On restoring motion-induced signal loss in single-voxel magnetic resonance spectra

Refaat E. Gabr, Shashank Sathyanarayana, Michael Schär, Robert G. Weiss, Paul A. Bottomley

Research output: Contribution to journalArticle

Abstract

Destructive interference from phase fluctuations caused by motion during 1H magnetic resonance spectroscopy (MRS) stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) acquisitions can significantly diminish the traditional √N-gain in signal-to-noise ratio (SNR) afforded by averaging N signals, especially in the torso. The SNR loss is highly variable among individuals, even when identical acquisition protocols are used. This paper presents a theory for the SNR loss, assuming that the phase fluctuates randomly. It is shown that SNR in conventional averaging is reduced by the factor sinc(σφ√3/π), where σφ is the standard deviation (SD) of the phase. "Constructive averaging," whereby each individual acquisition is phase-corrected using the phase of a high-SNR peak before averaging, reverses the SNR loss from motion-induced dephasing, resulting in a {1/ sinc(σφ3/π)}-fold SNR improvement. It is also shown that basing phase corrections on an average of √N adjacent points both improves correction accuracy and effectively eliminates false signal artifacts when corrections are based on low-SNR peaks. The theory is validated over a sevenfold range of variation in signal loss due to motion observed in 1H STEAM and PRESS data acquired from 17 human subjects (heart: N = 16; leg: N = 1). Constructive averaging should be incorporated as a routine tool for in vivo 1H MRS.

Original languageEnglish (US)
Pages (from-to)754-760
Number of pages7
JournalMagnetic resonance in medicine
Volume56
Issue number4
DOIs
StatePublished - Oct 1 2006

Keywords

  • Artifact reduction
  • H magnetic resonance spectroscopy
  • MRS
  • Motion correction
  • Spectral processing

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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