Gadolinium-based contrast agents (GBCAs) are molecularly heterogeneous with various chelates holding the paramagnetic element gadolinium. Chelates are either linear or macrocyclic, ionic or nonionic (Table 11-5). Historically, nephrologists did not differentiate among these agents. About 2 decades ago, the novel entity nephrogenic systemic fibrosis (NSF) was first reported by Cowper et al6 in patients with chronic kidney disease (CKD) stage 5 treated by dialysis (CKD5D). Several years later, its association with a GBCA was first noted.