High relaxivity contrast agents in MR angiography of the carotid arteries

Abstract

Magnetic Resonance Angiography (MRA) is one of the most practical diagnostic imaging modalities in the field of neurovascular imaging where risks associated with catheter angiography are high. Evaluation of the extracranial supraortic vessels, and in particular the carotid arteries, is the major field of application for MRA. Before the development of rapid contrast-enhanced (CE) acquisition sequences, the major limitations of MRA pertaining to the carotid arteries was the limited volume of study when 3D time-offlight (TOF) images were acquired, and the saturation effects together with low spatial resolution and movement artifacts when 2D TOF images were acquired. Although technical improvements helped overcome some of these limitations, MRA was still not considered a valid diagnostic alternative to DSA for the evaluation of carotid artery stenosis until the advent of CE acquisitions. Most published studies on CE-MRA of the carotid arteries have been performed with standard gadolinium-based chelates which have similar r1 relaxivity values. Newer gadolinium chelates such as gadobenate dimeglumine (Multihance, Gd-BOPTA, Bracco) have higher intravascular r1 relaxivity than other agents such as Gd-DTPA. This leads to higher vascular peak enhancement of longer duration which has proven beneficial for improving vascular contrast. CEMRA is today considered a highly suitable replacement for conventional MRA techniques and DSA for the evaluation of extracranial carotid artery disease. Compared with unenhanced MRA sequences, CE-MRA permits complete and reliable evaluation of the internal carotid artery from the bifurcation to the intracranial segment. Moreover, the technique offers better overall accuracy for the depiction of tight stenosis and more confident diagnosis of real carotid occlusion versus subocclusive stenosis.