New evidence supports the utility of spatial frequency domain imaging (SFDI) for identifying compromised circulation in patients at risk of peripheral arterial disease (PAD). These data were published in the Journal of Vascular Surgery, in a study that describes SFDI-based technology from Modulim as a promising non-invasive optical imaging method for rapidly assessing compromised circulation in tissue in the lower extremity of patients with and without diabetes.
The study examined the ability of SFDI, a new method that uses structured illumination combined with visible and non-infrared light to characterise 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 (University of Arizona, Tucson, USA) and David Armstrong (University of Southern California’s (USC’s) Keck School of Medicine, Los Angeles, USA) 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 (for example, atherosclerosis), which is common in patients with diabetes, the authors write.
“We demonstrated that SFDI was able to produce reliable measurements of local haemoglobin perfusion and oxygenation in subjects with and without diabetes,” says Weinkauf. “Evaluating both the tissue oxygen saturation and local haemoglobin 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 haemoglobin (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 aetiology,” comments Armstrong.
Finally, an SFDI-derived index of HbT2 (haemoglobin in the reticular dermis)/HbT1 (haemoglobin in the 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 shares. “That is 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, and his colleagues at UCI’s Beckman Laser Institute. Both Cuccia and Amaan Mazhar, Modulim’s vice president of research and development, are co-authors of the current study.