k-space filtering in 2D gradient-echo breath-hold hyperpolarized He-3 MRI: Spatial resolution and signal-to-noise ratio considerations

In this work some of the factors that can influence the signal-to noise ratio (SNR) and spatial resolution in MR images of inhale hyperpolarized gases are systematically addressed. In particular the effects of RF depletion of longitudinal polarization and image gradient diffusion dephasing were assessed in terms of their contribution to a k-space filter. By means of theoretical simulation and a novel method of experimental validation using a variable-transverse magnetization of the H-1 signal, systematic quantitative and qualitative investigations of the effects of k-space filtering intrinsic to imaging of hyperpolarized gas were made. A 2D gradient-echo image is considered for a range of flip angles wit! centric, sequential, and half-Fourier Cartesian phase-encoding strategies, and the results are assessed in terms of SNR an spatial resolution in the reconstructed images. Centric phase en coding was found to give the best SNR at higher flip angles, with a trade-off in spatial resolution compared to sequential phase encoding. A half-Fourier approach potentially offers increased SNR through the use of higher flip angles without compromising the spatial resolution, which is comparable to that achieved wit sequential encoding. (C) 2002 Wiley-Liss, Inc.