Feasibiliy of optical detection of soft tissue deformation during needle insertion

Needles provide an effective way to reach lesions in soft tissue and are frequently used for diagnosis and treatment. Examples include biopsies, tumor ablation, and brachytherapy. Yet, precise localization of the needle with respect to the target is complicated by motion and deformation of the tissue during insertion. We have developed a prototypical needle with an embedded optical fiber allowing to obtain optical coherence tomography images of the tissue in front of the needle tip. Using the data and particularly the Doppler information it is possible to estimate the motion of the needle tip with respect to the surrounding soft tissue. We studied whether it is feasible to approximate the depth in tissue by integrating over the relative velocity. To validate the approach, the needle was driven into tissue phantoms using an articulated robotic arm. The time when the needle entered and left the phantom was observed with optical cameras, and the total motion of the robot was compared with the values computed from the Doppler OCTmeasurements. Our preliminary results indicate that the Doppler data can provide additional information on the needle position inside soft tissue. It could be used in addition to other image data to improve precise needle navigation, particularly when other image modalities are subject to artifacts caused by the needles.