Accurate scatter correction is one of the major problems facing quantitative 3D PET. A new scatter correction method called Statistical Reconstruction-Based Scatter Correction (SRBSC) based on estimating the low-frequency component corresponding to scatter events using ordered subsets - expectation maximisation (OSEM) reconstructions is proposed in this paper and evaluated using Monte Carlo simulation studies, experimental phantom measurements and clinical studies. The rationale of the method is that the image corresponding to scattered events in the projection data consists of almost low-frequency components of activity distribution and that the low-frequency components will converge faster than the high-frequency ones in successive iterations of statistical reconstruction methods such as OSEM. The second assumption is that the high-frequency components will be smeared, i.e. filtered by the scatter response kernels. The scatter fraction and scatter response function for uniformly attenuating media are parametrised using Monte Carlo simulations.
The unscattered component estimated using SRBSC was compared to the true unscattered component as estimated by Monte Carlo simulations for simple phantom geometries and clinically realistic source distributions. Quantitative analysis was also performed on reconstructed images using simple metrics like the contrast, absolute concentration, recovery coefficient and signal-to-noise ratio. The SRBSC method tends to undercorrect for scatter in most regions of the 3D Hoffman brain phantom, but gives good activity recovery values which average within 3%. It was concluded that the proposed method improves image quality and the contrast compared to the case where no correction is applied and that an accurate modelling of the scatter component is essential for a proper scatter correction.
Key Words: 3D PET, scatter correction, OSEM, Monte Carlo
Ann. Nucl. Med. Sci. Vol 14, No 3, pp 161-171 (2001)
Oral presentation, The World Congress on Medical Physics and Biomedical Engineering 2000, Chicago, USA 23-28 July 2000