Large-deformation High-dimensional Mapping Research Articles

MRI‐based large deformation high dimensional mapping of the hippocampus in rats: Development and validation of the technique

To report the detection of structural and functional biological changes in living animals using small animal in vivo MRI that complements traditional ex vivo histological techniques. We report the development and validation of the application of large deformation high dimensional mapping (HDM-LD) segmentation for the hippocampus in the rat. High resolution volumetric T2 weighted MRI images were acquired at 4.7 Tesla from six male in-breed nonepileptic Wistar rats. Two HDM-LD segmentations of the hippocampus (automated 1 and automated 2) were compared with the manual segmentations of two investigators who independently segmented the hippocampi (manual 1 and manual 2). The mean overlap for the hippocampi between automated 1 and automated 2 for the right hippocampi was 94.4% (SD 1.0) and for the left hippocampi was 94.3% (SD 2.5), while the mean overlap between automated 1 and manual 1 for the right hippocampi was 91.4% (SD 1.3) and for the left hippocampi was 91.9% (SD 1.4). Mean values for absolute differences for comparisons of all the segmentations were the following: automated 1 versus automated 2, 3.2% (SD 1.0); manual 1 versus manual 2 6.82% (SD 5.22); automated 1 versus manual 1 13.0% (SD 1.8). HDM-LD can be applied to obtain accurate and reproducible three-dimensional segmentations of the hippocampus from rat MR images. HDM-LD will be a useful tool for investigations of hippocampal structural changes in vivo in rat models of human disease.

Morphometric abnormalities and hyperanxiety in genetically epileptic rats: A model of psychiatric comorbidity?

BackgroundImaging studies of epilepsy patients with comorbid affective disturbance demonstrate morphometric changes in limbic brain regions implicated in psychiatric disease. Genetic Absence Epilepsy Rats from Strasbourg (GAERS), specifically bred for their epilepsy phenotype, also exhibit elevated anxiety-like behaviors suggesting a common causality. Here we examined whether relevant cerebral morphological alterations exist in this rat strain using volumetric measurements and large deformation high dimensional mapping (HDM-LD), a tool recently validated to produce accurate three-dimensional surface representations of the hippocampus. MethodsVolumetric MRI and the Open Field test of anxiety were performed in adult female GAERS (n=12) and Non-Epileptic Controls (NEC; n=11). The volumes of selected brain regions, including cortex, hippocampus, amygdala, thalamus, hypothalamus and lateral ventricles, were measured using Region-Of-Interest analysis from the MRI data and total volumes compared between the two strains. ResultsGAERS had increased amygdala (right: p=0.003; left p<0.001), cortices (right: p=0.006; left p=0.012) and ventricular volumes (p=0.002) when compared with NEC rats. Further, HDM-LD showed GAERS to have hippocampal volume loss in two regions: the medial hippocampal surface immediately caudal to the hippocampal commissure, and the lateral hippocampal surface over the mid-portion of the septotemporal axis. GAERS exhibited increased anxiety in the Open Field compared with NEC rats: reduced distance traveled (p<0.001) and reduced time in the centre area (p=0.042). ConclusionsMorphometric brain changes in GAERS could be relevant to their hyperanxious and epileptic phenotypes. This model may be useful in illuminating the pathogenesis of affective disorders generally, as well as modeling psychiatric comorbidities of epilepsy.

Hippocampal deformation mapping in MRI negative PET positive temporal lobe epilepsy

Objectives:To compare hippocampal surface structure, using large deformation high dimensional mapping (HDM-LD), in subjects with temporal lobe epilepsy (TLE) with (HS+ve) and without (HS−ve) hippocampal sclerosis.Methods:The study included 30 HS−ve...