Gradient vector flow is an efficient external force for active contours, which can largely solve the
problems such as poor convergence to boundary concavities, leaking from discontinuous boundary
and miserable anti-noise ability of the active contour models. A detailed analysis of the original
method of Xu et al. is proposed. Due to the fact that GVF gives rise to a stiff and very large system
of initial-value problem for ordinary differential equations, an implicit method which has a larger
stability region is proposed. The efficacy of the scheme is demonstrated with numerical experiments
on synthesized and real medical images.['˜
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