A simple method of measuring gradient induced eddy currents to set compensation networks

Area of Science:

• Magnetic Resonance Imaging
• Applied Physics
• Electrical Engineering

Background:

• Eddy currents (EC) are induced by time-dependent magnetic fields, causing distortions in magnetic field gradients.
• Accurate measurement of these EC-induced field distortions is crucial for magnetic resonance imaging (MRI) performance.
• Existing methods may lack sensitivity or ease of implementation for characterizing these dynamic field effects.

Purpose of the Study:

• To develop and present a novel technique for measuring the time dependence and field distortions caused by eddy currents (EC).
• To provide a sensitive and interpretable method for quantifying magnetic field variations relevant to MRI.
• To offer a practical tool for optimizing preemphasis compensation networks in MRI systems.

Main Methods:

• Utilizes a sample with short T1 and T2 relaxation times.
• Employs a sequence of rapid radiofrequency (rf) excitation pulses.
• Analyzes the out-of-phase component of free induction decays (FIDs) to measure signal off-resonance (gamma delta B).

Main Results:

• The technique successfully measures time-dependent magnetic field distortions induced by eddy currents.
• The out-of-phase FID component is shown to be directly proportional to the off-resonance signal (gamma delta B).
• The method demonstrates high sensitivity and ease of implementation.

Conclusions:

• The described EC measuring technique is effective for characterizing magnetic field distortions.
• This method provides valuable data for tuning preemphasis compensation networks.
• The technique offers a sensitive, simple, and interpretable approach for MRI quality control.