Discrimination between Alzheimer dementia and controls by automated analysis of multicenter FDG PET

Clinical diagnosis of vascular dementia

Vascular dementia (VaD) is a heterogeneous clinical entity based on various vascular pathophysiological processes underlying the subtypes of cerebrovascular disease (CVD). Several diagnostic criteria are currently being used for the clinical diagnosis of VaD, but they are mostly more than 10 years old and need to be renovated including the use of functional brain imaging methods such as single photon emission computerized tomography (SPECT). There is a limitation in the diagnosis based on the strict dichotomy between AD and VaD, and the concept of "AD with CVD" or "mixed dementia" should be included in the clinical diagnosis of VaD.

Partial volume effect-corrected FDG PET and grey matter volume loss in patients with mild Alzheimer's disease

PURPOSE

Although( 18)F-fluorodeoxyglucose (FDG) PET is an established imaging technique to assess brain glucose utilisation, accurate measurement of tracer concentration is confounded by the presence of partial volume effect (PVE) due to the limited spatial resolution of PET, which is particularly true in atrophic brains such as those encountered in patients with Alzheimer's disease (AD). Our aim was to investigate the effects of PVE correction on FDG PET in conjunction with voxel-based morphometry (VBM) in patients with mild AD.

METHODS

Thirty-nine AD patients and 73 controls underwent FDG PET and MRI. The PVE-corrected grey matter PET images were obtained using an MRI-based three-compartment method. Additionally, the results of PET were compared with grey matter loss detected by VBM.

RESULTS

Before PVE correction, reduced FDG uptake was observed in posterior cingulate gyri (PCG) and parieto-temporal lobes (PTL) in AD patients, which persisted after PVE correction. Notably, PVE correction revealed relatively preserved FDG uptake in hippocampal areas, despite the grey matter loss in medial temporal lobe (MTL) revealed by VBM.

CONCLUSION

FDG uptake in PCG and PTL is reduced in AD regardless of whether or not PVE correction is applied, supporting the notion that the reduced FDG uptake in these areas is not the result of atrophy. Furthermore, FDG uptake by grey matter tissue in the MTL, including hippocampal areas, is relatively preserved, suggesting that compensatory mechanisms may play a role in patients with mild AD.

Metabolic correlates of executive dysfunction

This study was designed to examine the correlations between resting-state brain glucose metabolism (CMRglc), as measured with Positron Emission Tomography and performance on executive function tasks in Alzheimer's disease (AD), while taking into account the severity of cognitive deterioration. We addressed this issue in 50 AD patients, classified as very mild (n = 22) and mild (n = 28) AD on the basis of an extensive neuropsychological battery. Thirteen healthy subjects were selected as controls for the neuropsychological measures. Statistical Parametric Mapping (SPM) was used to examine voxel-wise correlations between CMRglc and scores on selected cognitive tests of executive functions: the Stroop Test, the Trail Making Test, the Dual Task and the Phonemic Fluency, while correcting for age and global CMRglc. All analyses were done separately for the two AD subgroups. The very mild AD patients showed significant associations between Stroop and Trail Making Test scores and prefrontal regions metabolism, whereas the mild AD patients exhibited more widely distributed cognitive-metabolic correlations extending to the posterior brain regions. These data suggest that a large cortical network is implicated in executive dysfunction in AD, and that the pattern of cognitive-metabolic correlations varies according to disease severity.

An easy Z-score imaging system for discrimination between very early Alzheimer??s disease and controls using brain perfusion SPECT in a multicentre study

BACKGROUND AND AIM

In Alzheimer's disease (AD), regional cerebral blood flow (rCBF) in the posterior cingulate gyrus and precuneus has been reported to decrease even at a very early stage. We performed a multicentre SPECT study to evaluate the discrimination ability of an easy Z-score imaging system (eZIS) by detecting an rCBF decrease in this area with a common normal database between very early AD patients at the stage of mild cognitive impairment and age-matched healthy volunteers.

METHODS

Brain perfusion SPECT images of 40 Alzheimer's disease patients and 40 healthy volunteers were acquired from four gamma camera systems in different institutions. Systematic differences of SPECT images between different gamma cameras were corrected using conversion maps calculated from the SPECT images of the same brain phantom. Ten observers with various degrees of expertise graded eZIS results for receiver operating characteristic (ROC) curves. ROC curves for a positive Z-score in the volume of interest (VOI) of the posterior cingulate gyrus and precuneus were also analysed.

