title: Total variation superiorization schemes in proton computed tomography image reconstruction.
abstract: OBJECTIVE
  Iterative projection reconstruction algorithms are currently the preferred reconstruction method in proton computed tomography (pCT). However, due to inconsistencies in the measured data arising from proton energy straggling and multiple Coulomb scattering, the noise in the reconstructed image increases with successive iterations. In the current work, the authors investigated the use of total variation superiorization (TVS) schemes that can be applied as an algorithmic add-on to perturbation-resilient iterative projection algorithms for pCT image reconstruction.
  
  
  METHODS
  The block-iterative diagonally relaxed orthogonal projections (DROP) algorithm was used for reconstructing GEANT4 Monte Carlo simulated pCT data sets. Two TVS schemes added on to DROP were investigated; the first carried out the superiorization steps once per cycle and the second once per block. Simplifications of these schemes, involving the elimination of the computationally expensive feasibility proximity checking step of the TVS framework, were also investigated. The modulation transfer function and contrast discrimination function were used to quantify spatial and density resolution, respectively.
  
  
  RESULTS
  With both TVS schemes, superior spatial and density resolution was achieved compared to the standard DROP algorithm. Eliminating the feasibility proximity check improved the image quality, in particular image noise, in the once-per-block superiorization, while also halving image reconstruction time. Overall, the greatest image quality was observed when carrying out the superiorization once per block and eliminating the feasibility proximity check.
  
  
  CONCLUSIONS
  The low-contrast imaging made possible with TVS holds a promise for its incorporation into future pCT studies.
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, New South Wales 2522, Australia. snp75@uow.edu.au
authors.forename: S N
authors.initials: SN
authors.lastname: Penfold
authors.forename: R W
authors.initials: RW
authors.lastname: Schulte
authors.forename: Y
authors.initials: Y
authors.lastname: Censor
authors.forename: A B
authors.initials: AB
authors.lastname: Rosenfeld
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D015233:Models, Statistical; D009010:Monte Carlo Method; D011381:Programming Languages; D011522:Protons; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D011522:Protons