Tomographic Apparatus

Abstract

A tomographic apparatus comprising: a principal linkage supporting an X-ray source and a film so that they face each other and having pivot fulcrums between these two members for being swingable in the directions of both axes X and Y; two servo motors for causing the linkage to move in the directions X and Y; means for setting the travel paths of the said two members comprising a plurality of sets of cams provided rotatably on a single rotatable shaft; means for driving only a selected set of cams corresponding to the required paths of the said two members, and cam follower members associated with the said sets of cams, respectively; and adjusting means for comparing the positions of both the X-ray source and the film to be assumed successively in the paths set by the said setting means in the directions of X and Y with the positions of the principal linkage to be assumed successively on the said paths, and for actuating the servo motors until these two groups of positions are brought into agreement with each other. With this arrangement, it is possible to displace, on the established required paths during the X-ray irradiation, both the X-ray source and the film by a mere selection of the required set of cams and to thereby obtain a sharply focused tomogram of any desired region of the object while satisfactorily blurring unnecessary regions of the object not required on the tomogram, without needing any special technical training or experience in this particular field.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is concerned with an apparatus for performing tomography, which is suitable for obtaining satisfactory tomograms of various required regions of the body or an animal body.

2. Description of the Prior Art

Various types of tomographic apparatuses are being used to obtain X-ray tomograms of a variety of regions of the human body for diagnostic as well as therapeutic purposes.

An X-ray tomography is intended, in principle, to obtain a sharply focused tomogram of a desired particular region of the body of a patient on a film which is adapted to move in associated positional relationship with the X-ray source while an X-ray beam is directed onto the required region of the body of the patient in a certain optimum direction selected from a variety of directions, in such a way that the X-rayed image of those un-required regions of the body other than that particular region required for tomographic purposes is satisfactorily blurred so as to be blanked out.

According to the knowledge obtained in the past with respect to the technology in this field, it is commonly known that the amount of blurring of the X-rayed image of the said unnecessary regions of the object will increase with an increase in the length of the path of travel of the X-rays from the source and that such a blurred image of the unnecessary regions -- which are obtained in elongated patterns -- such as the images of bones which are located in parallel with the path of movement of the X-ray source, is difficult to blank out since these unnecessary images appear on the film in superposed relationship on top of the image of the required particular region. Therefore, in order to obtain a satisfactory tomogram of a particular region of body, such as in the chest, head or hip, where the arrangement of bones is complicated, it is necessary to use such an X-ray apparatus so arranged that the X-ray source travels in a path having the best angle for each region of body which is to be X-rayed.

For the foregoing reason, there have been developed and placed on the market tomographic apparatuses which are designed so that the X-ray source not only is able to make a rectilinear movement but also is able to move on a path which represents a curve of the second degree such as circular, oval or hypocycloidal. Also, in order to blank out the elongated images of those unnecessary regions of the object which lie outside the tomographic plane, there has been sucessfully devised a technique which is called selective X-ray irradiation such that an irradiation of X-ray beam is produced only within a specific section of the range of path of movement of the X-ray tube.

However, in those known tomographic apparatuses which have been put into practice already, the paths to be followed by the X-ray source are limited to very small group of directions. From the standpoint of being ideal, these known tomographic apparatuses and techniques have not yet attained satisfactory technical levels in view of the consideration that there exists an optimum path of movement -- which is different from other paths -- of the X-ray source for each region of the body to be X-rayed. In addition, these known tomographic apparatuses are too complicated to be operated easily. With these known apparatuses, there is required -- in case an alteration of the path of movement of the X-ray source is needed in accordance with the location or the angle of the required region of the object to be X-rayed -- complicated and time-consuming setting operations for each tomography and also a highly trained technician is required. The aforesaid selective X-ray irradiation method requires, in addition to the mechanism for driving the X-ray source, the provision of a particular mechanism for controlling the X-ray irradiation -- depending on the position of the X-ray source currently located on its path of movement -- for each region of the object to be X-rayed. Thus, this prior method gives rise to a further complexity in both the apparatus structure and the handling and these factors have made the practicability of this method very small.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an improved apparatus for obtaining quality tomograms, which permits the X-ray source to travel on any arbitrary path within the range in which it is allowed to move, without being impaired by any structural restrictions such as those stated above, and which produces a tomogram wherein the X-ray image of those unnecessary regions of the object is satisfactorily blurred.

Another object of the present invention is to provide an improved tomographic apparatus which allows the path to travel of the X-ray source to be selected as desired, only by the manipulation of a selective switch provided on the control panel of the apparatus, and which accordingly is easy to handle.

Still another object of the present invention is to provide an improved tomographic apparatus which enables the setting of the velocity of travel of the X-ray source to be made during any portion of the path of movement of the X-ray source already set as desired, and which is capable of effecting substantial control of the amount of irradiation of the X-ray beam by locally altering the said velocity during the travel of the X-ray source, and which, thus, is able to more satisfactorily blur the X-ray image of the unnecessary regions of the object to be X-rayed.

