Hybrid native phosphorescence and fluorescence spectroscopy for cancer detection

Native fluorescence of tissues in the UV and visible spectral regions has been investigated for over two decades. Native fluorescence has been demonstrated to be an accurate tools for distinguish normal tissue from malignant and pre-malignant. Prior investigations have demonstrated that there are several ratio-based algorithms, which can distinguish malignant tissue from normal with high sensitivity and specificity.1 The wavelength combinations used in these ratios isolate the contributions from pairs of tissue fluorophors, one of which is frequently tryptophan (trp), the predominant tissue fluorophore with excitation in the UV (250-300 nm). In this work, algorithms using a combination of native fluorescence and trp phosphorescence were developed which show promise for providing enhanced detection accuracy. Using optical fibers to collect the emission from the specimen allowed interrogation of small regions of tissue, providing precise spatial information. Using a specially designed setup, specimens were excited in the UV and spectra were collected in the range of 300 to 700 nm. Three main emission bands were selected for analysis: 340 nm (trp fluorescence); 420 - 460 nm band (fluorescence from the extra cellular matrix); and 500 - 520 nm (trp phosphorescence). Normal specimens consistently exhibited a low ratio (<10) of 345 to 500 nm emission intensity while this same ratio was consistently high (>15) for cancer specimens. Creating intensities ratio maps from the tissue allows one to localize the malignant regions with high spatial precision. The study was performed on ex vivo human breast tissues. The ratio analysis correlated well with histopathology.