Data consistency-driven determination of B 0 -fluctuations in gradient-echo MRI.

Purpose: Introduce a method to estimate B-0-fluctuations based on the analysis of raw k-space data, without sequence modifications or external hardware, and correct for their detrimental effects in gradient-echo MRI. Theory: Inconsistencies in multi-channel raw k-space data can be used to estimate B-0-fluctuations by exploiting coil-sensitivity information. Methods: The proposed method, dubbed consistency navigation, is used to extract B-0-fluctuations from T-2*-weighted 3D gradient-echo data. These results are compared with the results from an MR phase navigator and respiratory bellows. The spatial variation of the B-0-fluctuation amplitude is derived using the sensitivity maps of the coil array and compared with direct measurements based on dynamic 2D gradientecho data. Results: B-0-fluctuations derived from the consistency navigator and MR phase navigator are highly correlated. Images corrected for these fluctuations show marked improvements in homogeneity and tissue delineation. The spatial variation of the B-0-fluctuation amplitude follows closely the variation directly measured from time-resolved 2D scans. Conclusions: Based on the consistency navigator, an accurate estimation of the spatiotemporal characteristics of B-0-fluctuations and correction of T-2*-weighted images has been demonstrated.