Field-frequency locked in vivo proton MRS on a whole-body spectrometer

Pierre Gilles Henry, Pierre François Van De Moortele, Eric Giacomini, Arno Nauerth, Gilles Bloch

Research output: Contribution to journalArticlepeer-review

56 Scopus citations

Abstract

The stability of the main magnetic field is critical for prolonged in vivo magnetic resonance spectroscopy (MRS) acquisitions, especially for difference spectroscopy. This study was focused on the implementation and optimization of a field-frequency lock (FFL) on a whole body spectrometer, to correct the main field drift during localized proton MRS of the human brain. The FFL was achieved through a negative feed-back applied in real time on the Z0 shim coil current, after calculation of the frequency shift from a reference signal. This signal was obtained from the whole head with a small flip angle acquisition interleaved with the PRESS acquisition of interest. To avoid propagation of the important short-term time-correlated fluctuations of the head water frequency (mainly due to respiratory motion) onto Z0 correction, the sampling rate of the reference frequency and the smoothing window for the Z0 correction were carefully optimized. Thus, an effective FFL was demonstrated in vivo with no significant increase of the short-term variance of the water frequency.

Original languageEnglish (US)
Pages (from-to)636-642
Number of pages7
JournalMagnetic resonance in medicine
Volume42
Issue number4
DOIs
StatePublished - 1999

Keywords

  • Field-frequency lock
  • In vivo MRS
  • Noise propagation
  • Respiratory motion

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