Velocity tagging by rapid cycling in time-of-flight imaging

Images of flowing material in a stationary surround have been obtained using a modified spin-echo sequence with the initial 900 pulse replaced by a small-angle excitation. With this sequence, the longitudinal magnetization of a given volume of material alternates in sign and decreases in magnitude with successive excitation cycles. This results in reduced signal intensity from the stationary material and bands of intensity distribution in regions corresponding to the flowing material. The number, size, and intensity of these bands depend on the relaxation times, the velocity distribution of the moving material, and the pulse sequence timing parameters