Abstract
319
Objectives: One of the greatest challenges facing iterative fully-3D PET reconstruction is the issue of long reconstruction times due to the large data size as compared to 2D mode. A fast 3D projector has been developed which exploits symmetries in the geometry to compute volumetric projections to multiple oblique sinograms in a computationally efficient manner. Methods: The projector is based on a 2D rotation-based projector using the three-pass method of shears, and it conserves the rotator computations for multiple projections to each oblique sinogram set. The projector is equally applicable to both evenly-spaced projections and raw unevenly-spaced line-of-response (LOR) data (where the arc correction is modeled within the projector). The LOR-based version models the location of the raw LORs measured by the tomograph, suitable for “ordinary Poisson” reconstruction. The projector was implemented in C with several optimizations for speed, including the vertical symmetry of the oblique projection process, a coarse-depth compression, and array indexing schemes which maximize serial memory access. Results: Five reconstruction schemes for fully-3D PET were evaluated and compared: (1) Fourier rebinning followed by 2D attenuation-weighted ordered-subsets expectation-maximization (AW-OSEM) with a ray-driven projector; (2) 3D AW-OSEM with ray-driven projector; and 3D LOR-OSEM with (3) ray-driven projector, (4) distance-driven projector, and (5) new rotate-and-slant projector. In terms of spatial resolution, contrast, and background noise measures, 3D LOR-OSEM with the rotate-and-slant projector performed as well as or better than the other methods. Total processing times, measured on a single cpu Linux workstation, were markedly faster for the rotate-and-slant projector than for the other 3D projectors studied, and the new projector provided fully-3D iterative reconstruction in approximately the same time as FORE 2D-OSEM. Total processing time, 4 iterations 3D LOR-OSEM, to reconstruct a 128×128 × 47 slice image from 249 LOR × 47 slice × 210 angle × 23 segment projection data (typical of DiscoveryST scanner) was 22.8 sec. Conclusions: The rotate-and-slant projector is a viable option for fast 3D iterative reconstruction in PET, offering quality statistical reconstruction in times only marginally slower than for 2D or rebinning methods.
Research Support (if any): NIH R01 CA107353
- Society of Nuclear Medicine, Inc.