EDDY-CURRENT CORRECTION IN VOLUME-LOCALIZED MR SPECTROSCOPY

The quality of volume-localized magnetic resonance spectroscopy is aff ected by eddy currents caused by gradient switching. Eddy currents can be reduced with improved gradient systems; however, it has been sugge sted that the distortion due to eddy currents can be compensated for d uring postprocessing with a single-frequency reference signal. The aut hors propose modifying current techniques for acquiring the single-fre quency reference signal by using relaxation weighting to reduce interf erence from components that cannot be eliminated by digital filtering alone. Additional sequences with T1 or T2 weighting for reference sign al acquisition are shown to have the same eddy current characteristics as the original signal without relaxation weighting. The authors also studied a new eddy current correction method that does not require a single-frequency reference signal. This method uses two free induction decays (FIDs) collected from the same volume with two sequences with opposite gradients. Phase errors caused by eddy currents are opposite in these two FIDs and can be canceled completely by combining the FIDs . These methods were tested in a phantom. Eddy current distortions wer e corrected, allowing quantitative measurement of structures such as t he -CH=CH- component, which is otherwise undetectable.