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

PURPOSE: To determine the feasibility of anatomical neuroimaging studies using 0.55 T MRI. METHODS: 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. RESULTS: 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. CONCLUSION: 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.