These and other objects as well as the advantages and features of the present invention will become apparent by reading the detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat diagrammatic front elevation, showing the essential parts of a preferred example of the apparatus of the present invention, in which the link means is tilted only in the direction of axis Y.

FIG. 2 is a somewhat diagrammatic side elevation of the same apparatus, in which the link means is tilted only in the direction of axis X, showing also the positional relationship between the object to be photographed and the apparatus.

FIG. 3 is a somewhat diagrammatic fragmentary perspective view, showing a part of the means for setting the travel path of the X-ray source and a part of the means for adjusting the outputs of the driving motors.

FIGS. 4 to 6 are somewhat diagrammatic illustrations to explain the said setting means and the said adjusting means shown in FIG. 3; in which:

FIG. 4 is a plan view,

FIG. 5 is a fragmentary plan view, showing the means of FIG. 4 in a different position, and

FIG. 6 is a side view, showing the structure of the cam means which represents the said setting means.

FIG. 7 is a somewhat diagrammatic explanatory illustration, representing a plan view of the cam-selecting mechanism of a set of cams provided in the means for setting the travel path of the X-ray source.

FIG. 8 is a somewhat diagrammatic explanatory plan view of the control mechanism for setting the stopping position of a required set of cams which are provided in the means for setting the travel path of the X-ray source.

FIGS. 9A, 9B, and 10A, 10B are explanatory illustrations, showing the relationship between the path of movement of the X-ray source and the shape of the cam faces; in which:

FIGS. 9A and 9B show the relationship between the two when the X-ray source makes a rectilinear movement, and

FIGS. 10A and 10B show the relationship between the two when the X-ray source makes a circular movement.

FIG. 11 is a longitudinal sectional view of a servo valve means employed in the present invention as the means for adjusting the outputs of servo motors, showing the structural details thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIGS. 1 and 2, there is shown an example of the tomographic apparatus embodying the present invention. In the drawings, it will be noted that, on a base frame 1, there is supported a shaft 2 in bearings 3 and 4 in such a way that this shaft 2 is rotatable about its own axis in the direction Y which is shown by an arrow. Two main link arms 5 and 6 of a link means are supported on pins 7 and 8, respectively, on the ends of shaft 2, so that these link arms 5 and 6 are rotatable in a direction perpendicular to the direction of rotation of the said shaft 2, or in other words, these main link arms 5 and 6 are rotatable in the direction of axis X. The directions of rotation of the shaft 2 and the link means are expressed as the directions of axis Y and axis X hereinafter as well as in the claims. Two bridge arms 9 and 10 are rotatably coupled to the said main link arms 5 and 6, respectively. These four arms 9, 10, 5 and 6 constitute a parallelogram linkage which can make swinging motion about the pins 7 and 8 on the shaft 2, in directions crossing at right angles or in other words in the directions of axes Y and X. Auxiliary arms 11 and 12 are operatively coupled to the ends of the extension 5' of the main link arm 5 and the extension 10' of the bridge arm 10, respectively, to form another parallelogram linkage in this portion of the link means. The aforesaid arrangement provides a link means which may be defined as a pantographically arranged linking mechanism which, as a whole, can be rotated in the directions of axis Y and axis X.

An X-ray tube 13 which serves as the X-ray source is secured to the auxiliary arm 12. On the other hand, a film holder 14 is secured to the foremost end of the extension of the bridge arm 9. The X-ray source 13, the center of the film mounted on the film holder 14 and a point A located on the extension of the longitudinal axis of the shaft 2 are arranged so that these three points will always lie on a rectilinear line irrespective of whatever angle of inclination is assumed by the link means as it is tilted in the directions of axis Y and axis X.

The bridge arm 9 which supports the film holder 14 is supported by bearings 58 and 59 which, in turn, are rotatably mounted on the link arms 5 and 6, respectively. Reference numeral 15 represents a balance load for balancing the forces existing on both sides of the shaft 2. An arm 17' is fixed to the said bridge arm 9. This arm 17' is coupled, at a position closer to one end thereof by a ball joint, to an auxiliary arm 17 which is provided between the link arms 5 and 6. This arm 17' is arranged to be parallel with the said link arms 5 and 6. The opposite and portion of the auxiliary arm 17 is coupled via a ball joint to another auxiliary arm 16 which is fixed to the base frame 1. Because of this arrangement, it will be understood that when the link arms 5 and 6 are rotated in the direction of axis X about the pins 7 and 8, the film holder 14 will carry out a movement, in parallel with and in correlation with the X-ray tube 13, in such a way that the center of the film mounted on the film holder 14, the focus of the X-ray source 13 and the point A on the extension of the longitudinal axis of the shaft 2 lie on a straight line. When the link arms 5 and 6 are rotated in the direction of axis Y about the shaft 2, on the other hand, the auxiliary arm 17 tilts about its pivotal point on the auxiliary arm 16 through an angle which is the same as that of the tilting of the link arms 5 and 6, so that the arm 17' rotates the bridge arm 9 to maintain the film holder 14 horizontal in position in spite of the tilting of the link arms 5 and 6. At the same time therewith, the center of the film mounted on the film holder 14 keeps the aforesaid correlationship with the X-ray tube 13 and the point A.

