Perfusion Mapping of Flaps Using Indocyanine Green Fluorescence Angiography and Laser Speckle Contrast Imaging

Abstract

Background: Indocyanine green fluorescence angiography (ICG-FA) is often used for assessing tissue circulation in reconstructive surgery. Indocyanine green (ICG) is injected intravenously and visualized in the tissue with an infrared camera. The information is used to plan the surgery, for example, in free flap breast reconstructions. Laser speckle contrast imaging (LSCI) is another method that uses laser to assess tissue perfusion in the skin. Unlike ICG-FA, LSCI is noninvasive and may therefore have an advantaged compared with ICG-FA. The aim of this study was to evaluate the correlation between information obtained from these two techniques.

Methods: Five deep inferior epigastric perforator patients were included. The flaps were assessed with LSCI and ICG-FA. For LSCI, the perfusion was calculated in 32 regions of interest. For ICG-FA, the maximum slope and area under curve (AUC) were calculated based on average pixel intensity data.

Results: Large variations in maximum slope values could be seen between flaps, whereas AUC had lower variability within the same flap and between flaps. Pearson rank correlation comparing average perfusion (LSCI) and AUC (ICG-FA) showed a correlation between the values (r = 0.55, P < 0.0001). No significant correlation was observed between perfusion and maximum slope (r = 0.11, P = 0.18).

Conclusions: There is a significant correlation between data obtained using LSCI and ICG-FA, when ICG-FA data are presented as AUC of the ICG-FA intensity curve. Maximum slope lacks significant correlation with flap data obtained with LSCI. The study indicates that LSCI may be used in reconstructive surgery to assess tissue circulation in a way similar to ICG-FA.

Fig. 1.

Methods. A, LSCI measurements of a DIEP free flap. The perforator is situated under the green area in the right medial zone. B, The ICG-FA assessment of the same flap. The circles indicate the different ROIs. C, The pixel intensity in the 32 different ROIs of the ICG-FA assessment seen above. The steeper curves represent the ROI situated above the perforator. D, For each ROI, the AUC for 20 seconds from the start of the increase of intensity and the maximum slope for the same time span was calculated.

Fig. 2.

LSCI data from all five flaps (A) showed significant differences between zone I and III (P = 0.0043); zone I and IV (P = 0.0001); zone II and III (P < 0.0001) and zone II and IV (P < 0.0001). In the ICG-FA data from all flaps, presented as slope (B), multiple comparisons only showed significant difference between zone I and IV (P = 0.0115). ICG-FA data from all flaps, presented as AUC (C), showed no significant differences.

Fig. 3.

Scatter plots of ICG-FA data presented as AUC and PU values from LSCI measurements (A) and ICG-FA data presented as maximum slope and PU values from LSCI measurements (B). A significant correlation can only be seen in the former.

Fig. 4.

In two right-angled triangles with the same base (A) but different height (B–C), the ratio between the two areas (AUC A and B) will be the same as the ratio between the slopes. However, in an uneven curve, the spread of the values of the slope may be larger than the spread of the values of the AUC. This might explain the poorer correlation between the LSCI measurements and the ICG-FA data presented as maximum slope.