Positron emission tomography scans obtained for the evaluation of cognitive dysfunction

Early-phase 18F-Florbetapir and 18F-Flutemetamol images as proxies of brain metabolism in a memory clinic setting

Background: Alzheimer's disease (AD) neuropathologic changes are β-amyloid (Aβ) deposition, pathologic tau, and neurodegeneration. Dual-phase amyloid-PET might be able to evaluate Aβ deposition and neurodegeneration with a single tracer injection. Early-phase amyloid-PET scans provide a proxy for cerebral perfusion, which has shown good correlations with neural dysfunction measured through metabolic consumption, while the late frames depict amyloid distribution. Our study aims to assess the comparability between early-phase amyloid-PET scans and 18F-fluorodeoxyglucose (18F-FDG)-PET brain topography at the individual level, and their ability to discriminate patients. Methods: 166 subjects evaluated at the Geneva Memory Center, ranging from cognitively unimpaired to Mild Cognitive Impairment (MCI) and dementia, underwent early-phase amyloid-PET - using either 18F-florbetapir (eFBP) (n = 94) or 18F-flutemetamol (eFMM) (n = 72) - and 18F-FDG-PET. Aβ status was assessed. Standardized uptake value ratios (SUVR) were extracted to evaluate the correlation of eFBP/eFMM and their respective 18F-FDG-PET scans. The single-subject procedure was applied to investigate hypometabolism and hypoperfusion maps and their spatial overlap by Dice coefficient. Receiver operating characteristic analyses were performed to compare the discriminative power of eFBP/eFMM, and 18F-FDG-PET SUVR in AD-related metaROI between Aβ-negative healthy controls and cases in the AD continuum. Results: Positive correlations were found between eFBP/eFMM and 18F-FDG-PET SUVR independently of Aβ status and Aβ radiotracer (R>0.72, p<0.001). eFBP/eFMM single-subject analysis revealed clusters of significant hypoperfusion with good correspondence to hypometabolism topographies, independently of the underlying neurodegenerative patterns. Both eFBP/eFMM and 18F-FDG-PET SUVR significantly discriminated AD patients from controls in the AD-related metaROIs (AUCFBP = 0.888; AUCFMM=0.801), with 18F-FDG-PET performing slightly better, however not significantly (all p-value higher than 0.05), than others (AUCFDG=0.915 and 0.832 for subjects evaluated with 18F-FBP and 18F-FMM, respectively). Conclusion: The distribution of perfusion was comparable to that of metabolism at the single-subject level by parametric analysis, particularly in the presence of a high neurodegeneration burden. Our findings indicate that eFBP/eFMM imaging can replace 18F-FDG-PET imaging, as they reveal typical neurodegenerative patterns, or allow to exclude the presence of neurodegeneration. The finding shows cost-saving capacities of amyloid-PET and supports the routine use of the modality for individual classification in clinical practice.

Artificial Intelligence on FDG PET Images Identifies Mild Cognitive Impairment Patients with Neurodegenerative Disease

The purpose of this project is to develop and validate a Deep Learning (DL) FDG PET imaging algorithm able to identify patients with any neurodegenerative diseases (Alzheimer's Disease (AD), Frontotemporal Degeneration (FTD) or Dementia with Lewy Bodies (DLB)) among patients with Mild Cognitive Impairment (MCI). A 3D Convolutional neural network was trained using images from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. The ADNI dataset used for the model training and testing consisted of 822 subjects (472 AD and 350 MCI). The validation was performed on an independent dataset from La Fe University and Polytechnic Hospital. This dataset contained 90 subjects with MCI, 71 of them developed a neurodegenerative disease (64 AD, 4 FTD and 3 DLB) while 19 did not associate any neurodegenerative disease. The model had 79% accuracy, 88% sensitivity and 71% specificity in the identification of patients with neurodegenerative diseases tested on the 10% ADNI dataset, achieving an area under the receiver operating characteristic curve (AUC) of 0.90. On the external validation, the model preserved 80% balanced accuracy, 75% sensitivity, 84% specificity and 0.86 AUC. This binary classifier model based on FDG PET images allows the early prediction of neurodegenerative diseases in MCI patients in standard clinical settings with an overall 80% classification balanced accuracy.

