Differential background clearance of fluorodeoxyglucose activity in normal tissues and its clinical significance

The clearance of FDG activity in normal tissues (and thus the background level) varies significantly with extended distribution time. Although most tissues have lower SUV values on 2-hour/3-hour delayed images, others may have stable or higher FDG activity with longer distribution times. This finding has to be taken into consideration when interpreting an FDG-PET study that is performed with significantly short or long distribution time, and when comparing 2 studies with different distribution times. The continuously decreased SUV value from 1 to 3 hours in some tissues, especially in the liver, indicates that longer distribution time will decrease background activity and improve imaging quality, whereas the continuously increased SUV values from 1 to 3 hours in the heart suggest that longer distribution time will improve detection of viable myocardium in a viability study.