Methods, apparatus (100), and computer program products for determining lifetimes and distribution of fluorophores (102) embedded in samples (104). Fluorophores are placed into the sample, light from a source (110) selected to excite the fluorophores illuminates the sample, light emitted from the excited fluorophores is detected by a device (138), and a time-domain analysis is performed on the detected emitted light to determine a three-dimensional distribution of the fluorophores in the sample.