Influence of the imaging parameters on the signal intensity of three-dimensional MR angiography

On three-dimensional time-of-flight MR angiography (3DFT-MRA), bright signal from flowing blood is produced by the inflowing effect. Inflowing effect decreases as a function of distance into the imaging volume and the decrease of signal relates to the flow velocity and imaging parameters such as TR, TE, flip angle (FA), matrix size and so on. The phantom study was designed to reveal the influence of the imaging parameters. MRA using 3D-FISP sequence were performed on the flowing water with various velocities in the straight tube with various TRs and flip angles. The signal-difference to noise ratio (SD/N) was calculated from the obtained angiographic images. Longer TR gave higher SD/D at every depth of imaging volume. With higher flip angle, SD/N of the flowing water increased at entering point to the 3D imaging volume, however, SD/N decreased at the deep point. At lower flow velocity, SD/N was more rapidly decreased at deep points. At the entering point, SD/N decreased at the flow velocity increased. Considering these influences, imaging parameters should be arranged to the particular objected vessels. (author)