Chart shows phases of gadolinium-based contrast agent (GBCA) and iron nanoparticle (ferumoxytol) MRI changes in early and delayed phases of imaging. A and B, Unlike GBCAs (A), ferumoxytol (B) has long intravascular half-life that results in long blood pool phase before detectable contrast extravasation within brain tumor microenvironment. This facilitates dual assessment of GBCA and ferumoxytol T1-weighted enhancement characteristics for assessment of brain tumor–associated neuroinflammation. (Reprinted from Kidney International, 92, Toth GB, Varallyay CG, Horvath A, et al., Current and potential imaging applications of ferumoxytol for MRI, 47–66, Copyright [2017], www.sciencedirect.com/journal/kidney-international, with permission from International Society of Nephrology)