Beta-amyloid burden in the temporal neocortex is related to hippocampal atrophy in elderly subjects without dementia

Potential predictors of hippocampal atrophy in Alzheimer's disease

The hippocampus is a vulnerable and plastic brain structure that is damaged by a variety of stimuli, e.g. hypoxia, hypoperfusion, hypoglycaemia, stress and seizures. Alzheimer's disease is a common and important disorder in which hippocampal atrophy is reported. Indeed, the available evidence suggests that hippocampal atrophy is the starting point of the pathogenesis of Alzheimer's disease and a significant number of patients with hippocampal atrophy will develop Alzheimer's disease. Studies indicate that hippocampal atrophy has functional consequences, e.g. cognitive impairment. Deposition of tau protein, formation of neurofibrillary tangles and accumulation of β-amyloid (Aβ) contributes to hippocampal atrophy together with damage caused by several other factors. Some of the factors associated with the development of hippocampal atrophy in Alzheimer's disease have been identified, e.g. hypertension, diabetes mellitus, hyperlipidaemia, seizures, affective disturbances and stress, and more is being learnt about other factors. Hypertension can potentially damage the hippocampus through ischaemia caused by atherosclerosis and cerebral amyloid angiopathy. Diabetes can produce hippocampal lesions via both vascular and non-vascular pathologies and can reduce the threshold for hippocampal damage. Carriers of the apolipoprotein E (ApoE)-ε4 genotype have been shown to have greater mesial temporal atrophy and poorer memory functions than non-carriers. In addition to giving rise to abnormal lipid metabolism, the ApoE-ε4 allele can affect the course of Alzheimer's disease via both Aβ-dependent and -independent pathways. Repetitive seizures can increase Aβ-peptide production and cause neurotransmission dysfunction and cytoskeletal abnormalities or a combination of these. Affective disturbances and stress are proposed to increase corticosteroid-induced hippocampal damage in many different ways. In the absence of any specific markers for predicting Alzheimer's disease progression, it seems appropriate to learn more about the various predictors of hippocampal atrophy that determine the progression of Alzheimer's disease from mild cognitive impairment (MCI), and then attempt to address these. It would be interesting to know to what extent these predictors play a role in the development of MCI or hasten the conversion of MCI to full-blown Alzheimer's disease. Finally, it would be useful to know the extent to which these predictors can worsen or aggravate existing Alzheimer's disease. Of the clinically used drugs in Alzheimer's disease, anticholinesterases have been shown to slow down the rate of progression of hippocampal atrophy. One study observed that the neuroprotective effect of these agents is possibly due to an anti-Aβ effect produced by cholinergic stimulation. Similarly, antihypertensive and antihyperglycaemic drugs (pioglitazone and insulin) have been shown to reduce the risk of Alzheimer's disease or disease progression. Currently, there are no disease-modifying therapies available for Alzheimer's disease. It has been suggested that for treatment to be most effective, the regimen must be started before significant downstream damage has occurred (i.e. before the clinical diagnosis of Alzheimer's disease, at the stage of MCI or earlier). Since the hippocampus is a plastic structure and atrophy of this structure is closely related to the pathophysiology of Alzheimer's disease, if we could control blood pressure, regulate blood sugar, treat behavioural and psychological symptoms, achieve satisfactory lipid lowering and maintain a seizure-free state in patients with Alzheimer's disease, this may not only improve disease control but could also potentially affect the rate of disease progression.

