  This article deals with the so called GVF (Gradient Vector Flow) introduced
by C. Xu, J.L. Prince . We give existence and uniqueness results for the front
propagation flow for boundary extraction that was initiated by Paragios,
Mellina-Gottardo et Ralmesh . The model combines the geodesic active contour
flow and the GVF to determine the geometric flow. The motion equation is
considered within a level set formulation to result an Hamilton-Jacobi
equation.
