title: Slow-rotation dynamic SPECT with a temporal second derivative constraint.
abstract: OBJECTIVE
  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, denoted d2EM, 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 99mTc -DTPA renal SPECT data, to assess any improvement in image quality.
  
  
  RESULTS
  In both phantom simulations and healthy volunteer experiments, the d2EM 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 and d2EM 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, with d2EM providing somewhat smoother mean TACs and more consistent TAC shapes.
  
  
  CONCLUSIONS
  The d2EM 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.
authors.affiliation: Department of Mathematics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Humphries
authors.forename: A
authors.initials: A
authors.lastname: Celler
authors.forename: M
authors.initials: M
authors.lastname: Trummer
mesh_terms: D000328:Adult; D000465:Algorithms; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging; D007677:Kidney Function Tests; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D012399:Rotation; D016284:Technetium Tc 99m Pentetate; D015899:Tomography, Emission-Computed, Single-Photon / Q000706:statistics & numerical data*
chemical_list: D019275:Radiopharmaceuticals; D016284:Technetium Tc 99m Pentetate