Feasibility of dual-isotope coincidence/single-photon imaging of the myocardium.

Hybrid PET scanners offer the possibility of obtaining myocardial viability information from coincidence imaging of the positron emitter (18)F-FDG and perfusion measurements from a single-photon tracer-potentially simultaneously. This new approach is less costly and more readily available than dedicated PET and offers potential for improved FDG resolution and sensitivity compared with SPECT with 511-keV collimators. Simultaneous imaging of the coincidence and single-photon events offers the further advantages of automatic image registration and reduced imaging time. However, the feasibility of simultaneous coincidence/single-photon imaging or even immediately sequential imaging is unknown. In this study, the potential of using standard low-energy high-resolution (LEHR) collimators with hybrid PET to obtain coincidence and SPECT data was assessed. METHODS: Phantom and human studies were performed to investigate the effect of LEHR collimators on FDG coincidence imaging with a hybrid PET system, the effect of the presence of (99m)Tc during FDG coincidence imaging with LEHR collimators, and the effect of the presence of FDG during (99m)Tc SPECT imaging. RESULTS: FDG images were somewhat degraded (a measure of myocardial nonuniformity increased 10%) with LEHR collimators. With 148 MBq (4 mCi) (99m)Tc present during FDG imaging of a phantom, image quality was maintained and the number of detected coincidences changed by <5%. With (99m)Tc/(18)F whole-body ratios of 7:1, crosstalk from (18)F photons accounted for the majority of counts in the (99m)Tc SPECT images and resulted in severe artifacts. The artifacts were decreased with a simple crosstalk correction scheme but remained problematic. CONCLUSION: (99m)Tc/(18)F ratios of at least 9:1 and state-of-the-art reconstruction and crosstalk correction are likely to be required to perform immediately sequential coincidence/single-photon imaging of the myocardium with clinically useful results. Additional challenges remain before simultaneous imaging of coincidence events and single photons can be realized in practice.