Ultrasound sensing-based intuitive proportional control: An evaluation study with upper-extremity amputees

Introduction/Background Recent studies have shown that unintuitive control is a key factor leading to upper-extremity, myoelectric prostheses abandonment. We have developed a non-invasive modality to extract proportional control signals in the residuum using ultrasound imaging. In this study, we investigate the performance of this technology in upper-extremity amputees. Material and method We recruited 4 amputee subjects ( Table 1 ) who currently use myoelectric prostheses. Subjects were instrumented with a portable ultrasound system connected to a low-profile transducer on the volar aspect of their residuum. Ultrasound images were processed in real-time to extract graded muscle activity signal in response to volitional user-intended motions (UIMs). Subjects were trained by iterating each UIM while being provided with visual feedback of ultrasound images and muscle-activity signal. Participants were then given control of an on-screen cursor that responded proportionally to the level of muscle-activity for a particular UIM and asked to reach and hold the cursor at predefined set-points. Control steadiness (standard deviation) and control error (difference between cursor and target) were computed. Results All subjects were able to complete the training phase within 15 minutes (25 iterations or less) for at least 4 degrees-of-freedom (DoF), while achieving motion prediction accuracies greater than 88% ( Table 1 ). 3 subjects participated in the motion control task. The congenital amputee subject performed 2 motions and the rest performed at least 4 motions with control errors between 2.1% and 9.36% ( Table 2 ). Our approach provides direct positional control based on muscle deformation, resulting in improved proprioceptive feedback, unlike myoelectric control. We believe that ultrasound images coupled with the muscle activity signals serve as an intuitive visual feedback mechanism, resulting in reduced training time and improved performance. Conclusion We demonstrated intuitive proportional control using ultrasound-based muscle activity sensing paradigm for multiple DoFs with traumatic and congenital amputees.