Magnetic Resonance Relaxation Anisotropy: Physical Principles and Uses in Microstructure Imaging

Michael J. Knight, Serena Dillon, Lina Jarutyte, Risto A. Kauppinen

Research output: Contribution to journalArticle (Academic Journal)peer-review

21 Citations (Scopus)
364 Downloads (Pure)


Magnetic resonance imaging (MRI) provides an excellent means of studying tissue microstructure noninvasively since the microscopic tissue environment is imprinted on the MRI signal even at macroscopic voxel level. Mesoscopic variations in magnetic field, created by microstructure, influence the transverse relaxation time (T2) in an orientation-dependent fashion (T2 is anisotropic). However, predicting the effects of microstructure upon MRI observables is challenging and requires theoretical insight. We provide a formalism for calculating the effects upon T2 of tissue microstructure, using a model of cylindrical magnetic field perturbers. In a cohort of clinically healthy adults, we show that the angular information in spin-echo T2 is consistent with this model. We show that T2 in brain white matter of nondemented volunteers follows a U-shaped trajectory with age, passing its minimum at an age of ∼30 but that this depends on the particular white matter tract. The anisotropy of T2 also interacts with age and declines with increasing age. Late-myelinating white matter is more susceptible to age-related change than early-myelinating white matter, consistent with the retrogenesis hypothesis. T2 mapping may therefore be incorporated into microstructural imaging.
Original languageEnglish
Pages (from-to)1517-1528
Number of pages12
JournalBiophysical Journal
Issue number7
Early online date11 Apr 2017
Publication statusPublished - 11 Apr 2017

Structured keywords

  • CRICBristol
  • Brain and Behaviour
  • Cognitive Science


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