Tissue Oxygenation Measurements to Aid Scalpel Debridement Removal in Patients With Diabetes

Abstract

Background: Callus formation in the diabetic foot increases the risk of ulcer onset. It is standard procedure to remove these dead tissue layers to reduce rising pressures. In a surgical procedure known as scalpel debridement, or chiropody the callus tissue is removed up to the epidermal layer. Factors may influence the outcome of this surgical process such as clinician inexperience. In an effort to standardize the debridement process, tissue oxygenation (TO) measurements are obtained before and after to study the effect of debridement on callus tissue.

Methods: Fifteen debridement cases were analyzed using near infrared (NIR) imaging to study changes in TO. The NIR-based device used in this study estimates effective changes in TO in terms of oxy-, deoxy-, total hemoglobin, and oxygen saturation. Weber contrasts between callus tissue and the surrounding normal tissue were compared following debridement for all TO parameters. In a secondary analysis, callus tissue was segmented into quadrants and a percent of significance (in terms of total TO change) was calculated using a t-test.

Results: Results show majority of cases displayed greater than 80% as the significant change in TO following debridement, except in cases with the presence of blood clot (a common precursor for ulceration). In cases where incomplete debridement was suspected, a significant change in TO was still observed.

Conclusions: With extensive systematic studies in the future, NIR imaging technique to measure changes in TO may be implemented as a low-cost hand-held imaging device useful for objectively assessing the effectiveness of the scalpel debridement process.

Keywords: chiropody; diabetic foot ulcers; near infrared imaging; scalpel debridement; tissue oxygenation; ulcer prevention.

Figure 1.

Location of callus is highlighted within the red-boxed region on the inner sole of patient’s foot. (a) Prior to debridement the callus tissue is dark in color. (b) Following removal of the superficial layers, (c) only pink skin remains, satisfying the clinician for completion of the scalpel debridement process (or chiropody).

Figure 2.

NIROS device using CMOS detector and multi-wavelength NIR LEDs, with laptop for data acquisition and processing. The articulating arm allows for easy and stable positioning during imaging.

Figure 3.

Fifteen callus sites are shown before debridement as diffuse reflectance NIR signal (at 735nm) demarcating the overall field of view imaging area (gray) and the region of interest (pseudo-color area) where imaging analysis was performed. Here, red corresponds to higher intensities and blue corresponds to lower intensities of the measured diffuse reflectance signals.

Figure 4.

Tissue oxygenation maps in terms of (a) ∆HbR (b) ∆HbO (c) ∆HbT and (d) ∆StO₂ before (top) and after (bottom) scalpel debridement for case #14. Here, red corresponds to higher concentrations and blue corresponds to lower concentrations of the given parameter.

Figure 5.

Method of callus and peri-callus area selection C:PC for one case with (i) C:PC contrast, and (ii) Weber contrast for each parameter (example case for ∆HbR shown).

Figure 6.

Method of [C:PC] region selection for each quadrant and quadrant significance percentage calculations for each TO parameter (∆HbR, ∆HbO, ∆HbT, ∆StO₂).

Figure 7.

Bar plots of Weber contrast in C:PC following debridement. Results are shown for each debridement case and for each TO parameter: (a) ∆HbR, (b) ∆HbO, (c) ∆StO₂, (d) ∆HbT. The error bar is shown with respect to three repetitive data analysis (described in Section 2.4.2). Orange asterisks indicate cases displaying blood clot post-debridement and blue asterisks indicate suspected incomplete debridement by clinician.

Figure 8.

Percent significance of TO change (80% threshold) determined per quadrant for clinical representation of effectiveness in scalpel debridement from an objective physiological imaging approach. White light images were not available for cases 1 and 2 hence the percent significance results were overlain onto the NIR gray scale images (obtained at 735nm).

Figure 9.

Average significance of tissue oxygenation changes within callus (compared to peri-callus) following debridement for 15 cases. An arbitrary threshold (80%) selected for this study defines the minimum average quadrant significance expected following debridement.