In this chapter the physics of medical ultrasound will be discussed at an introductory level for users of the technology. Several texts exist which readers can consult to deepen their understanding.1–5 Discussed later in this chapter are parameters related to ultrasound in tissue such as speed of ultrasound, attenuation and acoustic impedance. Values of these parameters for commonly encountered tissues and materials are quoted (for more values see Duck6 and Hill et al.7). The clinical user is not required to have a detailed knowledge of these values but some knowledge helps in the production and interpretation of ultrasound images and Doppler blood flow measurements. Basic physics is also of central importance in considerations of safety.
PRODUCTION OF ULTRASOUND 3
INTENSITY AND POWER 5
DIFFRACTION AND INTERFERENCE 5
IMAGE SPECKLE 6
FOURIER COMPONENTS 7
STANDING WAVES AND RESONANCE 7
REFLECTION 9
SCATTERING 9
REFRACTION 10
LENSES AND MIRRORS 10
ABSORPTION AND ATTENUATION 11
NON-LINEAR PROPAGATION 11
TISSUE CHARACTERISATION AND ELASTOGRAPHY 12
DOPPLER EFFECT 13
RESOLUTION 14