Positron emission tomography (PET) is a established quantitative and noninvasive imaging modality. With the PET reporter gene (PRG)/PET reporter probe (PRP) system, based on a mutant form of herpes simplex virus 1 thymidine kinase (HSV1-sr39tk), the PET signal is directly proportional to the enzymatic activity of sr39TK9-14. In this protocol, we describe in detail a method for reporter gene labeling of islets and quantitative scanning using a reporter probe. - [Read In Vivo Functional Real-Time Imaging of Transplanted Islets Using Positron Emission Tomography (PET)]