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Slow‐rotation dynamic SPECT with a temporal second derivative constraint
Author(s) -
Humphries T.,
Celler A.,
Trummer M.
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3589129
Subject(s) - imaging phantom , smoothness , voxel , projection (relational algebra) , rotation (mathematics) , computer science , iterative reconstruction , image quality , computer vision , artificial intelligence , region of interest , algorithm , image (mathematics) , mathematics , physics , optics , mathematical analysis
Purpose: Dynamic tracer behavior in the human body arises as a result of continuous physiological processes. Hence, the change in tracer concentration within a region of interest (ROI) should follow a smooth curve. The authors propose a modification to an existing slow‐rotation dynamic SPECT reconstruction algorithm (dSPECT) with the goal of improving the smoothness of time activity curves (TACs) and other properties of the reconstructed image. Methods: The new method, denotedd 2EM, imposes a constraint on the second derivative (concavity) of the TAC in every voxel of the reconstructed image, allowing it to change sign at most once. Further constraints are enforced to prevent other nonphysical behaviors from arising. The new method is compared with dSPECT using digital phantom simulations and experimental dynamic 99m Tc ‐DTPA renal SPECT data, to assess any improvement in image quality. Results: In both phantom simulations and healthy volunteer experiments, thed 2EM method provides smoother TACs than dSPECT, with more consistent shapes in regions with dynamic behavior. Magnitudes of TACs within an ROI still vary noticeably in both dSPECT andd 2EM images, but also in images produced using an OSEM approach that reconstructs each time frame individually, based on much more complete projection data. TACs produced by averaging over a region are similar using either method, even for small ROIs. Results for experimental renal data show expected behavior in images produced by both methods, withd 2EM providing somewhat smoother mean TACs and more consistent TAC shapes. Conclusions: Thed 2EM method is successful in improving the smoothness of time activity curves obtained from the reconstruction, as well as improving consistency of TAC shapes within ROIs.