Spatial patterns of brain amyloid-beta burden and atrophy rate associations in mild cognitive impairment

Amyloid-β accumulation in the brain is thought to be one of the earliest events in Alzheimer's disease, possibly leading to synaptic dysfunction, neurodegeneration and cognitive/functional decline. The earliest detectable changes seen with neuroimaging appear to be amyloid-β accumulation detected by (11)C-labelled Pittsburgh compound B positron emission tomography imaging. However, some individuals tolerate high brain amyloid-β loads without developing symptoms, while others progressively decline, suggesting that events in the brain downstream from amyloid-β deposition, such as regional brain atrophy rates, play an important role. The main purpose of this study was to understand the relationship between the regional distributions of increased amyloid-β and the regional distribution of increased brain atrophy rates in patients with mild cognitive impairment. To simultaneously capture the spatial distributions of amyloid-β and brain atrophy rates, we employed the statistical concept of parallel independent component analysis, an effective method for joint analysis of multimodal imaging data. Parallel independent component analysis identified significant relationships between two patterns of amyloid-β deposition and atrophy rates: (i) increased amyloid-β burden in the left precuneus/cuneus and medial-temporal regions was associated with increased brain atrophy rates in the left medial-temporal and parietal regions; and (ii) in contrast, increased amyloid-β burden in bilateral precuneus/cuneus and parietal regions was associated with increased brain atrophy rates in the right medial temporal regions. The spatial distribution of increased amyloid-β and the associated spatial distribution of increased brain atrophy rates embrace a characteristic pattern of brain structures known for a high vulnerability to Alzheimer's disease pathology, encouraging for the use of (11)C-labelled Pittsburgh compound B positron emission tomography measures as early indicators of Alzheimer's disease. These results may begin to shed light on the mechanisms by which amyloid-β deposition leads to neurodegeneration and cognitive decline and the development of a more specific Alzheimer's disease-specific imaging signature for diagnosis and use of this knowledge in the development of new anti-therapies for Alzheimer's disease.

Amyloid-β associated cortical thinning in clinically normal elderly

Objective

Both amyloid-β (Aβ) deposition and brain atrophy are associated with Alzheimer's disease (AD) and the disease process likely begins many years before symptoms appear. We sought to determine whether clinically normal (CN) older individuals with Aβ deposition revealed by positron emission tomography (PET) imaging using Pittsburgh Compound B (PiB) also have evidence of both cortical thickness and hippocampal volume reductions in a pattern similar to that seen in AD.

Methods

A total of 119 older individuals (87 CN subjects and 32 patients with mild AD) underwent PiB PET and high-resolution structural magnetic resonance imaging (MRI). Regression models were used to relate PiB retention to cortical thickness and hippocampal volume.

Results

We found that PiB retention in CN subjects was (1) age-related and (2) associated with cortical thickness reductions, particularly in parietal and posterior cingulate regions extending into the precuneus, in a pattern similar to that observed in mild AD. Hippocampal volume reduction was variably related to Aβ deposition.

Interpretation

We conclude that Aβ deposition is associated with a pattern of cortical thickness reduction consistent with AD prior to the development of cognitive impairment. ANN NEUROL 2010;

Longitudinal assessment of Aβ and cognition in aging and Alzheimer disease

OBJECTIVE

Assess Aβ deposition longitudinally and explore its relationship with cognition and disease progression.

METHODS

Clinical follow-up was obtained 20 ± 3 months after [¹¹C]Pittsburgh compound B (PiB)-positron emission tomography in 206 subjects: 35 with dementia of the Alzheimer type (DAT), 65 with mild cognitive impairment (MCI), and 106 age-matched healthy controls (HCs). A second PiB scan was obtained at follow-up in 185 subjects and a third scan after 3 years in 57.

RESULTS

At baseline, 97% of DAT, 69% of MCI, and 31% of HC subjects showed high PiB retention. At 20-month follow-up, small but significant increases in PiB standardized uptake value ratios were observed in the DAT and MCI groups, and in HCs with high PiB retention at baseline (5.7%, 2.1%, and 1.5%, respectively). Increases were associated with the number of apolipoprotein E ε4 alleles. There was a weak correlation between PiB increases and decline in cognition when all groups were combined. Progression to DAT occurred in 67% of MCI with high PiB versus 5% of those with low PiB, but 20% of the low PiB MCI subjects progressed to other dementias. Of the high PiB HCs, 16% developed MCI or DAT by 20 months and 25% by 3 years. One low PiB HC developed MCI.

