Time-resolved fluorescence imaging and tomography
Our technological specialty is the use of time-resolved excitation and detection, which allows fluorescence lifetime detection on the nanosecond time scale. Ongoing advances in the design of molecular probes specific to disease pathologies can enable the visualization of multiple pathways/mechanisms/targets simultaneously in vivo, with the use of spectral and lifetime contrast. Our approach is to employ multiple lifetime labeling (or “Lifetime multiplexing”) in combination with spectral contrast, with both intrinsic fluorescence (such as tissue auto-fluorescence, fluorescent protein fluorescence) and extrinsically targeted probes. We are continuously updating this website with more details regarding our technology, but in the mean time, more details of our methods and applications can be found in the sample publications below.
Experimental and theoretical methods for in vivo lifetime tomography
Spatial frequency domain detection applied to time resolved fluorescence:
In Vivo Applications
On the theoretical front, the bases of our approach is a detailed and rigorous theoretical model for time resolved diffuse fluorescence light propagation in turbid media. This model expresses the long-time diffuse time domain signal for each measurement (source-detector pair) as a sum of exponentials with time-dependent decay amplitudes. A particularly attractive outcome of this approach is an algorithm for separating multiple lifetime targets in vivo in three dimensions. This approach is analogous to fluorescence lifetime imaging microscopy (FLIM) as follows: In FLIM, time resolved measurements at each pixel are analyzed as a sum of exponential decays with constant amplitudes. In tomographic FLIM, however, the decay amplitudes are time dependent and are also source detector dependent (at least for point excitation). However, the decay amplitudes become constant for long times and constitute a measurement set for the 3D yield distributions (product of fluorescence lifetime, concentration and extinction coefficient) of the corresponding lifetime components. Thus, if multiple lifetime targets are present within the imaging medium, they can be completely separated in vivo, as if measurements were done separately with only a single fluorophore present at a time. Among the benefits of this approach is the ability to reslove targets located well below the intrinsic point spread function of diffuse optics, as described in this publication.
The powerpoint presentations below provide a step-by-step description of the theoretical model for time resolved fluorescence in diffuse media as detailed in this paper. (You need to click on "View full-size presentation" for the animation to work.)