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
In this paper, nebulized or intravenous cetuximab (also known as Erbitux) labeled with NIR dyes is administered in the
lungs of the mouse and imaged using a time-domain fluorescence imaging system (Optix<sup>(R)</sup>). Time resolved
measurements provide lifetime of the fluorescent probes. In addition, through time-of-flight information contained in the
data, one can also assess probe localization and concentration distribution quantitatively. Results shown include
suppression of tissue autofluorescence by lifetime gating and recovery of targeted and non-targeted distributions of
cetuximab labeled with the NIR fluorophores.
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 <i>in-vivo</i> 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 <i>in-vivo</i> experiments. This paper exposes some results of natural fluorescence analysis from <i>in-vivo</i> mice experiments using a time domain small animal fluorescence imaging system: eXplore Optix<sup>TM</sup>. 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 2<sup>nd</sup> -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.
The interest in fluorescence imaging has increased steadily in the last decade. Using fluorescence techniques, it is
feasible to visualize and quantify the function of genes and the expression of enzymes and proteins deep inside tissues.
When applied to small animal research, optical imaging based on fluorescent marker probes can provide valuable
information on the specificity and efficacy of drugs at reduced cost and with greater efficiency. Meanwhile,
fluorescence techniques represent an important class of optical methods being applied to in vitro and in vivo
biomedical diagnostics, towards noninvasive clinical applications, such as detecting and monitoring specific
pathological and physiological processes. ART has developed a time domain in vivo small animal fluorescence
imaging system, eXplore Optix. Using the measured time-resolved fluorescence signal, fluorophore location and
concentration can be quickly estimated. Furthermore, the 3D distribution of fluorophore can be obtained by
fluorescent diffusion tomography. To accurately analyze and interpret the measured fluorescent signals from tissue,
complex theoretical models and algorithms are employed. We present here a numerical simulator of eXplore Optix. It
generates virtual data under well-controlled conditions that enable us to test, verify, and improve our models and
algorithms piecewise separately. The theoretical frame of the simulator is an analytical solution of the fluorescence
diffusion equation. Compared to existing models, the coupling of fluorophores with finite volume size is taken into
consideration. Also, the influences of fluorescent inclusions to excitation and emission light are both accounted for.
The output results are compared to Monte-Carlo simulations.