Evaluation of Flow Technical Foundations: How is it Done?

Phase contrast MR methods are used routinely in clinics world-wide to quantitatively assess the velocity and flow of blood. Phase contrast methods employ additional gradients to sensitize MR imaging sequences (typically fast gradient echo sequences) to motion (1-5). The gradients (a positive and negative amplitude pair, together forming what is referred to as a bipolar gradient set) are applied after the magnetization is tipped into the transverse plane, and the result is that stationary spins are imparted zero net phase, whereas moving spins are imparted a phase that is linearly proportional to their velocity.