Gadolinium (chemical symbol Gd) is a metallic element that can be chelated into paramagnetic complexes for use as gadolinium contrast media.
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Chemistry
Basic chemistry
Gadolinium is a silvery rare earth metal, and a member of the lanthanides, with the atomic number 64 and an atomic weight of 157.25.
Electronic configuration (neutral atom): [Xe] 4f7 5d1 6s2
Electronic configuration Gd3+: [Xe] 4f7
Gd3+, in accordance with Hund's rule (maximum multiplicity), contains seven unpaired electrons and is thus strongly paramagnetic 4.
Applied chemistry
The gadolinium ion is useful as an MRI agent because it has seven unpaired electrons, which is the greatest number of unpaired electron spins possible for an atom, conferring on it a very large magnetic moment 3.
Gadolinium molecules shorten the spin-lattice relaxation time (T1) of voxels in which they are present. As a result, on T1-weighted images they have a brighter signal. This can have a number of uses:
detection of focal lesions (e.g. tumor, abscess, metastasis)
imaging of vessels in MR angiography or MR venography
calculating MR perfusion parameters (e.g. MTT, CBV, ktrans, Tmax)
Excretion
Most gadolinium contrast agents are excreted through the renal system and therefore have a prolonged half-life in renal failure. It is important to note that the dissociated gadolinium ion is not naturally excreted from the body and instead tends to accumulate in the tissues.
Toxicity
There is a recognized association between gadolinium contrast medium administration and nephrogenic systemic fibrosis (NSF) in patients with severe renal impairment 2. Concern has arisen of deposition of gadolinium in various tissues in the body (e.g. dentate nucleus of the cerebellum, globus pallidus) however, the clinical significance of these deposits is still unknown 4.
Experimental work supports the theory that the toxicity relates to free gadolinium ions dissociating themselves from their chelated ligands and that different contrast agents have different stabilities in solution.
History and etymology
Gadolinium was discovered in 1880 by Jean Charles Galissard de Marignac (1817-1894), a Swiss chemist 1,2. But the element was named after the mineral gadolinite, itself named after Johan Gadolin (1760-1852), a Finnish chemist, who made his name by being the first to extract the rare earth elements in the 1790s 3.
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