Techniques for vascular depiction using magnetic resonance angiography

Magnetic Resonance Angiography provides an effective method to evaluate vascular morphology that involves very little risk to the patient. The quality of vascular delineation rests on a suitable choice of imaging parameters. This requires a detailed understanding of both the physics of MRI, and the physiology of blood flow in vivo. Three primary strategies are used: Time-of-Flight MR angiography creates differences in magnetization magnitude between flowing and stationary spins by manipulation of imaging parameters alone; Phase-contrast MR angiography induces changes in the spatial orientation, or phase, of flowing spins relative to stationary spins; and Contrast-Enhanced MR angiography creates differences in magnetization magnitude between flowing and stationary spins by injection of a contrast agent. The anatomy of interest can be covered using either sequential 2D single slice methods or 3D volume acquisition methods. The 2D methods are more sensitive to slow flow while the 3D methods have better resolution. The most appropriate technique to use depends on the presenting clinical situation. As in other angiographic modalities, presentation of the acquired data is of key importance for clear illustration of the vascular anatomy. For this purpose, both reformatted images and projection images are of value.