INTERPRETATION

Aβ deposition increases slowly from cognitive normality to moderate severity DAT. Extensive Aβ deposition precedes cognitive impairment, and is associated with ApoE genotype and a higher risk of cognitive decline in HCs and progression from MCI to DAT over 1 to 2 years. However, cognitive decline is only weakly related to change in Aβ burden, suggesting that downstream factors have a more direct effect on symptom progression.

Relationships between β-amyloid and functional connectivity in different components of the default mode network in aging

Although beta-amyloid (Aβ) deposition is a characteristic feature of Alzheimer's disease (AD), this pathology is commonly found in elderly normal controls (NC). The pattern of Aβ deposition as detected with Pittsburgh compound-B positron emission tomography (PIB-PET) imaging shows substantial spatial overlap with the default mode network (DMN), a group of brain regions that typically deactivates during externally driven cognitive tasks. In this study, we show that DMN functional connectivity (FC) during rest is altered with increasing levels of PIB uptake in NC. Specifically, FC decreases were identified in regions implicated in episodic memory (EM) processing (posteromedial cortex, ventral medial prefrontal cortex, and angular gyrus), whereas connectivity increases were detected in dorsal and anterior medial prefrontal and lateral temporal cortices. This pattern of decreases is consistent with previous studies that suggest heightened vulnerability of EM-related brain regions in AD, whereas the observed increases in FC may reflect a compensatory response.

Iatrogenic risk factors for Alzheimer's disease: surgery and anesthesia

Increasing evidence indicates that patients develop post-operative cognitive decline (POCD) following surgery. POCD is characterized by transient short-term decline in cognitive ability evident in the early post-operative period. This initial decline might be associated with increased risk of a delayed cognitive decline associated with dementia 3 to 5 years post-surgery. In some studies, the conversion rates to dementia are up to 70% in patients who are 65 years or older. The factors responsible for the increased risk of dementia are unclear; however, clinical studies investigating the prevalence of POCD and dementia following surgery do not show an association with the type of anesthesia or duration of surgery. Epidemiological studies from our group support this observation. The adjusted Hazard Ratios for developing dementia (or AD specifically) after prostate or hernia surgery were 0.65 (95% CI, 0.51 to 0.83, prostate) and 0.65 (95% CI, 0.49 to 0.85, hernia) for cohorts of subjects exposed to general anesthesia compared to those exposed only to local anesthesia. Animal studies suggest that prolonged exposure to some volatile-inhalational anesthetics increase production of amyloid-β and vulnerability to neurodegeneration, but these results are weakened by the absence of clinical support. Inflammation and a maladaptive stress response might also contribute to the pathophysiology of this disorder. Future research needs to identify predisposing factors, and then strategies to protect against POCD and subsequent dementia. The field also needs to adopt a more rigorous approach to codifying the frequency and extent of early and delayed post-operative cognitive decline.

Independent contribution of temporal beta-amyloid deposition to memory decline in the pre-dementia phase of Alzheimer's disease

The relationship between β-amyloid deposition and memory deficits in early Alzheimer's disease is unresolved, as past studies show conflicting findings. The present study aims to determine the relative contribution of regional β-amyloid deposition, hippocampal atrophy and white matter integrity to episodic memory deficits in non-demented older individuals harbouring one of the characteristic hallmarks of Alzheimer's disease, i.e. with β-amyloid pathology. Understanding these relationships is critical for effective therapeutic development. Brain magnetic resonance imaging and [(11)C]Pittsburgh Compound B-positron emission tomography scans were obtained in 136 non-demented individuals aged over 60 years, including 93 healthy elderly and 43 patients with mild cognitive impairment. Voxel-based correlations were computed between a memory composite score and grey matter volume, white matter volume and β-amyloid deposition imaging datasets. Hierarchical linear regression analyses were then performed using values extracted in regions of most significant correlations to determine the relative contribution of each modality to memory deficits. All analyses were conducted pooling all groups together as well as within separate subgroups of cognitively normal elderly, patients with mild cognitive impairment and individuals with high versus low neocortical β-amyloid. Brain areas of highest correlation with episodic memory deficits were the hippocampi for grey matter volume, the perforant path for white matter volume and the temporal neocortex for β-amyloid deposition. When considering these three variables together, only hippocampal volume and temporal β-amyloid deposition provided independent contributions to memory deficits. In contrast to global β-amyloid deposition, temporal β-amyloid deposition was still related to memory independently from hippocampal atrophy within subgroups of cognitively normal elderly, patients with mild cognitive impairment or cases with high neocortical β-amyloid. In the pre-dementia stage of Alzheimer's disease, subtle episodic memory impairment is related to β-amyloid deposition, especially in the temporal neocortex, and independently from hippocampal atrophy, suggesting that both factors should be independently targeted in therapeutic trials aimed at reducing cognitive decline.

