B0 Eddy Current Compensation of an Unshielded Pulsed Z2 Gradient for Applications in Human Brain Proton MRSI

Motivation: ECLIPSE1 is a novel method to achieve robust outer volume suppression (OVS) in 1H-MRSI of the human brain. To-date ECLIPSE has been performed with an unshielded-Z2 coil that led to significant B0-eddy currents, necessitating the use of pre/post gradient pulses2,3 for MEGA-edited MRSI acquisitions. Goal(s): An inner volume selection (IVS) based ECLIPSE approach would provide B1 and T1 independent lipid suppression, however editing efficiency is compromised due to B0-eddy currents. Approach: A home-built 64-channel gradient controller4 was extended with B0-compensation capabilities to drive a Z0-shim coil. Results: B0-eddy currents were attenuated by 200-fold following B0-compensation, and allows robust MEGA-edited ECLIPSE-IVS based MRSI acquisitions. Impact: Constructing a shielded-Z2 coil for ECLIPSE is complex compared to an unshielded coil. A simpler approach is to construct an unshielded-Z2 with B0 compensation and gradient pre-emphasis, provided that eddy currents induced by switching an unshielded-Z2 gradient can be well-characterized.