Ultrasound is sound with frequencies greater than 20 kilohertz. This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, including ultrasound. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz. 

In the present book, twelve typical literatures about ultrasound published on international authoritative journals were selected to introduce the worldwide newest progress, which contains reviews or original researches on ultrasound. We hope this book can demonstrate advances in ultrasound as well as give references to the researchers, students and other related people.