MEDICAL X-RAY APPARATUS SUITABLE FOR THE FORMATION OF TOMOGRAPHIC IMAGES

Abstract: A conventional medical X-ray apparatus, provided with a circular support (4) for the X-ray source (10) and the X-ray image intensifier (12), is arranged to enable coupling of a reciprocating rotary motion of the support (4) to a linear reciprocating motion (14) of the support (4) relative to the patient table (8). The combination of this linear motion to the reciprocating rotation enables the imaging of the plane other than the plane containing the axis of rotation. The choice of the stroke of the reciprocating motion defines the location of the plane to be imaged. Two mutually perpendicualr rotations in combination with two mutually perpendicular translations are also feasible.

Description: Medical X-ray apparatus suitable for the formation of tomographic images. The invention relates to a medical X-ray apparatus, including: a patient table, * an X-ray source and an X-ray detector, a support which is situated in a support plane and supports the X-ray source at a first end and the X-ray detector at a second end, said support being rotatable about an axis extending perpendicularly to the support plane as well as about an axis situated in the support plane, * means for performing a translatory movement of the support and the patient table relative to one another in a plane in which the connecting line between the X-ray source and the X-ray detector is situated. An apparatus of this kind is known from United States Patent 4,481,656. The apparatus disclosed therein is an X-ray examination apparatus provided with a column with an arc-shaped support for an X-ray tube and an X-ray detector in the form of an X-ray image intensifier. The arc-shaped support is a segment of a plane circle, which segment is secured in a holder so that it can rotate about an axis which extends perpendicularly to the support plane and through the center of the circle. The X-ray source is mounted at one end of the segment of circle and the X-ray detector is mounted at the other end. The holder is mounted on a shaft which is situated in the support plane, so that the segment of circle can rotate about said shaft; in other words the plane of the segment of circle can thus pivot about said shaft. The column is capable of performing a translatory motion in the direction of the shaft on which the holder is mounted, so that the support and the patient table can perform a translatory motion relative to one another in a plane in which the connecting line between the X-ray source and the X-ray detector is situated. In order to form an X-ray image, the patient to be examined can be arranged between the X-ray tube and the X-ray image intensifier by means of a patient table which occupies a fixed position within the examination room. The combination consisting of the X-ray source and the X-ray image intensifier can be displaced in a variety of directions in order to reach the correct orientation and position of the patient relative to the X-ray tube and the X-ray image intensifier. The known apparatus has been designed for making conventional X-ray irradiation images, i.e. the facing X-ray source and X-ray detector are placed in an orientation and position such that the requirements of the user of the apparatus in respect of the direction of view and magnification of the X-ray image are satisfied. Once the desired orientation and position have been adjusted, an image is formed, or the observation desired for medical purposes is executed, while the X-ray source and the X-ray detector are in a stationary state. This type of apparatus is generally known for the formation of conventional X-ray irradiation images. The apparatus described in the cited United Patent 4,481,656 enables a translatory motion of the support and the patient table relative to one another in a plane in which the connecting line between the X-ray source and the X-ray detector is situated (notably a translatory motion and a rotary motion about an axis situated in the support plane) for correct adjustment of the orientation and position of the X-ray source and the X-ray detector relative to the patient as specified by the user. However, such apparatus has not been designed for the formation of so-called tomographic images, i.e. images where the source and the detector move in a specified manner relative to the patient during the exposure, a region to be observed (in the form of a slice of comparatively small thickness) being continuously exposed during this motion. It is an object of the invention to provide a medical X-ray apparatus of the kind set forth which is suitable for forming tomographic images in addition to the conventional X-ray irradiation images. To achieve this, the medical X-ray apparatus according to the invention is characterized in that it includes adjustable coupling means for adjustably coupling the rotation of the support to said translatory motion. A tomographic image can then be formed by pivoting the support to and fro in an oscillating fashion (so that the X-ray source and the X-ray detector perform a respective circular motion in, for example a vertical plane through the longitudinal axis of the patient) while, coupled to this motion, the support and the patient table perform a sliding motion relative to one another (i.e. the support and the patient table perform a translatory motion relative to one another in a plane in which the connecting line between the X-ray source and the X-ray detector is situated). The amplitude of the reciprocating translation defines the plane in which the point on the connecting line between the X-ray source and the X-ray detector which does not move relative to the patient is situated. The slice to be reproduced in the tomographic image can thus be selected by suitably choosing said amplitude. The X-ray detector in conventional apparatus for forming X-ray irradiation images is situated at a small distance from the patient for a number of reasons: 1. The occurrence of scattered radiation between the patient and the X-ray detector is to be minimized. At the lower side of the patient table the problem of scattered radiation is mitigated in that a shield is provided at that area or in that the attending staff wears a protective apron. 