Optimization and validation of a fully-integrated pulse sequence for modified Look-Locker inversion-Recovery (MOLLI) T1 mapping of the heart

Cardiac MRI Unit, Franz-Volhard-Klinik, Charité Campus Buch, Universitätsmedizin Berlin, Helios-Klinikum Berlin, Germany.
Journal of Magnetic Resonance Imaging (Impact Factor: 3.21). 10/2007; 26(4):1081-6. DOI: 10.1002/jmri.21119
Source: PubMed


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.

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    • "Motion-encoding gradients were applied separately in the x, y and z directions to encode the motion in all directions during suspended breathing. 3. T1 modified Look-Locker inversion recovery (MOLLI) and T2-prepared b-SSFP sequences were also applied before contrast to acquire a single basal short-axis slice, matching the slice position used to acquire the MRE images [17] [18]. T1 post-contrast maps were obtained 10 minutes after injection of the contrast agent. "
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    ABSTRACT: Introduction: Myocardial stiffness is an important determinant of cardiac function and is currently invasively and indirectly assessed by catheter angiography. This study aims to demonstrate the feasibility of quantifying right ventricular (RV) stiffness noninvasively using cardiac magnetic resonance elastography (CMRE) in dogs with severe congenital pulmonary valve stenosis (PVS) causing RV hypertrophy, and compare it to remote myocardium in the left ventricle (LV). Additionally, correlations between stiffness and selected pathophysiologic indicators from transthoracic echocardiography (TTE) and cardiac magnetic resonance imaging were explored. Methods: In-vivo CMRE was performed on nine dogs presenting severe congenital PVS using a 1.5T MRI scanner. T1-MOLLI, T2-prepared-bSSFP, gated-cine GRE-MRE and LGE (PSIR) sequences were used to acquire a basal short-axis slice. RV and LV-free-wall (FW) stiffness measurements were compared against each other and also correlated to ventricular mass, RV and LV FW thickness, T1 and T2 relaxation times, and extracellular volume fraction (ECV). Peak transpulmonary pressure gradient and myocardial strain were also acquired on eight dogs by TTE and correlated to RV-FW systolic stiffness. Potential correlations were evaluated by Spearman's rho (rs). Results: RV-FW stiffness was found to be significantly higher than the LV-FW stiffness both during end-systole (ES) (p=0.002) and end-diastole (ED) (p=0.029). Significant correlations were observed between RV-FW ES and LV-FW ED stiffness versus ECV (rs=0.75; p-value=0.05). Non-significant moderate correlations were found between LV-FW ES (rs=0.54) and RV-FW ED (rs=0.61) versus ECV. Furthermore, non-significant correlations were found between RV or LV-FW stiffness and the remaining variables (rs<0.54; p-value>0.05). Conclusion: This study demonstrates the feasibility of determining RV stiffness. The positive correlations between stiffness and ECV might indicate some interdependence between stiffness and myocardial extracellular matrix alterations. However, further studies are warranted to validate our initial observations.
    Magnetic Resonance Imaging 10/2015; DOI:10.1016/j.mri.2015.10.001 · 2.09 Impact Factor
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    • "" Conventional MOLLI " , based on the optimised original MOLLI sequence,[2] 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. "
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    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 · 2.09 Impact Factor
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    • "After recent technical improvements, T1 measurement (multi-breath-hold or multiple images requiring curve fitting and processing) has been replaced by T1 mapping. In a single breath-hold, using various approaches, a T1 colour relaxation map is made [11–13]. Within the map, each given pixel value directly corresponds its underlying relaxation time that can be seen (in colour) or more formally measured, standardized, calibrated to histology [14••, 15, 16], compared across diseases and with normal reference ranges [17]. "
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    ABSTRACT: Heart failure (HF) is a major and growing cause of morbidity and mortality. Despite initial successes, there have been few recent therapeutic advances. A better understanding of HF pathophysiology is needed with renewed focus on the myocardium itself. A new imaging technique is now available that holds promise. T1 mapping is a cardiovascular magnetic resonance (CMR) technique for non-invasive myocardial tissue characterization. T1 alters with disease. Pre-contrast (native) T1 changes with a number of processes such as fibrosis, edema and infiltrations. If a post contrast scan is also done, the extracellular volume fraction (ECV) can be measured, a direct measure of the interstitium and its reciprocal, the cell volume. This dichotomy is fundamental - and now measurable promising more targeted therapy and new insights into disease biology.
    Current Cardiovascular Imaging Reports 09/2014; 7(9):9287. DOI:10.1007/s12410-014-9287-8
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