A suite of emerging techniques, known collectively as “molecular imaging,” now offer scientists an unprecedented opportunity to identify, follow, and quantify biologic processes at the cellular level with molecular specificity in intact organisms. For instance, it is now possible to evaluate, with imaging, the distribution, magnitude, and timing of gene expression in genetically altered animals (1–3). Even though nonimaging methods are also available to monitor gene expression, such methods—usually based on tissue sampling—are invasive and unattractive as routine procedures for clinical investigations. In contrast, molecular imaging can provide a seamless translation from studies in animals to later studies in humans