Corrosion of Polished Cobalt-Chrome Stems Presenting as Cobalt Encephalopathy

Adverse reactions to metallic debris from corrosion of polished cobalt-chromium–cemented femoral stems are reported. Cobaltism (systemic cobalt poisoning) has not been reported from this phenomenon. Three patients presented to their surgeon for ongoing care 10-20 years after primary metal-on-plastic hip arthroplasty with the same polished cobalt-chromium–cemented femoral stems (Heritage, Zimmer). Urine cobalt was elevated, and the patients had symptoms consistent with cobaltism. Quantitative-F¹⁶DG-PET-CT brain imaging was performed showing generalized and focal brain hypometabolism consistent with cobalt encephalopathy. At revision, all stems were well fixed and grossly corroded. At 1 year after revision, cobalturia and cognitive symptoms were resolved or improved. Mechanically assisted crevice corrosion at the polymethylmethacrylate interface is a complication of polished cobalt-chromium–cemented stems that can result in systemic cobalt exposure and toxic encephalopathy. Our cases had only minor periprosthetic symptoms. Patients implanted with polished cobalt-chromium–cemented stems warrant monitoring with urine cobalt. Patients with cobaltemia warrant an evaluation for toxic encephalopathy.

The Italian INTERCEPTOR Project: From the Early Identification of Patients Eligible for Prescription of Antidementia Drugs to a Nationwide Organizational Model for Early Alzheimer's Disease Diagnosis

Alzheimer's disease is the most common age-related neurodegenerative disorder and its burden on patients, families, and society grows significantly with lifespan. Early modifications of risk-enhancing lifestyles and treatment initiation expand personal autonomy and reduce management costs. Many clinical trials with potentially disease-modifying drugs are devoted to mild cognitive impairment (MCI) prodromal-to-Alzheimer's disease. The identification of biomarkers for early diagnosis may thus be crucial for early intervention and identification of high-risk subjects, the most appropriate target of new drugs as soon as they will be discovered. INTERCEPTOR is a strategic project by the Italian Ministry of Health and the Italian Medicines Agency (AIFA), aiming to validate the best combination (highly accurate, non-invasive, available on the whole national territory and financially sustainable) of biomarkers and organizational model for early diagnosis. 500 MCI subjects will be enrolled at baseline and followed-up for 3 years for at least 400 of them in order to define a "hub & spoke" nationwide model with recruiting (spokes) centers for MCI identification and expert (hubs) centers for risk diagnosis.

F-18 FDG PET brain imaging in symptomatic arthroprosthetic cobaltism

PURPOSE

Imaging studies of cobalt toxicity from cobalt-chromium alloy arthroprosthetics have focused on the local intra-articular and peri-articular presentation from failing joint replacements. Most studies investigating neurological findings have been small case series focused on the clinical findings of memory loss, diminished executive function, tremor, hearing and vision loss, depression, and emotional lability. This study utilizes software-based quantitative analysis of brain metabolism to assess the degree of hypometabolism and areas of susceptibility, determine if a pattern of involvement exists, and measure reversibility of findings after prosthetic revision to cobalt-free appliances.

METHODS

Over 48 months, 247 consecutive patients presenting to an orthopedic clinic with an arthroprosthetic joint containing any cobalt-chromium part were screened with whole blood and urine cobalt levels. A clinically validated inventory of 10 symptoms was obtained. Symptomatic patients with a blood cobalt level above 0.4 mcg/L or urine cobalt greater than 1 mcg/L underwent F-18 FDG PET brain imaging. Analysis was performed with FDA-approved quantitative brain analysis software with the pons as the reference region. Control group was the normal brain atlas within the software.

RESULTS

Of the 247 consecutively screened patients, 123 had blood and urine cobalt levels above the threshold. The 69 scanned patients had statistically significant regional hypometabolism and higher symptoms inventory. Fifty-seven patients were retained in the study. Distribution of hypometabolism was in descending order: temporal, frontal, Broca's areas, anterior cingulate, parietal, posterior cingulate, visual, sensorimotor, thalamic, and lastly caudate. Metal-on-metal (MoM) and metal-on-plastic (MoP) joint replacements produced similar patterns of hypometabolism. Of 15 patients with necessary revision surgery, 8 demonstrated improved metabolism when later re-scanned.

CONCLUSION

All scanned patients had regions of significant hypometabolism. Neurological toxicity from elevated systemic cobalt levels following arthroprosthetic joint replacement has a pattern of regional susceptibility similar to heavy metals and solvents, differing from classical dementias and may occur at blood and urine cobalt levels as low as 0.4 mcg/L and 1 mcg/L, respectively. Presently accepted thresholds for cobalt exposure and monitoring may need revision. Quantitative F-18 FDG PET brain imaging may aid in the decision process for treatment options and timing of possible medical versus surgical intervention.

