The major risk factors are renal dysfunction, type of GBCA (highest risk for gadodiamide), and cumulative dose of contrast. The disease has been reported weeks to months after contrast injection and no effective treatment is available. An association with exposure to GBCA is accepted although the exact mechanism remains unknown. Nephrogenic systemic fibrosis (NSF): Systemic fibrosing disorder occurring in patients with renal dysfunction. Extracellular GBCAs are 100% excreted by the kidneys with the exception of gadobenate dimeglumine, which has a 95% renal excretion and a 5% hepatobiliary excretion. The evaluation of the genitourinary tract is conducted using extracellular agents, preferably with high relaxivity.Īpproved extracellular GBCAs include gadoterate meglumine, gadobutrol, gadopentetate dimeglumine, gadodiamide, gadoversetamide, gadoteridol, and gadobenate dimeglumine. Gadolinium-based MR contrast agents (GBCA) are paramagnetic compounds that increase signal intensity (SI) (i.e., enhancement) by increasing the T1 relaxation rate. Judy Squires MD, in Imaging in Urology, 2018 MR Contrast Media A limitation of this agent is that the hepatobiliary phase occurs approximately 1 to 2 hours after ingestion of the contrast agent, which is significantly longer compared with hepatobiliary agents. Gadobenate dimeglumine (MultiHance) is taken up by hepatocytes, and 5% of the administered dose is excreted in bile the remaining 95% is excreted renally. 2,3 Although use of blood pool agents is limited in imaging of solid abdominal organs, it is listed here for completeness.Ĭombined agents have extracellular, blood pool, and hepatobiliary characteristics. 6īlood pool agents stay intravascular for a longer time compared with the extravascular agents and are used for angiography. The delayed hepatobiliary phase ranges from 10 minutes to hours, which is significantly shorter compared with the combined agent gadobenate dimeglumine (MultiHance). 3-6 The average dose is 0.025 mmol/kg for approximately 10 mL, and there is around 50% hepatic and 50% renal excretion. Hepatobiliary agents such as gadoxetic acid (Eovist) are taken up by hepatocytes and excreted through the biliary system, which causes the liver, biliary ducts, and hepatocyte-containing lesions to be T1 hyperintense. These agents are distributed in the extracellular space 20 mL is administered and nearly entirely excreted by the kidneys. 2-6 A complete list and thorough review of the mechanism of action and side effects are beyond the scope of this chapter however, the indications for and MR techniques used to enhance these agents are briefly reviewed.Įxtracellular agents such as gadopentetate dimeglumine (Magnevist) have been in use for the longest time clinically. They can be categorized into five classes: extracellular, hepatobiliary, reticuloendothelial, blood pool, and combined agents. Multiple MR contrast agents are currently in use. Pritesh Patel, in Textbook of Gastrointestinal Radiology, 2-Volume Set (Fourth Edition), 2015 Magnetic Resonance Contrast Agents Since then, various MR contrast agents have been developed and applied in both preclinical and clinical oncology. Gd-DTPA (brand name Magnevist, made by the German company Schering AG) was introduced as the first worldwide paramagnetic MRI contrast agent in the early 1980s. However, this classification is not absolute, since most MR contrast agents may possess the capacities to affect both T1 and T2 relaxation times under certain conditions, such as the use of a T1 contrast agent for the previously mentioned DSC-MRI. By contrast, the substances that mainly shorten T2 relaxation time and reduce the SI of the tissue are called superparamagnetic, T2/T2*, or negative contrast agents. Thus, the substances that mainly shorten T1 relaxation time and cause a positive SI enhancement are called paramagnetic or T1 or positive contrast agents. This allows the protons to relax more rapidly by shortening significantly the T1 or T2 relaxation time of tissues. Briefly, some lanthanide elements such as Gd +3 and transition metal ions (Fe 3+ and Mn 2+) have unpaired electrons, which can interact with the resonating protons of hydrogen by altering the magnetic environment around the protons. The general mechanism of introducing MR contrast agents is to indirectly enhance the tissue or tumor contrast by facilitating altered relaxation of tissue hydrogen protons. Feng Chen, Yicheng Ni, in Cancer Theranostics, 2014 General Mechanisms of MR Imaging Contrast Agents
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