Wearable Electrical-impedance-tomography Armband for Noninvasive and Continuous Bone Monitoring

Medical inspection systems such as digital radiography (DR) and computed tomography (CT) are limited in the continuous monitoring of fracture healing due to cumulative radiation exposure. This work presents a wearable 16-electrode armband incorporating electrical impedance tomography (EIT) for noninvasive, continuous monitoring of arm bones. The EIT armband applies stimulation current on the skin surface with a defined drive pattern and detects response voltages across electrodes. These acquired signals, combined with reference signals from an artificial model that only comprises skin, fat, and muscle, enable differential EIT image reconstruction to reveal bone size, position, and conductivity. Key EIT armband configurations, including the number of electrodes and drive pattern of current stimulation and voltage acquisition, were optimized through finite-element modeling of a section of the forearm. A phantom experiment using 3D-printed forearm bones demonstrated acceptable accuracy in reconstructed cross-sectional images of the ulna and radius, successfully indicating a conductivity increase when the radius featured a 2.5 mm fracture notch. Subsequently, a reconstructed EIT image of a volunteer's forearm cross section closely matched actual anatomical conditions. Furthermore, an ex vivo study on the EIT monitoring of porcine metacarpal bones effectively tracked the conductivity variations induced by the resection of bone fragments from an intact porcine hoof, the implantation of steel pins, and the backfill of bone fragments to the fracture zone as an imitative fracture healing process. Therefore, this EIT armband enables noninvasive, long-term monitoring of arm bones, especially during fracture healing, and has potential to monitor other bones, such as the fibula and tibia.