Abstract : Hybrid pixels were originally developed for charged particle tracking in high energy physics. They now represent a true technology breakthrough when applied to X-ray imaging. Hybrid pixels combine a Si or a CdTe sensor consisting in thousands of pixels of a few hundreds of microns bump bonded to data acquisitioon microcircuits. Used as photon counters, each pixel detects every impinging X-ray that has an energy above one or two thresholds. Applied to X-ray CT, this allows to improve image contrast and to lower exposition dose with respect to traditional charge integration detectors. Moreover, in contrary to CCDs or CMOS cameras, photon couting provides access to the energy of the detected X-rays. This enables the development of spectral CT where the energy of the detected X-rays is analyzed to identify given elements according of their K-edge energy. Hence, the development of hybrid pixels might lead to a new molecular imaging modality that will be intrinsically anatomic and functional.