Thanks to Sandro for posting! M-Mode stands for "motion." It follows blood and valve actions, and is shining new light on CCSVI.
New Criteria Reduce Inter-Observer Variability in Chronic Cerebrospinal Venous Insufficiency: A Case Control Study

Conclusions: The new ECD criteria introduced by the revised protocol ensure, at this time, a substantial reduction of the inter-observer variability. Under this perspective, M-mode analysis is essential for its ability to identify the valvular abnormalities frequently not detectable by B-mode analysis.
Free Pdf: http://openventio.org/Volume4-Issue1/New-Criteria-Reduce-Inter-Observer-Variability-in-Chronic-Cerebrospinal-Venous-Insufficiency-A-Case-Control-Study-NOJ-4-123.pdf