The significance of ultrasound can be significantly increased by the application of the Doppler effect. A distinction is made between one-dimensional methods (pulsed-wave Doppler, also referred to as D-mode) of two-dimensional, color-coded applications (color Doppler-F-mode). The combination B-picture with pulsed wave Doppler (PW-Doppler) is also called duplex. Doppler techniques are used to determine blood flow velocities, to detect and assess heart valve defects, strictures (stenoses), occlusions or shunts (shunts.