MOLLI T₁ mapping versus T₂ W-SPAIR at 3T: myocardial area at risk measurements and the influence of microvascular obstruction

Background

Robust CMR imaging is required for the delineation of myocardial area at risk (AAR), so that the success of reperfusion therapies can be evaluated. In this work, we investigate the performance of T₁ mapping in assessing AAR one week post-STEMI, and explore the effect of microvascular obstruction (MVO) on T₁ relaxation times.

Methods

CMR imaging was conducted on a Philips 3T Achieva MRI scanner. T₂W-weighted spectral attenuated inversion recovery (T₂WW-SPAIR), modified look-locker inversion recovery (MOLLI) T₁ mapping and late gadolinium enhancement (LGE) sequences were applied as short axis stacks in 10 healthy volunteers and 62 STEMI patients. Receiver operator characteristic (ROC) analysis was applied to calculate a cut-off T₁ to to discriminate AAR from normal myocardium. The presence of LGE was used as the positive ROC test state, while healthy myocardium, as measured in volunteers, was used as the negative ROC test state. For comparison with T1 mapping, the AAR was also measured on T₂WW images using a threshold signal intensity > 2SD greater than remote. The derived myocardial edema volumes and salvage indices were compared between MVO+ and MVO- groups.

Results

For T₁ mapping, ROC analysis gave a significantly larger area-under-the-curve (AUC) as compared to T₂WW-SPAIR for delineating myocardial edema (AUC = 0.89 vs 0.83, p = 0.009) as well as better sensitivity/specificity (83/83% vs 73/73%). Neither method was significantly affected by the presence of MVO. The calculated ROC cut-off for T₁ mapping was 1243 ms, and this gave a significantly larger AAR than that measured with a T₂W-SPAIR 2SD threshold (p = 0.006). Using the T₁ mapping cut-off, patients with MVO had a significantly larger AAR and a poorer salvage index than patients without MVO (p < 0.05 for both). The AAR measured using each of the two methods is illustrated in Figure 1, and AAR and salvage index measurements are shown in Table 1.

Figure 1

The area at risk as delineated by (A) MOLLI T ₁ mapping and (B) T ₂ -weighted SPAIR.

Table 1 Area at Risk and Salvage Index

Conclusions

T₁ mapping at 3T can be used to automatically delineate AAR one week post-STEMI. It delimits larger volumes of edema and demonstrates less variability than T₂WW-SPAIR. MVO did not significantly affect the discriminatory power of either of these techniques at seven days post-STEMI.

Funding

This study was supported by a Medical Research Council (UK) grant, as a sub-study of Nitrites in Acute Myocardial Infarction, NCT01388504.