Helen E. D'Arceuil PhD, Abstract Co-Author: Nothing to Disclose

P. Ellen Grant MD, Presenter: Nothing to Disclose

Alex J. De Crespigny PhD, Abstract Co-Author: Nothing to Disclose

DTI is sensitive to structural ordering in brain tissue: nerve fibers show highly anisotropic diffusion, particularly in white matter tracts. Diffusion anisotropy changes with disease and also with neural development. In vivo DTI images are hard to acquire in human neonates, and with low resolution images (limited scan time), it is difficult to delineate tissue regions, such as the CSO/cingulum. Therefore we used high resolution 3-D DTI of fixed rabbit brains to study developmental changes in regional diffusion anisotropy and gray and white matter fiber tracts.

MRI was performed on a 4.7T Bruker Biospec Avance scanner using a 40G/cm gradients and custom built solenoid coils. Excised rabbit brains were acquired at postnatal ages 0, 4, 9, 16, 35, 75, 384 days, and perfused fixed with paraformaldehyde and then soaked in phosphate buffered saline with GdDTPA. 3-D spin-echo DTI scans were acquired: 20 diffusion weighting directions, b-value of 2500s/mm2, isotropic spatial resolution of 120-220m (depending upon age), scan time about 23 hours. Data were processed to yield trace apparent diffusion coefficient (ADC) and fractional diffusion anisotropy (FA) maps and were measured using MRVision (MRVision Co, Winchester, MA). Fibers were calculated by DTI tractography using the FACT algorithm (DTI Studio, Jiang & Mori, Johns Hopkins Univ.).

Post mortem DTI provided greatly superior image quality compared to in vivo scans. Two cortical zones were clearly resolved in all FA maps, in both neonates and adults. The brain was highly anisotropic at day 1 and the white matter became increasingly anisotropic with time, while FA in cortex reduced. DTI tractography was possible even in day 0 newborns. The cingulum (peri-splenial region) showed extensive connections to the rostral cortex, external and internal capsule, and the cerebella peduncle. The genu, unlike the body and splenum of the corpus callosum, showed no long range connections only frontal cortical connections.

Detailed regional DTI mapping of normal and pathological brains is possible with this methodology and may add new insight into the regionally specific disease conditions as well as neurodevelopment.

D'Arceuil, H, Grant, P, De Crespigny, A, High Resolution ex Vivo Diffusion Tensor Imaging (DTI) and Tractography in the Developing Rabbit Brain.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4415578.html