Systematic differences in myocardial blood flow and flow reserve quantification using Rubidium-82 and [¹⁵O]H₂O...

While Rubidium-82 (⁸²Rb) positron emission tomography (PET) myocardial perfusion imaging (MPI) has a well-established myocardial flow reserve (MFR) cut-off of <2 for prognosis, no consensus exists for [¹⁵O]H₂O PET.

Forty-four patients referred for routine ⁸²Rb PET MPI underwent same-day [¹⁵O]H₂O PET MPI. Myocardial blood flow (MBF) and MFR measurements corrected for nonlinear ⁸²Rb extraction were compared. Additionally, a pooled analysis including five similar studies was conducted.

Global MBF was higher at rest (relative difference 26%, 95% confidence interval [CI]: 21-31) and lower at stress (relative difference -17%, 95% CI: -24 to -10) measured by ⁸²Rb vs [¹⁵O]H₂O PET. Global MFR was lower measured by ⁸²Rb vs [¹⁵O]H₂O PET (relative difference -42%, 95% CI: -48% to -37%). The directions of the observed biases were confirmed in the pooled analysis. Correction for nonlinear ⁸²Rb extraction with the equation by Prior et al. compared to Lortie et al. demonstrated better agreement of stress MBF between the tracers. Applying the relative differences of MFR, the prognostic cut-off for MFR of 2 using ⁸²Rb PET corresponds to an MFR using [¹⁵O]H₂O PET of 3.1 (95% CI: 2.9-3.3) in the present study and 2.5 (95% CI: 2.4-2.6) in the pooled analysis.

⁸²Rb PET overestimates global MBF at rest, underestimates global MBF at stress, and underestimates global MFR compared with [¹⁵O]H₂O PET, despite correction for nonlinear extraction. Validation of prognostic cut-off values for [¹⁵O]H₂O PET is needed, and caution should be taken in directly comparing MBF and MFR obtained by these two tracers.