Laura McIntosh

Sensitivity characterization of a time-domain fluorescence imager: eXplore Optix

A key issue in the practical application of fluorescence imaging is the presence of a background signal detected during data acquisition when no target fluorescent material is present. Regardless of the technology employed, background signals cannot be completely eliminated, which limits the detection sensitivity of fluorescence imaging systems, especially for in vivo applications. We present a methodology to characterize the sensitivity of fluorescence imaging devices by taking the background effect into account through the fluorescent signal-to-background ratio (SBR). In an initial application of the methodology, tissuelike liquid phantoms with Cy5.5 fluorescent inclusions were investigated experimentally over a wide range of varying parameters, such as tissue absorption coefficient, scattering coefficient, fluorophore concentration, and inclusion location. By defining detectable and quantifiable SBR thresholds, empirical relations are established, and the sensitivity performance of Advanced Research Technologiess eXplore Optix using Cy5.5 is characterized.

Molecular Imaging of the Translocator Protein (TSPO) in a Pre-Clinical Model of Breast Cancer

PurposeTo quantitatively evaluate the utility of a translocator protein (TSPO)-targeted near-infrared (NIR) probe (NIR-conPK11195) for in vivo molecular imaging of TSPO in breast cancer.ProceduresNIR-conPK11195 uptake and TSPO-specificity were validated in TSPO-expressing human breast adenocarcinoma cells (MDA-MB-231). In vivo NIR-conPK11195 biodistribution and accumulation were quantitatively evaluated in athymic nude mice bearing MDA-MB-231 xenografts.ResultsFluorescence micrographs illustrated intracellular labeling of MDA-MB-231 cells by NIR-conPK11195. Quantitative uptake and competition assays demonstrated dose-dependent (p < 0.001) and TSPO-specific (p < 0.001) NIR-conPK11195 uptake. In vivo, NIR-conPK11195 preferentially labeled MDA-MB-231 tumors with an 11-fold (p < 0.001) and 7-fold (p < 0.001) contrast enhancement over normal tissue and unconjugated NIR dye, respectively.ConclusionsNIR-conPK11195 appears to be a promising TSPO-targeted molecular imaging agent for visualization and quantification of breast cancer cells in vivo. This research represents the first study to demonstrate the feasibility of TSPO imaging as an alternative breast cancer imaging approach.

A quantitative time-domain optical imager for small animals in vivo fluorescence studies

ART as developed a time-domain optical molecular imager that recovers size, position and concentration of fluorescent inclusions embedded in turbid media within 15-30% accuracy. Fluorescent lifetime also gives the capability to discriminate different fluorescent sources.

System IRF impact on fluorescence lifetime fitting in turbid medium

Fluorescence lifetime imaging is independent of signal intensity and is thus efficient and robust. Additionally, lifetime can be used to differentiate fluorophores and sense fluorophore micro-environment change. A time-resolved optical system is usually used to measure fluorescent decay kinetics, and then one fits the decay to get lifetime. Since the system impulse response function (IRF) is finite, it impacts lifetime fitting. Deconvolution of the IRF can diminish its impact. In thick tissues, light diffusion due to scattering is also convolved with the fluorescence decay. One can recover the decay using an inversion algorithm. However, processing data in this way is computationally intensive and therefore not practical for real time imaging. We present here results of our studies on the IRF impact to fluorescence lifetime fitting in a turbid medium over a wide range of parameters, using a unique time-domain imaging system. Fluorophores were submerged inside a turbid medium that models tissue. Analytical analysis and computation show that when the lifetime is 1.5 times larger than the FWHM of system IRF, reasonable fluorescence lifetimes can be obtained by fitting the decay tail without taking into account IRF. For small source-fluorophore-detector separation, the effect of optical diffusion on the lifetime fitting is also negligible. This gives a guidance of system precision limit for fluorescence lifetime imaging by fast tail fitting. Experimental data using a fs laser with a streak camera and a pulsed diode laser with PMT-TCSPC for ICG, Cy5.5, and ATTO 680 support the theoretical results.