Kromoscopic analysis: a possible alternative to spectroscopic analysis for noninvasive measurement of analytes in vivo.

Light that penetrates scattering media shows nonlinearities that mask the broad and shallow perturbations made by trace analytes on the background illuminant spectrum. Narrow-band spectroscopic decomposition and deconvolution of such weak bands is a formidable analytical task that pushes the fundamentally linear spectroscopic method beyond practical limits. Kromoscopy is a high-dimensional analog of human color perception; it has broad-band spectrally overlapping detectors similar to those of the visual system, but in the infrared. Analyte bands are integrated fully in two or more detectors with different relative weightings. As in color vision, the analyte information is coded in the direct correlations between detector signals, which individually have higher signal-to-noise ratios than their spectroscopic counterparts. Our Kromoscopic instrument responds directly to glucose in aqueous solution, is not affected by temperature disturbances, and is fast enough to measure physiologically induced Kromoscopic changes in the arterial pulse waveform with high precision.