Decreased Glucose Utilization Contributes to Memory Impairment in Patients with Glufosinate Ammonium Intoxication

The symptoms of glufosinate ammonium (GLA) intoxication include gastrointestinal and neurologic symptoms, respiratory failure, and cardiovascular instability. Among these, neurologic symptoms including loss of consciousness, memory impairment, and seizure are characteristic of GLA poisoning. However, the mechanism of brain injury by GLA poisoning is still poorly understood. We investigated nine patients who had performed an F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) scan because of memory impairment caused by GLA ingestion. FDG-PET images of patients with GLA intoxication were compared with 24 age- and sex-matched healthy controls to evaluate whether the patients had abnormal patterns of glucose metabolism in the brain. Decreased glucose metabolism was observed in the inferior frontal and temporal lobes of these patients with GLA intoxication when compared with 24 age- and sex-matched healthy controls. Three patients performed follow-up FDG-PET scans. However, it was shown that the results of the follow-up FDG-PET scans were determined to be inconclusive. Our study showed that memory impairment induced by GLA intoxication was associated with glucose hypometabolism in the inferior frontal and temporal lobes in the brain.

Alcohol Intoxication and Cognition: Implications on Mechanisms and Therapeutic Strategies

Binge alcohol drinking is highly prevalent in young adults and results in 30% deaths per year in young males. Binge alcohol drinking or acute alcohol intoxication is a risk factor for developing alcohol use disorder (AUD). Three FDA approved drugs are currently in use as therapy for AUD; however, all of them have contra-indications and limitations. Structural brain imaging studies in alcoholics have shown defects in the brain regions involved in memory, cognition and emotional processing. Positron emission tomography (PET) using radiotracers (e.g., 18FDG) and measuring brain glucose metabolism have demonstrated diagnostic and prognostic utility in evaluating patients with cognitive impairment. Using PET imaging, only a few exclusive human studies have addressed the relationship between alcohol intoxication and cognition. Those studies indicate that alcohol intoxication causes reduction in brain activity. Consistent with prior findings, a recent study by us showed that acute alcohol intoxication reduced brain activity in the cortical and subcortical regions including the temporal lobe consisting the hippocampus. Additionally, we have observed a strong correlation between reduction in metabolic activity and spatial cognition impairment in the hippocampus after binge alcohol exposure. We have also demonstrated the involvement of a stress response protein, cold inducible RNA binding protein (CIRP), as a potential mechanistic mediator in acute alcohol intoxication. In this review, we will first discuss in detail prior human PET imaging studies on alcohol intoxication as well as our recent study on acute alcohol intoxication, and review the existing literature on potential mechanisms of acute alcohol intoxication-induced cognitive impairment and therapeutic strategies to mitigate these impairments. Finally, we will highlight the importance of studying brain regions as part of a brain network in delineating the mechanism of acute alcohol intoxication-induced cognitive impairment to aid in the development of therapeutics for such indication.

A Hierarchical Bayesian Model for the Identification of PET Markers Associated to the Prediction of Surgical Outcome after Anterior Temporal Lobe Resection

We develop an integrative Bayesian predictive modeling framework that identifies individual pathological brain states based on the selection of fluoro-deoxyglucose positron emission tomography (PET) imaging biomarkers and evaluates the association of those states with a clinical outcome. We consider data from a study on temporal lobe epilepsy (TLE) patients who subsequently underwent anterior temporal lobe resection. Our modeling framework looks at the observed profiles of regional glucose metabolism in PET as the phenotypic manifestation of a latent individual pathologic state, which is assumed to vary across the population. The modeling strategy we adopt allows the identification of patient subgroups characterized by latent pathologies differentially associated to the clinical outcome of interest. It also identifies imaging biomarkers characterizing the pathological states of the subjects. In the data application, we identify a subgroup of TLE patients at high risk for post-surgical seizure recurrence after anterior temporal lobe resection, together with a set of discriminatory brain regions that can be used to distinguish the latent subgroups. We show that the proposed method achieves high cross-validated accuracy in predicting post-surgical seizure recurrence.

Brain metabolic maps in Mild Cognitive Impairment predict heterogeneity of progression to dementia

[¹⁸F]FDG-PET imaging has been recognized as a crucial diagnostic marker in Mild Cognitive Impairment (MCI), supporting the presence or the exclusion of Alzheimer's Disease (AD) pathology. A clinical heterogeneity, however, underlies MCI definition. In this study, we aimed to evaluate the predictive role of single-subject voxel-based maps of [¹⁸F]FDG distribution generated through statistical parametric mapping (SPM) in the progression to different dementia subtypes in a sample of 45 MCI. Their scans were compared to a large normal reference dataset developed and validated for comparison at single-subject level. Additionally, Aβ42 and Tau CSF values were available in 34 MCI subjects. Clinical follow-up (mean 28.5 ± 7.8 months) assessed subsequent progression to AD or non-AD dementias. The SPM analysis showed: 1) normal brain metabolism in 14 MCI cases, none of them progressing to dementia; 2) the typical temporo-parietal pattern suggestive for prodromal AD in 15 cases, 11 of them progressing to AD; 3) brain hypometabolism suggestive of frontotemporal lobar degeneration (FTLD) subtypes in 7 and dementia with Lewy bodies (DLB) in 2 subjects (all fulfilled FTLD or DLB clinical criteria at follow-up); and 4) 7 MCI cases showed a selective unilateral or bilateral temporo-medial hypometabolism without the typical AD pattern, and they all remained stable. In our sample, objective voxel-based analysis of [¹⁸F]FDG-PET scans showed high predictive prognostic value, by identifying either normal brain metabolism or hypometabolic patterns suggestive of different underlying pathologies, as confirmed by progression at follow-up. These data support the potential usefulness of this SPM [¹⁸F]FDG PET analysis in the early dementia diagnosis and for improving subject selection in clinical trials based on MCI definition.

