Patent Number: 046413367
Section: description

DETAILED DESCRIPTION OF THE INVENTION In the drawing, reference numeral 1 designates an X-ray tube which generates X-radiation that is directed to a patient P and restricted to a suitable beam of rays 3 for imaging by diaphragm 2. The radiation penetrated through the patient is recorded on a film 4. X-ray tube 1 and the support of film 4 are preferably fixed together for providing fixed imaging coordinates (not shown in figure). The patient is positioned on the imaging coordinates by means of ear plugs 5 or the like supports. This is to ensure that a given part of each patient, e.g. the ear cavity, will be imaged on the same spot in a film square. The device also comprises an adjustable nasion and/or forehead support 6 whose distance from ear plugs is indicated with D. Thus, this distance is a patientwise measure the same way as the mutual distance between ear plugs, i.e. the width dimension W of a patient's skull. According to the invention, dimension D is utilized for the adjustment of soft tissue filter means 7. This dependence and adjustment is designated by a control signal 9. The adjustment can be effected manually by a control knob 8 which is preferably fitted with a proper control scale. Also for distance D, the apparatus is provided with a numerical control scale according to which said control knob scale is preferably precalibrated for facilitating the adjustment. The control scale of distance D and setting mechanisms of support or measuring means 6 as well as setting mechanisms of supports 5 are not illustrated in detail in the figure, as they represent conventional technology and are generally available in cephalostats. In practice, ear plugs 5 are in the cross-sectional plane perpendicular to X-rays bound to the imaging coordinates, whereby the patientwise variation of dimension D is effected by adjusting support or measuring means 6. Instead of the above-described manual control, the adjustment of filter means 7 can be preferably automated in a manner that the control elements of filter means 7 are directly controlled to effect necessary resetting actions on the basis of the dimensional data obtained of the patientwise positioning e.g. by means of sensor elements. When effected by means of modern microprocessor technology, the question is merely about a simple programming procedure. Since it is also rather simple to find out dimension W or the width of a patient's skull from cephalostats by means of ear supports 5, said dimension generally correlating rather well with dimension D, said control of filter means may be effected also on the basis of dimension W, if so desired. Also, supporting of filter means 7 can of course be effected in a manner different from the figure. The essential point is to effect the positional control of filter means in a controllable manner with respect to imaging coordinates. In addition to the position of a soft tissue filter, it may become necessary to adjust the slope or V-shape of a filter, which depends on the width of a patient's skull. The slope control can be effected e.g. by adapting the filter means to be rotatable around an axis substantially perpendicular to X-rays and to the direction in which the position of filter means is displaced. See FIG. 2. The invention is not limited to the above-described embodiment but a plurality of modifications thereof are conceivable within the scope of the annexed claims.