SCMR 22nd Annual Scientific Sessions
Successful myocardial blood flow (MBF) increase with vasodilation stress is key to ischemia evaluation in cardiovascular magnetic resonance (CMR). Splenic switch-off has been described as a practical method to assess these changes but it does not allow for direct evaluation of the myocardium and only provides information after contrast injection. T2* reflects different levels of myocardial blood oxygenation and may be useful in providing pre-contrast evaluation of vasodilation in the heart. We sought to study the correlation of myocardial T2*, splenic perfusion and MBF changes at different levels of vasodilation using quantitative measurements for all variables.
Patients scheduled for a non-stress CMR study were selected and underwent vasodilation stimulus with different doses of dipyridamole (0.18mg/kg to 0.56mg/kg) or no vasodilation (repeat perfusion) in a Siemens Skyra 3T scanner. Myocardial T2*/R2* were acquired before and after vasodilation, pre-contrast, using a free-breathing sequence with automated maps using the Gadgetron framework. MBF was obtained from a quantitative automated map also generated with Gadgetron, after contrast infusion at rest and stress, with myocardial perfusion (MP) ratios calculated from stress/rest maps. Splenic switch off was quantified using the peak signal intensity at stress and rest, corrected for pre-contrast signal, and calculating the spleen signal intensity ratio (SSIR). Correlation coefficients between MBF, MP ratios, changes in T2*/R2* and SSIR were evaluated and ROC curves were used to assess the accuracy of both T2*/R2* maps and splenic switch-off to determine effective vasodilation.
Forty patients (62.9±12.2 years, 55% males) participated in the study. Changes in T2* and SSIR with vasodilation stimulus and at rest were significantly correlated to MP ratio (r=0.56 [0.31 to 0.75] and r=-0.49 [-0.7 to -0.22]; p=0.0001 and p=0.001 respectively). Both variables also significantly correlated to the maximum obtained MBF (r=0.62 [0.39 to 0.78] and r=-0.55 [-0.74 to -0.29]; p 1.4 as the cutoff for a positive vasodilation stimulus, a decrease in R2* ≤ -1.54Hz provided better discrimination for identifying successful stimulus compared to changes in SSIR (AUC = 0.978 vs 0.827, P=0.04) – Figure 1). The use of SSIR misclassified 8/40 patients in comparison to 2/40 cases with T2* maps (P=0.04). An example of a normal case (no stimulus), matching T2* and SSIR changes and mismatches between T2* and SSIR findings are shown in Figure 2.
Conclusion: Myocardial T2* values before and after vasodilation stimulus significantly correlate to changes in MBF and may provide better discrimination of successful stimulus in comparison to quantitative splenic switch-off analysis.