Pilot Assessment of the Repeatability of Indocyanine Green Fluorescence Imaging and Correlation with Traditional Foot...

Ankle brachial index (ABI), toe pressures (TP), and transcutaneous oxygen pressure (TcPO₂) are traditionally used in the assessment of critical limb ischemia (CLI). Indocyanine green (ICG) fluorescence imaging can be used to evaluate local circulation in the foot and to evaluate the severity of ischemia. This prospective study analyzed the suitability of a fluorescence imaging system (photodynamic eye [PDE]) in CLI.

Forty-one patients with CLI were included. Of the patients, 66% had diabetes and there was an ischemic tissue lesion in 70% of the limbs. ABI, toe pressures, TcPO₂ and ICG-fluorescence imaging (ICG-FI) were measured in each leg. To study the repeatability of the ICG-FI, each patient underwent the study twice. After the procedure, foot circulation was measured using a time-intensity curve, where T1/2 (the time needed to achieve half of the maximum fluorescence intensity) and PDE10 (increase of the intensity during the first 10 s) were determined. A time-intensity curve was plotted using the same areas as for the TcPO₂ probes (n=123).

The mean ABI was 0.43, TP 21 mmHg, TcPO₂ 23 mmHg, T1/2 38 s, and PDE10 19 AU. Time-intensity curves were repeatable. In a Bland-Altman scatter plot, the 95% limits of agreement of PDE10 was 9.9 AU and the corresponding value of T1/2 was 14 s. Correlation between ABI and TP was significant (R=.73, p<.001), and it was weaker in diabetic patients (R=.47, p=.048) compared with non-diabetic patients (R=.89, p=.002). Correlations between ABI and TcPO₂ and TP and TcPO₂ were weak (R=.37, p=.05 and R=.43, p=.037, respectively). Correlation between TcPO₂ and PDE10 was strong in diabetic patients (R=.70, p=.003).

According to this pilot study, ICG-FI with PDE can be used in the assessment of blood supply in the ischemic foot.