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We used an optimized voxel-based single-subject [¹⁸F]FDG-PET analysis

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We showed different hypometabolic patterns (AD and non-AD) underlying MCI condition

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Heterogeneous PET profiles predicted progression into specific dementia subtypes.

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Statistical analyses showed high positive and negative post-test probability values.

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CSF findings agreed with [¹⁸F]FDG-PET imaging in single cases.

Validation of an optimized SPM procedure for FDG-PET in dementia diagnosis in a clinical setting

Diagnostic accuracy in FDG-PET imaging highly depends on the operating procedures. In this clinical study on dementia, we compared the diagnostic accuracy at a single-subject level of a) Clinical Scenarios, b) Standard FDG Images and c) Statistical Parametrical (SPM) Maps generated via a new optimized SPM procedure. We evaluated the added value of FDG-PET, either Standard FDG Images or SPM Maps, to Clinical Scenarios. In 88 patients with neurodegenerative diseases (Alzheimer's Disease—AD, Frontotemporal Lobar Degeneration—FTLD, Dementia with Lewy bodies—DLB and Mild Cognitive Impairment—MCI), 9 neuroimaging experts made a forced diagnostic decision on the basis of the evaluation of the three types of information. There was also the possibility of a decision of normality on the FDG-PET images. The clinical diagnosis confirmed at a long-term follow-up was used as the gold standard. SPM Maps showed higher sensitivity and specificity (96% and 84%), and better diagnostic positive (6.8) and negative (0.05) likelihood ratios compared to Clinical Scenarios and Standard FDG Images. SPM Maps increased diagnostic accuracy for differential diagnosis (AD vs. FTD; beta 1.414, p = 0.019). The AUC of the ROC curve was 0.67 for SPM Maps, 0.57 for Clinical Scenarios and 0.50 for Standard FDG Images. In the MCI group, SPM Maps showed the highest predictive prognostic value (mean LOC = 2.46), by identifying either normal brain metabolism (exclusionary role) or hypometabolic patterns typical of different neurodegenerative conditions.

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Brain FDG-PET was evaluated with a new optimized SPM procedure in dementias.

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We compared the diagnostic accuracy of clinical information, visual and SPM FDG-PET.

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SPM had the best sensitivity (96%), specificity (84%) and positive and negative LR.

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In an MCI subgroup, SPM had the highest predictive prognostic value.

Prospective randomized trial to assess effects of continuing hormone therapy on cerebral function in postmenopausal women at risk for dementia

The objective of this study was to examine the effects of estrogen-based hormone therapy (HT) on regional cerebral metabolism in postmenopausal women (mean age = 58, SD = 5) at risk for development of dementia. The prospective clinical trial design included pre- and post-intervention neuroimaging of women randomized to continue (HT+) or discontinue (HT−) therapy following an average of 10 years of use. The primary outcome measure was change in brain metabolism during the subsequent two years, as assessed with fluorodeoxyglucose-18 positron emission tomography (FDG-PET). Longitudinal FDG-PET data were available for 45 study completers. Results showed that women randomized to continue HT experienced relative preservation of frontal and parietal cortical metabolism, compared with women randomized to discontinue HT. Women who discontinued 17-β estradiol (17βE)-based HT, as well as women who continued conjugated equine estrogen (CEE)-based HT, exhibited significant decline in metabolism of the precuneus/posterior cingulate cortical (PCC) area. Significant decline in PCC metabolism was additionally seen in women taking concurrent progestins (with either 17βE or CEE). Together, these findings suggest that among postmenopausal subjects at risk for developing dementia, regional cerebral cortical metabolism is relatively preserved for at least two years in women randomized to continue HT, compared with women randomized to discontinue HT. In addition, continuing unopposed 17βE therapy is associated specifically with preservation of metabolism in PCC, known to undergo the most significant decline in the earliest stages of Alzheimer's disease.

