Optical techniques for tissue diagnostics currently are experiencing tremendous growth in biomedical applications, mainly due to their noninvasive, inexpensive, and real-time functionality. Here, we demonstrate a hand-held fiber optic probe instrument based on fluorescence/reflectance spectroscopy for precise tumor delineation. It is mainly aimed for brain tumor resection guidance with clinical adaptation to minimize the disruption of the standard surgical workflow and is meant as a complement to the state-of-the-art fluorescence surgical microscopy technique. Multiple light sources with fast pulse modulation and detection enable precise quantification of protoporphyrin IX (PpIX), tissue optical properties, and ambient light suppression. Laboratory measurements show the system is insensitive to strong ambient light. Validation measurements of tissue phantoms using nonlinear least squares support vector machines (LS-SVM) regression analysis demonstrate an error of <5% for PpIX concentration ranging from 400 to 1000 nM, even in the presence of large variations in phantom optical properties. The mean error is 3% for reduced scattering coefficient and 5% for blood concentration. Diagnostic precision of 100% was obtained by LS-SVM classification for in vivo skin tumors with topically applied 5-aminolevulinic acid during photodynamic therapy. The probe could easily be generalized to other tissue types and fluorophores for therapy guidance and monitoring.
Total resection of glioblastoma multiform (GBM), the most common and aggressive malignant brain tumor, is challenging among other things due to difficulty in intraoperative discrimination between normal and residual tumor cells. This project demonstrates the potential of a system based on a combination of autofluorescence and diffuse reflectance spectroscopy to be useful as an intraoperative guiding tool. In this context, a system based on 5 LEDs coupled to optical fibers was employed to deliver UV/visible light to the sample sequentially. Remitted light from the tissue; including diffuse reflected and fluorescence of endogenous and exogenous fluorophores, as well as its photobleaching product, is transmitted to one photodiode and four avalanche photodiodes. This instrument has been evaluated with very promising results by performing various tissue-equivalent phantom laboratory and clinical studies on skin lesions.
Glioblastoma multiforme (GBM) has long been known as the most common and aggressive form of brain malignancy. The morphological similarities of the malignant and surrounding tissue cause difficulties to distinct the tumors during surgery. In order to achieve better results in resecting malignant brain tumors, a fiber based optical system which can be used intraoperative is developed in this project. In this context, the system hardware details, system controlling interfaces and laboratory testing results are presented. Based on the results obtained from various tests with tissue-equivalent phantoms, the system is proved to have stable performance, robust structure, and have good linearity as well as high sensitivity to low PpIX concentration under strong ambient light conditions.
Accurate quantification of photosensitizers is in many cases a critical issue in photodynamic therapy. As a noninvasive and sensitive tool, fluorescence imaging has attracted particular interest for quantification in pre-clinical research. However, due to the absorption of excitation and emission light by turbid media, such as biological tissue, the detected fluorescence signal does not have a simple and unique dependence on the fluorophore concentration for different tissues, but depends in a complex way on other parameters as well. For this reason, little has been done on drug quantification in vivo by the fluorescence imaging technique. In this paper we present a novel approach to compensate for the light absorption in homogeneous turbid media both for the excitation and emission light, utilizing time-resolved fluorescence white Monte Carlo simulations combined with the Beer-Lambert law. This method shows that the corrected fluorescence intensity is almost proportional to the absolute fluorophore concentration. The results on controllable tissue phantoms and murine tissues are presented and show good correlations between the evaluated fluorescence intensities after the light-absorption correction and absolute fluorophore concentrations. These results suggest that the technique potentially provides the means to quantify the fluorophore concentration from fluorescence images.
We report for the first time continuous flow synthesis of NaYF4:Yb3+/Er3+ upconverting nanocrystals in a
capillary-based microfluidic reaction system. Two sequential temperature steps were employed for heating with
an initial high temperature (180°C) to burst nuclei and a subsequent low temperature (110°C) to promote
growth of the nanocrystals in order to obtain high-performance nanocrystals. The prepared nanocrystals emit
bright green and red emissions under excitation of 974 nm diode laser. Our research opens the door for the
synthesis of upconverting nanocrystals in microfluidic systems.
We report preliminary clinical results of autofluorescence imaging of malignant and benign skin lesions, using pulsed
355 nm laser excitation with synchronized detection. The novel synchronized detection system allows high signal-tonoise
ratio to be achieved in the resulting autofluorescence signal, which may in turn produce high contrast images that
improve diagnosis, even in the presence of ambient room light. The synchronized set-up utilizes a compact, diode
pumped, pulsed UV laser at 355 nm which is coupled to a CCD camera and a liquid crystal tunable filter. The excitation
and image capture is sampled at 5 kHz and the resulting autofluorescence is captured with the liquid crystal filter cycling
through seven wavelengths between 420 nm and 580 nm. The clinical study targets pigmented skin lesions and evaluates
the prospects of using autofluorescence as a possible means in differentiating malignant and benign skin tumors. Up to
now, sixteen patients have participated in the clinical study. The autofluorescence images, averaged over the exposure
time of one second, will be presented along with histopathological results. Initial survey of the images show good
contrast and diagnostic results show promising agreement based on the histopathological results.
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