CAQ-CVTS key terms

A physical relationship stating that volume flow through a cylindrical vessel rises with the fourth power of radius and the pressure gradient, and falls with fluid viscosity and vessel length. It explains why small caliber changes cause large flow changes.

The angle between the ultrasound beam and the direction of blood flow, ideally kept at 60 degrees or less. A larger angle inflates velocity error because the cosine of the angle becomes small and unstable.

The formula relating Doppler frequency shift to transmitted frequency, flow velocity, the cosine of the beam-to-vessel angle, and the speed of sound in tissue. It underlies every velocity measurement made with duplex ultrasound.

A display artifact in spectral or color Doppler where peak velocities exceed the Nyquist limit and wrap to the opposite side of the scale. Raising the scale, lowering frequency, or shifting the baseline can resolve it.

The highest Doppler frequency shift that can be unambiguously displayed at a given pulse repetition frequency, equal to half that frequency. Velocities above it appear as aliasing rather than true direction.

A setting that removes low-frequency, high-amplitude Doppler signals produced by vessel wall and soft tissue motion. Setting it too high can erase slow flow in low-resistance or venous studies.

A real-time display that maps mean Doppler frequency shift to a color scale and overlays it on the gray-scale image. It shows flow direction and presence but is not a substitute for spectral velocity measurement.

A Doppler mode that displays the amplitude or strength of the Doppler signal rather than its frequency shift. It is angle-independent and sensitive to slow flow but gives no direction or velocity information.

Widening of the Doppler waveform envelope reflecting a range of velocities within the sample volume. It can result from disturbed flow at a stenosis or from an inappropriately large sample gate.

The opposition to flow through a vessel, determined mainly by vessel radius, length, and blood viscosity. In vascular testing it is inferred from waveform shape, with high-resistance beds showing sharp peaks and little diastolic flow.

A calculated index equal to peak-to-trough velocity difference divided by mean velocity across the cardiac cycle. Higher values indicate greater distal resistance and are used to characterize waveforms in arteries and grafts.

A normal peripheral arterial spectral pattern with a sharp systolic upstroke, early diastolic reversal, and a small forward flow component in late diastole. It indicates a low-resistance supply feeding a high-resistance distal bed.

An arterial spectral pattern with a damped, rounded systolic peak and continuous forward diastolic flow, lacking reversal. It suggests flow proximal to a stenosis or a dilated, low-resistance distal bed.

A damped waveform with a delayed, rounded systolic upstroke and low peak velocity seen downstream of a significant stenosis. The name refers to slow and small flow, reflecting reduced pressure reaching the distal bed.

The maximum velocity recorded during systole in a spectral Doppler tracing, commonly used as the primary criterion for grading stenosis. It is compared with adjacent segments and with published thresholds for each vessel.

The peak systolic velocity at a stenosis divided by the peak systolic velocity in a normal proximal segment. It helps separate true focal disease from generalized velocity changes such as high cardiac output.

Narrowing of the internal carotid artery, usually from atherosclerosis at the bulb. Duplex grading combines peak systolic velocity, end-diastolic velocity, and plaque appearance, with conventional thresholds for moderate and severe disease.

A critical carotid narrowing in which flow is reduced to a thin stream, producing unexpectedly low or undetectable velocities rather than very high ones. It must be recognized to avoid underestimating severity.

Symptoms such as dizziness, diplopia, or gait instability arising from reduced posterior circulation flow. Duplex evaluation of the vertebral arteries assesses direction, patency, and subclavian steal physiology.

Reversal of flow in a vertebral artery caused by proximal subclavian artery stenosis or occlusion. Blood is diverted retrograde down the vertebral to supply the arm, and the waveform changes with arm exercise.

Ultrasound examination of intracranial arteries through acoustic windows in the skull, used to assess velocities, vasospasm, and embolic signals. It requires knowledge of window locations and expected depth and direction for each vessel.

Blood pressure measurements taken with cuffs at multiple levels of a limb and compared with the contralateral side. A pressure drop between adjacent segments localizes arterial occlusive disease.

The ratio of ankle systolic pressure to the higher brachial systolic pressure, used to screen for lower extremity arterial disease. Values of 0.90 or below are generally considered abnormal.

The ratio of great toe systolic pressure to brachial pressure, measured with a small digital cuff and photoplethysmography. It remains informative when ankle vessels are stiff and falsely elevate ankle pressures.

Calcification of the arterial media, common in diabetes and kidney disease, that makes vessels poorly compressible. It produces falsely high ankle pressures and an artifactually elevated ankle-brachial index.

A plethysmographic tracing of limb volume changes with each cardiac cycle, used to assess arterial flow without relying on compressible vessels. Loss of the dicrotic notch and reduced amplitude suggest proximal disease.

Serial duplex evaluation of a bypass graft to detect failing flow before thrombosis, typically tracking peak systolic velocity and velocity ratio. It aims to prompt intervention while the graft is still patent.

Retrograde venous flow caused by incompetent valves, measured as duration of reverse flow after a distal augmentation maneuver. Thresholds differ by vein segment and by superficial versus deep systems.

A forced expiration against a closed airway used to raise intra-abdominal pressure and test for reflux in the proximal venous segments. Reflux is timed from the start of the reversal.

The transient increase in venous Doppler signal produced by squeezing or releasing the calf distal to the sample site. A weak or absent response suggests obstruction between the sample and the compression point.

Normal venous spectral flow that varies with respiration and cardiac activity rather than staying flat. Continuous nonphasic flow can indicate proximal obstruction or altered hemodynamics.

Clot within the deep venous system, diagnosed by noncompressibility of the vein, intraluminal echoes, and absent or abnormal flow. Duplex compression is the primary noninvasive diagnostic method.

Narrowing of a renal artery that can cause hypertension or ischemic nephropathy. Duplex criteria rely on elevated direct velocity and a tardus-parvus distal waveform, with attention to accessory arteries.

Compression of the celiac artery by the median arcuate ligament, producing a characteristic focal velocity increase that worsens with expiration. It is a differential for abdominal pain and must be distinguished from atherosclerotic stenosis.

Persistent flow outside the graft but within the aneurysm sac after endovascular repair. Surveillance imaging classifies leaks by source and guides whether reintervention is needed.

A permanent dilation of the abdominal aorta, commonly defined by a maximum diameter of 3.0 cm or more. Duplex measurement of outer wall to outer wall guides surveillance intervals and referral for repair.

The process by which an arteriovenous fistula or graft develops sufficient flow and diameter for reliable cannulation. Assessment includes vessel diameter, depth, flow volume, and absence of stenosis.

The calculated volume of blood moving through a dialysis access per unit time, often derived from Doppler velocity and vessel cross-sectional area. Falling flow can signal stenosis before thrombosis.

Preoperative ultrasound assessment of upper extremity vein diameter, depth, continuity, and compressibility before access creation. It identifies suitable segments and unsuspected obstruction.

The practice of keeping radiation and ultrasound exposure as low as reasonably achievable while obtaining diagnostic information. It guides adjustment of power, dwell time, and output settings during every examination.

An on-screen estimate of the potential temperature rise in tissue from absorbed ultrasound energy. Higher values prompt the operator to reduce output or shorten exposure, especially in sensitive examinations.