Trial Registration

ClinicalTrials.govNCT00097058

Neuroimaging biomarkers and cognitive function in non-CNS cancer and its treatment: current status and recommendations for future research

Cognitive changes in patients undergoing treatment for non-central nervous system (CNS) cancers have been recognized for several decades, yet the underlying mechanisms are not well understood. Structural, functional and molecular neuroimaging has the potential to help clarify the neural bases of these cognitive abnormalities. Structural magnetic resonance imaging (MRI), functional MRI (fMRI), diffusion tensor imaging (DTI), MR spectroscopy (MRS), and positron emission tomography (PET) have all been employed in the study of cognitive effects of cancer treatment, with most studies focusing on breast cancer and changes thought to be induced by chemotherapy. Articles in this special issue of Brain Imaging and Behavior are devoted to neuroimaging studies of cognitive changes in patients with non-CNS cancer and include comprehensive critical reviews and novel research findings. The broad conclusions that can be drawn from past studies and the present body of new research is that there are structural and functional changes associated with cancer and various treatments, particularly systemic cytotoxic chemotherapy, although some cognitive and fMRI studies have identified changes at pre-treatment baseline. Recommendations to accelerate progress include well-powered multicenter neuroimaging studies, a better standardized definition of the cognitive phenotype and extension to other cancers. A systems biology framework incorporating multimodality neuroimaging, genetics and other biomarkers will be highly informative regarding individual differences in risk and protective factors and disease- and treatment-related mechanisms. Studies of interventions targeting cognitive changes are also needed. These next steps are expected to identify novel protective strategies and facilitate a more personalized medicine for cancer patients.

Neuroimaging, cancer, and cognition: state of the knowledge

OBJECTIVES

To review neuroimaging research concerning cancer- and cancer treatment-related changes in brain structure and function, clinical perspectives, and future directions.

DATA SOURCES

Peer-reviewed literature.

CONCLUSION

Cancer and chemotherapy are associated with cerebral structural and functional alterations in breast cancer patients that may persist for years; many of these changes are correlated with cognitive complaints or performance. In other cancers there is some evidence that metabolism is altered by cancer, but more research is needed.

IMPLICATIONS FOR NURSING PRACTICE

Understanding the role of neuroimaging is important to identify the basis of cognitive changes associated with cancer and cancer treatment.

Implication of the nutritional and nonnutritional factors in the context of preservation of cognitive performance in patients with dementia/depression and Alzheimer disease

It has been postulated that Alzheimer disease (AD) is a systemic process, which involves multiple pathophysiological factors. A combination of pharmacotherapy and nonpharmacological interventions has been proposed to treat AD and other dementia. The nonpharmacological interventions include but are not limited to increasing sensory input through physical and mental activities, in order to modify cerebral blood flow and implementing nutritional interventions such as diet modification and vitamins and nutraceuticals therapy to vitalize brain functioning. This article highlights the recent research findings regarding novel treatment strategies aimed at modifying natural course of the disease and delaying cognitive decline through simultaneous implementation of pharmacological and nonpharmacological modulators as standardized treatment protocols.

Visual-statistical interpretation of (18)F-FDG-PET images for characteristic Alzheimer patterns in a multicenter study: inter-rater concordance and relationship to automated quantitative evaluation

BACKGROUND AND PURPOSE

The role of (18)F-FDG-PET in the diagnosis of Alzheimer disease is increasing and should be validated. The aim of this study was to assess the inter-rater variability in the interpretation of (18)F-FDG-PET images obtained in the Japanese Alzheimer's Disease Neuroimaging Initiative, a multicenter clinical research project.

MATERIALS AND METHODS

This study analyzed 274 (18)F-FDG-PET scans (67 mild Alzheimer disease, 100 mild cognitive impairment, and 107 normal cognitive) as baseline scans for the Japanese Alzheimer's Disease Neuroimaging Initiative, which were acquired with various types of PET or PET/CT scanners in 23 facilities. Three independent raters interpreted all PET images by using a combined visual-statistical method. The images were classified into 7 (FDG-7) patterns by the criteria of Silverman et al and further into 2 (FDG-2) patterns.

RESULTS

Agreement among the 7 visual-statistical categories by at least 2 of the 3 readers occurred in >94% of cases for all groups: Alzheimer disease, mild cognitive impairment, and normal cognitive. Perfect matches by all 3 raters were observed for 62% of the cases by FDG-7 and 76 by FDG-2. Inter-rater concordance was moderate by FDG-7 (κ = 0.57) and substantial in FDG-2 (κ = 0.67) on average. The FDG-PET score, an automated quantitative index developed by Herholz et al, increased as the number of raters who voted for the AD pattern increased (ρ = 0.59, P < .0001), and the FDG-PET score decreased as those for normal pattern increased (ρ = -0.64, P < .0001).

CONCLUSIONS

Inter-rater agreement was moderate to substantial for the combined visual-statistical interpretation of (18)F-FDG-PET and was also significantly associated with automated quantitative assessment.

