Monte Carlo and experimental evaluation of accuracy and noise properties of two scatter correction methods for SPECT

Abstract

Scatter correction is a prerequisite for quantitative SPECT, but potentially increases noise. Monte Carlo simulations (EGS4) and physical phantom measurements were used to compare accuracy and noise properties of two scatter correction techniques: the triple-energy window (TEW), and the transmission dependent convolution subtraction (TDCS) techniques. Two scatter functions were investigated for TDCS: (i) the originally proposed mono-exponential function (TDCSmono) and (ii) an exponential plus Gaussian scatter function (TDCSGauss) demonstrated to be superior from our Monte Carlo simulations. Signal to noise ratio (S/N) and accuracy were investigated in cylindrical phantoms and a chest phantom. Results from each method were compared to the true primary counts (simulations), or known activity concentrations (phantom studies). 99mTc was used in all cases. The optimized TDCS(Gauss) method overall performed best, with an accuracy of better than 4% for all simulations and physical phantom studies. Maximum errors for TEW and TDCS(mono) of -30 and -22%, respectively, were observed in the heart chamber of the simulated chest phantom. TEW had the worst S/N ratio of the three techniques. The S/N ratios of the two TDCS methods were similar and only slightly lower than those of simulated true primary data. Thus, accurate quantitation can be obtained with TDCS(Gauss), with a relatively small reduction in S/N ratio.