Optimization and validation of a fully-integrated pulse sequence for modified Look-Locker inversion-recovery (MOLLI) T1 mapping of the heart
ABSTRACT To optimize and validate a fully-integrated version of modified Look-Locker inversion-recovery (MOLLI) for clinical single-breathhold cardiac T1 mapping.
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.
In phantoms, a readout flip angle of 35 degrees , minimum 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 T1 measurements. Using this pulse sequence scheme in humans, T1 relaxation times in normal myocardium were comparable to data from previous studies, and showed narrow ranges both pre- and postcontrast without heart rate dependency.
We present an optimized implementation of MOLLI for fast T1 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.
- SourceAvailable from: Donnie Cameron
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- "" Conventional MOLLI " , based on the optimised original MOLLI sequence, was chosen as a standard for comparisons—to evaluate any improvements relative to this widely reported method. The sequence consisted of three IR blocks, in a 3b(3b)3b(3b)5b arrangement, with b's indicating images were acquired one-per-beat, with a three beat pause between consecutive IR blocks. "
ABSTRACT: Background: The purpose of this work was to evaluate different magnetisation preparation and readout sequences for modified Look-Locker inversion recovery (MOLLI) towards improved T1 mapping in the heart. Elements investigated include: catalysation sequences to prepare the magnetisation before readout, alternate k-space trajectories, a spoiled gradient recalled echo (GRE) readout, and a 5b(3b)3b MOLLI sampling scheme (‘b’ denoting beats). Methods: Conventional 3b(3b)3b(3b)5b MOLLI with a linear k-space trajectory was compared to four variants in simulations, in vitro and in vivo (at 3T). Variants were centric conventional MOLLI, centric-paired conventional MOLLI, linear 5b(3b)3b MOLLI and spoiled GRE MOLLI. Each of these was applied with three magnetisation catalysation methods, and T1 measurement accuracy and precision were evaluated in simulations via a Monte Carlo algorithm, in a set of calibrated phantoms, and in ten healthy volunteers. Contrast-to-noise, heart rate dependence and B1+ dependence were also evaluated. Results: A linear k-space trajectory was superior in vitro to centric and centric-paired trajectories. Of the catalysation methods, preparation of transverse magnetisation only—using a linearly increasing flip angle catalysation—improved MOLLI T1 measurement accuracy, precision, and map quality versus methods that include catalysation of the longitudinal magnetisation. The 5b(3b)3b MOLLI scheme offered comparable native T1 measurement accuracy and precision to conventional MOLLI, despite its shortened acquisition. Conclusions: MOLLI T1 measurement accuracy, precision, and map quality depends on the method of catalysation of magnetisation prior to image acquisition, as well as on the readout method and MOLLI sampling scheme used.Magnetic Resonance Imaging 02/2015; DOI:10.1016/j.mri.2015.02.004 · 2.02 Impact Factor
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