What are rates of false positives and false negatives in ultrasonography for stroke?

Updated: Nov 30, 2018
  • Author: Andrew Danziger; Chief Editor: L Gill Naul, MD  more...
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Answer

Ultrasound is an operator-dependent modality, and errors may occur with improper technique. For example, inaccurate Doppler waveforms and velocities may be obtained with improper applied angles of insonation. Maintaining a constant angle of 60% is believed to yield the most accurate results. [97]

Abnormal velocities may be seen from stenosis beyond the areas that can usually be evaluated with ultrasound, namely the intracranial internal carotid artery, aortic arch, and common carotid artery origin. Although the aortic arch can be assessed with standard ultrasound, its evaluation is not part of routine carotid ultrasound examinations.

Near-complete occlusion may produce velocities that are high, low, or undetectable. [97] Also, identification of residual patent lumen not appreciable on grayscale images requires careful color Doppler and power Doppler sonographic analysis.

Elevated velocities without corresponding levels of stenosis may be seen in patients with high-grade stenosis in the contralateral carotid system or in patients with hyperdynamic cardiac states. Similarly, low velocities may be seen with more proximal flow limiting stenosis or in patients with low cardiac output.

High-grade internal carotid stenoses may produce an abnormal high resistance and low-end diastolic flow waveform in the common carotid due to external carotid artery shunting.


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