The study presents a method to estimate the mass transfer rate during primary drying based on mu-computed tomographic measurements of a freeze-dried cake. The study was carried out in a defined setup in a lyomicroscope and confined geometry in which freezing occurred under homogeneous nucleation, and drying under mass-transfer-limited conditions. Pore size distribution, effective diffusivity, and primary drying rates of maltodextrin solutions at different weight concentrations (5%, 10%, and 20% (w/w)) and different cooling rates were determined. Furthermore, the effect of annealing treatment on primary drying rate was studied. Two different annealing treatments were tested, one for 90 min at -10 degrees C and another for 180 min at -5 degrees C. It was shown that solid concentration and annealing above Tg' have the strongest impact on pore size and, subsequently, on primary drying rate. Therefore annealing represents a powerful tool to accelerate primary drying which is the most time-consuming step during lyophilisation.