Parametric Imaging of Ligand-Receptor Binding in PET Using a Simplified Reference Region Model

A method is presented for the generation of parametric images of radioligand–receptor binding using PET. The method is based on a simplified reference region compartmental model, which requires no arterial blood sampling, and gives parametric images of both the binding potential of the radioligand and its local rate of delivery relative to the reference region. The technique presented for the estimation of parameters in the model employs a set of basis functions which enables the incorporation of parameter bounds. This basis function method (BFM) is compared with conventional nonlinear least squares estimation of parameters (NLM), using both simulated and real data. BFM is shown to be more stable than NLM at the voxel level and is computationally much faster. Application of the technique is illustrated for three radiotracers: [ 11C]raclopride (a marker of the D2 receptor), [ 11C]SCH 23390 (a marker of the D1 receptor) in human studies, and [ 11C]CFT (a marker of the dopamine transporter) in rats. The assumptions implicit in the model and its implementation using BFM are discussed.