Camera-Based Bipedal Plantar Pulse Transit Time Difference Measurement for Lower Limb Arterial Stenosis Detection

Peripheral arterial disease (PAD) can lead to severe foot problems, including claudication and amputation in extreme cases. Currently, clinical diagnosis primarily relies on costly and cumbersome methods like spectral Doppler ultrasound and Ankle-Brachial index (ABI). This highlights the urgent need for a low-cost and convenient screening approach. The lower extremity arterial stenosis caused by PAD leads to a delay in pulse wave transmission from the heart to the feet. This study proposes a novel PAD screening method, the bipedal plantar pulse transit time difference (PTTD), calculated as the time difference between photoplethysmographic (PPG) signals extracted from RGB videos of the feet. A simulation experiment was conducted on 19 healthy adult subjects, in which five different vascular obstruction conditions (i.e., PAD degrees) were simulated by applying varying pressures to the calf. The experimental results show that PTTD achieved 90.53% accuracy in PAD-simulation detection and 80.00% in five-class PAD-simulation grading, offering improvements of 10.53% and 28.42% over the baseline perfusion index (PI)-based detection and grading models, respectively. Additionally, we collected plantar video recordings from 10 PAD patients at the Department of Ultrasound in a hospital, demonstrating the feasibility in real clinical settings. This indicates that PTTD measured between bipedal plantars exhibits high sensitivity to vascular obstruction and holds promise as an efficient tool for PAD screening.