Ramona Woitek MD, Abstract Co-Author: Nothing to Disclose

Gregor Kasprian MD, Abstract Co-Author: Nothing to Disclose

Michael Weber, Abstract Co-Author: Nothing to Disclose

Peter Christian Brugger MD, PhD, Abstract Co-Author: Nothing to Disclose

Daniela Prayer, Presenter: Nothing to Disclose

In rat-pups diffusion anisotropy imaging has been shown to demonstrate postnatally increasing white matter myelination of the brainstem more sensitively than other conventional imaging modalities (Prayer D, Neuroradiology 1997). Therefore we investigated whether diffusion tensor imaging (DTI) in fetuses with normal CNS development is capable of showing changes in fractional anisotropy (FA) or apparent diffusion coefficient (ADC) in the midbrain correlating with gestational age. Especially an increasing FA would point to represent ongoing prenatal myelination as formation of myelin constrains diffusion perpendicular but not parallel to fibers.

Clinically indicated fetal MRI was performed on a 1.5 T system using a five-element phased array cardiac coil in 55 fetuses from 17-38 GW with normal CNS development. T2W-FSE sequences in three orthogonal planes of the fetal brain and an axial, single-shot, echo planar diffusion tensor sequence (32 non-collinear diffusion gradient encoding directions) perpendicular to the long axis of the fetal brainstem were acquired. After coregistering T2W-FSE axial images with axial FA colour coded maps a region of interest (ROI) was drawn in the midbrain to calculate FA and ADC.

A significant positive correlation between gestational age (GA) and FA was found (r= .496, p=.005) but no significant correlation was found between GA and ADC (r=-.205, p=.268).

We could show a significant positive correlation of GA with FA but not with ADC measured in the fetal midbrain. Increasing FA rather than ADC represents The increase in FA during gestation can be explained by physiologically increasing myelination. Therefore DTI is capable of demonstrating prenatal myelination in fetuses with normal CNS development based on FA measurements.

Fetal DTI might serve to investigate (ab-) normal myelination in the midbrain or might be helpful in assessing brainstem compression in fetuses with hydrocephalus or Chiari malformations.

Woitek, R, Kasprian, G, Weber, M, Brugger, P, Prayer, D, DTI of the Fetal Midbrain and Myelination.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11012623.html