Gated 99mTc-tetrofosmin and 18F-FDG studies: a comparison of single-acquisition and separate-acquisition protocols

18F-FDG is a well-established tracer for evaluating myocardial viability, as is (99m)Tc-tetrofosmin (TET) for evaluating myocardial perfusion. Dual-isotope single-acquisition (DISA) studies using a (99m)Tc perfusion agent and (18)F-FDG have been performed to evaluate myocardial viability. The purpose of this investigation was to determine whether there is a difference in the results of gated SPECT DISA, compared with gated SPECT DIDA (dual-isotope dual-acquisition) studies using (99m)Tc-TET/(18)F-FDG and a high-energy collimated dual-head SPECT system.

We prospectively studied 13 patients with depressed left ventricular function using both acquisition protocols. Summed rest scores were calculated for both (99m)Tc and (18)F-FDG studies using a 12-segment model and a 5-grade severity score. Images were evaluated by a single reader who did not know whether the images were acquired separately or simultaneously.

The concordance of DISA and DIDA protocols for (99m)Tc-TET when allowing no difference in the SRS was 57%, or 89 of 156 segments. The concordance of DISA and DIDA protocols for (18)F-FDG was 86%, or 134 of 156 segments. The concordance of segments determined to be viable versus nonviable was 92%, or 143 of 156 segments. Ejection fraction measurements obtained by gated (99m)Tc-TET studies correlated strongly with those obtained by gated (18)F-FDG studies.

A high concordance for (18)F-FDG studies was shown between gated DISA and gated DIDA. A lower concordance was shown between gated DISA and gated DIDA studies using (99m)Tc-TET, most likely because of downscatter from (18)F into the (99m)Tc window. An excellent concordance was demonstrated between the 2 techniques for viability assessment. The gated (99m)Tc-TET/(18)F-FDG DISA protocol can be both a reliable and an efficient way to evaluate myocardial function, perfusion, and viability.