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- Open Access
T2-dependent errors in MOLLI T1 values: simulations, phantoms, and in-vivo studies
© Chow et al; licensee BioMed Central Ltd. 2012
- Published: 1 February 2012
- Bloch Equation
- Diffuse Myocardial Fibrosis
- SSFP Image
- Great Underestimation
- 80ms Increment
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.
Comparison of MOLLI and SASHA T1 values in 10 healthy volunteers prior to and 20 minutes following 0.1 mmol/kg Magnevist. All comparisons between MOLLI and SASHA are significant (p<0.01, two-tailed, paired Student’s t-test).
Post Gd (20 min)
Post Gd (20 min)
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.
We acknowledge the work of Dr. Andreas Greiser in programming the MOLLI sequence used.
This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.