New computer-aided diagnosis of dementia using positron emission tomography: brain regional sensitivity-mapping method

Mitochondrial complex-I abnormalities underlie neurodegeneration and cognitive decline in Alzheimer's disease

BACKGROUND

Abnormal mitochondrial metabolism has been described in Alzheimer's disease (AD) brain. However, the relationship between AD pathophysiology and key mitochondrial processes remains elusive. The purpose of this study is to investigate whether mitochondrial complex I dysfunction is associated with amyloid aggregation, or glucose metabolism and brain atrophy in patients with mild AD using positron emission tomography (PET).

METHODS

Amyloid and tau positive symptomatic AD patients with clinical dementia rating 0.5 or 1 (N=30; mean age ± standard deviation: 71.8 ± 7.6 years) underwent magnetic resonance imaging and PET scans with [¹⁸ F]BCPP-EF, [¹¹ C]PiB and [¹⁸ F]FDG for assessing brain atrophy, mitochondrial complex I dysfunction, amyloid deposition, and glucose metabolism, respectively. Local cortical associations among these biomarkers and gray matter volume were evaluated with voxel-based regressions models.

RESULTS

[¹⁸ F]BCPP-EF standardized uptake value ratio (SUVR) was positively correlated with [¹⁸ F]FDG SUVR in the widespread brain area, while its associations with gray matter volume were restricted to the parahippocampal gyrus. Reductions in [¹⁸ F]BCPP-EF SUVR were associated with domain-specific cognitive performance. We did not observe regional associations between mitochondrial dysfunction and amyloid burden.

CONCLUSIONS

In symptomatic cases, although mitochondrial complex I reduction is linked to a wide range of downstream neurodegenerative processes such as hypometabolism, atrophy, and cognitive decline, the link to amyloid was not observable. The data presented here support [¹⁸ F]BCPP-EF as an excellent imaging tool to investigate mitochondrial dysfunction in AD.

Multimodality Imaging of Dementia: Clinical Importance and Role of Integrated Anatomic and Molecular Imaging

Neurodegenerative diseases are a devastating group of disorders that can be difficult to accurately diagnose. Although these disorders are difficult to manage owing to relatively limited treatment options, an early and correct diagnosis can help with managing symptoms and coping with the later stages of these disease processes. Both anatomic structural imaging and physiologic molecular imaging have evolved to a state in which these neurodegenerative processes can be identified relatively early with high accuracy. To determine the underlying disease, the radiologist should understand the different distributions and pathophysiologic processes involved. High-spatial-resolution MRI allows detection of subtle morphologic changes, as well as potential complications and alternate diagnoses, while molecular imaging allows visualization of altered function or abnormal increased or decreased concentration of disease-specific markers. These methodologies are complementary. Appropriate workup and interpretation of diagnostic studies require an integrated, multimodality, multidisciplinary approach. This article reviews the protocols and findings at MRI and nuclear medicine imaging, including with the use of flurodeoxyglucose, amyloid tracers, and dopaminergic transporter imaging (ioflupane). The pathophysiology of some of the major neurodegenerative processes and their clinical presentations are also reviewed; this information is critical to understand how these imaging modalities work, and it aids in the integration of clinical data to help synthesize a final diagnosis. Radiologists and nuclear medicine physicians aiming to include the evaluation of neurodegenerative diseases in their practice should be aware of and familiar with the multiple imaging modalities available and how using these modalities is essential in the multidisciplinary management of patients with neurodegenerative diseases.^©RSNA, 2020.

Endogenous dopamine release under transcranial direct-current stimulation governs enhanced attention: a study with positron emission tomography

Transcranial direct-current stimulation (tDCS) to the dorsolateral prefrontal cortex (DLPFC) has been established as an effective and noninvasive method to modulate cognitive function. Nevertheless, the mechanisms causing those cognitive changes under the tDCS remain largely unknown. We strove to elucidate the cognito-biological relation under the tDCS condition by examining whether the dopamine system activated by tDCS is involved in cognitive changes in human participants, or not. To evaluate the dopamine system, we used [¹¹C]-raclopride positron emission tomography (PET) scanning: 20 healthy men underwent two [¹¹C]-raclopride PET scans and subsequent neuropsychological tests. One scan was conducted after tDCS to the DLPFC. One was conducted after sham stimulation (control). Results of [¹¹C]-raclopride PET measurements demonstrate that tDCS to the DLPFC caused dopamine release in the right ventral striatum. Neuropsychological tests for attentiveness revealed that tDCS to the DLPFC-enhanced participants' accuracy. Moreover, this effect was correlated significantly with dopamine release. This finding provides clinico-biological evidence, demonstrating that enhancement of dopamine signaling by tDCS in the ventral striatum is associated with attention enhancement.

Age-Related Sex-Specific Changes in Brain Metabolism and Morphology

With a large database, we aimed to evaluate sex-specific distinctive changes in brain glucose metabolism and morphology during normal aging using MRI and (18)F-FDG PET.

METHODS

A total of 963 cognitively healthy adults were included in this study. All subjects completed a medical questionnaire, took the mini-mental state examination, and underwent brain MRI and whole-body (18)F-FDG PET. The MR and PET images were statistically analyzed using 3-dimensional stereotactic surface projection. All images were corrected for whole-brain pixel value to identify the brain regions with significant changes, and regions of interest were set up with reference to Brodmann areas. We evaluated morphologic and glucose metabolic changes by cross-sectional analysis. The baseline database consisted of subjects from 30 to 40 y old, and the age-step for comparison was 5-y ranges. We also compared sex-specific differences in MR and PET images in each age group.

