The continuously expanding number of fluorescent probes developed for molecular imaging in vivo requires
new instruments, more flexible and with higher quantification power. Responding to those requirements we propose a
new instrument: it combines the sensitivity of time correlated single photon detection with the extended spectral
coverage of a pulsed supercontinuum laser in a sensitive and flexible time-domain platform for in vivo molecular
imaging in small animals. The performance of the system is demonstrated on a case study, using NEO-STEM-PMSR50-
PEG fluorescent silica nanoprobes and sequential imaging of CD-1 nude mice.
Tomographic imaging of a glioma tumor with endogenous fluorescence is demonstrated using a noncontact single-photon counting fan-beam acquisition system interfaced with microCT imaging. The fluorescence from protoporphyrin IX (PpIX) was found to be detectable, and allowed imaging of the tumor from within the cranium, even though the tumor presence was not visible in the microCT image. The combination of single-photon counting detection and normalized fluorescence to transmission detection at each channel allowed robust imaging of the signal. This demonstrated use of endogenous fluorescence stimulation from aminolevulinic acid (ALA) and provides the first in vivo demonstration of deep tissue tomographic imaging with protoporphyrin IX.
Fluorescence molecular tomography (FMT) has the potential to become a powerful quantitative research tool for pre-clinical
applications such as evaluating the efficacy of experimental drugs. In this paper, we show how a time-domain
FMT/microCT instrument can in principle be used to monitor volumetric fluorescence intensity over time for low
fluorophore concentration levels. The experimental results we present relate to Protoporphyrin IX which has a quantum
efficiency as much as two orders of magnitude lower compared to more conventional extrinsic dyes used for molecular
imaging (e.g., Alexa Fluor dyes, Cyanine dyes). Our results highlight the high sensitivity of the single photon counting
technology on which the optical system we have built is based. In conjunction with this system we have developed a
diffuse optical fluorescence reconstruction technique that is robust and shown here to perform adequately even in cases
when the contribution of noise to the data is important. Related to this, we show that the regularization scheme we have
developed is reliable even for low fluorophore concentration values and that no adjustment of the regularization
parameter needs to be made for different levels of noise. This generic reconstruction approach insures that images
reconstructed from data sets acquired at different times and for different fluorescence levels can be compared on an
equal footing.
This study describes the process of design, development and validation of phantoms that mimic the optical
properties of human tissue that could be used for performance verification of Diffuse Optical Tomography (DOT) and
Diffuse Optical Spectroscopy (DOS) instruments. The process starts with choosing and qualifying the ingredients
(hosting matrix, scatterers and absorbers) that allow adjusting of the scattering and absorption coefficients
independently and linearly scalable. Results of the evaluation of liquid and solid phantoms are presented.
In addition, the study evaluates the reproducibility and long-term stability of the designed phantoms. The
results show that some of the phantoms could be reliable references for performance assessment and periodic
calibration-validation of the systems, during pre-clinical and clinical stages.
One important challenge for in-vivo imaging fluorescence in cancer research and related pharmaceutical studies is to discriminate the exogenous fluorescence signal of the specific tagged agents from the natural fluorescence. For mice, natural fluorescence is composed of endogenous fluorescence from organs like the skin, the bladder, etc. and from ingested food. The discrimination between the two kinds of fluorescence makes easy monitoring the targeted tissues. Generally, the amplitude of the fluorescence signal depends on the location and on the amount of injected fluorophore, which is limited in in-vivo experiments. This paper exposes some results of natural fluorescence analysis from in-vivo mice experiments using a time domain small animal fluorescence imaging system: eXplore OptixTM. Fluorescence signals are expressed by a Time Point Spread Function (TPSF) at each scan point. The study uses measures of similarity applied purposely to the TPSF to evaluate the discrepancy and/or the homogeneity of scanned regions of a mouse. These measures allow a classification scheme to be performed on the TPSF's based on their temporal shapes. The work ends by showing how the exogenous fluorescence can be distinguished from natural fluorescence by using the TPSF temporal shape.
In order to precisely recover fluorescence lifetimes from bulk tissues, one needs to employ complex light propagation
models (e.g., the radiative transfer equation or a simpler yet consistent approximation, the diffusion equation) requiring
knowledge of the tissue optical properties. This can be computationally expensive and therefore not practical in many
applications. We present a novel method to estimate the fluorescence lifetimes of multiple fluorophores embedded in
mice. By assuming that the photon diffusion does not significantly change the fluorescence decay slope, the light
propagation is simply modeled as a time-delay during lifetime estimation. Applications of this approach are
demonstrated by simulation, phantom data, and in vivo experiments.
It is expected that the optical signatures of physiological changes are biomarkers reacting faster to breast tumor
evolution than structural changes, meaning that diffuse optical tomography (DOT) could be a promising modality for
monitoring and detecting early changes of the lesion during neoadjuvant treatment. Numerous publications as well as
our preliminary results revealed that the heterogeneity inside the breast and the variability within the population are
challenging for such application. Moreover the sensitivity of the breast physiology to the external pressure applied
during data acquisition is adding a significant variance to the process.
In the present study we evaluate key factors that could make neoadjuvant treatment monitoring, using DOT,
successfully: 1) sensitivity-the clue for earlier detection; 2) repeatability-minimizing the impact of the artificially
induced variance (related with pressure, angle of the view, etc.); 3) accurate co-localization of the ROI within the
sequential measurements performed during the neoadjuvant treatment.
