Sequence for simultaneous measurement of long-limit diffusion and longitudinal relaxation in unilateral NMR.

Abstract

When unilateral NMR is employed with large gradients (20 T/m), measurements of T1 using standard sequences become affected by Brownian motion of spins, particularly in samples with long spin-lattice relaxation times T1 (>2000 ms) and a large diffusion coefficient D (2*10-6 mm2/ms). In light of this, a modified saturation sequence which we have called GAUSS-SR is proposed that allows direct measurement of both D and T1 to be carried out subject to certain constraints. The evolution of Mz magnetization is the main phenomenon to be modeled. The sequence is composed of three main parts: (i) a saturation train designed to render the Mz profile in Gaussian form, (ii) a main delay where by the simultaneous effects of T1 and D on this profile has been solved analytically and (iii) a detection train to ensure a good signal-to-noise ratio. An NMR-MOUSE was used to acquire the desired measurement through this sequence. By relying on the coherence of the longitudinal rather than the transverse magnetization component, the sequence successfully provides the long-limit value of the diffusion coefficient.