Neuronuclear imaging in the evaluation of dementia and mild decline in cognition

Recently, the National Institute on Aging and the Alzheimer's Association identified specific structural and functional neuroimaging findings as valuable markers of biological processes occurring in the human brain, especially processes that herald impending dementia caused by Alzheimer's disease (AD) in its prodromal form. In particular, the imaging modalities of magnetic resonance imaging and positron emission tomography (PET) were singled out, along with certain biomarkers in cerebrospinal fluid, to serve this purpose. We review the clinical tests available for neuropsychologic evaluation and in cases when the differential diagnosis for the causes of cognitive impairment is difficult to make, we consider biomarkers, beginning with cerebrospinal fluid, for assessment of cognitive decline. For more direct information on dementia-related pathologic changes in brain tissue, structural features observed in magnetic resonance imaging scans are regarded. We next discuss the use of single-photon emission computed tomography for evaluating functional changes. Then, pertinent to the recent National Institute on Aging and the Alzheimer's Association's consensus statement on the diagnosis of prodromal AD, we focus on assessing the cerebral metabolic changes associated with neurodegenerative diseases that are identified with fluorodeoxyglucose PET, as well as consider the most appropriate roles for amyloid imaging based on recent studies examining the use of PET with tracers having higher retention in brain tissue-harboring plaques composed of insoluble beta-amyloid. We also consider the leading causes for the current underuse of neuronuclear imaging in evaluating patients with cognitive problems, along with strategies for combating them. Finally, we suggest an overall diagnostic algorithm to guide optimal use of all the neuroimaging tools in assessing patients with cognitive decline.

Ovariectomy induces a shift in fuel availability and metabolism in the hippocampus of the female transgenic model of familial Alzheimer's

Previously, we demonstrated that reproductive senescence in female triple transgenic Alzheimer's (3×TgAD) mice was paralleled by a shift towards a ketogenic profile with a concomitant decline in mitochondrial activity in brain, suggesting a potential association between ovarian hormone loss and alteration in the bioenergetic profile of the brain. In the present study, we investigated the impact of ovariectomy and 17β-estradiol replacement on brain energy substrate availability and metabolism in a mouse model of familial Alzheimer's (3×TgAD). Results of these analyses indicated that ovarian hormones deprivation by ovariectomy (OVX) induced a significant decrease in brain glucose uptake indicated by decline in 2-[¹⁸F]fluoro-2-deoxy-D-glucose uptake measured by microPET-imaging. Mechanistically, OVX induced a significant decline in blood-brain-barrier specific glucose transporter expression, hexokinase expression and activity. The decline in glucose availability was accompanied by a significant rise in glial LDH5 expression and LDH5/LDH1 ratio indicative of lactate generation and utilization. In parallel, a significant rise in ketone body concentration in serum occurred which was coupled to an increase in neuronal MCT2 expression and 3-oxoacid-CoA transferase (SCOT) required for conversion of ketone bodies to acetyl-CoA. In addition, OVX-induced decline in glucose metabolism was paralleled by a significant increase in Aβ oligomer levels. 17β-estradiol preserved brain glucose-driven metabolic capacity and partially prevented the OVX-induced shift in bioenergetic substrate as evidenced by glucose uptake, glucose transporter expression and gene expression associated with aerobic glycolysis. 17β-estradiol also partially prevented the OVX-induced increase in Aβ oligomer levels. Collectively, these data indicate that ovarian hormone loss in a preclinical model of Alzheimer's was paralleled by a shift towards the metabolic pathway required for metabolism of alternative fuels in brain with a concomitant decline in brain glucose transport and metabolism. These findings also indicate that estrogen plays a critical role in sustaining brain bioenergetic capacity through preservation of glucose metabolism.

Regional, kinetic [(18)F]FDG PET imaging of a unilateral Parkinsonian animal model

Positron emission tomography (PET) imaging with the glucose analog 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F] FDG) has demonstrated clinical utility for the monitoring of brain glucose metabolism alteration in progressive neurodegenerative diseases. We examined dynamic [(18)F]FDG PET imaging and kinetic modeling of atlas-based regions to evaluate regional changes in the cerebral metabolic rate of glucose in the widely-used 6-hydroxydopamine (6-OHDA) rat model of Parkinson's disease. Following a bolus injection of 18.5 ± 1 MBq [(18)F]FDG and a 60-minute PET scan, image-derived input functions from the vena cava and left ventricle were used with three models, including Patlak graphical analysis, to estimate the influx constant and the metabolic rate in ten brain regions. We observed statistically significant changes in [(18)F]FDG uptake ipsilateral to the 6-OHDA injection in the basal ganglia, olfactory bulb, and amygdala regions; and these changes are of biological relevance to the disease. These experiments provide further validation for the use of [(18)F]FDG PET imaging in this model for drug discovery and development.

