Optimization and validation of a fully-integrated pulse sequence for modified look-locker inversion-recovery (MOLLI) T1 mapping of the heart

Purpose: To optimize and validate a fully-integrated version of modified Look-Locker inversion-recovery (MOLLI) for clinical single-breathhold cardiac T1 mapping. Materials and Methods: A MOLLI variant allowing direct access to all pulse sequence parameters was implemented on a 1.5T MR system. Varying four critical sequence parameters MOLLI was performed in eight gadolinium-doped agarose gel phantoms at different simulated heart rates. T1, values were derived for each variant and compared to nominal T1 values. Based on the results, MOLLI was performed in midcavity short-axis views of 20 healthy volunteers pre-and post-Gd-DTPA. Results: In phantoms, a readout flip angle of 35 degrees, mini- mum TI of 100 msec, TI increment of 80 msec, and use of three pausing heart cycles allowed for most accurate and least heart rate-dependent TI measurements. Using this pulse sequence scheme in humans, TI relaxation times in normal myocardium were comparable to data from previous studies, and showed narrow ranges both pre- and post- contrast without heart rate dependency. Conclusion: We present an optimized implementation of MOLLI for fast TI mapping with high spatial resolution, which can be integrated into routine imaging protocols. T1 accuracy is superior to the original set of pulse sequence parameters and heart rate dependency is avoided.