Introduction of Spread Field Imaging—a Novel High Performance Collimation for SPECT

Abstract

Collimation plays a vital role in single photon emission computed tomography systems. Spread field imaging is a class of high-sensitivity, high-resolution collimation and imaging technologies that utilizes shared photon paths to improve collimator performance. In this article we introduce a novel design, called spread field imaging-narrow angle , that shares some characteristics of both parallel-hole and pinhole collimators. In this approach, the holes are long and narrow, similar to the holes in a parallel hole collimator; however, as opposed to parallel-hole collimators, there is space between the holes and the detector. With that spacing, the overall thickness of the collimator is around 7-11 cm. In addition, the holes are not identical, possibly varying in shape, size, etc., and may even include closed holes. The hole-detector spacing provides an extended "virtual" hole length that improves resolution. Holes with wider acceptance angle may be used to achieve higher resolution and sensitivity compared with parallel-hole collimators. An ordered subset expectation and maximization based algorithm has been developed to reconstruct the object image. Simulations were developed with three-dimensional software hot-rod and Hoffman brain phantoms to compare reconstructed results obtained with from spread field imaging collimation with conventional low-energy, high-resolution parallel hole collimators with full, half or a quarter of conventional imaging times. The results showed that the spread field imaging-narrow angle collimator yielded better or similar reconstruction compared with low-energy, high-resolution even when the imaging time was cut to a quarter of the conventional time. These results demonstrate that spread field imaging-narrow angle collimators have the potential to be high-resolution, low-dose collimators applicable to conventional single photon emission computed tomography systems, and suitable for a wide range of clinical applications.