In this proposal we introduce the capability of dynamic vascular functional imaging (DVFI) as a novel approach to investigate the spatio-temporal properties of hemoglobin states in large tissue structures. The methodology we have developed employs non-ionizing near infrared optical sources to perform fast, multi-wavelength, tomographic measurements, from which a time series of cross-sectional images are generated. We hypothesize that analysis of these data, using suitable linear and nonlinear time-series analysis methods, is capable of revealing important functional features of the vascular tree, in particular that associated with the microvasculature. Functioning, general purpose, fast optical imaging hardware of our design that is capable of examining nearly any anatomical site within the limits of optical penetration (15 cm thickness) is already in place. Also available, and well tested, is an array of image recovery and analysis software well suited for the investigation of dynamic imaging data. We present extensive preliminaiy evidence documenting our ability to detect and differentiate complex spatio-temporal dynamics associated with measures of hemoglobin states (e.g., blood volume and hemoglobin oxygen saturation levels) in the human forearm and other media in a full cross-sectional view. The objective of the proposed research is to conduct a feasibility study for the purpose of identifying the suitability of our imaging technology to investigate possible functional deficits in muscle of the forearm from otherwise healthy subjects and from those with type-2 diabetes who are at least 50 years of age. For each subject group we will compute various spatio-temporal dynamic features from the imaging data collected from baseline studies and from data collected in response to specific provocations. These data will be evaluated for their correlations with known anatomical landmarks and specific functional properties associated with vascular reactivity. Supplementing these investigations will be numerical studies involving MR maps of the forearm, and measurements performed on laboratory phantoms intended to identiying limits of the accuracy by which different spatio-temporal features can be detected and differentiated.
