Tecniche di angio-RM: Stato dell'arte

Abstract

MRI is very sensitive to flow effects and they may be exploited to develop non-invasive techniques for imaging of the vascular anatomy. These techniques are referred to as Magnetic Resonance Angiography (MRA). MRA techniques can be classified in two major categories: time-of-flight (TOF) and phase contrast (PC). Both techniques rely on different physical effects; inflow-enhancement and flow-induced phase shift respectively. In both techniques definitive angiographic images are obtained by means of post-processing of data with a Maximum Intensity Projection (MIP) algorithm. TOF MRA can be classified in three major categories: 2D-sequential, 3D-volumetric and multi-slab-3D (MOTSA). To improve vessel-background contrast in TOF MRA, new techniques, such as ramped radiofrequency (rf), pulses across the slab to partially compensate for the progressive saturation of spins (TONE) and magnetization transfer contrast (MTC) have been introduced. In PC MRA complex subtraction of two data sets with a different amount of flow sensitivity produces an image with signal intensities depending on flow velocity. Quantitative information about flow velocity and flux can also be obtained in PC MRA. More recently the use of contrast agents with ultrafast imaging (CE-MRA) has shown significant improvements in the delineation of the vessel lumen.