What technique uses two PZT crystals, one for sending and the other for receiving signals?

The technique that utilizes two PZT (lead zirconate titanate) crystals, one for transmitting and the other for receiving signals, is known as Continuous Wave (CW) Doppler. This method is distinct from other Doppler imaging techniques because it allows for the simultaneous and continuous measurement of blood flow velocity without the limitations associated with pulsed wave Doppler imaging, such as depth resolution or the maximum measurable velocity.

In CW Doppler, the two separate crystals enable uninterrupted transmission and reception of ultrasound waves, which is crucial for capturing fast-moving blood flow accurately. The continuous nature of this technique makes it particularly useful in assessing conditions like valvular heart disease or high-velocity flow situations without aliasing, as it does not require the signal to be pulsed at intervals like in pulsed or color Doppler techniques.

Other techniques listed might employ single PZT crystals or operate under different principles that may not require separate transmitting and receiving elements. For instance, Pulsed Doppler utilizes a single transducer to alternate between sending and receiving, while Color Doppler is essentially an extension of pulsed Doppler that visually represents blood flow direction and velocity through color coding. Spectral analysis, while related to interpreting Doppler signals, does not specifically refer to the use