Shining New Light on Chronic Wound Assessment: NIRF Imaging with ICG

Hard-to-heal lower leg wounds remain a complex, high-burden clinical challenge, both for the patients who endure them and the systems trying to manage them. In a pilot observational cohort study published in the International Wound Journal, researchers explored a compelling diagnostic complement to traditional wound assessment: Near-Infrared Fluorescent (NIRF) imaging using Indocyanine Green (ICG). The study offers real-world insight into the role of perfusion imaging in revealing the otherwise unseen dynamics of wound healing—or stagnation.

The 12-week, prospective cohort study involved 17 patients (mean age 64) from Otago and Southland, New Zealand. Each had lower limb wounds over 10 cm in diameter and at least four weeks’ duration. 47% had diabetes and 45% had peripheral arterial disease (PAD), reflecting a typical chronic wound population.

Participants received standard multidisciplinary wound care, with NIRF imaging sessions scheduled at baseline, six weeks, and 12 weeks. ICG dye was administered intravenously, and perfusion was visualized using the SPY Elite system. Dye fluorescence was quantitatively analyzed across several imaging parameters, including peak and baseline intensities and area under the fluorescence curve (AUC).

A Fluorescent Perspective: What the Imaging Revealed
A total of 13 participants completed the full 12-week course. No imaging-related adverse events were reported, and 14 patients (82%) experienced a measurable reduction in wound area or volume during the observation period. While traditional assessments confirmed healing trajectories in many cases, NIRF imaging revealed a nuanced view of underlying perfusion dynamics.

• Decreasing dye intensity over time tended to align with improved clinical outcomes—such as wound area reduction and increased granulation.
• Increasing intensity, however, often flagged underlying pathology. Notably, three participants with rising intensity were later diagnosed with infection or malignancy, none of which were detectable via visual inspection at the time of imaging.

Quantitative metrics added further texture. Spearman's correlation showed a trend between AUC change and wound volume reduction (ρ = 0.46, p = 0.06) and a strong inverse relationship between slough reduction and granulation improvement (ρ = −0.54, p = 0.02). Though not statistically significant across all metrics due to the small sample size, these findings suggest a meaningful relationship between perfusion changes and healing biology.

Beyond the Eye: Detecting What’s Hidden
One of the most compelling takeaways is the ability of NIRF imaging to visualize inflammation and vascular changes before they manifest clinically. This early detection is especially relevant in diabetic foot ulcers and PAD, where subclinical changes often precede serious complications. In two cases, increased intensity preceded visible signs of infection; in another, it was a signal of malignancy.

Interestingly, even wounds that showed visual improvement, such as a 92% area reduction, could retain “hot spots” of high dye intensity, potentially signaling underlying inflammation or tissue vulnerability. This disconnect between surface appearance and subdermal activity underscores the need for deeper assessment tools.

While this pilot study supports the feasibility and potential value of integrating NIRF imaging into wound care, it stops short of drawing definitive conclusions. The lack of a control group, small sample size, and absence of long-term follow-up limit the generalizability. Moreover, economic factors like cost-effectiveness and implementation in low-resource settings remain unexamined.

Still, the study makes a clear case for NIRF’s clinical promise. By offering a dynamic, non-invasive window into tissue viability and perfusion, it invites a more proactive, precision-based approach to chronic wound management.

Reference:
Clifford KA, Schmidt E, Johnstone J, Krysa J. Assessment of Hard-To-Heal Lower Leg Wounds With Near-Infrared Fluorescent Imaging: A Pilot Cohort Study. Int Wound J. 2025;22(7):e70723. doi:10.1111/iwj.70723