title: Monte Carlo-based down-scatter correction of SPECT attenuation maps.
abstract: Combined acquisition of transmission and emission data in single-photon emission computed tomography (SPECT) can be used for correction of non-uniform photon attenuation. However, down-scatter from a higher energy isotope (e.g. 99mTc) contaminates lower energy transmission data (e.g. 153Gd, 100 keV), resulting in underestimation of reconstructed attenuation coefficients. Window-based corrections are often not very accurate and increase noise in attenuation maps. We have developed a new correction scheme. It uses accurate scatter modelling to avoid noise amplification and does not require additional energy windows. The correction works as follows: Initially, an approximate attenuation map is reconstructed using down-scatter contaminated transmission data (step 1). An emission map is reconstructed based on the contaminated attenuation map (step 2). Based on this approximate 99mTc reconstruction and attenuation map, down-scatter in the 153Gd window is simulated using accelerated Monte Carlo simulation (step 3). This down-scatter estimate is used during reconstruction of a corrected attenuation map (step 4). Based on the corrected attenuation map, an improved 99mTc image is reconstructed (step 5). Steps 3-5 are repeated to incrementally improve the down-scatter estimate. The Monte Carlo simulator provides accurate down-scatter estimation with significantly less noise than down-scatter estimates acquired in an additional window. Errors in the reconstructed attenuation coefficients are reduced from ca. 40% to less than 5%. Furthermore, artefacts in 99mTc emission reconstructions are almost completely removed. These results are better than for window-based correction, both in simulation experiments and in physical phantom experiments. Monte Carlo down-scatter simulation in concert with statistical reconstruction provides accurate down-scatter correction of attenuation maps.
authors.affiliation: Department of Nuclear Medicine, Image Sciences Institute, University Medical Centre Utrecht, Universiteitsweg 100, STR 5.203, Utrecht, The Netherlands.
authors.forename: Tomislav
authors.initials: T
authors.lastname: Bokulić
authors.forename: Brendan
authors.initials: B
authors.lastname: Vastenhouw
authors.forename: Hugo W A M
authors.initials: HW
authors.lastname: de Jong
authors.forename: Alice J
authors.initials: AJ
authors.lastname: van Dongen
authors.forename: Peter P
authors.initials: PP
authors.lastname: van Rijk
authors.forename: Freek J
authors.initials: FJ
authors.lastname: Beekman
mesh_terms: D000465:Algorithms; D006321:Heart / Q000000981:diagnostic imaging*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D013909:Thorax / Q000000981:diagnostic imaging; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*