Instantaneous signal loss simulation (InSiL): An improved algorithm for myocardial T1 mapping using the MOLLI sequence

Abstract

Purpose: To propose a T1 mapping algorithm for the modified Look-Locker inversion-recovery (MOLLI) sequence that can improve T1 estimation accuracy. Materials and Methods: The modified T1 mapping algorithm (InSiL) is based on the simulation of MOLLI signal evolution and simulates the longitudinal magnetization signal perturbation by each single-shot image acquisition in MOLLI as an instantaneous signal loss. InSiL was evaluated against original MOLLI using Bloch simulations, phantom studies, and in 15 healthy volunteers at 1.5T. Results: In phantom studies, the maximum absolute error by InSiL is less than 2%, while that by MOLLI is more than 20% for T1 values from 221 msec to 1539 msec. The benefit of InSiL is greatest at heart rate (HR) >80 bpm and T1 >1000 msec, and InSiL reduced MOLLI T1 error from 14.964.5% to 0.460.3%. Average InSiL-derived native myocardial T1 values at 1.5T in healthy volunteers were significantly higher than MOLLI-derived values by 236.9±11.7 msec (1160.3±25.1 msec vs. 923.4±22.3 msec, P<0.001) at an average HR of 65.1±14.7 bpm. Conclusion: The proposed InSiL approach yields better T1 mapping accuracy than MOLLI, and is less sensitive to HR variation in tissues with longer T1 values.