The present invention relates to methods for determining whether a mammal has a disease, such as diabetes, using PET data analysis techniques. These methods include administering to a mammal a PET-compatible tracer, such as a radioligand specific for a vesicular monoamine transporter 2 (VMAT2) receptor, and measuring total functional β-cell capacity (volume) of the mammal's pancreas using PET data analysis techniques. Methods for tracking the efficacy of a treatment for diabetes, for evaluating the regeneration of β-cells in a pancreas, and for monitoring a patient with a transplanted pancreas are also provided.