Non-clinical and clinical studies were performed using a multi-wavelength time-domain platform, with
transmission detection configuration, and 3D images of optical and physiological properties were generated using
diffuse propagation approximation. The results of non-clinical studies show that the sensitivity of the system allows
detection and quantification of absorption changes equivalent to less than 1 micromole of blood.
Clinical studies, involving more than 40 patients, revealed that with the appropriate precautions during patient
positioning and compression adjustment, the repeatability of the results is very good and the similarities between the
two breasts are high suggesting that the contra-lateral breast could be used as a reliable reference for DOT as well.
Recent years have seen significant efforts deployed to apply optical imaging techniques in clinical indications. Optical mammography as an adjunct to X-ray mammography is one such application. 3D optical mammography relies on the sensitivity of near-infrared light to endogenous breast chromophores in order to generate in vivo functional views of the breast. This work presents prospective tissue characterization results from a multi-site clinical study targeting optical tomography as an adjunct to conventional mammography. A 2nd -generation multi-wavelength time-domain acquisition system was used to scan a wide population of women presenting normal or suspicious X-ray mammograms. Application specific algorithms based on a diffusive model of light transport were used to quantify the breast's optical properties and derive 3D images of physiological indices. Using histopathological findings as a gold standard, results confirm that optically derived parameters provide statistically significant discrimination between malignant and benign tissue in wide population of subjects. The methodology developed for case reviews, lesion delineation and characterization allows for better translation of the optical data to the more traditional x-ray paradigm while maintaining efficacy. They also point to the need for guidelines that facilitate correlation of optical data if those results are to be confirmed in a clinical setting.
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.
Near-infrared (NIR) technology appears promising as a non-invasive clinical technique for breast cancer screening and diagnosis. The technology capitalizes on the relative transparency of human tissue in this spectral range and its sensitivity to the main components of the breast: water, lipid and hemoglobin. In this work we present initial results obtained using the SoftScan® breast-imaging system developed by ART, Advanced Research Technologies inc., Montreal. This platform consists of a 4-wavelength time-resolved scanning system used to quantify non-invasively the local functional state of breast tissue. The different aspects of the system used to accurately retrieve 3D optical contrast will be presented. Furthermore, preliminary data obtained from a prospective study conducted at The Royal Victoria Hospital of the McGill University Health Center in Montreal will be presented. During this study, 65 volunteers with either abnormal or normal mammograms were enrolled. Analysis of the data gathered by SoftScan demonstrated the potential of the technology in discriminating between healthy and diseased tissue.
Tissue-like phantom experiments were performed in order to investigate the possibility of using the polarized light scattering spectroscopy for skin cancer diagnosis. Using a two-layer model, particle size distribution (PSD) was analyzed for a thin layer of latex spheres on top of 1% Intralipid. The results show that PSD of the latex spheres in the top layer can be extracted with and without a priori information about the shape of the particle size distribution.
Amorphous and hydrogenated (a-SiC:H) as well as crystalline silicon carbide are widespread materials for optoelectronic applications. In this paper, we studied the effect of laser/RF plasma jet treatment of a-SiC:H thin films deposited by Plasma Enhanced Chemical Vapor Deposition, on Si wafers. A Nd:YAG laser ((lambda) equals 1.06 micrometers , tFWHM equals 14 ns, E0 equals 0.015 J/pulse) was used with a fluence of 4 mJ/cm2 incident on the sample, the number of pulses being varied. Plasma treatments were performed in a plasma jet generated by a capacity coupled RF discharge in N2. Different analysis techniques were used to investigate the films, before and after the irradiation: X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. We followed the modification of their structure and composition as an effect of the laser/plasma treatment. A comparison with the excimer and also with the RF treatments was performed.
We present static light scattering measurements of size-shape distributions of biological particles in suspension. Results are compared to the Rayleigh-Debye-Gans theory predictions. They are inverted to retrieve the geometrical parameters of the suspended particles and their size-distribution function. The inversion of data is performed by a combined method using normalized cubic B spline functions and linear programming, which is firstly applied to different sets of simulated data, to study its efficiency and stability in the presence of experimental noise.
Results of the experimental investigations of absorption of laser pulses in amorphous (a-) and crystalline (c-) As2S3 films are presented. The optical transmission hysteresis and reversible film photodarkening at interband excitation of a-As2S3 films in a blue-green spectral region are reported. It was suggested that the nonlinear light absorption could be explained by taking into account the light interaction with nonequilibrium localized lattice vibrations anharmonically coupled with the extended phonons. The measurements of peculiarities of the pulse absorption in crystalline As2S3 films can confirm the proposed explanation.
The influence of some factors that affect the diode pumped solid state lasers (DPSSL) efficiency is analyzed. By using simple phenomenological models few simple and efficient criteria fora n optimal design of such DPSSL in an end-pumping configuration were derived. Some numerical results for a Nd:YAG laser are discussed.
This paper describes an analytical and numerical modeling of photon flux dynamics in passively Q-switched Nd:YAG lasers. The types of solutions to the system of nonlinear- coupled equations are related to various possible modes in which such laser systems may operate: before the bleaching of the saturable absorber, the giant pulse mode, the self- oscillating mode.
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