REDUCING THE INFLUENCE OF THE PARTIAL VOLUME EFFECT ON SPECT ACTIVITYQUANTITATION WITH 3D MODELING OF SPATIAL-RESOLUTION IN ITERATIVE RECONSTRUCTION

Quantitative parameters such as the maximum and total counts in a volu me are influenced by the partial volume effect. The magnitude of this effect varies with the non-stationary and anisotropic spatial resoluti on in SPECT slices. The objective of this investigation was to determi ne whether iterative reconstruction which includes modelling of the th ree-dimensional (3D) spatial resolution of SPECT imaging can reduce th e impact of the partial volume effect on the quantitation of activity compared with filtered backprojection (FBP) techniques which include l ow-pass, and linear restoration filtering using the frequency distance relationship (FDR). The iterative reconstruction algorithms investiga ted were maximum-likelihood expectation-maximization (MLEM), MLEM with ordered subset acceleration (MLOS), and MLEM with acceleration by the rescaled-block-iterative technique (ML-RBI). The SIMIND Monte Carlo c ode was used to simulate small hot spherical objects in an elliptical cylinder with and without uniform background activity as imaged by a l ow-energy ultra-high-resolution (LEUHR) collimator. Centre count ratio s (CCRs) and total count ratios (TCRs) were determined as the observed counts over true counts. CCRs were unstable while TCRs had a bias of similar to 10% for all iterative techniques. The variance in the TCRs for ML-OS and ML-RBI was clearly elevated over that of MLEM, with ML-R BI having the smaller elevation. TCRs obtained with FDR-Wiener filteri ng had a larger bias (similar to 30%) than any of the iterative recons truction methods but near stationarity is also reached. Butterworth fi ltered results varied by 9.7% from the centre to the edge. The additio n of background has an influence on the convergence rate and noise pro perties of iterative techniques.