism must take care of moving the center of rotation horizontally. In addition to this, the mechanism must support the entire equipment vertically, in which direction the bearing also had to be stable and backlash-free to achieve a proper imaging result.

In previously known devices, said orthogonality has been successfully resolved in the region of the dental arch. In the known devices, little attention has been paid to the jaw joints in this respect. Similarly, keeping the magnification ratio constant has not been resolved in the devices on the market, a drawback which can be seen in the tomography images so that the anterior region of the dental arch and / or the entire dental arch is imaged at a clearly higher magnification than the jaw joints. The reason is that the film cassette in known devices comes to the side area much closer to the subject than to the front area.

In addition, in the known solutions, the geometry of the rotational movement is such that the instantaneous center of rotation throughout the imaging is located in or in the immediate vicinity of the area bounded by the jawbone of the object, causing a large local radial load on this area. For the same reason, the jaw joints are imaged at an oblique angle, which is a clear drawback for diagnostic reasons on the X-ray machine.

In the following, the state of the art related to the invention will be described in more detail with reference to the patent literature most closely related to the invention.

FI-pat.hak. No. 833754 (Instrumentarium Oy) presents a panoramic tomograph in which the problem of standard magnification is solved in one way. Em. however, the reference does not comment on how the projection is produced. Em. the solution according to GB Patent No. 1,594,499, referred to in the application, produces a projection in which the jaw joints are described rather obliquely (not orthogonally). In addition, em. in the device according to the application, the movement in the direction of the beam required for constant magnification is generated by a linear bearing, which is a constructively difficult and expensive solution.

FI-pat.hak. No. 783233 (cont. U.S. Pat. No. 4,264,820) discusses an X-ray method and apparatus that addresses the problem of constant magnification. Again, this reference does not take a position on the projection in the area of ​​the jaw joint, but only orthogonality is considered in the area of ​​the dental arch. In order to achieve a standard magnification, two implementations are proposed in which the following shortcomings can be identified:

- ns. the reversible slides slide in the grooves, making them difficult, even impossible, to make them clearance-free;

- the stability of the device in the horizontal plane is questionable at those points of the rotational movement where the pivot slide guide grooves according to the invention come at an unfavorable angle to each other;

- the reference method for transmitting the driving force of the rotational movement results in impure rotation of the traction wheel (axial displacement);

- in the special arrangement according to the reference, in which one of the grooves of the turntable slides is replaced by a crank, the guidance of the turntable slides in the grooves is a critical factor for the shooting result, since the turntable slide does not stably follow either edge of the groove;

- in the latter special arrangement of the above-mentioned reference, the transmission of the rotational movement can be arranged in such a way that the traction takes place purely when the traction wheel travels in a circular path, but the structure becomes complicated, large and expensive to implement.

With regard to the state of the art related to the invention, reference is also made to the following patents: FI 67 269, FI 69 523, US 3 806 731 and US 3 867 636.

It is a general object of the present invention to provide a device in which the problems discussed above have been solved by a device solution which can be implemented mechanically in a simple manner.

It is a particular object of the invention to provide a device which is free from harmful mechanical clearances and corresponding inaccuracies.

The object of the invention is to provide such a device in which the orthogonality of the description touched above is realized both in the region of the dental arch and in the posterior part of the jawbone up to the jaw joints with good accuracy.

The object of the invention is to provide such a device in which the magnification remains constant over the entire image area.

It is a further object of the invention to provide such a device in which the film level can be brought closer than normal to the patient in order to reduce the magnification ratio without the risk of the film cassette hitting the patient.

It is a further object of the invention to provide such a device in which the maximum local beam load is made even smaller.

