Simultaneous acquisition for T2-T2 Exchange and T1-T2 correlation NMR experiments

Rapid measurement of T1*-T2* relaxation correlation with a Look-Locker sequence

Measurement of longitudinal-transverse (T₁-T₂*) relaxation may be time-consuming for samples with a long T₁ lifetime. In this work, a fast measurement method of T₁*-T₂* relaxation correlation was presented based on a saturation recovery Look-Locker sequence. T₁* is the effective T₁ lifetime. The T₁ lifetime can be calculated from the measured T₁* lifetime and acquisition parameters. The new measurement method was verified by numerical simulation. Three representative samples, corn starch, Advil caplets, and shale in the fields of food, pharmaceutics, and energy, were employed as test samples. Comparisons of T₁*-T₂* and T₁-T₂* relaxation correlations show that the new two-dimensional magnetic resonance pulse sequence works well, with a high collection efficiency and good accuracy.

Low field, time domain NMR in the agriculture and agrifood sectors: An overview of applications in plants, foods and biofuels

In this contribution, a selective overview of low field, time-domain NMR (TD-NMR) applications in the agriculture and agrifood sectors is presented. The first applications of commercial TD-NMR instruments were in food and agriculture domains. Many of these earlier methods have now been recognized as standard methods by several international agencies. Since 2000, several new applications have been developed, using state of the art instruments, new pulse sequences and new signal processing methods. TD-NMR is expected, in the coming years, to become even more important in quality control of fresh food and agricultural products, as well as for a wide range of food-processed products. TD-NMR systems provide excellent means to collect data relevant for use in the agricultural environment and the bioenergy industry. Data and information collected by TD-NMR systems thus may support decision makers in business and public organizations.

A benchtop single-sided magnet with NMR well-logging tool specifications - Examples of application

This article was written in honor of Prof. Bernhard Blümich, who has heavily impacted many areas of Magnetic Resonance and, in particular, low-field and portable NMR with numerous advances, concepts, innovations, and applications of this impressive technology. Many years ago, we decided to research and develop single-sided magnets for the area of petroleum science and engineering to study oil reservoir rocks in the laboratory under well-logging conditions. The global urge to exploit oil reserves requires the analysis of reservoirs, intending to characterize the yields before starting the production. Thus, well-logging tools have been developed to estimate the quality of oil and reservoir productivity. NMR logging is included in these analytical tools, and numerous operations using this kind of device were performed since the early 1950s. To contribute to this vital research area, we show the development of a new benchtop single-sided NMR system, with well-logging tool characteristics, a cylindrical sweet spot with 4 cm of diameter and length, with magnetic field of 47 mT centered at 11 cm from the magnet's surface and a constant gradient of 35.7 G/cm along z. This system was used in self-diffusion, T₁-T₂, and D-T₂ measurements of standard liquids and rock cores, demonstrating its functionality.

New and rapid pulse sequences for two-dimensional D-T1 correlation measurements

Longitudinal relaxation time (T₁), transverse relaxation time (T₂) 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 T₁-T₂, D-T₂, and T₁-D-T₂. In this work, we studied four D-T₁ 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-T₁) and Small-Angle Flip-Flop (SAFF) for T₁ measurement. The results show that rapid D-T₁ measurements can be obtained with single shot CWFP-T₁ 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-T₂ experiment, or even faster, because it is not necessary to wait a recycle delay of 5 T₁. Another advantage of the CWFP-T₁ and SAFF methods, when compared to the one based on SR or CPMG (for D-T₂) 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.

Using T1 as a direct detection dimension in two-dimensional time-domain NMR experiments using CWFP regime

The transverse relaxation time (T₂), measured with Carr-Purcell-Meiboom-Gill (CPMG) sequence, has been widely used to obtain the direct dimension data in two-dimension time domain NMR (2D TD-NMR). In this paper we are demonstrating that Continuous Wave Free Precession sequence, with low flip angle (CWFP-T₁), can be an alternative to CPMG as direct detection dimension. CWFP-T₁ is a fast single shot sequence, like CPMG, and yields an exponential signal governed predominantly by the longitudinal (T₁) relaxation time. To obtain the correlations between T₁ and T₂ (T₁-T₂ maps) we are proposing the use of CPMG-CWFP-T₁ pulse sequence. In this sequence CPMG encodes T₂ information (indirect dimension) that modulates the CWFP-T₁ (direct dimension) signal amplitudes. CPMG-CWFP-T₁ experiments were compared with classical 2D sequences such as Saturation-Recovery-CPMG (SR-CPMG) and Inversion-Recovery-CPMG (IR-CPMG) sequence and yields similar results in phantom sample. The experimental time for the 2D sequences, using single scan, shows that SR-CPMG ≤ CPMG-CWFP-T₁ < IR-CPMG. Experimental and simulated results demonstrated that 2D-CPMG-CWFP-T₁ maps have higher resolution in T₁ dimension than the techniques that uses CPMG as direct dimension. CPMG-CWFP-T₁ sequence was also applied to study beef samples, and 2D maps showed higher resolution in the two fat signals than the classical IR-CPMG method.

Saturation-recovery as a T1-filter for T2-T2 exchange NMR

The Inversion-Recovery (IR) technique has already been proposed to be used as a T₁-filter for T₂-T₂ Exchange experiments. However, when the Exchange experiments are employed for studying samples that show T₁ distributions, where the pools are defined by broad relaxation time distributions, e.g. porous media, IR might be difficult to be used as a filter. This paper presents the difficulties found when using IR and proposes the use of Saturation-Recovery (SR) technique as an alternative to T₁-filter.