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 language | English (US) |
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Pages (from-to) | 754-760 |
Number of pages | 7 |
Journal | Magnetic resonance in medicine |
Volume | 56 |
Issue number | 4 |
DOIs | |
State | Published - Oct 2006 |
Keywords
- Artifact reduction
- MRS
- Motion correction
- Spectral processing
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging