A voxel based morphometry study on mild cognitive impairment

Alzheimer disease: quantitative structural neuroimaging for detection and prediction of clinical and structural changes in mild cognitive impairment

PURPOSE

To use structural magnetic resonance (MR) images to identify a pattern of regional atrophy characteristic of mild Alzheimer disease (AD) and to investigate whether presence of this pattern prospectively can aid prediction of 1-year clinical decline and increased structural loss in mild cognitive impairment (MCI).

MATERIALS AND METHODS

The study was conducted with institutional review board approval and compliance with HIPAA regulations. Written informed consent was obtained from each participant. High-throughput volumetric segmentation and cortical surface reconstruction methods were applied to MR images from 84 subjects with mild AD, 175 with MCI, and 139 healthy control (HC) subjects. Stepwise linear discriminant analysis was used to identify regions that best can aid discrimination of HC subjects from subjects with AD. A classifier trained on data from HC subjects and those with AD was applied to data from subjects with MCI to determine whether presence of phenotypic AD atrophy at baseline was predictive of clinical decline and structural loss.

RESULTS

Atrophy in mesial and lateral temporal, isthmus cingulate, and orbitofrontal areas aided discrimination of HC subjects from subjects with AD, with fully cross-validated sensitivity of 83% and specificity of 93%. Subjects with MCI who had phenotypic AD atrophy showed significantly greater 1-year clinical decline and structural loss than those who did not and were more likely to have progression to probable AD (annual progression rate of 29% for subjects with MCI who had AD atrophy vs 8% for those who did not).

CONCLUSION

Semiautomated, individually specific quantitative MR imaging methods can be used to identify a pattern of regional atrophy in MCI that is predictive of clinical decline. Such information may aid in prediction of patient prognosis and increase the efficiency of clinical trials.

The cortical signature of prodromal AD: regional thinning predicts mild AD dementia

OBJECTIVE

We previously used exploratory analyses across the entire cortex to determine that mild Alzheimer disease (AD) is reliably associated with a cortical signature of thinning in specific limbic and association regions. Here we investigated whether the cortical signature of AD-related thinning is present in individuals with questionable AD dementia (QAD) and whether a greater degree of regional cortical thinning predicts mild AD dementia.

METHODS

Participants included 49 older adults with mild impairment consistent with mild cognitive impairment (Clinical Dementia Rating [CDR] = 0.5) at the time of structural MRI scanning. Cortical thickness was measured in nine regions of interest (ROIs) identified previously from a comparison of patients with mild AD and controls.

RESULTS

Longitudinal clinical follow-up revealed that 20 participants converted to mild AD dementia (progressors) while 29 remained stable (nonprogressors) approximately 2.5 years after scanning. At baseline, QAD participants showed a milder degree of cortical thinning than typically seen in mild AD, and CDR Sum-of-Boxes correlated with thickness in temporal and parietal ROIs. Compared to nonprogressors, progressors showed temporal and parietal thinning. Using receiver operating characteristic curves, the thickness of an aggregate measure of these regions predicted progression to mild AD with 83% sensitivity and 65% specificity.

CONCLUSIONS

Thinning in specific cortical areas known to be affected by Alzheimer disease (AD) is detectable in individuals with questionable AD dementia (QAD) and predicts conversion to mild AD dementia. This method could be useful for identifying individuals at relatively high risk for imminent progression from QAD to mild AD dementia, which may be of value in clinical trials.

Quantitative EEG in progressing vs stable mild cognitive impairment (MCI): results of a 1-year follow-up study

OBJECTIVE

The study objective is to evaluate the use of qEEG data for the cross-sectional differentiation of mild cognitive impairment (MCI) from mild Alzheimer's disease (AD) and in the longitudinal prediction of cognitive decline in MCI.

METHODS

Eighty-eight subjects with MCI and 42 subjects with mild probable AD were enrolled. Baseline EEGs were recorded using a 32-channel system with electrode positioning according to the international 10-20 system. Digitalized EEG data were further studied by quantitative spectral analysis. Study subjects were followed up for 1 year and reassessed psychometrically. An increase of the total ADAS-cog score of >or= 4 points was regarded as a significant cognitive decline. Using this cut-off, MCI subjects were sub-grouped into stable MCI (s-MCI) and progressing MCI (p-MCI).

RESULTS

AD subjects and p-MCI subjects were differentiated from s-MCI subjects by a reduction of alpha power over posterior leads. Reduction of alpha power and mean frequency were significantly correlated with poorer cognitive performance in psychometric tests. Baseline values of alpha power over posterior leads had the highest positive predictive power for MCI and AD (69-80%) and predicted cognitive decline in MCI within a 1-year follow up.

CONCLUSIONS

qEEG revealed decreased alpha activity in progressing MCI and mild AD prior to an increase of slow wave activity, which typically occurs in advancing AD. This finding may reflect an affection of thalamo-cortical relay activity and cortical connectivity in the early disease course of AD. Reduced alpha activity in MCI subjects at baseline may have prognostic value regarding future cognitive decline.

Amnestic MCI future clinical status prediction using baseline MRI features

Amnestic mild cognitive impairment (aMCI) individuals are known to be at risk for progression to clinically probable Alzheimer's disease (AD). The objective of this work is to measure the accuracy of an automated classification technique based on clinical-quality, single time-point structural magnetic resonance imaging (MRI) scans for the retrospective prediction of future clinical status in aMCI. Thirty-one aMCI research subjects were followed with annual clinical reassessment after baseline MRI. Twenty subjects progressed to probable AD within an average 2.2 (1.4) years [mean age 76.6 (4.7) years, MMSE 27.1 (2.3)], while 11 remained non-demented on average 5.6 (2.6) years after baseline [mean age 73.3 (7.2) years, MMSE 28.2 (1.8)]. Leave-one-out classification was performed within a multidimensional MRI feature space built from intensity and local volume estimate data of a reference group of 75 probable AD and 75 age-matched control subjects. Prediction using aMCI data reached 81% accuracy, 70% sensitivity and 100% specificity. This automated and objective method has potential in helping predict future clinical status in aMCI.

Evidence that volume of anterior medial temporal lobe is reduced in seniors destined for mild cognitive impairment

The present study sought to determine if volumes of specific brain structures could discriminate cognitively normal seniors destined to develop mild cognitive impairment (MCI) within a few years from those who will remain normal. Brain scans were collected from seventy-one cognitively normal seniors. Seventeen individuals later developed MCI (the presymptomatic MCI; pMCI group), while fifty-four remained normal. Whole brain volume (WBV) and volumes of the entorhinal cortex (ERC), hippocampus, and three subregions of the hippocampus (head; HH, body; HB and tail; HT) were compared. Results indicated that the pMCI group had smaller volumes than the normal group in the ERC, HH and HB, but not the HT or WBV. When HH/HB volumes and baseline memory test scores were included in a single logistic regression model, classification accuracy was very high (area under the curve=0.93). These results show that smaller normalized volumes of anterior medial temporal lobe structures contribute to the development of MCI, a finding which may have implications for identifying seniors at risk for cognitive decline.

Novel MRI techniques in the assessment of dementia

INTRODUCTION

Positive markers of Alzheimer's disease (AD) have been established in MRI that may allow early detection of AD in at-risk groups. In the near future, these markers will be of high relevance for the selection of at-risk subjects in secondary preventive trials.

METHODS

We describe the methodology and diagnostic value of manual volumetry of the hippocampus and entorhinal cortex, automated voxel-based morphometry, cortical thickness measurement, basal forebrain volumetry and deformation-based morphometry, implementing multivariate statistics and machine learning algorithms to improve group separation and prediction of AD in at-risk groups. We also describe the methodological basis and results obtained in AD using the recently developed technique of diffusion tensor-based morphometry (DTI). This technique gives access to the integrity of subcortical fibre systems in the human brain.

RESULTS

The best established structural biomarker of AD to date is hippocampus volume that already has been implemented as secondary endpoint in clinical trials on disease modification in AD. Automated approaches will gain an increasing role as endpoints of clinical trials in the near future given the interest in these techniques expressed by the regulatory authorities. DTI is still a developing field where analysis techniques are presently being devised to make optimal use of the multivariate data. Data on changes of fibre tract in preclinical AD are still limited, but the first results are promising in respect to a further enhancement of diagnostic accuracy by combining MRI and DTI.

CONCLUSION

Besides their diagnostic use, MRI and DTI will broaden our understanding of the pathophysiology of AD and the structural and functional basis of normal cognition.

Differential patterns of hypoperfusion in subtypes of mild cognitive impairment

In this study the regional cerebral blood flow (rCBF) pattern of three Mild Cognitive Impairment (MCI) subtypes was measured with SPECT in 60 patients (nineteen with an amnestic deficit, sixteen with disexecutive deficits, and twenty five with mild multidomain deficits) and compared with that of 15 healthy matched older adults. The amnestic MCI subgroup showed significant hypoperfusion in the left hippocampus, parahippocampal gyrus and fronto-parieto-temporal areas. The disexecutive subgroup had significant hypoperfusion of the left superior, medial frontal and cingulate cortex. The multidomain subgroup had similar perfusion deficits to the amnestic subgroup, with an additional deficit in the left posterior cingulate gyrus. This study found differential patterns of hypoperfusion in MCI subtypes. Since all patients who progressed to dementia converted to probable Alzheimer's disease, the different rCBF patterns most likely reflect the neuropathological heterogeneity at onset and differences in disease stage.

Focal posterior cingulate atrophy in incipient Alzheimer's disease

Severe posterior cingulate cortex hypometabolism is a feature of incipient, sporadic Alzheimer's disease (AD). The aim was to test the hypothesis that this region is focally atrophic in very early disease by studying AD patients at the mild cognitive impairment (MCI) stage, and, if so, to determine whether the amount of atrophy was comparable to that of the hippocampus. Twenty-four patients meeting criteria for amnestic MCI, who all subsequently progressed to fulfil AD criteria, and 28 age-matched controls, were imaged with volumetric MRI. Four regions of interest were manually traced in each hemisphere: two posterior cingulate regions (BA 23 and BA 29/30), the hippocampus (as a positive control) and the anterior cingulate (as a negative control). BA 23 and BA 29/30 were both significantly atrophic and this atrophy was comparable to that found in the hippocampus, in the absence of anterior cingulate cortex (ACC) atrophy. Contrary to previous reports, there was no evidence that posterior cingulate atrophy is specifically associated with early-onset AD. The results indicate that posterior cingulate cortex atrophy is present from the earliest clinical stage of sporadic AD and that this region is as vulnerable to neurodegeneration as the hippocampus.

Magnetic resonance imaging characterization of brain structure and function in mild cognitive impairment: a review

Given the predicted increase in prevalence of Alzheimer's disease (AD) in the coming decades, early detection and intervention in persons with the predementia condition known as mild cognitive impairment (MCI) is of paramount importance. Recent years have seen remarkable advances in the application of neuroimaging and other biomarkers to the study of MCI. This article reviews the most recent developments in the use of magnetic resonance imaging (MRI) to characterize brain changes and to prognosticate clinical outcomes of patients with MCI. The review begins with description of methods and findings in structural MRI research, delineating findings regarding both gross atrophy and microstructural brain changes in MCI. Second, we describe the most recent findings regarding brain function in MCI, enumerating findings from functional MRI and brain perfusion studies. Third, we will make recommendations regarding the current clinical use of MRI in identification of MCI. As a conclusion, we will look to the future of neuroimaging as a tool in early AD detection.

Lexical semantic memory in amnestic mild cognitive impairment and mild Alzheimer's disease

OBJECTIVE

To study lexical semantic memory in patients with amnestic mild cognitive impairment (aMCI), mild Alzheimer's disease (AD) and normal controls.

METHOD

Fifteen mild AD, 15 aMCI, and 15 normal control subjects were included. Diagnosis of AD was based on DSM-IV and NINCDS-ADRDA criteria, and that of aMCI, on the criteria of the International Working Group on Mild Cognitive Impairment, using CDR 0.5 for aMCI and CDR 1 for mild AD. All subjects underwent semantic memory tests (Boston Naming-BNT, CAMCOG Similarities item), Rey Auditory Verbal Learning Test (RAVLT), Mini-Mental Status Examination (MMSE), neuropsychological tests (counterproofs), and Cornell Scale for Depression in Dementia. Data analysis used Mann-Whitney test for intergroup comparisons and Pearson's coefficient for correlations between memory tests and counterproofs (statistical significance level was p<0.05).

RESULTS

aMCI patients were similar to controls on BNT and Similarities, but worse on MMSE and RAVLT. Mild AD patients scored significantly worse than aMCI and controls on all tests.

CONCLUSION

aMCI impairs episodic memory but tends to spare lexical semantic system, which can be affected in the early phase of AD.

Structural and functional biomarkers of prodromal Alzheimer's disease: a high-dimensional pattern classification study

This work builds upon previous studies that reported high sensitivity and specificity in classifying individuals with mild cognitive impairment (MCI), which is often a prodromal phase of Alzheimer's disease (AD), via pattern classification of MRI scans. The current study integrates MRI and PET (15)O water scans from 30 participants in the Baltimore Longitudinal Study of Aging, and tests the hypothesis that joint evaluation of structure and function can yield higher classification accuracy than either alone. Classification rates of up to 100% accuracy were achieved via leave-one-out cross-validation, whereas conservative estimates of generalization performance in new scans, evaluated via bagging cross-validation, yielded an area under the receiver operating characteristic (ROC) curve equal to 0.978 (97.8%), indicating excellent diagnostic accuracy. Spatial maps of regions determined to contribute the most to the classification implicated many temporal, prefrontal, orbitofrontal, and parietal regions. Detecting complex patterns of brain abnormality in early stages of cognitive impairment has pivotal importance for the detection and management of AD.

Amnestic mild cognitive impairment: structural MR imaging findings predictive of conversion to Alzheimer disease

BACKGROUND AND PURPOSE

Mild cognitive impairment (MCI) is considered by many to be a prodromal phase of Alzheimer disease (AD). We used voxel-based morphometry (VBM) to find out whether structural differences on MR imaging could offer insight into the development of clinical AD in patients with amnestic MCI at 3-year follow-up.

MATERIALS AND METHODS

Twenty-four amnestic patients with MCI were included. After 3 years, 46% had progressed to AD (n = 11; age, 72.7 +/- 4.8 years; women/men, 8/3). For 13 patients (age, 72.4 +/- 8.6 years; women/men, 10/3), the diagnosis remained MCI. Baseline MR imaging at 1.5T included a coronal heavily T1-weighted 3D gradient-echo sequence. Localized gray matter differences were assessed with VBM.

RESULTS

The converters had less gray matter volume in medial (including the hippocampus) and lateral temporal lobe, parietal lobe, and lateral temporal lobe structures. After correction for age, sex, total gray matter volume, and neuropsychological evaluation, left-sided atrophy remained statistically significant. Specifically, converters had more left parietal atrophy (angular gyrus and inferior parietal lobule) and left lateral temporal lobe atrophy (superior and middle temporal gyrus) than stable patients with MCI.

CONCLUSION

By studying 2 MCI populations, converters versus nonconverters, we found atrophy beyond the medial temporal lobe to be characteristic of patients with MCI who will progress to dementia. Atrophy of structures such as the left lateral temporal lobe and left parietal cortex may independently predict conversion.

MRI patterns of atrophy associated with progression to AD in amnestic mild cognitive impairment

OBJECTIVE

To compare the patterns of gray matter loss in subjects with amnestic mild cognitive impairment (aMCI) who progress to Alzheimer disease (AD) within a fixed clinical follow-up time vs those who remain stable.

METHODS

Twenty-one subjects with aMCI were identified from the Mayo Clinic Alzheimer's research program who remained clinically stable for their entire observed clinical course (aMCI-S), where the minimum required follow-up time from MRI to last follow-up assessment was 3 years. These subjects were age- and gender-matched to 42 aMCI subjects who progressed to AD within 18 months of the MRI (aMCI-P). Each subject was then age- and gender-matched to a control subject. Voxel-based morphometry (VBM) was used to assess patterns of gray matter atrophy in the aMCI-P and aMCI-S groups compared to the control group, and compared to each other.

RESULTS

The aMCI-P group showed bilateral loss affecting the medial and inferior temporal lobe, temporoparietal association neocortex, and frontal lobes, compared to controls. The aMCI-S group showed no regions of gray matter loss when compared to controls. When the aMCI-P and aMCI-S groups were compared directly, the aMCI-P group showed greater loss in the medial and inferior temporal lobes, the temporoparietal neocortex, posterior cingulate, precuneus, anterior cingulate, and frontal lobes than the aMCI-S group.

CONCLUSIONS

The regions of loss observed in subjects with amnestic mild cognitive impairment (aMCI) who progressed to Alzheimer disease (AD) within 18 months of the MRI are typical of subjects with AD. The lack of gray matter loss in subjects with aMCI who remained clinically stable for their entire observed clinical course is consistent with the notion that patterns of atrophy on MRI at baseline map well onto the subsequent clinical course.

Core candidate neurochemical and imaging biomarkers of Alzheimer's disease

BACKGROUND

In the earliest clinical stages of Alzheimer's disease (AD) when symptoms are mild, clinical diagnosis can be difficult. AD pathology most likely precedes symptoms. Biomarkers can serve as early diagnostic indicators or as markers of preclinical pathologic change. Candidate biomarkers derived from structural and functional neuroimaging and those measured in cerebrospinal fluid (CSF) and plasma show the greatest promise. Unbiased exploratory approaches, eg, proteomics or cortical thickness analysis, could yield novel biomarkers. The objective of this article was to review recent progress in selected imaging and neurochemical biomarkers for early diagnosis, classification, progression, and prediction of AD.

METHODS

We performed a survey of recent research, focusing on core biomarker candidates in AD.

RESULTS

A number of in vivo neurochemistry and neuroimaging techniques, which can reliably assess aspects of physiology, pathology, chemistry, and neuroanatomy, hold promise as biomarkers. These neurobiologic measures appear to relate closely to pathophysiologic, neuropathologic, and clinical data, such as hyperphosphorylation of tau, amyloid beta (Abeta) metabolism, lipid peroxidation, pattern and rate of atrophy, loss of neuronal integrity, functional and cognitive decline, as well as risk of future decline. Current advances in the neuroimaging of mediotemporal, neocortical, and subcortical areas of the brain of mild cognitive impairment (MCI) and AD subjects are presented. CSF levels of Abeta42, tau, and hyperphosphorylated tau protein (p-tau) can distinguish subjects with MCI who are likely to progress to AD. They also show preclinical alterations that predict later development of early AD symptoms. Studies on plasma Abeta are not entirely consistent, but recent findings suggest that decreased plasma Abeta42 relative to Abeta40 might increase the risk of AD. Increased production of Abeta in aging is suggested by elevation of BACE1 protein and enzyme activity in the brain and CSF of subjects with MCI. CSF tau and p-tau are increased in MCI as well and show predictive value. Other biomarkers might indicate components of a cascade initiated by Abeta, such as oxidative stress or inflammation. These merit further study in MCI and earlier.

CONCLUSIONS

A number of neuroimaging candidate markers are promising, such as hippocampus and entorhinal cortex volumes, basal forebrain nuclei, cortical thickness, deformation-based and voxel-based morphometry, structural and effective connectivity by using diffusion tensor imaging, tractography, and functional magnetic resonance imaging. CSF Abeta42, BACE1, total tau, and p-tau are substantially altered in MCI and clinical AD. Other interesting novel marker candidates derived from blood are being currently proposed (phase I). Biomarker discovery through proteomic approaches requires further research. Large-scale international controlled multicenter trials (such as the U.S., European, Australian, and Japanese Alzheimer's Disease Neuroimaging Initiative and the German Dementia Network) are engaged in phase III development of the core feasible imaging and CSF biomarker candidates in AD. Biomarkers are in the process of implementation as primary outcome variables into regulatory guideline documents regarding study design and approval for compounds claiming disease modification.

Spatial patterns of brain atrophy in MCI patients, identified via high-dimensional pattern classification, predict subsequent cognitive decline

Spatial patterns of brain atrophy in mild cognitive impairment (MCI) and Alzheimer's disease (AD) were measured via methods of computational neuroanatomy. These patterns were spatially complex and involved many brain regions. In addition to the hippocampus and the medial temporal lobe gray matter, a number of other regions displayed significant atrophy, including orbitofrontal and medial-prefrontal grey matter, cingulate (mainly posterior), insula, uncus, and temporal lobe white matter. Approximately 2/3 of the MCI group presented patterns of atrophy that overlapped with AD, whereas the remaining 1/3 overlapped with cognitively normal individuals, thereby indicating that some, but not all, MCI patients have significant and extensive brain atrophy in this cohort of MCI patients. Importantly, the group with AD-like patterns presented much higher rate of MMSE decline in follow-up visits; conversely, pattern classification provided relatively high classification accuracy (87%) of the individuals that presented relatively higher MMSE decline within a year from baseline. High-dimensional pattern classification, a nonlinear multivariate analysis, provided measures of structural abnormality that can potentially be useful for individual patient classification, as well as for predicting progression and examining multivariate relationships in group analyses.

Hippocampal atrophy and EEG markers in subjects with mild cognitive impairment

OBJECTIVE

The present study evaluates the potential relationship between hippocampal atrophy and EEG brain rhythmicity, as assessed by relative band power and alpha frequency indices in a cohort of subjects with mild cognitive impairment (MCI).

METHODS

Eighty-eight subjects falling within the definition of MCI patients were enrolled. All subjects underwent EEG recording and magnetic resonance imaging (MRI). Volumetric morphometry estimates of the hippocampal region were computed. Individual EEG frequencies were indexed by the theta/alpha transition frequency (TF) and the individual alpha frequency (IAF). The relative power was separately computed for delta, theta, alpha1, alpha2 and alpha3 frequency bands. The MCI cohort was classified into four subgroups, based on the mean and standard deviations of the hippocampal volume of a normal elderly control sample.

RESULTS

The group with moderate hippocampal atrophy showed the highest increase in the theta power on frontal regions, and of the alpha2 and alpha3 powers on frontal and temporo-parietal areas. The analysis of the individual alpha frequency markers showed that the values for the alpha markers were highest in the group with the smallest hippocampal volume, whereas in the group with moderate hippocampal atrophy, these values were lower than in the group with severe atrophy.

CONCLUSIONS

The relationship between hippocampal atrophy and EEG activity changes in MCI subjects is not proportional to the hippocampal atrophy. Therefore, EEG markers could represent a new tool for differential diagnosis.

SIGNIFICANCE

The hippocampal atrophy induces different brain synchronization/desynchronization patterns. EEG changes model the brain activity induced by a discrete change of the hippocampal volume. The changes in the EEG rhythmicity differ greatly from those in MCI patients with subcortical vascular damage.

Multivariate deformation-based analysis of brain atrophy to predict Alzheimer's disease in mild cognitive impairment

Automated deformation-based analysis of MRI scans can be used to detect specific pattern of brain atrophy in Alzheimer's disease (AD), but it still lacks an established model to derive the individual risk of AD in at-risk subjects, such as patients with mild cognitive impairment (MCI). We applied principal component analysis to deformation maps derived from MRI scans of 32 AD patients, 18 elderly healthy controls and 24 MCI patients. Principal component scores were used to discriminate between AD patients and controls and between MCI converters and MCI non-converters. We found a significant regional pattern of atrophy (p<0.001) in medial temporal lobes, neocortical association areas, thalamus and basal ganglia and corresponding widening of cerebrospinal fluid (CSF) spaces (p<0.001) in AD patients compared to controls. Accuracy was 81% for CSF- and 83% for brain-based deformation maps to separate AD patients from controls. Nine out of 24 MCI patients converted to AD during clinical follow-up. Discrimination between MCI converters and non-converters reached 80% accuracy based on CSF maps and 73% accuracy based on brain maps. In a logistic regression model, principal component scores based on CSF maps predicted clinical outcome in MCI patients even after controlling for age, gender, MMSE score and time of follow-up. Our findings indicate that multivariate network analysis of deformation maps detects typical features of AD pathology and provides a powerful tool to predict conversion into AD in non-demented at risk patients.

[Neurobiological early diagnosis of Alzheimer's disease]

In order to improve diagnosis of Alzheimer's disease (AD), candidate biological markers in CSF as well as structural and functional imaging were investigated. Biomarkers are clearly needed to support detection of incipient AD in subjects with mild cognitive impairment (MCI). To date the most promising core candidate markers are total and hyperphosphorylated tau protein and amyloid beta peptides in the CSF, as well as hippocampus and whole brain volumetry using MRI. None of the candidates has been finally validated and established for clinical routine so far. International controlled multicenter cooperative studies are ongoing to further develop these core diagnostic marker candidates (phase III). The core markers are reviewed in detail. Promising novel approaches are discussed.

3D maps from multiple MRI illustrate changing atrophy patterns as subjects progress from mild cognitive impairment to Alzheimer's disease

Mild cognitive impairment (MCI), particularly the amnestic subtype (aMCI), is considered as a transitional stage between normal aging and a diagnosis of clinically probable Alzheimer's disease (AD). The aMCI construct is particularly useful as it provides an opportunity to assess a clinical stage which in most subjects represents prodromal AD. The aim of this study was to assess the progression of cerebral atrophy over multiple serial MRI during the period from aMCI to progression to AD. Thirty-three subjects were selected that fulfilled clinical criteria for aMCI and had three serial MRI scans: the first scan approximately 3 years before the diagnosis of AD, the second scan approximately 1 year before, and the third scan at the time of the diagnosis of AD. A group of 33 healthy controls were age and gender-matched to the study cohort. Voxel-based morphometry (VBM) was used to assess patterns of grey matter atrophy in the aMCI subjects at each time-point compared to the control group. Customized templates and prior probability maps were used to avoid normalization and segmentation bias. The pattern of grey matter loss in the aMCI subject scans that were 3 years before the diagnosis of AD was focused primarily on the medial temporal lobes, including the amygdala, anterior hippocampus and entorhinal cortex, with some additional involvement of the fusiform gyrus, compared to controls. The extent and magnitude of the cerebral atrophy further progressed by the time the subjects were 1 year before the diagnosis of AD. At this point atrophy in the temporal lobes spread to include the middle temporal gyrus, and extended into more posterior regions of the temporal lobe to include the entire extent of the hippocampus. The parietal lobe also started to become involved. By the time the subjects had progressed to a clinical diagnosis of AD the pattern of grey matter atrophy had become still more widespread with more severe involvement of the medial temporal lobes and the temporoparietal association cortices and, for the first time, substantial involvement of the frontal lobes. This pattern of progression fits well with the Braak and Braak neurofibrillary pathological staging scheme in AD. It suggests that the earliest changes occur in the anterior medial temporal lobe and fusiform gyrus, and that these changes occur at least 3 years before progression to the diagnosis of AD. These results also suggest that 3D patterns of grey matter atrophy may help to predict the time to the first diagnosis of AD in subjects with aMCI.

Voxel-based morphometry to detect brain atrophy in progressive mild cognitive impairment

Recent research has shown an increased rate of conversion to dementia in subjects with mild cognitive impairment (MCI) compared to controls. However, there are no specific methods to predict who will later develop dementia. In the present study, 22 controls and 56 MCI subjects were followed on average for 37 months (max. 60 months) and studied with magnetic resonance imaging (MRI) at baseline to assess changes in brain structure associated to later progression to dementia. Voxel-based morphometry (VBM) was used to investigate gray matter atrophy. During the follow-up, 13 subjects progressed to dementia. At baseline, no differences were detected in age or education between the control and MCI subjects, but they differed by several neuropsychological tests. The stable and progressive MCI subjects differed only by CDR sum of boxes scores and delayed verbal recall, which were also significant predictors of conversion to dementia. At the baseline imaging, the MCI subjects showed reduced gray matter density in medial temporal, temporoparietal as well as in frontal cortical areas compared to controls. Interestingly, the progressive MCI subjects showed atrophy in the left temporoparietal and posterior cingulate cortices and in the precuneus bilaterally, and a trend for hippocampal atrophy when compared to the stable MCI subjects. We conclude that widespread cortical atrophy is present already two and a half years before a clinical diagnosis of dementia can be set.

Clinical and neuropsychological features associated with structural imaging patterns in patients with mild cognitive impairment

AIM

To describe the clinical and neuropsychological features of mild cognitive impairment (MCI) patients with medial temporal atrophy (MTA), white matter hyperintensities (WMH), both, and neither and to assess whether the rate of progression differs among groups.

METHODS

Ninety-five MCI patients were divided into 4 groups based on the presence of MTA and WMH: 29 were MTA- WMH-, 11 MTA- WMH+, 23 MTA+ WMH-, and 32 MTA+ WMH+. MCI patients were compared with 30 normal subjects. MTA and WMH were assessed with MR-based visual rating scales. Subjects underwent an extensive clinical and neuropsychological investigation. Fifty-six underwent follow-up evaluation.

RESULTS

MTA- WMH- had relatively good neuropsychological performance, little vascular and physical comorbidity. MTA- WMH+ performed poorly only on executive neuropsychological tests. MTA+ WMH- patients had poor neuropsychological performances (mainly on memory tests), high physical and vascular comorbidity. MTA+ WMH+ were impaired in neuropsychological performances, had a high number of physical diseases and severe vascular comorbidity. On follow-up, 25% of MTA+ WMH- and 32% of MTA+ WMH+ and none in MTA- WMH- and in MTA- WMH+ converted to dementia (p = 0.05, log rank test).

CONCLUSION

Structural neuroimaging can identify subgroups of MCI patients with specific clinical and neuropsychological features.

Cortical thickness in single- versus multiple-domain amnestic mild cognitive impairment

Amnestic mild cognitive impairment (aMCI) can be classified into single domain (S-aMCI) and multiple domain (M-aMCI) subtypes. However, there have been no studies that specifically investigate the structural differences that support this classification. In an attempt to compare regional cortical thickness in two subtypes of aMCI, we aimed to map the distribution of cortical thinning using a surface based cortical analysis of magnetic resonance imaging. The cortical thickness across the entire brain was measured in 9 patients with S-aMCI, 22 patients with M-aMCI, and 61 normal healthy subjects. Differences in the patterns of cortical thinning between S-aMCI and M-aMCI were assessed using ANCOVA on a vertex-by-vertex basis, and statistical maps of differences in cortical thickness between the groups were constructed using a surface model. Relative to controls, S-aMCI patients showed cortical thinning in the left medial temporal lobe, and M-aMCI patients showed cortical thinning in the left medial temporal lobe, precuneus, and anterior and inferior basal temporal, insular, and temporal association cortices. When the two MCI groups were directly compared, M-aMCI patients showed cortical thinning in left precuneus. Our studies suggest that M-aMCI is a transitional state between S-aMCI and Alzheimer's disease, and that the cortical thinning is evidence that the precuneus is responsible for the multiple cognitive impairments in M-aMCI.

A magnetic resonance imaging study of patients with Parkinson's disease with mild cognitive impairment and dementia using voxel-based morphometry

BACKGROUND

Dementia is common in Parkinson's disease, but the underlying brain pathology is not yet fully understood.

AIM

To examine the changes in the brain of patients with Parkinson's disease with mild cognitive impairment (MCI) and dementia, using structural magnetic resonance imaging.

METHODS

Using voxel-based morphometry, the grey matter atrophy on brain images of patients with Parkinson's disease and dementia (PDD; n = 16) and Parkinson's disease without dementia (PDND; n = 20), and healthy elderly subjects (n = 20) was studied. In the PDND group, 12 subjects had normal cognitive status and 8 had MCI. Standardised rating scales for motor, cognitive and psychiatric symptoms were used.

RESULTS

Widespread areas of cortical atrophy were found in patients with PDD compared with normal controls (in both temporal and frontal lobes and in the left parietal lobe). Grey matter reductions were found in frontal, parietal, limbic and temporal lobes in patients with PDD compared with those with PDND. In patients with PDND with MCI, areas of reduced grey matter in the left frontal and both temporal lobes were found.

CONCLUSION

These findings show that dementia in Parkinson's disease is associated with structural neocortical changes in the brain, and that cognitive impairment in patients with PDND may be associated with structural changes in the brain. Further studies with larger groups of patients are needed to confirm these findings.

Auditory cortical activity in amnestic mild cognitive impairment: relationship to subtype and conversion to dementia

Mild cognitive impairment (MCI) patients have a high risk of converting to Alzheimer's disease. The most common diagnostic subtypes of MCI have an episodic memory disorder (amnestic MCI) occurring either alone [single domain (SD)] or with other cognitive impairments [multiple domain (MD)]. Previous studies report increased amplitudes of auditory cortical potentials in MCI, but their relationships to MCI subtypes and clinical outcomes were not defined. We studied subjects with amnestic MCI (n = 41: 28 SD, 13 MD), Alzheimer's disease (n = 14), and both younger (n = 22) and age-matched older controls (n = 44). Baseline auditory sensory (P50, N100) and cognitive potentials (P300) were recorded during an auditory discrimination task. MCI patients were followed for up to 5 years, and outcomes were classified as (i) continued diagnosis of MCI (MCI-stable, n = 16), (ii) probable Alzheimer's disease (MCI-convert, n = 18), or other outcomes (n = 7). Auditory potentials were analysed as a function of MCI diagnosis and outcomes, and compared with young, older controls, and mild Alzheimer's disease subjects. P50 amplitude increased with normal ageing, and had additional increases in MCI as a function of both initial diagnosis (MD > than SD) and outcome (MCI-convert > MCI-stable). P300 latency increased with normal ageing, and had additional increases in MCI but did not differ among outcomes. We conclude that auditory cortical sensory potentials differ among amnestic MCI subtypes and outcomes occurring up to 5 years later.

Whole-brain and regional brain atrophy in amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

Recent evidence from neuropsychologic and neuroimaging studies suggests that central nervous system involvement in amyotrophic lateral sclerosis (ALS) extends beyond motor neurons. Our purpose was to obtain measures of global and regional atrophy in nondemented patients with ALS to assess subtle structural brain changes.

METHODS

MR images, acquired from 16 patients and 9 healthy subjects (HS), were processed by using the Structural Imaging Evaluation of Normalized Atrophy (SIENA) software to estimate whole-brain atrophy measures and the voxel-based morphometry (VBM) method to highlight the selective volumetric decrease of single cerebral areas. In addition, each subject underwent a neuropsychologic examination.

RESULTS

In patients with ALS, brain parenchymal fraction was slightly lower compared with HS (P = .012), and seemed to be related to the presence of cognitive impairment. Patients showed a gray matter volume decrease in several frontal and temporal areas bilaterally (P < .001 uncorrected) compared with HS, with a slight prevalence in the right hemisphere. No volume reduction in primary motor cortices of patients was detected. Performances on Symbol Digit Modalities Test were significantly worse in patients compared with HS (P = .025).

CONCLUSIONS

The presence of mild whole-brain volume loss and regional frontotemporal atrophy in patients with ALS could explain the presence of cognitive impairment and confirms the idea of ALS as a degenerative brain disease not confined to motor system.

Mild cognitive impairment after lacunar infarction: voxel-based morphometry and neuropsychological assessment

BACKGROUND

The aim of the present study was to investigate whether there were differences in neuroradiological features, including white-matter lesions and gray-matter volumes, between patients with lacunar infarction with and without mild cognitive impairment of the vascular type (MCI-V).

METHODS

A total of 40 patients with lacunar infarction were studied within 1 month after stroke.

RESULTS

MCI-V was found in 22 patients, who in comparison with patients without cognitive impairment were significantly older and had fewer years of formal education. MRI subcortical hyperintensities especially in the basal ganglia (putamen and thalamus) were significantly more frequent in the MCI-V group. In the voxel-based morphometric study, patients with MCI-V showed more atrophy bilaterally in the middle temporal gyrus, right and left frontal and posterior bilateral occipitoparietal regions including the posterior cingulate as well as in the cerebellum. A region of interest analysis restricted to the parahippocampi and hippocampi showed further reduced bilateral parahippocampal gyrus and right hippocampus volume reductions in this group of patients. Finally, the amount of white-matter lesions among MCI-V showed negative correlations with gray-matter volume in frontal and temporal areas as well as with the thalamus and mesencephalon.

CONCLUSIONS

The present findings provide support for an anatomical substrate of the MCI entity in patients with lacunar infarction. Both gray- and white-matter changes seem to contribute to the cognitive impairment of such patients.

Neural correlates of naming newly learned objects in MCI

Our objective was to study the neural correlates of naming of newly learned unfamiliar objects in subjects with mild cognitive impairment (MCI) and in age-matched controls, by using positron emission tomography (PET). Prior to the PET scanning, each subject underwent a 4-day long training period in which 40 names of rare unfamiliar objects were taught. The stimuli consisted of five categories: unfamiliar objects for which both the name and the definition (=semantic support) were given during training, unfamiliar objects with only the name given, unfamiliar objects with no information given, familiar objects and visual noise patterns. The unfamiliar objects mainly represented ancient domestic tools unknown to modern-day people. When naming newly learned objects trained without semantic support, the MCI group showed increased activation in the anterior cingulate when compared with the controls. Our results suggest that the naming of newly learned objects posed additional executive and attentional demands on the patients.

The fornix and mammillary bodies in older adults with Alzheimer's disease, mild cognitive impairment, and cognitive complaints: a volumetric MRI study

The fornix and mammillary bodies are important limbic structures that have not been systematically investigated in the earliest stages of preclinical dementia. The present study examined volumetric changes in the fornix and mammillary bodies and improved previously established tracing guidelines to increase reliability and provide more comprehensive measurements. Volumetric measurements were made in euthymic older adults, including 16 patients with mild Alzheimer's disease (AD), 20 patients with amnestic mild cognitive impairment (MCI), 20 individuals with cognitive complaints (CC) but normal neuropsychological test performance, and 20 demographically matched healthy controls (HC). Structural magnetic resonance imaging included a T1-weighted 1.5-mm coronal volume, acquired on a GE 1.5T LX scanner. After adjustment for total intracranial volume (ICV), significant volume reductions were observed in the fornix and mammillary bodies in patients with AD as compared with HC, CC, and MCI participants. No volume differences were seen between the HC, CC, and MCI groups. Study findings are consistent with previous research showing volume decreases of the fornix and mammillary bodies in AD, and provide new data on the relative preservation of these structures in preclinical disease stages. Results suggest that atrophy of the fornix and mammillary bodies becomes apparent at the point of conversion from MCI to AD. Longitudinal assessments are needed to delineate the time course and extent of the observed volumetric changes.

Diffusion indices on magnetic resonance imaging and neuropsychological performance in amnestic mild cognitive impairment

BACKGROUND

Magnetic resonance diffusion tensor imaging (DTI) shows promise in the early detection of microstructural pathophysiological changes in the brain.

OBJECTIVES

To measure microstructural differences in the brains of participants with amnestic mild cognitive impairment (MCI) compared with an age-matched control group using an optimised DTI technique with fully automated image analysis tools and to investigate the correlation between diffusivity measurements and neuropsychological performance scores across groups.

METHODS

34 participants (17 participants with MCI, 17 healthy elderly adults) underwent magnetic resonance imaging (MRI)-based DTI. To control for the effects of anatomical variation, diffusion images of all participants were registered to standard anatomical space. Significant statistical differences in diffusivity measurements between the two groups were determined on a pixel-by-pixel basis using gaussian random field theory.

RESULTS

Significantly raised mean diffusivity measurements (p<0.001) were observed in the left and right entorhinal cortices (BA28), posterior occipital-parietal cortex (BA18 and BA19), right parietal supramarginal gyrus (BA40) and right frontal precentral gyri (BA4 and BA6) in participants with MCI. With respect to fractional anisotropy, participants with MCI had significantly reduced measurements (p<0.001) in the limbic parahippocampal subgyral white matter, right thalamus and left posterior cingulate. Pearson's correlation coefficients calculated across all participants showed significant correlations between neuropsychological assessment scores and regional measurements of mean diffusivity and fractional anisotropy.

CONCLUSIONS

DTI-based diffusivity measures may offer a sensitive method of detecting subtle microstructural brain changes associated with preclinical Alzheimer's disease.

Structural changes of the corpus callosum in mild cognitive impairment and Alzheimer's disease

BACKGROUND

Although previous studies demonstrate significant atrophy of the corpus callosum (CC) in patients with Alzheimer's disease (AD), CC alterations in mild cognitive impairment have not been investigated yet.

METHODS

21 subjects with mild cognitive impairment, 10 with AD and 21 healthy controls were investigated using magnetic resonance imaging. In the mid-sagittal slice the CC was traced manually. Additionally, voxel-based morphometry (VBM) was performed.

RESULTS

The CC was significantly smaller in patients with AD compared to healthy controls in both manual tracing and VBM. The atrophy was prominent in rostral parts of the CC. In subjects with mild cognitive impairment, the two rostral CC segments were smaller compared to controls when manually traced. In contrast, VBM revealed no significant difference between subjects with mild cognitive impairment and controls.

CONCLUSION

Manual tracing was more sensitive in detecting discrete structural CC changes than VBM. Alterations of the CC in mild cognitive impairment rank in between normal aging and AD, supporting the hypothesis that mild cognitive impairment most often represents a preclinical stage of AD.

Older adults with cognitive complaints show brain atrophy similar to that of amnestic MCI

OBJECTIVE

To examine the neural basis of cognitive complaints in healthy older adults in the absence of memory impairment and to determine whether there are medial temporal lobe (MTL) gray matter (GM) changes as reported in Alzheimer disease (AD) and amnestic mild cognitive impairment (MCI).

METHODS

Participants were 40 euthymic individuals with cognitive complaints (CCs) who had normal neuropsychological test performance. The authors compared their structural brain MRI scans to those of 40 patients with amnestic MCI and 40 healthy controls (HCs) using voxel-based morphometry and hippocampal volume analysis.

RESULTS

The CC and MCI groups showed similar patterns of decreased GM relative to the HC group on whole brain analysis, with differences evident in the MTL, frontotemporal, and other neocortical regions. The degree of GM loss was associated with extent of both memory complaints and performance deficits. Manually segmented hippocampal volumes, adjusted for age and intracranial volume, were significantly reduced only in the MCI group, with the CC group showing an intermediate level.

CONCLUSIONS

Cognitive complaints in older adults may indicate underlying neurodegenerative changes even when unaccompanied by deficits on formal testing. The cognitive complaint group may represent a pre-mild cognitive impairment stage and may provide an earlier therapeutic opportunity than mild cognitive impairment. MRI analysis approaches incorporating signal intensity may have greater sensitivity in early preclinical stages than volumetric methods.

Increased fMRI responses during encoding in mild cognitive impairment

Structural and functional magnetic resonance imaging (fMRI) was performed on 21 healthy elderly controls, 14 subjects with mild cognitive impairment (MCI) and 15 patients with mild Alzheimer's disease (AD) to investigate changes in fMRI activation in relation to underlying structural atrophy. The fMRI paradigm consisted of associative encoding of novel picture-word pairs. Structural analysis of the brain was performed using voxel-based morphometry (VBM) and hippocampal volumetry. Compared to controls, the MCI subjects exhibited increased fMRI responses in the posterior hippocampal, parahippocampal and fusiform regions, while VBM revealed more atrophy in MCI in the anterior parts of the left hippocampus. Furthermore, the hippocampal volume and parahippocampal activation were negatively correlated in MCI, but not in controls or in AD. We suggest that the increased fMRI activation in MCI in the posterior medial temporal and closely connected fusiform regions is compensatory due to the incipient atrophy in the anterior medial temporal lobe.

Memory performance in multiple sclerosis patients correlates with central brain atrophy

OBJECTIVE

To assess whole brain and central brain atrophy as well as their differential relation to memory, cognitive performance, fatigue, depression and quality of life in patients with relapsing-remitting multiple sclerosis (RRMS).

METHODS

A 3D flow compensated gradient recalled T1-weighted MRI was acquired in 45 RRMS patients. An automated analysis tool was used to calculate brain parenchymal fraction (BPF) and ventricular brain fraction (VF). All patients were assessed with neuropsychological tests focusing on memory and self-rating scales for depression, fatigue and quality of life. Age corrected partial correlations between brain atrophy, motor performance, psychological scales and test scores were calculated.

RESULTS

BPF correlated moderately (0.3 < or = r < 0.5) with duration of symptoms and disease, the Expanded Disability Status Scale (EDSS), the upper extremity motor performance, and with mental aspects of quality of life. VF correlated moderately with EDSS, upper and lower extremity motor performance and memory functions. Neither BPF nor VF correlated with fatigue and depression. Results of several cognitive tests correlated moderately with depression and fatigue, the Paced Auditory Serial Addition Test (PASAT) showing the largest correlation.

CONCLUSIONS

Memory performance shows a correlation with relative ventricular size in RRMS patients, indicating the strategic location of the ventricle system along the structures of the limbic system and its vulnerability in MS. The PASAT and several other cognitive tests show moderate correlations with depression and fatigue, arguing for an inter relation between the cognitive functioning and the emotional state of patients. However, this relation is independent of measurable brain atrophy.

Hippocampal atrophy confounds template-based functional MR imaging measures of hippocampal activation in patients with mild cognitive impairment

BACKGROUND AND PURPOSE

Functional MR imaging has been used to study patterns of hippocampal activation that distinguish pathologic from normal memory loss in the elderly population. Our objective was to assess whether hippocampal atrophy confounds measurements of hippocampal activation in subjects with mild cognitive impairment (MCI).

METHODS

Twenty subjects with MCI and 20 elderly control subjects with objectively normal memory were studied at 4T during a face-name paradigm designed to activate the hippocampus. Hippocampal activation was measured using 2 separate approaches: applying a preset region of interest (ROI) in standardized template space and applying a manually drawn ROI in native subject space. Pearson correlation coefficients were calculated to compare group-dependent relationships between hippocampal volume and activation. Analysis of covariance (ANCOVA) was performed to assess group differences in hippocampal activation during encoding and retrieval. Age and hippocampal volume were included as covariates, as was a term for the interaction between hippocampal volume and group.

RESULTS

When hippocampal activation was measured by the template-based method, the correlation coefficient in the right hippocampus of subjects with MCI but not control subjects during retrieval differed significantly from zero. There was a significant (P < .05) group-by-volume interaction in the ANCOVA model. No significant correlations or interactions were demonstrated when activation was measured in native subject space with manually drawn ROIs.

CONCLUSION

Our findings suggest a potential confounding relationship between hippocampal volume and activation for subjects with MCI in template-based analyses. Template-based measures of hippocampal activation that do not adequately account for hippocampal atrophy should be used with caution in patients with MCI.

The effect of apolipoprotein polymorphism on brain in mild cognitive impairment: a voxel-based morphometric study

We investigated the effect of apolipoprotein E (ApoE) on the whole brain in 51 individuals with mild cognitive impairment using voxel-based morphometry. Between cases heterozygous for the ApoE epsilon4 (n = 15) and those who were ApoE epsilon4 noncarriers (n = 28), only the right parahippocampal gyrus, with the entorhinal cortex included, reached the level of statistical significance. In cases homozygous for the epsilon4 allele (n = 8) versus noncarriers, the greatest atrophy was located in the right amygdala followed by the right parahippocampal gyrus, the left amygdala and the left medial dorsal thalamic nucleus.

Volumetric correlates of memory and executive function in normal elderly, mild cognitive impairment and Alzheimer's disease

In Alzheimer's disease (AD), atrophy negatively impacts cognition while in healthy adults, inverse relationships between brain volume and cognition may occur. We investigated correlations between gray matter volume and cognition in elderly controls, AD and mild cognitive impairment (MCI) patients with memory and executive deficits. AD demonstrated substantial loss in temporal, parietal and frontal regions while MCI exhibited moderate volume loss in temporal and frontal regions. In controls, memory and executive function were negatively correlated with frontal regions, while in AD, memory was positively correlated with temporal and frontal gyri, and executive function with frontal regions. The combination of the two patterns may explain the lack of correlations in MCI. Developmental versus pathological contributions to these relationships are discussed.

Four subgroups of Alzheimer's disease based on patterns of atrophy using VBM and a unique pattern for early onset disease

To clarify the involvement of the posterior cingulate cortex (PCC) in Alzheimer's disease (AD), we analyzed brain volume loss by voxel-based morphometry. Forty patients with non-familial AD and 20 patients with mild cognitive impairment (MCI) were recruited and compared to 88 elderly volunteers and 40 young volunteers. Local atrophy with aging was observed bilaterally in the perisylvian opercula, anterior cingulate cortex, caudate head, dorsomedial thalamus and parahippocampal cortex. In addition to those, atrophy in AD patients was observed in the amygdala, hippocampus, subcallosal region, posterior-associated cortices and PCC. We classified AD into four subgroups according to the atrophy pattern; atrophy in the amygdala/hippocampal formations (Hipp), in the Hipp and posterior cortices, in the Hipp and PCC and in the PCC and posterior cortices (PCC/-TOPa). As a result, the probability of PCC/-TOPa was 90% for ages <65 years, whereas that of the Hipp was 100% for disease duration >36 months. PCC atrophy was found in 16 of 40 AD patients and eight of 20 MCI patients. There seemed to be two subgroups with atrophy of the PCC, the one with disease progression and the other without. The latter had characteristic features of early onset and no significant atrophy in the amygdala/anterior hippocampus. There are at least four atrophy patterns that raise doubts about a single disease entity or progression in AD. This may reflect a different hierarchical pattern of progression in patients who have atrophy in PCC and posterior cortices when compared to the Braak staging scheme.

Magnetic resonance imaging of Alzheimer's disease

A modern challenge for neuroimaging techniques is to contribute to the early diagnosis of neurodegenerative diseases, such as Alzheimer's disease (AD). Early diagnosis includes recognition of pre-demented conditions, such as mild cognitive impairment (MCI) or having a high risk of developing AD. The role of neuroimaging therefore extends beyond its traditional role of excluding other conditions such as neurosurgical lesions. In addition, early diagnosis would allow early treatment using currently available therapies or new therapies in the future. Structural imaging can detect and follow the time course of subtle brain atrophy as a surrogate marker for pathological processes. New MR techniques and image analysis software can detect subtle brain microstructural, perfusion or metabolic changes that provide new tools to study the pathological processes and detect pre-demented conditions. This review focuses on markers of macro- and microstructural, perfusion, diffusion and metabolic MR imaging and spectroscopy in AD.

Source estimation of spontaneous MEG oscillations in mild cognitive impairment

Mild cognitive impairment (MCI) is a memory disorder often preceding Alzheimer's disease (AD). AD has been shown to be associated with abnormal generation of spontaneous electromagnetic activity. We investigated whether the cortical generation of spontaneous brain oscillations in MCI shows changes resembling those observed in AD. A minimum current estimates algorithm was applied to identify cortical sources of magnetoencephalographic (MEG) spontaneous brain oscillations in male MCI patients with a clear memory disorder and in healthy elderly controls. This data was subsequently compared to a male subsample of AD patients from an earlier study. While there were clear oscillatory abnormalities in AD patients, there was no evidence of significant changes in the alpha source distribution in MCI patients as compared to healthy controls. Deficits in the distribution of oscillatory sources in the resting state are thus likely to occur at later stages of cognitive impairment than MCI.

The role of quantitative structural imaging in the early diagnosis of Alzheimer's disease

The goal of this article is to review the role of structural neuroimaging in the diagnosis of Alzheimer's disease (AD). We present relevant neuroanatomy, highlight progress in the domain of AD imaging, and review the clinical characteristics of the prodromal phase of AD. We describe the history of the diagnostic issue by examining at cross-section and longitudinally the differences between patients who have AD and normal controls. We also present how subsequent works applied these characteristic traits to the early detection of the prodromal disease and to prediction of future decline. The article delineates the differences between subjects who have mild cognitive impairment and AD, which illustrate the spreading of the pathology with disease progression. The last section describes problems encountered in the differential diagnosis.

Predicting conversion to dementia in mild cognitive impairment by volumetric and diffusivity measurements of the hippocampus

In our prospective study of diffusion tensor imaging (DTI), we measured hippocampal mean diffusivity (MD) and volumes in amnestic mild cognitive impairment (MCI). Thirteen MCI patients were followed-up by clinical assessment over a mean 112-year period. MCI patients who converted to dementia (6 of 13) during the observation period had slightly elevated left hippocampal mean diffusivity at baseline compared with MCI patients who remained clinically stable. Hippocampal volumes as well as baseline verbal memory and MMSE did not differ significantly between stable MCI patients and converters. Hippocampal diffusivity was superior to hippocampal volumes for prediction of conversion to dementia in MCI patients during a 112-year period.

Neuroanatomy of Down syndrome in vivo: a model of preclinical Alzheimer's disease

Aging in Down syndrome (DS) is accompanied by neuropathological features of Alzheimer's disease (AD). Therefore, DS has been proposed as a model to study predementia stages of AD. MRI-based measurement of grey matter atrophy is an in vivo surrogate marker of regional neuronal density. A range of neuroimaging studies have described the macroscopic neuroanatomy of DS. Recent studies using sensitive quantitative measures of region-specific atrophy based on high-resolution MRI suggest that age-related atrophy in DS resembles the pattern of brain atrophy in early stages of AD. The pattern of atrophy determined in predementia DS supports the notion that AD-type pathology leads to neuronal degeneration not only in allocortical, but also in neocortical brain areas before onset of clinical dementia. This has major implications for our understanding of the onset and progression of AD-type pathology both in DS and in sporadic AD.

Comparisons between Alzheimer disease, frontotemporal lobar degeneration, and normal aging with brain mapping

Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD) are both common degenerative dementias in the under 65 age group. Although clinical criteria have been defined for both diseases, there is considerable overlap in clinical features, and hence, diagnosis still can be very difficult particularly in the early stages of the disease. As a result, there has been increasing interest in using magnetic resonance imaging to better characterize these diseases and to aid in diagnosis. Voxel-based morphometry (VBM) is an automated technique that assesses patterns of regional gray matter atrophy on magnetic resonance imaging between 2 groups of subjects. It is unbiased in that it looks throughout the whole brain and does not require any a priori assumptions concerning which structures to assess, giving it a significant advantage over traditional region of interest-based methods. Voxel-based morphometry has been widely used to assess patterns of regional atrophy in subjects with AD and FTLD. These studies have demonstrated specific patterns of regional loss in both diseases, compared the 2 diseases to look for differences that could be diagnostically useful, and have correlated regions of gray matter loss to cognitive and behavioral deficits in these subjects. This article will review the findings of these studies and discuss the role of VBM in these neurodegenerative diseases.

'Alzheimer's disease': more data, but are we any more informed?

PURPOSE OF REVIEW

While we adhere to traditional misconceptions regarding the nature of age-associated neurodegenerative, and vascular and other brain changes, we will not re-design our research projects, and we will not reconsider and improve our pragmatic diagnostic and therapeutic approach.

RECENT FINDINGS

This review focuses (1) on the continuum of cognitive deficits from mild cognitive impairment to manifest dementia, (2) on the spectrum of neurodegenerative, vascular and other cerebral co-morbidity, and (3) on some reversible examples of the rare outliers (limbic encephalitis, Hashimoto encephalopathy) not to be included in the common severity and cerebral co-morbidity spectrum of senile cognitive impairment.

SUMMARY

We will only be more informed if we accept appropriate concepts and draw the right conclusions. Important new research has not yet filtered into the minds of dementia researchers specializing in 'normal ageing' or 'mild cognitive impairment', 'Alzheimer's disease' or 'dementia with Lewy bodies', tauopathies or synucleopathies, etc.

Network analysis of mild cognitive impairment

We present a network analysis of a cross-sectional study of mild cognitive impairment (MCI). Network analysis, as opposed to univariate analysis, accounts for interactions among brain structures in explaining a clinical outcome. In this context, we analyze structural magnetic resonance (MR) data based on a Bayesian network representation of variables in the problem domain. The Bayesian network resulting from this analysis reveals complex, nonlinear multivariate associations among morphological changes in the left hippocampus and in the right thalamus and the presence of mild cognitive impairment. This Bayesian network could be used to predict the presence of mild cognitive impairment from structural MR scans.

Using voxel-based morphometry to map the structural changes associated with rapid conversion in MCI: A longitudinal MRI study

Capturing the dynamics of gray matter (GM) atrophy in relation to the conversion from mild cognitive impairment (MCI) to clinically probable Alzheimer's disease (AD) would be of considerable interest. In this prospective study we have used a novel longitudinal voxel-based method to map the progression of GM loss in MCI patients over time and compared converters to non-converters. Eighteen amnestic MCI patients were followed-up for a predefined fixed period of 18 months and conversion was judged according to NINCDS-ADRDA criteria for probable AD. Each patient underwent a high-resolution T1-weighted volume MRI scan both at entry in the study and 18 months later. We used an optimal VBM protocol to compare baseline imaging data of converters to those of non-converters. Moreover, to map GM loss from baseline to follow-up assessment, we used a modified voxel-based morphometry (VBM) procedure specially designed for longitudinal studies. At the end of the follow-up period, seven patients had converted to probable AD. Areas of lower baseline GM value in converters mainly included the hippocampus, parahippocampal cortex, and lingual and fusiform gyri. Regions of significant GM loss over the 18-month follow-up period common to both converters and non-converters included the temporal neocortex, parahippocampal cortex, orbitofrontal and inferior parietal areas, and the left thalamus. However, there was significantly greater GM loss in converters relative to non-converters in the hippocampal area, inferior and middle temporal gyrus, posterior cingulate, and precuneus. This accelerated atrophy may result from both neurofibrillary tangles accumulation and parallel pathological processes such as functional alteration in the posterior cingulate. The ability to longitudinally assess GM changes in MCI offers new perspectives to better understand the pathological processes underlying AD and to monitor the effects of treatment on brain structure.