Gastrinomas are gastrin-producing neuroendocrine tumors (NETs) located in the gastroenteropancreatic system. Gastrinomas are often small, multifocal, and found at late stages. Their unpredictable behavior and metastatic potential make it extremely challenging to develop therapeutic strategies. Surgery is the only potentially curative treatment for gastrinoma, but current tumor localization techniques such as intraoperative ultrasound and manual palpitation have poor sensitivity for small tumors, resulting in higher rates of recurrence and metastasis. Therefore, there is a strong clinical need for developing advanced intraoperative imaging technologies for tumor localization in treating gastrinoma. Polarized light imaging (PLI) is a promising method for label-free tissue characterization due to its sensitivity to micro and nanoscale structures, which are often influenced with the onset of cancer, but no works have yet investigated the application of PLI for gastrinoma localization.

To assess the suitability of PLI for gastrinoma localization, we imaged 11 formalin-fixed paraffin embedded (FFPE) specimens of gastrinoma using a five-wavelength Mueller Matrix Polarization Microscope. The Lu-Chipman decomposition was applied to spatial maps of the sixteen Mueller matrix parameters. Values for depolarization, diattenuation, and retardance were compared for regions of interest corresponding to tumor and adjacent tissues. There was significant difference between the average depolarization of the Brunner’s gland and tumors when imaged with light at 442, 543, and 632 nm (p<0.05), and the average diattenuation values of the two at 405 nm (p<0.05), suggesting that these properties could be used for label-free localization. These results motivate further study of the use of PLI for NET localization. Future steps include broadening the sample pool to other NETs and validating results in fresh tissue studies.

Mouse models are essential tools for understanding cancer growth and accelerating the development of therapeutic and diagnostic technologies. Xenografts, generated by implanting tumor cells directly into mice through injection, are frequently used to study cancer biology and therapeutics. In these models, assessment of tumor growth and development is necessary to support the study of disease progression and model validation. Unfortunately, such measurements often require sacrificing the animal to create organ explants or tissue cultures, resulting in increased animal use and hampering longitudinal measurements of individual tumors. A tool enabling in vivo tumor monitoring for xenograft models could improve the efficiency of these animal models and provide more robust growth measurements through true longitudinal measurement.

One method of optical tumor assessment involves tagging biomolecules of interest with fluorescent species to enable detection with minimally invasive fluorescence imaging, implemented endoscopically or laparoscopically. However, utilizing fluorescence imaging in vivo in murine models poses challenges due to both tortuous anatomy and small gastrointestinal lumen caliber.

This work reports a miniature fluorescence imaging probe equipped with a multiband filter and biopsy device to image and sample fluorescently-tagged, xenografted tumors as they develop in mouse models. We present the design and characterization of the device and report measurements of the modulation transfer function and ex vivo imaging performance, demonstrating its promise as a valuable research tool to advance cancer research in xenograft models, enabling the development of imaging biomarkers for cancer detection in a clinical setting without the need for exogenous contrast.