Fast chemical-shiftT 1 imaging in toroid cavities for the structural analysis of gels and emulsions

Abstract

Fast chemical-shift T~ imaging in toroid cavity cells (TCCs) is introduced and applications to diagnostic ultrasound gel and skin-care ointment are presented. TCCs are an advancement over previously used toroid cavity detectors because they combine resonator and sample container into one part. AdditionaLly, they are removable from the top of the probe and facilitate convenient probe and sample handling. Radially resolved Tt relaxation times in TCCs are obtained through combination of SR (saturation recovery) experiments with the RIPT (rapid imaging with a pulse train) technique. Because of the strong radial B~ gradient in TCCs, only pulse-burst saturation was found satisfactory to generate the most even starting condition for SR experiments. Because RIPT does not resolve chemical-shift information, magnetization and T~ profiles of individual components in mixed samples are monitored by doubLe-transient experiments with selective on-resonance saturation, which is achieved by converging trains of sinc pulses. The new techniques were applied to cellulose hydrogeL and oil-in-water emulsion both exposed to significant shear stress deformation during the charging of the TCC. In both cases, T L profiles as a function of time reveal structural recovery (thixotropy) that slowly progresses from one or more sample interfaces into the bulk.

Design and application of robust rf pulses for toroid cavity NMR spectroscopy

“…A conventional rectangular pulse thus rotates spins near the central conductor by a flip angle that is six times larger than the flip angle experienced by spins near the outer wall of the toroid resonator. This large and well-defined rf inhomogeneity of toroid probes can be exploited, e.g., in spatially resolved diffusion measurements and imaging [19,[31][32][33]. However, the large rf inhomogeneity has limited spectroscopic applications of toroid probes to relatively simple experiments.…”

“…This large and well defined rf inhomogeneity of toroid probes can be exploited, e.g., in spatially resolved diffusion measurements and imaging (19,31,32,33). However, the large rf inhomogeneity has limited spectroscopic applications of toroid probes to relatively simple experiments.…”

“…Details of the toroid design can be found in Ref. (31). Use of an earlier generation console produced systematic errors in the pulse waveform if the pulse generator did not have sufficient time to respond to changes in pulse phase.…”

Improved strategies for NMR diffusion measurements with magnetization-grating rotating-frame imaging (MAGROFI)

“…If MAGROFI is employed with Nyquist gratings, it is termed NYGROFI (Nyquist-grating rotating-frame imaging). Several NYGROFI experiments were conducted with a toroid cavity cell (TCC), 21 i.e., a TCD that simultaneously functions as the sample container. The TCC sample volume was 1.5 mL extending from r min ¼ 1.4 mm to r max ¼ 5.0 mm, and the probe was connected to a standard 100 W transmitter power source at the proton resonance frequency of 200 MHz (BRU-KER Avance DRX 200).…”

“…The TCC sample volume was 1.5 mL extending from r min ¼ 1.4 mm to r max ¼ 5.0 mm, and the probe was connected to a standard 100 W transmitter power source at the proton resonance frequency of 200 MHz (BRU-KER Avance DRX 200). The torus factor 21 was typically about A ¼ 1 mT mm, so that a RIPT pulse width of t P 2 ¼ 10 ms was sufficient 10 to radially image the entire sample. With A ¼ 1 mT mm, the maximum nutation frequency in the sample (i.e., the nutation frequency at r min ) is about 30 kHz, which leads to the maximum B 1 gradient G 1 @ r min ¼ 0.5 T m À1 (50 G cm À1 ).…”