Assessment of dementia risk in aging adults using both FDG-PET and FDDNP-PET imaging

BACKGROUND

In a previous study, positron emission tomography (PET) with 2-(1-{6-[(2-[F-18]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile (FDDNP), a molecule that binds to plaques and tangles in vitro, identified three subgroups of non-demented subjects according to FDDNP binding patterns: low global (LG) binding; high frontal, parietal, medial temporal binding (HF/PA); and high medial and lateral temporal and posterior cingulate (HT/PC) binding. In this follow-up investigation, we compared 2-deoxy-2-[F-18]fluoro- d-glucose (FDG)-PET cerebral metabolic patterns in the three FDDNP-PET binding subgroups.

METHODS

Fifty-four subjects with normal aging (N = 28) or amnestic forms of mild cognitive impairment (N = 26) underwent FDDNP-PET and FDG-PET scanning. Subjects in the LG, HF/PA, and HT/PC FDDNP subgroups were compared according to visual ratings, statistical parametric mapping, and automated region of interest analyses of their FDG-PET data.

RESULTS

The FDDNP-PET subgroups demonstrated different glucose metabolic patterns according to visual ratings, region of interest, and statistical parametric mapping analyses of FDG-PET data. The LG FDDNP subgroup showed no areas of significant hypometabolism relative to the other subgroups and had low Alzheimer's disease risk by FDG-PET standards. The HF/PA FDDNP subgroup demonstrated hypometabolism in bilateral inferior parietal/parietotemporal, bilateral posterior cingulate, perisylvian, mid-temporal gyrus, and dorsolateral prefrontal regions, which is a pattern suggestive of high Alzheimer's disease risk. The HT/PC FDDNP subgroup demonstrated heterogeneous FDG-PET patterns with predominant anterior frontal and anterior temporal hypometabolism, suggestive of mixed etiologies, including fronto-temporal dementia risk.

CONCLUSIONS

The FDG-PET data provided independent validation that different patterns of FDDNP-PET binding in non-demented individuals may be associated with differential dementia risk.

Imaging radiation-induced normal tissue injury

Technological developments in radiation therapy and other cancer therapies have led to a progressive increase in five-year survival rates over the last few decades. Although acute effects have been largely minimized by both technical advances and medical interventions, late effects remain a concern. Indeed, the need to identify those individuals who will develop radiation-induced late effects, and to develop interventions to prevent or ameliorate these late effects is a critical area of radiobiology research. In the last two decades, preclinical studies have clearly established that late radiation injury can be prevented/ameliorated by pharmacological therapies aimed at modulating the cascade of events leading to the clinical expression of radiation-induced late effects. These insights have been accompanied by significant technological advances in imaging that are moving radiation oncology and normal tissue radiobiology from disciplines driven by anatomy and macrostructure to ones in which important quantitative functional, microstructural, and metabolic data can be noninvasively and serially determined. In the current article, we review use of positron emission tomography (PET), single photon emission tomography (SPECT), magnetic resonance (MR) imaging and MR spectroscopy to generate pathophysiological and functional data in the central nervous system, lung, and heart that offer the promise of, (1) identifying individuals who are at risk of developing radiation-induced late effects, and (2) monitoring the efficacy of interventions to prevent/ameliorate them.

Effectiveness and safety of 18F-FDG PET in the evaluation of dementia: a review of the recent literature

Imaging that can detect pathophysiologic change in the brain holds great promise for diagnostic assessment of patients with Alzheimer disease (AD) and dementia. Although a previous metaanalysis centering on literature from 1990 to 2000 showed a summary accuracy of 86% for (18)F-FDG PET for AD diagnosis, the clinical value was considered uncertain because of methodologic shortcomings. Review of the recent literature since 2000 demonstrates that the evidence for (18)F-FDG PET in assessment of dementia has increased with new studies that include autopsy confirmation, wide-diagnostic-spectrum recruitment in primary care settings, historical and prospective cohort studies, and multicenter data analyses. These data support the role of (18)F-FDG PET as an effective and useful adjunct to other diagnostic information in the assessment of patients with symptoms of dementia. Findings are in line with recently revised diagnostic criteria of AD that for the first time recognize the unique role of biomarker evidence in disease definition.

