Introduction
Structural imaging
Study | Imaging modality | Sample | Main findings |
---|---|---|---|
Du et al. [6] | Structural MRI | 20 AD, 25 cognitively normal (CN) | AD patients demonstrated GM loss in the hippocampus and ERC, with a higher atrophy rate in the ERC |
Pennanen et al. [7] | Structural MRI | 48 AD, 65 MCI, 59 controls | Hippocampal and ERC atrophies were found in AD and MCI patients, with MCI patients showing intermediate levels |
Li et al. [9] | Structural MRI | 64 AD, 72 controls (14 with AD on follow-up) | Early in the course of AD, the ERC and hippocampus are the primary sites of atrophy. In later stages, other MTL brain structures are affected |
Cavedo et al. [13] | Structural MRI | 19 AD, 19 controls | GM reductions were demonstrated in the amygdala for AD patients |
Thomann et al. [14] | Structural MRI | 21 early AD, 21 controls | Atrophy of the olfactory bulb tract was found for AD patients |
Guo et al. [15] | Structural MRI | 13 AD, 14 controls | GM reductions in parahippocampal gyrus, middle and superior temporal gyrus, insula, parietal lobule, thalamus, hippocampus, and cingulate gyrus were demonstrated for AD patients |
De Jong et al. [16] | Structural MRI | 69 probable AD, 70 subjects with memory complaints | Compared to subjects with memory complaints, GM loss was shown in the putamen and thalamus for AD patients |
Kilimann et al. [19] | Structural MRI | 134 AD, 41 MCI, 148 controls | Volumetric reductions in brain areas within the basal forebrain cholinergic system were displayed for AD and MCI patients |
Duarte et al. [20] | Structural MRI | 14 probable AD, 32 MCI, 14 controls | Frontal, parietal and temporal lobe atrophies were found for AD patients and frontal and temporal GM losses were present for MCI patients |
Vasavada et al. [22] | Structural MRI | 15 AD, 21 MCI, 27 CN | Brain atrophy was displayed in the hippocampus and the primary olfactory cortex for AD and MCI patients |
Tabatabaei-Jafari et al. [23] | Structural MRI | 191 AD, 398 MCI, 229 CN | GM reductions in the cerebellum were found for AD patients |
Lee et al. [24] | Structural MRI | 50 AD, 50 controls | Volumetric reductions in the brainstem were displayed in AD patients |
Capizzano et al. [27] | Structural MRI | 81 probable AD, 19 controls | A high degree of WMHs was found in AD patients: 70% in the frontal lobe, 22% in the parietal lobe, 3.5% in the temporal lobe, and 1% in the occipital lobe |
Advanced MR techniques
Study | Imaging modality | Sample | Main findings |
---|---|---|---|
Sexton et al. [34] | DTI | Meta-analysis of 41 studies | MD increases were found globally in WM in AD and in temporal and parietal WM in MCI. FA decreases were found in temporal, occipital and frontal WM in AD and frontal and temporal WM in MCI |
Alexopoulos et al. [41] | ASL | 19 AD, 24 MCI, 24 controls | Hypoperfusion was noted in parietal, temporal, and occipital cortex, and the precuneus in MCI and AD patients |
Mak et al. [42] | ASL | 13 AD, 15 controls | Reductions in CBF were found in the hippocampus and posterior cingulate for patients with AD |
Dai et al. [43] | ASL | 37 AD, 29 MCI, 38 controls | In MCI, decreases in CBF were found in the posterior cingulate and precuneus and increases in CBF were found in the hippocampus, basal ganglia, and amygdala. In AD decreases in CBF were found in frontal, parietal, temporal, orbitofrontal cortex, and the precuneus and increases in CBF were found in the anterior cingulate gyrus. Compared to MCI patients, AD patients showed decreased CBF in temporal, parietal, frontal orbitofrontal cortex and temporal regions such as hippocampus, amygdala, and thalamus |
Zhu et al. [49] | MRS | 14 AD, 22 CN elderly subjects | Increased mI, mI/Cr and decreased NAA and NAA/Cr ratios were found in parietal areas for patients with AD. NAA/mI ratios were the best classifier for AD |
Tumati et al. [50] | MRS | Meta-analysis of 29 studies | In the posterior cingulate, Cho/Cr ratios are increased, and NAA/mI ratios are decreased for AD patients. In the hippocampus, mI/Cr ratios are increased for AD patients |
Functional imaging
Study | Imaging modality | Sample | Main findings |
---|---|---|---|
Small et al. [57] | Task-based fMRI | 4 AD, 12 subjects with isolated memory decline, 4 controls | Reduced activation in regions of the hippocampus was found during a facial recognition task for AD patients. A similar finding was observed for patients with isolated memory decline |
Sperling et al. [58] | Task-based fMRI | 7 AD, 10 young control subjects, 10 elderly control subjects | Reduced activation in hippocampal areas and increased activation in the parietal regions and the posterior cingulate were found during an encoding task for AD patients |