RESULTS

Regarding age-related changes, in both sexes brain atrophy was observed in the lateral frontal and parietal regions and glucose hypometabolism in the medial frontal regions. There were significant differences in these parameters between the sexes; parallel changes in volume and metabolism were manifested in the medial frontal cortex in men and in the lateral and medial temporal cortex in women. By contrast, metabolism-dominant reductions were manifested in the lateral and medial parietal cortex in men and in the ventrolateral prefrontal cortex, including the Broca area, in women. These differences became insignificant in individuals 66 y or older.

CONCLUSION

Our brain mapping study with a large number of reference human brain data demonstrated age-related parallel changes between morphology and metabolism in the medial frontal regions and sex-specific hypometabolism in the parietal (male) and ventrolateral prefrontal (female) cortices. These findings may suggest an aging vulnerability in sex-specific brain regions: the parietal cortex for visuospatial ability in men and the Broca area for speech processing in women.

The Possible Link between GABAergic Dysfunction and Cognitive Decline in a Patient with Idiopathic Hypoparathyroidism

Idiopathic hypoparathyroidism (IHP) is accompanied by cognitive impairment. We report the case of a 70-year-old IHP patient with cognitive disturbance. Brain computed tomography showed bilateral calcification in basal ganglia, thalamus, and cerebellum. Neuropsychological assessment revealed low scores for intelligence, memory, and perseverative errors. Brain positron emission tomography showed a significant reduction in [(18)F]-Fludeoxyglucose (FDG) uptake in bilateral frontal, left temporal and parietal cortices, along with a marked reduction in [(11)C]-flumazenil binding in left frontal, temporal, parietal, and bilateral cerebellum. These findings suggest cognitive impairment in IHP may be ascribed to GABAergic dysfunction, thus leading to, or coexisting with, cerebral hypometabolism.

Volume of interest-based [18F]fluorodeoxyglucose PET discriminates MCI converting to Alzheimer's disease from healthy controls. A European Alzheimer's Disease Consortium (EADC) study

An emerging issue in neuroimaging is to assess the diagnostic reliability of PET and its application in clinical practice. We aimed at assessing the accuracy of brain FDG-PET in discriminating patients with MCI due to Alzheimer's disease and healthy controls. Sixty-two patients with amnestic MCI and 109 healthy subjects recruited in five centers of the European AD Consortium were enrolled. Group analysis was performed by SPM8 to confirm metabolic differences. Discriminant analyses were then carried out using the mean FDG uptake values normalized to the cerebellum computed in 45 anatomical volumes of interest (VOIs) in each hemisphere (90 VOIs) as defined in the Automated Anatomical Labeling (AAL) Atlas and on 12 meta-VOIs, bilaterally, obtained merging VOIs with similar anatomo-functional characteristics. Further, asymmetry indexes were calculated for both datasets. Accuracy of discrimination by a Support Vector Machine (SVM) and the AAL VOIs was tested against a validated method (PALZ). At the voxel level SMP8 showed a relative hypometabolism in the bilateral precuneus, and posterior cingulate, temporo-parietal and frontal cortices. Discriminant analysis classified subjects with an accuracy ranging between .91 and .83 as a function of data organization. The best values were obtained from a subset of 6 meta-VOIs plus 6 asymmetry values reaching an area under the ROC curve of .947, significantly larger than the one obtained by the PALZ score. High accuracy in discriminating MCI converters from healthy controls was reached by a non-linear classifier based on SVM applied on predefined anatomo-functional regions and inter-hemispheric asymmetries. Data pre-processing was automated and simplified by an in-house created Matlab-based script encouraging its routine clinical use. Further validation toward nonconverter MCI patients with adequately long follow-up is needed.

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¹⁸F-FDG-PET/CT analysis of metabolic differences between MCI converting to AD and HC

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Large and very well controlled cohorts from EADC-Consortium were investigated.

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Data were analyzed by a friendly-to-use Matlab-based script and Support Vector Machine.

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Excellent discrimination between MCI and HC (sensitivity 92%; specificity 91%)

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Highest accuracy reported so far in MCI and promising implementation in clinical routine

Use of FDG PET as an imaging biomarker in clinical trials of Alzheimer’s disease

PET with the glucose analog FDG as a tracer is a mature and increasingly available clinical imaging technique that can improve the diagnostic accuracy for Alzheimer’s disease, which is of particular value at an early stage of the disease when clinical symptoms are still mild and nonspecific. It can also monitor progression of Alzheimer’s disease, and the findings are closely related to clinical symptoms. FDG PET, therefore, could also potentially be used as an imaging biomarker for selection of patients and assessment of outcome in clinical trials. Several published intervention studies indicate a good correspondence between clinical outcome and FDG PET findings, but study designs and methods used for data analysis vary widely. Recent developments towards standardization of largely user-independent methods for quantification of regional metabolic impairment on FDG PET scans will allow a new generation of studies that could provide the required evidence for full qualification of FDG PET as an imaging biomarker in clinical trials.