Modeling of the Plane Needle Cutting Edge Rake and Inclination Angles for Biopsy

Hollow needles are one of the most common medical devices, yet little study has focused on the needle tip cutting geometry for biopsy, which is a tissue cutting process. This research develops mathematical models to calculate the inclination and rake angles along cutting edges on needle tips generated by planes. Three types of plane needle tips, the one-plane bias bevel, multi-plane symmetrical, and two-plane nonsymmetric needles, are investigated. The models show that the leading tip of a bias bevel needle has an inclination angle of 0 deg, the worst configuration for cutting. Symmetric multiplane needles on the other hand have very high inclination angles, 60, 56.3, and 50.8 deg, given a needle formed by two-, three-, and four-plane, respectively, for a bevel angle of 30 deg and can assist more effective needle biopsy. The rake angle is at its greatest value (the best configuration for cutting), which equals the 90 deg minus the bevel angle, at the initial cutting point for the bias bevel needle. Experiments are performed using three 11 gauge two-plane symmetric needles with 20, 25, and 30 deg bevel angles on bovine liver and demonstrate that the needle tip geometry affects biopsy performance, where longer biopsy samples are collected with needles of higher rake and inclination angle.