Abstract: A method and associated apparatus for imaging an oxygen-containing, internal body portion of a host animal which comprises: (a) adding to a body fluid of the host animal a phosphorescent composition (e.g., zinc verdin or a metal porphyrin compound) compatible with said body fluid, the phosphorescence of said composition being quenchable with oxygen in said body portion; (b) irradiating said body portion with a pulse of light at a wavelength and for a time sufficient to effect phosphorescence of said composition to be emitted as light from said body portion; (c) scanning across said body portion to measure the decay of said emitted phosphorescence across said body portion; (d) relating any variations in said decay measured across said body portion to variations in structure of said body portion based on oxygen contained by the body portion; and displaying an image of said body portion.