In vivo near infrared Förster resonance energy transfer small animal imaging

Abstract

In this thesis, a wide-field time-domain optical imaging system for quantitative FRET imaging in small animals is developed, optimized and employed to transferrin based FRET assays. The work is classified in three components, which are hardware integrations, software developments and FRET applications for image-guided drug delivery optimization. On the hardware part, a DMD-based spatial light modulator is exploited to enhance the power efficiency and uniformity of spatially- coded wide-field illumination, and small animal research equipment is integrated with our wide-field time-domain optical imaging system. A multi-modal imaging cassette is designed for accurate image-coregistration and validation between a 3D optical imaging system and a Micro-MRI system. On the software part, an active wide-field illumination method is developed to enhance the signal-to-noise ratio and weak-signal sensitivity for enhanced accuracy in fluorescence lifetime estimation. A compressive sensing-based image reconstruction method and a sparse data collection strategy are also developed and utilized to enhance optical reconstructions' performances, and to shorten acquisition times dramatically for 3D FRET fluorescence molecular tomography. On the application side, an NIR FRET pair is validated with in vitro cell-based, ex vivo and in vivo studies and applied to monitor iron-binding transferrin protein endocytic process in tumor-bearing small animals.

If one fluorophore (donor) allows its energy to radiationless propagated from itself to another fluorophore (acceptor) in several nanometers, this process is regarded as Förster Resonance Energy Transfer (FRET). By detecting the change from their distance and coupling orientation, FRET can estimate protein-protein interactions at a nanoscale, which overcomes the resolution limitation of current imaging techniques, such as fluorescence microscopy or super-resolved imaging microscopy. Unfortunately, the FRET method has not been broadly translated from in vivo cell-based studies to preclinical studies, in which the in vivo physiological information is crucial for investigating diseases, optimizing drugs, as well as basic biological research.