Single-filament spatial calibration for robotic ultrasound

We present a straightforward spatial calibration method for robotic ultrasound using only a single nylon filament as a geometric reference. By tracking the probe motion and extracting the filament intersection in each 2D ultrasound frame, the rigid transformation between the ultrasound image and the robot end-effector is estimated through a point-to-line optimization. The procedure requires no specialized phantoms and can be performed within minutes, making it well suited for automated robotic ultrasound applications.