RESULTS

An area under the ROC curve value (AZ) for ten observers showed the highest value of 0.866 on average with the smallest standard deviation of 0.027 in the condition of the lower threshold of a Z-score map of 2 without superimposition of VOI. Automated analysis of a Z-score in the VOI showed an AZ value of 0.895.

CONCLUSION

Since the degree of expertise of the observers with respect to reading eZIS did not influence the performance and an eZIS can use a common normal database by converting site-specific SPECT data to the core data, the eZIS was considered to be very useful for diagnosing early AD in routine studies in many institutions.

The Utility of PET Brain Imaging in the Initial Evaluation of Dementia

Given the challenges and benefits of timely and accurate diagnosis of neurodegenerative disorders and the importance of appropriate subsequent treatments, physicians and patients alike desire tools that aid in diagnosing dementia as early and as precisely as possible. One of these tools may be functional brain imaging, specifically positron emission tomography (PET). Recent technological advancements, ongoing research studies, and approval for reimbursement by various insurance companies and Medicare, under certain circumstances, have led to an increased interest in the use of this tool in the evaluation of dementia. This article will review PET brain imaging in the initial assessment and diagnosis of dementia, including its place in current guidelines and role in diagnostic algorithms, its applicability in differentiating among various dementia syndromes and major psychiatric disorders, and some of the controversies surrounding its utility in general clinical practice.

Single photon emission computed tomography perfusion differences in mild cognitive impairment

OBJECTIVE

To relate cerebral perfusion abnormalities to subsequent changes in clinical status among patients with mild cognitive impairment (MCI).

METHODS

Perfusion single photon emission computed tomography (SPECT) images were acquired in 105 elderly patients without dementia with MCI, using 99mTc-HMPAO. Clinical outcome after a 5-year follow-up period was heterogeneous.

RESULTS

Baseline SPECT data differed in those patients with MCI who were later diagnosed with Alzheimer's disease (the converter group) from those patients with MCI who experienced clinically evident decline but did not progress to a diagnosis of Alzheimer's disease within the follow-up period (the decliner group), from patients with MCI who had no clinical evidence of progression (the stable group), and from a group of 19 normal subjects (the control group). The most consistent decreases in relative perfusion in converters compared with the normal, stable and decliner groups were observed in the caudal anterior cingulate, and in the posterior cingulate. In addition, converters showed increased relative perfusion in the rostral anterior cingulate in comparison to the stable and decliner groups. A group of patients with Alzheimer's disease were also included for purposes of comparison. The group of patients with Alzheimer's disease at baseline differed from each of the other groups, with temporoparietal regions showing the most significant reductions in perfusion.

CONCLUSIONS

These results suggest that clinical heterogeneity in MCI is reflected in SPECT perfusion differences, and that the pattern of perfusion abnormalities evolves with increasing clinical severity.

Atrophy is associated with posterior cingulate white matter disruption in dementia with Lewy bodies and Alzheimer's disease

Hippocampal atrophy and posterior cingulate hypometabolism are common features of both Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). These regions show correlated activity at rest as part of the 'default network', and they are connected by the cingulum, a white matter (WM) tract. We hypothesised that hippocampal atrophy would be associated with disruption of the cingulum, as determined by diffusion tensor imaging. We recruited 15 people with AD, 16 with DLB, and 15 healthy control subjects of similar age. They were scanned on a 1.5 T MRI system with a T1 weighted 3D sequence and diffusion tensor FLAIR imaging. The T1 images were segmented into grey and white matter and spatially normalised using SPM. Hippocampal atrophy was estimated by calculating the mean grey matter (GM) volume from a region of interest in standard space and global atrophy from the total CSF segmentation. Fractional anisotropy (FA) maps were calculated and also spatially normalised. Using SPM, a multivariate correlation of FA against hippocampal GM, global atrophy and disease group was performed. We found a bilateral region adjacent to the posterior cingulate and encompassing a branch of the cingulum where global atrophy correlated with fractional anisotropy, after controlling for diagnosis and hippocampal GM. The results suggest that dementia disease progression as measured by global atrophy is associated with disruption of the white matter which connects posterior cingulate and lateral parietal regions. Hence, in addition to the hypometabolism in these regions in AD and DLB, there is also disruption to the white matter connecting them. Future studies are needed to determine whether the disruption precedes or is consequent on atrophy or hypometabolism.

