There are two major reasons for having this symposium. First, Tohoku Univer sity is the place where ultrasound investigations in Japan originated. Starting from the research studies of Professors H. Nukiyama and Y. Kikuchi of To hoku University, Professor J. Saneyoshi of Tokyo Institute of Technology, and Dr. K. Kato of Osaka University - all graduates of Tohoku University - the results spread to all parts of Japan. More recently we have had acoustic macro scopic studies by researchers like Professor N. Chubachi. As regards tissue char acterization, which was the main theme of the symposium, the collaboration among research workers in Japan and the United States started 10 years ago between Professor F. Dunn of the University of Illinois and staff members of Tohoku University and the Tokyo Institute of Technology. So this conference commemorates the lOth anniversary of that joint research effort. The second reason for this conference is that the application of ultrasound has become wide spread and indispensable in the routine clinical activities of medicine. But there have not been many breakthroughs in terms of quantitative and qualitative measurement of the living body tissues. Also, there are many problems with regard to practical application. There are various points that have not been elucidated yet as to the physical and acoustical characteristics of ultrasound itself. The methodology has not in all cases been well established. Therefore, the scientific elucidation of these areas is essential.

Ultrasonic Scattering in Biological Tissues contains 14 chapters written by world-renowned authorities who describe current work related to theoretical and experimental aspects of ultrasonic scattering phenomenon in biological tissues. Introductory material regarding ultrasonic scattering in biological tissues is presented, followed by discussions on theoretical treatments, experimental approaches, in vitro results on selective tissues, in vivo results on various tissues, and the current status of quantitative backscatter imaging. Ultrasonic Scattering in Biological Tissues will be an excellent reference for biomedical engineers, ultrasound specialists, biophysicists, and radiology researchers.

The second E. C. Workshop on Ultrasonic Tissue Characterization was organized for the assessment of research goals and plans as the basis to a grant proposal for a "Concerted Action" which will be forwarded to the European Commission. It should, therefore, not only be considered as a work in progress exhibition which succeeded the former activities within the E. C. (Inventory on Tissue Characterization in Europe and first Workshop). The Steering Group invited a 1 imited group of Institutes to send its group leader and a research fel low in the entitled field, who should expose the overall research program, as wei 1 as the more specific work on tissue characterization by RF signal analysis and spectroscopy. The ultimate goal of the Workshop has been the formulation of schemes of interaction among the Institutes and individuals and the definition of cooperative research programs. The remainder of the groups and some of the groups present are working in the field of analysis and processing of cl inical A- and B-mode echograms (i. e. video signals). Because this work is more closely related to the cl inical diagnostics it was decided that for that reason no preparatory workshop was needed. In the final proposal for the Concerted Action this work wi 1 1 get ample attention. Although not many clinicians were present, their positive interest in the sophisticated analysis techniques and their contribution to the dis cussions again have been a most valuable and stimulating experience.