Patent Number: 054066115
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows a radiation apparatus in which the gating device disclosed herein can be used that, for example, is in the form of a computer tomography apparatus. In this radiation apparatus, an X-ray radiator 1 transmits an x-ray beam 2 to a radiation detector 3 that is arcuately fashioned and comprises individual detector elements adjoining one another. For gating the beam 2, a slotted diaphragm 4 is provided in the region of the X-ray radiator 1. A pre-diaphragm 5, a first diaphragm 6 and a second diaphragm 7 immediately in front of the radiation detector 3 for setting the slice widths are provided over the course of the further beam path. In this radiation apparatus, the aforementioned arrangement rotates around a measurement field 8 in which an examination subject can be disposed. Dependent on the radiation penetrating through the examination subject, signals corresponding to the radiation intensity incident on the individual detectors are obtained at the respective outputs of the individual detectors. These signals are supplied to an image processor 50 whose output signals can be portrayed on a monitor 51 as an image of the examination subject. FIG. 2 shows a gating device 9 of the invention in plan view for gating radiation from a radiation source, for example, the x-ray radiator 1. This gating device 9 has first and second diaphragm plates 10 and 11 having respective longitudinal axes 12 and 13 aligned parallel to one another, so that the first and second diaphragm plates 10 and 11 form a slot-shaped opening 14. Each diaphragm plate 10 and 11 has at least one guide. In the embodiment of FIG. 2, the plates 10 and 11 each have two guides, referenced 15 and 16, and 17 and 18. In the exemplary embodiment, the guides 15 and 16 parallel to one another and are disposed obliquely relative to the longitudinal axis 12 as are the guides 17 and 18 relative to the longitudinal axis 13. The guides 15 and 16 are respectively formed by recesses 19 and 20 in the diaphragm plate 10 and first and second pin 23, 24 and 25, 26 respective engaging into the recesses 19 and 20. Similarly, the guides 17 and 18 are respectively formed by recesses 21 and 22 in the diaphragm plate 11 into which first and second pins 27, 28 and 29, 30 extend. The diaphragm plates 10 and 11 can be adjusted especially easily at their guides 15, 16, 17 and 18 when the pins 23-30 are provided with a bearing implemented as, for example, a rolling bearing, whereby the bearing of each first pin 23, 25, 27 and 29 engages a long side of its recess 19, 20, 21, or 22 and the bearing of each second pin 24, 26, 28 and 30 engages the opposite long side of the same recess 19, 20, 21 or 22. The bearings can operate without play if eccentrically mounted on the pins 23-30. Within the context of the invention, the guides 15, 16, 17 and 18 can, of course, each be executed with only one pin, but are then less precise. The pins 23-30 are part of the housing 49 of the device 9. Longitudinal movement of the first and second diaphragm plates 10 and 11 thus also causes the plates 10 and 11 to move in a direction perpendicular to their longitudinal axes 12 and 13 to make the slot-shaped opening 14 is larger or smaller. Such movement ensues with an adjustment mechanism 31. This adjustment mechanism 31 includes a threaded spindle 32 rotatable in a threaded bore or bushing of a carriage 35 movable on rails 33 and 34. One end of each of first and second articulations 36 and 37 is pivotally attached at the carriage 35; the other ends thereof are respectively connected to the first and second diaphragms plates 10 and 11. In the illustrated position, the diaphragm plates 10 and 11 are in a position in which a medium-sized slot-shaped opening 14 is established. When the slot-shaped opening 14 is to be enlarged, the spindle 32 is rotated around its longitudinal axis so that the carriage 35 is displaced toward the left in the plane of the drawing. The diaphragm plates 10 and 11 are thereby adjusted by the guides 15, 16, 17 and 18 via the first and second articulations 36 and 37, as a result of which the spacing between the diaphragm plates 10 and 11 increases. The diaphragm plates 10 and 11 are thereby preferably adjusted simultaneously and symmetrically relative to the central longitudinal axis of the radiation receiver. Within the context of the invention, however, one diaphragm plate can be stationary, while the other diaphragm plate is adjustable for varying the slot-shaped opening 14. It is also possible that the guides of diaphragm plates arranged opposite one another exhibit a different pitch, so that the diaphragm plates are asymmetrically adjustable relative to the central longitudinal axis of the radiation receiver 3. Dependent on the angle that the guides 15, 16, 17 and 18 describe relative to the longitudinal axes 12 and 13 and dependent on their lengths, the maximum spacing between the diaphragm plates 10 and 11 which can be achieved can be predetermined. If the angle becomes obtuse, then a high exertion of force is required for the adjustment of the diaphragm plates 10 and 11 and the precision with which a spacing can be set between the diaphragm plates 10 and 11 is low. With an acute angle, the adjustability of the first and second diaphragm plates 10 and 11 is facilitated and the precision with which a predetermined spacing of the diaphragm plates 10 and 11 can be set is high. It has proven advantageous when the guides 15, 16 17 and 18 describe an angle of approximately 15.degree.