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

A system design for fast sequential SPECT/transmission CT on a three-headed SPECT camera is evaluated using Monte Carlo simulation. A long focal length (114 cm) asymmetric fan beam collimator is used with a stationary line source positioned at the focal line for transmission acquisition. The advantages of this system include: large field-of-view with 360 degree acquisition, high sensitivity to the transmission line source, high spatial resolution, easy transition between SPECT and transmission acquisition, and no moving line source. For transmission reconstruction an ML-EM algorithm was implemented for the asymmetric fan beam geometry. The results showed that with a 40 cm detector width, transmission reconstructions of a 38 x 26 cm elliptical body were effectively artifact-free. Reconstructions of a 46 x 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 using a high resolution 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 on a three-headed SPECT camera.