Non contrast MR Angio by intrinsic dephasing of true FISP SMS: Ssfp Minus Ssfp

Introduction: Contrast enhanced MRA is widely used due to the large blood signal, the fast acquisition and decreased motion artifacts at high spatial resolution. Very fast sequences and a proper timing of the high dose contrast bolus with the data acquisition, allows the separation of arterial from venous blood vessels. However, in patients with high risk for developing NSF (Nephrogenic Systemic Fibrosis), ce-MRA needs to be avoided. Non-ce MRA techniques can be performed in this group of high-risk patients. Now, new applications will broaden the spectrum of non-ce MRA. There are some alternative techniques: Time-of-flight MR Angio (ToF-MRA) is a noninvasive scheme exploiting the inflow of unsaturated spins perpendicular to the 3D volume, for the application of peripheral vessels a time consuming multi stack measurement is necessary. Phase sensitive methods needs a priori knowledge of the velocity range to avoid phase wrapping of the vessels to be imaged. Here we propose a SSFP (Steady State Free Precession) sequence scheme which is based on the intrinsic very high signal sensitivity of flow phase instabilities from TR to TR interval. It does not need any kind of gating or triggering to separate veins from arteries needed as in non-ce MRA methods like Fresh Blood Imaging FBI [1].