Vascular tree imaging by magnetic resonance techniques: recent developments

Studies of the circle of Willis based on magnetic resonance angiography have revealed a huge amount of variants where certain connecting vessels are missing or hypo-plastic. State-of-the-art techniques have to be used to provide proper assessment of an individual’s vascular tree anatomy and function. Dr. Günther (mediri GmbH, Heidelberg and University Hospital Mannheim, Germany) has summarized recent developments in non-invasive measurement of macro-vascular blood flow and micro-vascular perfusion and has published some results on cerebral vasculature imaging in Applied Cardiopulmonary Pathophysiology 13 (issue 3-2009).

Magnetic Resonance Angiography (MRA) can be divided into two main categories: MRA with and without the use of intravenously injected contrast agents.

Contrast-enhanced MRA is capable of acquiring time-resolved MRAs by capturing the passage of the contrast agent through the vascular tree at several times. However, since this bolus passage only occurs over a period of several seconds, the time for acquisition is limited. Therefore, a tradeoff exists between image resolution, image quality and temporal resolution.

Methods not using contrast agents include Phase-contrast MRA, Time-of-Flight MRA as well as arterial spin labelling (ASL) techniques which are described in more detail by Dr. Günther. He concludes that within the modern imaging techniques, especially MR techniques can help to assess vessel anatomy and function. Here, arterial spin labelling based techniques promise to yield a greater amount of information than was previously available.