As will be described later, the point A represents a point lying on the tomographic plane of the object to be photographed by X-rays. Thus, it may be said that both the X-ray tube 13 and the film mounted on the film holder 14 are adapted to make spherical movements, respectively, about a point lying on the tomographic plane.

With the linking mechanism having the aforesaid arrangement, let us now assume that a force is applied to the main link arm 5 in any arbitrary direction. Whereupon, the link arm 5 tilts in the direction in which the force is applied. Thus, the main link arm 5 is able to assume any arbitrary angle of inclination within the range of the maximum angle of inclination which is limited by the linking mechanism as a whole and also by the base frame 1. Accordingly, the X-ray tube 13 and the film holder 14 are able to travel on any desired paths of movement, starting at any arbitrary positions on the faces of spheres formed about the point A, respectively. At the same time, the line which is formed by connecting the X-ray source 13, the point A located on the extension of the central longitudinal axis of the shaft 2 and the center of the film holder 14 will be a straight line in all cases.

The servo motors which impart to the linking mechanism having the aforesaid arrangement the required angles of inclination in both directions of Y and X, in this embodiment, are comprised of two hydraulically operated cylinders 18 and 19. Cylinder 18 of these two hydraulic cylinders is arranged between the shaft 2 and the main link arm 5. The other hydraulic cylinder 19 is arranged between the base frame 1 and the main link arm 5. The action of the hydraulic cylinder 18 causes both the X-ray source 13 and the film holder 14 to move in the direction of the axis X, whereas the action of the hydraulic cylinder 19 causes both the X-ray source 13 and the film holder 14 to move in the direction of the axis Y.

These two hydraulically driven cylinders 18 and 19 are controlled in their actions by follow up linkage means for adjusting the action of the servo motors which will be described later. In FIGS. 3 to 5, it will be seen that the main link arm 5 has, operatively coupled thereto at an arbitrary point B located within the length of this arm, a first corner joint of the bridges of a square follow up linkage which is formed by four links or bridge arms 20, 21, 22 and 23. Another joint of this latter linkage, which is located at a diagonally opposite corner of the square bridges relative to the aforesaid first corner joint is pivotably supported at a fixed point C on the base frame 1 in such a way that, when the main link arm 5 is located at a certain reference position in the directions of both the axis X and the axis Y, the said two bridge arms 20 and 23 of the aforesaid square linkage are positioned in parallel relationship with the direction of the axis X, and the other two bridge arms 21 and 22 are positioned in parallel with the direction of the axis Y. The bridge arms 22 and 23 have, on the sides closer to the fixed point C, joints 24 and 25, respectively, to substantially divide each of these two bridge arms into two arm segments. An arm segment 22' which is located between the joint 24 and the fixed point C is provided with a hydraulic servo valve means 26 and an arm segment 23' which is located between the joint 25 and the fixed point C is provided with another hydraulic servo valve means 27, both of which servo valve means 26 and 27 are for controlling the actions of the aforesaid hydraulic cylinders 18 and 19. These two servo valve means each has an actuator rod, and these two rods are in contact with the said arm segments 22' and 23' via levers 57' and 57, respectively, to actuate the said hydraulic cylinders 18 and 19, respectively.

These two servo valve means are each coupled to the two hydraulic cylinders by two oil pipes. To each servo valve means is coupled a pressurized oil supply pipe extending from a pressurized oil source not shown and also coupled thereto is an oil discharge pipe extending from a hydraulic cylinder. FIG. 11 shows a preferred example of such a servo valve means. These two servo valve means serve to control both the supply and discharge of a pressurized oil to and from the hydraulic cylinders 18 and 19, respectively, in association with the motion of the link arm segments 22' and 23', respectively. A spool 54 of each servo valve means is urged against the arm segments 22' or 23' by a spring 56 so that the spool 54 opens and closes the respective orifices of the valve means in accordance with the movement of these arm portions, to thereby control the supply and discharge of the pressurized oil to and from the hydraulic cylinders 18 or 19. It should be understood that the hydraulic circuitry as a whole including the two hydraulic cylinders 18 and 19 and the servo valve means 26 and 27 is known, and accordingly, the description of its details is omitted.

