Limited spatial resolution, flow signal intensity loss as a result of saturation or phase dispersion, susceptibility artifacts near sphenoid sinus, and over- and underestimation of stenosis due to dephasing artifacts
High level of technical and procedural skill is required to obtain the best quality images. Reliable insonation of the posterior circulation is particularly difficult
For MCA stem (M1)
90%–99%
90%–99%
For intracranial segment (V4) of vertebral and basilar artery
CDDI: Color Doppler-assisted duplex imaging, PFI: power-flow imaging.
*Data are percentages using DSA as the reference standard. ‡North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria were used for stenosis calculations: , where is normal diameter and is stenosed diameter. NASCET stenoses were grouped according to the following grading scale: normal (0%–9%), mild (10%–29%), moderate (30%–69%), severe (70%–99%), or occluded (no flow detected). Normal (0%–9%) and mild (10%–29%) stenosis were not considered diseased vessel segments and were excluded from analysis. †Ultrasound emission energy and gain cannot be increased high enough without the appearance of disturbing acoustic noise that diminishes the reliable depiction of orthograde flow signals.