Measuring blood oxygen saturation along a capillary vessel in human.

Measuring oxygen saturation in capillary vessels could provide valuable information on oxygen transport and tissue viability. Most spectroscopic measurement techniques, however, lack the spatial resolution to account for the small vessel dimensions within a scattering tissue and the steep gradients of oxygen saturation levels. Here, we developed a noninvasive technique for image-guided confocal measurement of the optical absorption spectrum from a small region that is comparable in size to the cross section of a single capillary vessel. A wide range of oxygen saturation levels were measured in a single capillary in a human volunteer, with blood deoxygenation rates of 7.1% per hundred microns. The technique could help in studying oxygen exchange dynamics in tissues and could play a key role in future clinical diagnosis and therapeutic applications that require localized functional tissue inspection.