RVT cheat sheet

An ICA peak systolic velocity of 125 cm/s or greater together with an ICA/CCA velocity ratio of 2.0 or greater identifies a 50% or greater diameter stenosis under the SRU consensus criteria.

NASCET stenosis (%) = (1 - residual lumen diameter / normal distal ICA diameter) x 100.

ICA/CCA ratio = peak systolic velocity in the ICA divided by peak systolic velocity in the distal (mid) common carotid artery.

A normal ICA spectral waveform is low resistance, with a broad systolic peak and continuous antegrade diastolic flow.

PSV of 230 cm/s or greater, or end diastolic velocity of 100 cm/s or greater, in the ICA suggests 80% or greater stenosis; a thread-like residual channel indicates near occlusion.

Reversed ophthalmic artery flow is an indirect sign of hemodynamically significant ipsilateral ICA stenosis or occlusion.

Retrograde vertebral artery flow, especially after ipsilateral arm exercise, supports subclavian steal.

Echolucent plaque carries a higher embolic risk than densely calcified plaque; plaque surface ulceration is likewise associated with increased stroke risk.

ABI = highest ankle systolic pressure (dorsalis pedis or posterior tibial) divided by the higher of the two brachial systolic pressures.

ABI interpretation: above 1.30 non-compressible; 1.00-1.30 normal; 0.91-0.99 borderline; 0.90 or less abnormal.

A triphasic waveform is normal in limb arteries; monophasic, dampened flow indicates a proximal stenosis or collateral-dependent segment.

A segmental pressure gradient greater than 20-30 mmHg between adjacent cuffs localizes a hemodynamically significant lesion to that segment.

A peak systolic velocity ratio of 2.0 or greater across a stenosis corresponds to roughly 50% or greater diameter reduction, with higher ratios indicating tighter lesions.

Toe-brachial index above 0.70 is normal and is preferred when medial calcinosis makes ankle pressures falsely elevated.

Poiseuille relationship: volume flow varies with the fourth power of radius, so a 50% diameter reduction lowers flow roughly sixteen-fold at constant pressure.

A fall in ABI greater than 20% from baseline after treadmill exercise indicates hemodynamically significant occult disease.

Normal venous Doppler is spontaneous, phasic with respiration, augments with distal compression, and ceases or briefly reverses with Valsalva.

Deep vein thrombosis criteria: non-compressibility, intraluminal echogenicity, absent spontaneous flow, and loss of respiratory phasicity.

Reflux thresholds: greater than 0.5 second in superficial and perforating veins; greater than 1.0 second in common femoral and popliteal veins.

Acute thrombus is hypoechoic with a distended vein; chronic thrombus is echogenic, the vein is small, and collaterals have formed.

Continuous, non-phasic femoral venous flow suggests obstruction proximal to the sampling site.

Blunted or absent augmentation after distal compression indicates obstruction between the compression point and the sample volume.

Reflux in the great saphenous vein is assessed with the patient standing and the limb dependent, sampling at the saphenofemoral junction and along the thigh.

Calf veins are paired (posterior tibial and peroneal); soleal and gastrocnemius muscular sinuses are not paired and require careful compressibility assessment.

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 growth over about 1 cm per year.

Renal artery PSV below 180 cm/s is normal; 180-200 cm/s or greater with a renal-aortic ratio of 3.5 or more suggests 60% or greater stenosis.

Renal-aortic ratio = renal artery peak systolic velocity divided by abdominal aortic peak systolic velocity.

A tardus-parvus waveform (slow upstroke, low peak velocity) distal to a stenosis indicates hemodynamically significant obstruction.

Normal hepatic artery resistive index is approximately 0.55-0.70; an index below 0.5 after transplantation raises concern for stenosis or thrombosis.

Portal hypertension is suggested by main portal vein diameter above 13 mm with mean velocity below about 15 cm/s (normal 15-30 cm/s).

Superior mesenteric artery PSV above 275 cm/s suggests 70% or greater stenosis; the normal fasting SMA waveform is high resistance with low diastolic flow.

Endograft surveillance evaluates sac diameter, endoleaks, and graft limb stenosis; any perfused endoleak with sac enlargement requires intervention planning.

Doppler equation: frequency shift = (2 x transmitted frequency x velocity x cosine of Doppler angle) / speed of sound in tissue (about 1540 m/s).

Maintain a Doppler angle of 60 degrees or less, ideally 45-60 degrees, because cosine error grows rapidly as the angle approaches 90 degrees.

Nyquist limit = pulse repetition frequency / 2; velocities above this value alias.

Aliasing corrections: increase pulse repetition frequency or scale, lower transducer frequency, adjust baseline, increase Doppler angle, or switch to continuous wave Doppler.

Continuous wave Doppler has no depth resolution; pulsed Doppler with a sample volume provides range gating.

A higher transmitted frequency improves spatial resolution but increases attenuation and reduces penetration depth.

The wall filter is a high-pass filter; set too high it removes low-velocity flow such as venous or post-stenotic flow.

Power Doppler is angle-independent, does not alias, and detects slow flow, but provides no direction or velocity information.

Routine QA includes daily image uniformity checks, vertical and horizontal distance accuracy within about 2% or 1 mm, and an annual comprehensive system evaluation.

Velocity measured in a calibrated flow phantom should agree with the true value within approximately 10%.

Tissue-mimicking phantoms assess dead zone, axial and lateral resolution, penetration depth, and gray-scale uniformity.

Lindegaard ratio = middle cerebral artery mean velocity divided by ipsilateral extracranial internal carotid velocity; above 3.0 indicates vasospasm rather than hyperemia.

Transcranial Doppler: middle cerebral artery mean velocity above 120 cm/s suggests vasospasm; normal mean velocity is roughly 40-70 cm/s.

Treadmill protocol: 2 mph at 12% grade for up to 5 minutes, with ankle-brachial indices obtained before and after walking.

Dialysis access surveillance: access flow below 500-600 mL/min or an intra-access peak systolic velocity ratio above 2 suggests significant stenosis.

Bioeffects are managed with ALARA, monitoring thermal index and mechanical index, and minimizing dwell time at high output.