Systemic Sclerosis Calcinosis Outcomes with Wearable Ultrasound Technology (SCOUT)

Abstract

Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by progressive fibrosis of the skin and internal organs. A debilitating complication of SSc is calcinosis: the deposition of calcium hydroxyapatite in soft tissue. These deposits, which most commonly develop in the hands/fingers, can cause severe pain, ulceration, infection, and functional impairment, yet remain difficult to monitor objectively using current technologies. Ultrasound is commonly employed for its noninvasive, accessible, and cost-effective qualities; however, its diagnostic performance is hindered by poor acoustic coupling, the anatomical complexity of small joints, and strong acoustic impedance mismatch caused by calcium within soft tissues. These limitations contribute to delayed diagnosis and treatment, highlighting a clinical and market need for improved imaging fidelity within existing workflows.

To address this, we propose a tissue-conforming hydrogel coupling material engineered to enhance acoustic transmission between commercial ultrasound probes and the surfaces of the hand. The hydrogel conforms intimately to joint contours, serving as an optimized acoustic matching layer that reduces impedance discontinuities between skin and probe. By improving acoustic energy transmission and minimizing reflection artifacts induced by dense calcified deposits, the hydrogel aims to yield sharper boundary definition and higher-fidelity imaging.

Key design specifications include an acoustic impedance of 1.6×10⁶kg/m²·s, an electrical impedance of 50Ω ± 10Ω, phase ≈ 0° at probe center, and –15°≤ arg(Z􀀀) ≤ +15° across 2–15MHz to maintain a nearly resistive load and minimal waveform distortion. The hydrogel operates under ≤ 5kPa pressure and below 37°C. Manufacturing emphasizes scalable polymer formulations, photochemical crosslinking, and sheet casting for high-volume production. Preliminary cost modeling estimates a per-unit cost of $7.57, including $1.57 for polyurethane gel and $6.00 for manufacturing and overhead. By improving ultrasound fidelity without hardware modification, this hydrogel may enable earlier detection and better monitoring in systemic sclerosis care.

Video