Multiple pencil beams for proton computed tomography

A device for generating and scanning multiple pencil beams has been designed and constructed for proton computed tomography (CT). It consists of two sets of brass blocks with slits attached to cylinders moved by highly pressurized oil. One set of slits is placed in front of a specimen in order to chop multiple pencil beams from a parallel beam. The other set of slits is placed behind the specimen to stop protons scattered at a large angle in the object in order to improve the spatial resolution of proton CT. The slits are moved to scan the object. Using the multiple-beam-scanning method, the scanning time of CT was reduced to less than eight minutes. The displacement of each block was controlled by an oil-servo system. Positional accuracy of less than 35 μm (rms) has been achieved in a full stroke of 30 or 39 mm under the condition that the load weight was about 26 kg and the maximum instantaneous speed of the block was about 20 cm/s. The device was used to perform the proton CT and was found to work well. (orig.)