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The study examined the ability of SFDI, a new method that uses structured illumination combined with visible and non-infrared light to characterize sub-surface tissue beneath the skin to evaluate lower extremity circulation in 94 limbs (47 patients).

In the first-of-use study in PAD, lead researchers Craig Weinkauf, M.D., Ph.D., an assistant professor of surgery at the University of Arizona, and David Armstrong, D.P.M., M.D., Ph.D., a professor of surgery at University of Southern California’s (USC’s) Keck School of Medicine, compared SFDI outputs to current non-invasive testing standards, including the ankle-brachial index (ABI), toe-brachial index (TBI), pedal pulses, and doppler waveforms. Existing assessment tools have been shown to be unreliable and/or limited in their ability to detect local tissue perfusion due to their high subjectivity, time consumption, and vessel stiffening (i.e., atherosclerosis), which is common in patients with diabetes.

“We demonstrated that SFDI was able to produce reliable measurements of local hemoglobin perfusion and oxygenation in subjects with and without diabetes,” said Weinkauf. “Evaluating both the tissue oxygen saturation and local hemoglobin in patients with diabetes gives us new insight into the compromised circulation in this population, which is at a particularly high risk for PAD.”

The results showed that SFDI revealed a distinct perfusion profile of the diabetic foot. The recruited subjects with diabetes had significantly elevated tissue oxygen saturation (StO₂) and lower superficial hemoglobin (HbT₁) supplying the capillary beds compared to subjects without diabetes. These findings suggested that, in patients with diabetes, oxygen was not appropriately extracted by the tissue due to capillary dysfunction.

“The phenomenon of arteriovenous (AV) shunting associated with vascular dysfunction (diabetic neuropathy) has been observed in diabetes patients, but SFDI gives us a non-invasive and objective method to validate the compromised circulation due to this etiology,” said Armstrong.

Finally, an SFDI-derived index of HbT₂ (hemoglobin in the reticular dermis)/HbT₁ (hemoglobin papillary dermis) was found to differentiate between diabetes patients with and without PAD.

“The early results of the current study suggest that SFDI technology could potentially overcome the shortcomings of existing methods that are confounded by vessel stiffening,” Weinkauf shared. “That’s why we are expanding our study and continuing our evaluation of SFDI technology.”

The study was completed in collaboration with Modulim and researchers from the University of Arizona, Icahn School of Medicine and USC. SFDI is an advanced imaging technique co-invented by Modulim’s CEO and CTO David Cuccia, Ph.D., and his colleagues at UCI’s Beckman Laser Institute. Both Cuccia and Amaan Mazhar, Ph.D., Modulim’s VP of Research and Development, are internationally recognized experts in the field of medical photonics and co-authors of the current study, which was funded by the NIDDK at the National Institutes of Health (NIH).

About Modulim

Modulim is a pioneer in sub-surface optical imaging powered by SFDI. SFDI is an FDA-cleared non-invasive tissue oxygen saturation technology that combines structured illumination with multiple wavelengths of light (visible and near-infrared) to allow for deeper and layer-specific assessment of tissue oxygenation and hemoglobin. This unique technology quantifies two key perfusion metrics not identified by any other technology: HbT₁ and HbT₂. Modulim’s new Clarifi^™ Imaging System, powered by SFDI, is indicated for measuring tissue oxygenation in patients with potential circulatory compromise. SFDI demonstrates Modulim’s continuing mission to deliver technology that provides clinically-actionable information about compromised micro- and macro-vascular tissue in a clinical setting, so clinicians can intervene as early as possible to prevent the onset or escalation of diabetic foot ulcers and other complications. With its widespread adoption, SFDI-based technologies have the potential to save thousands of limbs and lives and billions of dollars in treatment costs. For more information, visit modulim.com.