An imaging spectroscopy approach for measurement of oxygen saturation and hematocrit during intravital microscopy

Oxygen supply and partial pressure are key determinants of tissue metabolic status and are also regulators of vascular function including production of reactive oxygen species, vascular remodeling, and angiogenesis. The objective of this study was to develop an approach for the determination of oxygen saturation and hematocrit for individual microvessels in trans- and epi-illumination intravital microscopy.

A spectral approach was used, taking advantage of the availability of commercial imaging systems that allow digital recording of intravital images at a number of predetermined wavelengths within a relatively short time. The dependence of validity and precision of saturation measurements on critical experimental variables (reference spectra, number and selection of wavelengths, exposure time, analysis area, analysis model) was evaluated. In addition, a software approach for two-dimensional analysis of images was developed.

Exposure times per wavelength of about 200 ms and use of up to 50 wavelengths evenly spaced from 500 to 598 nm allow automatic discrimination of microvessels from tissue background (segmentation) with reliable determination of oxygen saturation (in trans- and epi-illumination) and hematocrit (in transillumination).

The present imaging spectroscopy approach allows detailed assessment of oxygen transport and other functional parameters at the microcirculatory level.