The Additional Value of PET in the Assessment of Cerebral Small Vessel Disease

Middle-age cerebral small vessel disease and cognitive function in later life: a population-based prospective cohort study

Background

Cerebral small vessel disease (cSVD) is a major pathologic substrate of vascular contribution to cognitive impairment. However, population based long-term longitudinal cognitive function data in relation to cSVD are rare. We investigated the relationship between cSVD and cognitive decline over time in middle-aged through elderly population.

Methods

This prospective cohort study was conducted in a community-based adult population (avg. age 58.5 ± 6.4) who underwent both magnetic resonance imaging (MRI) and comprehensive neuropsychological tests at baseline (2011-2014). The participants were followed-up with the same neuropsychological test battery 4-yearly in two more cycles (in 2015-2018 and 2019-2022). A total of 2454 participants who were free of dementia and cerebrovascular disease at baseline with cognitive function testing at least 2 time points over the time were analyzed. Data analysis was performed from May 1, 2023 to January 31, 2024. SVD was defined by the presence of any of the visible MRI markers (age-related white matter change, lacunes and cerebral microbleeds) at baseline. The main outcomes were multivariable adjusted mean differences of cognitive test performances by cSVD groups over time. The neuropsychological assessment battery included verbal and visual memory, verbal fluency, Digit Symbol-coding, Trail Making Test-A, and Stroop Test. To examine the relationship between cSVD and cognitive function, we used linear mixed model for repeated measurements to compare the means (95% CIs) by cSVD groups.

Findings

Of the total, 908 (37.0%) participants had cSVD on MRI reading at baseline. By location, cSVD were mostly found in the frontal lobe followed by basal ganglia area of the brain. None of the cognitive test scores, except Trail Making Test-A, were significantly different between the cSVD groups at baseline. At 8-year follow-up, participants without cSVD performed significantly better than participants with cSVD in Stroop-color reading [Mean difference 1.19 (95% CI: 0.02-2.36), p = 0.0451] and visual reproduction-recognition [Mean difference 0.11 (95% CI: 0.01-0.21), p = 0.0221]. While no other cognitive tests showed any differential changes by cSVD groups, logical memory (Story Recall Tests) increased and Stroop-word reading decreased over time in both cSVD groups almost identically.

Interpretation

Silent cSVD was independently associated with decline in executive functioning over 8-year follow-up period in this Korean middle-aged through elderly general population. Future studies considering wider spectrum of cSVD and longer follow-up durations may help predict further cognitive outcomes.

Funding

This study was funded by the Korea Centers for Disease Control and Prevention.

Molecular Imaging with PET in the Assessment of Vascular Dementia and Cerebrovascular Disease

Vascular dementia (VaD) is a unique form of cognitive decline caused by impairment of blood flow to the brain. Atherosclerosis is strongly associated with VaD as plaque accumulation can lead to tissue hypoperfusion or stroke. VaD and atherosclerosis are both diagnosed relatively late in their disease courses, prompting the need for novel diagnostic approaches such as PET to visualize subclinical pathophysiologic changes. This review discusses the use of PET in the assessment of VaD and cerebrovascular disease, focusing on the application of [18F] fluorodeoxyglucose to study neurometabolism and [18F] sodium fluoride to quantify arterial calcification.

Focused magnetic stimulation for motor recovery after stroke

BACKGROUND AND OBJECTIVES

The effects of noninvasive focused magnetothermal brain stimulation using magnetic nanoparticles (MNPs) on post-stroke motor deficits and metabolic dormancy in subacute ischemic injury are not well-established. This study examined if magnetothermal brain stimulation using magnetic nanoparticles (Nano-MS) enhances motor recovery after stroke.

METHODS

We randomly distributed rats into Sham, Control, MNP injection only, and Nano-MS groups. We administered focused magnetic stimulation for 30 min daily following an MNP injection (15 mg/mL) into the targeted motor cortex via the carotid artery three weeks after the transient (90 min) middle cerebral artery occlusion. We assessed motor functionality via behavioral tests and conducted positron emission tomography (PET) imaging to verify cerebral metabolic activity. We assessed neuronal excitability, neuroinflammation, blood-brain barrier (BBB) integrity, and neurogenesis four weeks post-stroke.