-45.degree., preferably 25.degree. relative to the respective longitudinal axis 12 and 13 of the diaphragm plates 10 and 11. Within the context of the invention, the guide can be executed not only as a recess and pin but also as a channel into which a ridge (or web) engages. A ridge (or web) can also be provided with roller bearings. FIG. 3 shows a preferred exemplary embodiment of an adjustment mechanism 38 for the first and second diaphragm plates 10 and 11. Differing from the above-described adjustment mechanism 31, wherein a threaded bushing or bore into which the spindle 32 extends must be provided at the carriage 35, the adjustment mechanism 38 of FIG. 3 has a spindle 39 having threads at a pitch such that bearing means held in the carriage 40 and preferably executed as a roller bearing 41 and 42 can engage the threads. The roller bearings 41 and 42 can be adjusted such via eccentric mounts such that no play occurs between the carriage 40 and the spindle 39. The first and second articulations 36 and 37 described with reference to FIG. 2 attach at the carriage 40 for adjusting the first and second diaphragm plates 10 and 11. Also shown in FIG. 3 is a motor 43, which can be a stepping motor or DC motor, is attached to the spindle 39, for example via a chain or via a toothed belt 44. In addition to the absence of play in the bearings of the adjustment mechanism 38, it should be emphasized that it is extremely rugged and insensitive to dirt. The spindle 32 according to FIG. 2 can, for example, be provided with a thread according to DIN13 as a commercially available spindle. In order to reduce the play between the carriage 35 and the spindle 32 (or the carriage 40 and the spindle 39) the spindle 32 or 39 can also be provided with a trapezoidal thread that engages a bushing of the carriage 35 (or 40) that is provided with a corresponding thread. The bushing can be executed as a nut. In order to reduce play, the bushing is axially divided and is prestressed via a spring element, for example a rubber ring. The bearing play is also considerably reduced as a result of this measure. Adjustment of the diaphragm plates at their guides 15, 16, 17 and 18, can alternatively ensue via an adjustable eccentric attached to at least one of the diaphragm plates 10 and 11. For identifying the position of the diaphragm plates 10 and 11, a position sensor 45 as shown in FIGS. 2 and 4 can be provided, such as an encoder, potentiometer or resolver. When the gating device of the invention is to be utilized in a computer tomography apparatus and, in particular, as a diaphragm in front of the individual detector elements, then it is advantageous when, as shown in FIG. 4, a plurality of diaphragm plates 10 and 11 according to FIG. 2 adjoin one another and are fashioned arcuately. Due to the connection of the diaphragm plates 10 and 11 to one another, only one adjustment mechanism 31 or 38 is required via which the adjustment of the diaphragm plates 10 and 11 can ensue. The diaphragm plates can be entirely composed of a material having high radiation absorption. Within the context of the invention, however, it is an alternative to provide diaphragm plates with carrier plates 46 and 47 composed, for example, of aluminum and having the guides described above, so that a material having high radiation absorption must be provided only in the region of one end face of each plate. When such diaphragm plates are to be arcuately joined to one another, preferably two or more carrier plates 46 and 47 are arranged at a distance from one another, joined to one another via a ring segment or a ring 48 composed of a material having high radiation absorption. The individual carrier plates 46 and 47 can include one or more guides as described above. An advantage of this embodiment is that the mass to be moved given an adjustment of the diaphragm plates is extremely low. The described gating device, of course, can be utilized not only in a computer tomography apparatus but also in other radiation systems, for example, x-ray diagnostics installations, electron beam devices, radiation therapy devices and in light sources for gating the beam. The gating device can have only one diaphragm plate, or a plurality of diaphragm plates. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.