A 'Normal' Carotid Velocity in a Symptomatic Patient

No - the draft is not defensible, and issuing it could contribute to a preventable stroke.

Reasoning chain:

• Standard velocity criteria (PSV, ICA/CCA ratio) were derived in patients with patent, normally compliant vessels. They are not valid when flow is markedly reduced.
• Three findings cluster here and point the same direction:
  1. A visibly tiny residual lumen on B-mode and color.
  2. A blunted, low-resistance distal ICA waveform - the post-stenotic bed is vasodilated because perfusion pressure has fallen.
  3. An ipsilateral CCA PSV roughly half the contralateral value - a proximal low-flow state that reflects reduced inflow demand downstream.
• Low velocity in a vessel that looks tightly narrowed means near-occlusion, not no stenosis. The velocity dropped because volume flow fell, not because the lumen opened.
• The left ECA being normal and high-resistance confirms that the vessel sampled distally is the ICA (low-resistance cerebral bed) and that the technologist identified the vessels correctly.

Interpretation to report: severe ICA narrowing with hemodynamic compromise (near-occlusion pattern). State explicitly that velocity criteria cannot be applied and that the study cannot exclude a hairline lumen versus occlusion. Recommend urgent CTA or MRA and same-day vascular/neurology notification.

Each adjustment targets detection of slow flow in a very small lumen:

• Lower the PRF/scale to roughly 15-25 cm/s. High scale filtering is the single most common cause of failing to see a near-occlusion jet.
• Lower the wall filter (to approximately 50 Hz) so slow diastolic flow is not subtracted out.
• Increase color and power gain cautiously and switch to power Doppler if color dropout persists; power Doppler is angle-independent and more sensitive to low flow, though it does not give direction.
• Reduce sample volume to 1-1.5 mm and place it within the narrowest visible segment, not distal to it.
• Keep the angle at 60° or less and do not angle-correct on turbulent, spectral-broadened post-stenotic flow - report the waveform character rather than a falsely precise number.
• Scan high in the neck to see whether a distal ICA signal can be found at all; a string-like lumen over several centimeters is the classic string sign.
• Compare with the contralateral side on the same settings to distinguish a genuinely low-flow system from a technical artifact.

Document which maneuvers were used, because the report must be defensible if the velocity is later challenged.

Answer honestly: 'I cannot tell you it is occluded, and I cannot tell you it is open - the findings are indeterminate between near-occlusion and occlusion, and that distinction changes management.'

• Absence or near-absence of detectable color flow is not equivalent to occlusion; slow flow below the detection threshold behaves exactly like this.
• Supporting features of a pinhole lumen rather than true occlusion: a visible residual channel on B-mode, any distal ICA flow detected at all, and the asymmetric low CCA velocity.
• If no flow is found anywhere in the ICA despite optimized settings, say so and state the limitation.
• Next step is anatomic/contrast imaging - CTA (or catheter angiography if CTA is contraindicated by renal function or heavy calcification), plus MRA if needed. Ultrasound does not have the spatial resolution to settle this.
• Emphasize the symptomatic status and the time window; this patient's study should be communicated by direct conversation, not by a routine report entering the queue.