Dynamic Arm Impedance Regulation: Experiences from Medical Ultrasound Scanning Experts

Experienced sonographers can improve ultrasound (US) image quality by adjusting their hand impedance. However, little research exists on how the hand's impedance is adjusted, especially at different detection stages. The arm impedance of novices and experts at different scanning stages was measured and compared in depth using a developed ultrasonic scanning skill acquisition system with high operational transparency. The end-of-hand impedance was measured by introducing an external disturbance and fitting a mass-damper-spring model to the hand. US scanning quality was measured by filtering the variance of position signals and the variance of contact force through high-pass filters. Multivariate variance analysis indicated that experts exhibit lower position and contact force variances, as well as larger stiffness values than novices. In the normal direction, which is considered the most critical for US scanning, experts had less position variance and significantly greater hand stiffness than novices. When transitioning from coarse scanning (CS) to fine scanning (FS), experts improved the scanning effect by increasing hand stiffness in this direction. The impedance measurement results in this article provide a theoretical basis for robot remote or autonomous ultrasonic scanning and can help robots learn the impedance adjustment skills of experts.