Fluorescence imaging is an indispensable method for analysis of diverse cellular and molecular processes, enabling e.g. detection of ions, second messengers or metabolites. Intensity-based approaches, however, are prone to artefacts introduced by changes in fluorophore concentrations. This drawback can be overcome by fluorescence lifetime imaging (FLIM) based on time-correlated single-photon counting. FLIM often necessitates long photon collection times, resulting in strong temporal binning of dynamic processes. Recently, rapidFLIM was introduced, exploiting ultra-low dead-time photodetectors together with rapid electronics. Here, we demonstrate the applicability of rapidFLIM, combined with new and improved correction schemes, for spatiotemporal fluorescence lifetime imaging of low-emission fluorophores in a biological system. Using tissue slices of hippocampi of mice of either sex, loaded with the Na+ indicator ING2, we show that improved rapidFLIM enables quantitative, dynamic imaging of neuronal Na+ sig...