Magnetic Resonance Angiography

Abstract

In the last 20 years, magnetic resonance angiography (MRA) has emerged as a valid tool for vascular imaging, augmented by improvements made in MR software and hardware. MRA has proven to be a safe and non-invasive vascular imaging method, which provides images similar to those obtained by classical catheter angiography. MRA methods can be subdivided into two broad categories: DARK BLOOD imaging and BRIGHT BLOOD imaging techniques. Dark blood imaging techniques render vessels black and are especially useful when the focus of interest is not the vessel lumen, but the vessel wall. Bright blood imaging refers to MRA techniques, which enhance the signal intensity of blood within the vessel lumen. Bright blood imaging can be further subdivided into contrast-enhanced (CE) MRA and non-contrast enhanced (non-CE) MRA. CE-MRA relies on the paramagnetic properties of an intravenously injected gadolinium-based contrast agent, which shortens the T1-relaxation time of blood and renders vessels bright on T1-weighted sequences. Conversely, non-CE MRA on the other hand relies entirely on the intrinsic MR properties of flowing blood. Several variations are possible and only those techniques that are relevant to the field of neuroradiology will be discussed in this chapter: CE-MRA, time-of-flight (TOF) MRA, phase-contrast (PC) MRA, arterial spin labelling (ASL) MRA and vessel wall (VW) imaging. We will conclude with an overview of clinical applications and a clinical case.