Geometrical and Monte Carlo projectors in 3D PET reconstruction

• Published in: Medical physics (Lancaster) Vol. 37; no. 11; p. 5691
• Main Authors: Aguiar, Pablo, Rafecas, Magdalena, Ortuño, Juan Enrique, Kontaxakis, George, Santos, Andrés, Pavía, Javier, Ros, Domènec
• Format: Journal Article
• Language: English
• Published: United States 01.11.2010
• Subjects: Animals; Computer Simulation; Computers; Image Processing, Computer-Assisted - instrumentation; Image Processing, Computer-Assisted - methods; Imaging, Three-Dimensional - methods; Models, Statistical; Monte Carlo Method; Phantoms, Imaging; Positron-Emission Tomography - methods; Software; Time Factors
• ISSN: 0094-2405
• DOI: 10.1118/1.3501884

In the present work, the authors compare geometrical and Monte Carlo projectors in detail. The geometrical projectors considered were the conventional geometrical Siddon ray-tracer (S-RT) and the orthogonal distance-based ray-tracer (OD-RT), based on computing the orthogonal distance from the center of image voxel to the line-of-response. A comparison of these geometrical projectors was performed using different point spread function (PSF) models. The Monte Carlo-based method under consideration involves an extensive model of the system response matrix based on Monte Carlo simulations and is computed off-line and stored on disk. Comparisons were performed using simulated and experimental data of the commercial small animal PET scanner rPET. The results demonstrate that the orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions yield better images in terms of contrast and spatial resolution than those obtained after using the conventional method and the multiray-based S-RT. Furthermore, the Monte Carlo-based method yields slight improvements in terms of contrast and spatial resolution with respect to these geometrical projectors. The orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions represent satisfactory alternatives to factorizing the system matrix or to the conventional on-the-fly ray-tracing methods for list-mode reconstruction, where an extensive modeling based on Monte Carlo simulations is unfeasible.