 Due to the fact that almost all molecules are capable of nonradiative relaxation, photoacoustic microscopy has the potential to image a wide range of endogenous and exogenous agents.By contrast, fewer molecules are capable of radiative relaxation, thus limiting fluorescence microscopy techniques such as one-photon and two-photon microscopy.Current research in photoacoustic microscopy takes advantage of both endogenous and exogenous contrast agents to gain functional information about the body, from blood saturation levels to cancer proliferation rate.