A prototype coded aperture detector for small animal SPECT

In a previous simulation study, we demonstrated the feasibility of using coded apertures together with pixelated detectors for high resolution, high sensitivity small animal SPECT. We further explore the potential of this approach with a prototype detector and simulated multi-pinhole apertures. We also investigated the effect of multiplexing due to overlapped projections on convergence properties, image signal-to-noise ratio (SNR) and spatial resolution. The detector comprises a 48×44 array of NaI(Tl) crystals, each 1 mm×1 mm×5 mm on a 1.25 mm pitch. The crystal array is directly coupled to a Hamamatsu R3941 8 cm PS-PMT. Multi-pinhole apertures were simulated by performing repeated SPECT acquisitions of the same object with a single tungsten pinhole translated to different positions in the aperture plane. Image reconstruction is based on a 3D ray driven projector which is an extension of a method described for single pinhole SPECT with a displaced centre of rotation. Image estimates are updated using the MLEM algorithm. The effect of multiplexing was to slow convergence and reduce the achievable SNR by approximately 15% compared with non-multiplexed data (but the result may be achieved in 1/N^th the time). The reconstructed resolution obtained with a resolution phantom was 1.5 mm full width at half maximum and there was no appreciable difference between the resolution of multiplexed and non-multiplexed data. These results encourage us to develop a prototype coded aperture system for high sensitivity, high resolution small animal SPECT.