Abstracts

Rationale: Large deformation high dimensional mapping (HDM-LD) produces three-dimensional surface representations of the hippocampus with resolution at a subvoxel level. HDM-LD has been validated to be accurate and reproducible for human MR images, and shown to identify subtle neuroanatomical and longitudinal changes in diseases such as epilepsy, Alzhiemer Disease, depression and schizophrenia that are not detectable with standard volumetric methods. Small animal in-vivo MRI allows the detection of structural and functional biological changes in living animals that complements traditional ex-vivo histological techniques. Here we report the development and validation of the application of HDM-LD segmentation for the hippocampus in the rat. Methods: High resolution volumetric T2 weighted MRI images were acquired at 4.7 Tesla from 6 male in-breed non-epileptic Wistar rats. Two HDM-LD segmentations of the hippocampus (A1 and A2) were compared with the manual segmentations of two investigators who independently segmented the hippocampi (M1 and M2). Results: The mean overlap for the hippocampi between A1 and A2 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 A1 and M1 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: A1 versus A2, 3.2% (SD 1.0); M1 versus M2 6.82% (SD 5.22); A1 versus M1 13.0% (SD 1.8). Conclusions: HDM-LD can be applied to obtain accurate and reproducible 3-D 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.