Spurious signals in DQF spectroscopy: two-shot stimulated echoes.

Details

Serval ID
serval:BIB_7BDBC00E7050
Type
Article: article from journal or magazin.
Collection
Publications
Title
Spurious signals in DQF spectroscopy: two-shot stimulated echoes.
Journal
Magma
Author(s)
Pictet J., van der Klink J.J., Meuli R.
ISSN
0968-5243 (Print)
ISSN-L
0968-5243
Publication state
Published
Issued date
11/2004
Volume
17
Number
2
Pages
74-79
Language
english
Notes
Publication types: Evaluation Studies ; Journal Article ; Research Support, Non-U.S. Gov't Publication Status: ppublish
Abstract
The most widely used technique for double-quantum filtered (DQF) single-voxel spectroscopy (SVS) is based on a symmetric PRESS sequence with two additional spatially unselective pi/2 pulses, one of which is usually frequency selective. The actual filtering, rejecting signals from all uncoupled resonances, can be done by suitable phase cycling of the rf pulses in successive shots, but in practice gradient filtering is always used. Under usual conditions the sequence repetition time is comparable to the spin-lattice relaxation time, and a stimulated echo is formed by five out of the ten rf pulses in two consecutive shots. This echo is not filtered out by the gradients, and additional phase cycling is needed to eliminate it. Its spatial origin is the full transverse slice selected by the last pulse of the PRESS sequence. The SVS shimming procedure may create an important field variation in this slice (outside the volume of interest VOI). Water singlet signals therefore appear in a band of frequencies other than 4.7 ppm, and remain unaffected by water suppression pulses. In practice phase-alternation schemes can reduce these spurious signals by several orders of magnitude, but even then they may mask the weak metabolite signals of interest. We describe a strategy to minimize these spurious signals and propose a 16-step phase cycling scheme that attenuates the stimulated echo in every two-step subcycle.
Keywords
Algorithms, Artifacts, Magnetic Resonance Spectroscopy/methods, Signal Processing, Computer-Assisted
Pubmed
Web of science
Create date
08/04/2008 14:48
Last modification date
20/08/2019 14:37
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