A generic three-dimensional static force distribution basis for a medical needle inserted into soft tissue.

In this paper, the static interaction forces between a medical needle and soft tissue during CT (Computerized Tomography) guided insertion are studied. More precisely a set of linearly independent elements describing the forces (a basis) is identified. This forms a generic basis from which any forces that act on a static needle (that is not fixed at its base and that is inserted into human tissue) can be described accurately. To achieve this purpose, the same needle was inserted 62 times into fresh porcine shoulder tissue and CT scans were acquired after each push to determine the final trajectory of the needle. From this set of trajectories, a generic static force basis was determined by using static Beam, B-spline theories and Principal Component Analysis (PCA). This generic basis was first validated on theoretical simulations and then on 20 different needles inserted into in vivo human tissues during real clinical interventions. Such a basis could be of use to highlight the forces acting all along the length of a needle inserted into a complex tissue and enables models of needle deflection to be developed. These models could be used in the development of automated robot assisted and/or image guided strategies for needle steering.