| Positron emission tomography (PET) is an emerging clinical imaging modality that can be used to characterize many different aspects of physiology using various radiotracers. Current technology limits PET to a single tracer per imaging session, since all tracers give rise to indistinguishable 511 keV photons. This work focused primarily on the initial development of technology for rapid multi-tracer PET. In this approach, using dynamic imaging techniques and staggered tracer injections, overlapping signals from different PET tracers can be separated based on information such as tracer kinetics and half-lives. Simulation studies were performed to test the feasibility of rapid dual-tracer and triple-tracer tumor imaging using several different tracers and a parallel compartment modeling method for signal separation. This worked showed that rapid multi-tracer imaging with injections as short as 10 min apart can provide kinetic rate parameter estimates for each tracer with similar accuracy as compared to conventional single-tracer imaging. An extensive simulation study was then performed to test rapid dual-tracer PTSM + ATSM PET imaging of tumor blood flow and hypoxia as a function of injection delay, order, and relative dose for several copper isotopes. Using scans as short as 30 min, the dual-tracer method provided measures of blood flow and hypoxia similar to separate single-tracer imaging. Ongoing canine studies are being performed to further evaluate rapid PTSM + ATSM PET in a physiologically realistic model. A rapid dual-injection single-scan approach for quantification of myocardial blood flows using 13N-ammonia PET was proposed and tested using data from human subjects. Dynamic scans were acquired using imaging protocols that provided separate single-injection data as gold standards, and these data were combined to emulate rapid dual-injection imaging. Background subtraction and combined modeling methods were applied to recover rest and stress myocardial blood flow estimates, with results very similar to conventional single-injection standards. This work demonstrates that blood flow quantification can be obtained in only 20 min by the rapid dual-injection approach with accuracy similar to that of conventional separate rest and stress scans. These promising results suggest that rapid multi-tracer PET merits further development and evaluation for potential clinical use. |
