Recommendations for Multimodal Noninvasive and Invasive Screening for Detection of Extracranial Venous Abnormalities Indicative of Chronic Cerebrospinal Venous Insufficiency: A Position Statement of the International Society for Neurovascular Disease (ISNVD)
http://www.jvir.org/article/S1051-0443%2814%2900746-5/abstract


Recommendations for Multimodal Noninvasive and Invasive Screening for Detection of Extracranial...
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Bidirectional flow in the IJV seen in longitudinal view assessed by a Doppler spectral waveform. The duration of the reverse flow more than 1 second is well apparent in supine (a) or in sitting position (b), fulfilling the first VH criterion.