IntroductionThis database represents the normalized fractional anisotropy (FA) values of cerebral white matter, for the age and sex of normal individuals. FA is the main parameter of diffusion tensor imaging (DTI).
AcknowledgementThis research work was performed by the support of Grant-in-Aid for Scientific Research by Japan Society for the Promotion of Science (2005).
Towards early detection of cerebral white matter lesionsDTI is a newly developed magnetic resonance (MR) imaging technique, which non-invasively provides the microscopic structural information on orientation of tissues in vivo. It is mainly used in imaging of the brain, to detect the degree to which directionally ordered tissues (for instance, normal nervous tissue in brain) are manufacturing or losing normal integrity. It is expected that DTI is more sensitive than other MR imaging techniques in detection of diseases which involve white matter. The basic principle of DTI lies upon the fact that the diffusion of molecules in highly organized tissue is directionally dependent, i.e., diffusion along the longitudinal axis of tissue is greater than in any other directions.
FA is a quantitative measure of DTI. Information on alteration of FA of tissues, in pathological conditions, is achieved through comparison with normal FA values. However, the normal FA values of different types of tissue vary greatly. In general, normal cerebral white matter has higher degree of fractional anisotropy than other cerebral tissues. Further, FA of white matter varies among regions of the brain (spatial heterogeneity); splenium of the corpus callosum has the highest degree of FA. In addition, FA of the same tissue even varies with age. Newborn infants and aged individuals have lesser degree of fractional anisotropy than normal adults. Lastly, FA of a tissue measured at fibre crossing and branching points may differ from other parts of the same tissue. Thus, precise interpretation of FA maps is impossible without sufficient information on normal anisotropy values of different areas of the brain, at various ages and sexes (mean distribution and distribution width, or "the reference values").
To provide "the reference FA values", we (Diffusion tensor imaging database development team, Department of Radiology, Hokkaido University Hospital and Hokkaido University Graduate School of Medicine) have developed a database which contains the normal FA values for the age and sex of each individual.