Influence of spatially heterogeneous background activity on ''hot object'' quantitation in brain emission computed tomography

Purpose: Our goal was to evaluate the influence of spatially heterogeneous background activity on ''hot object'' quantitation in brain emission CT. Method: We studied the effects of spatially heterogeneous background activity on hot object quantitative recovery in simulations of both spheres and realistic brain distributions (utilizing human MRI data). Results: Significant underestimation of object activity concentration was seen for both cortical and subcortical hot objects, with increasing underestimation for increasing hot object/surrounding gray matter contrast. Significant ''spill-in'' of counts from surrounding activity was present. Conclusion: Hot objects are significantly influenced by both ''spill-out'' and ''spill-in.'' Qualitative and quantitative analyses of such objects must explicitly consider both spill-out and spill-in; this implies a correction scheme that goes beyond simple division of the observed value by a conventional recovery coefficient.