Background - Near-infrared (NIR) imaging of lymphatic drainage of injected indocyanine green (ICG) has emerged as a
new technology for clinical imaging of lymphatic architecture and quantification of vessel function, offering better
spatial and temporal resolution than competing imaging modalities. While NIR lymphatic imaging has begun to be
reported in the literature, the technology is still in its infancy and its imaging capabilities have yet to be quantitatively
characterized. The objective of this study, therefore, was to characterize the parameters of NIR lymphatic imaging to
quantify its capabilities as a diagnostic tool for evaluating lymphatic disease.
Methods - An NIR imaging system was developed using a laser diode for excitation, ICG as a fluorescent agent, and a
CCD camera to detect emission. A tissue phantom with mock lymphatic vessels of known depths and diameters was
used as an alternative to in vivo lymphatic vessels due to the greater degree of control with the phantom.
Results and Conclusions - When dissolved in an albumin physiological salt solution (APSS) to mimic interstitial fluid,
ICG experiences shifts in the excitation/emission wavelengths such that it is maximally excited at 805nm and produces
peak fluorescence at 840nm. Premixing ICG with albumin induces greater fluorescence intensity, with the ideal
concentration being: 900μM (60g/L) albumin and 193.5μM (150μg/mL) ICG. ICG fluorescence can be detected as deep as 6mm, but spatial resolution deteriorates severely below 3mm, thus skewing vessel geometry measurements. ICG packet travel, a common measure of lymphatic transport, can be detected as deep as 5mm.