Patent Number: 046413367
Section: summary

The present invention relates to a soft tissue filter arrangement. BACKGROUND OF THE INVENTION 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. SUMMARY OF THE PRESENT INVENTION 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.