Monte Carlo-based scatter correction considering the tailing effect of a CdTe detector for dual-isotope brain SPECT imaging

A Monte Carlo (MC)-based scatter correctionmethod considering the tailing effect of aCdTe detector was developed for dual-isotope brain single-photon emission computed tomography (SPECT) imaging using technetium-99m(Tc-99m) and iodine-123 (I-123), and its accuracywas validated bymeasuring phantoms. The tailing effectwasmodeled by convolutions of energy spectra obtained by geometry and tracking (GEANT) simulation with energy smoothing kernels. In our experimental phantomstudies, quantitative accuracy and image contrast in the reconstructed image of dual-isotope-filled phantoms with ourMC-based scatter correctionmethod (Dual_SC) were compared with those of single-isotopefilled phantoms (Single_SC). The quantitative accuracy was evaluated by the percent error between the estimated activity concentration and true activity concentration. In our six-compartment phantom studywith six different activity concentrations, themean absolute percent errors of Tc-99m for Single_SC andDual_SCwere 1.7% and 2.8%, respectively, while those of I-123 for Single_SCandDual_SCwere 4.8% and 5.6%, respectively. In our striatal phantomstudy, the percent errors in the background regions for Single_SCandDual_SCwere less than2% for both Tc-99m and I-123. The image contrast was evaluated by the percent contrast of a cold or hot spot region to a background region. In our cold rod phantom study, themean percent contrasts in the cold rod regions of 99mTc for Single_SCandDual_SCwere 66.2% and 65.0%, respectively, while those of I-123 for Single_SCandDual_SCwere 59.3% and 61.6%, respectively. In our striatal phantomstudy, the percent contrasts in the striatal regions of 99m Tc for Single_SCandDual_SCwere 56.1% and 56.1%, respectively, while those of I-123 for Single_SCand Dual_SCwere 39.8% and 40.0%, respectively. In conclusion, dual-isotope imaging with theCdTe-based brain SPECTsystemand ourMC-based scatter correctionmethod can provide comparable quantitative accuracy and image contrast to those of single-isotope imaging.