The principal effect of the SPIO particles is on T2* relaxation and thus MR imaging is usually performed using T2/T2*-weighted sequences in which the tissue signal loss is due to the susceptibility effects of the iron oxide core. Enhancement on T1-weighted images can also be seen with the smaller particles of Resovist. SPIO particles are sequestered by phagocytic Kupffer cells . Phagocytosed SPIO particles in Kupffer cells produce strong T2/T2* relaxation effects in the liver parenchyma. following the administration of this agent, the liver negatively enhances on T2- or T2*-weighted images (ie, it turns dark), resulting in increased conspicuity of pathologic lesions that do not contain reticuloendothelial cells.

A limitation of SPIO is that Structural and functional inhomogeneity in cirrhosis may cause false-positive lesions after SPIO administration.