COLLIMATOR WITH ADJUSTABLE APERTURE

Collimator for regulating the shape and size of the pattern of radiation projection on a radiation detector from a radiation source, particularly for regulating the beam of radiation in a medical diagnostic x-ray machine. One or more (preferably three) longitudinally stacked plates are provided, the top plate having a large aperture, the middle plate having a medium sized aperture, and the lower plate having a small aperture. The middle and lower plates are provided with means to substantially open up their apertures, rendering these plates inactive when they are not in use. Each plate is longitudinally movable between first and second extremities of travel, the first extremity being nearest the radiation source. When each plate is at its first extremity of travel the beam of radiation has its maximum size. The size is first reduced by advancing the first plate longitudinally to its second extremity of travel, then by placing the second in its active position in the beam and advancing it to its second extremity of travel, and finally by placing the third plate in its active position in the beam and advancing the third plate to its second extremity of travel. A drive means and associated structure is also disclosed for placing the plates in their active positions and advancing the three plates. The present invention allows continuous variation of the size of the x-ray beam projected on the detector over a wide range, while at the same time providing a collimator which is longitudinally compact. The collimator can be provided with apertures of any shape, allowing projection of an irregularly shaped pattern which is continuously variable in size.