Physics of Diagnostic Ultrasound

Abstract

This chapter presents the physics of ultrasound, probe design, and some of the typicel artifacts present in pulmonological applications. Some of the techniques used for optimal imaging of chest anatomy are explained as well as the diagnostic questions that can be answered by a pulmonologist.Diagnostic ultrasonography is the only clinical imaging technology currently in use that does not depend on electromagnetic radiation. This modality is based on the properties of sound waves, and hence the mechanical and acoustic properties of tissues.Diagnostic ultrasound is mechanical energy that causes alternating compression and rarefaction of the conducting medium, traveling in the body as a wave usually at frequencies of 2-10 MHz, well beyond audible frequencies. In general it is assumed that the speed of sound in tissue is constant at 1,540 m/s [1]. By knowing the frequency and the speed of sound, one can determine its wavelength (similar to electromagnetic radiation) [2-4]:(wavelength) ϭ c(speed)/f(frequency), or using the assumed speed:(wavelength in mm) ϭ 1.54/f(frequency in MHz).