X-ray or gamma ray systems or devices – Beam control – Filter
Patent
1996-11-29
1998-11-24
Porta, David P.
X-ray or gamma ray systems or devices
Beam control
Filter
378206, A61B 608
Patent
active
058418342
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a filter arrangement in a radiography apparatus to define the intensity of the radiation beam incident upon the patient, the radiography apparatus incorporating an X-ray source, a movable filter placed in front of it, and means for supporting the patient in order to keep the object to be radiographed immobile relative to the X-ray beam, there being in alignment with the patient light-emitting means to indicate the dimension of the filtered radiation beam at a given time, and there being between the said light-emitting means and the filter-moving means a signal communication to implement the positional dependency between them.
In radiography it is in general important to define suitably the shape and intensity of the beam of rays relative to the object to be radiographed, in order not to subject the patient to unnecessary radiation and also otherwise in order to obtain an image exposed with maximal expediency. For example, in cefalometry, the patient's head, or parts of the skull, is recorded as seen from the side, in which case it is often expedient to filter more that side of the beam of rays which is incident upon the patient's face, whereupon the outline of the patient's face will be visible in the X-ray image produced. This is, in a known manner, achieved by means of a wedge-shaped filter placed between the source of radiation and the object to be radiographed, the filter being in general arranged so as to be movable in a plane perpendicular to the main axis of the radiation beam so that the thinner edge of the wedge is closer to the main axis of the beam.
In the positioning of the wedge-shaped filter of the radiation beam it is, of course, important to know to which point in the patient at a given location of the filter the filtering effect extends. In said cefalometry it is prior known, for example, to measure, by using the means for supporting the patient's head, certain important dimensions and to position the filter on the basis of these, either manually or automatically by using a motor. A system of this type is disclosed, for example, in FI patent 68515.
A slightly different known method, resembling this, is one in which a movable light-emitter is arranged in the vicinity of the means for supporting the patient's head, the emitter emitting a beam of light indicating the boundary of the radiation beam filtered by the wedge filter. The technical implementation is such that from the means for moving the light-emitter there departs an electric signal to the filter motor, which then drives the filter to the correct position.
In adjusting the filtering of the ratiation beam is would, however, be desirable to work at a distance from the patient and not in the immediate vicinity of the patient positioned in place by using the head-supporting means, as in the cases described above. Furthermore, the transfer of the filter by using a motor, of course, makes the structure more complicated and increases its price. It is therefore an object of the present invention to provide a reliably functioning arrangement which is, nevertheless, relatively simple in its implementation.
To achieve this object, the invention is characterized in that to the filter-moving means there are coupled circuit means which create an electric signal dependent on the position of the moving means, there being further arranged a signal communication from the circuit means to light emitters which are fitted in the vicinity of the object to be radiographed and are arranged in a row so that, according to the position of the filter-moving means, a certain light emitter or a plurality of light emitters will become illuminated to indicate the boundary of the filtered radiation beam.
Compared with known methods, the principle in the present invention is thus the opposite: the light emitters serve to indicate to the operator the boundary of the filtered radiation beam produced by the filter wedge. In other words, when the operator moves the filter, a signal proportional to the filter position is applied to a lig
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Orion-yhtyma Oy
Porta David P.
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