T1 measurements in the human myocardium: the effects of magnetization transfer on the SASHA and MOLLI sequences.
Robson MD., Piechnik SK., Tunnicliffe EM., Neubauer S.
PURPOSE: Quantitative mapping of the native T1 of the heart using the modified look-locker inversion recovery (MOLLI) technique provides high quality diagnostic information without requiring contrast agents. Previous work has considered the effects of T2 relaxation on MOLLI T1 measurements, finding that the T1 measured by MOLLI is biased, and that Saturation-recovery single-Shot Acquisition generates a more precise T1. However, despite detailed experiments and simulation the exact relaxation times observed in vivo remain unexplained, but might be due to magnetization transfer (MT). METHODS: We used an MT simulation based on the Bloch-McConnell equations to evaluate the most common MOLLI and saturation-recovery single-shot acquisition sequence variants. RESULTS: For myocardial tissue we find that the T1 measured by saturation-recovery single-shot acquisition is insensitive to MT and T2, whereas MT reduces the T1 measured by MOLLI (>10%) in addition to the effects due to T2 relaxation. CONCLUSIONS: The consequences of this T1 underestimation by MOLLI are relevant. Increases in the actual T1 and T2 and decreases in MT will all result in an increase in T1 measured by MOLLI. Myocardial infarction demonstrates increased native T1 and T2 and decreased MT, indicating that these biases enhance the sensitivity of MOLLI to detect this and possibly other cardiovascular disease states.