RVS cheat sheet

Doppler equation: f_d = (2·f₀·v·cosθ)/c, where c ≈ 1540 m/s in soft tissue; flow velocity v = (f_d·c)/(2·f₀·cosθ).

At a 60° Doppler angle cosθ = 0.5, so the velocity scale factor is f_d·c/f₀; error grows steeply above 60°, and angles >60° are avoided because small angle errors cause large velocity errors.

Bernoulli simplified: ΔP = 4v² across a stenosis (v in m/s), used to estimate pressure gradient from peak systolic velocity.

Resistive index RI = (PSV − EDV)/PSV; RI approaches 1.0 with high distal resistance and falls with low-resistance beds (e.g., ICA, renal artery).

Pulsatility index PI = (PSV − EDV)/TAMAX; TAMAX is time-averaged maximum velocity over the cardiac cycle.

Continuous-wave Doppler lacks depth resolution but has no Nyquist limit; pulsed-wave Doppler gives depth selection but aliases when PRF/2 is exceeded.

Nyquist limit = PRF/2; aliasing is corrected by increasing PRF, lowering transmit frequency, shifting baseline, or using continuous-wave Doppler.

Color Doppler encodes mean velocity and direction; variance maps (often green/yellow) display spectral broadening from turbulence.

Wall filter removes low-frequency, high-amplitude signals from vessel wall motion; setting it too high can erase low-velocity flow.

Aortic arch branches in order: brachiocephalic trunk (innominate), left common carotid artery, left subclavian artery.

Circle of Willis components: anterior cerebral arteries, anterior communicating artery, internal carotid arteries, posterior communicating arteries, posterior cerebral arteries, and basilar artery.

Normal ICA waveform is low resistance with broad systolic peak and continuous diastolic flow; ECA is high resistance with sharp upstroke and little diastolic flow.

Temporal tap: tapping the superficial temporal artery augments ECA waveform and produces artifact in the ECA spectrum; it does not affect the ICA.

Venous lower extremity system: deep veins (CFV, FV, POPV, posterior tibial, peroneal) drain via popliteal and femoral veins into the external iliac vein.

Calf muscle pump and venous valves direct flow cephalad; perforating veins connect superficial to deep systems and normally flow inward.

Arterial wall layers: intima (endothelium), media (smooth muscle/elastin), adventitia (connective tissue); atherosclerosis begins in the intima.

Poiseuille law: flow ∝ ΔP·r⁴/(8ηL); halving radius reduces flow 16-fold, explaining the hemodynamic impact of stenosis.

Normal ABI is 1.0–1.4; values <0.9 indicate peripheral arterial disease, and >1.4 suggests non-compressible calcified vessels.

ICA stenosis criteria (velocity-based): peak systolic velocity >125 cm/s plus ICA/CCA ratio >2.0 suggests ≥50% stenosis; PSV >230 cm/s with EDV >100 cm/s and ratio >4.0 suggests ≥70% stenosis.

Total ICA occlusion: no flow in ICA, high-resistance/thumping CCA waveform, and often reversed flow in the ipsilateral ophthalmic artery.

Subclavian steal: vertebral artery flow reversal (or mid-systolic deceleration) ipsilateral to a subclavian stenosis or occlusion; symptoms with arm exertion.

DVT diagnosis: non-compressibility of the vein is the primary criterion; loss of phasic flow, loss of augmentation, and intraluminal echogenic thrombus support it.

Acute vs chronic DVT: acute thrombus is hypoechoic, vein dilated; chronic thrombus is echogenic, vein contracted, with collateralization and valve damage.

Carotid body tumor: splaying of the ICA and ECA at the bifurcation with a hypervascular mass; biopsy is avoided because of bleeding risk.

Renal artery stenosis: peak systolic velocity >180–200 cm/s in the renal artery plus a tardus-parvus waveform (delayed upstroke, low RI) distally.

Pseudoaneurysm: color flow in a sac with a 'yin-yang' sign and a to-and-fro spectral waveform at the neck; treated by compression or thrombin injection.

Arteriovenous fistula: high-velocity, low-resistance flow with turbulent spectral broadening, pulsatile venous flow, and elevated flow volume.

ALARA principle: use the lowest output power and shortest exposure time that yields diagnostic information; ultrasound is non-ionizing but thermal and mechanical bioeffects exist.

Mechanical index (MI) indicates cavitation risk; thermal index (TI) estimates heating; both are displayed on modern systems and should be kept low in sensitive exams.

Do not perform lower extremity venous compression in a patient with suspected DVT and severe pain, recent surgery, or known thrombus-risk of embolization; use color and spectral Doppler instead.

Compression stockings and limb elevation are contraindicated in acute arterial ischemia; keep the limb dependent and warm pending intervention.

Universal precautions: gloves for all vascular exams, eye protection when splash risk exists, and proper transducer disinfection between patients.

Patient positioning: supine for carotid and abdominal exams, reverse Trendelenburg or semi-Fowler for lower extremity venous filling; arms at sides for subclavian access.

Document allergies (especially to contrast or thrombin), anticoagulant use, and recent procedures before invasive or contrast-enhanced studies.

Vasovagal syncope during carotid manipulation: stop the exam, lower the head, monitor vitals; avoid prolonged carotid sinus pressure.

Pregnancy: ultrasound is preferred over ionizing imaging; Doppler should be limited to indicated exams, with attention to MI/TI in early gestation.