An evaluation of brain volume and cortical thickness measurement at 0.55 T

To determine the feasibility of anatomical neuroimaging studies using 0.55 T MRI.

MPRAGE images with 1 mm isotropic resolution were acquired from a cohort of five healthy subjects using both 0.55 T and 3 T scanners, including repeat scans of each subject at each field strength. The 0.55 T images were denoised to mitigate the effects of high resolution and low-field strength. All scans were analyzed using BrainSuite and FreeSurfer image analysis software, which performs operations including tissue classification, region segmentation/labeling, and thickness/volume measurements for different brain regions. Regional cortical thickness measurements and regional brain volume measurements were compared, and test-retest repeatability at each field strength was evaluated.

For both image analysis software tools, we observed reasonably good correlations between field strengths for cortical thickness measures and regional brain volume measures. Test-retest repeatability analysis suggests that experimental variability was generally higher at 0.55 T than at 3 T, although the amount of difference was dependent on the specific measure being considered and the software tool that was used.

While our sample size was small which limits the strength of the conclusions we can draw, this small-scale pilot study suggests the potential feasibility of certain types of anatomical neuroimaging studies at 0.55 T (especially those involving volume measurements), assuming that appropriate adjustments are made to account for increased experimental variability at this field strength.