EFFECTS OF TIME DISCREPANCIES BETWEEN INPUT AND MYOCARDIAL TIME-ACTIVITY CURVES ON ESTIMATES OF REGIONAL MYOCARDIAL PERFUSION WITH PET

Estimates of myocardial perfusion with PET using kinetic models requir e faithful recording of radioactivity content in blood and myocardium. Typically the arterial time-activity curve is obtained by placing a r egion of interest (ROIs) within the left atrial or left ventricular ca vity. However, curves generated from these regions appear earlier in t ime than tissue time-activity curves obtained from ROls within the myo cardial tissue, and such time discrepancies can lead to errors in flow estimates. Methods: The magnitude of these time discrepancies and the ir effect on estimates of regional myocardial perfusion using oxygen-1 5-water were measured in 30 normal subjects evaluated at rest and agai n after administration of dipyridamole. Results: Under baseline condit ions, the left atrial curve appeared 0.97 +/- 0.67 (s.d.) before the a scending aorta input curve (p < 0.05) and estimated perfusion decrease d from 1.28 +/- 0.28 ml/g/min using the left atrial curve uncorrected for time to 0.98 +/- 0.27 ml/g/min after correction (p < 0.05). After dipyridamole, the left atrial curve appeared 0.68 +/- 0.72 sec before the ascending aorta curve (p < 0.05) and estimated perfusion decreased from 3.60 +/- 1.40 ml/g/min using the left atrial curve uncorrected f or time to 3.24 +/- 1.26 ml/g/min using the time-corrected curve (p < 0.05). Because the magnitude of time discrepancies between the left ve ntricular and ascending aortic curves was less (0.25 +/- 0.34 and 0.19 +/- 0.23 sec at rest and after dipyridamole, respectively), effects o n flow estimates were more modest. Conclusions: The results of this st udy demonstrate that time discrepancies between input and tissue time- activity curves can affect estimates of myocardial flow. Correction fo r this potential source of error is proposed.