In order to achieve the above and later objects, the invention is essentially characterized in that said traction device comprises a traction and guide groove or a corresponding rail arrangement symmetrical with respect to the central plane of the device and having substantially straight side portions and a curved portion connecting these portions. a traction unit comprising a traction wheel is adapted to co-operate with or the like, which, when rotated by a traction unit, rotates said pivoting body part, that said rotatable body part is articulated to pivot! said fixed body portion by a crank mechanism articulated by a bearing from the X-ray tube side crank mechanism portion to the pivotable body portion and from the opposite part of the crank mechanism to the fixed body portion, that when said rotating body part is in the middle position, both opposite articulation axes of said palm are located in the vertical central plane of the device, and that said traction and steering device and said crank mechanism are adapted to cooperate in such a way that that in the foreground of the tooth arc or the like and in the traction and guidance of the corresponding curved portion of the guide and traction groove, the rotating body rotates around the front axle pin of said palm X-ray film cassette and

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to the details of which the invention is in no way narrowly limited.

Figure 1 shows an imaging projection produced by a device according to the invention.

Figure 2 is a schematic top view of a rotation mechanism according to the invention in its second extreme edge position.

Figure 3 shows the mechanism in its intermediate position in a manner similar to Figure 2.

Figure 4 shows the mechanism in its central position in a manner similar to Figures 2 and 3.

Fig. 5 shows a central vertical section of the mechanism and device according to the invention, and Fig. 5 is at the same time a section VV in Fig. 4, i.e. with the mechanism in its central position.

Figure 6 is a section VI-VI in Figure 5.

Figure 1 shows the imaging geometry and projection realized by the device according to the invention. The X-ray tube is marked with the reference number 10, its focus in a different position with the references Εθ-Εθ. The X-ray tube 10 transmits the X-ray beam X through the teeth T and the jaw bone L to the film 20 along the line α. The course of the X-ray X is shown in Fig. 1 in seven different positions βθ .-. Βθ. In the extreme position, the X-ray tube is denoted by reference 10 'and the film by reference numeral 20' and the focus of the tube by reference numeral. The jaw bone L joints are indicated by reference J.

In the anterior region of the dental arch, represented by radii ^aQ^-a| the gap (sector c) is rotated horizontally around the vertical axis 0 £ by the body 11 connecting the X-ray tube 10 and the film 20. Between the radii a £ and a ^ (sector d) the center of rotation 0 £ shifts smoothly along a curved path to the vertical axis O3, after which the center of rotation further moves away from the central axis a_Q (CC). With the geometry shown in Fig. 1, the orthogonality of the description is realized with good accuracy not only in the anterior and lateral areas of the dental arch but also in the posterior part of the jawbone up to the joints J. The magnification also remains constant throughout the image area, which can be seen e.g. that the distance of the 20 levels of the film b_Q... b ^ of the described layer remains constant with sufficient accuracy over the entire area of ​​the trajectory. Due to the constant b ^ -b ^ distance, the plane of the film 20 can be brought even closer to the patient P (Fig. 5) to reduce the magnification ratio without the risk of the film cassette hitting the patient. With the above geometry, it is also realized that the beam stress is substantially lower than the known devices, because the lateral centers of rotation of the body 11 are located outside the patient.

The transfer mechanism of the X-ray tube 10 and the film 20 implementing the imaging projection and geometry described above will now be described with reference to Figs. First, the structure of the device according to the invention will be described with reference to all Figures 2 to 6, after which the operation of the rotation mechanism of the body 11 will be described in more detail with reference to Figures 2, 3 and 4, in which the rotation mechanism is shown in different positions.

The rotation mechanism comprises a body part 30, which is fixed to the stand 60 known per se, which rests on the floor level. The body portion 30 may be vertically movable on a tripod 60 to a suitable working height. Suspended on the body part 30 by a mechanism according to the invention is a horizontally pivotable body part 11, which is, for example, Figure 4 shows a substantially elongate arm with an X-ray tube 10 on one end 11a and a film cassette 20 on the other end 11b. X-ray film RF with transmission mechanisms and other devices known per se, the detailed description of which is not necessary in this connection. The pivoting body portion 11 is suspended on bearings 12a and 12b for pivoting about a vertical axis Oj-Oj. The vertical axis 0 ^ -0 ^ is not fixed, but rotates horizontally during shooting with respect to the fixed body 30. The rear axle pin 13 of the pivotable body portion 11 is fixedly connected to the X-ray tube 10 end of the palm 50. At the other end of the pivoting palm 50 in the space 30a of the body 30, there is a front axle pin 51 which is fitted with bearings 53a, 53b in connection with the fixed body 30. Both bearings of the shaft pins 13 and 51 of the palm 50 are provided by two opposed angular contact ball bearings 12a, 12b; during the turning movement. Instead of angular contact ball bearings 12,53, it is also possible to use corresponding tapered ball bearings or other similar combined axial and radial bearings. A well-designed and properly implemented and installed bearing as described above is quite important for the operation of the rotation mechanism.