Petrella et al. [59] | Task-based fMRI | 13 AD, 34 aMCI, 28 healthy elderly control subjects | Decreased activation was found in middle temporal areas and increased activation was shown in posteromedial cortical regions for AD patients during an encoding task. Patients with MCI showed an intermediate but similar profile |
Trivedi et al. [60] | Task-based fMRI | 16 aMCI, 23 controls | Reduced activation was noted in frontal areas and increased activation was present in hippocampal areas for MCI patients during an encoding task. During recognition, this region-specific pattern of activation was reversed |
Parra et al. [61] | Task-based fMRI | 10 AD, 10 MCI, 10 controls | Comparing control subjects and MCI patients, decreased activation was found in the hippocampus and parahippocampus in AD patients during incidental encoding. Increased activation was found for MCI patients relative to control subjects |
Yetkin et al. [62] | Task-based fMRI | 11 AD, 10 MCI, 9 controls | Increased activation in frontal and temporal regions, fusiform gyrus, and anterior cingulate gyrus was displayed for AD and MCI patients during a working memory task. For selected areas, MCI patients showed greater activation than AD patients |
Thiyagesh et al. [63] | Task-based fMRI | 12 AD, 13 elderly control subjects | Declines in activation in parietal, parieto-occipital, and premotor cortical areas and increased activation of additional parietal structures was found in AD during an observational visuospatial task |
Li et al. [64] | Task-based fMRI | 10 AD, 9 MCI, 9 elderly control subjects | Reduced activation was found in prefrontal cortical areas for AD patients and increased activation in these same regions was found for MCI patients during a Stoop colour–word interference task |
McGeown et al. [65] | Task-based fMRI | 29 AD, 19 controls | No activation in parietal regions and decreased activation in prefrontal areas was found for AD patients during a semantic knowledge task |
Vidoni et al. [66] | Task-based fMRI | 9 AD, 10 controls | Reduced activation was found in the premotor and supplementary motor regions, and the cerebellum, whilst increased activation was evidenced in the primary motor cortices for AD patients during a motor task |
Van Dam et al. [67] | Task-based fMRI | 8 aMCI, 8 controls | Increased activation was shown in the tempero-parietal junction, angular gyrus, and precuneus, whereas attenuated activation was seen in prefrontal regions and the anterior cingulate for aMCI patients during an attentional (executive control, alerting and orienting) task |
Greicius et al. [69] | Resting-State fMRI | 15 AD, 18 controls | Reduced connectivity was shown between medial temporal structures and the posterior cingulate cortex for AD patients |
Damoiseaux et al. [71] | Resting-State fMRI | Baseline: 21 AD, 18 controls Follow-up: 11 AD, 10 controls | Compared to control subjects at baseline, declines in connectivity were seen in the posterior DMN and increased activation was found for areas within the ventral and anterior DMN for AD patients. Compared to control subjects at follow-up, decreased connectivity between regions within the anterior, ventral, and posterior DMN in addition to sensorimotor network were shown for AD patients. Compared to control subjects, declines in activation over time were greater for AD patients |
Yu et al. [72] | Resting-State fMRI | 32 AD, 26 MCI, 58 controls | Increased connectivity between posterior cingulate and non-DMN regions but declines in activation between the posterior cingulate and areas within the DMN were found for AD patients. An opposite pattern of connectivity was shown for MCI patients |
Das et al. [73] | Resting-State fMRI | 17 aMCI, 31 controls | A greater degree of functional connectivity was shown within regions belonging to the medial temporal lobe, whereas declines in activity were seen between DMN and medial temporal structures for MCI patients |
Zhou et al. [74] | Resting-State fMRI | 35 AD, 27 MCI, 27 controls | Declines in functional connectivity within a range of regions within the thalamo-cortical network and thalamo-DMN were observed for AD patients. MCI patients showed similar but intermediate deteriorations |
Li et al. [75] | Resting-State fMRI | 15 AD, 16 healthy elderly control subjects | Declines in functional connectivity within a range of regions within the dorsal attention network but not the ventral attention network were found for AD patients |
Zheng et al. [76] | Resting-State fMRI | 32 AD, 38 controls | Disturbed functional connectivity was seen in several main networks including the DMN, visual network, and sensorimotor network in AD patients |