A review of the literature on neuroimaging of serotoninergic function in Alzheimer's disease and related disorders

Behavioural and psychological disorders are frequent not only in frontotemporal dementia (FTD), but also in Alzheimer's disease (AD), and many of them are related to serotoninergic dysfunction. In vitro biochemical measurements on brain samples show both pre- and post-synaptic impaired brain serotoninergic function in degenerative dementia, sometimes related to hyperactivity or aggressive behaviour. To date, few studies have explored in vivo 5HT2A and 5HT1A brain receptors in AD and FTD. They suggest that brain cells are lost in the associative cortices (5HT2A) and hippocampus (5HT1A) of AD patients, and in the medial prefrontal and orbitofrontal cortices of FTD subjects (5HT2A). Apart from reflecting a loss of local neurons, the meaning of the decrease in 5HT receptors is not yet clear and larger populations are required to establish relationships with clinical symptoms such as dementia severity and search for possible consequences for patients' behavioural and affective status.

Evaluation of a new expert system for fully automated detection of the Alzheimer's dementia pattern in FDG PET

OBJECTIVE

Fluorodeoxyglucose (FDG) positron emission tomography (PET) is increasingly used to support a diagnosis of Alzheimer's disease. The aim of the present study was to evaluate a new expert system (PALZ) for the fully automated analysis of FDG PET images for diagnosis of the disease.

METHODS

The PALZ tool is based on the detection of the typical disease pattern in FDG PET images. Its potential for this task was evaluated in 22 consecutive patients with suspected Alzheimer's disease who had been graded as positive for the pattern by an experienced reader (visual analysis supported by statistical parametric mapping (SPM)), and in 18 controls. Dependence on scanner performance was assessed by variation of the spatial resolution of the PET images.

RESULTS

All the Alzheimer's disease subjects were classified as pattern-positive by the PALZ tool. Fifteen controls were classified as normal. Sensitivity and specificity for differentiation of the patients with suspected Alzheimer's disease from the controls were 100% and 83%, respectively. The false positive finding in three controls most likely was caused by differences in attenuation correction between the normal data base of the PALZ tool (cold transmission scan) and the local data sets (hot transmission scan). There was only mild dependence on spatial resolution.

CONCLUSIONS

The results of the present study suggest that the PALZ tool provides similar performance for the detection of the typical Alzheimer's disease pattern in FDG PET images as an experienced reader supported by SPM. The PALZ tool is fully automated, easy to use, and insensitive to the spatial resolution of the PET scanner used. Therefore, it has the potential for widespread clinical use.

Patterns of regional brain hypometabolism associated with knowledge of semantic features and categories in Alzheimer's disease

The study of semantic memory in patients with Alzheimer's disease (AD) has raised important questions about the representation of conceptual knowledge in the human brain. It is still unknown whether semantic memory impairments are caused by localized damage to specialized regions or by diffuse damage to distributed representations within nonspecialized brain areas. To our knowledge, there have been no direct correlations of neuroimaging of in vivo brain function in AD with performance on tasks differentially addressing visual and functional knowledge of living and nonliving concepts. We used a semantic verification task and resting 18-fluorodeoxyglucose positron emission tomography in a group of mild to moderate AD patients to investigate this issue. The four task conditions required semantic knowledge of (1) visual, (2) functional properties of living objects, and (3) visual or (4) functional properties of nonliving objects. Visual property verification of living objects was significantly correlated with left posterior fusiform gyrus metabolism (Brodmann's area [BA] 37/19). Effects of visual and functional property verification for non-living objects largely overlapped in the left anterior temporal (BA 38/20) and bilateral premotor areas (BA 6), with the visual condition extending more into left lateral precentral areas. There were no associations with functional property verification for living concepts. Our results provide strong support for anatomically separable representations of living and nonliving concepts, as well as visual feature knowledge of living objects, and against distributed accounts of semantic memory that view visual and functional features of living and nonliving objects as distributed across a common set of brain areas.

