ABSTRACT
Water and lipids are key participants in many biological processes, but there are few non-invasive methods that provide quantification of these components in vivo, and none that can isolate and quantify lipids in the blood. Here we develop a new imaging modality termed shortwave infrared meso-patterned imaging (SWIR-MPI) to provide label-free, non-contact, spatial mapping of water and lipid concentrations in tissue. The method utilizes patterned hyperspectral illumination to target chromophore absorption bands in the 900-1,300 nm wavelength range. We use SWIR-MPI to monitor clinically important physiological processes including edema, inflammation, and tumor lipid heterogeneity in preclinical models. We also show that SWIR-MPI can spatially map blood-lipids in humans, representing an example of non-invasive and contact-free measurements of in vivo blood lipids. Together, these results highlight the potential of SWIR-MPI to enable new capabilities in fundamental studies and clinical monitoring of major conditions including obesity, cancer, and cardiovascular disease.
Subject(s)
Infrared Rays , Lipids/blood , Optical Imaging/methods , Radio Waves , Spectroscopy, Near-Infrared/methods , Water/analysis , Adipose Tissue, Brown/diagnostic imaging , Adipose Tissue, Brown/pathology , Adult , Animals , Biomarkers/blood , Cardiovascular Diseases/diagnostic imaging , Edema/diagnostic imaging , Edema/pathology , Female , Heterografts , Humans , Inflammation/diagnostic imaging , Inflammation/pathology , Male , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Middle Aged , Neoplasms/diagnostic imaging , Neoplasms/pathology , Obesity/diagnostic imaging , Optical Imaging/instrumentation , Prostatic Neoplasms/diagnostic imaging , Prostatic Neoplasms/pathology , Spectroscopy, Near-Infrared/instrumentationABSTRACT
We demonstrate the possibility of measuring FRET efficiency with a low-cost frequency-domain fluorescence lifetime imaging microscope (FD-FLIM). The system utilizes single-frequency-modulated excitation, which enables the use of cost-effective laser sources and electronics, simplification of data acquisition and analysis, and a dual-channel detection capability. Following calibration with coumarin 6, we measured the apparent donor lifetime in mTFP1-mVenus FRET standards expressed in living cells. We evaluated the system's sensitivity by differentiating the short and long lifetimes of mTFP1 corresponding to the known standards' high and low FRET efficiency, respectively. Furthermore, we show that the lifetime of the vinculin tension sensor, VinTS, at focal adhesions (2.30 ± 0.16 ns) is significantly (p < 10 - 6) longer than the lifetime of the unloaded TSMod probe (2.02 ± 0.16 ns). The pixel dwell time was 6.8 µs for samples expressing the FRET standards, with signal typically an order of magnitude higher than VinTS. The apparent FRET efficiency (