Use of florbetapir-PET for imaging beta-amyloid pathology

CONTEXT

The ability to identify and quantify brain β-amyloid could increase the accuracy of a clinical diagnosis of Alzheimer disease.

OBJECTIVE

To determine if florbetapir F 18 positron emission tomographic (PET) imaging performed during life accurately predicts the presence of β-amyloid in the brain at autopsy.

DESIGN, SETTING, AND PARTICIPANTS

Prospective clinical evaluation conducted February 2009 through March 2010 of florbetapir-PET imaging performed on 35 patients from hospice, long-term care, and community health care facilities near the end of their lives (6 patients to establish the protocol and 29 to validate) compared with immunohistochemistry and silver stain measures of brain β-amyloid after their death used as the reference standard. PET images were also obtained in 74 young individuals (18-50 years) presumed free of brain amyloid to better understand the frequency of a false-positive interpretation of a florbetapir-PET image.

MAIN OUTCOME MEASURES

Correlation of florbetapir-PET image interpretation (based on the median of 3 nuclear medicine physicians' ratings) and semiautomated quantification of cortical retention with postmortem β-amyloid burden, neuritic amyloid plaque density, and neuropathological diagnosis of Alzheimer disease in the first 35 participants autopsied (out of 152 individuals enrolled in the PET pathological correlation study).

RESULTS

Florbetapir-PET imaging was performed a mean of 99 days (range, 1-377 days) before death for the 29 individuals in the primary analysis cohort. Fifteen of the 29 individuals (51.7%) met pathological criteria for Alzheimer disease. Both visual interpretation of the florbetapir-PET images and mean quantitative estimates of cortical uptake were correlated with presence and quantity of β-amyloid pathology at autopsy as measured by immunohistochemistry (Bonferroni ρ, 0.78 [95% confidence interval, 0.58-0.89]; P <.001]) and silver stain neuritic plaque score (Bonferroni ρ, 0.71 [95% confidence interval, 0.47-0.86]; P <.001). Florbetapir-PET images and postmortem results rated as positive or negative for β-amyloid agreed in 96% of the 29 individuals in the primary analysis cohort. The florbetapir-PET image was rated as amyloid negative in the 74 younger individuals in the nonautopsy cohort.

CONCLUSIONS

Florbetapir-PET imaging was correlated with the presence and density of β-amyloid. These data provide evidence that a molecular imaging procedure can identify β-amyloid pathology in the brains of individuals during life. Additional studies are required to understand the appropriate use of florbetapir-PET imaging in the clinical diagnosis of Alzheimer disease and for the prediction of progression to dementia.

Why docosahexaenoic acid and aspirin supplementation could be useful in women as a primary prevention therapy against Alzheimer's disease?

The assumption that disease specific risk factors are similar or the same in men and women may lead to incorrect primary prevention strategies. This study focused on the evaluation of gender-specific Alzheimer's disease (AD) risk factors. In AD, female gender appears to be an important risk factor associated with the aberrant production of beta amyloid (βA) peptides. Although decreased levels in plasma DHA concentration are associated with cognitive decline in healthy elderly and Alzheimer's patients, pre-treatment with DHA significantly reduced the survival of cortical neurons incubated with beta amyloid (βA). Hence, in the presence of an increasing amount of βA, paradoxically women - who have higher plasma levels of DHA - are more likely to develop AD. Aspirin (ASA) converts cyclooxygenase (COX)-2 into a form that generates new neuroprotective docosanoids from DHA; therefore, ASA might positively resolve the paradoxical effect of the concomitant presence of DHA and βA.