Positron emission tomography radiopharmaceuticals for imaging brain Beta-amyloid

Alzheimer's disease (AD) is defined histologically by the presence of extracellular β-amyloid (Aβ) plaques and intraneuronal neurofibrillary tangles in the cerebral cortex. The diagnosis of dementia, along with the prediction of who will develop dementia, has been assisted by magnetic resonance imaging and positron emission tomography (PET) by using [(18)F]fluorodeoxyglucose (FDG). These techniques, however, are not specific for AD. Based on the chemistry of histologic staining dyes, several Aβ-specific positron-emitting radiotracers have been developed to image neuropathology of AD. Among these, [(11)C]PiB is the most studied Aβ-binding PET radiopharmaceutical in the world. The histologic and biochemical specificity of PiB binding across different regions of the AD brain was demonstrated by showing a direct correlation between Aβ-containing amyloid plaques and in vivo [(11)C]PiB retention measured by PET imaging. Because (11)C is not ideal for commercialization, several (18)F-labeled tracers have been developed. At this time, [(18)F]3'-F-PiB (Flutemetamol), (18)F-AV-45 (Florbetapir), and (18)F-AV-1 (Florbetaben) are undergoing extensive phase II and III clinical trials. This article provides a brief review of the amyloid biology and chemistry of Aβ-specific (11)C and (18)F-PET radiopharmaceuticals. Clinical trials have clearly documented that PET radiopharmaceuticals capable of assessing Aβ content in vivo in the brains of AD subjects and subjects with mild cognitive impairment will be important as diagnostic agents to detect in vivo amyloid brain pathology. In addition, PET amyloid imaging will also help test the amyloid cascade hypothesis of AD and as an aid to assess the efficacy of antiamyloid therapeutics currently under development in clinical trials.

Brain fuel metabolism, aging, and Alzheimer's disease

Lower brain glucose metabolism is present before the onset of clinically measurable cognitive decline in two groups of people at risk of Alzheimer's disease--carriers of apolipoprotein E4, and in those with a maternal family history of AD. Supported by emerging evidence from in vitro and animal studies, these reports suggest that brain hypometabolism may precede and therefore contribute to the neuropathologic cascade leading to cognitive decline in AD. The reason brain hypometabolism develops is unclear but may include defects in brain glucose transport, disrupted glycolysis, and/or impaired mitochondrial function. Methodologic issues presently preclude knowing with certainty whether or not aging in the absence of cognitive impairment is necessarily associated with lower brain glucose metabolism. Nevertheless, aging appears to increase the risk of deteriorating systemic control of glucose utilization, which, in turn, may increase the risk of declining brain glucose uptake, at least in some brain regions. A contributing role of deteriorating glucose availability to or metabolism by the brain in AD does not exclude the opposite effect, i.e., that neurodegenerative processes in AD further decrease brain glucose metabolism because of reduced synaptic functionality and hence reduced energy needs, thereby completing a vicious cycle. Strategies to reduce the risk of AD by breaking this cycle should aim to (1) improve insulin sensitivity by improving systemic glucose utilization, or (2) bypass deteriorating brain glucose metabolism using approaches that safely induce mild, sustainable ketonemia.

Comparing fludeoxyglucose F18-PET assessment of regional cerebral glucose metabolism and [11C]dihydrotetrabenazine-PET in evaluation of early dementia and mild cognitive impairment

OBJECTIVE

To compare assessment of regional cerebral metabolic changes with [(11)C]dihydrotetrabenazine (DTBZ)-positron emission tomography (PET) measurement of regional cerebral blood flow (K(1)) and fludeoxyglucose F18 (FDG)-PET measurement of regional cerebral glucose uptake (CMR(glc)) in a clinically representative sample of subjects with mild dementia and mild cognitive impairment (MCI).

DESIGN

[(11)C]Dihydrotetrabenazine-PET K(1) and FDG-PET CMR(glc) measurements were performed.

SETTING

University-based cognitive disorders clinic.

PARTICIPANTS

Fifty subjects with either mild dementia (Mini-Mental State Examination score > or = 18) or MCI. Their results were compared with those of 80 normal control subjects.

MAIN OUTCOME MEASURES

The DTBZ-PET regional K(1) and FDG-PET CMR(glc) measurements were compared with standard correlation analysis. The overall patterns of DTBZ-PET K(1) and FDG-PET CMR(glc) deficits were assessed with stereotaxic surface projections (SSPs) of parametric images.

RESULTS

The DTBZ-PET regional K(1) and FDG-PET CMR(glc) measurements were highly correlated, both within and between subjects. The SSP maps of deficits in DTBZ-PET regional K(1) and FDG-PET CMR(glc) measurements were markedly similar. The DTBZ-PET K(1) SSP maps exhibited a mild decrease in sensitivity relative to FDG-PET CMR(glc) maps.

CONCLUSIONS

Both DTBZ-PET K(1) and FDG-PET CMR(glc) measurements provide comparable information in assessment of regional cerebral metabolic deficits in mild dementia and MCI. Blood flow measures can assess regional cerebral metabolism deficits accurately in mild dementia and MCI. Blood flow assessments of regional cerebral metabolic deficits can be combined with tracer binding results to improve utility of PET imaging in mild dementia and MCI.