Figure 1.
Flow chart shows the different steps performed in this study.
First (1) data acquisition was performed on 10 healthy subjects at both 1.5 T and 3.0 T field strengths (2), prior knowledge required in the segmentation procedure were determined (3), the brain tissue segmentation procedure were performed, and finally (4) the results were compared between the field strengths.
Figure 2.
Pure tissue clusters WM, GM, CSF, and the mixtures of 50% WM/GM, 50% WM/CSF and 50% GM/CSF shown in the R1-R2-PD space.
Projections on a) R1-R2, b) R1-PD and c) R2-PD planes. The contour lines show the 95% prediction ellipses for simulations with 20. Coloured ellipses are for 3.0 T and corresponding grey clusters are for 1.5 T. This figure shows the differences in tissue characteristics between 1.5 T and 3.0 T field strengths.
Figure 3.
Lookup grids formed by joining together the 95% prediction ellipses of the 3,000 simulated partial-volume clusters (dashed lines).
The transition GM↔WM is shown in green, WM↔CSF in red and WM↔CSF in blue. The top panels a-c shows the results for 1.5 T and the bottom panels d-f shows results for 3.0 T. The solid lines represent the observations in the absence of noise where each diamond corresponds to a change of 20% tissue fractions and each dot correspond to a change of 10% tissue fractions. R1-R2-PD space is projected on a, d) R1-R2, b, e) R1-PD and c, f) R2-PD planes.
Figure 4.
Brain tissue segmentation, of one slice in one healthy subject, at both 1.5 T (top panel) and 3.0 T (lower panel).
From left to right: T2-weighted conventional image, white matter (blue), grey matter (green) and CSF (purple). The red lines are the brain intracranial mask calculated automatically by the SyMRI software.
Figure 5.
Bland-Altman plots comparing the volumes between 1.5 T and 3.0 T.
Volumes of a) WM, b) GM, c) CSF and d) ICV for all 10 subjects measured at 1.5 T and 3.0 T. The dashed lines indicate the limits of agreement and the mean of all measurements (bias).
Figure 6.
Results from voxel-wise t-tests comparing brain segmentation from all 10 subjects between 1.5 T and 3.0 T.
Statistically significant differences are indicated where WM volume is estimated to be larger on the 3.0 T system.