Optical spectroscopy has been shown to be an effective method for detecting neoplasia. Guided Therapeutics has
developed LightTouch, a non invasive device that uses a combination of reflectance and fluorescence spectroscopy for
identifying early cancer of the human cervix. The combination of the multispectral information from the two
spectroscopic modalities has been shown to be an effective method to screen for cervical cancer. There has however
been a relative paucity of work in identifying the individual spectral components that contribute to the measured
fluorescence and reflectance spectra. This work aims to identify the constituent source spectra and their concentrations.
We used non-negative matrix factorization (NNMF) numerical methods to decompose the mixed multispectral data into
the constituent spectra and their corresponding concentrations. NNMF is an iterative approach that factorizes the
measured data into non-negative factors. The factors are chosen to minimize the root-mean-squared residual error.
NNMF has shown promise for feature extraction and identification in the fields of text mining and spectral data analysis.
Since both the constituent source spectra and their corresponding concentrations are assumed to be non-negative by
nature NNMF is a reasonable approach to deconvolve the measured multispectral data. Supervised learning methods
were then used to determine which of the constituent spectra sources best predict the amount of neoplasia. The
constituent spectra sources found to best predict neoplasia were then compared with spectra of known biological
Optical spectroscopy has been shown to be an effective method for detecting neoplasia of epithelial tissues. Most studies to date in this realm have applied fluorescence or reflectance spectroscopy alone as a preferred method of disease detection. We have been developing instrumentation which can acquire both reflectance and fluorescence images of the human cervix in vivo, with the goal of combining multispectral information from the two spectroscopic modalities. This instrumentation has been tested on a group of patients in a clinical setting. We have applied spectral and spatial analysis techniques to the acquired images to assess the capabilities of this technology to discriminate neoplastic from normal cervical tissue.
We describe the fabrication and testing of an optical pH sensor based on fluorescence lifetime measurements and sol-gel technology. The sensor is based on the phenomenon of fluorescence resonance energy transfer (FRET), from a pH-insensitive donor to a pH-sensitive acceptor. The pH-dependent increase in the bromothymol blue acceptor absorbance results in increased energy transfer, reducing the lifetime of the Texas red hydrazide donor. The lifetimes were measured by the phase and modulation of the emission, relative to the modulated incident light, and were found to be insensitive to the total signal level and fluctuations in light intensity. However, the present sensors are sensitive to salt concentration and/or ionic strength. Importantly, this sol-gel sensor is not fragile, providing stable readings for days and can be repeatedly autoclaved without loss of sensitivity to pH. The use of FRET as the pH transduction mechanism can be reliably extended to longer wavelengths, and allows the future use of laser diode excitation sources.