Recommended Ultrasound Terminology
V
vascular
Adjective relating to a blood vessel.
vascularity
Amount of blood vessels per unit volume or area. Similar to vessel density.
vascular contrast agent
See contrast agent, vascular.
vascular morphology
Related to the geometry and structural features of blood vessels and typically used to describe vascular function or abnormalities.
Related term: vessel tortuosity
vascular phases of enhancement
Used to indicate the phases when contrast agent microbubbles circulate within the vascular system of the body. This is useful because some contrast media also show a postvascular phase.
vector
A quantity possessing both magnitude and direction.
vector Doppler
A type of vector flow technique that determines both longitudinal and transverse flow directions simultaneously.
vector flow
An ultrasound method used to determine flow in both longitudinal and transverse directions simultaneously.
velocity
A vector, the magnitude of which is the speed of a moving object and the direction is that in which the object is moving.
velocity, critical
The flow velocity at which the Reynolds number attains its critical value and the onset of turbulence occurs.
velocity gradient
The rate of change of velocity with position. With steady laminar flow in a blood vessel, this gradient is usually in a radial direction.
velocity hydrophone
A hydrophone whose output voltage is proportional to particle velocity.
velocity of sound
The speed of sound in a specified direction.
See speed of sound.
velocity profile
The variation of velocity with radial position for flow in a tube.
velocity profile, blunted
A modification of the parabolic flow profile that is commonly encountered in physiologic circumstances. The central laminae move at almost the same velocity.
Related term: velocity profile, parabolic
velocity profile, parabolic
The form of the velocity profile found with steady flow in a round vessel that exhibits flow resistance only. The parabolic flow profile has the special property that the average velocity across the vessel is exactly one-half of the maximum velocity in the center stream. Also called Poiseuille flow.
Related term: velocity profile, blunted
venous phase of enhancement
The phase of contrast medium circulation when contrast-enhanced blood leaves an organ through its venous drainage. For liver imaging, it is synonymous with the sinusoidal phase rather than the portal phase.
vessel tortuosity
A geometric feature of some vessels characterized by abnormally excessive curvature and shape.
Related term: vessel morphology
Vibro-acoustography
A method of soft tissue imaging that uses the dynamic radiation force from an amplitude-modulated ultrasound signal to drive acoustic emission from tissue at the modulation frequency. Because the intensity of the acoustic emission is proportional to the modulus of the tissue, it is considered a method of elastography. In its most common implementation, two ultrasound beams of slightly different frequencies are focused at the same spatial location to produce an amplitude-modulated signal. The resulting acoustic emission occurs at the difference frequency between these two signals, and it is usually detected with a hydrophone.
Related term: radiation force imaging, elastography
video signal
The processed envelopes of echo signals in an ultrasonic imaging system generally are referred to as “video signals” by analogy with television nomenclature. Processing may include compression and postprocessing and/or preprocessing.
video signal (ultrasound)
The envelope of echo signals in an ultrasonic imaging system generally are referred to as “video signals” by analogy with television nomenclature. The final stream of information from which images are displayed.
viscoelastic
Pertaining to a substance having both viscous and elastic properties.
Related term: viscoelasticity
viscoelasticity
A property of a material that is viscous and also exhibits elasticity. The application of a stress to a viscoelastic material gives rise to a strain that approaches its equilibrium value slowly.
viscosity
The tendency of a material or fluid to resist deformation. The slow response to either a stress or strain stimulus.
viscous damping
Mechanical damping that occurs to a wave or particle moving in a medium in which there is a resisting force that opposes the motion. The magnitude of the resisting force is often proportional to the particle velocity and in a direction opposing that of the particle. This process results in a viscous loss and most often with a change in phase velocity.
Voigt model
A viscoelastic model of a material that can be represented by a dashpot η in parallel with a purely elastic spring E, as shown in the diagram below. Also known as the Kelvin-Voigt model.
Related terms: Burgers model, dashpot, elastic spring, Maxwell model, Kelvin-Voigt model, standard viscoelastic linear model
volume acquisition
A process of scanning in which many ultrasound scans are obtained to image a structure in 3 dimensions.
Related term: 3-dimensional acquisition
volume flow
The volume of fluid passing through a surface (usually imaginary) per unit time. In a blood vessel, volume flow (F) equals the product of the cross-sectional area (A) and the average blood velocity (v); ie, F = A · v. The unit is liters per second (L/s).
volume scattering coefficient
The quotient of the scattering cross section of the volume considered divided by that volume.
volume strain
The change in volume divided by the original volume.
See strain.
volume velocity
Integral, over a vibration surface, of the product of the component of particle velocity normal to the surface and the differential surface area.
vortex
See vortices.
vortices
Elements of rotational flow often seen with flow separation, disturbance, and turbulence. Rotating flow comprises a wide range of velocities aligned in both directions along a line passing through its center. Doppler shifts from vortical flow are thus characterized by spectral broadening. Simultaneous forward and reverse flow will also be seen if the vortex velocity exceeds the component of the longitudinal flow speed along the beam.
voxel
The smallest volume element or cell size in a digitized 3-dimensional (3D) image. Each voxel has an address and a brightness or color. The address is given by a set of x, y, and z coordinates corresponding to the voxel’s position in the 3D array. Compare with pixel, the smallest element of a 2-dimensional image.