RESULTS

The Nano-MS group exhibited significantly improved motor deficits and cerebral metabolic activity compared to the Control and MNP groups (p < 0.05). Focused Nano-MS modulated neuronal excitability, evident by a depolarized action potential threshold for spike initiation and reduced firing frequency post-stroke. The Nano-MS group demonstrated markedly decreased inflammatory markers, such as IL-1β, IL-6, TNF-α, MCP-1, and ICAM-1, compared to the Control and MNP groups. BBB integrity and immunofluorescence for neurogenesis markers were substantially improved in the Nano-MS group.

CONCLUSIONS

Focused Nano-MS facilitates the recovery of motor deficits and metabolic inactivity in the brain by effectively modulating excitability, reducing neuroinflammation, enhancing BBB stability, and promoting neurogenesis. Nano-MS is a potential novel, noninvasive therapy for stroke rehabilitation. Further investigation is warranted.

Assessment of Microvascular Disease in Heart and Brain by MRI: Application in Heart Failure with Preserved Ejection Fraction and Cerebral Small Vessel Disease

The objective of this review is to investigate the commonalities of microvascular (small vessel) disease in heart failure with preserved ejection fraction (HFpEF) and cerebral small vessel disease (CSVD). Furthermore, the review aims to evaluate the current magnetic resonance imaging (MRI) diagnostic techniques for both conditions. By comparing the two conditions, this review seeks to identify potential opportunities to improve the understanding of both HFpEF and CSVD.

Multimodal comparisons of QSM and PET in neurodegeneration and aging

Quantitative susceptibility mapping (QSM) has been used to study susceptibility changes that may occur based on tissue composition and mineral deposition. Iron is a primary contributor to changes in magnetic susceptibility and of particular interest in applications of QSM to neurodegeneration and aging. Iron can contribute to neurodegeneration through inflammatory processes and via interaction with aggregation of disease-related proteins. To better understand the local susceptibility changes observed on QSM, its signal has been studied in association with other imaging metrics such as positron emission tomography (PET). The associations of QSM and PET may provide insight into the pathophysiology of disease processes, such as the role of iron in aging and neurodegeneration, and help to determine the diagnostic utility of QSM as an indirect indicator of disease processes typically evaluated with PET. In this review we discuss the proposed mechanisms and summarize prior studies of the associations of QSM and amyloid PET, tau PET, TSPO PET, FDG-PET, 15O-PET, and F-DOPA PET in evaluation of neurologic diseases with a focus on aging and neurodegeneration.

Brain Metabolic Network Redistribution in Patients with White Matter Hyperintensities on MRI Analyzed with an Individualized Index Derived from 18F-FDG-PET/MRI

OBJECTIVE

Whether metabolic redistribution occurs in patients with white matter hyperintensities (WMHs) on magnetic resonance imaging (MRI) is unknown. This study aimed 1) to propose a measure of the brain metabolic network for an individual patient and preliminarily apply it to identify impaired metabolic networks in patients with WMHs, and 2) to explore the clinical and imaging features of metabolic redistribution in patients with WMHs.

MATERIALS AND METHODS

This study included 50 patients with WMHs and 70 healthy controls (HCs) who underwent 18F-fluorodeoxyglucose-positron emission tomography/MRI. Various global property parameters according to graph theory and an individual parameter of brain metabolic network called "individual contribution index" were obtained. Parameter values were compared between the WMH and HC groups. The performance of the parameters in discriminating between the two groups was assessed using the area under the receiver operating characteristic curve (AUC). The correlation between the individual contribution index and Fazekas score was assessed, and the interaction between age and individual contribution index was determined. A generalized linear model was fitted with the individual contribution index as the dependent variable and the mean standardized uptake value (SUVmean) of nodes in the whole-brain network or seven classic functional networks as independent variables to determine their association.

RESULTS

The means ± standard deviations of the individual contribution index were (0.697 ± 10.9) × 10-3 and (0.0967 ± 0.0545) × 10-3 in the WMH and HC groups, respectively (p < 0.001). The AUC of the individual contribution index was 0.864 (95% confidence interval, 0.785-0.943). A positive correlation was identified between the individual contribution index and the Fazekas scores in patients with WMHs (r = 0.57, p < 0.001). Age and individual contribution index demonstrated a significant interaction effect on the Fazekas score. A significant direct association was observed between the individual contribution index and the SUVmean of the limbic network (p < 0.001).

CONCLUSION

The individual contribution index may demonstrate the redistribution of the brain metabolic network in patients with WMHs.

