Comparison of sestamibi, tetrofosmin, and Q12 retention in porcine myocardium

Although there are several ^99mTc perfusion tracers introduced for clinical use, there are no data available directly comparing these tracers with microsphere-determined flow. The aim of this study was to compare the myocardial retention of sestamibi, tetrofosmin, and Q12 in a porcine model. Methods: We used a pig model with (n = 6) or without (n = 3) coronary occlusion. Each pig received a simultaneous injection of sestamibi and either tetrofosmin (group 1, n = 5) or Q12 (group 2, n = 4) labeled with either ^99mTc or ^95mTc (physical half-life, 61 d; photon energy, 204 keV) during pharmacologic vasodilation. Absolute myocardial retention of each tracer was calculated from the myocardial tracer activity and arterial input function. Results: The plot of all three tracers versus flow achieved a plateau at a higher flow range. However, sestamibi showed a higher mean retention than either tetrofosmin (group 1, 0.27 ± 0.11 vs. 0.16 ± 0.06 mL/g/min, respectively; P < 0.01) or Q12 (group 2, 0.32 ± 0.13 vs. 0.09 ± 0.03 mL/g/min, respectively; P < 0.01). Furthermore, when a linear regression analysis was performed to assess the relationship between retention and microsphere-determined flow, sestamibi showed a greater increment in retention than did tetrofosmin or Q12. Conclusion: Although all of the tracers showed a nonlinear increase in retention as flow increased, sestamibi may display more favorable characteristics as a flow tracer in the porcine heart.