Pulse sequences for steady-state saturation of flowing spins.

It is useful to be able to suppress the NMR signal from spins in a flowing fluid, for example for "black-blood" visualization of blood vessels in vivo, for the suppression of flow artifacts, and for the estimation of tissue perfusion by continuous labeling of inflowing arterial spins. This work considers the flow of fluid through a region in which it is subjected to a train of saturation pulses. Computer simulations and in vitro measurements show that a train of equal-duration spoiler pulses produces less effective suppression than does a train of pulses of geometrically increasing duration. It is shown analytically that a long train of ideal equal-duration spoiler pulses converts initial magnetization (0, 0, M0) into a combination of longitudinal and transverse magnetization equal to 0. 29 (-M0, 0, M0) and is therefore unsatisfactory for continuous saturation.