Prof. Risto Kauppinen | Relaxation Anisotropy in MRI: Potential Mechanisms and Implications to White Matter Contrasts

Gastvortrag

  • Datum: 17.01.2019
  • Uhrzeit: 10:00 - 11:00
  • Vortragende(r): Prof. Risto Kauppinen
  • Professor of Imaging University of Bristol United Kingdom
  • Ort: MPI für Kognitions- und Neurowissenschaften
  • Raum: Wilhelm Wundt Raum (A400)
  • Gastgeber: Abteilung Neurophysik
  • Kontakt: amuehlberg@cbs.mpg.de
MR relaxation of water is influenced by cerebral physico-chemical environment, such as water, myelin and iron content. It is well established that cerebral tissue microstructure modifies T2* in white mater (WM) rendering T2* relaxation anisotropic. We have studied MRI relaxation in human WM at 3T by determining fibre-to-field angular dependencies of T1 and T2. T1 relaxation time was found to be longest in WM voxels with fractional anisotropy (FA) > 0.3 when the fibre-to-field angle was ~55o. i.e. close to the magic angle. M0 plots from WM also peaked close to 55o, indicating that the apparent T1 relaxation anisotropy may be mediated by MRI visibility of water, i.e. through a non-anisotropic mechanism. T2 showed even stronger angular dependency than T1, but at a distinct fibre-to-field angle. In structurally highly anisotropic WM T2 was found to be shortest in fibres running perpendicular to the field and longest in those parallel to the field. The T2 anisotropy is modelled as diffusion-mediated decoherence, where anisotropic susceptibility reduces nuclear spin phase. We developed a model to separate isotropically and anisotropically relaxing T2 components in WM. Our preliminary relaxometric data from argue that T1 relaxation anisotropy becomes weaker in WM with ageing. Ageing is also associated with decrease in anisotropic T2 components and concomitant increase in isotropic T2. Our findings link WM microstructure and MRI relaxation implicating that neurobiological value of relaxometric MRI may be richer than previously thought.

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