Evaluation of MR angiography at 7.0 Tesla MRI using birdcage radio frequency coils with end caps.

The purpose of this study was to evaluate the feasibility of MR angiography (MRA) at 7.0 Tesla (T) using optimized birdcage (BC) coils with simple end cap configurations. Shielded 16-rung high-pass BC coils were built with identical geometry and compared with different sizes and locations of end caps. To determine whether the end cap configuration was effective, the signal intensity profiles along the superior-inferior (S-I) direction were analyzed in phantom and in vivo human experiments. The effects were also investigated in two-dimensional (2D) and three-dimensional (3D) time-of-flight (TOF) MRA experiments. The signal intensity profiles showed that B1 homogeneity at the service end, that is, the end cap side, was improved as the diameter of the end caps increased and the end cap became closer to the coil end ring. The results of 2D and 3D TOF experiments showed the best improvement of vessel visibility at the BC coil with an 80% end cap, when compared with BC coils with other end cap sizes or without an end cap. In conclusion, the BC coil with an end cap was effective for improving S-I directional homogeneity and suitable for MRA applications, especially at ultrahigh field MRI, such as 7.0T.