Measuring non-radiative relaxation time of fluorophores by intensity-modulated laser induced photoacoustic effect

Most biological chromophores and molecules relax primarily through non-radiative processes; therefore, mapping of relaxation time related to non-rediative process can be a potential indicator of tissue status. In order to map relative nonradiative relaxation time, modulated tone-burst light is used to generate photoacoustic signals. Then nonradiative relaxation time is indicated by the amplitude decay rate as modulation frequency increases. The results show that although blood is an optically weak absorber at 808 nm, by using this method a significant enhancement of contrast-tonoise ratio of a blood target compared to pulsed photoacoustic imaging at this wavelength is achieved.