Aim: Digestive activity can interfere with the interpretation of myocardial perfusion single photon emission computed tomography using sestamibi or tetrofosmin. Compared with sestamibi, the liver clearance of tetrofosmin is more rapid, but its absolute cardiac uptake is lower. In this study, the activity of sestamibi and tetrofosmin was quantified after exercise or pharmacological stress and at rest to objectify the biokinetic differences and to evaluate whether there is a correlation between quantitative measurements and the visual assessment of image quality.
Methods: Left ventricular activity and five ratios (R1-R5) of cardiac to adjacent extra-cardiac activity were quantified in 204 sestamibi (68 exercise stress/56 pharmacological stress/80 rest) and 221 tetrofosmin (67 exercise stress/59 pharmacological stress/95 rest) studies. Image quality was assessed by a three-point score (1, good; 2, moderate; 3, poor) and correlated with the heart to left supra-diaphragmatic region (R1) and heart to right supra-diaphragmatic region (R2) ratios.
Results: The mean left ventricular activity was higher for sestamibi, especially at rest (sestamibi, 0.21+/-0.05 counts/pixel/injected MBq; tetrofosmin, 0.16+/-0.042 counts/pixel/injected MBq; P<0.001). By contrast, most ratios were higher with tetrofosmin, particularly for the exercise stress and rest studies. Using the three-point quality scoring, more sestamibi than tetrofosmin studies were scored as 3 (12.2% versus 6.3%), also particularly for the exercise stress and rest studies. A highly significant relationship was found between decreasing R1 and R2 and an increasing quality score, regardless of the radiopharmaceutical used (P values between 0.02 and <0.001).
Conclusions: Despite a lower cardiac uptake, the more rapid liver clearance of tetrofosmin than sestamibi significantly improves the ratios of cardiac to digestive activity, especially after exercise or at rest. These quantitative differences in biokinetics result in less poor scans with tetrofosmin in daily practice.