Which of the following techniques uses separate transmitter and receiver elements?

The technique that uses separate transmitter and receiver elements is continuous wave Doppler. In this method, one element continuously emits ultrasound waves while another element continuously listens for the echoes. This allows the system to detect high velocities of blood flow without being affected by the limitations of pulsed wave Doppler, which relies on alternating transmission and reception of signals.

Continuous wave Doppler is particularly advantageous when assessing fast-moving structures, as it can measure velocities without the aliasing effect that can occur in pulsed Doppler systems. By using dedicated transmit and receive elements, continuous wave Doppler can effectively gauge high-velocity blood flow, such as that found in valvular heart disease or congenital heart defects.

The other techniques listed do not use a configuration of separate transmit and receive elements. Duplex imaging combines both Doppler and gray-scale imaging but does not operate with dedicated elements for each function simultaneously. Motion mode, likewise, uses a single element for both transmission and reception. Amplitude mode primarily focuses on measuring the strength of the reflected echoes rather than utilizing distinct elements for sending and receiving ultrasound waves.