Regional coherence changes in the early stages of Alzheimer's disease: a combined structural and resting-state functional MRI study

Recent functional imaging studies have indicated that the pathophysiology of Alzheimer's disease (AD) can be associated with the changes in spontaneous low-frequency (<0.08 Hz) blood oxygenation level-dependent fluctuations (LFBF) measured during a resting state. The purpose of this study was to examine regional LFBF coherence patterns in early AD and the impact of regional brain atrophy on the functional results. Both structural MRI and resting-state functional MRI scans were collected from 14 AD subjects and 14 age-matched normal controls. We found significant regional coherence decreases in the posterior cingulate cortex/precuneus (PCC/PCu) in the AD patients when compared with the normal controls. Moreover, the decrease in the PCC/PCu coherence was correlated with the disease progression measured by the Mini-Mental State Exam scores. The changes in LFBF in the PCC/PCu may be related to the resting hypometabolism in this region commonly detected in previous positron emission tomography studies of early AD. When the regional PCC/PCu atrophy was controlled, these results still remained significant but with a decrease in the statistical power, suggesting that the LFBF results are at least partly explained by the regional atrophy. In addition, we also found increased LFBF coherence in the bilateral cuneus, right lingual gyrus and left fusiform gyrus in the AD patients. These regions are consistent with previous findings of AD-related increased activation during cognitive tasks explained in terms of a compensatory-recruitment hypothesis. Finally, our study indicated that regional brain atrophy could be an important consideration in functional imaging studies of neurodegenerative diseases.

Decreased cerebral blood flow and prognosis of Alzheimer's disease: A multicenter HMPAO-SPECT study

PURPOSE

To determine the usefulness of brain perfusion SPECT for evaluating the severity and progression of Alzheimer's disease (AD).

METHODS

Eighty-four AD patients were included. At entry, 99mTc-HMPAO-SPECT, the Mini Mental State Examination (MMSE), Mental Function Impairment Scale (MENFIS), and the Raven Colored Progression Matrix (RCPM) were performed for all 84 patients. During the follow-up periods, two individual MMSE evaluations in 34 patients, two MENFIS evaluations in 30 patients, and two RCPM evaluations in 20 patients were performed. Based on the regions of decreased cerebral blood flow demonstrated on 3D-SSP images of SPECT, the cases were classified as type A (no decrease), type B (decreased blood flow in the parietal or temporal lobe), type C (decreased blood flow in the frontal lobe and parietal or temporal lobe), type Pc (decreased blood flow in posterior cingulate gyrus only), and "other types". The types of decreased blood flow, scores on neuropsychological evaluations, and symptom progression were analyzed.

RESULTS

The MENFIS, MMSE, and RCPM scores were poorest in type C patients at entry. The degree of decrease of these scores during the follow-up periods was also greatest in type C. The greatest difference between patients with and without rapid progression in SPECT data of the mild AD patients (MMSE score > or = 24) was in the frontal lobe.

CONCLUSION

Decreased blood flow in the frontal lobe of AD patients is correlated not only with reduced cognitive function at the time of the evaluation but with rapid progression in the subsequent clinical course.

The frontal assessment battery does not differentiate frontotemporal dementia from Alzheimer's disease

BACKGROUND

An early differentiation of Alzheimer's disease (AD) from frontotemporal dementia (FTD) is important, since these conditions are essentially different regarding prognosis and therapeutical approach. Until now, no single test is available which allows a reliable differentiation. The Frontal Assessment Battery (FAB) has been found to have good reliability in identifying an executive deficit in frontal syndromes and in extrapyramidal disorders. The ability of the FAB to distinguish AD from FTD in mildly demented patients is less clearly assessed.

METHODS

We compared FAB scores in a consecutive series of 33 FTD (frontal variant) and 85 AD patients.

RESULTS

FAB global scores in the two groups were very similar, also when considering only mildly demented subgroups [Mini Mental State Examination (MMSE) score > or = 20; 20 FTD and 38 AD patients]. Considering FAB subscores, only the 'go-no go' subtest showed a significant difference, reflecting a poorer inhibitory motor control in AD patients. FAB scores in the two groups of patients correlated with global cognitive decline (MMSE), and with executive and visuospatial test scores, showing good concurrent validity.

CONCLUSION

The FAB does not differentiate patients with AD from those with FTD, like all other executive tests. However, it may be useful in the examination of executive function in AD, FTD and several other pathological conditions.

