In vivo characterization of brain ultrashort-T2 components

Magn Reson Med. 2018 Aug;80(2):726-735. doi: 10.1002/mrm.27037. Epub 2017 Dec 1.

Abstract

Purpose: Recent nuclear magnetic resonance and MRI studies have measured a fast-relaxing signal component with T2∗<1 ms in white matter and myelin extracts. In ex vivo studies, evidence suggests that a large fraction of this component directly arises from bound protons in the myelin phospholipid membranes. Based on these results, this ultrashort-T2 component in nervous tissue is a new potential imaging biomarker of myelination, which plays a critical role in neuronal signal conduction across the brain and loss or degradation of myelin is a key feature of many neurological disorders. The goal of this work was to characterize the relaxation times and frequency shifts of ultrashort-T2 components in the human brain.

Methods: This required development of an ultrashort echo time relaxometry acquisition strategy and fitting procedure for robust measurements in the presence of ultrashort T2∗ relaxation times and large frequency shifts.

Results: We measured an ultrashort-T2 component in healthy volunteers with a median T2∗ between 0.5-0.7 ms at 3T and 0.2-0.3 ms at 7T as well as an approximately -3 ppm frequency shift from water.

Conclusion: To our knowledge, this is the first time a chemical shift of the ultrashort-T2 brain component has been measured in vivo. This chemical shift, at around 1.7 ppm, is similar to the primary resonance of most lipids, indicating that much of the ultrashort-T2 component observed in vivo arises from bound protons in the myelin phospholipid membranes. Magn Reson Med 80:726-735, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Keywords: myelin imaging; myelin membranes; relaxometry; ultrashort echo time MRI; ultrashort-T2.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Brain / diagnostic imaging*
  • Humans
  • Imaging, Three-Dimensional / methods*
  • Magnetic Resonance Imaging / methods*
  • Male
  • Myelin Sheath / chemistry
  • Phantoms, Imaging
  • Protons
  • Young Adult

Substances

  • Protons