Pulsed second order fields for parallel acquisition of q-space

Abstract

Acquisition of displacement space with NMR, the conjugate of q-space, has many applications including diffusion, dispersion, velocimetry, tortuosity, and surface to volume ratio measurements in porous media and emulsions. Normally, acquisition of q-space data requires a series of scans over which current pulsed through a gradient coil producing a constant magnetic field gradient is varied to step through q-space. By replacing the constant magnetic field gradient with a second order field whose gradient strength varies in space, a range of gradient values are applied over the sample in a single experiment, and q-space encoded into real space. Using slice selection and a read gradient in conjunction with the second order field, a modified PGSE sequence has been developed which allows the parallel acquisition of q-space in a single-shot experiment for a homogeneous medium. A proof of concept is presented for the parallel acquisition of q-space under the diffusive process, allowing a single-shot, single-excitation, single observation time diffusion measurement to be made. In addition to this, the mapping between real space and q-space leads to a mapping between displacement space and time. This means that for this experiment, without the use of any Fourier transforms, the average propagator may be obtained simply by normalising the acquired echo and plotting it against displacement space.