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The design of a low-light level pixel in CMOS technology for biomedical applications is described. This pixel is also suitable for very high-speed applications, such as fluorescence lifetime imaging (FLIM) used for drug discovery and/or minimally-invasive optical biopsy. In order to achieve high-speed imaging using single-photon detection, a detector with a very low dead-time is needed. The single-photon avalanche-photodiode (SPAD) discussed in this work uses a mainstream deep-submicron CMOS technology in order to achieve ultrahigh-speed operation and high pixel fill-factor, with in-pixel active quench and reset circuits. The paper also presents an innovative approach for reducing the deadtime of the detector and an attractive technique for simultaneous high-speed image acquisition by all the pixels of an array in parallel.