History of medical and biological ultrasound at the University of Pennsylvania.

We briefly review my early contacts with bioacoustics and the bioacoustic work at the University of Pennsylvania that took place from the early 1950s to 1975. It was carried out with E. L. Carstensen, K. Li, A. Smith, H. Pauly, J. Reid, P. Edmonds and many students. The emphasis was first on basic biophysical studies. The work with E. Carstensen and H. Pauly was primarily concerned with the mechanism causing the high absorption typical for tissues and cell suspensions. Macromolecular content was shown to be largely responsible for the absorption. Practical applications concerned the relative merits of electromagnetic and ultrasonic diathermy techniques. P. Edmonds extended the range of macromolecular studies to 100 MHz and initiated work on the attenuation in lung tissues. After J. Reid came to Pennsylvania, the development of echocardiography took place.