Respiration-induced Bo fluctuations and their spatial distribution in the human brain at 7 Tesla

Pierre François Van de Moortele, Josef Pfeuffer, Gary H. Glover, Kamil Ugurbil, Xiaoping Hu

Research output: Contribution to journalArticlepeer-review

162 Scopus citations

Abstract

In functional magnetic resonance imaging (fMRI), it is known that physiological influences such as cardiac pulsation, respiration, and brain motion can induce fluctuations in signal intensity and phase. Some of the mechanisms potentially involved in those phenomena are expected to be amplified at higher magnetic fields. This study addresses the issue of Bo fluctuations induced by susceptibility changes during respiration attributed to movements of chest and diaphragm, and variations in the oxygen concentration. It is demonstrated that respiration-induced resonance offsets (RIROs) are significant at 7T. Data were acquired with an RF pulse (no gradients), multislice echo-planar imaging (EPI), and dynamic 3D fast low-angle shot (3D-FLASH) imaging. Three main observations summarize the experimental findings. First, in FIDs measured after a single RF pulse, a RIRO with a large amplitude was consistently detected, although the average amplitude varied between subjects from 1.45 Hz to 4 Hz. Second, in transverse EPI images obtained in the occipital lobe, the RIRO amplitude showed a monotonic increase along the z axis toward the lungs. Third, a more detailed spatial analysis with 3D-FLASH phase maps revealed that a previously published analytical model can accurately describe the spatial distribution of RIRO. Consequential apparent motions in the EPI series, as well as the implications of slice orientation for correction strategies are discussed.

Original languageEnglish (US)
Pages (from-to)888-895
Number of pages8
JournalMagnetic resonance in medicine
Volume47
Issue number5
DOIs
StatePublished - 2002

Keywords

  • Echo-planar imaging
  • Off-resonance
  • Physiological artifacts
  • Respiration artifacts

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