Minimally invasive determination of oxygen concentration can be made by measuring phosphorescence lifetime. We describe a technique for depth-resolved measurements of oxygen concentration using confocal imaging of phosphorescence lifetime. A confocal imaging system is used to obtain depth-resolved measurements of phosphorescence decay. The spatial resolution of the system is characterized in terms of the Line Spread Function and shown to be similar in both lateral and depth directions. Lifetimes are calculated with the use of the Rapid Lifetime Determination technique. One- and two-dimensional quantitative images of oxygen concentration in a test specimen are rapidly generated from luminescence decay data. Measurements are made for oxygen concentrations ranging from 2 to 90 μM. A linear relationship between Pdmeso-tetra-(4-sulfonato-phenyl)-porphine phosphorescence inverse lifetime and oxygen concentration is determined. The presence of an intervening solution of different oxygen concentration does not significantly affect the concentration measurements made with the use of depth-resolved imaging techniques.
Randall L. Plant and David H. Burns, "Quantitative, Depth-Resolved Imaging of Oxygen Concentration by Phosphorescence Lifetime Measurement," Appl. Spectrosc. 47, 1594-1599 (1993)