  Robotic three-dimensional (3D) ultrasound (US) imaging has been employed to
overcome the drawbacks of traditional US examinations, such as high
inter-operator variability and lack of repeatability. However, object movement
remains a challenge as unexpected motion decreases the quality of the 3D
compounding. Furthermore, attempted adjustment of objects, e.g., adjusting
limbs to display the entire limb artery tree, is not allowed for conventional
robotic US systems. To address this challenge, we propose a vision-based
robotic US system that can monitor the object's motion and automatically update
the sweep trajectory to provide 3D compounded images of the target anatomy
seamlessly. To achieve these functions, a depth camera is employed to extract
the manually planned sweep trajectory after which the normal direction of the
object is estimated using the extracted 3D trajectory. Subsequently, to monitor
the movement and further compensate for this motion to accurately follow the
trajectory, the position of firmly attached passive markers is tracked in
real-time. Finally, a step-wise compounding was performed. The experiments on a
gel phantom demonstrate that the system can resume a sweep when the object is
not stationary during scanning.
