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Gated ^99mTc-Tetrofosmin and ¹⁸F-FDG Studies: A Comparison of Single-Acquisition and Separate-Acquisition Protocols

¹ Division of Nuclear Medicine, Department of Radiology, Duke University Medical Center, Durham, North Carolina
² Division of Cardiology, Department of Internal Medicine, Duke University Medical Center, Durham, North Carolina

¹⁸F-FDG is a well-established tracer for evaluating myocardial viability, as is ^99mTc-tetrofosmin (TET) for evaluating myocardial perfusion. Dual-isotope single-acquisition (DISA) studies using a ^99mTc perfusion agent and ¹⁸F-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 ^99mTc-TET/¹⁸F-FDG and a high-energy collimated dual-head SPECT system.

Methods: We prospectively studied 13 patients with depressed left ventricular function using both acquisition protocols. Summed rest scores were calculated for both ^99mTc and ¹⁸F-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.

Results: The concordance of DISA and DIDA protocols for ^99mTc-TET when allowing no difference in the SRS was 57%, or 89 of 156 segments. The concordance of DISA and DIDA protocols for ¹⁸F-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 ^99mTc-TET studies correlated strongly with those obtained by gated ¹⁸F-FDG studies.

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

Key Words: dual-isotope single acquisition; downscatter; ¹⁸F-FDG