FreeSurfer Automatic Brain Segmentation Adaptation to Medial Temporal Lobe Structures: Volumetric Assessment and Diagnosis of Mild Cognitive Impairment
Alzheimer’s disease is a prevalent and progressive neurodegenerative disease that often starts clinically as a memory deficit. Specifically, the hippocampal formation (HF) and medial part of the temporal lobe (MTL) are severely affected. Those structures are at the core of the neural system responsible for encoding and retrieval of the memory for facts and events (episodic memory) which is dependent on the HF and MTL. Clinical lesions as well as experimental evidence point that the HF (hippocampus plus entorhinal cortex) and the adjacent cortex in the MTL, are the regions critical for normal episodic memory function. Structural MRI studies can be processed by FreeSurfer to obtain an automatic segmentation of many brain structures. We wanted to explore the advantages of complementing the automatic segmentation of FreeSurfer with a manual segmentation of the HF and MTL to obtain a more accurate evaluation of these memory centers.
We examined a library of cases in which neuroanatomical delimitation of the extent of the HF and MTL was made in 48 control and 16 AD brains, and the knowledge provided was applied to 7 cases (2 controls and 5 MCI patients) in which 3T MRI scans were obtained at two time points, one year and a half apart. Our results show that volumetric values were preserved in controls as well as non amnestic MCI patients, while the amnestic type (the more often to develop full AD) showed a volume decrease in the HF and MTL structures. The methodology still needs further development to a full automatization, but it seems to be promising enough for early detection of volume changes in patients at risk of developing AD.
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