Optimization of timing in the Carr-Purcell-Meiboom-Gill sequence

The Carr-Purcell-Meiboom-Gill sequence is widely used in grossly inhomogeneous fields to characterize fluid saturated porous media. The distribution of T2 relaxation times is a measure of the distribution of pore sizes. We present here a theoretical analysis of the spin dynamics of this sequence in strongly inhomogeneous fields. Based on this analysis, we optimize the timing of the sequence for maximal signal bandwidth. It is shown that the initial pulse spacing should be decreased by a time 2t90/π. Experimental results in a strayfield set-up confirm the theoretical analysis. The optimized timing increases the measured signal bandwidth and increases the ratio of signal-to-noise by 1.2 dB without affecting the measured relaxation time.