A method of real-time imaging of dissolved oxygen concentration, comprising adding an oxygen-quenched phosphorescent composition to a sample, exciting phosphorescence in the composition by illuminating the sample with pulses of light, detecting phosphorescence intensity as a function of position in the sample at first and second times following exciting pulses of light, determining oxygen concentration from the phosphorescence detected at the first and second times, generating an image of the oxygen concentration as a function of position, and repeating the exciting, detecting, determining, and image generating steps to produce a series of images showing the oxygen concentration varying over time.