A numerical investigation of the dependence of NMR signal from pulsatile blood flow in CINE pulse sequences.

The Bloch equations have been solved using numerical techniques for a uniform fluid undergoing periodic pulsatile flow in an NMR imaging experiment. The magnetization and NMR signal have been calculated for experimental parameters appropriate for a CINE sequence (TR = 40 ms, (TE = 14 ms) applied to the study of pulsatile aortic or other arterial flows. The flow velocity profile is obtained by Fourier superposition of different harmonics and it is shown that the steady-state NMR signal has reduced high-frequency components. There is also a time delay between peak signal intensity and flow because the backflow effects that can be as much as 100 ms. The apparent pulsatility depends on the NMR sequence parameters. Some limitations of the phase contrast flow-imaging method are also discussed for nonuniform flow.