Fronto-striatal deficit in Parkinson's disease during semantic event sequencing

Studies of Parkinson's disease (PD) suggest that cognitive deficits accompany the classically recognized motor symptoms, and that these cognitive deficits may result from damage to frontal-basal ganglia circuits. PD patients are impaired on ordering events and action components into coherent sequences. In this study, we examined early-stage, nondemented, medicated PD subjects and matched control subjects during a semantic event sequencing task using functional MRI (fMRI). The task required subjects to examine four pictures of meaningful events, determine the correct temporal relationship between each picture, and re-order the pictures into a coherent sequence. There were two main findings. First, we found abnormal activation within the prefrontal cortex (PFC) and the "default" network in the PD group. Distinct areas of the PFC showed both hypoactivation and hyperactivation, whereas the "default" network showed reduced levels of resting activation in PD. Secondly, we observed left caudate hyperactivation in the PD group. The findings are discussed in relationship to how more activation may be compensatory, but does not necessarily mean efficient and correlated brain function.

Alois Alzheimer revisited: differences in origin of the disease carrying his name

Based on the means of his time, Alois Alzheimer supposed that the disease, later carrying his name, is a disease of older age, and that the pathomorphological structures he described are due to disturbances in brain metabolism. In this contribution, it is discussed which cellular metabolic abnormalities may be representative for age-related sporadic Alzheimer disease (SAD) the predominant form of SAD in contrast to the very rare hereditary early-onset form. In focus are disturbances in glucose/energy metabolism which involve the deficits in acetylcholine, cholesterol and UDP-N-acetylglucosamine beside ATP. Another leading abnormality is the defect in cell membrane composition. The interrelation between abnormal glucose/energy metabolism and membrane defect may be assumed to form the basis for the induction of both the perturbed metabolism of the amyloid precursor protein leading to increased formation of beta-amyloid and hyperphosphorylation of tau-protein destroying cell structures. Alois Alzheimer may have been so prescient to assume most of this 100 years ago.

Orbitofrontal dysfunction related to both apathy and disinhibition in frontotemporal dementia

Orbitofrontal metabolic impairment is characteristic of the frontal variant of frontotemporal dementia (fv-FTD), as are early changes in emotional and social conduct. Two main types of behavioral disturbances have been distinguished in fv-FTD patients: apathetic and disinhibited manifestations. In this study, we searched for relationships between brain metabolism and presence of apathetic or disinhibited behavior. Metabolic activity and behavioral data were collected in 41 fv-FTD patients from European PET centers. A conjunction analysis of the PET data showed an expected impairment of metabolic activity in the anterior cingulate, ventromedial and orbital prefrontal cortex, the dorsolateral prefrontal cortex and the left anterior insula in fv-FTD subjects compared to matched controls. A correlation was observed between disinhibition scores on the Neuropsychiatric Inventory scale and a cluster of voxels located in the posterior orbitofrontal cortex (6, 28, -24). Comparison of brain activity between apathetic and nonapathetic fv-FTD patients from two centers also revealed a specific involvement of the posterior orbitofrontal cortex in apathetic subjects (4, 22, -22). The results confirm that the main cerebral metabolic impairment in fv-FTD patients affects areas specializing in emotional evaluation and demonstrate that decreased orbitofrontal activity is related to both disinhibited and apathetic syndromes in fv-FTD.

Anatomical and functional alterations in semantic dementia: a voxel-based MRI and PET study

Rare studies have used magnetic resonance imaging (MRI) and voxel-based morphometry (VBM) to assess atrophy, and only two positron emission tomography (PET) studies used SPM to examine functional changes in semantic dementia (SD). Our aim was to highlight both morphological and functional abnormalities in a same group of 10 SD patients, in the entire brain, using a "state of the art" methodology (optimized VBM procedure, PET data corrected for partial volume effects and voxel-based analyses). We also used an extensive neuropsychological battery. We showed that main alterations concerned the left temporal lobe, in accordance with the striking impairment of semantic memory in SD patients, as well as the hippocampal region, which may partly explain their moderate episodic memory deficits. Hypometabolism was more extensive than grey matter loss in both temporal lobes, and specifically concerned the orbitofrontal areas, consistent with the moderate impairment of executive functions and behavioural changes. While PET is more sensitive than MRI, there is striking concordance between morphological and functional abnormalities, which contrasts with the discordance observed in Alzheimer's disease and might be a typical feature of SD.