Means for setting the paths of travel of both the X-ray source 13 and the film holder 14 is shown in FIGS. 3 to 7. The said means for setting the travel paths is comprised of cam means which is generally indicated at 28. This cam means 28 comprises a plurality of sets of cams, each set being comprised of two cams having different cam face configurations, one 28x of each set being for controlling the movement of the said two members in the direction of the axis X, and the other cam 28y being for controlling their movements in the direction of the axis Y. These two cams 28x and 28y are rotatably mounted on a shaft 29. This cam means 28 -- in cooperation with the cam-selecting mechanism which will be described later and which is for selectively driving a required set of cams -- constitutes means for setting the travel paths of the said two members. Of these two cams forming one set, the cam 28y which controls the movement of the said two members in the direction of the axis Y is contacted by a roller 32 which, in turn, is rotatably supported on a shaft 31 on a frame which constitutes the arm segment 23'. On the other hand, the other cam 28x of the cams of a set is contacted by a roller 33 which, in turn, is rotatably supported on the arm segment 22'. With the aforesaid arrangement of the cam means, it will be understood that the rollers 32 and 33 are able to be displaced in accordance with the rotation of their corresponding cams, causing the rotation of the arm segments 22' and 23' so that the servo valve means 26 and 27 are actuated.

The details of the aforesaid cam selecting mechanism are shown in FIG. 7. Each set of two cams 28x and 28y is rotatably mounted on a boss 34 which, in turn, is fixed to the shaft 29. The arrangement is such that only the selected set of cams is directly coupled to the shaft 29 by a clutch mechanism which is provided for each set of cams, in such a way that these two cams 28x and 28y are adapted to be rotated simultaneously. More specifically, the aforesaid boss 34 is provided with an engaging groove 35 formed on the circumference thereof.

One cam 28y of the two cams is provided with a pawl member 37 which is pivotably attached thereto by a pin 36. This pawl member 37 is arranged on the cam so that it is engageable in the engaging groove 35 of the boss 34. This pawl member 37 normally is urged by a spring 38 to engage the said groove 35. In the rigid, fixed region close to each set of cams, there is provided a lever 40 which is rotatably supported on the said fixed region and which has an engaging end portion 41 adapted to engage the end portion of the pawl member 37 to act in such a fashion as to release the pawl member 37 from its engagement with the groove 35 against the force of the spring 38. The said lever 40 is rotated by a solenoid 42 and is adapted to be brought back to its normal position by a coil spring 43. Accordingly, when the solenoid 42 is energized, the pawl member 37 is relieved of its engagement with the end portion of the lever 40, and the pawl of the pawl member 37 is brought into engagement with the groove 35. As a result, the rotation of the shaft 29 is transmitted to the set of cams via the boss 34 and the pawl member 37, and thus, the said set of cams is rotated. Such a cam-selecting mechanism is provided for each set of cams as stated previously. By manipulating a selective switch not shown which is provided on the control panel not shown, a particular solenoid 42 is energized to control the required set of cams and to thereby actuate the hydraulic servo valve means.

A mechanism for controlling the velocity of revolution of the cams is provided on the shaft 29 which is intended to drive the cam means 28. As seen best in FIG. 8, the shaft 29 is rotatably supported on the base frame 1 and is rotated by a motor 45 (seen in FIG. 3). A cam 44 is fixed to the bottom of the shaft 29 and it is provided, on the periphery thereof, with two grooves 46 and 47. On the rigid fixed portion of the apparatus located close to this cam 44, or in other words on the base frame 1, there is arranged a lever 49 which, in turn, is rotatably supported on a pin 48. This lever 49 has a pawl 51 and is urged against the periphery of the cam 44 by a coil spring 50. In the normal state of the lever 49, the pawl 51 engages the groove 46 of the cam 44. A limit switch 52 which is controlled by the said lever 49 is provided to control the action of the motor 45 in the following manner. During the period in which the pawl 51 engages either one of the grooves 46 and 47, the said limit switch 52 is adapted to shut off the supply of current to the motor 45, and during the period in which the solenoid 53 is actuated or in other words during the period in which the pawl 51 engages neither one of the grooves 46 and 47, the limit switch 52 allows the current to be supplied to the motor 45 to set it in motion. More specifically, in the positions of these members shown in FIG. 8, the energization of the solenoid 53 will cause the pawl 51 to be disengaged from the groove 46 and, upon this disengagement, the limit switch 52 is actuated to drive the motor 45. Whereupon, the shaft 29 is rotated so that the cam 44 will be caused to rotate together with the cam means 28. During this part of operation, the pawl 51 of the lever 49 is in engagement with that portion of the cam 44 other than the grooves 46 and 47 or in other words the un-notched periphery portion of the cam 44. Accordingly, the limit switch 52 is closed so that the motor 45 is kept running. When, subsequently, the pawl 51 is received in the groove 47, the limit switch 53 is opened, so that the motor 45 is brought to a halt. With these members in the positions described the apparatus is ready for tomography. Subsequently, when the solenoid 53 is energized, the motor 45 is set into motion. When the cam 44 returns, as the motor 45 is rotated to its initial position, or in other words, when the pawl 51 is received in the groove 46, the rotation of the motor 45 is halted again.

