Prevention of motion-induced signal loss in diffusion-weighted echo-planar imaging by dynamic restoration of gradient moments

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Purpose:Head motion is a significant problem in diffusion-weighted imaging as it may cause signal attenuation due to residual dephasing during strong diffusion encoding gradients even in single-shot acquisitions. Here, we present a new real-time method to prevent motion-induced signal loss in DWI of the brain.Methods:The method requires a fast motion tracking system (optical in the current implementation). Two alterations were made to a standard diffusion-weighted echo-planar imaging sequence: first, real-time motion correction ensures that slices are correctly aligned relative to the moving brain. Second, the tracking data are used to calculate the motion-induced gradient moment imbalance which occurs during the diffusion encoding periods, and a brief gradient blip is inserted immediately prior to the signal readout to restore the gradient moment balance.Results:Phantom experiments show that the direction as well as magnitude of the gradient moment imbalance affects the characteristics of unwanted signal attenuation. In human subjects, the addition of a moment-restoring blip prevented signal loss and improved the reproducibility and reliability of diffusion tensor measures even in the presence of substantial head movements.Conclusion:The method presented can improve robustness for clinical routine scanning in populations that are prone to head movements, such as children and uncooperative adult patients. Magn Reson Med 71:2006–2013, 2014. © 2013 Wiley Periodicals, Inc.

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