Compliant Joint Based Robotic Ultrasound Scanning System for Imaging Human Spine

Robot-assisted ultrasound scanning acquires spatial-property labeled images under high consistency, holding the potential to reconstruct the volume with more intuitive images for examination and surgery guidance. Promisingly, the vertebral level identification, as a time-consuming procedure before spine surgery, can be achieved by robotic ultrasound systems. However, the quality of ultrasound images subjects to the conditions of the examination, including the probe placement, the ultrasound beam incidence angle and the applied contact force. Especially, the spine holds a long and narrow, multi-joint, chain-like structure which is not simply compliant to the probe, presenting challenges to acquire high quality images and keep safety. This letter presents a compliant joint based robotic ultrasound system (CJRUS) for imaging the human spine. A compliant joint based adjusting mechanism (CJAM) is attached to the robotic manipulator to adjust the contact force with patients. A floating scanning strategy is proposed for the manipulator to maintain a buffer zone from the human body and determine the pose of the probe indirectly from the collection of dorsal shape. Phantom experiments concluded that the system could provide inherent safety (the output force was constrained to 20 N by rotary buffer) and adaptive capacity (the settling time was < 1 s for targets with different stiffness and the maximum overshoot decreased 90% in prediction force control) to scanning objects. In human trials, the coronal slice of the reconstructed volume obtained by CJRUS showed comparative results as freehand scanning and equivalent image qualities evaluated by picture contrast and edge gradient. CJRUS is expected to play a significant role in radiation-free navigation of minimally invasive spinal surgery in the future.