For the phantom study, reconstruction with reduction factors 1, 2, 3, and 4 were obtained over the whole FOV using both conventional gridding and KSPA algorithms. MRS images reconstructed using conventional gridding with fully sampled k-space data were used as the reference standard for obtaining difference maps. The reconstructed water images and the difference maps in magnitude are shown , with the difference maps scaled up by 10 for visualization purposes. For reduction factors of 2, 3, and 4, the water images reconstructed using conventional gridding showed significant aliasing artifacts, whereas the water images reconstructed using the KSPA algorithm showed no visible aliasing artifacts.

Spectra reconstructed from representative voxels in the phantom for reduction factors of 1, 2, 3, and 4 are shown in . The results showed similar spectra for different reduction factors with an expected enhanced noise level. Metabolite maps of Cho, Cre, and NAA maps for different reduction factors were obtained by integrating the corresponding peaks. The metabolite maps generated were similar and only NAA maps, and their difference maps with the reference standard are presented in . shows the g-factor maps for reduction factors of 2, 3, and 4. Only regions in the volume of interest are shown for the g-factor maps as an accurate estimation of g-factors require referencing to the NAA signal. The mean and standard deviation of g-factors are 1.03 and 0.17 for reduction factors of 2, 1.16, and 0.22 for a reduction factor of 3, and 1.28 and 0.25 for a reduction factor of 4. As shown in the g-factor maps, there was no significant spatial variability in noise enhancement for reduction factors of 2, 3, and 4.

For the in vivo study, reconstruction with reduction factors of 1, 2, 3, and 4 were also obtained over the whole FOV using the KSPA algorithm. Similar to the phantom study, MRS images reconstructed using conventional gridding with fully sampled k-space data were used as the reference standard for obtaining difference maps. The reconstructed water images and the difference maps with the reference standard reconstructed with fully sampled k-space data using conventional gridding algorithm are shown in with the difference maps scaled up by 10 for visualization purposes.

Spectra reconstructed from representative voxels in the brain for reduction factors 1, 2, 3, and 4 are shown in . The results showed similar spectra for different reduction factors with an expected enhanced noise level. As in the phantom study, similar metabolite maps of Cho, Cre, and NAA maps for different reduction factors were obtained by integrating the corresponding peaks, and only the NAA maps and their difference maps with the reference standard are presented in . shows the g-factor maps for reduction factors of 2, 3, and 4. Once again, only regions in the volume of interest are shown for the g-factor maps. The mean and standard deviation of the g-factors are 1.05 and 0.15 for reduction factors of 2, 1.21, and 0.25 for a reduction factor of 3, and 1.31 and 0.28 for a reduction factor of 4. Similar to g-factor maps from the phantom study, there was no significant spatial variability in noise enhancement for reduction factors of 2, 3, and 4.