ASN CNSA flashcards

35 cards. Read the term and the definition here. The deck at the top of this page is optional.

Doppler equation

The Doppler shift equals twice the transmit frequency times velocity times the cosine of the angle, divided by the speed of sound in tissue.

Doppler angle limit

Insonation angle should not exceed 60 degrees because cosine error rises steeply with angle, causing velocity underestimation.

Speed of sound in tissue

Ultrasound travels approximately 1540 meters per second in soft tissue, the value used for depth and velocity calculations.

Transcranial Doppler probe frequency

A 2 MHz pulsed probe is standard for temporal, orbital, and suboccipital windows; 1 MHz improves penetration through thick bone.

Normal MCA velocity

Mean middle cerebral artery velocity in adults averages about 55 cm/s with a standard deviation near 12 cm/s.

Vasospasm velocity threshold

MCA mean velocities above 120 cm/s suggest vasospasm, and values above 200 cm/s suggest severe vasospasm.

Lindegaard ratio

The ratio of MCA mean velocity to ipsilateral extracranial ICA mean velocity; a value above 3 favors vasospasm over hyperemia.

Pulsatility index

Gosling index calculated as peak systolic minus end-diastolic velocity divided by time-averaged mean velocity; reflects distal resistance.

Resistive index

Pourcelot index calculated as peak systolic minus end-diastolic velocity divided by peak systolic velocity; normal ophthalmic values are about 0.55 to 0.70.

Temporal window location

The acoustic window lies above the zygomatic arch and anterior to the tragus, allowing insonation of the MCA, ACA, and PCA.

MCA depth range

The middle cerebral artery is typically insonated at depths of 30 to 60 millimeters with flow directed toward the probe.

ACA depth range

The anterior cerebral artery is typically insonated at depths of 60 to 80 millimeters with flow directed away from the probe.

Pulsed-wave Doppler advantage

A small sample volume with range gating allows depth-selective measurement of individual intracranial vessels rather than averaged flow.

Power Doppler

A Doppler mode displaying amplitude rather than shift, giving better detection of slow flow but no velocity or direction information.

Color Doppler aliasing

Ambiguous color display when velocity exceeds the Nyquist limit; corrected by increasing scale, lowering frequency, or adjusting the baseline.

Nyquist limit

The maximum detectable Doppler shift before aliasing, equal to half the pulse repetition frequency.

Spectral broadening

Widening of the spectral waveform indicating turbulent flow, commonly seen distal to a stenosis or at a high-grade lesion.

Suboccipital window

The foramen magnum approach used to insonate the vertebral arteries and basilar artery; flow in the basilar is directed away from the probe.

Orbital window

Approach through the closed eyelid used to insonate the ophthalmic artery and carotid siphon; mechanical index should be reduced.

Carotid PSV stenosis criterion

Peak systolic velocity of 230 cm/s or greater in the internal carotid artery indicates a stenosis of 70 percent or more.

End-diastolic velocity criterion

Internal carotid end-diastolic velocity of 100 cm/s or greater supports a stenosis of 70 percent or more.

ICA/CCA ratio

Ratio of internal to common carotid peak systolic velocity; a value of 4.0 or greater supports severe internal carotid stenosis.

Normal ICA waveform

Low-resistance flow with peak systolic velocity below 125 cm/s, continuous forward diastolic flow, and no spectral broadening.

String sign

A thin, high-resistance trickle of flow in a near-occluded internal carotid artery; velocity criteria may underestimate severity.

Ophthalmic artery flow reversal

Reversed or blunted ophthalmic flow indicates hemodynamically significant ipsilateral internal carotid stenosis or occlusion.

Vertebral artery steal

Reversed vertebral artery flow, often with a systolic notch, caused by proximal subclavian artery stenosis or occlusion.

Circle of Willis completeness

Only about 20 to 25 percent of people have a complete circle, which affects collateral flow and stroke risk.

TCD sickle cell criterion

Time-averaged mean velocity of 200 cm/s or greater in the MCA or terminal ICA indicates high stroke risk in sickle cell disease.

Microembolic signal features

Brief, unidirectional, high-intensity signals lasting under 300 milliseconds with a chirp quality, indicating active embolization.

NASCET stenosis method

Percent stenosis equals one minus the ratio of residual lumen to normal distal internal carotid lumen, multiplied by 100.

Asymptomatic stenosis evidence

Carotid endarterectomy for asymptomatic stenosis offers modest stroke reduction and depends on perioperative risk and life expectancy.

External carotid waveform

High-resistance flow with brisk systolic upstroke and low or absent diastolic flow, supplying the face and scalp.

Common carotid waveform

Mixed-resistance flow reflecting combined internal and external carotid beds, with broad systolic peak and forward diastolic flow.

Subclavian steal symptoms

Arm claudication, dizziness, or vertebrobasilar symptoms triggered by arm exercise ipsilateral to a proximal subclavian stenosis.

Hyperemia versus vasospasm

Elevated MCA velocity with a normal Lindegaard ratio reflects increased flow, whereas a ratio above 3 indicates true vasospasm.