Pulse sequence strategies for vascular contrast in time-of-flight carotid MR angiography

A systematic evaluation in healthy volunteers of the relative efficacy of various techniques for background suppression to improve two-dimensional (2D) and three-dimensional (3D) time-of-flight magnetic resonance angiography of the cervical carotid arteries was performed. Conventional 2D and 3D FISP (fast imaging with steady-state precession) sequences with flow compensation were compared with modifications of these sequences, including a tracking saturation pulse (2D), prolonged absolute TEs for fat suppression based on T2* decay (2D and 3D), frequency-selective saturation of fat (2D and 3D), in-plane spatial saturation (2D), and magnetization transfer contrast (2D and 3D). The tracking saturation pulse and slight overlap of the excitation sections provided uniform background suppression without impairing depiction of the morphology of the cervical carotid arteries. Frequency-selective fat saturation was the most effective background suppression scheme among the 2D and 3D techniques but was occasionally compromised by local field inhomogeneities. Magnetization transfer contrast provided little suppression of stationary tissues in the neck because of the intrinsic limitations of the coil. In-plane spatial saturation yielded the highest background suppression but reduced apparent arterial diameters and could not be implemented in a 3D version. The T2* decay method not only reduced the apparent size of the vessels but also their signal intensity.