ASN CNSA key terms

A non-imaging ultrasound technique that measures blood flow velocity in the major intracranial arteries using a low-frequency probe placed on thin skull windows. It records direction and speed of flow rather than producing a picture.

An imaging form of intracranial ultrasound that overlays color flow on a two-dimensional grayscale image of brain tissue and vessels. It allows the sonographer to see the artery being sampled and correct the angle.

The thin squamosal portion of the temporal bone above the zygomatic arch where ultrasound penetrates with least attenuation. It is the usual site for insonating the middle, anterior, and posterior cerebral arteries.

A suboccipital probe position at the base of the skull used to insonate the vertebral and basilar arteries. Flow is typically directed away from the probe in the normal vertebrobasilar circulation.

A probe position over the closed eyelid that allows insonation of the ophthalmic artery and the terminal internal carotid artery through the orbit. Output power must be reduced to limit ocular exposure.

The largest branch of the internal carotid circulation, insonated at depths of roughly 40 to 65 mm through the temporal window. Its M1 segment normally shows flow directed toward the probe.

A midline vessel formed by the union of the two vertebral arteries, insonated through the suboccipital window at depths of about 80 to 120 mm. It supplies the brainstem and posterior cerebral territories.

Paired posterior circulation vessels ascending through the neck and entering the skull at the foramen magnum. On suboccipital insonation they are found lateral to midline and show flow away from the probe.

A branch of the internal carotid that runs through the orbit and can be sampled transorbitally. Flow direction and pulsatility here help assess the distal internal carotid and collateral pathways.

The time-averaged velocity of blood through a vessel over the cardiac cycle, reported in centimeters per second. It is the main TCD parameter used to judge stenosis, spasm, and flow change.

The highest velocity recorded during systole at a given sample site, expressed in centimeters per second. Rising values suggest narrowing at or just before the insonated segment.

A calculated ratio describing the shape of the Doppler waveform, derived from the difference between peak systolic and end-diastolic velocities divided by the mean. Higher values suggest greater downstream resistance.

A waveform index computed as peak systolic minus end-diastolic velocity divided by peak systolic velocity. It reflects the resistance of the vascular bed distal to the sample site.

Narrowing of a cerebral artery by contraction of its muscular wall, most often after subarachnoid hemorrhage. TCD detects it as focal velocity elevation that may precede clinical deficit.

A brief, high-intensity transient signal within the Doppler spectrum caused by a small particle passing the sample volume. It appears as a short unidirectional spike lasting only milliseconds.

Monitoring of a cerebral artery over time to count microembolic signals, often after stroke or during carotid disease. Counts help estimate embolic risk and guide treatment decisions.

The capacity of cerebral vessels to dilate and increase flow when metabolic demand rises or perfusion pressure falls. It is tested by comparing velocities before and after a vasodilatory challenge.

Adjustment of velocity measurement for the angle between the ultrasound beam and the direction of blood flow. It is required when the vessel is not parallel to the beam, as in duplex imaging.

The angle between the emitted ultrasound beam and the axis of blood flow. Velocity estimates are most accurate when this angle is known and kept at or below 60 degrees.

Combined real-time grayscale imaging of vessel structure with pulsed Doppler measurement of flow. It lets the examiner see plaque and sample velocity at the same location.

A display that maps mean velocity and direction of flow onto a color scale over the vessel image. Color helps locate vessels and shows flow direction relative to the probe.

The velocity-versus-time graph produced by pulsed or continuous wave Doppler, showing systolic upstroke, diastolic flow, and waveform shape. Its contour reveals stenosis, resistance, and proximal or distal disease.

The measured distance between the inner and outer walls of the carotid artery on grayscale imaging, taken in a plaque-free segment. Increased thickness is a marker of early atherosclerosis.

A focal thickening of the arterial wall that projects into the lumen, characterized by echogenicity, surface regularity, and texture. Plaque features help estimate embolic and stroke risk.

Narrowing of the internal carotid artery, usually by atherosclerotic plaque, graded by velocity and imaging findings. Severity guides decisions about medical therapy and revascularization.

A plaque surface with a crater-like defect seen on grayscale or color imaging. It is associated with increased embolic risk and may be present even when stenosis is only moderate.

A very tight stenosis with markedly reduced flow beyond it, so velocities may fall rather than rise. Recognizing this pattern prevents underestimating severity from velocity alone.

Reversal of flow in a vertebral artery caused by proximal subclavian stenosis or occlusion, which diverts blood away from the brainstem. Duplex shows retrograde vertebral flow.

Narrowing of the subclavian artery proximal to the vertebral origin, often causing a pressure difference between arms. It can produce retrograde vertebral flow and arm symptoms.

A hypervascular mass at the carotid bifurcation that splays the internal and external carotid arteries apart. Duplex shows intense flow within the mass and widening of the bifurcation angle.

Non-atherosclerotic arterial disease producing a string-of-beads appearance on angiography and irregular vessel caliber on ultrasound. It commonly affects the mid and distal internal carotid artery.

A contained rupture of an artery in which blood communicates with a surrounding sac through a neck. Duplex shows swirling flow and a to-and-fro signal at the neck.

The length of the artery along the beam from which Doppler echoes are accepted for the spectral display. Correct placement ensures the signal comes from the intended vessel segment.

A setting that removes low-velocity, high-amplitude signals from vessel wall motion so they do not obscure the spectral display. It is set high enough to clear wall noise but low enough to keep slow flow.

An artifact in which velocities exceed the measurable limit of the scale and wrap to the opposite side of the display. Raising the scale, lowering frequency, or shifting the baseline resolves it.

The change in frequency of reflected ultrasound caused by moving red blood cells. Its magnitude is proportional to flow velocity and to the cosine of the angle between beam and flow.

The ability of cerebral resistance vessels to adjust caliber and keep blood flow relatively constant despite changes in arterial pressure. Impaired regulation raises risk of ischemic injury.