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.

Technology

Experimental and theoretical methods for in vivo lifetime tomography

"Tomographic fluorescence lifetime imaging," in Fluorescence Lifetime Spectroscopy and Imaging: Principles and Applications in Biomedical Diagnostics (2014)

Tomographic Lifetime Imaging using Combined Early and Late Arriving Photons (2014)

Resolution below the point spread function for diffuse optical imaging using fluorescence lifetime multiplexing (2014)

Lifetime-based tomographic multiplexing (2010)

A Time Domain Fluorescence Tomography System for Small Animal Imaging (2008)

Time resolved fluorescence tomography based on lifetime contrast (2006)

Spatial frequency domain detection applied to time resolved fluorescence:

Fluorescence lifetime detection in turbid media using spatial frequency domain filtering of time domain measurements (2013)

In Vivo Applications

Cancer Imaging

In vivo tomographic imaging of deep seated cancer using fluorescence lifetime contrast, (2015)

Preclinical whole body time domain fluorescence lifetime multiplexing of fluorescent proteins (2014)

Feasibility of in-vivo imaging of fluorescent proteins using lifetime contrast (2009)

Cardiac Imaging

In vivo fluorescence lifetime detection of an activatable probe in infarcted myocardium (2012)

Presentation by Craig J Goergen at OSA Biomed 2012

Theoretical Methods

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.)