Original ContributionsReduced anisotropy of water diffusion in structural cerebral abnormalities demonstrated with diffusion tensor imaging
Introduction
The brain is a highly organized organ with a complex microstructural organization.1 The microstructural organization of brain tissue affects the molecular motion (diffusion) of water. Diffusion therefore reflects the structural organization of tissue. Diffusion imaging is a magnetic resonance (MR) imaging technique that allows the quantification to the molecular motion of water.2, 3 Magnitude and directionality (anisotropy) of molecular motion of water can be described. Measurements of the magnitude of diffusion have been used to identify abnormal tissue in tumors,4, 5, 6 stroke,7, 8, 9, 10, 11 multiple sclerosis,12, 13 and status epilepticus.14 Diffusion tensor imaging (DTI) is a relatively new technique that allows rotationally invariant measurements of both magnitude and directionality of water diffusion.15 Echo planar imaging allows the acquisition of the full diffusion tensor in imaging times acceptable for human studies.16 Our aim was to investigate diffusion in long standing structural abnormalities of different etiology with DTI.
Section snippets
Materials and methods
Eighteen patients (mean age 35 years, range 17–49 years) with partial epilepsy of more than 5 years and a structural abnormality on standard T1- and T2-weighted magnetic resonance images and 10 control subjects (mean age 33 years, range 29–39 years) without a history of neurologic disease were scanned with DTI. Informed consent was obtained after the nature of the procedure had been fully explained before scanning. In this prospective study, we recruited patients with a lesion on standard
Results
FA maps provided contrast for myelinated tracts in normal controls. In the subcortical white matter of normal controls the mean FA in the white matter was 0.76 (SD 0.05). In cortical gray matter the mean FA was significantly lower. The mean FA in gray matter was 0.25 (SD 0.1) (Fig. 1). The mean diffusivity maps were uniform. The mean diffusivity in white matter was 0.75 × 10−3mm2/s (SD 0.05 × 10−3mm2/s) and for gray matter 0.78 × 10−3mm2/s (SD 0.05 × 10−3mm2/s) (this difference was not
Discussion
In this study we attempted to characterize diffusion in different structural abnormalities. In control subjects anisotropy of water diffusion in subcortical white matter was high, a finding in keeping with the measurements of other groups.16 In cortical gray matter of control subjects the anisotropy was significantly lower (Fig. 1) indicating isotropic or almost isotropic diffusion. We demonstrated that anisotropy was significantly lower in structural abnormalities anisotropy than in normal
Acknowledgements
This research has been kindly funded by an European Community Fellowship (U.C.W.), by the National Society for Epilepsy (M.R.S., K.D.B.), the Brain Research Trust (C.A.C., M.R.S.) and the Multiple Sclerosis Society of Great Britain and Northern Ireland (G.J.B.). We would like to thank Dr. B.E. Kendall and Dr. J.M. Stevens for their helpful comments. We thank Dr. J.S. Duncan for permission to study his patients.
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