title: Relationship between the diffusion time and the diffusion MRI signal observed at 17.2 Tesla in the healthy rat brain cortex.
abstract: OBJECTIVE
  To investigate the diffusion time dependency of water diffusion in cortical brain tissue.
  
  
  METHODS
  We have combined an oscillating gradient spin-echo (OGSE) and a pulse gradient spin echo (PGSE) spin-echo sequence to acquire diffusion-weighted MRI images in vivo in healthy rat brains over a wide range of diffusion times (1.9-29.2 ms) and estimated the parameters of the biexponential and cumulant expansion diffusion MRI signal models. Diffusion images were obtained at 17.2 Tesla with maximum gradient strength of 1000 mT/m allowing 40 b values up to approximately 4000 s/mm(2).
  
  
  RESULTS
  At all diffusion times the log plot of diffusion signal attenuation versus b value was curved, confirming that diffusion is not free, even at very short diffusion times. This suggests that the length scale of obstacles to diffusion must be smaller than the corresponding shortest observed diffusion distance (approximately 1.7 μm). The diffusion MRI signal was also not found in a steady-state, even at our longest diffusion time (29.2 ms), suggesting some degree of segregation of water in pools.
  
  
  CONCLUSIONS
  Overall, the results showed that the parameters derived from the two diffusion models could not well be related to specific tissue features. More specific models must be developed taking into account diffusion signal behavior at high b values and short diffusion times.
authors.affiliation: NeuroSpin, Commissariat à l'Energie Atomique et aux Energies Alternatives, Gif-sur-Yvette, France.
authors.forename: Nadya
authors.initials: N
authors.lastname: Pyatigorskaya
authors.forename: Denis
authors.initials: D
authors.lastname: Le Bihan
authors.forename: Olivier
authors.initials: O
authors.lastname: Reynaud
authors.forename: Luisa
authors.initials: L
authors.lastname: Ciobanu
mesh_terms: D000465:Algorithms; D000818:Animals; D002540:Cerebral Cortex / Q000033:anatomy & histology* / Q000737:chemistry*; D003198:Computer Simulation; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008959:Models, Neurological; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water
keywords: brain cortex; diffusion MRI; diffusion model; diffusion time