CAQ-CVTS cheat sheet

Doppler equation: f_d = (2 · f_0 · v · cos θ) / c, where c ≈ 1540 m/s in soft tissue; the factor 2 accounts for the round trip to and from the reflector.

Cos 60° = 0.50, so a 60° Doppler angle halves the measured shift; errors in angle estimation grow steeply beyond 60°, which is why 60° or less is the standard threshold.

Velocity from shift: v = (f_d · c) / (2 · f_0 · cos θ); with a 5 MHz probe, 1 kHz of shift at 60° corresponds to roughly 15.4 cm/s.

Nyquist limit = PRF/2; aliasing occurs when the Doppler shift exceeds it, and it is corrected by increasing PRF, lowering transmit frequency, increasing the angle toward 60°, or using continuous wave.

Continuous wave Doppler has no PRF and therefore no aliasing, but it lacks depth discrimination; pulsed wave Doppler provides range gating at the cost of a Nyquist limit.

Resistive index RI = (PSV − EDV)/PSV; values above 0.70–0.75 in native renal arteries suggest increased parenchymal or downstream resistance.

Pulsatility index PI = (PSV − EDV)/TAMV, using time-averaged mean velocity rather than peak velocity.

Spectral broadening indicates a wide range of velocities within the sample volume and is seen with turbulence, sampling over a stenosis, or a large sample gate.

Wall filter removes low-frequency, high-amplitude signals from vessel wall motion; setting it too high can erase low-velocity flow such as in a nearly occluded vessel.

ICA criteria for ≥70% stenosis include PSV >230–250 cm/s, EDV >100 cm/s, and ICA/CCA peak systolic ratio >3.2–4.0, often with spectral broadening and post-stenotic turbulence.

A PSV below roughly 50 cm/s with a damped, tardus-parvus waveform suggests near-occlusion or distal severe disease rather than a mild lesion.

The vertebral artery is normally lower resistance than the CCA; loss of diastolic flow or a high-resistance vertebral signal can indicate subclavian steal or distal stenosis.

Ophthalmic artery flow direction reversal suggests severe ipsilateral ICA disease or external carotid collateral supply; assess with compression or indirect testing only when safe.

A normal CCA waveform is low resistance with continuous diastolic flow; an externalized, high-resistance CCA signal suggests distal ICA occlusion or severe disease.

Temporal window insonation at 50–60 mm depth typically identifies the MCA at 30–60 mm; mean flow velocities above 120 cm/s suggest vasospasm in the appropriate clinical setting.

Ratio-based interpretation reduces angle and equipment variability; always document the angle, sample depth, and the reference vessel used for the ratio.

Ankle-brachial index ABI = highest ankle systolic pressure / highest brachial systolic pressure; normal is 1.00–1.40, and values above 1.40 suggest non-compressible calcified vessels.

ABI 0.90 or below is abnormal; 0.50–0.90 suggests claudication, and below 0.40 suggests critical limb ischemia when symptoms match.

Segmental pressures drop by more than 20–30 mmHg between adjacent cuffs to localize disease; a gradient across a cuff level indicates stenosis at or above that level.

Pulse volume recordings show a damped, rounded, or absent waveform distal to a hemodynamically significant stenosis; loss of the dicrotic notch is an early sign.

Toe-brachial index TBI above 0.70 is normal; TBI is preferred in diabetics and dialysis patients with medial calcinosis because toe vessels are less often calcified.

Exercise testing with post-exercise ankle pressures that fall by more than 20 mmHg, or fail to recover within 5 minutes, supports hemodynamically significant disease.

A uniphasic or biphasic waveform indicates damping; triphasic flow with a sharp systolic upstroke and reversal is normal in a resting limb artery.

Reactive hyperemia and cuff-induced hyperemia can unmask borderline disease; document the protocol and timing because values change rapidly after cuff release.

Normal lower extremity venous flow is phasic with respiration and augments with distal compression; absence of phasicity or augmentation suggests obstruction or valve failure.

