title: Mapping an index of the myelin g-ratio in infants using magnetic resonance imaging.
abstract: Optimal myelination of neuronal axons is essential for effective brain and cognitive function. The ratio of the axon diameter to the outer fiber diameter, known as the g-ratio, is a reliable measure to assess axonal myelination and is an important index reflecting the efficiency and maximal conduction velocity of white matter pathways. Although advanced neuroimaging techniques including multicomponent relaxometry (MCR) and diffusion tensor imaging afford insight into the microstructural characteristics of brain tissue, by themselves they do not allow direct analysis of the myelin g-ratio. Here, we show that by combining myelin content information (obtained with mcDESPOT MCR) with neurite density information (obtained through NODDI diffusion imaging) an index of the myelin g-ratio may be estimated. Using this framework, we present the first quantitative study of myelin g-ratio index changes across childhood, examining 18 typically developing children 3months to 7.5years of age. We report a spatio-temporal pattern of maturation that is consistent with histological and developmental MRI studies, as well as theoretical studies of the myelin g-ratio. This work represents the first ever in vivo visualization of the evolution of white matter g-ratio indices throughout early childhood.
authors.affiliation: Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA. Electronic address: deaniii@wisc.edu.
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Dean
authors.affiliation: Department of Neuroimaging, King's College London, Institute of Psychiatry, London SE5 8AF, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: O'Muircheartaigh
authors.affiliation: Advanced Baby Imaging Lab, Brown University School of Engineering, Providence, RI 02912, USA.
authors.forename: Holly
authors.initials: H
authors.lastname: Dirks
authors.affiliation: Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Kinesiology, University of Wisconsin-Madison, Madison, WI 53705, USA.
authors.forename: Brittany G
authors.initials: BG
authors.lastname: Travers
authors.affiliation: Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA.
authors.forename: Nagesh
authors.initials: N
authors.lastname: Adluru
authors.affiliation: Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Psychiatry, University of Wisconsin-Madison, Madison, WI 53719, USA; Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705, USA.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Alexander
authors.affiliation: Advanced Baby Imaging Lab, Brown University School of Engineering, Providence, RI 02912, USA; Department of Pediatric Radiology, Children's Hospital Colorado, Aurora, CO, USA; Department of Radiology, University of Colorado Denver, Denver, CO, USA.
authors.forename: Sean C L
authors.initials: SCL
authors.lastname: Deoni
mesh_terms: D001921:Brain / Q000033:anatomy & histology* / Q000254:growth & development*; D002648:Child; D002675:Child, Preschool; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007223:Infant; D008279:Magnetic Resonance Imaging; D008297:Male; D009186:Myelin Sheath; D066127:White Matter / Q000033:anatomy & histology