Near-infrared imaging in vivo (II): 2-Dimensional visualization of tissue oxygenation state.

By measuring NIR projection images at 700 and 800 nm, we examined 2-dimensional visualization of Hb oxygenation state in the human forearm of about 50 mm thickness. Equations for selective quantification of oxy-Hb, deoxy-Hb, and SO2 were derived from in vitro experiment, and validity of the equations were checked by using a test phantom which simulates optical properties of living tissues. Forearm occlusion caused increase in 2-dimensional O.D. image at 700 nm, while slight decrease was observed in the image at 800 nm. These results were consistent with changes in NIR spectra caused by the forearm occlusion and explained by Hb deoxygenation and slight decrease in blood volume. Although several uncertain errors seemed to remain in our results, we obtained an essentially reasonable image which demonstrates 2-dimensional changes in Hb oxygenation in the human forearm caused by forearm ischemia.