Perivascular is the region around (surrounding) vessels.

Duplex ultrasonography (duplex scan) consists of two ultrasound modalities to study blood flow and the perivascular tissue. This includes B-mode / gray scale imaging used in combination with spectral Doppler / pulsed-wave Doppler.
The real-time visualization of the vessels and tissue by the B-mode component improves the PW Doppler positioning and the direction of blood flow can be inferred. The angle between the direction of the PW Doppler signal and the estimated direction of blood flow can be measured.
Duplex techniques are available on phased array, linear array, and mechanical scanners. A phased array probe is able to create nearly simultaneous images and flow information. A linear array transducer can also do this if the Doppler probe is attached separately to one end of the scanhead. A mechanical transducer freeze the image; the crystals must be static to produce a Doppler image. The first two transducers are therefore the best choice for Duplex.

See also Compound B-Mode, and Duplex Scanner.

A linear probe contains one or more acoustic linear array transducer elements arranged in a line to send pulses of sound into a material. The linear array gives a large probe surface (footprint) and near field. In Doppler mode, a linear probe operates a subset of its elements as a linear phased array and can thus steer the Doppler beam at a selected angle to the imaging beam. This is a popular configuration for peripheral vascular and perivascular scanning.