Vascular Ultrasound
Vascular Ultrasound tests hemodynamic interpretation as much as image acquisition: you must combine grayscale plaque appearance, velocity measurements and waveform shape into a stenosis or thrombosis grade.
Core rules
- Carotid stenosis uses peak systolic velocity, end-diastolic velocity, the ICA/CCA ratio and plaque. The widely taught consensus thresholds are: ICA PSV <125 cm/s, <50%; 125–230 cm/s, 50–69%; >230 cm/s with ICA/CCA ratio >4 and EDV >100 cm/s, 70–99%.
- The ECA has higher resistance, lower PSV, and branches; the ICA is low-resistance with continuous forward diastolic flow.
- Vertebral arteries normally show continuous forward flow; a highly resistive or reversed waveform suggests proximal stenosis or subclavian steal.
- For DVT, non-compressibility is the primary criterion; normal veins are phasic, augment with distal compression, and collapse fully.
- Venous reflux is defined as >0.5 s in superficial and >1.0 s in deep veins.
Worked example
An ICA shows PSV 260 cm/s, EDV 110 cm/s and an ICA/CCA ratio of 5.0, with heterogeneous plaque. Each element crosses the 70–99% threshold, so this is a severe stenosis. Note that PSV 260 cm/s alone would not be sufficient in the consensus scheme; the ratio >4 and EDV >100 cm/s confirm it. If the contralateral ICA were occluded, velocities could be artificially elevated, so interpret in context.
Traps that cost marks
Angle-correcting beyond 60°; sampling a tortuous segment; confusing ECA and ICA on the basis of depth alone; diagnosing DVT from color fill without compression; and grading stenosis from PSV when tandem or contralateral disease is present.