Phase-Contrast Velocity Mapping for Highly Diffusive Fluids: Optimal Bipolar Gradient Pulse Parameters for Hyperpolarized Helium-3

作者：Martin Lionel; Maitre Xavier; de Rochefort Ludovic; Sarracanie Mathieu; Friese Marlies; Hagot Pascal; Durand Emmanuel^*

来源：Magnetic Resonance in Medicine, 2014, 72(4): 1072-1078.

DOI：10.1002/mrm.25005

• phase-contrast
• flow
• diffusion
• gas
• hyperpolarized helium-3
• airflow velocity
• phase-contrast MRI

PurposeIn MR-velocity phase-contrast measurements, increasing the encoding bipolar gradient, i.e., decreasing the field of speed, usually improves measurement precision. However, in gases, fast diffusion during the bipolar gradient pulses may dramatically decrease the signal-to-noise ratio, thus degrading measurement precision. These two effects are contradictory. This work aims at determining the optimal sequence parameters to improve the velocity measurement precision.
Theory and MethodsThis work presents the theoretical optimization of bipolar gradient parameters (duration and amplitude) to improve velocity measurement precision. An analytical approximation is given as well as a numerical optimization. It is shown that the solution depends on the diffusion coefficient and T-2*. Experimental validation using hyperpolarized He-3 diluted in various buffer gases (He-4, N-2, and SF6) is presented at 1.5 Tesla (T) in a straight pipe.
ResultsExcellent agreement was found with the theoretical results for prediction of optimal field of speed and good agreement was found for the precision in measured velocity, but for SF6 buffered gas.
ConclusionThe theoretical predictions were validated, providing a way to optimize velocity mapping in gases. Magn Reson Med 72:1072-1078, 2014.

• 出版日期2014-10