Gadopentetic acid, sold under the brand name Magnevist, is a

gadolinium Gadolinium is a chemical element; it has Symbol (chemistry), symbol Gd and atomic number 64. It is a silvery-white metal when oxidation is removed. Gadolinium is a malleable and ductile rare-earth element. It reacts with atmospheric oxygen or moi ...

-based

MRI contrast agent MRI contrast agents are contrast agents used to improve the visibility of internal body structures in magnetic resonance imaging (MRI). The most commonly used compounds for contrast enhancement are gadolinium-based contrast agents (GBCAs). Suc ...

. It is usually administered as a salt of a complex of gadolinium with DTPA (''d''iethylene''t''riamine''p''ent''a''cetate) with the chemical formula A₂ d(DTPA)(H₂O) when cation A is the protonated form of the

amino sugar In organic chemistry, an amino sugar is a sugar molecule in which a hydroxyl group has been replaced with an amine group. More than 60 amino sugars are known, with one of the most abundant being N-Acetylglucosamine, ''N''-acetyl--glucosamine (a 2- ...

meglumine Meglumine is a sugar alcohol derived from glucose that contains an amino group modification. It is often used as an excipient in pharmaceuticals and in conjunction with iodinated compounds in contrast media A contrast agent (or contrast medium ...

the salt goes under the name "gadopentetate dimeglumine". It was described in 1981 by Hanns-Joachim Weinmann and colleagues and introduced as the first MRI

contrast agent A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...

in 1987 by the

Schering AG Schering AG was a research-centered German multinational pharmaceutical company headquartered in Wedding, Berlin, which operated as an independent company from 1851 to 2006. In 2006, it was bought by Bayer AG and merged to form the Bayer su ...

. 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

intracranial The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain. The skull is also known as the cranium. The cranial cavity is formed by eight cranial bones known as the neurocranium that in human ...

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

s with abnormal

vascularity Vascularity, in bodybuilding, is the condition of having many highly visible, prominent, and often extensively-ramified superficial veins. The skin appears "thin"—sometimes virtually transparent—due to an extreme reduction of subcutaneous fat ...

or abnormalities in the

blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that regulates the transfer of solutes and chemicals between the circulatory system and the central nervous system ...

. It is usually injected intravenously. Gd-DTPA is classed as an acyclic, ionic gadolinium contrast medium. Its

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

property reduces the T1

relaxation time Relaxation stands quite generally for a release of tension, a return to equilibrium. In the sciences, the term is used in the following ways: * Relaxation (physics), and more in particular: ** Relaxation (NMR), processes by which nuclear magneti ...

(and to some extent the T2 and T2* relaxation times) in

NMR Nuclear magnetic resonance (NMR) is a physical phenomenon in which atomic nucleus, nuclei in a strong constant magnetic field are disturbed by a weak oscillating magnetic field (in the near and far field, near field) and respond by producing ...

, which is the source of its clinical utility. Magnevist Bottle

Gadolinium based agents may cause a toxic reaction known as nephrogenic systemic fibrosis (NSF) in patients with severe kidney problems. Compared to other gadolinium-based MRI contrast agents, Gadopentetate dimeglumine (Gd-DTPA2-) chelates allow delayed Gadolinium-enhanced Magnetic Resonance of Cartilage (dGEMRIC). The unique charge characteristic of this complex allows researchers to inversely measure spin-lattice relaxation times as they are related to the concentration of

proteoglycan Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to w ...

aggregates and charged

glycosaminoglycan Glycosaminoglycans (GAGs) or mucopolysaccharides are long, linear polysaccharides consisting of repeating disaccharide units (i.e. two-sugar units). The repeating two-sugar unit consists of a uronic sugar and an amino sugar, except in the case o ...

side chains in

articular cartilage Hyaline cartilage is the glass-like (hyaline) and translucent cartilage found on many joint surfaces. It is also most commonly found in the ribs, nose, larynx, and trachea. Hyaline cartilage is pearl-gray in color, with a firm consistency and has ...

Chemical structure and mode of action

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.. This water molecule is

labile Lability refers to the degree that something is likely to undergo change. It is the opposite ( antonym) of stability. Biochemistry In reference to biochemistry, this is an important concept as far as kinetics is concerned in metalloprotein ...

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

with an ⁸S electronic ground state. The

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.

Concerns

Gadolinium is highly toxic and the accumulation of gadolinium in the brain has become a concern. The EU banned linear chelates in 2017.

References

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