Neural correlates of anosognosia for cognitive impairment in Alzheimer's disease

We explored the neural substrate of anosognosia for cognitive impairment in Alzheimer's disease (AD). Two hundred nine patients with mild to moderate dementia and their caregivers assessed patients' cognitive impairment by answering a structured questionnaire. Subjects rated 13 cognitive domains as not impaired or associated with mild, moderate, severe, or very severe difficulties, and a sum score was calculated. Two measures of anosognosia were derived. A patient's self assessment, unconfounded by objective measurements of cognitive deficits such as dementia severity and episodic memory impairment, provided an estimate of impaired self-evaluative judgment about cognition in AD. Impaired self-evaluation was related to a decrease in brain metabolism measured with 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in orbital prefrontal cortex and in medial temporal structures. In a cognitive model of anosognosia, medial temporal dysfunction might impair a comparison mechanism between current information on cognition and personal knowledge. Hypoactivity in orbitofrontal cortex may not allow AD patients to update the qualitative judgment associated with their impaired cognitive abilities. Caregivers perceived greater cognitive impairments than patients did. The discrepancy score between caregiver's and patient's evaluations, an other measure of anosognosia, was negatively related to metabolic activity located in the temporoparietal junction, consistent with an impairment of self-referential processes and perspective taking in AD.

18FDG PET in vascular dementia: differentiation from Alzheimer's disease using voxel-based multivariate analysis

The brain metabolic pattern of vascular dementia (VaD) remains poorly characterized. Univariate voxel-based analysis ignores the functional correlations among structures and may lack sensitivity and specificity. Here, we applied a novel voxel-based multivariate technique to a large ((18)F)2-fluoro-2-deoxy-D-glucose positron emission tomography data set. The sample consisted of 153 subjects, one-third each being probable subcortical VaD, probable Alzheimer disease (AD) (matched for Mini-Mental-State examination (MMSE) and age), and normal controls (NCs). We first applied principal component (PC) analysis and removed PCs significantly correlated to age. The remainders were used as feature vectors in a canonical variate analysis to generate canonical variates (CVs), that is, linear combinations of PC-scores. The first two CVs efficiently separated the groups. CV(1) separated VaD from AD with 100% accuracy, whereas CV(2) separated NC from demented subjects with 72% sensitivity and 96% specificity. Images depicting CV(1) and CV(2) showed that lower metabolism differentiating VaD from AD mainly concerned the deep gray nuclei, cerebellum, primary cortices, middle temporal gyrus, and anterior cingulate gyrus, whereas lower metabolism in AD versus VaD concerned mainly the hippocampal region and orbitofrontal, posterior cingulate, and posterior parietal cortices. The hypometabolic pattern common to VaD and AD mainly concerned the posterior parietal, precuneus, posterior cingulate, prefrontal, and anterior hippocampal regions, and linearly correlated with the MMSE. This study shows the potential of voxel-based multivariate methods to highlight independent functional networks in dementing diseases. By maximizing the separation between groups, this method extracted a metabolic pattern that efficiently differentiated VaD and AD.

Schooling mediates brain reserve in Alzheimer's disease: findings of fluoro-deoxy-glucose-positron emission tomography

BACKGROUND

Functional imaging studies report that higher education is associated with more severe pathology in patients with Alzheimer's disease, controlling for disease severity. Therefore, schooling seems to provide brain reserve against neurodegeneration.

OBJECTIVE

To provide further evidence for brain reserve in a large sample, using a sensitive technique for the indirect assessment of brain abnormality (18F-fluoro-deoxy-glucose-positron emission tomography (FDG-PET)), a comprehensive measure of global cognitive impairment to control for disease severity (total score of the Consortium to Establish a Registry for Alzheimer's Disease Neuropsychological Battery) and an approach unbiased by predefined regions of interest for the statistical analysis (statistical parametric mapping (SPM)).

METHODS

93 patients with mild Alzheimer's disease and 16 healthy controls underwent 18F-FDG-PET imaging of the brain. A linear regression analysis with education as independent and glucose utilisation as dependent variables, adjusted for global cognitive status and demographic variables, was conducted in SPM2.

