Magnetic Resonance Angiography: Techniques, Prospects, and Limitations

Vascular flow is characterized by its velocity, velocity spectrum, and pulsatility. The flow in the veins is slow, more or less regular, and mainly modulated by respiration and atrial contraction (Fig. 1a, b). On the contrary, the shape of arterial flow varies according to the vascular resistance. At rest, the extremities have a high resistance vascular system, with only flow during systole and some reversed or no flow during diastole (Fig. 1c). On the other hand, the arterial system of the vital organs like kidneys or brain is characterized by a low resistance, with flow during both the arterial and the venous phases (Fig. 1d).