Controlling susceptibility mismatch effects, signal lifetimes, and SNR through variation of B in MRI of rock core plugs.

H relaxometry measurements of petroleum core plugs are commonly performed on low field magnets (<0.5 Tesla) to reduce the influence of magnetic susceptibility mismatch on measurements of the spin-spin relaxation time, T. The Signal to Noise Ratio (SNR) of the MR signal, however, generally decreases with lower magnetic fields.

Local T-T distribution measurements in porous media.

A novel slice-selective T-T measurement is proposed to measure spatially resolved T-T distributions. An adiabatic inversion pulse is employed for slice-selection. The slice-selective pulse is able to select a quasi-rectangular slice, on the order of 1 mm, at an arbitrary position within the sample.

A high-pressure metallic core holder for magnetic resonance based on Hastelloy-C.

A metallic core holder, fabricated from non-magnetic Hastelloy-C276, has been designed for Magnetic Resonance (MR) and Magnetic Resonance Imaging (MRI) of core plug samples at high pressures and temperatures. Core plug samples, 1.5″ in diameter and 2″ in length, can be tested in the core holder at elevated pressures and temperatures, up to 5000 psi and 80 °C.

Local diffusion and diffusion-T distribution measurements in porous media.

Slice-selective pulsed field gradient (PFG) and PFG-T measurements are developed to measure spatially-resolved molecular diffusion and diffusion-T distributions. A spatially selective adiabatic inversion pulse was employed for slice-selection. The slice-selective pulse is able to select a coarse slice, on the order of 1cm, at an arbitrary position in the sample.

Local T2 measurement employing longitudinal Hadamard encoding and adiabatic inversion pulses in porous media.

Band selective adiabatic inversion radio frequency pulses were employed for multi-slice T2 distribution measurements in porous media samples. Multi-slice T2 measurement employing longitudinal Hadamard encoding has an inherent sensitivity advantage over slice-by-slice local T2 measurements. The slice selection process is rendered largely immune to B1 variation by employing hyperbolic secant adiabatic inversion pulses, which simultaneously invert spins in several well-defined slices.

Mapping B(1)-induced eddy current effects near metallic structures in MR images: a comparison of simulation and experiment.

Magnetic resonance imaging (MRI) in the presence of metallic structures is very common in medical and non-medical fields. Metallic structures cause MRI image distortions by three mechanisms: (1) static field distortion through magnetic susceptibility mismatch, (2) eddy currents induced by switched magnetic field gradients and (3) radio frequency (RF) induced eddy currents. Single point ramped imaging with T1 enhancement (SPRITE) MRI measurements are largely immune to susceptibility and gradient induced eddy current artifacts.

B(1) mapping with a pure phase encode approach: quantitative density profiling.

In MRI, it is frequently observed that naturally uniform samples do not have uniform image intensities. In many cases this non-uniform image intensity is due to an inhomogeneous B1 field. The 'principle of reciprocity' states that the received signal is proportional to the local magnitude of the applied B1 field per unit current.