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    Device Technologies and Biomedical Robotics

    (J-378) Compact Wearable Ultrasound System for Controlling Upper-Limb Prosthetics

    Saturday, October 14, 2023
    9:30 AM – 10:30 AM PDT
    Location: Exhibit Hall - Row J - Poster # 378

      Presenting Author(s)

    • AR

      Afsana Hossain Rima

      Graduate Research Assistant
      George Mason University
      Fairfax, Virginia, United States

      • Co-Author(s)

    • AB

      Ahmed Bashatah

      Research Engineer
      George Mason University, United States

      • Primary Investigator(s)

    • SS

      Siddhartha Sikdar

      Professor
      George Mason University, United States

    Introduction:: Upper-limb amputees face challenges in performing everyday tasks that require fine motor skills. Development of sophisticated prosthetic technology is an important priority for functional restoration and rehabilitation of people with limb loss. However robust methods for non-invasively inferring the volitional intent of the user continues to be an unmet need. Sonomyography (SMG) is an emerging approach that utilizes ultrasound transducers to detect and analyze muscle deformation associated with intended functional movements in real-time. By interpreting this muscle deformation, sonomyography can derive control signals that can be used to operate external devices such as prosthetic hands. To optimize upper-limb prosthetic control, there is a pressing need to create low-profile ultrasound transducers and miniaturize the system. In this study, we focused on the development and evaluation of a compact sonomyographic transducer prototype and its corresponding system. Our custom-designed transducers were incorporated into a 4-channel system, utilizing the time delay spectrometry (TDS) technique instead of the traditional pulse-echo method. This approach uses a low power wide band chirp signal to build a relationship between the time of flight of the signal and transmit frequency and allows us to capture 4-channel M-mode images of muscle interfaces from human subjects. The ultimate goal is to improve the functionality and precision of prosthetic control through our developed sonomyographic system. 

    Materials and Methods:: The study utilized front–end instrumentation of a 4-channel wearable ultrasound system along with four single element transducers for reconstructing ultrasound scan lines by using the TDS principle. The TDS system comprises several subsystems: power conditioning, chirp, analog TDS, TI C2000 DSP microprocessor, and single element transducers. The power subsystem converts a dual cell 7.4V LiPo battery to ±5V for analog circuitry and +3.3V for the chirp subsystem. The chirp subsystem includes an AD5930 swept-frequency source, programmable by the microprocessor. The TDS subsystem incorporates RF transmit and receive amplifiers, a demodulator, and a low-pass filter for signal processing using FFT on the microprocessor. We developed compact sonomyographic transducers using 4MHz single element 1-3 piezocomposites (10mm diameter and 0.4mm thick) and compared with the conventional PZT transducers. To acquire a good matching between the human tissue and piezocomposite we evaluated silver epoxy, polyimide film, PolyVinyliDeneFluoride (PVDF) film for the matching layer of the transducer. To dampen the reverberation, we evaluated E-solder 3022, Hysol epoxy and RTV silicone backing. All these material selections and optimization have been made considering the acoustic properties and biocompatibility. Among the combinations, we found the piezocomposite transducer with PVDF (~110um thick) matching and RTV silicone backing is optimum for capturing muscle activity from the forearm. The transducer was enclosed in a 6mm thick 3D printed housing and characterized with pulse echo method and tested using TDS in a tissue mimicking phantom as well as in vivo to evaluate its performance in detecting muscle contractions. 

    Results, Conclusions, and Discussions:: The system can scan up to 7 hours and using the specified TDS drive parameters, we achieved successful in-vivo M-mode imaging with consistently tracked muscle-tissue boundaries at imaging depths of up to 4cm. We also evaluated the transducer designs using -6dB bandwidth and SNR as metrics. With the bare piezocomposite transducer, the bandwidth increased from 8.5% to 36.7% and SNR improved by ~10dB compared to bare PZT. The bandwidth of piezocomposite transducer with PVDF matching and RTV backing increased from 36.7% to 46% with improved SNR compared to bare piezocomposite. In vivo M-mode images of muscle deformation acquired with the piezocomposite transducer with PVDF matching and RTV backing resembled images acquired using high-resolution clinical linear array transducers. 
    Our developed TDS based ultrasound system enables real time scanning of muscle contraction in vivo with the help of ultrasound imaging. The result demonstrates that the developed sonomyographic system has the potential to significantly improve the functionality and usability of upper-limb prosthetic control systems. 


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