Comparing myelin-sensitive magnetic resonance imaging measures and resulting g-ratios in healthy and multiple sclerosis brains
Ronja C. Berg,
Aurore Menegaux,
Thomas Amthor,
Guillaume Gilbert,
Maria Mora,
Sarah Schlaeger,
Viola Pongratz,
Markus Lauerer,
Christian Sorg,
Mariya Doneva,
Irene Vavasour,
Mark Mühlau,
Christine Preibisch
Affiliations
Ronja C. Berg
Technical University of Munich, School of Medicine, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany; Technical University of Munich, School of Medicine, Department of Neurology, Munich, Germany; Corresponding author at: Technical University of Munich, School of Medicine, Klinikum rechts der Isar, Department of Diagnostic and Interventional Neuroradiology, Ismaninger Str. 22, 81675, München, Germany.
Aurore Menegaux
Technical University of Munich, School of Medicine, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany; Technical University of Munich, School of Medicine, TUM Neuroimaging Center, Munich, Germany
Thomas Amthor
Philips Research Europe, Hamburg, Germany
Guillaume Gilbert
MR Clinical Science, Philips Healthcare, Mississauga, ON, Canada
Maria Mora
Technical University of Munich, School of Medicine, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany
Sarah Schlaeger
Technical University of Munich, School of Medicine, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany
Viola Pongratz
Technical University of Munich, School of Medicine, Department of Neurology, Munich, Germany; Technical University of Munich, School of Medicine, TUM Neuroimaging Center, Munich, Germany
Markus Lauerer
Technical University of Munich, School of Medicine, Department of Neurology, Munich, Germany; Technical University of Munich, School of Medicine, TUM Neuroimaging Center, Munich, Germany
Christian Sorg
Technical University of Munich, School of Medicine, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany; Technical University of Munich, School of Medicine, TUM Neuroimaging Center, Munich, Germany; Technical University of Munich, School of Medicine, Department of Psychiatry, Munich, Germany
Mariya Doneva
Philips Research Europe, Hamburg, Germany
Irene Vavasour
University of British Columbia, Department of Radiology, Vancouver, BC, Canada
Mark Mühlau
Technical University of Munich, School of Medicine, Department of Neurology, Munich, Germany; Technical University of Munich, School of Medicine, TUM Neuroimaging Center, Munich, Germany
Christine Preibisch
Technical University of Munich, School of Medicine, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany; Technical University of Munich, School of Medicine, Department of Neurology, Munich, Germany; Technical University of Munich, School of Medicine, TUM Neuroimaging Center, Munich, Germany
The myelin concentration and the degree of myelination of nerve fibers can provide valuable information on the integrity of human brain tissue. Magnetic resonance imaging (MRI) of myelin-sensitive parameters can help to non-invasively evaluate demyelinating diseases such as multiple sclerosis (MS). Several different myelin-sensitive MRI methods have been proposed to determine measures of the degree of myelination, in particular the g-ratio. However, variability in underlying physical principles and different biological models influence measured myelin concentrations, and consequently g-ratio values. We therefore investigated similarities and differences between five different myelin-sensitive MRI measures and their effects on g-ratio mapping in the brains of both MS patients and healthy volunteers.We compared two different estimates of the myelin water fraction (MWF) as well as the inhomogeneous magnetization transfer ratio (ihMTR), magnetization transfer saturation (MTsat), and macromolecular tissue volume (MTV) in 13 patients with MS and 14 healthy controls. In combination with diffusion-weighted imaging, we derived g-ratio parameter maps for each of the five different myelin measures.The g-ratio values calculated from different myelin measures varied strongly, especially in MS lesions. While, compared to normal-appearing white matter, MTsat and one estimate of the MWF resulted in higher g-ratio values within lesions, ihMTR, MTV, and the second MWF estimate resulted in lower lesion g-ratio values.As myelin-sensitive measures provide rough estimates of myelin content rather than absolute myelin concentrations, resulting g-ratio values strongly depend on the utilized myelin measure and model used for g-ratio mapping. When comparing g-ratio values, it is, thus, important to utilize the same MRI methods and models or to consider methodological differences. Particular caution is necessary in pathological tissue such as MS lesions.
