Abstracts

Rationale: The most successful treatment for MTS epilepsy hippocampal resection2; however, the lack of consistent imaging evidence from PET and MRI, including hippocampal volume, has limited the early and sensitive detection of MTS and use of surgical treatment options3. Magnetic resonance elastography (MRE) is a novel imaging contrast based on tissue viscoelastic properties4 that may have utility in characterizing MTS given large differences in brain mechanical properties in other neurodegenerative conditions5-7.  This technique holds potential as well for very early detection and changing clinical management in the future, possibly avoiding the need for surgery.   Methods: Subjects: Five patients diagnosed with MTS were included in this study (4/1 female/male; ages: 21-58). Diagnosis was based on EEG, PET, and T2-FLAIR enhancement as part of clinical care. Seven age- and gender-matched control subjects without MTS or other epilepsy were also included (6/1 female/male; ages 26-60).Imaging: All scanning was performed using a Siemens 3T Trio scanner. The imaging battery included MRE, T1-weighted MPRAGE, and T2-FLAIR. MRE displacement data was acquired using a 3D multislab, multishot spiral sequence10 with high spatial resolution (1.6x1.6x1.6 mm3 isotropic voxels). Vibrations were generated at 50 Hz using a pneumatic driver with soft, pillow-like actuator under the head (Resoundant, Inc., Rochester, MN).Stiffness Estimation: The MRE images were processed to create stiffness measures using the nonlinear inversion (NLI) algorithm11, which returns the viscoelastic complex shear modulus (G=G’+G’’).Analysis: Both hippocampus and TL results were analyzed unilaterally depending on seizure side: affected (epileptogenetic) and unaffected. The left side was affected in all MTS patients, and we chose the left side as the “affected” side in controls for comparison. Each measure and side were compared between groups using a t-test and we report percent differences from control and Cohen’s d effect sizes.  Results: The average hippocampal shear stiffness is lower for the MTS patients than the healthy controls with differences of -13.4% and -15.2% in the affected and unaffected sides, respectively. These differences were not statistically significant, in part due to the small number of subjects currently enrolled in the study. However, large effect sizes (0.64 and 1.21) suggest a high sensitivity of hippocampal stiffness to the presence of MTS. Further, this effect appears to be confined to the hippocampus, as there was minimal effect in the overall TL (-1.6% and 1.1%). Conclusions: Our data indicates that MRE is sensitive to hippocampal degradation that occurs in MTS epilepsy. Here, we show that the hippocampus is softer both on the affected side, but also on the unaffected side, supporting that there is also tissue damage occurring contralateral to seizure onset. This damage is centralized to the hippocampi, as the TL on either side do not appear to exhibit any measurable degradation. Future work will look to expand on these results by examining more patients and controls from in each groups, in order to determine if these effects are significant, and further investigate the role of disease progression in these results to determine the potential role for MRE in the diagnosis and treatment of MTS. Funding: Carle Neuroscience Institute of Carle Foundation Hospital, the Biomedical Imaging Center of the Beckman Institute at University of Illinois, and by a grant from the ACCEL Program of the Delaware Center for Translational Research. The ACCEL Program is funded by NIGMS IDeA Grant U54-GM104941.