title: New insight into the contrast in diffusional kurtosis images: does it depend on magnetic susceptibility?
abstract: OBJECTIVE
  In this MRI study, diffusional kurtosis imaging (DKI) and T2 * multiecho relaxometry were measured from the white matter (WM) of human brains and correlated with each other, with the aim of investigating the influence of magnetic-susceptibility (Δχ (H2O-TISSUE) ) on the contrast.
  
  
  METHODS
  We focused our in vivo analysis on assessing the dependence of mean, axial, and radial kurtosis (MK, K‖ , K⊥ ), as well as DTI indices on Δχ (H2O-TISSUE) (quantified by T2 *) between extracellular water and WM tissue molecules. Moreover, Monte Carlo (MC) simulations were used to elucidate experimental data.
  
  
  RESULTS
  A significant positive correlation was observed between K⊥ , MK and R2 * = 1/T2 *, suggesting that Δχ (H2O-TISSUE) could be a source of DKI contrast. In this view, K⊥ and MK-map contrasts in human WM would not just be due to different restricted diffusion processes of compartmentalized water but also to local Δχ (H2O-TISSUE) . However, MC simulations show a strong dependence on microstructure rearrangement and a feeble dependence on Δχ (H2O-TISSUE) of DKI signal.
  
  
  CONCLUSIONS
  Our results suggests a concomitant and complementary existence of multi-compartmentalized diffusion process and Δχ (H2O-TISSUE) in DKI contrast that might explain why kurtosis contrast is more sensitive than DTI in discriminating between different tissues. However, more realistic numerical simulations are needed to confirm this statement.
authors.affiliation: Physics Department "Sapienza" University of Rome, Rome, Italy; Neuroimaging laboratory, IRCCS Santa Lucia foundation, Rome, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Palombo
authors.forename: Silvia
authors.initials: S
authors.lastname: Gentili
authors.forename: Marco
authors.initials: M
authors.lastname: Bozzali
authors.forename: Emiliano
authors.initials: E
authors.lastname: Macaluso
authors.forename: Silvia
authors.initials: S
authors.lastname: Capuani
mesh_terms: D000328:Adult; D001921:Brain / Q000033:anatomy & histology* / Q000378:metabolism*; D003337:Corpus Callosum / Q000033:anatomy & histology / Q000378:metabolism; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods*; D045604:Extracellular Fluid / Q000502:physiology*; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D008962:Models, Theoretical; D009010:Monte Carlo Method; D016011:Normal Distribution; D009716:Numerical Analysis, Computer-Assisted; D012016:Reference Values; D013223:Statistics as Topic; D066127:White Matter / Q000033:anatomy & histology* / Q000378:metabolism*
keywords: DKI; DTI; human brain; magnetic susceptibility; white matter