A new optical bioimaging technique developed at Rensselaer Polytechnic Institute (RPI) in New York (US) enables the acquisition of time-resolved fluoresce signals from macroscopic samples simultaneously over 16 spectral channels and at picosecond time-resolution. Faster and less expensive than existing technology, the advanced approach could find application in medical diagnostics, guided surgery and drug testing.
Imaging Förster resonance energy transfer
“We combined compressive sensing methodologies with spatial light modulators and time-resolved spectrophotometry to enable the acquisition of dense spatial, temporal and spectral data sets over a large field of view,” explains Xavier Intes, professor of biomedical engineering at RPI. The team demonstrated the pioneering imaging technique by imaging in vivo Förster resonance energy transfer — or FRET. “We reported that we could image efficiently FRET occurrence in preclinical models with far reaching implications for targeted drug delivery assessment,” Intes reports.
Quantitative hyperspectral fluorescence lifetime imaging
Intes notes that hyperspectral lifetime imaging implementations are lacking due to the complexity in acquiring spatial, spectral and temporal data sets. He says especially for clinical and preclinical applications, the current methodologies are typically slow and/or bulky. “We demonstrated that our proposed approach enables the acquisition of time-resolved fluoresce signals over macroscopic samples, for instance a small animal, simultaneously over 16 spectral channels and at picosecond time-resolution,” the professor says, adding that such data sets enable 2D, potentially 3D quantitative hyperspectral fluorescence lifetime imaging, for increased utility in biological applications. “The innovation solves the problem of acquisition of large data sets that are increasingly required in many biomedical applications in which time is a constraint.”
Key applications for this new kind of optical bioimaging technology
Optical imaging techniques are becoming central to molecular investigation of samples at the macroscopic scale, in particular, spectrally resolved imaging facilitating medical diagnosis, such as in guided surgery due to the spectrum-dependent nature of optical contrasts. MFLI, says Intes, offers the advantage of high sensitivity as well as spectra and fluorescence lifetime-based biomarker unmixing. “As an intrinsic characteristic of a fluorophore and its state, fluorescence lifetime can be used to investigate the molecular environment (e.g., pH, ion concentration, pO2, temperature) with robustness, since lifetime measurements are independent of intensity, which can be significantly altered by tissue heterogeneities and depth location.” Thus, he and his team expect the methodology to be useful in “many important biomedical applications.”
Speaking on challenges during the research project, the expert emphasizes that the methodology combines theoretical and instrumental developments that have to be tuned to each other. Namely, the optical chain lead to the alteration of the theoretical scheme for measurements, and hence, calibration protocols had to be devised to mitigate these effects.
Advancing to the next generation of imaging technology: Computational optics
“This work is a contribution to the fast growing field of computational optics,” says Intes, sharing that some of the elements developed in this work are currently being implemented in optical systems dedicated to applications ranging from optical mammography to brain functional imaging by other groups. “We foresee that such developments will lead to faster acceptance by the community of these approaches that can appear daunting at a fist glance.”
“On the engineering side, we are currently starting the optimization phase to improve the overall imaging performances, ranging from faster acquisition times to improved resolution capabilities,” Intes says looking at the road ahead with this research endeavor. “On the application side, we are getting ready to leverage the system capabilities to perform multiplexed FRET imaging in vivo for the quantification of cellular drug delivery non-invasively.”
At the same time, he and his team are beginning to implement theoretical and instrumental tools to fuse this novel optical imaging approach with advanced X-Ray techniques to enable functional, molecular and anatomical imaging in live subjects concurrently.
The work is detailed in the paper “Compressive hyperspectral time-resolved wide-field fluorescence lifetime imaging,” published in Nature Photonics.
Written by Sandra Henderson, Research Editor, Novus Light Technologies Today