Daigle, N. | bioRxiv Science

bioRxiv2023

Combined multiphoton microscopy and somatostatin receptor type 2 imaging of pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (PNETs) are a rare but increasingly more prevalent cancer with heterogeneous clinical and pathological presentation. Surgery is the preferred treatment for all hormone-expressing PNETs and any PNET greater than 2 cm, but difficulties arise when tumors are multifocal, metastatic, or small in size due to lack of effective surgical localization. Existing techniques such as intraoperative ultrasound provide poor contrast and resolution, resulting in low sensitivity for such tumors. Somatostatin receptor type 2 (SSTR2) is commonly overexpressed in PNETs and presents an avenue for targeted tumor localization. SSTR2 is often used for pre-operative imaging and therapeutic treatment, with recent studies demonstrating that somatostatin receptor imaging (SRI) can be applied in radioguided surgery to aid in removal of metastatic lymph nodes and achieving negative surgical margins. However not all PNETs express SSTR2, indicating labeled SRI could benefit from using a supplemental label-free technique such as multiphoton microscopy (MPM), which has proven useful in improving the accuracy of diagnosing more common exocrine pancreatic cancers. Our work tests the suitability of combined SRI and MPM for localizing PNETs by imaging and comparing samples of PNETs and normal pancreatic tissue. Specimens were labeled with a novel SSTR2-targeted contrast agent and imaged using fluorescence microscopy, and subsequently imaged using MPM to collect four autofluo-rescent channels and second harmonic generation. Our results show that a combination of both SRI and MPM provides enhanced contrast and sensitivity for localizing diseased tissue, suggesting that this approach could be a valuable clinical tool for surgical localization and treatment of PNETs.

bioengineering↗

bioRxiv2022

Backscattering Mueller Matrix polarimetry on whole brain specimens shows promise for minimally invasive mapping of microstructural orientation features

Understanding microscale physiology and microstructural cellular features of the brain is key to understanding the mechanisms of neurodegenerative diseases and injury, as well as the prominent changes that neurons and glia in the brain undergo in development and aging which reflect functional state. Non-invasive imaging modalities sensitive to the microscale - especially diffusion magnetic resonance imaging (dMRI) - are extremely promising for three-dimensional mapping of cellular microstructure of brain tissues and brain connectivity via tractography; however, there is a need for robust validation techniques to verify and improve the biological accuracy of fiber orientation information derived from these techniques. Recent advances in dMRI acquisition and modeling have moved toward probing of the more complex grey matter architecture, challenging current validation techniques, which are largely based on ex vivo staining and microscopy focusing on white matter. Polarized light imaging (PLI) has been shown to be a successful technique for high resolution, direct, microstructural imaging and has been applied to dMRI validation with clear advantages over conventional staining and microscopy techniques. Conventionally, PLI is applied to thin, sectioned samples in transmission mode, but unlike histologic staining, PLI can be extended to operate with high sensitivity in reflectance mode and even extended to 3D imaging to bridge the gap toward in vivo validation of dMRI measurements of orientation features in both gray and white matter of the brain. In this report we investigate the use of backscattering Mueller Matrix polarimetry to characterize the microstructural content of intact Ferret brain specimens. The experimental results show that backscattering polarimetry can probe white matter fiber coherence and fiber orientation in whole brain specimens, and show promise for probing grey matter microstructure. Ultimately, these preliminary results motivate further study to fully understand how backscattering polarimetry can best be used for validation of in vivo microstructural imaging of the brain.

bioengineering↗