Longitudinal Diffusion-Weighted Imaging and T2 Relaxometry of the Hippocampus in Temporal Lobe Epilepsy

• Author / Creator

  Adel, Seyed Amir Ali

• Hippocampal sclerosis (HS) is an important predictor of surgical outcome in temporal lobe epilepsy (TLE). High-resolution (1 mm isotropic) diffusion tensor imaging (DTI) of the hippocampus in TLE patients has shown patterns of hippocampal subfield diffusion abnormalities which were consistent with HS subtype on surgical histology in a pilot sample of four patients. T2 relaxometry has also demonstrated focal hippocampal abnormalities which correlated with HS pathological features of neuron loss, gliosis, and granule cell dispersion. The objectives of this thesis were to determine the stability of focal hippocampus diffusion changes over time in TLE patients, compare diffusion and quantitative T2 abnormalities of the sclerotic hippocampus and correlate pre-surgical mean diffusivity (MD) and T2 maps with post-surgical histology.

  To address these objectives, 19 TLE patients and 19 controls underwent two high-resolution (1 × 1 × 1 mm3) DTI and (1.1 × 1.1 × 1 mm3) T2 relaxometry scans (in a subset of 16 TLE patients and 9 controls) of the hippocampus at 3T, with a 2.6±0.8 year inter-scan interval. Within-participant hippocampal volume, MD and T2 were compared between the scans. Contralateral hippocampal changes 2.3±1.0 years after surgery and ipsilateral pre-operative MD maps versus post-operative subfield histopathology were evaluated in 8 patients who underwent surgical resection of the hippocampus.

  The results showed significantly reduced volume and elevated MD and T2 of sclerotic hippocampi compared to healthy and non-HS hippocampi. These whole-hippocampus measures remained unchanged between the longitudinal scans. Focal regions of elevated MD and T2 in bilateral hippocampi of HS TLE were detected consistently at both scans. Regions of high MD and T2 correlated and remained consistent over time. Volume, MD and T2 remained unchanged in post-operative contralateral hippocampus. Regional elevations of MD identified subfield neuron loss on post-surgical histology with 88% sensitivity and 88% specificity. Focal T2 elevations identified subfield neuron loss with 75% sensitivity and 88% specificity.

  The findings of this work suggest no significant change in diffusion and T2 abnormalities in ipsilateral and contralateral hippocampi between the two scans, suggesting permanent micro-structural alterations. While both MD and T2 accurately predicted HS subtypes, MD was more sensitive than T2 in detecting neuron loss on post-surgical histology. Both DTI and T2 acquisitions were acquired using a clinically feasible protocol (at 3T in under 6 minutes each), potentially providing the opportunity to diagnose precise HS subtypes as well as detect subtle or regional contralateral hippocampal abnormalities, which may aide in predicting surgical outcomes preoperatively.

• Subjects / Keywords

  • hippocampal sclerosis
  • diffusion tensor imaging
  • quantitative T2
  • histology
  • post-operative

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-9jr3-8r89

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.