A description will now be given of the shape of the cam means 28. In a tomographic apparatus utilizing X-rays, the X-ray tube moves through a wide range of paths from one position to another. Therefore, it would be reasonable to keep the X-ray tube at the most harmless position, i.e., at the retreated position, whenever the X-ray apparatus is not in use. Also, it will be understood that, in case the selection of the cam means is performed in the aforesaid manner, the rollers 32 and 33 must not contact the bulging peripheries of the faces of those cams not selected. Also, irrespective of the type of mechanism for selecting the cam means in addition to the aforesaid one, the arrangement must be such that any arbitrary set of cams may be selected as desired. Because of these reasons, the position of the X-ray tube when the apparatus is not in use, i.e., the retreated position of the X-ray tube, in the tomographic apparatus of the present invention, is set at either one of the four corners which are within the given range of movement of the X-ray tube. In order to accomplish this purpose, the positions of the cam means are arranged so that the rollers 32 and 33 will be in contact with the recessed portions of the cam faces whenever the X-ray tube is in its retreated position. Also, in case it is intended to take a tomogram by a rectilinear movement of the X-ray tube, arrangement is such that as shown in FIG. 9A, the X-ray tube will first move from its initial retreated position a over to the second position b at which it is ready for photography and which is located in the middle of the path in the direction of axis Y and also at the end on the axis X, and therefrom the X-ray tube will carry out a rectilinear travel to the third position c. X-ray irradiation will be given during the travel of the X-ray tube between the point b and the point c for the purpose of photography. Upon completion of photography by X-rays, the X-ray tube will be returned to its initial retreated position. More specifically, the X-ray tube will travel at a sufficiently accelerated velocity from the point b to the point b'. The irradiation of X-rays will be started at the point b' and will be stopped at point c' which is located this side of the point c. Upon the stopping of irradiation of X-rays, the X-ray tube will be moved at a progressively reduced velocity as it proceeds to the point c at which the movement of the tube will be stopped. Therefrom the X-ray tube will be brought back to its retreated position a. In order to accomplish the aforesaid movement of the X-ray tube, the cams are required to have cam faces with a specific shape. This shape of cam face is as shown in FIG. 9B. The shape is shown in the form in which it is developed in the rectilinear direction, which is obtained by using the retreated position as the reference point and by dividing the paths into the direction of axis X and the direction of axis Y, and by connecting the respective points of junction. More specifically, the movement of the X-ray tube from point a to point b is only in the direction of the axis Y and not the direction of axis X at all. Whereas, the movement from point b to point c represents no change in the direction of axis Y, but concerns strictly the axis X. From point c to the reference point a, on the other hand, the movement of the X-ray tube follows a path which represents a combination of the said two axes X and Y. In order to convert the aforesaid rectilinear patterns into circular cam face configuration, it is necessary that the distances between the respective adjacent points be converted to the distances of radii of the cams and that the respective ends of the radii be connected to produce a continuous face line of each cam in such a way that the starting point is in agreement with the ending point which represents the said retreated position.

Also, when it is intended to perform a tomography by causing an arcuate movement of the X-ray tube, the path of travel which is followed by the X-ray tube is arranged as shown in FIG. 10A. More specifically, the X-ray tube will move from its retreated position a to the position b ready for photography, and therefrom, in accordance with the instructions for photography, the speed of movement of the X-ray tube will be sufficiently accelerated during the part of path from point b to point c at which irradiation of X-rays is started while making an arcuate movement passing the points d, e and f in succession and returning to point c at which the irradiation is ceased. The X-ray tube will move from point c at a reduced velocity till it reaches point g at which it will stop for a small length of time, and then it will return to the initial retreated position a. In order to have the X-ray tube follow such a series of movements, the shapes of the cam faces of the two cams which form a set are shown in FIG. 10B in developed styles.

A description has been given of two instances, i.e., an instance where the X-ray tube is required to make a rectilinear movement, and another instance where the X-ray tube is required to make a circular movement. It will be understood clearly that, when it is intended to cause the X-ray tube to follow any other kind of path, such a path of travel is divided into a directional component of axis X and another directional component of axis Y and the positions of the X-ray tube at the respective points on the selected path are connected together and, thus, the required shapes of the two cam faces can be obtained.

The cam faces have been described with respect to the instances where the X-ray tube is given a motion at a constant speed during the period of tomography. However, in case it is intended to locally alter the velocity of travel of the X-ray tube during the course of the path to be followed, this can be accomplished as follows. With respect to that part of path where the travel velocity of the X-ray tube has to be increased, the corresponding portion of the cam face configuration will have a reduced length in relationship with the time axis. Conversely, for the part of path where the X-ray tube has to be moved slowly, the corresponding part of the cam face configuration will have a prolonged portion of face in relation to the time axis. In an extreme case where it is intended to halt the movement of the X-ray tube for a certain length of time, the corresponding portion of the cam face will have a constant length of radius. By arranging the cam faces in the aforesaid manner, there are obtained a set of cams having faces which cause the X-ray tube to travel through the predetermined respective sections of the path at different velocities while following the same predetermined path.

