PULSE SEQUENCES FOR STEADY-STATE SATURATION OF FLOWING SPINS

It is useful to be able to suppress the NMR signal from spins in a flo wing fluid, for example for ''black-blood'' visualization of blood ves sels in vivo, for the suppression of flow artifacts, and for the estim ation of tissue perfusion by continuous labeling of inflowing arterial spins. This work considers the flow of fluid through a region in whic h it is subjected to a train of saturation pulses. Computer simulation s and in vitro measurements show that a train of equal-duration spoile r pulses produces less effective suppression than does a train of puls es of geometrically increasing duration. It is shown analytically that a long train of ideal equal-duration spoiler pulses converts initial magnetization (0, 0, M-o) into a combination of longitudinal and trans verse magnetization equal to 0.29 (-M-o, 0, M-o) and is therefore unsa tisfactory for continuous saturation. (C) 1998 Academic Press.