New and rapid pulse sequences for two-dimensional D-T correlation measurements.

Longitudinal relaxation time (T), transverse relaxation time (T) and diffusion coefficient (D) values have been widely used for the characterizations of materials using low field Time Domain Nuclear Magnetic Resonance (TD-NMR). Each parameter can be determined using one-dimensional techniques or their values and correlations by multi-dimensional experiments such as T-T, D-T, and T-D-T. In this work, we studied four D-T sequences for TD-NMR combining Stejskal-Tanner Pulse Gradient Spin Echo (PGSE) diffusion measurement with Inversion-Recovery (IR), Saturation-Recovery (SR), Small-Angle Continuous Wave Free Precession (CWFP-T) and Small-Angle Flip-Flop (SAFF) for T measurement. The results show that rapid D-T measurements can be obtained with single shot CWFP-T and SAFF sequences. The two sequences were two and eight time fast than sequences based on SR and IR, respectively. Although the two fast sequences yield low signal-to-noise ratio signal, they can be as fast as the traditional D-T experiment, or even faster, because it is not necessary to wait a recycle delay of 5 T. Another advantage of the CWFP-T and SAFF methods, when compared to the one based on SR or CPMG (for D-T) are the low specific absorption rate (SAR) of these sequences due the low flip angles in the sequences, that reduces the sample heating problem. These sequences were initially studied using phantom samples. They also were used to study plant tissues to observe the anisotropic diffusion in asparagus. Therefore, they can be useful methods for practical application in TD-NMR.