In addition to the palm 50 and its shaft pins 13 and 51 described above, the rotating mechanism according to the invention comprises as an integral part a counter-profile 42 fixedly fixed to the upper side of the arm 11 so that one end of the counter-profile 42 is at the shaft journal 51. In cooperation with the round end surface 42a and the planar sides 42b of the counter-profile 42, a guide profile 43 is stably attached to the fixed body 30, the shape of the vertical guide surface of which is shown in broken lines in Figures 2, 3 and 4. Said guide surface 43 is symmetrical with respect to the central plane CC and has in the middle a circular recess 43a to which the circular end portion 42a of the mating profile 42 corresponds, making the mechanism stable in its central position according to Fig. 4 and acting on both sides of this position. In the mechanism, the co-operation of the counter-profile 42 and the guide profile 43 in different operating positions will be returned to in more detail later.

An essential aspect of the mechanism according to the invention is an apparatus for transmitting the rotating force to the rotatable body 11. This apparatus comprises a guide groove 31 in the fixed body 30 which opens to its underside and is substantially uniform to the main jaw and arch shape described in connection with Figure 1 ^ taking into account. The guide groove 31 is symmetrical with respect to the vertical center plane CC and has side portions 31S at a small angle u to the plane CC, which terminate in the end 32, and a curved portion 31R connecting the side portions 31S. The curved portion 31R has, first, a portion having a constant radius of curvature R with the center of curvature on the vertical axis 0 and, second, portions where the constant radius R changes and grows smoothly to infinitely large, joining the straight portions 31S. The second half of the constant radius portion corresponds in Figure 1 to sector c and to said second portion having an increasing radius of curvature by sector d, by which the center of rotation moves from the axis to the axis 0 ^. The angle u is usually in the range u = 10 ° -20 °. The guide groove has a narrower base portion 31b and a wider mouth portion 31a, which portions are standard plates along the entire length of the groove 31.

The groove 31 acts as a guide and traction response in cooperation with the traction unit 33 attached to the pivoting body 11. The unit 33 comprises, as a traction motor, an electric motor and a gearbox which rotates the traction sheave 40 on the drive shaft 37 of the unit 33. The unit 33 is mounted to pivot on an axle pin 38 connected to the body part 11. The unit 33 is pivoted about a shaft pin 38 in the traction position of the traction sheave 40 by a spring 37 arranged between the pins 34 and 36, which gives a constant load to the traction sheave 40 specifically against the outside of the traction portion 31a of the groove 31. The draw point is shown in Figure 5 by D.

As shown in Figs. 5 and 6, the traction sheave 40 has a protruding portion 11c in the body portion 11, which extends over the traction sheave 40. Attached to the side of the projection 11c is a shaft pin 41, at the end of which a steering wheel 39 is mounted, which is loaded to rest against the inner side of the guide portion 31b of the groove 31, i.e. against the opposite side to which the traction wheel 40 is loaded with the portion 31a. The traction sheave 40 and the steering wheel 39 are arranged so that their centers of rotation coincide. In this case, the load from the spring 35 does not generate any additional torque in the rotational movement which interferes with the movement of the arm 11.

Figs.

An important feature of the above traction mechanism is that the traction unit 33 by means of a load spring 35 ensures that the traction wheel 40 in all positions of the arm 11 follows the outside of the traction portion 31a of the groove 31 and the guide wheel 39 respectively follows the inside of the guide portion 31b. reliable, smooth and jerky traction in all positions of the body part 11.

