Based on these factors, macrocyclic agents are thought to be less likely related to the release of free Gd3+ in vivo than the linear agents. ![]() 11 The rate of dissociation and thermodynamic stability of the compounds are listed in Table 1. This is one of the mechanisms thought to provoke an inflammatory response resulting in NSF. It has been suggested that the displacement of Gd3+ from the chelating agent, a process known as transmetallation, is involved in the accumulation of free Gd3+ within the body tissues. Among patients with end-stage renal disease, the incidence of NSF in those who received Gd-chelate contrast agent ranged from 2.9% to 5%, and was independent of dose. These reported cases of NSF were related to advanced renal dysfunction and appeared to develop over a period of several days or months. An estimate of kidney function should be performed through laboratory testing for patients at risk of having reduced kidney function. In that case, clinicians should administer only once during an imaging session, and monitor for signs and symptoms of NSF if GBCA is administered to patients with acute kidney injury, or chronic or severe kidney disease. ![]() 9 Recent FDA warnings on the use of gadolinium based contrast agents recommends the avoidance of GBCA in patients suspected or known to have impaired drug elimination, unless the imaging is essential and not available without contrast. Five cases of NSF were unassociated with GBCA. 5 The rate of adverse events has been low and reported to be 1 GBCA. The incidence of side effects is low by comparison with the CT contrast agents. The recommended dose for Eovist is 0.025 µmol/kg (0.1 mL/kg). Close to 100% of the injected dose is eliminated through the kidneys, with the exception of Eovist and MultiHance. The recommended dose for most of these agents depends on the amount of Gd and stands at 0.1 µmol/kg (0.2 mL/kg). Multiphasic contrast evaluation should be performed using a bolus tracking technique. This should also include a precontrast phase. In liver imaging, fast gradient recalled echo T1-weighted (T1W) sequences (such as dynamic 3D-LAVA, GE Healthcare) provide sufficient spatial and temporal resolution to allow for lesion characterization. The GBCAs shorten the T1 relaxation times of the surrounding protons. The last 2 agents, Multihance and Eovist, are partly excreted in bile (hereafter referred to as HPB-Gd agents). Giles, U.K.), Gd-HP-DO3A (ProHance ®, Bracco Diagnostics, Princeton, NJ), Gd-DTPA-BMEA (Optimark™, Covidien Pharmaceuticals, Hazelwood, MO), Gd-EOB-DTAP (Eovist ®, Bayer HealthCare Pharmaceuticals) and Gd-BOPTA (MultiHance ®, Bracco Diagnostics). Examples include Gd-DTPA-BMA (OMNISCAN™, GE Healthcare, Chalfont, St. 3 Since then, other GBCAs have been developed by pharmaceutical companies. This was approved by the United States Food and Drug Administration (FDA) for use in humans in 1988. The first GBCA to be used in clinical practice was Gd-DTPA (MAGNEVIST ®, Bayer HealthCare Pharmaceuticals, Wayne, NJ). The HPB agents are accumulated in the hepatocytes and excreted in bile. The RE agents are accumulated in the reticuloendothelial system (i.e., Kupffer cells in the liver). Based on the biological distribution, GBCAs behave similar to iodinated contrast used in computed tomography (CT), by distributing into the extracellular compartment. The GBCAs and HPB agents are paramagnetic, while the RE agents are super-paramagnetic. The non-GBCAs include reticuloendothelial (RE) agents and hepatobiliary (HPB) agents. They can be divided into gadolinium-based chelated agents (GBCA) and non-GBCA. MR contrast agents have been classified based on their chemical properties, mechanism of action and their biological distribution. We also discuss recent advancements in imaging features of focal liver lesions. ![]() 1,2 In this article, we briefly discuss the various MR contrast agents used in liver imaging, including classification, dose and mechanism of action, and side effects. There has been much discussion about the use of CE MRI of liver masses. With the advent of newer sequences and higher magnetic fields, which allow for greater temporal and spatial resolution, dynamic contrast-enhanced (CE) imaging of the liver now plays a dominant role in lesion characterization. Liver imaging has improved with advances in magnetic resonance imaging (MRI) technology.
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