Protein aggregation containing β-amyloid, α-synuclein and hyperphosphorylated τ in cultured cells of hippocampus, substantia nigra and locus coeruleus after rotenone exposure

BACKGROUND

Protein aggregates containing alpha-synuclein, beta-amyloid and hyperphosphorylated tau are commonly found during neurodegenerative processes which is often accompanied by the impairment of mitochondrial complex I respiratory chain and dysfunction of cellular systems of protein degradation. In view of this, we aimed to develop an in vitro model to study protein aggregation associated to neurodegenerative diseases using cultured cells from hippocampus, locus coeruleus and substantia nigra of newborn Lewis rats exposed to 0.5, 1, 10 and 25 nM of rotenone, which is an agricultural pesticide, for 48 hours.

RESULTS

We demonstrated that the proportion of cells in culture is approximately the same as found in the brain nuclei they were extracted from. Rotenone at 0.5 nM was able to induce alpha-synuclein and beta amyloid aggregation, as well as increased hyperphosphorylation of tau, although high concentrations of this pesticide (over 1 nM) lead cells to death before protein aggregation. We also demonstrated that the 14 kDa isoform of alpha-synuclein is not present in newborn Lewis rats.

CONCLUSION

Rotenone exposure may lead to constitutive protein aggregation in vitro, which may be of relevance to study the mechanisms involved in idiopathic neurodegeneration.

Differential effects of age and history of hypertension on regional brain volumes and iron

Aging affects various structural and metabolic properties of the brain. However, associations among various aspects of brain aging are unclear. Moreover, those properties and associations among them may be modified by age-associated increase in vascular risk. In this study, we measured volume of brain regions that vary in their vulnerability to aging and estimated local iron content via T2* relaxometry. In 113 healthy adults (19-83 years old), we examined prefrontal cortex (PFC), primary visual cortex (VC), hippocampus (HC), entorhinal cortex (EC), caudate nucleus (Cd), and putamen (Pt). In some regions (PFC, VC, Cd, and Pt) age-related differences in iron and volume followed similar patterns. However, in the medial-temporal structures, volume and iron content exhibited different age trajectories. Whereas age-related volume reduction was mild in HC and absent in EC, iron content evidenced significant age-related declines. In hypertensive participants significantly greater iron content was noted in all examined regions. Thus, iron content as measured by T2* may be a sensitive index of regional brain aging and may reveal declines that are more prominent than gross anatomical shrinkage.

β-Amyloid affects frontal and posterior brain networks in normal aging

Although deposition of β-amyloid (Aβ), a pathological hallmark of Alzheimer's disease (AD), has also been reported in cognitively intact older people, its influence on brain structure and cognition during normal aging remains controversial. Using PET imaging with the radiotracer Pittsburgh compound B (PIB), structural MRI, and cognitive measures, we examined the relationships between Aβ deposition, gray matter volume, and cognition in older people without AD. Fifty-two healthy older participants underwent PIB-PET and structural MRI scanning and detailed neuropsychological tests. Results from the whole-brain voxel-based morphometry (VBM) analysis revealed that gray matter volume in the left inferior frontal cortex was negatively associated with amyloid deposition across all participants whereas reduced gray matter volume was shown in the posterior cingulate among older people with high amyloid deposition. When gray matter density measures extracted from these two regions were related to other brain regions by applying a structural covariance analysis, distinctive frontal and posterior brain networks were seen. Gray matter volume in these networks in relation to cognition, however, differed such that reduced frontal network gray matter volume was associated with poorer working memory performance while no relationship was found for the posterior network. The present findings highlight structural and cognitive changes in association with the level of Aβ deposition in cognitively intact normal elderly and suggest a differential role of Aβ-dependent gray matter loss in the frontal and posterior networks in cognition during normal aging.

