? Laser scanning, multiphoton fluorescence microscopy has become the method of choice for visualizing developmental and cellular dynamics of living tissue. Recently two new imaging modalities have been developed that provide extra dimensions of data from fluorescence signals. Spectral imaging can allow multiple fluorescent probes to be resolved even if their spectra significantly overlap. Lifetime imaging can provide information about the molecular environment of a probe and also has considerable potential for making accurate FRET measurements, a technique that can measure molecular interactions in vivo. We are proposing to develop a very high-speed time-correlated photon counting system that has 32 parallel channels. ft is designed to be used with a spectrometer that has been developed for multiphoton microscopy so t h a t simultaneous spectral and lifetime data can be acquired at photon counting rates that are more than an order ot magnitude greater that what can be obtained with currently-available instrumentation. The system uses ultra high-speed timer integrated circuits that have recently become available. The proposed system should be economical to produce and is being designed so that it can be easily added to currently available laser scanning microscopes. ? ?
