T₂ preparation method for measuring hyperemic myocardial O ₂ consumption: In vivo validation by positron emission tomography

Purpose To validate a new T₂-prepared method for the quantification of regional myocardial O₂ consumption during pharmacologic stress with positron emission tomography (PET). Materials and Methods A T₂ prepared gradient-echo sequence was modified to measure myocardial T₂ within a single breath-hold. Six beagle dogs were randomly selected for the induction of coronary artery stenosis. Magnetic resonance imaging (MRI) experiments were performed with the T₂ imaging and first-pass perfusion imaging at rest and during either dobutamine- or dipyridamole-induced hyperemia. Myocardial blood flow (MBF) was quantified using a previously developed model-free algorithm. Hyperemic myocardial O ₂ extraction fraction (OEF) and consumption (MVO₂) were calculated using a two-compartment model developed previously. PET imaging using ¹¹C-acetate and ¹⁵O-water was performed in the same day to validate OEF, MBF, and MVO₂ measurements. Results The T ₂-prepared mapping sequence measured regional myocardial T ₂ with a repeatability of 2.3%. By myocardial segment-basis analysis, MBF measured by MRI is closely correlated with that measured by PET (R ² = 0.85, n = 22). Similar correlation coefficients were observed for hyperemic OEF (R² = 0.90, n = 9, mean difference of PET - MRI = -2.4%) and MVO₂ (R² = 0.83, n = 7, mean difference = 4.2%). Conclusion The T₂-prepared imaging method may allow quantitative estimation of regional myocardial oxygenation with relatively good accuracy. The precision of the method remains to be improved.