INVITED COMMENTARY Gated PET and Ventricular Volume Cardiac research increasingly relies

on small animals (rats and mice) in which the study of phenotypic expres-sions of genomic defects as well as the evaluation of gene therapies is possible. Accordingly, over the past few years new dedicated instruments have been developed that allow noninvasive imag-ing with ultrasound, magnetic resonance, and PET in small animals in vivo. These techniques can be used to monitor gene expression in vivo but can also simulta-neously assess physiologic parameters such as myocardial blood flow in the same animal (1). Accurate measurement of physiologic parameters in small ani