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Optimization of encoding gradients for MR‐ARFI
Author(s) -
Chen Jing,
Watkins Ron,
Pauly Kim Butts
Publication year - 2010
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.22299
Subject(s) - acoustic radiation force , imaging phantom , displacement (psychology) , acoustics , weighting , distortion (music) , physics , sensitivity (control systems) , ultrasound , robustness (evolution) , signal (programming language) , encoding (memory) , optics , materials science , computer science , artificial intelligence , chemistry , electronic engineering , psychology , amplifier , biochemistry , optoelectronics , cmos , psychotherapist , gene , programming language , engineering
MR acoustic radiation force imaging provides a promising method to monitor therapeutic ultrasound treatments. By measuring the displacement induced by the acoustic radiation force, MR acoustic radiation force imaging can locate the focal spot, without a significant temperature rise. In this work, the encoding gradient for MR acoustic radiation force imaging is optimized to achieve an enhanced accuracy and precision of the displacement measurement. By analyzing the sources of artifacts, bulk motion and eddy currents are shown to introduce errors to the measurement, and heavy diffusion‐weighting is shown to result in noisy displacement maps. To eliminate these problems, a new encoding scheme is proposed, which utilizes a pair of bipolar gradients. Improved precision is achieved with robustness against bulk motion and background phase distortion, and improved accuracy is achieved with reduced diffusion‐weighting and optimized encoding pulse width. The experiment result shows that the signal‐to‐noise ratio can be enhanced by more than 2‐fold. These significant improvements are obtained at no cost of scan time or encoding sensitivity, enabling the detection of a displacement less than 0.l μm in a gel phantom with MR acoustic radiation force imaging. Magn Reson Med 63:1050–1058, 2010. © 2010 Wiley‐Liss, Inc.