Common Shared Pathogenic Aspects of Small Vessels in Heart and Brain Disease

Small-vessel disease (SVD), also known as microvascular endothelial dysfunction, is a disorder with negative consequences for various organs such as the heart and brain. Impaired dilatation and constriction of small vessels in the heart lead to reduced blood flow and ischemia independently of coronary artery disease (CAD) and are associated with major cardiac events. SVD is usually a silent form of subcortical vascular burden in the brain with various clinical manifestations, such as silent-lacunar-ischemic events and confluent white-matter hyperintensities. Imaging techniques are the main help for clinicians to diagnose cardiac and brain SVD correctly. Markers of inflammation, such as C-reactive protein, tumor-necrosis-factor α, and interleukin 6, provide insight into the disease and markers that negatively influence nitric-oxide bioavailability and promote oxidative stress. Unfortunately, the therapeutic approach against SVD is still not well-defined. In the last decades, various antioxidants, oxidative stress inhibitors, and superoxide scavengers have been the target of extensive investigations due to their potential therapeutic effect, but with unsatisfactory results. In clinical practice, traditional anti-ischemic and risk-reduction therapies for CAD are currently in use for SVD treatment.

The spectrum and systemic associations of microvascular dysfunction in the heart and other organs

Microvascular dysfunction (MVD) contributes to several conditions that increase morbidity and mortality, including ischemic heart disease, heart failure, dementia, chronic kidney disease and hypertension. Consequently, MVD imposes a substantial burden on healthcare systems worldwide. In comparison to macrovascular dysfunction, MVD has been incompletely investigated, and it remains uncertain whether MVD in an organ constitutes a distinct pathology or a manifestation of a systemic disorder. Here, we summarize and appraise the techniques that are used to diagnose MVD. We review the disorders of the heart, brain and kidneys in which the role of MVD has been highlighted and summarize evidence hinting at a systemic or multi-organ nature of MVD. Finally, we discuss the benefits and limitations of implementing MVD testing in clinical practice with a focus on new interventions that are beginning to emerge.

EEG measures for clinical research in major vascular cognitive impairment: recommendations by an expert panel

Vascular contribution to cognitive impairment (VCI) and dementia is related to etiologies that may affect the neurophysiological mechanisms regulating brain arousal and generating electroencephalographic (EEG) activity. A multidisciplinary expert panel reviewed the clinical literature and reached consensus about the EEG measures consistently found as abnormal in VCI patients with dementia. As compared to cognitively unimpaired individuals, those VCI patients showed (1) smaller amplitude of resting state alpha (8-12 Hz) rhythms dominant in posterior regions; (2) widespread increases in amplitude of delta (< 4 Hz) and theta (4-8 Hz) rhythms; and (3) delayed N200/P300 peak latencies in averaged event-related potentials, especially during the detection of auditory rare target stimuli requiring participants' responses in "oddball" paradigms. The expert panel formulated the following recommendations: (1) the above EEG measures are not specific for VCI and should not be used for its diagnosis; (2) they may be considered as "neural synchronization" biomarkers to enlighten the relationships between features of the VCI-related cerebrovascular lesions and abnormalities in neurophysiological brain mechanisms; and (3) they may be tested in future clinical trials as prognostic biomarkers and endpoints of interventions aimed at normalizing background brain excitability and vigilance in wakefulness.

Emerging Concepts in Vascular Dementia: A Review

OBJECTIVE

Vascular dementia (VaD) is the second most common cause of dementia and a major health concern worldwide. A comprehensive review on VaD is warranted for better understanding and guidance for the practitioner. We provide an updated overview of the epidemiology, pathophysiological mechanisms, neuroimaging patterns as well as current diagnostic and therapeutic approaches.

MATERIALS AND METHODS

A narrative review of current literature in VaD was performed based on publications from the database of PubMed, Scopus and Google Scholar up to January, 2021.

RESULTS

VaD can be the result of ischemic or hemorrhagic tissue injury in a particular region of the brain which translates into clinically significant cognitive impairment. For example, a cerebral infarct in the speech area of the dominant hemisphere would translate into clinically significant impairment as would involvement of projection pathways such as the arcuate fasciculus. Specific involvement of the angular gyrus of the dominant hemisphere, with resultant Gerstman's syndrome, could have a pronounced effect on functional ability despite being termed a "minor stroke". Small vessel cerebrovascular disease can have a cumulate effect on cognitive function over time. It is unfortunately well recognized that "good" functional recovery in acute ischemic or haemorrhagic stroke, including subarachnoid haemorrhage, does not necessarily translate into good cognitive recovery. The victim may often be left unable to have gainful employment, drive a car safely or handle their affairs independently.