Reflux is defined as reversed flow lasting more than 0.5 seconds in the common femoral and femoral veins, and more than 1.0 second in the popliteal and calf veins.

Perform the exam with the patient standing or reverse Trendelenburg for reflux, and supine or semi-upright with limb dependency for acute DVT assessment.

Acute DVT findings: hypoechoic, non-compressible vein with expanded caliber, loss of spontaneous flow, and continuous or absent phasicity.

Chronic DVT findings: echogenic, narrowed, or recanalized vein with collateral channels, thickened walls, and persistent partial compressibility.

Compression is the primary diagnostic maneuver; color Doppler alone can miss non-occlusive thrombus, so compress in short-axis increments along the vein.

Superficial venous thrombosis is assessed with compression and reflux mapping; document distance from the saphenofemoral junction because proximity affects management.

Calf vein evaluation is limited by depth and anatomy; isolated calf DVT is more common in symptomatic patients and warrants repeat study if initially negative.

Normal renal artery PSV is typically below 180–200 cm/s; values above 180–200 cm/s with post-stenotic turbulence suggest stenosis, and the renal-aortic ratio above 3.5 supports it.

The parvus-tardus waveform in the renal parenchyma, with a prolonged acceleration time above 0.07 seconds, suggests upstream stenosis or reduced perfusion.

The abdominal aorta is measured outer wall to outer wall in anteroposterior and transverse planes; an infrarenal diameter of 3.0 cm or more defines an aneurysm.

Aortic endograft surveillance requires measurement of the sac, detection of endoleaks with color and spectral Doppler, and assessment of graft limb patency.

Hepatic artery evaluation after transplant focuses on the resistive index, normally 0.55–0.80; a very low RI can reflect stenosis or arterioportal fistula.

Portal vein flow is normally hepatopetal with velocities around 15–30 cm/s; reversed flow suggests portal hypertension or a shunt.

Mesenteric ischemia evaluation includes peak systolic velocities in the SMA and celiac artery; elevated velocities with post-stenotic turbulence support stenosis.

Preoperative mapping assesses arterial inflow with segmental pressures and duplex, venous diameter and compressibility, and central venous patency by history or imaging.

A minimum venous diameter of about 2.0–2.5 mm with a tourniquet, and arterial diameter of about 2.0 mm, supports a usable autogenous fistula.

A mature arteriovenous fistula typically has flow above 500–600 mL/min; brachial artery flow volume is calculated as TAMV × cross-sectional area × 60.

Access stenosis is suggested by a greater than 50% diameter reduction on grayscale, a peak systolic velocity ratio above 2:1, and a doubling of the velocity at the stenosis versus the adjacent segment.

A thrill on palpation and a low-resistance, high-diastolic waveform in the feeding artery indicate a functioning access; loss of diastolic flow suggests outflow obstruction.

Steal syndrome is suggested by reversed flow in the artery distal to the anastomosis and symptoms of hand ischemia; document direction of flow in the distal radial or ulnar artery.

Pseudoaneurysm is diagnosed by a yin-yang color pattern and a neck with to-and-fro spectral flow; document size and neck dimensions.

ALARA applies to all Doppler modes: power, dwell time, and frame rate determine exposure, and Doppler exposes tissue to higher intensities than B-mode.

The mechanical index MI estimates cavitation risk and should be kept below 1.9; the thermal index TI should be kept at or below 1 where practical.

The recommended maximum output for ophthalmic and neonatal exams is lower; follow the on-screen MI and TI and reduce output when the indication allows.

Standard precautions require gloves and hand hygiene for all patients; add gown, mask, and eye protection when splash or body fluid exposure is anticipated.

Informed consent, patient identification with two identifiers, and documentation of the indication, findings, limitations, and comparison studies are required standards.

Ergonomic injury prevention includes adjusting bed height, using arm support, alternating scanning hands, and taking micro-breaks during long venous or mapping studies.

Professional scope and credentialing are governed by the interpreting physician and institutional policy; technologists should not issue final diagnoses outside their scope.