High-resolution and high sensitivity mesoscopic fluorescence tomography based on de-scanning EMCCD: system design and thick tissue imaging applications

Abstract

Optical microscopy has been one of the essential tools for biological studies fordecades, however, its application areas was limited to supercial investigation due tostrong scattering in live tissues. Even though advanced techniques such as confocalor multiphoton methods have been recently developed to penetrate beyond a few hundreds of microns deep in tissues, they still cannot perform in the mesoscopicregime (millimeter scale) without using destructive sample preparation protocolssuch as clearing techniques. They provide rich cellular information; however, they cannot be readily employed to investigate the biological processes at larger scales. Herein, we will present our effort to establish a novel imaging approach that can quantify molecular expression in intact tissues, well beyond the current microscopy depth limits.

Mesoscopic Fluorescence Molecular Tomography (MFMT) is an emerging imaging modality that offers unique potential for the non-invasive molecular assessment of thick in-vitro and in-vivo live tissues. This novel imaging modality is based on an optical inverse problem that allows for retrieval of the quantitative spatial distribution of fluorescent tagged bio-markers at millimeter depth. MFMT is well-suited for in-vivo subsurface tissue imaging and thick bio-printed specimens due to its high sensitivity and fast acquisition times, as well as relatively large fields of view.

Herein, we will first demonstrate the potential of this technique using our first generation MFMT system applied to multiplexed reporter gene imaging (in-vitro) and determination of Photodynamic Therapy (PDT) agent bio-distribution in a mouse model (in-vivo). Second, we will present the design rationale, in silico benchmarking, and experimental validation of a second generation MFMT (2GMFMT) system. We will demonstrate the gain in resolution and sensitivity achieved due to the de-scanned dense detector conguration implemented. The potential of this novel platform will be showcased by applying it to the longitudinal assessment of Ink-Jet Bio-Printed tumor models. This preliminary investigation focuses on monitoring four patient-derived glioblastoma multiforme (GBM) spheroids within their bioreactor for up to 70 days and following their volume change prior to and after exposure to a cytotoxic drug.

Overall, our studies indicate that 2GMFMT is a powerful technique for in-vitro and in-vivo thick tissue molecular imaging applications due to its high resolution, fast tomographic imaging capability, and high sensitivity.