Magnetic Resonance Imaging of Myocardial Contrast Enhancement with MS-325 and Its Relation to Myocardial Blood Flow and the Perfusion Reserve

Purpose: To determine with an intravascular contrast agent the relation between the rate of myocardial signal enhancement during the first pass (upslope) and myocardial blood flow (MBF), and to derive and validate a corrected perfusion reserve (PR) index from the upslope parameter. Materials and Methods: Measurements of the upslope parameter for myocardial contrast enhancement with an intravascular contrast agent (MS-325) were performed in a porcine model with ameroid coronary constrictor. MBF was estimated with MRI and was validated against separate invasive measurements with labeled microspheres. PR indices were calculated from the upslope of the tissue curves. A new PR index was corrected by the time delay between appearance of the tracer and the upslope maximum. Results: MBFs determined by MRI vs. MBFs measured with microspheres were in agreement within the 95% confidence intervals (CIs) for the identity relation. The new PR index slightly overestimated the MBF reserve by an average + 1.4% (95% CI = -44% to +46%). The uncorrected PR index underestimated the MBF reserve by -33% (95% CI = -92% to +25%). Conclusion: A perfusion index derived from the maximum upslope of myocardial contrast enhancement produces accurate estimates of the PR if corrected by the time-to-maximum upslope.