Characterization and correction of system delays and eddy currents for MR imaging with ultrashort echo‐time and time‐varying gradients

Reconstruction of high‐quality MR images requires precise knowledge of the dynamic gradient magnetic fields used to perform spatial encoding. System delays and eddy currents can perturb the gradient fields in both time and space and significantly degrade the image quality for acquisitions with an ultrashort echo time or with rapidly varying readout gradient waveforms. A technique for simultaneously characterizing and correcting the system delay and linear‐ and zero‐order eddy currents of an MR system is proposed. A single set of calibration scans were used to compute a set of system constants that describe the effects of system delays and eddy currents to enable accurate reconstruction of data collected before uncorrected eddy currents have decayed. The ability of the proposed technique to reproducibly characterize small fixed delays (<50 μs) and short‐time constant (<1 ms) eddy currents is demonstrated. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.