Ana-Maria Oros-Peusquens1,
Sandra M. Meyers2, Alex L. MacKay2, Nadim Jon Shah1,
3
1INM-4,
Research Centre Jlich, Jlich, Germany; 2Department of Physics
and Astronomy, University of British Columbia, Vancouver, B.C., Canada; 3Faculty
of Medicine, JARA, RWTH Aachen University, Aachen, Germany
It is increasingly recognised that myelin is ubiquitous in determining MR contrast in the living brain, especially at high fields. Investigating its distribution is not only useful in the study of several neurodegenerative diseases but can also be used for the in vivo parcellation of the brain. The current gold standard method for characterisation of myelin content in vivo is based on the investigation of the water trapped between myelin layers. Separation of the myelin water and tissue water pools, which have different mobility, is possible with an NNLS-based analysis of T2 decay curves. We introduce here a method which allows for discrimination between the two water pools based on their T2* properties. The data are acquired at 3T with either a 2D or a 3D multiple-echo gradient echo sequence and analysed with NNLS. Evaluation of the raw data (no additional resampling or image filtering) allows for separation of myelin (T2* < 20ms) and tissue water (T2*> 20ms) in the majority of white matter voxels. The average value of brain myelin water fraction for 12 volunteers is found to be 6.4%. Several improvements in data analysis are suggested. The method is proposed as an alternative to (high-SAR) spin-echo based myelin water analysis for use with high-field systems.