Signal behaviour in magnetic resonance angiography using rapid field echo sequences

The signal from stationary and flowing material in rapid field echo magnetic resonance imaging sequences is examined theoretically and experimentally. Three sequence variants are considered which differ according to their use of transverse magnetization coherences. One sequence variant attempts to eliminate coherences by cycling the phase of the RF pulses. This approach is analyzed numerically and an optimal RF phase increment is presented. The theoretical response from flowing material is derived by considering the temporal derivatives of position and the gradient waveform moments evaluated over each repetition period. Numerical simulations are used to predict the net response from a voxel.;These signal models are used to optimize time-of-flight field echo angiographic sequence parameters for studies of the extra and intra-cranial arteries by assuming mean blood velocities and transit times respectively. The contrast-to-noise ratio per unit time is the function maximized in this analysis and both 2-D multi-slice and 3-D volume acquisitions are considered.