Design of rotating collimator for high performances radioisotopic imaging

A high resolution radioisotopic detector allows detection of small structures, but its sensitivity is poor. Increased parallel collimator sensitivity is obtained by enlarging the hole diameter. However, a hole diameter greater than the detector intrinsic spatial resolution leads to artifacts on acquired images. Linear collimator motions can remove these artifacts. However a practical realization of such motions is difficult to perform. To this end, a circular translation motion is studied in this work. Motion effectiveness was evaluated by an homogeneity index based on hexagon center loci. Several rotation radii optimizing this homogeneity were found. Moving collimator transparency was deterministically simulated. The smallest suitable motion radius is 0.32 times the structure diameter, which leads to a very small field of view decrease. A device performing such collimator motions was realized for a high resolution gamma imaging probe based on a position sensitive photomultiplier tube. The measured spatial impulse response was the same on the whole field of view for a given source to detector distance. The image restoration process allows one to recover the spatial resolution. In conclusion, moving a medium sensitivity collimator allows one to obtain both good sensitivity and high resolution in radioisotopic imaging.