CONCLUSIONS

This review should serve as a compendium of updated information on VaD and provide guidance in terms of newer diagnostic and potential therapeutic approaches.

Brain MRI in Monogenic Cerebral Small Vessel Diseases: A Practical Handbook

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Monogenic cerebral small vessel diseases are a topic of growing interest, as several genes responsible have been recently described and new sequencing techniques such as Next generation sequencing are available. Brain imaging is a key exam in these diseases. First, since it is often the first exam performed, an MRI is key in selecting patients for genetic testing and for interpreting Next generation sequencing reports. In addition, neuroimaging can be helpful in describing the underlying pathological mechanisms involved in cerebral small vessel disease. With this review, we aim to provide Neurologists and Stroke physicians with an up-to date overview of the current neuroimaging knowledge on monogenic small vessel diseases.

FDG PET Data is Associated with Cognitive Performance in Patients from a Memory Clinic

BACKGROUND

Various reasons may lead to cognitive symptoms in elderly, including the development of cognitive decline and dementia. Often, mixed pathologies such as neurodegeneration and cerebrovascular disease co-exist in these patients. Diagnostic work-up commonly includes imaging modalities such as FDG PET, MRI, and CT, each delivering specific information.

OBJECTIVE

To study the informative value of neuroimaging-based data supposed to reflect neurodegeneration (FDG PET), cerebral small vessel disease (MRI), and cerebral large vessel atherosclerosis (CT) with regard to cognitive performance in patients presenting to our memory clinic.

METHODS

Non-parametric partial correlations and an ordinal logistic regression model were run to determine relationships between scores for cortical hypometabolism, white matter hyperintensities, calcified plaque burden, and results from Mini-Mental State Examination (MMSE). The final study group consisted of 162 patients (female: 94; MMSE: 6-30).

RESULTS

Only FDG PET data was linked to and predicted cognitive performance (r(157) = -0.388, p < 0.001). Overall, parameters linked to cerebral small and large vessel disease showed no significant association with cognition. Further findings demonstrated a relationship between white matter hyperintensities and FDG PET data (r(157) = 0.230, p = 0.004).

CONCLUSION

Only FDG PET imaging mirrors cognitive performance, presumably due to the examination's ability to reflect neurodegeneration and vascular dysfunction, thus capturing a broader spectrum of pathologies. This makes the examination a useful imaging-based diagnostic tool in the work-up of patients presenting to a memory clinic. Parameters of vascular dysfunction alone as depicted by conventional MRI and CT are less adequate in such a situation, most likely because they reflect one pathology complex only.

Clinical Use of Integrated Positron Emission Tomography-Magnetic Resonance Imaging for Dementia Patients

Combining magnetic resonance imaging (MRI) with 2-deoxy-2-F-fluoro-D-glucose positron emission tomography (FDG-PET) data improve the imaging accuracy for detection of Alzheimer disease and related dementias. Integrated FDG-PET-MRI is a recent technical innovation that allows both imaging modalities to be obtained simultaneously from individual patients with cognitive impairment. This report describes the practical benefits and challenges of using integrated FDG-PET-MRI to support the clinical diagnosis of various dementias. Over the past 7 years, we have performed integrated FDG-PET-MRI on >1500 patients with possible cognitive impairment or dementia. The FDG-PET and MRI protocols are the same as current conventions, but are obtained simultaneously over 25 minutes. An additional Dixon MRI sequence with superimposed bone atlas is used to calculate PET attenuation correction. A single radiologist interprets all imaging data and generates 1 report. The most common positive finding is concordant temporoparietal volume loss and FDG hypometabolism that suggests increased risk for underlying Alzheimer disease. Lobar-specific atrophy and FDG hypometabolism patterns that may be subtle, asymmetric, and focal also are more easily recognized using combined FDG-PET and MRI, thereby improving detection of other neurodegeneration conditions such as primary progressive aphasias and frontotemporal degeneration. Integrated PET-MRI has many practical benefits to individual patients, referrers, and interpreting radiologists. The integrated PET-MRI system requires several modifications to standard imaging center workflows, and requires training individual radiologists to interpret both modalities in conjunction. Reading MRI and FDG-PET together increases imaging diagnostic yield for individual patients; however, both modalities have limitations in specificity.