Figure 4
![Figure 4](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1475-925X-10-26/MediaObjects/12938_2010_Article_438_Fig4_HTML.jpg)
Results of the carotid artery boundary detection. A. Results of directional gradients. B. Results of using Otsu's thresholding technique. C. The ROI (R e) is transformed to the polar representation (R p)for dynamic programming. D. Results of circle model guided dynamic programming. (α = 0.3, σ = 2, and d r = 1).