Microscopic observations of needle and soft-tissue simulant interactions

Currently, physicians have no means of correctly estimating the needle tip location during percutaneous needle insertion. A model of needle-tissue interaction that predicts the needle tip location would assist physicians in pre-operative planning and hence improve needle targeting accuracy. This study is aimed to investigate the interactions of bevel-tipped needles and soft tissue in situ, using agarose gel as a soft-tissue simulant. An experimental setup is designed to record the needle-gel interaction forces and torques during needle insertion. Gel rupture during needle insertion is observed using a Laser Scanning Confocal Microscope and recorded in time series and three-dimensional images (Figure). Experimental results show the possibility of observing in situ gel rupture during needle insertion and relating them to the needle-gel interaction forces and torques. Moreover, it is seen that the maximum force along the insertion axis, |Fz max|, is proportional to bevel angle and inversely proportional to insertion speed. The maximum resultant torque, ||Tr max||, is found to be inversely proportional to bevel angle and proportional to insertion speed. However, the influence of the increase in insertion speed in |Fz max| and ||Tr max|| diminishes as insertion speed increases. These results concur with observations noted in gel rupture images.