[MR-based tridirectional flow imaging. Acquisition and 3D analysis of flows in the thoracic aorta]

Tridirectional MR flow imaging is a novel method that extends the well-established technique of phase-contrast flow measurement by vectorial velocity encoding, i.e., by encoding in all three spatial directions. Modern sequence protocols allow the acquisition of velocity vector fields with high spatial resolutions of 1-3 mm and temporal resolutions of 20-50 ms over the heart cycle. Using navigating techniques, data on the entire thoracic aorta can be acquired within about 20 min in free breathing. The subsequent computer-based data processing includes automatic correction of aliasing effects, eddy currents, gradient field inhomogeneities, and Maxwell terms. The data can be visualized in three dimensions using vector arrows, streamlines, or particle traces. The parallel visualization of morphological slices and of the surface of the vascular lumen in 3D enhances spatial and anatomical orientation. Furthermore, quantitative values such as blood flow velocity and volume, vorticity, and vessel wall shear stress can be determined. Modern software systems support the integrated flow-based analysis of typical aortic pathologies such as aneurysms and aortic insufficiency. To what extent this additional information will help us in making better therapeutic decisions needs to be studied in clinical trials.