Blood-pool Agent-enhanced Magnetic Resonance Angiography of the Abdomen and Thorax

Christian Fink, Henrik J Michaely, Stefan O Schoenberg
European Cardiology, 2007;3(1):64-67
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Contrast-enhanced magnetic resonance angiography (ce-MRA) has become an established and routinely used imaging modality and has largely replaced invasive diagnostic digital subtraction angiography (DSA). There have been ongoing technical developments in magnetic gradient hardware, coil design and pulse sequence design for ce-MRA, resulting in an increased spatial and temporal resolution. The short intravascular half-life and the rapid interstitial distribution of conventional extracellular gadolinium-based contrast agents have limited the imaging time window and spatial resolution of ce-MRA. To overcome these limitations, several intravascular or blood-pool agents have been developed that allow longer acquisition time. In contrast to conventional extracellular MR contrast agents, blood-pool contrast agents are characterised by a longer retention in the vascular compartment. Blood-pool contrast agents are either paramagnetic or superparamagnetic. Paramagnetic blood-pool agents are typically gadolinium-based, whereas superparamagnetic agents are iron oxide particles. The longer retention of blood-pool agents in the vascular space is achieved by binding to macromolecules such as albumin, polysaccharides, polymers or lipids. Blood-pool contrast agents have a higher relaxivity than standard extracellular agents.1

Gadofosveset trisodium (Vasovist®, Bayer Schering Pharma AG, Berlin, Germany) is the first blood-pool contrast agent that has been approved in Europe for ce-MRA for the visualisation of abdominal or limb vessels in adults with suspected or known vascular disease.2 With blood-pool MR contrast agents, the imaging time for ce-MRA is prolonged. Thus, blood-pool agents provide the opportunity for alternative imaging strategies, such as navigator-gated MRA, which cannot be used with conventional extracellular MR contrast agents.1,3 Due to the longer imaging window and higher relaxivity, the spatial resolution of blood-pool agent-enhanced MRA might be increased. In addition to the first-pass bolus imaging phase, blood-pool agent-enhanced MRA can be performed at the steady-state imaging phase. This allows for a prolongation of the arterial examination and submillimetric spatial resolution. In addition, several MRA studies (e.g. time-resolved pulmonary MRA, high-resolution pulmonary MRA and whole-body MR venography) can be performed after a single bolus injection.4

Various classes of blood-pool agents have been developed that differ in their pharmacokinetic and physicochemical properties. Rapid-clearance blood-pool agents show a limited diffusion across normal endothelium, whereas their clearances are equivalent to the glomerular filtration rate. Examples for this type include macromolecular gadolinium chelates such as Gadomer-17 (Bayer-Schering-Pharma, Berlin, Germany) or P792 (Vistarem, Guerbet, Aulnay Sous Bois, France).

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