Abstract
The medial temporal lobe is one of the most well-studied brain regions affected by Alzheimer’s disease (AD). Although the spread of neurofibrillary pathology in the hippocampus throughout the progression of AD has been thoroughly characterized and staged using histology and other imaging techniques, it has not been precisely quantified in vivo at the subfield level using simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI). Here, we investigate alterations in metabolism and volume using [18F]fluoro-deoxyglucose (FDG) and simultaneous time-of-flight (TOF) PET/MRI with hippocampal subfield analysis of AD, mild cognitive impairment (MCI), and healthy subjects. We found significant structural and metabolic changes within the hippocampus that can be sensitively assessed at the subfield level in a small cohort. While no significant differences were found between groups for whole hippocampal SUVr values (p = 0.166), we found a clear delineation in SUVr between groups in the dentate gyrus (p = 0.009). Subfield analysis may be more sensitive for detecting pathological changes using PET-MRI in AD compared to global hippocampal assessment.
Highlights
The medial temporal lobe (MTL), which includes the hippocampus and adjacent entorhinal and perirhinal cortices, is critical to memory formation and retrieval and well known to be involved in most forms of Alzheimer’s disease (AD)[1]
dentate gyrus (DG) and cornu ammonis 1 (CA1) subfield volumes were significantly smaller in AD/mild cognitive impairment (MCI) compared to controls (Fig. 2, Table 2) with CA1 volume having the largest difference (p = 0.001) between groups
By using simultaneous TOF-positron emission tomography (PET) and high-resolution magnetic resonance imaging (MRI) acquisition along with automated subfield segmentation, we found significantly reduced FDG SUV ratio (SUVr) in DG and significantly reduced volume in CA1, DG, and whole hippocampus of AD/MCI patients compared to healthy controls
Summary
The medial temporal lobe (MTL), which includes the hippocampus and adjacent entorhinal and perirhinal cortices, is critical to memory formation and retrieval and well known to be involved in most forms of Alzheimer’s disease (AD)[1]. Neurodegeneration within the MTL leads to memory impairments in both AD and amnestic mild cognitive impairment (MCI)[2]. This neurodegeneration results in atrophy that can be measured using structural MRI3 and a reduction in metabolism of [ 18F]fluoro-deoxyglucose (FDG) in PET imaging[4]. Several MRI studies have shown that hippocampal subfield morphological measurements detect sensitive differences between AD, MCI, and healthy subjects. Prior to co-registered MRI and PET, most studies were unable to resolve small regions such as hippocampal
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