Radiologists, basic scientists and technologists performing contrast-enhanced MR examinations for clinical or research purposes

1. To review chemical properties of commercially available gadolinium based contrast agents (GBCAs)

2. To review applications of commercially available GBCAs

3. To review current recommendations for safe use of GBCAs

This presentation will focus on those contrast agents that are used in clinical practice, namely gadolinium-based contrast agents (GBCAs). These can be broadly divided by their biodistribution, which dictates where they are most effectively clinically. GBCAs fall under 3 main categories: extracellular agents, dual agents and blood pool agents.

The chemical properties of each contrast agent will be described, with regards to structure, pharmacokinetics and relaxivity. In general, GBCAs decrease the T1 relaxation time within blood/ enhancing tissue, appearing relatively brighter on T1 weighted imaging compared to unenhanced tissue.

Biodistribution of the various GBCAs influences how they are best used, and recommended dose:

1. Extracellular agents: the majority of GBCAs, which can aid in the diagnosis and assessment of a wide variety of conditions including neoplasm, infection/ inflammation, and vascular disease. Such agents include gadoterate meglumine (Dotarem), gadoteridol (ProHance), gadobutrol (Gadavist), gadopentatate dimeglumine (Magnevist) and gadodiamide (Omniscan).

2. Dual contrast agents: these are eliminated via both renal and hepatobiliary routes, and therefore have particular application in the assessment of liver disease, particularly focal liver lesions. Gadoxetic acid (Eovist/ Primovist) has approximately 50% hepatobiliary excretion, requiring a shorter delay for hepatobiliary phase imaging than gadobenate dimeglumine (MultiHance).

3. Blood pool agents: gadofosveset trisodium (Ablavar) is an agent that binds to albumin with very high T1 relaxivity. As such, it has particular application in vascular (both arterial and venous) imaging, and may also be applied to tissue perfusion.

Safety considerations are paramount, and there must be sufficient benefit to outweigh risks of contrast agent use. General risks of any contrast agent include allergy and puncture site complications. More specific risks related to gadolinium chelates will also be discussed, including Nephrogenic Systemic Fibrosis, and tissue deposition of contrast, highlighting contrast agents associated with greater risk and at-risk patient groups.

Current recommendations for safe use will be reviewed, and discussion of situations when contrast need not necessarily be used.

Off-label/ Emerging Contrast Agents will be briefly discussed, time permitting, in particular ferumoxytol (Feraheme/ Rienso), a superparamagnetic iron oxide that is clinically approved for treatment of iron deficiency anemia in chronic kidney disease, but that has off-label application as a MRI contrast agent.