Filter Arrangement for Soft Tissue

The present invention relates to a soft tissue filter arrangement.

In cephalometry, the skull of a patient is X-rayed on a film from the side. Visible in a conventional X-ray image is then primarily the bone structure of a skull. It is often desirable, however, that the soft facial tissues of a patient would also be visible to a certain degree in a patient's skull. For this purpose, it is known in the art to adapt between the patient's skull and the film a V-shaped X-ray absorbing filter which prevents the X-radiation, which is penetrated through soft tissues and is in abundance with respect to the bony parts of a skull, from exposing the film too much on these areas as otherwise said soft tissues are not at all visible on the film. Since the shape and size of the patient's skulls differ considerably from each other, the position of said filter must be set patientwise in order to obtain each time an image exposed as properly as possible also for soft tissues. In practice, the positioning and setting of a filter is done by the operator according to his own judgement with the consequence that up to 2/3 of the images may be failures because of wrong filter position, in which case a patient may have to be re-exposed to X-radiation.

An object of the invention is to eliminate the prior art deficiencies by providing a novel soft tissue filter arrangement whereby the setting of a soft tissue filter can be effected in a simple and reliable manner, so that proper exposure of the images can be ensured in most cases. Another object of the invention is to reduce an X-radiation dose received by a patient. According to the invention, the position of soft tissue filter means is determined on the basis of the accurate distance between earplugs or the like supports and a nasion and/or forehead support or measuring means used for setting up a patient. If the imaging coordinates are set on the basis of the patient's ear cavity, the consideration and utilization of the variation of said distance for the patientwise positioning of filter means improves substantially the possibilities of exposing soft tissues patientwise correctly. In most cases, re-imagings can be avoided this way. Furthermore, the X-radiation dose received by the patient can be reduced by positioning said filter means between a source of X-rays and a patient and by supporting said means e.g. on shutter means or on the body of an X-ray tube itself.

The invention will now be described in more detail with reference made to the accompanying drawing in which

FIG. 1 is a top view of a filter arrangement of the invention; and

FIG. 2 is a partial perspective view of a modification thereof.

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.