Optimized saturation pulse rrains for SASHA T1 mapping at 3T

Joint myocardial T1 and T2 mapping using a combination of saturation recovery and T2 -preparation

PURPOSE

To develop a heart-rate independent breath-held joint T1 -T2 mapping sequence for accurate simultaneous estimation of coregistered myocardial T1 and T2 maps.

METHODS

A novel preparation scheme combining both a saturation pulse and T2 -preparation in a single R-R interval is introduced. The time between these two pulses, as well as the duration of the T2 -preparation is varied in each heartbeat, acquiring images with different T1 and T2 weightings, and no magnetization dependence on previous images. Inherently coregistered T1 and T2 maps are calculated from these images. Phantom imaging is performed to compare the proposed maps with spin echo references. In vivo imaging is performed in ten subjects, comparing the accuracy and precision of the proposed technique to existing myocardial T1 and T2 mapping sequences of the same duration.

RESULTS

Phantom experiments show that the proposed technique provides accurate quantification of T1 and T2 values over a wide-range (T1 : 260 ms to 1460 ms, T2 : 40 ms to 200 ms). In vivo imaging shows that the proposed sequence quantifies T1 and T2 values similar to a saturation-based T1 mapping and a conventional breath-hold T2 mapping sequence, respectively.

CONCLUSION

The proposed sequence allows joint estimation of accurate and coregistered quantitative myocardial T1 and T2 maps in a single breath-hold. Magn Reson Med 76:888-896, 2016. © 2015 Wiley Periodicals, Inc.

Characterization of T1 bias in skeletal muscle from fat in MOLLI and SASHA pulse sequences: Quantitative fat-fraction imaging with T1 mapping

PURPOSE

To characterize the effects of fat on commonly used T₁ mapping sequences and evaluate a new method of quantitative fat fraction (FF) imaging for low fractions based on the modulation of T₁ values by the fat pool.

METHODS

Bloch equation simulations and phantom and in vivo (skeletal muscle) experiments were used to characterize the response of the modified Look-Locker inversion recovery (MOLLI) and saturation recovery single-shot acquisition (SASHA) T₁ mapping sequences to fat-water systems with known FFs (0%-10%) at 1.5T. FFs were measured with single voxel spectroscopy and Dixon imaging methods. A new T₁ -based FF imaging method was evaluated using Monte Carlo simulations and phantom and in vivo experiments.

RESULTS

SASHA and MOLLI had similar T₁ dependence on FF, with characteristic under- or overestimation of T₁ values as a function of off-resonance frequency (30-70 ms variation in native T₁ per 1% FF). FF maps generated from the SASHA method yielded a low variability of ±0.25% for a signal-to-noise ratio of 150:1 in the nonsaturation image, with good agreement with spectroscopy and a performance that is superior to that of Dixon methods at low FFs.

CONCLUSION

Fat results in negative or positive shifts in native tissue T₁ measured with MOLLI and SASHA over a narrow range of off-resonance frequencies; T₁ shifts from fat can be used to accurately quantify FF. Magn Reson Med 77:237-249, 2017. © 2016 Wiley Periodicals, Inc.