Average fluorescence intensity is affected by distance and penetration depth with near-infrared fluorescence imaging with indocyanine green in an ex vivo model.

OBJECTIVE

The objective of this study was to evaluate the effect of indocyanine green (ICG) concentration, distance, angle, and penetration depth on average fluorescence intensity (AFI) when using 2 imaging devices in a canine ex vivo model.

METHODS

3 concentrations of ICG were evaluated (0.006, 0.011, and 0.022 mg/mL) for the effect of distance, penetration depth, angle, and ambient light on AFI. Penetration depth was assessed using serially stacked 1-mm sheets of a gelatin phantom. Each set of conditions was tested using a VITOM 3D and 30° 10-mm laparoscope. Polynomial regression was used to evaluate for significance.

RESULTS

Average fluorescence intensity increased with increasing distance for the 30° 10-mm laparoscope. The VITOM 3D displayed higher AFIs at closer and farther distances. Average fluorescence intensity decreased as penetration depth increased for both devices. Ambient light had no effect on AFI, and AFI varied by angle, but statistical analysis for these variables was limited by insufficient data points.

CONCLUSIONS

Average fluorescence intensity was affected by distance, penetration depth, and angle for each ICG concentration and imaging device. There was no apparent effect on AFI with or without ambient light.

CLINICAL RELEVANCE

The interest in near-infrared fluorescence with ICG is growing in veterinary medicine. Optimization of protocols using these techniques can provide veterinarians with guidelines for the implementation of near-infrared fluorescence with ICG. Further studies are needed to assess the relationship between distance, depth, angle, and ambient light with AFI in vivo.