Enhanced liver MR: contrast agents and imaging strategy

Contrast enhancement in liver MR can be achieved by a variety of fundamentally different strategies. The published clinical literature regarding Gd DTPA (gadopentetate dimeglumine), Gd HP-DO3A (gadoteridol), Gd BOPTA (gadobenate dimeglumine), Mn DPDP, and AMI-25 is reviewed, followed by a brief discussion of two new iron particulate agents currently in preclinical trials. Different imaging techniques also must be used for visualization of contrast enhancement depending on the specific type of agent utilized. With both gadolinium and manganese chelates, T1 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 relaxation. With iron particulate agents, T2 weighted sequences are used. In this instance, there is negative enhancement (a decrease in signal intensity) of normal liver post-contrast due to enhanced T2 relaxation. Clinical use at present is limited to the extracellular gadolinium chelates, with bolus injection and dynamic imaging improving efficacy. Current research also supports the use of a high dose (0.3 mmol/kg) for improved lesion detectability, a finding now clinically relevant due to the recent approval of Gd HP-DO3A at both standard and high doses.