Revising the definition of Alzheimer's disease: a new lexicon

Alzheimer's disease (AD) is classically defined as a dual clinicopathological entity. The recent advances in use of reliable biomarkers of AD that provide in-vivo evidence of the disease has stimulated the development of new research criteria that reconceptualise the diagnosis around both a specific pattern of cognitive changes and structural/biological evidence of Alzheimer's pathology. This new diagnostic framework has stimulated debate about the definition of AD and related conditions. The potential for drugs to intercede in the pathogenic cascade of the disease adds some urgency to this debate. This paper by the International Working Group for New Research Criteria for the Diagnosis of AD aims to advance the scientific discussion by providing broader diagnostic coverage of the AD clinical spectrum and by proposing a common lexicon as a point of reference for the clinical and research communities. The cornerstone of this lexicon is to consider AD solely as a clinical and symptomatic entity that encompasses both predementia and dementia phases.

Brain beta-amyloid measures and magnetic resonance imaging atrophy both predict time-to-progression from mild cognitive impairment to Alzheimer's disease

Biomarkers of brain Aβ amyloid deposition can be measured either by cerebrospinal fluid Aβ42 or Pittsburgh compound B positron emission tomography imaging. Our objective was to evaluate the ability of Aβ load and neurodegenerative atrophy on magnetic resonance imaging to predict shorter time-to-progression from mild cognitive impairment to Alzheimer’s dementia and to characterize the effect of these biomarkers on the risk of progression as they become increasingly abnormal. A total of 218 subjects with mild cognitive impairment were identified from the Alzheimer’s Disease Neuroimaging Initiative. The primary outcome was time-to-progression to Alzheimer’s dementia. Hippocampal volumes were measured and adjusted for intracranial volume. We used a new method of pooling cerebrospinal fluid Aβ42 and Pittsburgh compound B positron emission tomography measures to produce equivalent measures of brain Aβ load from either source and analysed the results using multiple imputation methods. We performed our analyses in two phases. First, we grouped our subjects into those who were ‘amyloid positive’ (n = 165, with the assumption that Alzheimer's pathology is dominant in this group) and those who were ‘amyloid negative’ (n = 53). In the second phase, we included all 218 subjects with mild cognitive impairment to evaluate the biomarkers in a sample that we assumed to contain a full spectrum of expected pathologies. In a Kaplan–Meier analysis, amyloid positive subjects with mild cognitive impairment were much more likely to progress to dementia within 2 years than amyloid negative subjects with mild cognitive impairment (50 versus 19%). Among amyloid positive subjects with mild cognitive impairment only, hippocampal atrophy predicted shorter time-to-progression (P < 0.001) while Aβ load did not (P = 0.44). In contrast, when all 218 subjects with mild cognitive impairment were combined (amyloid positive and negative), hippocampal atrophy and Aβ load predicted shorter time-to-progression with comparable power (hazard ratio for an inter-quartile difference of 2.6 for both); however, the risk profile was linear throughout the range of hippocampal atrophy values but reached a ceiling at higher values of brain Aβ load. Our results are consistent with a model of Alzheimer’s disease in which Aβ deposition initiates the pathological cascade but is not the direct cause of cognitive impairment as evidenced by the fact that Aβ load severity is decoupled from risk of progression at high levels. In contrast, hippocampal atrophy indicates how far along the neurodegenerative path one is, and hence how close to progressing to dementia. Possible explanations for our finding that many subjects with mild cognitive impairment have intermediate levels of Aβ load include: (i) individual subjects may reach an Aβ load plateau at varying absolute levels; (ii) some subjects may be more biologically susceptible to Aβ than others; and (iii) subjects with mild cognitive impairment with intermediate levels of Aβ may represent individuals with Alzheimer’s disease co-existent with other pathologies.

