OPTIMAL SAMPLING STRATEGIES FOR THE MEASUREMENT OF SPIN-SPIN RELAXATION-TIMES

It is shown how Cramer-Rao theory may be used to determine the optimal sampling pattern for measuring the NMR spin-spin relaxation time, T-2 . The results may also be applied to the measurement of any other expo nential decay, including some pulse sequences for measuring the spin-l attice relaxation time, T-1. The optimal sampling pattern involves pla cing 22% of the sample points at zero time and the remaining 78% at 1. 28 T-2, or, more practically and almost as accurately, one point at ze ro and four at 1.30 T-2, These sampling patterns are very different fr om those commonly used, The Cramer-Rao results are compared with exper imental measurements and computer simulations, Some limitations of the method are described, and its extension to the simultaneous measureme nt of a range of T-2 values is addressed. (C) 1996 Academic Press, Inc .