2. The magnification of the object (the tissue structure to be imaged) to the X-ray detector preferably equals one. Post-magnification, if desired, is performed by means of the television monitor customarily used in this equipment, so that the adjusted magnification is always accurately known and can be readily changed, if desired. 3. The X-ray source can now be arranged at an ample distance from the patient so that so-called X-ray hot spots on the body of the patient are avoided. 4. It is undesirable to move the patient to and fro between the formation of a conventional X-ray irradiation image and a subsequent tomographic image. 5. During the formation of a conventional X-ray irradiation image, movement of the tissue structure to be imaged is to be avoided on the monitor screen upon rotation or pivoting of the support. Therefore, the X-ray detector/patient must be situated at the center of the (circular) support and the axis of the support, situated in the support plane, must also pass through this center. One consequence of the combination of the above points 1 and 5 is that a small distance exists between the axis of the support, situated in the support plane, and the lower side of the X-ray detector in the case of conventional X-ray irradiation imaging. This small distance is undesirable in the case of tomographic imaging, because the motion of the support is autonomous during such tomographic imaging and hence a safety clearance should remain between the upper side of the patient and the lower side of the X-ray detector. (There is only provided a collision protection which, upon activation, stops the entire motion and interrupts the exposure procedure; the patient has then been exposed to an X-ray dose without an actual diagnostic or therapeutic treatment having taken place. This is an undesirable situition.) For the above reasons it is undesirable to arrange the X-ray detector at an arbitrary height above the patient. As has already been stated, however, the point on the connecting line between the X-ray source and the X-ray detector which is stationary during the tomographic motion should be situated at a desired height during the formation of a tomographic image. This is made possible by the steps of the invention. The adjustable coupling means in a further embodiment of the invention are arranged for adjustably coupling said rotation of the support in a first plane to said translatory motion, simultaneously with the adjustable coupling of a rotation of the support in a second plane, perpendicular to the first plane, to a second translatory motion perpendicular to said first translatory motion. These steps allow the support to perform a motion such that the X-ray source as well as the X-ray detector performs a circular or elliptical motion so that the connecting line between the X-ray source and the X-ray detector describes a surface of cone. The apex of the cone is then the desired stationary point. In a preferred embodiment of the invention the support is arranged to perform the translatory motion relative to the stationary patient table. When the support is made to perform the rotary as well as the reciprocating motion, the patient can remain stationary during the treatment, so that he or she is not burdened by to the motion (which is particularly important in the case of serious trauma patients) and tissues to be imaged (notably in organs) are not shaken during the formation of the image so that the imaging sharpness is not affected. The invention will be described in detail hereinafter with reference to the Figures. Therein: Fig. 1 is a perspective view of a medical X-ray apparatus according to the invention; Fig. 2 is a diagrammatic front view of the support so as to illustrate the motion to be performed by the X-ray source and the X-ray detector during tomographic imaging according to the invention; Fig. 3 shows a block diagram of a control unit for implementing a coupling between a rotary motion and a translatory motion according to the invention. Fig. 1 is a perspective view of a medical X-ray apparatus according to the invention installed in a medical treatment room. The apparatus is formed as an assembly consisting of a stand 2, a support 4 which supports an X-ray source 10 at one end and an X- ray detector in the form of an X-ray image intensifier 12 at its other end, and a patient table 8 which is connected to the stand via a supporting arm 6 and serves to accommodate the patient to be treated. In this case the support 4 is formed by a circular C-arc. The C-arc 4 is mounted on a carriage 14 which is displaceable in the longitudinal direction (in the direction of the arrow 5 shown at the carriage) . The C-arc is thus displaceable on the stand 2 via a trackway 16, said displacement being driven by means of a separate drive motor which is not shown in the Figure. Furthermore, the C-arc is rotatable in its own plane, being the support plane, via a trackway 20 which itself is also about a shaft 7 which extends according to a center line of the C-arc. (The physical shaft is not shown in this Figure, because it is situated inside the stand; for the sake of clarity this shaft is diagrammatically denoted by a dash-dot line 7) . Each of the two rotations described above is driven by a respective drive motor which is not shown in the Figure. The displacement of the X-ray source 10 and the X-ray image intensifier 12, associated with the rotation about the shaft 7, is denoted by the arrows 11 and 13, respectively, in the Figure. The X-ray tube and the X-ray image intensifier can thus be adjusted in such a manner that the patient to be treated can be irradiated in all desired directions and from all desired positions. The patient table 8 can be adjusted to the desired height by means of a vertical trackway 18 on which the supporting arm 6 can move up and down. A connecting line 9 is shown between the X-ray image intensifier and the X-ray source. This imaginary line is the centre line of the X-ray beam irradiating the patient. This line extends from the location in the X-ray source 10 in which the X-rays arise, being the X-ray focus, to the center of the detection surface of the X-ray image intensifier 12. Fig. 2 is a diagrammatic front view of the support 4 in order to illustrate motions to be performed by the X-ray source 10 and the X-ray image intensifier 12 during tomographic imaging according to the invention. In this Figure the support 4 pivots about the shaft 7; the support is shown in three positions 4a, 4b and 4c. The X-ray source 10 and the X-ray image intensifier 