Our thanks go to our colleagues at the VU Univer- Preface to the Third Edition sity Medical Center and to those in other hospitals Reading through the prefaces of the two previous edi- who referred their patients to us. We are indebted to tions,we can say that much of what was said there still all colleagues who allowed us to use their MR images, holds. At the same time,however,much has changed. published or unpublished,making it possible for us to There has been immense progress in the technical present illustrations of nearly all known white matter possibilities of magnetic resonance and in the know- disorders. Two colleagues were particularly helpful ledge of genetic defects, biochemical abnormalities, and provided us with essential and unpublished f- and cellular processes underlying myelin disorders. ures: our friends Susan Blaser,from the Hospital for This immense progress has prompted us to embark Sick Children in Toronto,and Zoltán Patay,from the upon the enormous task of rewriting the previous King Faisal Hospital in Riyadh. edition and adding 40 chapters. In doing so we have Many people at the VU University Medical Center tried to cover most white matter disorders,hereditary have been of great technical help to us in producing and acquired,and to present a collection of images to high quality images and in providing secretarial illustrate the field to the fullest possible extent. This assistance. The contributions of these people are edition will therefore be more complete than the pre- mentioned separately in the acknowledgements.