T2-dependent errors in MOLLI T1 values: simulations, phantoms, and in-vivo studies
Journal of Cardiovascular Magnetic Resonance volume 14, Article number: P281 (2012)
Diffuse myocardial fibrosis occurs in various cardiomyopathies and can be indirectly assessed with blood and myocardial T1 mapping at baseline and after gadolinium administration. The widely used MOdified Look-Locker Inversion-recovery (MOLLI)  sequence is known to underestimate myocardial T1 at higher heart rates, but its dependence on T2 has not been explored. We investigate MOLLI’s T1 accuracy in phantoms and confirm with simulations and in-vivo studies. T1 values are further compared with a saturation-recovery T1 mapping sequence .
14 NiCl2 agarose phantoms with a broad range of T1 and T2 values were imaged with a gold-standard inversion-recovery spin-echo (IR-SE) sequence, MOLLI, and a new SAturation-recovery single-SHot Acquisition (SASHA) technique (Siemens Avanto 1.5T). IR-SE: 16 TIs 100-5000ms, TE=11ms, TR>5s, 90° flip. MOLLI: 2 inversion sets of 3 and 5 images, 75% partial Fourier, TImin=110ms with 80ms increment, 35° flip, TE/TR=1.3/2.9ms, simulated HR=60bpm. SASHA: single-shot SSFP images from 10 consecutive heartbeats with incremented TI spanning the RR interval in the last 9 images (no saturation in the first image), 70° flip, TE/TR=1.3/2.6ms, full k-space, simulated HR=60bpm. T2: spin-echo (SE) with 7 TEs 11-200ms. Simulations: Bloch equation simulations of MOLLI and SASHA were performed in MATLAB using actual acquisition and physiology parameters and SE measured T1 and T2 values.
For 10 healthy volunteers (5 male, 28.8±6.6yrs), blood and myocardial T1s were measured using MOLLI and SASHA (parameters as above) in a mid-ventricular short-axis slice at baseline and 20 minutes following 0.1mmol/kg Magnevist.
In blood-like phantoms with long T2 (179-196ms), SASHA and MOLLI T1s agree well with IR-SE (0.7±0.5% and 2.2±1.8% absolute difference respectively), while shorter T2 (46-76ms) tissue-like phantoms have greater underestimation with MOLLI (8.4±3.5%) than SASHA (0.9±0.6%) (Fig. 1). MOLLI simulations predict underestimated T1s, with 1.3±0.9% absolute difference from observed values (vertical lines, Fig. 1). SASHA simulations also agree well with observations (0.8±0.5%, not shown). In healthy volunteers (63.3±8.4bpm), MOLLI T1s also show greater underestimation compared to SASHA in tissue than blood, although the difference is larger than observed in phantoms or predicted by simulations in all cases (Table 1).
MOLLI significantly underestimates T1s in shorter T2 tissue-like phantoms but less so in longer T2 blood-like phantoms, as predicted by simulations. Similar trends were observed in-vivo with MOLLI, although with greater T1 underestimation (compared to SASHA) than predicted. SASHA had good agreement with IR-SE T1 phantom measurements and simulations and can be acquired in less time than MOLLI.
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We acknowledge the work of Dr. Andreas Greiser in programming the MOLLI sequence used.
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Chow, K., Flewitt, J., Pagano, J.J. et al. T2-dependent errors in MOLLI T1 values: simulations, phantoms, and in-vivo studies. J Cardiovasc Magn Reson 14 (Suppl 1), P281 (2012). https://doi.org/10.1186/1532-429X-14-S1-P281