Describe two methods of Doppler imaging.

1. Continuous-wave Doppler uses a continuous signal and is capable of measuring very small velocities. It samples all depths in the beam and thus is poor at determining the position of an individual signal. Continuous-wave Doppler is used for peripheral vascular studies in patients with suspected atherosclerosis.
2. Pulsed-wave Doppler uses pulses of finite length. Received signals are time gated to sample only a given depth. Pulsed-wave Doppler is less sensitive to low velocity than continuous-wave Doppler.