Hybrid parallel-slant hole collimators for SPECT imaging

We propose a new collimator geometry, the hybrid parallel-slant hole geometry (HPS), to improve sensitivity for SPECT imaging with large field of view (LFOV) gamma cameras. A HPS collimator has one segment with parallel holes and one or more segments with slant holes. The collimator can be mounted on a conventional SPECT LFOV system that uses parallel-beam collimators, and no additional detector or collimator motion is required for data acquisition. The parallel segment of the collimator allows for the acquisition of a complete data set of the organs-of-interest and the slant segments provide additional data. In this work, simulation studies of an MCAT phantom were performed with an HPS collimator with one slant segment. The slant direction points from patient head to patient feet with a slant angle of 30°. We simulated 64 projection views over 180°, and we modeled nonuniform attenuation effect. Images were reconstructed using an OSEM algorithm that incorporated the hybrid geometry. Sensitivity to the cardiac region of the phantom was increased by approximately 50% when using the HPS collimator compared with a parallel-hole collimator. No visible artifacts were observed in the reconstructed images and the signal-to- noise ratio (SNR) of the cardiac walls was improved. Compared with collimators with other geometries, using a HPS collimator has the following advantages: (a) significant sensitivity increase, (b) a complete data set obtained from the parallel segment that allows for artifact-free image reconstruction, and (c) no additional collimator or detector motion. This work demonstrates the potential value of hybrid geometry in collimator design for LFOV SPECT imaging.