A description will hereinafter be given of the operation of the tomographic apparatus of the present invention having the foregoing arrangement. As shown in FIG. 2, the patient 54 or the object to be tomographed is laid on a bed 55. The bed 55 is moved in accordance with the position for photography of the required region of the patient's body. A film is loaded on the film holder 14. Then, one of the selective switches provided on the control panel is operated to select the particular set of cams for imparting to the X-ray source a movement optimum for taking a tomography of the said particular region of the object to be photographed. Whereupon, the specific one 42 of the solenoids which is assigned for the selection of the said particular set of cams is energized. As a result, the engaging end portion 41 of the lever 40 is relieved of its engagement with the pawl member 37. The pawl of the resulting pawl member 37 is then caused to engage the groove 35 of the boss 34. As the shaft 29 is rotated, the required set of cams is caused to rotate therewith. With the parts of the apparatus in this state, the photography preparing button not shown which is provided on the control panel is depressed. Whereupon, the solenoid 53 is energized to close the limit switch 52 to rotate the motor 45. Thus, the required set of cams is rotated. If the selected set of cams is for a rectilinear movement of the X-ray tube, the position at which the cams 28x and 28y for the axis X and for the axis Y are brought into contact with their mating rollers 32 and 33 will undergo a change in orientation in accordance with the curves shown in FIGS. 9A and 9B. More specifically, in the portion of the path between point a and point b, the direction of axis X will not undergo any change in orientation at all but only the direction of axis Y undergoes a change. The cam 28y which produces this change in the axis Y will push the roller 32 towards the right in FIG. 4. Since the bridge arm 21 remains stationary, at such a time, only the bridge arm 23 and the arm segment 23' have their positions changed into the angular positions with the joint 25 serving as the apex of this angle, in the manner as shown in solid lines in FIG. 5. On the other hand, the servo valve means 27 will supply a pressurized oil to the hydraulic cylinder 19. As a result, the linking mechanism which is comprised of the main link arms 5 and 6, the bridge arms 9, 10 and the auxiliary arms 11 and 12 is rotated clockwise about the shaft 2 in FIG. 1. This rotation of the linking mechanism causes the bridge arm 21 of the adjusting means, which is coupled to a fixed point (B) of the main link arm 5, to be pushed towards the right side in FIG. 4. Whereupon, the bridge arm 23 is rotated counter-clockwise about the axis 31 of the roller 32 as shown by broken line in FIG. 5 so as to bring the arm segment 23' to its initial position. As the linkage which is comprised of link members 5, 6, 9-12 is rotated up to the required position, the said arm segment 23' returns completely to its initial position, and the actuator rod of the servo valve means 27 also resumes its normal position, thereby suspending the supply of the pressurized oil to the hydraulic cylinder 19. The hydraulic cylinder 19 continues to be operative until the desired position of travel in the direction of the axis Y which is established by the cam 28y selected in the aforesaid manner comes into agreement with the current positions of both the film and the X-ray tube 13. Then, in accordance with the rotation of the cams, the linking mechanism which supports both the X-ray tube and the film holder 14 is caused to tilt in the direction of the axis Y. When the X-ray tube reaches point b shown in FIG. 9A, the pawl 51 of the lever 49 engages the groove 47 of the cam 44, so that the limit switch 52 is opened to stop the rotation of the motor 45, and with this the preparation for photography is completed.

After confirming the conditions of photography, the exposure button, not shown, which is provided on the control panel is depressed. Whereupon the solenoid 53 is energized to set the lever 49 into motion. As result, the limit switch 52 is actuated to rotate the motor 45, followed by the revolution of the selected cam means. Since the photography is performed during the course of travel of the X-ray tube between point b and point c in FIG. 9A, the face of the cam 28y which is assigned for the control of direction of the axis Y undergoes no change in terms of its radius, whereas only the cam 28x which controls the axis Y exhibits rectilinear changes in its radius during the said portion of path. As a result, the roller 33 is pushed so that the bridge arm 22 and the arm segment 22' will be at an angle, causing the servo valve means 26 to be actuated. Accordingly, a pressurized oil is supplied to the hydraulic cylinder 18, so that the linkage which is formed by link members 5, 6, 9-12 is rotated clockwise about the pins 7 and 8 serving as the fulcrums in FIG. 2. As a consequence, the X-ray tube 13 is moved clockwise. As the cam 28x rotates progressively, the X-ray tube 13 is moved farther. During the predetermined portion of path of its travel, X-rays are emitted from the tube 13 so that the photograph by X-rays is produced.

