Quantification of myocardial blood flow with Rb positron emission tomography: clinical validation with O-water.

Purpose: Quantification of myocardial blood flow (MBF) with generator-produced Rb is an attractive alternative for centres without an on-site cyclotron. Our aim was to validate Rb-measured MBF in relation to that measured using O-water, as a tracer 100% of which can be extracted from the circulation even at high flow rates, in healthy control subject and patients with mild coronary artery disease (CAD). Methods: MBF was measured at rest and during adenosine-induced hyperaemia with Rb and O-water PET in 33 participants (22 control subjects, aged 30 ± 13 years; 11 CAD patients without transmural infarction, aged 60 ± 13 years). A one-tissue compartment Rb model with ventricular spillover correction was used. The Rb flow-dependent extraction rate was derived from O-water measurements in a subset of 11 control subjects. Myocardial flow reserve (MFR) was defined as the hyperaemic/rest MBF. Pearson's correlation r, Bland-Altman 95% limits of agreement (LoA), and Lin's concordance correlation ρ (measuring both precision and accuracy) were used. Results: Over the entire MBF range (0.66-4.7 ml/min/g), concordance was excellent for MBF ( r = 0.90, [Rb-O-water] mean difference ± SD = 0.04 ± 0.66 ml/min/g, LoA = −1.26 to 1.33 ml/min/g, ρ = 0.88) and MFR (range 1.79-5.81, r = 0.83, mean difference = 0.14 ± 0.58, LoA = −0.99 to 1.28, ρ = 0.82). Hyperaemic MBF was reduced in CAD patients compared with the subset of 11 control subjects (2.53 ± 0.74 vs. 3.62 ± 0.68 ml/min/g, p = 0.002, for O-water; 2.53 ± 1.01 vs. 3.82 ± 1.21 ml/min/g, p = 0.013, for Rb) and this was paralleled by a lower MFR (2.65 ± 0.62 vs. 3.79 ± 0.98, p = 0.004, for O-water; 2.85 ± 0.91 vs. 3.88 ± 0.91, p = 0.012, for Rb). Myocardial perfusion was homogeneous in 1,114 of 1,122 segments (99.3%) and there were no differences in MBF among the coronary artery territories ( p > 0.31). Conclusion: Quantification of MBF with Rb with a newly derived correction for the nonlinear extraction function was validated against MBF measured using O-water in control subjects and patients with mild CAD, where it was found to be accurate at high flow rates. Rb-derived MBF estimates seem robust for clinical research, advancing a step further towards its implementation in clinical routine. [ABSTRACT FROM AUTHOR]