RVT flashcards

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

ICA/CCA velocity ratio

Peak systolic velocity in the internal carotid artery divided by peak systolic velocity in the distal common carotid artery; a value of 2.0 or greater supports a 50% or greater ICA stenosis.

NASCET stenosis formula

Percent stenosis equals one minus the residual lumen diameter divided by the normal distal internal carotid diameter, multiplied by 100; it is the angiographic standard used to validate duplex criteria.

Ophthalmic artery flow reversal

Reversed ophthalmic artery flow on orbital Doppler is an indirect sign of hemodynamically significant ipsilateral internal carotid stenosis or occlusion, with collateral supply reaching the orbit from the contralateral side.

Subclavian steal flow reversal

Retrograde vertebral artery flow, often provoked by ipsilateral arm exercise, occurs when a proximal subclavian stenosis or occlusion reverses the normal vertebrobasilar pressure gradient.

Normal internal carotid waveform

A low-resistance spectral pattern with a broad systolic peak and continuous antegrade diastolic flow, reflecting the low-resistance cerebral vascular bed served by the internal carotid artery.

String sign near occlusion

A thin, thread-like residual color and spectral flow channel in a nearly occluded internal carotid artery; distal velocities may fall rather than rise, so stenosis grading by velocity alone fails.

Ankle-brachial index formula

Highest ankle systolic pressure from the dorsalis pedis or posterior tibial artery divided by the higher of the two brachial systolic pressures, using the higher-pressure lower extremity value.

ABI interpretation thresholds

Values above 1.30 indicate non-compressible calcified arteries, 1.00 to 1.30 is normal, 0.91 to 0.99 is borderline, and 0.90 or less defines peripheral arterial disease.

Triphasic waveform significance

Three-phase flow, with sharp systolic forward flow, early diastolic reversal, and late diastolic forward flow, indicates a normal compliant conduit without an upstream hemodynamically significant stenosis.

Segmental pressure gradient

A pressure drop greater than 20 to 30 mmHg between adjacent thigh, calf, and ankle cuffs localizes a hemodynamically significant arterial stenosis to the segment between those cuffs.

Toe-brachial index

Toe systolic pressure divided by brachial systolic pressure; normal exceeds 0.70, and the index is preferred over ankle pressure when medial calcinosis makes ankle vessels non-compressible.

Post-exercise ABI

Ankle-brachial index measured after treadmill walking; a fall of more than 20 percent from baseline, or a delayed return to baseline, indicates hemodynamically significant occult disease.

Venous spontaneity and phasicity

Normal limb vein Doppler shows spontaneous flow that varies with respiration; continuous non-phasic flow suggests obstruction proximal to the sample site, while absent spontaneous flow suggests occlusion at that site.

Venous reflux thresholds

Reflux lasting more than 0.5 second defines incompetence in superficial and perforating veins, while more than 1.0 second is required in the common femoral and popliteal deep veins.

Acute versus chronic thrombus

Acute thrombus is hypoechoic with a distended, non-compressible vein; chronic thrombus becomes echogenic, the vein contracts, and collaterals develop, often leaving residual valvular reflux.

Valsalva response in femoral vein

A normal Valsalva maneuver abolishes or briefly reverses femoral venous flow; failure to do so, or continuous flow, implies a patent pathway around a proximal obstruction.

Venous augmentation test

Manual distal compression should sharply increase venous velocity at the sampled site; blunted or absent augmentation indicates obstruction between the compression point and the Doppler sample volume.

Aortic aneurysm size criteria

An infrarenal aortic diameter of 3.0 cm or more defines an aneurysm; elective repair is generally considered at 5.5 cm in men and 5.0 cm in women, or with rapid growth.

Renal-aortic ratio

Peak systolic velocity in the renal artery divided by peak systolic velocity in the abdominal aorta; a ratio of 3.5 or greater supports a 60 percent or greater renal artery stenosis.

Tardus-parvus waveform

Dampened downstream flow with a slow systolic upstroke and low peak velocity, produced by a hemodynamically significant stenosis or occlusion proximal to the sampling location.

Hepatic artery resistive index

Normal hepatic arterial resistive index is about 0.55 to 0.70; a value below 0.5 after transplantation raises concern for hepatic artery stenosis, thrombosis, or outflow abnormality.

Portal hypertension duplex signs

Main portal vein diameter above 13 mm with mean velocity below roughly 15 cm per second, plus loss or reversal of hepatopetal flow, suggests portal hypertension.

Doppler equation

Doppler shift equals two times the transmitted frequency times blood velocity times the cosine of the Doppler angle, divided by the speed of sound in tissue of about 1540 m/s.

Nyquist limit

The highest frequency shift a pulsed Doppler system can detect without ambiguity, equal to half the pulse repetition frequency; velocities exceeding it produce aliasing.

Aliasing correction options

Increase the pulse repetition frequency or velocity scale, lower the transducer frequency, adjust the baseline, increase the Doppler angle toward 60 degrees, or switch to continuous wave Doppler.

Wall filter function

A high-pass filter that removes low-frequency, high-amplitude echoes from vessel wall and valve motion; set too high it also removes slow venous or post-stenotic flow.

Power Doppler characteristics

Uses Doppler amplitude rather than frequency shift, so it is angle-independent, does not alias, and detects slow flow, but gives no direction or velocity information.

Lindegaard ratio

Mean flow velocity in the middle cerebral artery divided by velocity in the ipsilateral extracranial internal carotid artery; a ratio above 3.0 supports vasospasm rather than hyperemia.

Transcranial Doppler vasospasm threshold

Middle cerebral artery mean velocity above 120 cm per second suggests vasospasm, and is most meaningful when compared with the Lindegaard ratio and serial baseline values.

Treadmill exercise protocol

Walk at 2 miles per hour on a 12 percent grade for up to 5 minutes, with ankle-brachial indices measured before and immediately after exercise to provoke occult disease.

Flow phantom velocity accuracy

Velocity measured in a calibrated Doppler flow phantom should agree with the true value within about 10 percent; larger deviations indicate angle, scale, or transducer calibration error.

Dialysis access flow threshold

A native fistula or graft with access flow below 500 to 600 mL per minute, or a stenosis with a peak systolic velocity ratio above 2, suggests significant stenosis.