At the point c in FIG. 9A representing the final position of movement of the X-ray tube in the course of photography, the inclination of the face of the cam 28x for controlling the axis X becomes opposite to the angle of the inclination of the face of the cam 28y for controlling the axis Y. Therefore, the bridge arm 22 as well as the arm segment 22' will undergo a change in their positions in a direction opposite to the direction assumed by them in that part of operation described previously. Because of the change in positions of these link members, the servo valve means 26 and 27 are, at this time, actuated simultaneously to pull back the actuator rods of the hydraulic cylinders 18 and 19 so as to actuate the said linkage -- which is comprised of link members 5, 6, 9-12 -- to bring the X-ray tube 13 to its retreated position. During this part of the operation, it should be noted that the amount or angle of inclination of the cam shape is arranged different for the cam for controlling the axis X than for the cam for controlling the axis Y, and that, therefore, the component of movement in the direction of the axis X of the X-ray tube is different from the component of movement in the direction of the axis Y in proportion to the respective different angles of facial inclination of these two cams 28x and 28y. When the cam means returns to the initial position, the pawl 51 of the lever 49 plunges into the groove 46 of the cam 44. As a result, the limit switch 52 is opened to halt the rotation of the motor 45, followed by the stopping the driving of the cam means. As a result, the X-ray tube 13 returns to its retreated position at which the apparatus is prepared for the next photography.

If the selected set of cams is assigned for imparting to the X-ray tube a circular movement, the depression of the button indicated as "preparation" not shown will cause the X-ray tube to move from its retreated position to the preparatory position. Upon subsequent depression of the exposure button, the set of cams will control the servo valve means 26 and 27 so that the X-ray tube will make the required circular movement. Along with this, the hydraulic cylinders 18 and 19 will be actuated in accordance with the revolutions of the cams for controlling the axis X and the axis Y to give the X-ray tube the desired circular movement. Upon completion of this circular movement of the X-ray tube 13, this X-ray tube is returned to its initial retreated position. When it is intended to have the X-ray tube follow a path different from any one of the paths stated above, such a desire can be accomplished by selecting a set of cams having cam faces corresponding to such a path. The operation and actions of the members for such an operation will be easily understood by reading the description dealing with FIGS. 9A and 9B and also from FIGS. 10A and 10B.

The kinds of paths of travel of both the X-ray tube and the film which are available include straight line, large circle, small circle, oval, hypocycloid, spiral and any other desired patterns. Any one of these kinds of travel paths can be obtained by merely selecting or replacing the cam means.

When the X-ray tube and the film are moved by following the paths selected from one of these kinds of courses and when a beam of X-rays is irradiated during the travel of these two members on the said paths, there is focused -- on the film -- only the image in the plane of the tomogram of the object which is parallel with the film face and which includes the point A located on the straight line connecting the focus of the beam from the X-ray tube 13 and the center of the film, whereas the images of the regions of the object located above and below the plane of tomogram and not required to be photographed will be in a path which is similar to that of the movement of the X-ray tube and will appear on the film as blurred images so that they can be ruled out easily. During the travel of the X-ray tube, by locally increasing the velocity of movement of the X-ray tube for those unnecessary regions of the body of the object where the path of travel of the X-ray tube becomes parallel with such regions, i.e., by increasing the said velocity so that it will be greater than the velocity for the remaining region which is required for the photography, so as to control the amount of X-rays per unit time for the non-required regions so that it is smaller than for the required region, it is possible to obtain a tomogram where the images of those non-required regions has a much reduced density and, therefore, such blurred images can be ruled out more satisfactorily.

As has been stated above, according to the present invention, complicated or any specific paths of travel of the X-ray tube which cannot be obtained according to the known tomographic apparatuses can be very easily obtained, simply by the provision of cams having cam faces corresponding to such paths. Therefore, it is possible to give the X-ray tube the optimum path of travel for the photograph of any required region of the object, and also to obtain a clear tomogram wherein the images of those un-required regions are satisfactorily blurred so as to be easily ruled out. Also, in any part of the path of travel of the X-ray tube, it is possible to move, as desired, the X-ray tube and the film at any specific different velocities by a mere shaping of the faces of the cam means. This allows the apparatus of the present invention to produce the same effect as that produced by the selective irradiation method of the prior art which requires complicated apparatus structure and complicated operations, merely by the selection of a required set of cams. As stated above, the tomographic apparatus of the present invention having a simplified structure can be used for photographic conditions over a wide range, and yet such use can be effected easily and positively by an operator having little technical training in this field, in view of the fact that any desired photographic program can be established by the mere selection of the required set of cams.

The example which has been described and shown in the drawings employs a hydraulic servo mechanism for the control of movements of both the X-ray tube and the film. It should be understood by those skilled in the art that this servo mechanism can be replaced by any known electrical or electronic control mechanism or by a pneumatic servo mechanism to obtain the same effect. It should be understood also that the present invention is not restricted to the said example, but that many other changes and modifications may be made without departing from the spirit of the present invention. Furthermore, various applications having all of the features of the present invention are possible also. It should be understood , therefore, that such changes, modifications and applications are equivalent to what is stated in the appended claims and are all included within the scope of these claims.

