A method of segmentation of a medical image of a human brain including obtaining a voxelized 3D medical image of the human brain, computing at least two surface models of the human brain using a BET method, each surface model being computed for a unique fractional constant bt. For each computed surface model, determining a volume included in the computed surface model, thereby obtaining a set of sample pairs, fitting a curve to the sample pairs of the set, determining an inflection point of the curve, identifying a fractional constant bt corresponding to the determined inflection point, and computing the surface model of the human brain using the BET method that is dependent of bt.