Patent Number: 051951215
Section: abstract

An apparatus for modulating the intensity of an X-ray beam generated by an X-ray tube. The apparatus comprises a set of at least three blades made of a material opaque to X-ray. Each blade comprises a central hub and a pair of symmetrical wings extending away from the hub. All the blades have their hubs slidably mounted on radially projecting shafts symmetrically positioned about a rotor positioned adjacent the X-ray beam and driven at variable speeds. Matching pins and threads are provided on each pair of hub and shaft to cause the corresponding blade to pivot about the shaft on which it is mounted when the speed of the rotor increases and the blades are then moved in unison radially outwardly against the action of a return spring, because of the centrifugal force. The rotor, the blades and the shafts are positioned and sized to cause the blades to intersect the X-ray beam when the rotor is driven. This in turn causes the blades to modulate the intensity of the X-ray beam as a function of the angular position of the blades about their shafts, which allow more or less radiation to pass therebetween.