In the following, the operation of the crank mechanism and its details of its structure, which have not been mentioned above, will be described mainly with reference to Figs. This description begins with the center position of Figure 4, although in practice the device generally moves from the body end position 11 'shown in Figure 2 and the arm 11 pivots through the intermediate position shown in Figure 3 to the center position shown in Figure 4 and then advances to the opposite end position of Figure 2. On both sides of the center position shown in Fig. 4, i.e. in the sector C between the radii a ° and a ^ shown in Fig. 1, the part 11 rotates about the pivot axis by the co-operation of the constant radius curved portion 31R, the traction wheel 40 and the steering wheel 39. In this position, the crank 50 is parallel to the length of the arm part 11 and the axes of rotation 0 and 0 of the shaft pins 13 and 51 of the palm 50 are located in the vertical central plane CC of the arm part 11. In order to control the center position of the crank mechanism 11,13,50,51 and 30 and not to be indeterminate, the mechanism includes a counter-profile 42, the guide head 42a of which non-reciprocally corresponds to the circular recess 43a of the guide profile 43 of the fixed body 30. In this case, the parts 42a and 43a partly define the stable pivot center of the mechanism. When the mechanism is started to be turned from the central position shown in Fig. 4 to, for example, the intermediate position shown in Fig. 3, the turning center determined by the parts 42a and 43a is maintained by the constant radial portion 31R of the guide groove 31. The shape of the groove 31 corresponds mainly to the shape of the jawbone.

When the steering wheel 39 and the traction wheel 40 come from the standard radius R of the groove 31_qthe center of rotation of the arm portion 11 begins to move from the center 0 and from the center plane CC to the side, which occurs so that the crank 50 begins to rotate in a different direction from the longitudinal direction of the arm 11, whereby the straight vertical side 42b n of the counter-profile 42

corresponds to the curved side of the guide profile 43 laterally sideways and possibly sliding along them so that this lateral line rolls and possibly further slides from the recess 43a of the guide profile 43 to the side area of ​​the guide profile 43, at the same time In the meantime (sector d in Fig. 1) the arm part 11 and the crank 50 turn horizontally in the same direction. Moving from the position of Figure 3 to the position of Figure 2 (sector e in Figure 1), the crank 50 pivots in the opposite direction to the arm 11. In the area of ​​the straight guide grooves 31S, the counter-profile 42 is inoperative. In the foreground of the toothed arc, i.e. as the arm 11 rotates about the axis 0, the exact position of the instantaneous center of rotation and the smooth transition from one control stage to another in addition to the counter-profile 42 and the guide profile 43 are ensured by a deflection spring 55. A guide spring 55 is located between the pin 54 extending through the groove 44 of the fixed body 30 at the shaft pin 13 and the pin 56 of the body 30. The spring 55 ensures that the guide profile 43 and the counter-profile 42 remain in stable contact with each other at all times during delivery in the region 31R of the groove 31.

It should be emphasized that only one preferred embodiment of the invention has been described above, the details of which may vary in several respects within the scope of the inventive idea. Instead of a guide groove 31, for example, a corresponding guide rail can be used, the shape of which corresponds to the shape of the guide groove 31, and which guide rail can be adapted to operate, for example, so that a traction wheel 40 acts against one side and a steering wheel 39 against the other side. In this way, too, stable traction and its control are achieved. The traction unit 33 can also be arranged in a different way than shown in the figure, and its spring load 35 can be realized in several different ways. The details of the crank mechanism may also vary and differ from the above.

The mechanism according to the invention realizes a particularly advantageous shape of the path of the RF exposed part of the film to be exposed inside the film cassette 20, shown in Fig. 1 by the dotted line A, as well as other above-mentioned advantages synergistically with both device operation and mechanical structure.

An embodiment has been described above in which the traction groove 31 is located in the fixed part 30 and the traction unit 33 in the pivotable body part 11. In some special cases, although such an implementation does not currently seem advantageous, it may be possible to implement the guide and traction device so that the traction unit with guide wheels is located in connection with the fixed body 30 and the guide groove or similar rail is arranged in connection with the pivoting body 11. or the like have changed places. However, the embodiment of the invention described above in connection with the figures is currently one which the applicant considers most advantageous, taking into account both functional and structural aspects.

The following claims define the scope of the invention.