The microstructural evolution of Al–15.8 wt.% Cu slurry held at 555 °C was characterized in situ by X-ray microtomography. The average solid grain coordination and size measured on the reconstructed three-dimensional (3D) objects are compared with the values derived via image analysis carried out on 2D sections of the same objects. A new method is proposed for obtaining the average grain coordination by 2D image analysis. The method proves to be more accurate than the procedure commonly used in the literature.