Patent ID: 7295869

Claim:
A method for use in conjunction with a C-arm imaging apparatus, for visual servoing of a needle in a plane in a fixed number of iterations, with: a given position of said C-arm being modeled on an image plane, a given target point for needle biopsy, a given entry point on a patient, and a given plane within which said needle can rotate around said given entry point, said method comprising: placing said needle in an arbitrary orientation around said given entry point, said orientation being associated with an angle θ 1 with respect to an arbitrary reference direction; obtaining a 2-dimensional (2-D) projection image of said needle in, said image plane; measuring the position 11 of said 2-D projection image; rotating said needle around said entry point by an angle Δθ to a position (θ 1 +Δθ) in said given plane; measuring the position 12 of said 2-D projection image; rotating said needle around said entry point by an angle Δθ to a position θ 3 =(θ 1 +2*Δθ); measuring the position 13 of said 2-D projection image; locating 2-D points f and t in said 2-D projection image that are the respective 2-D projections of said target point and said entry point, said points f and t defining an image line It=(ft); calculating the cross-ratio c=(11, 12, 13, It); determining a 3-D angle θt such that c=(θ 1 , θ 2 , θ 3 , θt); and rotating said needle around said entry point by θt from position θ 3 in said given plane, whereby said needle is positioned in three dimensional space at said entry point along a direction such that said needle is visually aligned to 2-D projection image of said target in said image plane.