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Published on: November 9, 2018
Reduced hippocampal metabolism in MCI and AD: automated FDG-PET image analysis
L Mosconi1, W-H Tsui, S De Santi
1Department of Psychiatry, New York University School of Medicine, 560 First Avenue, New York, NY 10016, USA.
Background:
To facilitate image analysis, most recent 2-[18F]fluoro-2-deoxy-d-glucose PET (FDG-PET) studies of glucose metabolism (MRglc) have used automated voxel-based analysis (VBA) procedures but paradoxically none reports hippocampus MRglc reductions in mild cognitive impairment (MCI) or Alzheimer disease (AD). Only a few studies, those using regions of interest (ROIs), report hippocampal reductions. The authors created an automated and anatomically valid mask technique to sample the hippocampus on PET (HipMask).
Methods:
Hippocampal ROIs drawn on the MRI of 48 subjects (20 healthy elderly [NL], 16 MCI, and 12 AD) were used to develop the HipMask. The HipMask technique was applied in an FDG-PET study of NL (n = 11), MCI (n = 13), and AD (n = 12), and compared to both MRI-guided ROIs and VBA methods.
Results:
HipMask and ROI hippocampal sampling produced significant and equivalent MRglc reductions for contrasts between MCI and AD relative to NL. The VBA showed typical cortical effects but failed to show hippocampal MRglc reductions in either clinical group. Hippocampal MRglc was the only discriminator of NL vs MCI (78% accuracy) and added to the cortical MRglc in classifying NL vs AD and MCI vs AD.
Conclusions:
The new HipMask technique provides accurate and rapid assessment of the hippocampus on PET without the use of regions of interest. Hippocampal glucose metabolism reductions are found in both mild cognitive impairment and Alzheimer disease and contribute to their diagnostic classification. These results suggest re-examination of prior voxel-based analysis 2-[18F]fluoro-2-deoxy-d-glucose PET studies that failed to report hippocampal effects.
Insights
A new HipMask technique accurately assesses hippocampal glucose metabolism in mild cognitive impairment (MCI) and Alzheimer disease (AD) using PET scans. This method reveals significant reductions, aiding in diagnostic classification.
Area of Science:
- Neuroimaging
- Biomarkers
- Metabolic Imaging
Background:
- Automated voxel-based analysis (VBA) in 2-[18F]fluoro-2-deoxy-d-glucose PET (FDG-PET) studies paradoxically fails to detect hippocampal glucose metabolism reductions in mild cognitive impairment (MCI) and Alzheimer disease (AD).
- Region of interest (ROI) based analyses have reported hippocampal reductions, suggesting limitations in current automated methods for analyzing this specific brain region.
- The development of an automated, anatomically valid mask technique (HipMask) for hippocampus sampling on PET was necessitated by these discrepancies.
Purpose of the Study:
- To introduce and validate a novel automated mask technique (HipMask) for accurate hippocampal sampling in PET imaging.
- To compare the efficacy of the HipMask technique against traditional MRI-guided ROIs and automated VBA for assessing hippocampal glucose metabolism.
- To investigate the diagnostic utility of hippocampal metabolic changes in distinguishing between healthy elderly (NL), MCI, and AD groups.
Main Methods:
- The HipMask technique was developed using hippocampal ROIs from MRI scans of 48 subjects (20 NL, 16 MCI, 12 AD).
- The HipMask was applied to FDG-PET data from 11 NL, 13 MCI, and 12 AD subjects.
- Comparisons were made between HipMask, MRI-guided ROIs, and VBA methods for analyzing hippocampal and cortical metabolic rates.
Main Results:
- Both HipMask and ROI methods demonstrated significant and equivalent reductions in hippocampal glucose metabolism when comparing MCI and AD groups to NL.
- Voxel-based analysis (VBA) identified typical cortical effects but failed to detect hippocampal metabolic reductions in MCI or AD.
- Hippocampal metabolic rate, analyzed via HipMask, was the sole discriminator between NL and MCI (78% accuracy) and improved classification accuracy for NL vs. AD and MCI vs. AD when combined with cortical data.
Conclusions:
- The HipMask technique offers a rapid and accurate method for assessing hippocampal glucose metabolism on PET without manual ROI delineation.
- Significant reductions in hippocampal glucose metabolism are present in both MCI and AD, playing a crucial role in their diagnostic classification.
- Prior FDG-PET studies employing VBA that did not report hippocampal effects warrant re-examination using methods like HipMask.
