Membrane gas diffusion measurements with MRI

Zero-mode TEM parallel-plate resonator for high-resolution thin film magnetic resonance imaging

A parallel-plate radio frequency resonator has been designed for high-resolution thin film magnetic resonance imaging. The B1 field produced by the resonator was evaluated through experiment and numerical simulation. The resonator, composed of two conductive plates sandwiching the sample, generates a uniform B1 field parallel to the plates. This feature renders the resonator largely immune to radio frequency screening from conductive layers parallel to the sample. The resonator is custom fabricated according to the dimensions of the sample, yielding a high filling factor. The radio frequency probe is shown to facilitate high-sensitivity depth profiling of thin films. Three variations on the basic design are examined. Since the intention is to employ these resonators for functional studies of membranes, we introduce perforations in the parallel plates to permit mass transfer in and out of the thin films under study. One-dimensional depth profiles of Nafion 117 are presented with and without the addition of additional plates of conductive material. One-dimensional depth profiles of Nafion 1110 and a two-dimensional image of Nafion 117 in an operating fuel cell, which was integrated into the radio frequency circuit, are also illustrated.

Non-Cartesian sampled centric scan SPRITE imaging with magnetic field gradient and B0(t) field measurements for MRI in the vicinity of metal structures

This paper proposes the possibility of spatially resolved MRI measurements undertaken inside metallic cells. MRI has been rarely usable inside conducting vessels due to the eddy currents in the walls caused by switching magnetic field gradients, which render most advanced MRI pulse sequences impossible. We propose magnetic field gradient waveform monitoring (MFGM) for MRI of samples inside metallic cells. In this work the MFGM method was extended to measure the B(0) field temporal evolution associated with gradient waveforms. MFGM was used to observe and correct eddy current effects associated with a metallic cell. High quality centric scan SPRITE images result from such corrections. MRI of samples held under pressure, most notably rock core samples, traditionally employs cells that are non-magnetic and fabricated from polymeric materials. The natural material for high-pressure MRI is however non-ferromagnetic metal given their high tensile strengths and high thermal conductivity. MRI measurement of macroscopic samples at high pressure would be generally possible if metallic pressure vessels could be employed. This study will form the basis of new MRI compatible metallic pressure vessels, which will permit MRI of macroscopic systems at high pressure.

Spatial and temporal mapping of water content across Nafion membranes under wetting and drying conditions

Water transport and water management are fundamental to polymer electrolyte membrane fuel cell operation. Accurate measurements of water content within and across the Nafion layer are required to elucidate water transport behavior and validate existing numerical models. We report here a direct measurement of water content profiles across a Nafion layer under wetting and drying conditions, using a novel magnetic resonance imaging methodology developed for this purpose. This method, multi-echo double half k-space spin echo single point imaging, based on a pure phase encode spin echo, is designed for high resolution 1D depth imaging of thin film samples. The method generates high resolution (<8 microm) depth images with an SNR greater than 20, in an image acquisition time of less than 2 min. The high temporal resolution permits water content measurements in the transient states of wetting and drying, in addition to the steady state.