It is usually administered as a salt of a complex of gadolinium with DTPA (diethylenetriaminepentacetate) with the chemical formula A2[Gd(DTPA)(H2O)]; when cation A is the protonated form of the amino sugarmeglumine the salt goes under the name "gadopentetate dimeglumine". It was described in 1981 by Hanns-Joachim Weinmann and colleagues[4] and introduced as the first MRI contrast agent in 1987 by the Schering AG. It is used to assist imaging of blood vessels and of inflamed or diseased tissue where the blood vessels become "leaky". It is often used when viewing intracraniallesions with abnormal vascularity or abnormalities in the blood–brain barrier. It is usually injected intravenously. Gd-DTPA is classed as an acyclic, ionic gadolinium contrast medium. Its paramagnetic property reduces the T1relaxation time (and to some extent the T2 and T2* relaxation times) in NMR, which is the source of its clinical utility.
Gadolinium based agents may cause a toxic reaction known as nephrogenic systemic fibrosis (NSF) in patients with severe kidney problems.[5][6]
In the complex of Gd3+ and DTPA5− the gadolinium ion is 9-coordinate, surrounded by the 3 nitrogen atoms and 5 oxygen atoms from the carboxylate groups. The ninth coordination site is occupied by a water molecule.Sherry AD, Caravan P, Lenkinski RE (December 2009). "Primer on gadolinium chemistry". Journal of Magnetic Resonance Imaging. 30 (6): 1240–1248. doi:10.1002/jmri.21966. PMC2853020. PMID19938036. This water molecule is labile and exchanges rapidly with water molecules in the immediate vicinity of the gadolinium complex. The gadolinium ion has 7 unpaired electrons with parallel spins and is strongly paramagnetic with an 8S electronic ground state. The relaxation time of the water molecules is affected by their intermittent binding to the paramagnetic centre. This alters their MRI properties and enables contrast enhancement to be achieved.[9]
Concerns
Gadolinium is highly toxic and the accumulation of gadolinium in the brain has become a concern. The EU banned linear chelates in 2017.[10][11]
^Thomsen HS, Morcos SK, Dawson P (November 2006). "Is there a causal relation between the administration of gadolinium based contrast media and the development of nephrogenic systemic fibrosis (NSF)?". Clinical Radiology. 61 (11): 905–906. doi:10.1016/j.crad.2006.09.003. PMID17018301.
^Bashir A, Gray ML, Boutin RD, Burstein D (November 1997). "Glycosaminoglycan in articular cartilage: in vivo assessment with delayed Gd(DTPA)(2-)-enhanced MR imaging". Radiology. 205 (2): 551–558. doi:10.1148/radiology.205.2.9356644. PMID9356644.