Influence of imaging parameters, flow velocity, and pulsatile flow on three-dimensional time-of-flight MR angiography: experimental studies.

OBJECTIVE: The purpose of this study is to evaluate the influence of imaging parameters (TR and flip angle), velocity and pulsatility of flow on three-dimensional time-of-flight magnetic resonance (3D TOF MR) angiography by using a flow phantom.
METHODS: The 3D TOF MR angiography of a flow phantom was performed at 1.5-T with various TRs, flip angles and flow velocity. The influence of pulsatile flow was also evaluated.
RESULTS: The imaging parameters and flow velocity affected the saturation effects of inflowing spins. Signal loss due to saturation of inflowing spins was more pronounced with a shorter TR, larger flip angle, or lower flow velocity. However signal intensity of stationary tissue were more suppressed with a shorter TR resulting in a larger signal difference to noise ratio of the flowing fluid. Velocity of the flow also affected the signal loss due to intravoxel phase dispersion, which was apparently observed with a stenotic tube. Pulsatility of flow resulted in decreased intensity of flowing fluid and in ghost artifacts along the phase-encoding and slice-select directions. The spacing between these ghosts and intensity of them were dependent on TR, flip angle and pulse rates.
CONCLUSIONS: Understanding the influence of imaging parameters and flow characteristics is essential for evaluating the MR angiograms or for improving their quality.