Use of a novel spectral bio-imaging system as an imaging oximeter in intact rat brain

The use of reflection spectrophotometry to measure the spectra of oxy-hemoglobin and deoxy-hemoglobin, strong absorbers of light in the visible region of the spectrum, is a well established method for determining tissue oxygenation. This type of spectral measurement is typically made with a point-spectrometer and provides information only at a single point. An imaging spectrometer, on the other, can measure the hemoglobin spectra at every pixel in the image, thus providing a two-dimensional (spatial) map of tissue ischemia. A novel spectral bio-imaging system based on the SpectraCube™ technology, an optical method based on proven Fourier transform (FT) spectroscopy, has been applied successfully in intact rat brain to measure oxy- and deoxy-hemoglobin spectra. Spectral images containing 10,000 spectra were acquired in a rat ventilated with 30% O₂, and repeated when the inspired gas mixture was switched for 45 seconds to 100% nitrogen. Differences in hemoglobin spectra corresponding to real differences in tissue oxygenation are readily apparent under these two conditions. There is also some evidence that information concerning cytochromes is present in these spectral images, and algorithms are currently being developed to extract the signatures of cytochromes. Details of the spectral bio-imaging system and the results of the measurements made in intact rat brain are discussed.