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Correlations Between Uptake of Technetium-99m Q12 and Thallium-201: Myocardial Perfusion and Viability in a Model of Acute Coronary Reperfusion

Myocardial Isotope Research Laboratory and Departments of Medicine and Nuclear Medicine, University of Massachusetts Medical Center, Worcester, Massachusetts

Correspondence: For correspondence or reprints contact: Jeffrey A. Leppo, MD, Department of Nuclear Medicine, University of Massachusetts Medical Center, 55 Lake Avenue North, Worcester, MA 01655-0243.

ABSTRACT

To investigate whether Q12 uptake is affected by myocardial viability, as has been noted for ²⁰¹Tl and sestamibi, we analyzed the initial and delayed distribution patterns of Q12 in a rat coronary artery occlusion-reperfusion model. Methods: Animals were intubated and ventilated, and their arterial pressures were monitored. A left thoracotomy was performed. After a 1-hr occlusion and a 1-hr reperfusion of a major branch of the circumflex artery, ²⁰¹Tl and Q12 were injected intravenously. Radiolabeled microspheres were used to document the areas of risk and reperfusion. The animals were killed at 5 min or 1 hr after administration of the diffusible tracers. Tracer distribution was determined by segmental tissue analysis, and tissue viability was determined by histochemical staining. Results: Both the initial uptake and delayed retention of Q12 are sensitive to myocardial viability as shown by significantly lower uptake (28% ± 8%) and retention (41% ± 13%) of Q12 in the nonviable as compared to the viable segments (p < 0.001). In addition, the myocardial retention of Q12 was significantly less in the nonviable tissue when compared to the initial uptake (p < 0.01). Conclusion: The clinical implication of these observations suggests that initial and delayed imaging after Q12 administration would reflect both the initial regional blood flow pattern and myocardial viability. Also, delayed imaging of Q12 may reflect viability better than the initial imaging.

Key Words: technetium-99m Q12 • myocardial viability • ischemia • coronary artery disease • thallium-201