Hemispectrum substitution after water signal fitt

Authors: Yann Le Fur Patrick J Cozzone

Publish Date: 2014/06/03

Volume: 28, Issue: 1, Pages: 67-85

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Abstract

In a previous study we have shown that modulus postprocessing is a simple and efficient tool to both phase correct and frequency align magnetic resonance MR spectra automatically Furthermore this technique also eliminates sidebands and phase distortions The advantages of the modulus technique have been illustrated in several applications to brain proton MR spectroscopy Two possible drawbacks have also been pointed out The first one is the theoretical decrease in signaltonoise ratio SNR by a factor up to √2 when comparing the spectrum obtained after modulus versus conventional postprocessing The second pitfall results from the symmetrization of the spectrum induced by modulus postprocessing since any resonance or artifact located at the left of the water resonance is duplicated at the right of the water resonance thus contaminating the region of the spectrum containing the resonances of interest Herein we propose a strategy in order to eliminate these two limitationsConcerning the SNR issue two complementary approaches are presented here The first is based on the application of modulus postprocessing before spatial apodization and the second consists in substituting the left half of the spectrum by the fit of the water resonance before applying modulus postprocessing The symmetrization induced by modulus postprocessing then combines the right half of the original spectrum containing the resonances of interest with the left half of the water fit free of noise and artifacts Consequently the SNR is improved when compared to modulus postprocessing alone As a bonus any artifact or resonance present in the left half of the original spectrum is removed This solves the second limitation

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