Near infrared spectroscopic reflectance imaging: Methods for functional imaging and in-vivo monitoring

Ten near infrared spectroscopic reflectance images were collected from the forearm of a volunteer subject during the course of two ischemia-reperfusion events, one involving complete circulator arrest (full ischemia), the other a compromised venous out flow (venous occlusion). The data from this time series of spectroscopic images was then analyzed using an unsupervised classification scheme. Fuzzy C-means clustering was performed on a spectroscopic imaging cube, on a time series of 760 nm optical density images extracted from the ten timepoints, and on the time series of hemodynamic images derived from applying a two-wavelength, non-isobestic point oxygen saturation algorithm and a six-wavelength Delta hemoglobin, Delta oxy-hemoglobin and Delta cytochrome-aa(3) algorithm to the spectra from each time point. Periods of full ischemia and venous occlusion cause very difference changes in the absorption, scattering and hemodynamic parameters of the forearm. The application of various algorithms to the spectra of each timepoint was successful to varying degrees. Near infrared spectroscopic imaging is shown to be an excellent technique to monitor spatial variations in the tissue response to ischemic events.