Physical Principles of Ultrasound Propagation and Image Formation

This chapter provides a comprehensive review of the physical principles of ultrasound propagation and image formation, with examples of the eye and orbit. Ultrasonic waves are first defined according to their speed, frequency and wavelength. The reflection and transmission of an ultrasonic wave, as well as scattering and the concept of attenuation, are subsequently outlined. The main steps of ultrasound image formation are then described, with a piezoelectric transducer acting as the ultrasound source and receiver, followed by an analysis of image resolution, and the conditions for its optimization at a given frequency. Finally, the principle of tissue characterization is discussed, based on the estimation of the backscatter coefficient as a function of frequency, and different applications to ophthalmology are presented.