Claims

We claim:

1. A tomographic apparatus for taking X-ray tomographs, comprising:

link means having supports thereof for supporting an X-ray source and a film so as to directly oppose each other along a line through an image point between them;

a base frame on which said link means is mounted with the mounting point in a position in a plane containing said image point for swinging movement for moving said supports in the directions of an axis X and an axis Y;

two servo motors on said base frame and coupled to said link means for moving the said link means in the swinging movement;

travel path setting means comprising at least one set of cams including a first cam for setting positions corresponding to positions on axis X and a second cam for setting positions corresponding to positions on axis Y on the paths of travel to be followed by the said X-ray source support and said film support, a rotatable cam shaft, a coupling mechanism for each set of cams for selectively coupling the cams of the set to said cam shaft, cam drive means coupled to said shaft, and cam followers engageable with said cams, respectively;

servo motor control means coupled to said servo motor means for controlling the operation of said servo motor means, and follow up means on which said cam followers are mounted and coupled to said servo motor control means for transmitting the motion of said cam followers during the course of their displacement to the control means for operating the servo motors to move the link means to the desired positions so that the paths which are to be followed by the X-ray source support and the film support in the directions of the axes X and Y are according to said travel path setting means, said follow up means being coupled to said link means for moving said cams and for actuating said control means in response to the movement of said link means for causing the control means to stop the operation of said servo motors when the desired movements of said link means have been completed;

whereby the X-ray source support and the film support are cause to follow the paths according to the travel path setting means.

2. A tomographic apparatus according to claim 1, in which there are a plurality of sets of cams, and said apparatus further comprises means for selectively activating the coupling mechanism for the respective sets of cams corresponding to the desired paths of travel of the X-ray source and the film, whereby only the set of cams corresponding to the desired path of travel is coupled to the base frame for the rotation of the said cams, whereby both the X-ray source and the film are moved to follow the desired paths of travel during the irradiation of X-rays by a mere selection of the appropriate set of cams.

3. A tomographic apparatus according to claim 2, in which the said cam means comprises means for controlling the rotation of the said cam shaft for rotating the selected set of cams so that both the X-ray source support and the film support are moved along the desired path from retreated positions relative to the object to be photographed to positions for starting the photography and that thereafter said supports are returned to their initial retreated positions via the positions at which the exposure of film is completed.

4. A tomographic apparatus according to claim 1, in which the said set of cams have cam faces having contour for causing an increase in velocity of travel of the x-ray source and the film during the course of the travel path of the X-ray source corresponding to regions of the object which it is not desired to photograph, said velocity being in excess of the velocity of movement of the X-ray source along the portions of the said path corresponding to the region to be photographed.

5. A tomographic apparatus according to claim 1, in which: the said link means comprises:

a pantograph constituted by a parallellogram linkage having a first link arm and a second link arm, a rotatable shaft on which both link arms are pivotably mounted, said shaft being rotatably supported horizontally on the base frame, a first bridge arm and a second bridge arm connected between the ends of said link arms and located on opposite sides of said rotatable shaft in parallel relationship therewith, and another parallelogram linkage comprised of a link arm extension on the first link arm, a bride arm extension on the bridge arm which is adjacent to the first extension, a first auxiliary arm pivotably coupled at one end to the said link arm extension and a second auxiliary arm pivotably coupled at one end to the link arm extension and at the other end to said first auxiliary arm, said auxiliary arms being parallel with the link arm extension and the bridge arm extension respectively,

the said X-ray source support being secured to the said second auxiliary arm;

an extension on the other bridge arm and said film holder being supported normally horizontally thereon;

one of said servo motors being coupled to one of the said link arms and to said rotatable shaft at a point between said two link arms and the other servo motor being coupled to one of the said link arms and to the said base frame between said two link arms, to thereby cause the said link means to move in the directions of both axes X and Y to move both the X-ray source and the film along the desired travel paths.

6. A tomographic apparatus according to claim 1, in which said follow up means comprises:

a follow up parallelogram linkage having one corner pivotably coupled to a point on the said link means and the diagonally opposite corner pivotably coupled to a fixed point on the base frame so that the movement of the said link means for moving the supports in the directions of the axes X and Y is transmitted to said follow up parallelogram linkage,

two adjacent arms of said follow up parallelogram linkage adjacent said fixed point having joints therein dividing the arms into segments, said cam followers being mounted on the segments of said two arms which are connected to the other links of said follow up linkage, the other segments of the two arms engaging said servo motor control means for transmitting the motion of said cam followers thereto.

7. A tomographic apparatus according to claim 6, in which the said servo motor means are comprised of hydraulically operated cylinders and the said control elements are comprised of servo valve means.