Abstract #2205

Rapid Eddy Currents Insensitive Field Map Estimation for Accurate B0 Shimming

Hai Luo¹, Bin Wang¹, Gaojie Zhu¹, Wenzhou Wang¹, Xiang Zhou¹, Ziyue Wu¹, and Leping Zha^1,2

¹AllTech Medical Systems, Chengdu, China, People's Republic of, ²AllTech Medical Systems, Cleveland, OH, United States

3D dual echo gradient echo sequence is commonly used to obtain the field map for B0 shimming. The maps contain the true B0 fields mixed with eddy currents induced magnetic field changes averaged over the echo time difference, which compromise the shimming accuracy. A calibration sequence with alternating gradient polarities is proposed to measure the eddy currents term. Quadratic surface fitting is then applied to produce smooth eddy currents calibration maps over the full imaging volume containing only the first and second order components. The actual rapid in-vivo shimming sequence runs later, using the calibration maps to remove the eddy currents influences during the post-processing, with partial Fourier acquisition on phase encoding and slice encoding directions to reduce the scan time. The fast method provides means of eddy currents insensitive shimming, as well as reduced sensitivity to motion.

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