Synopsis

Brain MR Elastography (MRE) has been shown to add value to neurological imaging. Brain biomechanical properties are correlated with age, gender, exercise and memory in normal volunteers. In patients with neurological diseases, such as multiple sclerosis, dementia and intracranial tumors, global and regional brain mechanical properties may be sensitive biomarkers. Characterization of the cross-platform performance of regional stiffness measurements using 3D brain MRE is important for future multiplatform, multicenter brain MRE studies. The purpose of our study was to compare regional 3D brain MRE in normal volunteers using two vendor platforms.

INTRODUCTION

METHODS

Regional 3D Brain MRE: A SE-EPI technique was performed using a GE Signa HDxt 3T scanner (Milwaukee, WI) and a Siemens Prisma 3T scanner (Erlangen, Germany), with the same flexible brain MRE passive driver. MRE imaging parameters included: slice thickness/gap = 3 mm/0 mm, 48 axial slices, TR = 3601 ms (GE) or 6420 ms (Siemens), TE = 62.3 ms (GE) or 40 ms (Siemens), FOV = 24×24 cm, acquisition matrix = 72×72, 3 orthogonal motion-encoding gradients, motion sensitivity = 3.0 μm/rad (GE) or 2.5 μm/rad (Siemens), and driver frequency = 60 Hz. A T1-weighted volume for atlas registration⁷ was acquired with 196 sagittal, 1.2-mm-thick, slices (TR/TE = 6.96/2.83 ms, FOV = 27 cm, matrix = 256×256) on the GE platform and was used to generate 7 regions of interest (ROIs) in the brain (cerebellum, cerebrum, deep gray/white matter, frontal, occipital, parietal, and temporal). The ROIs were registered to the MRE images and the median stiffness (kPa) and mean Octahedral Shear Strain Signal-to-Noise Ratio (OSS-SNR) was reported ¹⁰.

Subjects: 5 healthy volunteers without known brain disease were enrolled in this prospective, IRB-approved study, with written informed consent.

Statistical Analysis: For each of the 7 brain regions, Bland-Altman analysis was performed to compare stiffness and OSS-SNR values from the two techniques, and a paired two-sided T-test was also performed (p < 0.05 indicates statistical significance). A linear mixed effect model was used to analyze the component coefficient of variation (CV, standard deviation/mean, %) from each random factor (platform, brain regions and volunteers) and the residual; the intercept was a fixed effect. The total CV due to the different platforms was calculated as $$$ CV_{total}= \sqrt{CV^2_{platform}+CV^2_{residual}} $$$. With this total CV, 95% of the measurements will fall in the rage of $$$ ± 1.96 × CV_{total} $$$ across the two platforms, which is the cross-platform variability. Because the brain regions belong to each individual volunteer, the brain region variable was nested in the volunteer variable in the statistical analysis. JMP 12 Pro (Cary, NC) was used for the statistical analysis.

RESULTS

An example of the 3D brain MRE images from the two platforms is shown in Fig. 1. The brain stiffness and OSS-SNR in the 7 brain regions are shown for each vender in Fig. 2. Among the 7 regions, two (occipital: p = 0.048, temporal: p = 0.048) were observed to have statistically significantly different stiffnesses between the two platforms (Fig. 3a). No regions had a statistically significant difference in OSS-SNR (Fig. 3b). The mixed effect model shows that the platform variable alone was responsible for 0% (OSS-SNR) and 1.4% (stiffness) CV of the model. The residual CV of 22% (OSS-SNR) and 3.6% (stiffness) cannot be explained by the current model (Fig. 3c). For a stiffness measurement in a specific brain region between the two platforms, there was ± 7.6% variation with 95% confidence (Fig. 3d).

DISCUSSION

CONCLUSION

Regional 3D brain MRE is equivalent between GE and Siemens implementations of SE-EPI brain MRE for measuring the stiffness of the cerebellum, cerebrum, deep gray/white matter, frontal, and parietal regions. For a stiffness measurement in a specific brain region, the two platforms have a ± 7.6% variation with 95% confidence.

Acknowledgements

References

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