11.1 Basic Principles
Ultrasound imaging was first introduced in 1950 by (Wild 1950) together with Reid. Since then, it developed to one of the most important diagnostic imaging modalities. With today's scanners, two-dimensional cross-sectional images of the body can be produced in real time with a spatial resolution below 1 mm. Ultrasound imaging relies on the propagation of mechanical waves with frequencies beyond the audible range into the body, the reflection and scattering of sound by tissue structures, and the registration of the echoes. Similar to sonar and radar, it is a pulse-echo ranging technique. Using the acoustical Doppler effect, the quantitative measurement of blood flow is possible, and flow velocity and direction can be presented in real time as colored overlays. To enhance the echoes from blood, ultrasound contrast media were developed. They show nonlinear behavior that can be used for their specific and sensitive detection. With the introduction of nonlinear imaging modes for contrast media also, nonlinear imaging of tissue became of interest and showed a significant improvement in many imaging situations. Recently, the higher integration of electronics and the increasing computer power led to the realization of real-time three-dimensional imaging, which is of special ...