Sound and Ultrasound

Abstract

Sound plays two important roles in medicine and biology: animals hear sound and thereby sense what is happening in their environment, and physicians use high-frequency sound waves called ultrasound to image structures inside the body. We first derive the wave equation governing the propagation of sound, and then discuss the many properties of waves including frequency, wavelength, the speed of sound, the acoustic impedance, the intensity, and attenuation measured by the decibel scale. We review the anatomy of the ear and describe how hearing occurs. We then analyze how physicians use ultrasound imaging for medical diagnosis, including piezoelectric transducers, pulse echo techniques, and Doppler imaging.