title: Age-related changes in conventional, magnetization transfer, and diffusion-tensor MR imaging findings: study with whole-brain tissue histogram analysis.
abstract: OBJECTIVE
  To investigate the influence of aging on conventional magnetic resonance (MR) imaging-, magnetization transfer MR imaging-, and diffusion-tensor MR imaging-derived measurements.
  
  
  METHODS
  Dual-echo T1-weighted magnetization transfer and diffusion-tensor MR images of the brain were obtained in 89 healthy subjects. Normalized brain parenchymal volume (NBV) was measured by using a fully automated technique. Magnetization transfer ratio (MTR), apparent diffusion coefficient (ADC), and fractional anisotropy (FA) histograms were created for the whole brain (MTR values) or for a large representative portion of it (ADC and FA values). Bivariate correlations were assessed by using the Spearman rank correlation coefficient. A stepwise selection procedure was used to identify the combination of variables that were most influenced by subject age in a multivariate regression model.
  
  
  RESULTS
  Significant correlations were found between subject age and the following variables: number of hyperintense areas in the brain at T2-weighted MR imaging (r = 0.63, P <.001), NBV (r = -0.79, P <.001), mean ADC (r = 0.34, P =.001), ADC peak height (r = -0.34, P =.001), and FA peak height (r = -0.57, P <.001). NBV correlated significantly with number of hyperintense areas (P <.001), MTR peak height (P <.001), mean ADC (P =.001), ADC peak height (P =.001), and FA peak height (P <.001). The final multivariable regression model included NBV and number of hyperintense areas at T2-weighted MR imaging as independent predictors of subject age.
  
  
  CONCLUSIONS
  In addition to the extent of T2-weighted MR imaging hyperintense areas and the measurement of NBV, diffusion-tensor MR imaging provides additional in vivo information about microstructural age-related brain tissue changes.
authors.affiliation: Neuroimaging Research Unit, Department of Neuroscience, Scientific Institute and University Ospedale San Raffaele, Via Olgettina 60, 20132 Milan, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Rovaris
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Iannucci
authors.forename: Mara
authors.initials: M
authors.lastname: Cercignani
authors.forename: Maria Pia
authors.initials: MP
authors.lastname: Sormani
authors.forename: Nicola
authors.initials: N
authors.lastname: De Stefano
authors.forename: Simonetta
authors.initials: S
authors.lastname: Gerevini
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Comi
authors.forename: Massimo
authors.initials: M
authors.lastname: Filippi
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology*; D001921:Brain / Q000033:anatomy & histology*; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D012044:Regression Analysis