Safe Contact Force Generation for Robotic Thyroid Ultrasound Imaging

Ultrasound (US) imaging is a first-line medical imaging modality for detecting thyroid cancer; however, it suffers from operator-dependent variability in image quality and diagnostic accuracy. To address this issue, various robotic US systems have been proposed to assist in thyroid US examinations. Nevertheless, ensuring an appropriate contact force that balances image quality and patient safety during robotic thyroid US scanning remains a challenge. Thyroid US procedures require physicians to be very cautious in applying pressure to the neck due to the sensitivity of the scanned area. Excessive contact force not only discomforts patients, but also degrades the quality of acquired images, such as a distortion of the organ. This study presents a comprehensive analysis of contact force management during robotic thyroid US imaging, focusing on safety and image quality. The study introduces a series-elastic actuated end-effector designed for robotic thyroid US imaging, which is capable of generating low constant force without feedback control with robot arms such as admittance control. The developed end-effector comprises several components, including a linear servo actuator, a force sensor, two linear springs, and a constant spring. By controlling the compression of the linear spring, the end-effector can safely exert the desired contact force. With the developed system, the quality of obtained US images and the contact force during the scanning were analyzed through a phantom, and the subjective assessments of subjects' discomfort was conducted in human trials. The findings from this study indicate that the newly developed system is capable of acquiring diagnostic images safely and reliably by utilizing a stable contact force. Moreover, the results demonstrate that a minimal contact force of 1-2 N can be effectively employed in robotic thyroid US imaging, highlighting the system's potential clinical utility in thyroid cancer diagnosis.