1. A method for computing a vesselness measure, comprising: initializing a plurality of rays from a center point of a vessel and collecting an intensity profile of the vessel and a background of the vessel along each ray; modeling each intensity profile by dividing the intensity profile into first, second and third intervals, wherein the first interval represents an intensity value inside the vessel, the second interval represents an intensity value outside the vessel and the third interval represents an intensity value between a boundary of the vessel and the background; for each ray, obtaining a difference between an originally measured intensity profile of the vessel and the background and the originally measured intensity profile's corresponding modeled intensity profile, wherein the difference is a fit measure of the ray, the fit measure is given by 
 ƒ i =arg min R,σ ( γ 1 ⁢ ∑ x = 0 R ⁢  V i ⁡ ( x , R ⁢ , σ ) - I i ⁡ ( x )  2 ⁢ f ⁡ ( x ) + γ 2 ⁢ ∑ x = R x 0 ⁢  V i ⁡ ( x , R , σ ) - I i  2 + γ 3 ⁢ ∑ x = x B x B ⁢  V i ⁡ ( x , R , σ ) - I i  2 ⁢ g ⁡ ( x ) ) where ƒ(x)=u(I v −I(x)), g(x)=u(I(x)−I o ), u(x) is a step function, γ 1 , γ 2 , and γ 3 are weights for the first to third intervals, respectively, V i is a vessel model along the ray, R is the radius of the ray, I v is the intensity value inside the vessel and I o is the intensity value outside the vessel; and summing the fit measures for each ray, wherein the total sum is the vesselness measure.