Needles provide percutaneous access to tissues deep within the body in order to deliver therapy or acquire biological samples for diagnostic purposes. The effectiveness of needle-based access often requires very accurate targeting of the needle tip within tissue. We designed a device that uses suction to fixate tissue during robotic needle insertion and measured its ability to improve targeting accuracy and decrease tissue deformation in artificial and ex vivo tissue. The deformation of the tissue was tracked in ultrasound images to evaluate the device's performance. The device was particularly effective at fixating ex vivo tissue with an attached skin layer and decreased tissue deformation by up to 96%. When accessing an embedded target within tissue, suction fixation reduced the targeting error by over 1 mm in chicken breast without a membrane and over 2 mm in chicken breast with an attached skin. Suction fixation could be used to improve the accuracy of robotic needle insertion through the skin and into internal organs with capsules.

Insertion velocity, tip asymmetry, and shaft diameter may influence steerable needle insertion paths in soft tissue. In this paper we examine the effects of these variables on needle paths in ex vivo goat liver, and demonstrate practical applications of robotic needle steering for ablation, biopsy, and brachytherapy. All experiments were performed using a new portable needle steering robot that steers asymmetric-tip needles under fluoroscopic imaging. For bevel-tip needles, we found that larger diameter needles resulted in less curvature, i.e. less steerability, confirming previous experiments in artificial tissue. The needles steered with radii of curvature ranging from 3:4 cm (for the most steerable pre-bent needle) to 2:97m (for the least steerable bevel needle). Pre-bend angle significantly affected needle curvature, but bevel angle did not. We hypothesize that biological tissue characteristics such as inhomogeneity and viscoelasticity significantly increase path variability. These results underscore the need for closed-loop image guidance for needle steering in biological tissues with complex internal structure.