T 2 -dependent errors in MOLLI T 1 values: simulations, phantoms, and in-vivo studies
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POSTER PRESENTATION
Open Access
T2-dependent errors in MOLLI T1 values: simulations, phantoms, and in-vivo studies Kelvin Chow1*, Jacqueline Flewitt2, Joseph J Pagano1, Jordin D Green3, Matthias G Friedrich2, Richard B Thompson1 From 15th Annual SCMR Scientific Sessions Orlando, FL, USA. 2-5 February 2012 Background 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) [1] 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. T 1 values are further compared with a saturation-recovery T 1 mapping sequence [2]. Methods Phantoms
14 NiCl 2 agarose phantoms with a broad range of T 1 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: singleshot 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.
1
Department of Biomedical Engineering, University of Alberta, Edmonton, AB, Canada Full list of author information is available at the end of the article
In-Vivo
For 10 healthy volunteers (5 male, 28.8±6.6yrs), blood and myocardial T1 s 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.
Results In blood-like phantoms with long T 2 (179-196ms), SASHA and MOLLI T 1 s 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 T 1 s 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). Conclusions 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
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