12 are also shown in three positions, i.e. 10a, 10b, 10c, and 12a, 12b, 12c, respectively. An X-ray beam 26 emanating from the X-ray source 10 in each of the three positions is denoted by a central ray 9 (the connecting line between the X-ray source 10 and the X-ray image intensifier 12). When the support 4 pivots about the shaft 7, as shown in Fig. 2, the X- ray source 10 and the X-ray image intensifier 12 follow a trajectory as denoted by the arrows 11 and 13, respectively. If the patient table were to stand still during these motions (which is the most desirable situation) and if, moreover, the support 4 were not to perform a reciprocating motion, the point of intersection of the connecting lines 9a, 9b and 9c would be situated in the prolongation of the shaft 7. Therefore, in the case shown in Fig. 2 a plane situated outside the body of the patient would be imaged. The position of said point of intersection is moved downwards by appropriately coupling the pivoting motion of the support 4 (denoted by the arrows 11 and 13) to a reciprocating motion of this support (denoted by the arrows 14). The stroke of the motion 14 should be adjustable so as to enable adjustment of the location of the slice to be imaged (i.e. the set of points of intersection). The coupling of the rotary motions 11 and 13 to the translatory motions 14 can be implemented by way of a processor-controlled motion. Fig. 3 illustrates this procedure in the form of a block diagram. A microprocessor 30 is connected to a memory unit 34 via a data and address bus 32. Via a second bus 36, the microprocessor 30 is also connected to an interface circuit 38. The interface circuit constitutes the connection between the microprocessor 30 on the one side and the environment on the other side. The latter connections extend via n individual conductors 40-1 to 4-n, generally 40-i. The connection between the control unit formed by the microprocessor 30, the memory unit 24 and the interface circuit 38 and the drive motor of the carriage 14 and that of the support 4 is implemented via a number of connections 40-i. Furthermore, the variables to be adjusted (for example, the stroke of the translatory motion and the nature of the motions, such as plane or conical) can be applied to the microprocessor via these connections. For a given type of motion (for example, singular pivoting 11, 13 of the support 14 and associated singular translation 14) and a slice desired and hence adjusted by the user, the microprocessor 30 can provide the orientation of the support 4 as well as the associated current translatory position of the support during the execution of the exposure. The processor can do so by calculation on the basis of an algorithm which couples the position of the slice to be imaged to the stroke of the translation. It is alternatively possible to store control data for the current position in the form of a look-up table in the memory 34. An intermediate mode is also possible, i.e. storage of the control data for a limited number of points and calculation of the control data for intermediate points by interpolation. It is alternatively possible to realize the rotary motion of the support 4 so as to be independent; in that case the rotary position of the support is continuously measured and the microprocessor continuously determines the current associated translatory position in conformity with one of the above methods. It is to be noted that rotation is possible not only about the shaft 7, but also about an axis extending perpendicularly to the plane of the support 4, i.e. rotation of the support 4 by the trackway 20. In that case the associated reciprocating translatory motion must be performed in a direction parallel to the shaft 7. To this end, the shaft 7 may be constructed so as to be displaceable in its longitudinal direction, i.e. the shaft 7 must be slid into and out of the carriage 14 while performing this motion. This possibility of motion is not shown in the Figures, but will be evident to those skilled in the art. It is also very well possible to combine the above two rotations. The X- ray image intensifier 12 and the X-ray source 10 then perform a respective circular or elliptical motion, the reciprocating motion also taking place in two mutually perpendicular directions, i.e. in a direction extending parallel to the shaft 7 and a direction extending perpendicularly thereto in a horizontal plane. Finally, it is also possible to rotate the C-arc by means of the trackway 20 in such a manner that the connecting line 9 between the X-ray source 10 and the X-ray image intensifier 12 extends horizontally, parallel to the shaft 7. In order to execute the coupled translatory motion, the shaft 7 should then be displaceable in the vertical direction or it will be necessary to move the patient table 8 up and down.

Claims: CLAIMS: 1. A medical X-ray apparatus, including: * a patient table (8), * an X-ray source (10) and an X-ray detector (12), * a support (4) which is situated in a support plane and supports the X-ray source (10) at a first end and the X-ray detector (12) at a second end, said support (4) being rotatable about an axis extending perpendicularly to the support plane as well as about an axis (7) situated in the support plane, * means (14, 16) for performing a translatory motion (5) of the support (4) and the patient table (8) relative to one another in a plane in which the connecting line (9) between the X-ray source (10) and the X-ray detector (12) is situated, characterized in that the apparatus includes adjustable coupling means (30, 34, 38) for adjustably coupling the rotation of the support (4) to said translatory motion (5). 2. An X-ray apparatus as claimed in Claim 1, in which the adjustable coupling means (30, 34, 38) are arranged for adjustably coupling said rotation of the support (4) in a first plane to said translatory motion, simultaneously with the adjustable coupling of a rotation of the support (4) in a second plane, perpendicular to the first plane, to a second translatory motion perpendicular to the first translatory motion. 3. An X-ray apparatus as claimed in Claim 1 or 2, in which the support (4) is arranged to perform the translatory motion (5) relative to the stationary patient table (8).

Inventors: VAN DER ENDE ADRIANUS, VAN DER ENDE, ADRIANUS
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1997
Main classification: A61B6
IPC codes: A61B6