PGSE MASSEY, A SEQUENCE FOR OVERCOMING PHASE INSTABILITY IN VERY-HIGH-GRADIENT SPIN-ECHO NMR

Whereas the resolution in conventional (k space) imaging is limited by signal-to-noise, the dynamic displacement resolution in pulsed-gradient spin-echo (q space) imaging is limited only by the practical difficulty in producing well-matched gradient pulses. At present this limit is of order 100 nm and the lowest self-diffusion coefficients which can be measured using PGSE NMR are around 10-14 m2 s-1. Here a new pulse sequence is proposed (PGSE-MASSEY) in which the gradient pulse mismatch can be rendered insignificant by using a read gradient to resolve the associated phase twist. This effect as well as sporadic phase shifts due to sample movement can be removed by signal averaging on the modulus-squared spectrum. © 1990.