Introduction

Starting in the late 1940s, medical applications of ultrasound in Japan were explored by Kenji Tanaka and Toshio Wagai. Two Japanese investigators, Shigeo Satomura and Yasuhara Nimura, were credited with the earliest development of ultrasonic Doppler devices for monitoring tissue motion and blood flow in 1955. Virtually simultaneously with the work going on in Japan and in the U.S., Inge Edler and Hellmuth Hertz at the University of Lund in Sweden worked on echocardiography, an ultrasound imaging technique for imaging cardiac structures and monitoring cardiac functions. In parallel with these developments on the diagnostic front, William Fry and his colleagues at the University of Illinois at Urbana worked on using high-intensity ultrasound beams to treat neurological disorders in the brain.