Fluorescence Lifetime Imasing Based on Heterodyne Detection Techinique

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Fluorescence lifetime imaging systems based on heterodyne detection using two dimentional photo-detectors have been developed. An image intensifier (I.I.) and an image dessector tube (IDT) were used as the two dimensional photo-detector.The gain control characteristics of the channel electron multiplier in the gated I.I.tube are utilized to allow heterodyne detection with low-voltage control signal. Heterodyning the modulated fluorescence and reference signals at the multichannel plate of the I.I.tube provides high-frequency response up to several hundred MHz.The P20 fluorecsence screen (decay constant of about 100 mus) of the I.I.tube behaves as a low pass filter for the heterodyned signal, rejecting hi-frequency components. A CCD camera with electronic shutter down to 100 mus coupled to the I.I.slices at the time interval and shutter duration of 100 mus the time sequence of the heterodyned fluorescence image and stores them in the memory of a personal computer. The phase resolved image, i.e.the llife time image is calculated the stored data. The time resolution of the system is about 1 ns.A new technique has also been developed for component pattern analysis based on phase resolved fluorescence image detection and a ratio method calculatin. Differences in fluorescence lifetimes, providing corresponding phase retadations, are positively utilized to estimate the spatial distribution of each component.