Selective disruption of the cerebral neocortex in Alzheimer's disease

Background

Alzheimer's disease (AD) and its transitional state mild cognitive impairment (MCI) are characterized by amyloid plaque and tau neurofibrillary tangle (NFT) deposition within the cerebral neocortex and neuronal loss within the hippocampal formation. However, the precise relationship between pathologic changes in neocortical regions and hippocampal atrophy is largely unknown.

Methodology/Principal Findings

In this study, combining structural MRI scans and automated image analysis tools with reduced cerebrospinal fluid (CSF) Aß levels, a surrogate for intra-cranial amyloid plaques and elevated CSF phosphorylated tau (p-tau) levels, a surrogate for neocortical NFTs, we examined the relationship between the presence of Alzheimer's pathology, gray matter thickness of select neocortical regions, and hippocampal volume in cognitively normal older participants and individuals with MCI and AD (n = 724). Amongst all 3 groups, only select heteromodal cortical regions significantly correlated with hippocampal volume. Amongst MCI and AD individuals, gray matter thickness of the entorhinal cortex and inferior temporal gyrus significantly predicted longitudinal hippocampal volume loss in both amyloid positive and p-tau positive individuals. Amongst cognitively normal older adults, thinning only within the medial portion of the orbital frontal cortex significantly differentiated amyloid positive from amyloid negative individuals whereas thinning only within the entorhinal cortex significantly discriminated p-tau positive from p-tau negative individuals.

Conclusions/Significance

Cortical Aβ and tau pathology affects gray matter thinning within select neocortical regions and potentially contributes to downstream hippocampal degeneration. Neocortical Alzheimer's pathology is evident even amongst older asymptomatic individuals suggesting the existence of a preclinical phase of dementia.

Global trends in hybrid imaging

At the 2009 Scientific Assembly and Annual Meeting of the Radiological Society of North America, a special session was devoted to global trends in hybrid imaging. This article expands on the key points of the session, focusing primarily on positron emission tomography/computed tomography. Global trends in hybrid imaging equipment acquisition, usage, and image interpretation practices are reviewed, and emerging requirements for training and clinical privileging are discussed. Also considered are the current benefits of hybrid imaging for patient care and workflow and the potential of hybrid imaging for advancing drug development and personalized medicine.

Role of structural MRI in Alzheimer's disease

Atrophy measured on structural magnetic resonance imaging (sMRI) is a powerful biomarker of the stage and intensity of the neurodegenerative aspect of Alzheimer's disease (AD) pathology. In this review, we will discuss the role of sMRI as an AD biomarker by summarizing (a) the most commonly used methods to extract information from sMRI images, (b) the different roles in which sMRI can be used as an AD biomarker, and (c) comparisons of sMRI with other major AD biomarkers.

Larger temporal volume in elderly with high versus low beta-amyloid deposition

β-Amyloid deposition is one of the main hallmarks of Alzheimer's disease thought to eventually cause neuronal death. Post-mortem and neuroimaging studies have consistently reported cases with documented normal cognition despite high β-amyloid burden. It is of great interest to understand what differentiates these particular subjects from those without β-amyloid deposition or with both β-amyloid deposition and cognitive deficits, i.e. what allows these subjects to resist the damage of the pathological lesions. [¹¹C]Pittsburgh compound B positron emission tomography and magnetic resonance brain scans were obtained in 149 participants including healthy controls and patients with subjective cognitive impairment, mild cognitive impairment and Alzheimer's disease. Magnetic resonance data were compared between high versus low-[11C]Pittsburgh compound B cases, and between high-[¹¹C]Pittsburgh compound B cases with versus those without cognitive deficits. Larger temporal (including hippocampal) grey matter volume, associated with better episodic memory performance, was found in high- versus low-[¹¹C]Pittsburgh compound B healthy controls. The same finding was obtained using different [¹¹C]Pittsburgh compound B thresholds, correcting [¹¹C]Pittsburgh compound B data for partial averaging, using age, education, Mini-Mental State Examination, apolipoprotein E4 and sex-matched subsamples, and using manual hippocampal delineation instead of voxel-based analysis. By contrast, in participants with subjective cognitive impairment, significant grey matter atrophy was found in high-[¹¹C]Pittsburgh compound B cases compared to low-[¹¹C]Pittsburgh compound B cases, as well as in high-[¹¹C]Pittsburgh compound B cases with subjective cognitive impairment, mild cognitive impairment and Alzheimer's disease compared to high-[¹¹C]Pittsburgh compound B healthy controls. Larger grey matter volume in high-[¹¹C]Pittsburgh compound B healthy controls may reflect either a tissue reactive response to β-amyloid or a combination of higher 'brain reserve' and under-representation of subjects with standard/low temporal volume in the high-[¹¹C]Pittsburgh compound B healthy controls. Our complementary analyses tend to support the latter hypotheses. Overall, our findings suggest that the deleterious effects of β-amyloid on cognition may be delayed in those subjects with larger brain (temporal) volume.

