Introduction:
Normative T1-relaxation times atlases enable individualized brain tissue abnormality assessments, offering insights into pathophysiological processes1. Mesial temporal lobe epilepsy (MTLE) is the most common adult form and evidence suggests that pathophysiological changes may extend beyond temporal lobe (TL)2. In this study we used normative atlases of T1 to identify tissue alterations.
Methods:
Thirty-seven individuals with MTLE (29 females; 36.7±14.6 years) underwent 3T-brain MRI. Twenty-two out of 37 subjects were drug-responsive and treated with one or more anti-seizure medications (ASMs), while 12/37 patients were drug-resistant to ASMs. Protocol included high resolution T1-weighted MPRAGE (TR=2300ms, TE=2.34ms, voxel size 1.0×1.0x1.0mm, FOV 256×256mm) and MP2RAGE (TI1/TI2/TE/TR=700/2500/2.96/5000ms; flip angles 4/5deg; 1x1x1mm3; GRAPPAx3) sequences. Individual T1 maps were registered3 onto reference atlases established using linear regression models1. For each voxel, deviations were evaluated as z-scores and a threshold was applied to maintain only voxels exceeding 2 standard deviations from corresponding normative value1.
Results&Conclusion:
All patients showed positive T1 deviations from the normative population (z>2) in the hippocampus and TL, as well as diffusely in white matter and subcortical structures (striatum and thalamus) (Figure 1). Drug-resistant MTLE subjects demonstrated larger and diffuse deviations compared to drug-responsive patients (Figures 2 and 3). T1 z-score maps of MTLE patients with identified alterations of tissue properties with respect to normative atlases2. Results support the hypothesis that MTLE-related pathophysiological changes extend beyond TL and involve different brain regions. Furthermore, MRI alterations appear to align with clinical severity: subjects with drug-resistant epilepsy exhibited more diffuse changes compared to drug-responsive MTLE.
Figure 1: Percentage map of all MTLE patients (n=37) in which voxel has positive deviation (z>2) compared to the healthy population of normative atlas. These clusters are presented in a range from 25 to 75 percent of MTLE patients. Images are displayed in radiological view
Figure 2: Percentage of drug-responsive MTLE (n=22) in which a voxel has z>2. Images are displayed in radiological view.
Figure 3: Percentage of drug-resistant MTLE (n=12) in which a voxel has z > 2. Images are displayed in radiological view.
[1] Piredda GF, Hilbert T, Granziera C, Bonnier G, Meuli R, Molinari F, Thiran JP, Kober T. Quantitative brain relaxation atlases for personalized detection and characterization of brain pathology. Magn Reson Med. 2020;83(1):337-351.
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[3] VoxelMorph: A Learning Framework for Deformable Medical Image Registration. Guha Balakrishnan, Amy Zhao, Mert R. Sabuncu, John Guttag, and Adrian V. Dalca. Aug 2019, IEEE Transactions on Medical Imaging, Vols. , vol. 38, no. 8, pp. 1788-1800, Aug. 2019, doi: 10.1109/TMI.2019.2897538.
