Near-instant noninvasive optical imaging of tissue perfusion for vascular assessment

Background: Noninvasive vascular tests are critical for identifying patients who may benefit from surgical revascularization, but current tests have significant limitations in people with diabetes. This study aimed to evaluate the ability of spatial frequency domain imaging (SFDI), an optical imaging method capable of measuring tissue oxygen saturation (StO ₂ ) and tissue hemoglobin, to assess lower extremity blood supply. Methods: Ankle-brachial index, toe-brachial index, pedal Doppler waveforms, and SFDI images were prospectively evaluated in 47 consecutive patients with and without diabetes in whom there was concern for peripheral artery disease (PAD). SFDI is a noncontact optical imaging technology that uses structured illumination to quantify subsurface (2-3 mm in depth) StO ₂ and tissue hemoglobin in the dermal microcirculation (HbT ₁ ) and macrocirculation (HbT ₂ ) over a large field of view (15 × 20 cm) within 10 seconds. Results: This demonstrates the ability of SFDI to capture reliable clinical measurements of perfusion in plantar aspects of the feet. SFDI StO ₂ values differentiate nondiabetic patients with and without arterial disease, defined as ankle-brachial index <0.9 (P =.06), but are limited in those with diabetes (P =.43). An elevated StO ₂ and reduced HbT ₁ are observed in people with diabetes compared with nondiabetic patients (P <.05). An SFDI-derived HbT ₂ /HbT ₁ index differentiates diabetics with PAD vs no PAD (P <.01) using toe-brachial index <0.7 as a cutoff for PAD in diabetes. Conclusions: SFDI is a feasible, rapid, and easy to use widefield measurement of perfusion in a clinical setting. This first-of-use study suggests that the technology has potential to evaluate lower extremity perfusion in people with and without diabetes. Further studies with increased numbers of patients and end points including wound healing will need to be designed to fully evaluate the applicability of this new technology.