in the apparatus shown in fig1 a rotating frame 2 is mounted on a frame member 1 for rotating about an axis 4 which substantially coincides with the longitudinal axis of a subject 3 to be examined . an x - ray tube 5 and a radiation measuring arrangement 6 are mounted on the rotating frame 2 . the x - ray tube 5 is fixed to the rotating frame 2 , whereas the measuring arrangement 6 is arranged on a rail 9 for linear movement perpendicularly of the central ray of the x - ray tube 5 and the axis of rotation 4 . the rotating frame 2 is rotated about the axis 4 by a drive system 10 . another drive system 11 produces the linear scanning movement of the measuring arrangement 6 by means of a cable 12 . a box - shaped ( or cuboid ) compensating element 13 , of a strong plastics material equivalent to body tissue in its density , for example acrylic glass , is also fixedly connected to the rotating frame 2 . this compensating body 13 comprises , symmetrically to the axis of rotation 4 , a cylindrical recess into which a form - body in the shape of a ring 14 , which also consists of a strong plastics material equivalent to body tissue in its density , is slidingly inserted in a form locking manner . a contouring member 15 of an elastic material is attached to the inside of the ring 14 . this contouring member 15 can be filled with water by means of a pump ( not shown ) so that under selectable pressure it will fit firmly against the outside of the photographic subject , which may be the head of a patient , for example . the ring 14 is fixedly connected to a supporting table 17 by means of a bracket or plate 16 so that , despite the rotational movement of the compensating element 13 , no torque is applied to the photographic subject 3 resting on the supporting table 17 . the x - ray tube 5 is connected to an x - ray generator 18 which supplies it with constant electrical voltage of selectable magnitude . the radiation receiver 6 is connected via a circuit arrangement or measurand converter 19 to a computer 20 which delivers the data computed by it to a page printer 21 and / or to a data display unit 22 for documentation and / or visual evaluation . the drive system 10 for the circular movement and 11 for the linear movement are connected to a control device 23 which controls the two movements in accordance with a principle of motion to be explained hereinafter . the x - ray tube 5 is fixedly arranged on the rotating frame 2 and comprises a primary diaphragm 24 which is fixedly arranged in relation to the x - ray tube 5 and which determines the beam ( or aperture ) angle of the issuing x - rays in accordance with the scanning range of the measuring arrangement 6 . preceding the opening accommodating the photographic subject 3 with respect to the radiation direction is a diaphragm 25 which is displaceable parallel to the path of the measuring arrangement 6 and which is attached to a cable 26 by means of a supporting bar 7 . the cable 26 is moved by a drive system 27 including an adjustment motor 27a , the drive system 27 also being connected to the drive control device 23 . the diaphragm 25 has a narrow slit 28 which transmits a part of the x - radiation issuing from the x - ray tube 5 which is condensed by the primary diaphragm 24 . the x - ray beam allowed through by the slit 28 is used for penetrating the photographic subject 3 , and its cross - sectional spread perpendicularly of the layer under examination is equal to the thickness of that layer . parallel to this layer , the extent of the beam transmitted by primary diaphragm 24 is substantially equal to or less than the thickness of the layer . after the apparatus has been switched on , the drive control 23 initially actuates the drive system 10 which moves the rotating frame 2 into a starting position offset through 90 ° relative to the position illustrated . once this position has been reached , scanning of the object 3 to be examined begins with the drive systems 11 and 27 putting the measuring arrangement 6 and the diaphragm 25 into a linear scanning movement , during which the desired transversal layer of subject 3 is penetrated and scanned with the aid of the x - rays which have been condensed into a narrow beam by means of the diaphragm 25 . the linear scanning of parts 6 , 24 and 25 is shown in fig2 . during a scanning movement , the diaphragm 25 and the measuring arrangement 6 are displaced in the direction of the arrows 29 and 30 in such a way that , during its displacement , the measuring arrangement 6 is struck in each position by the x - ray beam which is defined by the aperture 28 of diaphragm 25 . the synchronous displacement of the components 6 and 25 is ensured by the control device 23 by way of the drive motors 11a , 27a , fig1 . a further position of the beam 31 and measuring arrangement 6 is indicated by dash lines at 31 &# 39 ; and 6 &# 39 ; in fig2 . the radiation which has penetrated the photographic subject 3 is measured by the measuring arrangement 6 and the measured values are fed by the circuit arrangement 19 into the computer 20 where they are initially stored . during each scanning movement , the output of the measuring arrangement 6 is probed ( or sampled ) by the circuit arrangement 19 in such a way that , during this movement , approximately 100 individual values are determined and fed into the computer 20 . on completion of the first scanning movement , the control device 23 actuates the drive system 10 which rotates the rotating frame 2 through an angle of , for example , 2 °. thereafter , the control device 23 again sets the drive systems 11 and 27 in motion in a direction opposite to the instance described above , so that a second linear scanning movement can take place . on completion of this second scanning movement , the control device 23 switches the drive system 10 on again so that the rotating frame 2 again rotates through an angle of about 2 °. thereafter the control device 23 reactivates the drive systems 11 and 27 so that a third scan can be carried out . this operation is repeated , for example , 90 times . during these scanning movements , the computer 20 computes an image of the penetrated layer on the basis of the measured values fed into it . this image appears either in digital form on the page printer 21 or on the data display unit 22 . fig3 illustrates a plan view of the photographic subject 3 . by way of example , the examined body layer 30 is illustrated . this body layer is scanned by an x - ray beam 31 which is condensed by means of diaphragm 25 ; namely through its slit 28 . in the example , the x - ray beam has an approximately circular cross - section whose diameter is equal to the thickness of layer 30 . however , it is also possible within the framework of the invention to limit ( or define ) the x - ray beam in such a manner that its cross - sectional spread , perpendicular to layer 30 , is equal to the thickness of this layer , and that , parallel to layer 30 , it is less than the layer thickness . it will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts and teachings of the present invention .
in an illustrated embodiment linear scanning of a narrow x - ray beam is produced by linear movement of an apertured diaphragm interposed between the x - ray source and the patient receiving space , a measuring arrangement being linearly moved in step with the diaphragm aperture so as to provide a desired number of samples such as one hundred , for each angular position of the components . in the illustrated embodiment a primary diaphragm is interposed between the x - ray source and the linearly movable diaphragm and serves to determine the beam angle in accordance with the scanning range of the measuring arrangement .