Single pinhole and coded aperture collimation systems for high-resolution gamma-ray imaging in nuclear medicine: a comparative study

The increased interest in compact imaging systems with high spatial resolution for nuclear medicine and small animal imaging has resulted in the development of new gamma-ray detectors characterized by high intrinsic spatial resolution. Beside the resolution of the detector, the contribution given by the collimator must also be carefully considered in the design of a complete imager. It is well known that for a pinhole collimator the reduction of the pinhole size to improve the resolution results in reduced sensitivity. Coded aperture collimation (CA) decouples resolution from sensitivity. In CA, when the pinhole size is reduced, sensitivity can be preserved by opening the necessary number of pinholes. Consequently, a high number of copies of the object is projected onto the detector. In presence of overlap, however, increased sensitivity does not imply increased signal-to-noise ratio (SNR). In this work we have studied when a CA collimation system is advantageous with respect to a more conventional double knife-edge collimator. Although this problem has been already theoretically studied, we propose in this work a simulation 'tool' which should help the imaging system designer to choose between different collimation systems, once given the class of objects to be imaged. The basic principles of the simulator are discussed. Then, the results of the simulations of different objects, characterized by different ratios of hot spots intensity over the whole intensity are discussed