Automatic filter placement device for Region of Interest (ROI) Fluoroscopy

In Region of Interest (ROI) Fluoroscopy, an ROI filter is inserted into the x-ray beam in order to decrease the patient exposure in the peripheral part of the field of view. A filter placement device has been designed and constructed for the practical implementation of ROI fluoroscopy. When unmodified spot films are required during fluoroscopic procedures, an electronic signal from the high voltage generator triggers the filter placement device to remove the ROI filter automatically from the field of view and to reinsert it after the conclusion of the spot film exposure. The filter placement device is easily fastened to existing tracks on undertable tube fluoroscopic collimators. A transmission ionization chamber may be placed above the filter assembly so that radiation to the patient may be monitored during ROI fluoroscopic procedures. The mechanical design is compact and involves only one miniature gear-head motor. The filter placement device allows rapid filter positioning in 200 ms so that there is no interference with spot filming. A simple electronic circuit provides 8 volts for rapid motion of the filter support arm and 4 volts for holding the filter in place. This device demonstrates that ROI fluoroscopy with its associated large reduction in patient integral dose can be practically implemented in standard fluoroscopic equipment.