The blanking distance is the minimum sensing range in an ultrasound proximity sensor. Blanking distance is a function of the ring down time of the transducer as the transducer must ring down before it can receive the sound reflected from the tissue.

The velocity of flowing blood is usually measured in cm/s. It is always zero at the vessel wall and the velocity profile across a vessel can have various shapes depending upon the type of flow being observed (see also pulsatile flow). Laminar flow giving rise to a laminar velocity profile, plug flow giving rise to a flat velocity profile and disturbed flow can be distinguished.
Normal peak systolic velocities in the femoral and popliteal arteries vary from 90 to 110 cm/s in the femoral artery and from 40 to 70 cm/s in the popliteal artery.

See also Bi-directional Flow, Pulsatility Index, and Acceleration Index.

A bolus is a rapid infusion of high dose contrast agent. Dynamic and accumulation phase imaging can be performed after bolus injection. Since the transit time of the bolus is only a short time, images with high frame rate show the wash in and wash out of the contrast material. The injection rate and the total injected volume modifies the bolus peak profile. Substantial changes in the concentrations during signal acquisition induce artifacts. Furthermore, the hemodynamic parameters (cardiac output, blood pressure) influence the bolus profile. However, the characteristics of ultrasound contrast agents are favorable with a continuous perfusion.

See also Negative Bolus.

(TIB) The bone thermal index is an exposure model for the case that the ultrasound beam passes through soft tissue and a focal region is in the immediate vicinity of bone.
The longitudinal waves of ultrasound are reflected and transformed into transverse waves, creating a heating effect. Muscle and bone absorb more energy at interfaces with other heterogeneous tissues.

See also Sheer Wave.

The boundary layer is a thin layer of quasi-stationary fluid in contact with the walls of the containing vessel.