Comparing spatial distributions of ALA-PpIX and indocyanine green in a whole pig brain glioma model using 3D fluorescence cryotomography.

Significance: ALA-PpIX and second-window indocyanine green (ICG) have been studied widely for guiding the resection of high-grade gliomas. These agents have different mechanisms of action and uptake characteristics, which can affect their performance as surgical guidance agents. Elucidating these differences in animal models that approach the size and anatomy of the human brain would help guide the use of these agents. Herein, we report on the use of a new pig glioma model and fluorescence cryotomography to evaluate the 3D distributions of both agents throughout the whole brain. Aim: We aim to assess and compare the 3D spatial distributions of ALA-PpIX and second-window ICG in a glioma-bearing pig brain using fluorescence cryotomography. Approach: A glioma was induced in the brain of a transgenic Oncopig via adeno-associated virus delivery of Cre-recombinase plasmids. After tumor induction, the pro-drug 5-ALA and ICG were administered to the animal 3 and 24 h prior to brain harvest, respectively. The harvested brain was imaged using fluorescence cryotomography. The fluorescence distributions of both agents were evaluated in 3D in the whole brain using various spatial distribution and contrast performance metrics. Results: Significant differences in the spatial distributions of both agents were observed. Indocyanine green accumulated within the tumor core, whereas ALA-PpIX appeared more toward the tumor periphery. Both ALA-PpIX and second-window ICG provided elevated tumor-to-background contrast (13 and 23, respectively). Conclusions: This study is the first to demonstrate the use of a new glioma model and large-specimen fluorescence cryotomography to evaluate and compare imaging agent distribution at high resolution in 3D.

Comparing fluorescent contrast agents for fluorescence guided surgery using 3-D cryo-imaging.

Fluorescence cryo-imaging is a high-resolution optical imaging technique that produces 3-D whole-body biodistributions of fluorescent molecules within an animal specimen. To accomplish this, animal specimens are administered a fluorescent molecule or reporter and are frozen to be autonomously sectioned and imaged at a temperature of -20°C or below. Thus, to apply this technique effectively, administered fluorescent molecules should be relatively invariant to low temperature conditions for cryo-imaging and ideally the fluorescence intensity should be stable and consistent in both physiological and cryo-imaging conditions. Herein, we assessed the mean fluorescence intensity of 11 fluorescent contrast agents as they are frozen in a tissue-simulating phantom experiment and show an example of a tested fluorescent contrast agent in a cryo-imaged whole pig brain. Most fluorescent contrast agents were stable within ~25% except for FITC and PEGylated FITC derivatives, which showed a dramatic decrease in fluorescence intensity when frozen.