FIGURE 2.  Correlation between MBF estimated from ¹⁵O-water and MBF measured directly using radiolabeled microspheres (MIC) (A) and the corresponding residual plot (B). Mean residual error (MRE) was calculated as the average of the absolute difference between measured and predicted MBF values from the regression analysis in A. •, resting perfusion; , perfusion during dobutamine; , perfusion during propranolol infusion.