Simulation-based Assessment of the Impact of Contrast Medium on CT-based Attenuation Correction in PET

Although diagnostic quality CT relies on the administration of contrast agents to allow improved lesion detectability, the misclassification of contrast medium as high density bone during CT-based attenuation correction (CTAC) procedure is known to overestimate the attenuation coefficients, thus biasing activity concentration estimates of PET data. In this study, the influence of contrast medium on CTAC was investigated through Monte Carlo (MC) simulations and experimental phantom studies. Our recently developed MC x-ray CT simulator and the Eidolon 3D PET MC simulator were used to generate realigned PET/CT data sets. The influence of contrast medium was studied by simulation of a cylindrical phantom containing different concentrations of contrast medium. Moreover, an experimental study using an anthropomorphic striatal phantom was conducted for quantitative evaluation of errors arising from the presence of contrast medium by calculating the apparent recovery coefficient (ARC). The ARC was 190.7% for a cylindrical volume of interest located in the main chamber of the striatal phantom containing contrast medium corresponding to 2000 Hounsfield units, whereas the ARC was overestimated by less than 5% for the main chamber and 2% for the left/right putamen and caudate nucleus compared to the absence of contrast medium. It was concluded that the contrast-enhanced CT images may create considerable artifacts during CTAC in regions containing high concentrations of contrast medium.