A double-tuned NMR microprobe with dual RF microcoil
assemblies was fabricated and tested. The coils for the
proton and X (low frequency) nuclei were a variant of a
loop gap resonator and Helmholtz pair, respectively. 1-D
31P spectra of phosphoric acid and 13C-labeled spectra
of methanol were recorded from 1.4-μL samples. Signal
was easily observable in one scan. A COSY spectrum of
13C-labeled acetic acid was acquired in ∼1 h, demonstrating sufficient sensitivity to perform 2-D 13C direct detect
experiments. Thus, the ability to obtain direct detection
spectra of low-γ nuclei is demonstrated.
A miniaturized spiral Helmholtz rf coil was fabricated using standard photolithography and electroplating. A commercial 0.6 T superconductive magnet was used to test the coil performance for both nuclear magnetic resonance (NMR) spectroscopy and imaging applications. NMR spectra of water, methanol, and 1-propanol were obtained as well as static and flow images of a water phantom. The spectral resolution was sufficient to allow chemical identification. Additionally, the viscosity of water was estimated from the experimental velocity profile and was equal to the expected value of 1 cP. Results obtained demonstrated the prospect of using the Helmholtz rf coil as part of a portable low-field NMR system for applications in analytical chemistry and process measurements in industrial settings.
A package of two planar gradient coils combined with an RF coil was microfabricated for low-field MRI measurements of velocity flow profiles. The package generates orthogonal gradients in the radial and velocity encoding directions for standard flow imaging experiments. A commercial 0.6 T superconductive magnet was used to test coil performance. For comparison flow imaging was also performed using a commercial set of gradient coils. Velocity profiles were obtained for several volumetric flow rates of water in tubes with inner diameters of 1.02 mm and 1.4 mm. Velocity resolution was 0.13 mm s−1, comparable to that achieved with commercial gradient coils. The quality of the velocity profile was sufficient for viscosity calculations, and thus permits future utilization of this coil package in the design of a portable MRI viscometer.
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