Oxygen Distributions in Tissue Measured by Phosphorescence Quenching

Abstract

Oxygen dependent quenching of phosphorescence is a powerful new method for measuring oxygen. Although it can be adapted for almost any conditions, it is in measuring oxygen in biological systems, particularly tissue in vivo, that the advantages are most apparent. Some of the important features of the method are: high specificity, minimal invasiveness, absolute calibration with a linear relationship between the measured parameter and oxygen pressure (Stern-Volmer relationship), high accuracy in the physiological range of oxygen pressures, and, since phosphorescence lifetimes are measured, there is no interference by absorption or fluorescence of other tissue pigments. Phosphors are being synthesized that absorb and emit in the near infrared region of the spectrum and are dendrimer-encapsulated to make them non-toxic and soluble in the blood or other biological fluids. These new phosphors permit oxygen measurements throughout substantial thickness of tissue. New phosphorescence lifetime instruments are being tested that can determine the distributions of phosphorescence lifetimes within heterogeneous samples and therefore can measure the distribution of oxygen (oxygen histogram) within the samples.