Inverse dynamics control of needle in prostate brachytherapy

Needle insertion into the soft tissue has been the subject of many studies during the last decade, while needle control has become a crucial training tool, evaluating surgeon´s skills in such critical incision. This study considers a model-based dynamics equation for the needle movement through the soft tissue. In the proposed model, the force distribution along the needle shaft is estimated through the use of tissue deformation data and tissue model. A novel algorithm for the needle control simulation is also proposed based on the developed dynamics equation of the needle movement. To point out the role of mechanical properties of the soft tissue, an inverse dynamics control method is used to demonstrate the system performance in presence of the tissue mechanical parameters uncertainty. It is shown that the uncertainty in the tissue mechanical parameters dramatically affects the system performance. Hence subsequently, a sensitivity analysis is conducted on the controller parameters (gains) and needle velocity indices are introduced to evaluate the performance of the controller. Eventually it is shown that the inverse dynamics controller provides suitable position control.