Gadolinium contrast agents
Citation, DOI and article data
Gadolinium-based contrast media (GBCM), gadolinium-based contrast agents (GBCAs), or simply gadolinium contrast agents are molecular complexes containing the rare earth metal gadolinium, chelated to a carrier ligand. They are a type of paramagnetic contrast agent, which are the primary class of MRI contrast media. The intravenous route of administration is the most common.
The gadolinium ion is useful as an MRI contrast agent because it has seven unpaired electrons, which is the greatest number of unpaired electron spins possible for an atom.
- 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)
- IV contrast is not required for all MR angiography, MR venography and MR perfusion sequences
- some of the MRI contrast media employ other chemical elements than gadolinium, e.g. iron, manganese
GBCAs are categorized ionic or nonionic based on their net charge in solution and as linear or macrocyclic based on the molecular structure of the organic ligand.
Mechanism of enhancement
Tissue that demonstrates enhancement following administration of gadolinium-containing IV contrast does so because of a combination of the following two mechanisms 3:
- intravascular enhancement
- interstitial enhancement
Which one of these dominates depends on the characteristics of the tissue.
Effect on T2 relaxation time
Gadolinium shortens T2 relaxation time and actually results in a hypointense signal, indeed at very high concentrations of gadolinium contrast media a signal void may appear to be present.
Most gadolinium contrast agents are excreted through the renal system and therefore have a prolonged half-life in renal failure.
Allergic reactions to gadolinium-based contrast agents are relatively rare, occurring in 0.04-0.3% of administrations, of which 0.4-9% are severe 1-6. These adverse reactions can be acute or chronic.
There is 30% possibility in recurrence of hypersensitivity in patients those who known to have a previous hypersensitivity episode to gadolinium based contrast media 9. The risk if adverse reactions are higher in patients with bronchial asthma, known allergy to iodine based contrast media or others.
Gadolinium deposits in trace amounts in various organs, especially the brain (e.g. dentate nucleus of the cerebellum, globus pallidus) following administration of gadolinium-based contrast agents. The clinical significance of gadolinium deposition is heretofore unknown 4.
Nephrogenic systemic fibrosis
See full article here: nephrogenic systemic fibrosis (NSF)
There is an association between the use of gadolinium-based contrast agents in patients with renal failure and nephrogenic systemic fibrosis (NSF). However, nearly all unconfounded cases of NSF have been linked to one of the three linear Group I GBCAs. Recent consensus states that the risk of NSF or nephrotoxicity following administration of a Group II GBCAs is extremely low and that the potential harm of delayed diagnosis or misdiagnosis from delaying or withholding Group II GBCAs for a clinically indicated MRI in a patient with acute kidney injury or estimated glomerular filtration rate less than 30 mL/min per 1.73 m2 may outweigh the risk of NSF, regardless of dialysis status 11.
The ACR has divided gadolinium-based contrast agents (GBCAs) into three groups depending on the risk of NSF 10,11,12.
- Group I linear (greatest number of reported NSF cases)
- Group II macrocyclic (few, if any, cases of NSF)
Group III linear ionic (few, if any cases of NSF but limited data available)
- gadoxetic acid disodium salt (Eovist® Primovist® )
Macrocyclic agents have less chemical instability than linear agents, resulting in a lower risk of nephrogenic systemic fibrosis and lower gadolinium deposition. On the other hand, cyclic agents have been associated with a higher risk of allergic reactions.
The gadolinium contrast agents can be divided according to whether A) the carrier ligand is linear or macrocyclic and B) whether they are ionic or non-ionic, leading to four groupings.
- linear - ionic
- linear - non-ionic
- macrocyclic - ionic
- Gd-DOTA, gadoterate meglumine (Dotarem® Artirem®)
- macrocyclic - non-ionic
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