title: Quantification and compensation of eddy-current-induced magnetic-field gradients.
abstract: Two robust techniques for quantification and compensation of eddy-current-induced magnetic-field gradients and static magnetic-field shifts (ΔB0) in MRI systems are described. Purpose-built 1-D or six-point phantoms are employed. Both procedures involve measuring the effects of a prior magnetic-field-gradient test pulse on the phantom's free induction decay (FID). Phantom-specific analysis of the resulting FID data produces estimates of the time-dependent, eddy-current-induced magnetic field gradient(s) and ΔB0 shift. Using Bayesian methods, the time dependencies of the eddy-current-induced decays are modeled as sums of exponentially decaying components, each defined by an amplitude and time constant. These amplitudes and time constants are employed to adjust the scanner's gradient pre-emphasis unit and eliminate undesirable eddy-current effects. Measurement with the six-point sample phantom allows for simultaneous, direct estimation of both on-axis and cross-term eddy-current-induced gradients. The two methods are demonstrated and validated on several MRI systems with actively-shielded gradient coil sets.
authors.affiliation: Department of Radiology, Washington University, St. Louis, MO 63110, USA. spees@wustl.edu
authors.forename: William M
authors.initials: WM
authors.lastname: Spees
authors.forename: Niels
authors.initials: N
authors.lastname: Buhl
authors.forename: Peng
authors.initials: P
authors.lastname: Sun
authors.forename: Joseph J H
authors.initials: JJ
authors.lastname: Ackerman
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Neil
authors.forename: Joel R
authors.initials: JR
authors.lastname: Garbow
mesh_terms: D000465:Algorithms; D001499:Bayes Theorem; D003627:Data Interpretation, Statistical; D004574:Electromagnetic Fields; D007091:Image Processing, Computer-Assisted / Q000706:statistics & numerical data*; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data*; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011092:Polyethylene Glycols / Q000737:chemistry; D012984:Software
chemical_list: D011092:Polyethylene Glycols