 Positron emission tomography PET is a molecular imaging modality that can probe various aspects of tumor function using a variety of radio-labeled imaging agents tracers. Oncologic PET imaging has seen a dramatic rise in clinical utilization over the past decade for cancer detection, staging, and evaluating residual or recurrent disease following therapy. These clinical scans use the tracer 18Ffluoro-2-deoxy-D-glucose FDG, which accumulates in cells in proportion to GLUT transporter and hexokinase activity. FDG thus provides a measure of tissue glucose metabolism. Concurrent with this clinical growth, a number of other PET tracers have received significant attention in research for a variety of imaging targets. Of special interest are the tracers 3-deoxy-3-18Ffluorothymidine FLT, 1-11C-acetate ACE, and 15Owater H2O. The uptake, retentionwashout, and ultimate biodistribution of these tracers are each related to different functional or molecular processes. As such, each can be used to probe a different aspect of tumor function: FLT directly assesses tumor proliferation, ACE provides a measure of tumor growth related to fatty acid and membrane synthesis, and H2O quantifies tumor perfusion. 