Magnetic resonance angiography of the portal venous system
Background. Imaging of the portal venous system is necessary in different clinical conditions. Three-dimensional (3D) contrast-enhanced magnetic resonance angiography (MRA) is useful in obtaining high quality portal vein images. A fast gradient-echo MR imaging sequence with minimum repetition time and echo time is used. Up to 40 ml of paramagnetic contrast is injected into peripheral vein as a bolus. The Arrival of contrast medium in the aorta is preferably detected with an automated system, when breath-hold sequence is started, and repeated two times, to depict arterial and venous phase. Maximum-intensity-projection (MIP) imaging is the usual postprocessing method.
Conclusions. In patients with portal hypertension, MRA can present collateral pathway and patency of the portal vein or portosystemic shunt. In portal vein thrombosis MRA provides information about the location and length of portal vein obstruction and helps in therapeutic strategy decision. MRA is a proper technique in Budd-Chiari syndrome, where it is important to determine the location and length of hepatic outflow obstruction. MRA is a very good modality before liver transplantation to depict vascular anatomy and portal vein patency, and after liver transplantation to image possible liver complications. Its limitations include inappropriate positioning of the 3D acquisition slab, respiratory motion artefacts, and metal implants (e.g. pacemaker).