For non-contrast MR Angiography Siemens currently offers two techniques under the category of NATIVE — NATIVE TrueFISP and NATIVE SPACE. NATIVE TrueFISP is based on the TrueFISP (True Fast Imaging with Steady state Precession) sequence, which is a balanced steady state gradient echo technique. The contrast mechanism for NATIVE TrueFISP comes from the preparation of the imaging volume with a spatially selective inversion pulse, resulting in the suppression of stationary tissue within the imaging volume and suppression of signal from blood in the imaging volume (e.g. venous blood). Blood which flows into the imaging volume during the inversion time has the same high-signal characteristics exhibited in that TrueFISP. The contrast is further enhanced by the suppression of the background by the inversion pulse. The sequence can be made selective for arteries or veins by appropriate positioning of the inversion pulse, which can be positioned independently from the imaging volume. The sequence accommodates 3D, 2D, breath-hold, syngo PACE (Prospective Acquisition CorrEction) navigated and respiratory triggered approaches depending on clinical environment.
The NATIVE SPACE technique is a modified variable flip angle 3D Turbo Spin Echo sequence in which the contrast mechanism for visualizing vessels is based on the difference in intravascular signal between maximal and minimal flow during the cardiac cycle. The subtracted image is calculated Inline and with Inline MIP generation, instantaneous clinical results are produced for completely non-invasive MR angiography, further improving workflow at the scanner. The NATIVE SPACE technique can also accommodate multi-phase imaging that enables dynamic angiography — for example, in the lower legs.