In the CWD mode, the transducer has two crystals: one to send and the other to receive the reflected waves continuously. ∴, the maximal frequency shift that can be recorded is not limited by the pulsed repetition frequency or the Nyquist limit as with PWD. Unlike PWD, CWD measures all the frequency shifts (i.e., velocities) present along its beam path; hence, it is used to detect and record the highest flow velocity accessible. (Oh, Chapter 4)
- Range ambiguous
- Continuous bursts of ultrasound to receive reflected wave
- Recording of all velocities along the ultrasound beam
- The main goal of CWD is to obtain the highest flow velocity along its path, so that intracardiac or intrapulmonary pressures can be estimated, and pressure gradient across a stenotic or regurgitant orifice can be calculated.
- Occasionally, recording of a high-velocity flow is the first clue to an unsuspected lesion within the path of a CWD beam. (Oh, Chapter 4)