OPTIMAL TIME SPACINGS FOR T-2 MEASUREMENTS - MONOEXPONENTIAL AND BIEXPONENTIAL SYSTEMS

We have developed an optimal design strategy, i.e. a choice of times a t which the magnetization should be measured, in spin-echo measurement s, when the number of measurements is fixed in advance. Results are gi ven for samples whose relaxation is described by either an exponential or biexponential decay curve. The analysis is based on having an init ial estimate of the ranges in which the relaxation times are likely to lie. The optimal design consists of a set of easily parameterized non -uniformly spaced measurement times, as opposed to present implementat ion of spin-echo experiments. Analysis of the biexponential case shows that an order of magnitude greater signal-to-noise is required to ach ieve T-2 estimates of comparable precision to monoexponential measurem ents with the same number of data points. The optimal designs lead to an improved ability to discriminate between two relatively similar rel axation times. (C) 1998 John Wiley & Sons, Ltd.