Jennifer A. McNab1,2, Jonathan A. Polimeni1,2,
Julien A. Cohen-Adad1,2, Lawrence L. Wald1,3
1A.A. Martinos Center for Biomedical
Imaging, Department of Radiology, Massachusetts General Hospital,
Charlestown, MA, United States; 2Harvard Medical School, Boston,
MA, United States; 3Harvard-MIT Division of Health Sciences and
Technology, Massachusetts Institute of Technology, Cambridge, MA, United
States
Sum-of-squares
(SoS) is the standard method for combining multi-channel coil images. SoS
implicitly assumes that the pixel intensity is a reasonable estimate of the
coil sensitivity profile. While this may hold true for acquisitions with high
SNR and ideal arrays, diffusion-weighted images often have low SNR. We
demonstrate improved sensitivity to diffusion measures using coil sensitivity
estimates from high SNR b = 0 images as well as a quick determination of the
noise covariance between coil channels to improve the channel combination.
This approach adds 20 s of scan time but can increase fractional anisotropy
estimates, for example, by 30%.