It is becoming increasingly evident that material strength and other mechanical properties depend not only on the density but also on the internal architecture of the structure in question. The internal structures of five different stereolithographic samples were examined noninvasively using high resolution magnetic resonance imaging (MRI). The image analysis techniques of segmentation applied to the acquired images allowed the quantification of the structural parameters mean pore size and pore separation. These parameters were quantified along many angular orientations with a spatial resolution of 0.12 mm, and their distributions clearly revealed the structural anisotropy of the samples.