This work analyzes the microstructure changes of various copper-based powder systems during sintering from 3D images provided by in-situ synchrotron microtomography. The investigated systems include a copper powder with a wide particle size distribution 0-63 µm poured into a quartz capillary, a presintered copper compact with artificially created large pores and a mixture of copper and alumina particles. The experiments were carried out at the European Synchrotron in Grenoble, France. Powders were sintered up to 1060°C under reducing atmosphere in a furnace located between the X-ray source and the detector. During each experiment, 3D images were taken at various times of the thermal cycle. We have obtained images with a resolution of 1.5 microns and the time of acquisition of every image was about one minute. Quantitative analysis of these images allowed the changes of various important parameters to be followed. Such parameters characterize the sintering process at the particle length scale: interparticle coordination, pore size distribution and particle centre to centre distance. Moreover, by tracking the displacement of each particle centre and comparing it to the displacement predicted by classical mean field assumption, we have been able to assess the magnitude of particle rearrangement occurring during sintering. From this set of information, the sintering behaviour of heterogeneous powder systems is discussed with particular emphasis of collective particle phenomena.