Recent studies have demonstrated that spatial heterogeneities in voidage and pore size, over lengthscales of 0.1-1 mm, significantly affect the transport of liquids within a given porous medium. Nuclear magnetic resonance imaging is used to probe the structure of porous catalyst support pellets, and four image analysis techniques characterize the degree and nature of heterogeneities observed in the spin-lattice relaxation-time images of six pellets taken from the same batch. Power-spectrum, cluster-size, and percolation analysis reveal significant differences in spatial correlations and topological characteristics of the sir images. The fractal dimension of all the images, however, is the same suggesting that this quantity characterizes the intrinsic heterogeneities associated with the particular batch of porous pellets studied in this work. The results suggest that structural models of such pellets should account for these macroscopic variations in pellet structure, as characterized here.