title: Study of the point spread function (PSF) for 123I SPECT imaging using Monte Carlo simulation.
abstract: The iterative reconstruction algorithms employed in brain single-photon emission computed tomography (SPECT) allow some quantitative parameters of the image to be improved. These algorithms require accurate modelling of the so-called point spread function (PSF). Nowadays, most in vivo neurotransmitter SPECT studies employ pharmaceuticals radiolabelled with 123I. In addition to an intense line at 159 keV, the decay scheme of this radioisotope includes some higher energy gammas which may have a non-negligible contribution to the PSF. The aim of this work is to study this contribution for two low-energy high-resolution collimator configurations, namely, the parallel and the fan beam. The transport of radiation through the material system is simulated with the Monte Carlo code PENELOPE. We have developed a main program that deals with the intricacies associated with tracking photon trajectories through the geometry of the collimator and detection systems. The simulated PSFs are partly validated with a set of experimental measurements that use the 511 keV annihilation photons emitted by a 18F source. Sensitivity and spatial resolution have been studied, showing that a significant fraction of the detection events in the energy window centred at 159 keV (up to approximately 49% for the parallel collimator) are originated by higher energy gamma rays, which contribute to the spatial profile of the PSF mostly outside the 'geometrical' region dominated by the low-energy photons. Therefore, these high-energy counts are to be considered as noise, a fact that should be taken into account when modelling PSFs for reconstruction algorithms. We also show that the fan beam collimator gives higher signal-to-noise ratios than the parallel collimator for all the source positions analysed.
authors.affiliation: Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Cot
authors.forename: J
authors.initials: J
authors.lastname: Sempau
authors.forename: D
authors.initials: D
authors.lastname: Pareto
authors.forename: S
authors.initials: S
authors.lastname: Bullich
authors.forename: J
authors.initials: J
authors.lastname: Pavía
authors.forename: F
authors.initials: F
authors.lastname: Calviño
authors.forename: D
authors.initials: D
authors.lastname: Ros
mesh_terms: D005462:Fluorine Radioisotopes; D015902:Gamma Cameras; D005720:Gamma Rays; D006801:Humans; D007457:Iodine Radioisotopes / Q000494:pharmacology*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D018377:Neurotransmitter Agents / Q000378:metabolism; D019047:Phantoms, Imaging; D017785:Photons; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D012984:Software; D013223:Statistics as Topic; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D005462:Fluorine Radioisotopes; D007457:Iodine Radioisotopes; D018377:Neurotransmitter Agents