Long focal length, asymmetric fan beam collimation for transmission acquisition with a triple camera SPECT system

A system design has been proposed for fast sequential SPECT/transmission CT on a three-headed SPECT camera. The design consists of a long focal length (114 cm) asymmetric fan beam collimator and a stationary transmission line source. The advantages of this system include: increased field-of-view, high sensitivity to the transmission line source, low sensitivity to radionuclide within the patient (reduced cross-talk effects), high spatial resolution, easy transition between SPECT and transmission acquisition, and no moving line source. An iterative ML-EM reconstruction algorithm for transmission data was implemented and adapted to the proposed acquisition geometry. Evaluations were performed using Monte Carlo simulated data. With a 40 cm detector width, transmission reconstructions of a 38×26 cm elliptical body were effectively artifact-free. Reconstructions of a 46×31 cm body contained only minor truncation artifacts that did not substantially affect the attenuation compensated SPECT image. Contamination of the transmission data from radionuclide within the patient can be substantially reduced with this system by increasing the resolution of the fan beam collimator. We conclude that long focal length, asymmetric fan beam collimation, combined with iterative reconstruction, offers a promising approach for fast sequential SPECT/TCT acquisition on a three-headed SPECT camera