Three-dimensional steady-state MR angiography of the lower extremities

Volume steady-state black-blood magnetic resonance imaging was evaluated as a method for depicting lower extremity vasculature. In steady-state imaging, flow has low signal intensity because motion destroys the coherence of transverse magnetization. To optimize image contrast, computations and measurements were obtained for the three-dimensional (3D) GRASS (gradient-recalled acquisition in the steady state) and 3D SSFP (steady-state free precession) sequences and a range of TRs and flip angles to determine optimal vessel-muscle contrast. The best results were achieved with a 3D GRASS sequence with a TR msec/TE msec of 25/5 and a flip angle of 30 degrees. Coronal images of the femoral and popliteal vessels were obtained in healthy volunteers with various fields of view and voxel sizes. Inflow of unsaturated spins from outside the image region, yielding high signal intensity, could be a potential drawback in steady-state black-blood imaging; however, problems can be avoided by using coronal acquisitions and large fields of view. Steady-state black-blood imaging depicts vessels with high accuracy and is faster and free of flow artifacts.