Abstracts

Rationale:
Advances in high-field imaging have significantly improved spatial resolution of MRI, allowing for an increasingly detailed anatomical characterization of the mesiotemporal lobe, a key component of the limbic system and the disease hallmark in temporal lobe epilepsy (TLE) 1. For surgical planning, registering functional data onto anatomical targets requires high-level precision. However, this cannot be guaranteed in case of a discrepancy in spatial resolution between the template (used for nonlinear warps) and the atlas (used to define the structure of interest) leading to misalignment, particularly of small structures, and thus to wrong assumptions 2. To overcome this limitation, we generated a ultra-high resolution template, the MNI-NOEL50, and an atlas of mesiotemporal structures.
Method:
Submillimetric 3D T1-weighted MPRAGE images (0.6mm3 voxels) were acquired in 50 healthy individuals on a 3T MRI system. To create an unbiased population template, we used an iterative procedure which non-linearly matches individual subjects to an average template, similar to the one generating the symmetric MNI-ICBM152 template 3, the most commonly used reference in neuroimaging. Hippocampal (HC) subfields, amygdala (AM) nuclei, piriform and entorhinal cortices were manually segmented on this new MNI-NOEL50 template 1,4–6.
Results:
Fig. 1 shows  representative slices of the MNI-NOEL50 template and corresponding sections of the MNI-ICBM152. The increased spatial resolution of the MNI-NOEL50 provides superior anatomical definition, including sharper sulco-gyral patterns with better identification of secondary gyri. Moreover, improved visualization of myelinated white matter laminae allows for the delineation of individual AM nuclei and HC subfields, and separation between the HC and AM. Fig. 2 illustrates the mesiotemporal lobe atlas, including HC subfields, the subiculum, AM nuclei (lateral, basolateral, basomedial, central, corticomedial, hippocampal-amygdala transition area), piriform and entorhinal cortices.
Conclusion:
The MNI-NOEL50 template and atlas provide unparalleled anatomical detail. They will be made publicly available to facilitate structural and functional studies, particularly targeting the mesiotemporal lobe. They may also assist surgical planning of emerging approaches, such as minimally-invasive thermal ablation.   References •Kulaga-Yoskovitz J, Bernhardt BC, Hong S-J, et al. Multi-contrast submillimetric 3 Tesla hippocampal subfield segmentation protocol and dataset. Scientific Data. 2015;2:150059. •Ewert S, Plettig P, Li N, et al. Toward defining deep brain stimulation targets in MNI space: A subcortical atlas based on multimodal MRI, histology and structural connectivity. NeuroImage. 2018;170:271–282. •Fonov V, Evans AC, Botteron K, Almli CR, McKinstry RC, Collins DL. Unbiased average age-appropriate atlases for pediatric studies. NeuroImage. 2011;54:313–327. •Tyszka JM, Pauli WM. In vivo delineation of subdivisions of the human amygdaloid complex in a high-resolution group template. Human Brain Mapping. 2016;37:3979–3998. •Bernasconi N, Bernasconi A, Andermann F, Dubeau F, Feindel W, Reutens DC. Entorhinal cortex in temporal lobe epilepsy: a quantitative MRI study. Neurology. 1999;52:1870–1876. •Pereira PMG, Insausti R, Artacho-Perula E, Salmenpera T, Kalviainen R, Pitkanen A. MR Volumetric Analysis of The Piriform Cortex and Cortical Amygdala in Drug-Refractory Temporal Lobe Epilepsy. Epub 2005.:14.
Funding:
:Dr. Foit receives support from the German Research Foundation (DFG, FO996/1-1)