title: A comparison of different energy window subtraction methods to correct for scatter and downscatter in I-123 SPECT imaging.
abstract: OBJECTIVE
  One of the main problems in quantification of single photon emission computer tomography imaging is scatter. In iodine-123 (I-123) imaging, both the primary 159 keV photons and photons of higher energies are scattered. In this experimental study, different scatter correction methods, based on energy window subtraction, have been compared with each other.
  
  
  METHODS
  Iodine-123 single photon emission computed tomography images of a phantom with a known intensity ratio between background and hollow spheres were acquired for three different collimators (low energy high resolution, low energy general purpose, and medium energy general purpose). The hollow spheres were filled with a higher activity concentration than the uniform background activity concentration, resulting in hot spots. Counts were collected in different energy windows, and scatter correction was performed by applying different methods such as effective scatter source estimation, triple and dual energy window (TEW and DEW), double peak window (DPW) and downscatter correction. The intensity ratio between the spheres and the background was used to compare the performance of the different methods.
  
  
  RESULTS
  The results revealed that the efficiency of the scatter correction techniques vary depending on the collimator used. For the low energy high resolution collimator, all correction methods except the effective scatter source estimation and the DPW perform well. For the medium energy general purpose collimator, even without scatter correction, the calculated ratio is close to the real ratio. The DEW and DPW methods tend to overestimate the ratio. For the low energy general purpose collimator, only the DEW and the combined DEW and downscatter correction methods perform well.
  
  
  CONCLUSIONS
  The only correction method that provides a ratio that differs by less than 5% from the real ratio for all the collimators is the combined DEW and downscatter correction method.
authors.affiliation: Department of Clinical Physiology, Nuclear Medicine and PET, Copenhagen University Hospital, Copenhagen, Denmark. vera.lagerburg@catharinaziekenhuis.nl
authors.forename: Vera
authors.initials: V
authors.lastname: Lagerburg
authors.forename: Robin
authors.initials: R
authors.lastname: de Nijs
authors.forename: Søren
authors.initials: S
authors.lastname: Holm
authors.forename: Claus
authors.initials: C
authors.lastname: Svarer
mesh_terms: D000465:Algorithms; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007457:Iodine Radioisotopes; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D007457:Iodine Radioisotopes