Determination of blood curve and tissue uptake from left ventricle using FADS in rat FDG-PET studies

Blood input function is necessary for quantitative pharmacokinetic studies in Positron Emission Tomography (PET). However, external blood sampling from small animals presents many limitations. In this work, we show that the blood input function in rats can be extracted from the left ventricular blood pool using Factor Analysis of Dynamic Structures (FADS). Images of the heart from eight rats were acquired with the Sherbrooke animal PET scanner. A region of interest (ROI) was drawn around the left ventricle (LV) and decomposed into the blood pool and the myocardium tissue using FADS. The input curve (IC) obtained with FADS is comparable to that obtained from measured images for the first frames, while it significantly decreases with increasing time. The myocardium tissue segments present lower amplitude at early times and approximately no change at later times in comparison to the same ROIs obtained from measured images. On average, the variation of the total counts were about 18%, 19% and 43% in the IC, anterior and septal ROIs obtained from images reconstructed with maximum likelihood algorithm. IC and myocardium tissue uptake can be safely obtained from rat heart scans and corrected for spillover using FADS for images obtained with either iterative reconstruction or with the usual filtered backprojection.