ENHANCED LIVER MR - CONTRAST AGENTS AND IMAGING STRATEGY

Contrast enhancement in liver MR can be achieved by a variety of funda mentally different strategies. The published clinical literature regar ding Gd DTPA (gadopentetate dimeglumine), Gd HP-DO3A (gadoteridol), Gd BOPTA (gadobenate dimeglumine), Mn DPDP, and AMI-25 is reviewed, foll owed by a brief discussion of two new iron particulate agents currentl y in preclinical trials. Different imaging techniques also must be use d for visualization of contrast enhancement depending on the specific type of agent utilized. With both gadolinium and manganese chelates, T 1 weighted sequences are used to visualize the effect of the contrast agent. There is positive enhancement (an increase in signal intensity) of normal liver parenchyma post-contrast due to enhanced T1 relaxatio n. With iron particulate agents, T2 weighted sequences are used. In th is instance, there is negative enhancement (a decrease in signal inten sity) of normal liver post-contrast due to enhanced T2 relaxation. Cli nical use at present is limited to the extracellular gadolinium chelat es, with bolus injection and dynamic imaging improving efficacy. Curre nt research also supports the use of a high dose (0.3 mmol/kg) for imp roved lesion detectability, a finding now clinically relevant due to t he recent approval of Gd HP-DO3A at both standard and high doses.