Addressing population aging and Alzheimer's disease through the Australian imaging biomarkers and lifestyle study: collaboration with the Alzheimer's Disease Neuroimaging Initiative

The Australian Imaging Biomarkers and Lifestyle (AIBL) study is a longitudinal study of 1112 volunteers from healthy, mild cognitive impairment, and Alzheimer's disease (AD) populations who can be assessed and followed up for prospective research into aging and AD. AIBL aims to improve understanding of the pathogenesis, early clinical manifestation, and diagnosis of AD, and identify diet and lifestyle factors that influence the development of AD. For AIBL, the magnetic resonance imaging parameters of Alzheimer's Disease Neuroimaging Initiative (ADNI) were adopted and the Pittsuburgh compound B ((11)C-PiB) positron emission tomography (PET) acquisition and neuropsychological tests were designed to permit comparison and pooling with ADNI data. Differences to ADNI include assessment every 18-months, imaging in 25% (magnetic resonance imaging, (11)C-PiB PET but no fluorodeoxyglucose PET), more comprehensive neuropsychological testing, and detailed collection of diet and lifestyle data. AIBL has completed the first 18-month follow-up and is making imaging and clinical data available through the ADNI website. Cross-sectional analysis of baseline data is revealing links between cognition, brain amyloid burden, structural brain changes, biomarkers, and lifestyle.

Pro: Can biomarkers be gold standards in Alzheimer's disease?

Recent advances in biomarkers for Alzheimer's disease (AD) now allow the visualization of one of the hallmark pathologies of AD in vivo, and combination biomarker profiles can now approximate the diagnostic accuracy of autopsy in patients with dementia. Biomarkers are already employed in clinical trials in prodromal AD for both subject selection and in monitoring therapeutic response. Ultimately the greatest utility of biomarkers may be in the preclinical stages of AD, to identify and track progression of the disease prior to significant cognitive impairment, at the point when disease modifying therapies are likely to be most efficacious.

Amyloid imaging results from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study of aging

The Australian Imaging, Biomarkers and Lifestyle (AIBL) study of aging, a participant of the worldwide Alzheimer's Disease Neuroimaging Initiative (ADNI), performed (11)C-Pittsburgh Compound B (PiB) scans in 177 healthy controls (HC), 57 mild cognitive impairment (MCI) subjects, and 53 mild Alzheimer's disease (AD) patients. High PiB binding was present in 33% of HC (49% in ApoE-epsilon4 carriers vs 21% in noncarriers) and increased with age, most strongly in epsilon4 carriers. 18% of HC aged 60-69 had high PiB binding rising to 65% in those over 80 years. Subjective memory complaint was only associated with elevated PiB binding in epsilon4 carriers. There was no correlation with cognition in HC or MCI. PiB binding in AD was unrelated to age, hippocampal volume or memory. Beta-amyloid (Abeta) deposition seems almost inevitable with advanced age, amyloid burden is similar at all ages in AD, and secondary factors or downstream events appear to play a more direct role than total beta amyloid burden in hippocampal atrophy and cognitive decline.