An Efficient Method to Correct Signal Drop-Out in EPI
Marshall H, Larkman D, Hajnal J
Hammersmith Hospital, Imperial College London
Echo planar imaging suffers from signal loss when B0 varies in the through-slice direction. This can be corrected by the z-shim method at the expense of multiple image acquisitions with different correction gradients applied. A method that requires only two z-shim images and an efficient calibration procedure is described and tested. At 3T with a 3mm slice thickness full signal restoration (to within 2% of the correct value) was achieved in 95% of all brain pixels when parameter values were determined for each slice and 94% when a single calibration for the whole brain was used.