MRI of the liver: choosing the right contrast agent
Authors: Welle C.L., Guglielmo F.F., Venkatesh S.K.
Journal: Abdom Radiol (NY), 2020 February, 45:384–392
doi 10.1007/s00261-019-02162-5
Liver MRI is the modality of choice due to its excellent contrast resolution. Correct imaging protocol is crucial for obtaining a correct final diagnosis. Radiologist performing liver MRI should be familiar with types of contrast agents available, diagnostic data they provide as well as their contraindications. Failing to do so can cause diagnosis delay, unnecessary additional imaging and interventional procedures increasing healthcare costs and patient’s morbidity.
In this review article, the authors present contrast agents currently available for liver imaging in United States. They discuss advantages and disadvantages and speculate about product choice in controversial clinical scenarios.
Majority contrast agents used in liver MRI are gadolinium-containing agents. They differ in terms of relaxativity characteristics, protein binding and biodistribution. There are extracellular contrast agents (ECA) and hepatobiliary agents (HBA). Intravascular agents are not considered in this review (1).
ECAs are extracellular compounds which circulate in blood flow and accumulate in areas with increased extracellular space. Based on their molecular composition, ECAs can be either macrocyclic or linear.
HBA agents are actively taken by hepatocytes. They get excreted into the bile, allowing for additional evaluation of hepatic parenchyma and biliary system. Gd-EOB-DTPA (Eovist/Primovist®) is primary HBA compound used for hepatobiliary applications. Gd-BOPTA (MultiHance®) is another product which can also be applied as ECA due to its strong relaxativity. Its HBA properties are inferior to Gd-EOB-DTPA because it has 5% of biliary excretion versus 50% for Gd-EOB-DTPA what accounts for a prolonged hepatobiliary phase which occurs around 1-3 hours after injection (2).
When comparing different types of agents, ECAs offer better evaluation during the arterial phase than HBAs. This is due to less frequent respiratory motion artefacts and higher Gd concentration. ECAs are also excellent for lesion wash-out. Gd-EOB-DTPA uptake by hepatocytes lowers its concentration in extracellular space. Gd-BOPTA, however, has later cellular uptake compared to Gd-EOB-DTPA and can compete with ECA agents in wash-out properties. Biological and relaxativity characteristics of ECAs provide better evaluation of extrahepatic organs and shorten examination time (3).
HBA advantages are their liver-specific biology and subsequent biliary excretion. It is especially useful for liver lesions differentiation as well as for evaluation of biliary ducts diseases.
What contrast agent is right for liver MRI? Different factors will contribute to this decision. If the purpose of examination is to evaluate a lesion detected by another modality, ECA agents are commonly recommended. Optimal arterial, portal venous, and equilibrium phases help in characterization of common lesions like hemangiomas. ECAs are also superior for evaluation and follow-up malignances in extrahepatic organs
Patients with severe hepatic iron deposition/steatosis, poor hepatic function or elevated blood bilirubin level are often suboptimally evaluated with HBAs due to decreased enhancement of liver parenchyma. In such cases, ECAs are also preferred (4).
HBAs are agents of choice for differentiating lesions originating from hepatocytes: FNH vs hepatic adenoma. Other indications for HBAs include detection of liver metastasis in surgical candidates; evaluation of bile ducts abnormalities; anatomical biliary mapping and evaluation of hepatic function (5).
Authors emphasize awareness about genetic variations in Gd-EOB-DTPA uptake. Polymorphisms of liver human anion transporting polypeptide (OATP) 1B1 and OATP1B3 are signal confounders in Gd-EOB-DTPA enhanced liver imaging responsible up to 40% of signal reduction. Several drugs can also compete with Gd-EOB-DTPA uptake.
Sometimes, it is difficult to decide between ECA and HBA. HCC is one of such examples. While ECAs offer better arterial phase, enhancement and wash-out characteristics; HBAs help in detection of small lesions and differentiation between perfusion abnormalities and true lesions. Similarly, small recurrences at the periphery of a treated lesion with ablation are easy to detect with ECA. However, due to unspecific hyperenhancement it the same area, HBA can be more useful sometimes.
Last, it is important to bear in mind differences in international regulations concerning use of contrast agents for MRI. Thus, in Europe restrictions regarding linear agents apply (6). Primovist® and Multihance® are allowed for liver MRI while others like Omiscan®, Magnevist® and OptiMARK® are suspended by European Medicines Agency.
Finally, authors conclude that both ECAs and HBAs offer unique advantages for liver evaluation. Information about examination’s purpose, patient’s history and knowledge about agent’s benefits and drawbacks and local regulations will define the choice of contrast media for specific clinical situation.
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Viktoria Pozdniakova is a fourth-year radiology resident at Diakonhjemmet Hospital in Oslo. She started her residency in Norway after completing undergraduate medical studies in Saint-Petersburg Medical University in Russia in 2009. Viktoria has a broad range of interests in diagnostic imaging and several visiting internships from the Medical University of Graz and Vienna, the Technical University of Zürich, and the harite Klinikk in Berlin. She also did an ESOR visiting scholarship at La Fe University Hospital in Valencia. Viktoria is passionate about liver imaging and considering pursuing her career in abdominal radiology.
Comments may be sent to: v.a.pozdnyakova@gmail.com