Six years ago the editors of the Encyclopedia of Medical Radiology selected two additional editors from the emerging generation of young radiologists to complete this unique compendium of radiology. Klaus Ranniger was one of them and he worked with enthusiasm and great energy at the challenge facing him. His editorial work was excellent and he succeeded in winning internationally acclaimed scientists to contribute to this volume. Their chapters have met the requirements and goals we set out to achieve in every aspect and to the highest degree. The majority of the authors valued Klaus Ranniger not only as a fellow scientist and doctor but also as a personal friend. In America, his adopted country, he found acknowledgement of his personal achievement and scientific research. He was highly respected and admired among specialists in the field of radiology. Klaus Ranniger, our coeditor and friend, died suddenly and unexpectedly before this volume could be published. We are honored to present this volume as his legacy. FRIEDRICH HEUCK Vorwort Die Herausgeber des Handbuches der medizinischen Radiologie nahmen vor sechs Jahren aus der nachfolgenden Generation von Radiologen zwei Mitarbeiter in ihren Kreis auf, urn dieses im wissenschaftlichen Schrifttum der Welt einmalige Sammelwerk der Radiologie aus dem Springer-Verlag zum AbschluB zu bringen. Mit groBer Tatkraft und echter Begeisterung hat Klaus RANNIGER die ihm gestellten Aufgaben tibernommen.