Image Processing in Contrast-Enhanced MR Angiography

Magnetic resonance angiography (MRA) is a medical imaging modality used to reveal the shape of vessels for diagnosis and therapeutic purposes. This technique receives much attention because it is non-invasive and provides three-dimensional (3D) data sets as opposed to the planar or two-dimensional (2D) projections of conventional x-ray digital subtraction angiography (DSA) [1-7]. Like DSA, contrast-enhanced MRA (CE MRA) uses contrast agents to enhance the vascular lumen. The term post-processing refers to a vast number of image manipulation techniques that facilitate the assessment of arterial and venous structures at an independent console. It refers to all operations from data transfer and image visualization to automatic quantification of vessel lesions. For accurate image interpretation, knowledge of the available image processing tools is mandatory. A varietyof reformatting techniques are now available, and it is advantageous to be well versed in as many of these as possible. Each technique has its own strengths and weaknesses, which can lead to pitfalls and artifacts in inexperienced hands. The main challenges for MRA image processing include proper visualization of vessel lumen, optimized thresholding of vessel-to-background image contrast, and arterial-venous separation. The most widely available methods for post-processing MRA data sets are multiplanar reformatting (MPR), maximum-intensity projection (MIP), subvolume MIP, surface-rendering (SR), volumerendering (VR) and virtual intraluminal endoscopy (VIE). This article will focus on the three main areas of the MRA post-processing systems: data handling, image visualization and vascular analysis (Fig. 1).