Abstract
PurposePrecise and reproducible hippocampus outlining is important to quantify hippocampal atrophy caused by neurodegenerative diseases and to spare the hippocampus in whole brain radiation therapy when performing prophylactic cranial irradiation or treating brain metastases. This study aimed to quantify systematic differences between methods by comparing regional volume and outline reproducibility of manual, FSL-FIRST and FreeSurfer hippocampus segmentations.Materials and methodsThis study used a dataset from ADNI (Alzheimer’s Disease Neuroimaging Initiative), including 20 healthy controls, 40 patients with mild cognitive impairment (MCI), and 20 patients with Alzheimer’s disease (AD). For each subject back-to-back (BTB) T1-weighted 3D MPRAGE images were acquired at time-point baseline (BL) and 12 months later (M12). Hippocampi segmentations of all methods were converted into triangulated meshes, regional volumes were extracted and regional Jaccard indices were computed between the hippocampi meshes of paired BTB scans to evaluate reproducibility. Regional volumes and Jaccard indices were modelled as a function of group (G), method (M), hemisphere (H), time-point (T), region (R) and interactions.ResultsFor the volume data the model selection procedure yielded the following significant main effects G, M, H, T and R and interaction effects G-R and M-R. The same model was found for the BTB scans. For all methods volumes reduces with the severity of disease.Significant fixed effects for the regional Jaccard index data were M, R and the interaction M-R. For all methods the middle region was most reproducible, independent of diagnostic group. FSL-FIRST was most and FreeSurfer least reproducible.Discussion/ConclusionA novel method to perform detailed analysis of subtle differences in hippocampus segmentation is proposed. The method showed that hippocampal segmentation reproducibility was best for FSL-FIRST and worst for Freesurfer. We also found systematic regional differences in hippocampal segmentation between different methods reinforcing the need of adopting harmonized protocols.
Highlights
The hippocampus is an important brain structure that plays a crucial role in episodic memory [1]
The most commonly used publicly available software tools to the academic community, with active user communities and active support from the developers, are FreeSurfer [Martinos Center for Biomedical Imaging, Harvard-MIT, Boston USA] [15,16] and FSL-FIRST [FMRIB Integrated Registration and Segmentation Tool, University of Oxford, Oxford UK] [17] and we focus on these methods
When studying anatomical changes accompanying the development of neurodegenerative diseases or when testing drugs against these diseases, it is well possible that these changes occur in specific regions of the hippocampus and global measures such as volume would be too coarse to notice them
Summary
The hippocampus is an important brain structure that plays a crucial role in episodic memory [1]. Longitudinal decline of hippocampal volume is related to memory impairment and clinical dementia [2,3]. The most commonly used publicly available software tools to the academic community, with active user communities and active support from the developers, are FreeSurfer [Martinos Center for Biomedical Imaging, Harvard-MIT, Boston USA] [15,16] and FSL-FIRST [FMRIB Integrated Registration and Segmentation Tool, University of Oxford, Oxford UK] [17] and we focus on these methods. FreeSurfer slightly agreed better with manual segmentation than FSL-FIRST [29,30,31,32,33]
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