title: q-space and conventional diffusion imaging of axon and myelin damage in the rat spinal cord after axotomy.
abstract: Parallel and perpendicular diffusion properties of water in the rat spinal cord were investigated 3 and 30 days after dorsal root axotomy, a specific insult resulting in early axonal degeneration followed by later myelin damage in the dorsal column white matter. Results from q-space analysis (i.e., the diffusion probability density function) obtained with strong diffusion weighting were compared to conventional anisotropy and diffusivity measurements at low b-values, as well as to histology for axon and myelin damage. q-Space contrasts included the height (return to zero displacement probability), full width at half maximum, root mean square displacement, and kurtosis excess of the probability density function, which quantifies the deviation from gaussian diffusion. Following axotomy, a significant increase in perpendicular diffusion (with decreased kurtosis excess) and decrease in parallel diffusion (with increased kurtosis excess) were found in lesions relative to uninjured white matter. Notably, a significant change in abnormal parallel diffusion was detected from 3 to 30 days with full width at half maximum, but not with conventional diffusivity. Also, directional full width at half maximum and root mean square displacement measurements exhibited different sensitivities to white matter damage. When compared to histology, the increase in perpendicular diffusion was not specific to demyelination, whereas combined reduced parallel diffusion and increased perpendicular diffusion was associated with axon damage.
authors.affiliation: Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Jonathan A D
authors.initials: JA
authors.lastname: Farrell
authors.forename: Jiangyang
authors.initials: J
authors.lastname: Zhang
authors.forename: Melina V
authors.initials: MV
authors.lastname: Jones
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Deboy
authors.forename: Paul N
authors.initials: PN
authors.lastname: Hoffman
authors.forename: Bennett A
authors.initials: BA
authors.lastname: Landman
authors.forename: Seth A
authors.initials: SA
authors.lastname: Smith
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Reich
authors.forename: Peter A
authors.initials: PA
authors.lastname: Calabresi
authors.forename: Peter C M
authors.initials: PC
authors.lastname: van Zijl
mesh_terms: D000818:Animals; D001369:Axons / Q000473:pathology*; D019771:Axotomy; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D009186:Myelin Sheath / Q000473:pathology*; D051381:Rats; D011917:Rats, Inbred Lew; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013119:Spinal Cord Injuries / Q000473:pathology*