Study of the effect of cannula rotation on tissue cutting for needle biopsy.

Needle biopsy is a medical procedure to extract tissue for diagnosis of cancer and other diseases. The quality of tissue samples acquired by needle biopsy greatly depends on the cutting forces of the cannula. The reduction of cutting forces is crucial for obtaining good tissue samples. There exist many factors that influence the cutting forces, some of which include the cannula tip geometry, translation speed, and rotation speed. In the present paper, the effects of rotating the cannula on tissue cutting for needle biopsy are studied. A fracture-mechanics-based approach is used to analyze the cutting forces. Analysis has shown that the cutting forces decrease with the increases in the slice/push ratio defined as the ratio of speed component parallel to the cutting edge/speed perpendicular to the cutting edge. Experiments are performed to demonstrate this phenomenon. Mathematical models of the slice/push ratio for bevel tip cannulas are formulated. The results are used to determine the optimal cannula rotation/translation speed and the desired tip geometry for needle biopsy. It is shown that a minimal slice/push ratio of 2 is recommended. A cannula with a large bevel angle is more suitable for rotational needle biopsy.