|
Imaging of indocyanine green (ICG) can reveal vascular permeability, and it has been previously demonstrated in pancreatic adenocarcinoma tumors [1]. The relevance of this to clinical use has remained speculative, although it is likely that these vascular permeability measurements could be used for resection guidance or could also be predictive of drug retention or immune infiltration in dysplastic tissues in non-surgical tumors. Second-Window Indocyanine Green (SWIG) imaging, in which a high ICG dose is administered followed by imaging at hours or days post-injection, has been shown to have potential in several oncologic indications [2,3], and is dependent upon dysplastic tissues having a higher degree of bulk tissue retention. Herein, we evaluated the capability of early phase vascular permeability estimates within minutes after ICG injection, and how they may be related to the degree of ICG retention in SWIG imaging.
Pancreatic cell lines, AsPC1 or BxPC3 were grown into tumors in nude mice, providing models that display different capillary network morphologies. Using a clinical surgical fluorescence imaging system, mice were imaged for 10 minutes following bolus IV injection of 4mg/kg ICG. Mice were subsequently imaged 24 hours after the initial injection to measure the intensity of the tumor relative to a muscle tissue reference for SWIG images. The temporal slope of tissue uptake within the first few minutes was used to estimate vascular permeability.
Initial vascular permeability estimates from flow kinetics imaging were not predictive of the ICG retention in SWIG imaging. This would indicate that lymphatics or other factors likely play a larger role in determining retention.
|