RESULTS

The regression analysis showed a marked inverse association between years of schooling and glucose metabolism in the posterior temporo-occipital association cortex and the precuneus in the left hemisphere.

CONCLUSIONS

In line with previous reports, the findings suggest that education is associated with brain reserve and that people with higher education can cope with brain damage for a longer time.

Evaluation of voxel-based methods for the statistical analysis of PIB PET amyloid imaging studies in Alzheimer's disease

Deposition of amyloid plaques is believed to be a central event in the development of Alzheimer's disease (AD). The present study was undertaken to evaluate statistical methods for the assessment of group differences in retention of an amyloid imaging agent, PIB, throughout the brain and to compare these results to FDG studies of glucose metabolism performed in the same subjects on the same day. PET studies were performed in 10 mild to moderate AD and 11 control subjects. Parametric images of PIB retention (over 90 min post-injection) were generated using the Logan graphical analysis with cerebellar (CER, reference region) data as input. FDG parametric images were created by summing the uptake over 40-60 min post-injection and normalizing that to the CER to give a standardized uptake value ratio. Data were compared using parametric (SPM) and non-parametric (SnPM) statistical methods with familywise error (FWE) and false discovery rate (FDR) corrections. PIB results were consistent with previous regional results as AD subjects showed highly significant retention in frontal, parietal, temporal, and posterior cingulate cortices (FDR-corrected p<1.4e-10). FDG results showed regions of marginally significant decreases in uptake in AD subjects (frontal, parietal, temporal, posterior cingulate cortices: FDR-corrected p<0.1) consistent with previous studies. Relative to FDG, the PIB analyses were of greater statistical significance and larger spatial extent. Additionally, the PIB analyses retained significance after both FWE and FDR corrections. These results indicate that voxel-based methods will be useful for future larger longitudinal studies of amyloid deposition that could improve AD diagnosis and anti-amyloid therapy assessment.

Alzheimer's disease

Alzheimer's disease is the most common cause of dementia. Research advances have enabled detailed understanding of the molecular pathogenesis of the hallmarks of the disease--ie, plaques, composed of amyloid beta (Abeta), and tangles, composed of hyperphosphorylated tau. However, as our knowledge increases so does our appreciation for the pathogenic complexity of the disorder. Familial Alzheimer's disease is a very rare autosomal dominant disease with early onset, caused by mutations in the amyloid precursor protein and presenilin genes, both linked to Abeta metabolism. By contrast with familial disease, sporadic Alzheimer's disease is very common with more than 15 million people affected worldwide. The cause of the sporadic form of the disease is unknown, probably because the disease is heterogeneous, caused by ageing in concert with a complex interaction of both genetic and environmental risk factors. This seminar reviews the key aspects of the disease, including epidemiology, genetics, pathogenesis, diagnosis, and treatment, as well as recent developments and controversies.

Task-induced deactivations during successful paired associates learning: An effect of age but not Alzheimer's disease

Task-induced fMRI deactivations during successful encoding and retrieval of visuospatial paired associates were examined at different levels of task difficulty in younger and older adults (Experiment 1), and older adults with and without mild probable Alzheimer's disease (AD) (Experiment 2). Irrespective of the level of task difficulty, common deactivations (determined through the use of conjunction analyses) were observed in the lateral and medial prefrontal, anterior and posterior cingulate, and temporal brain regions and in the claustrum during both encoding and retrieval in younger and older adults (Experiment 1). In AD patients and healthy older adults, common deactivations were found in posterior cingulate, temporal, and lateral parietal regions and in the insula and claustrum during encoding and retrieval of paired associates (Experiment 2). As task difficulty increased, irrespective of the type of task, the magnitude of task-induced deactivations increased in the medial prefrontal/superior frontal gyrus and middle/posterior cingulate cortex in younger and older adults (Experiment 1), and in the middle cingulate cortex in older adults with and without AD (Experiment 2). In Experiment 1, greater deactivation was observed in the anterior cingulate gyrus in older compared to younger adults during retrieval of paired associates which was attributed to greater suppression of task-unrelated thoughts in the older group. No significant differences in task-induced deactivation, or in the type of relationship exhibited between deactivation and task difficulty, were observed between older adults with and without AD (Experiment 2). It was suggested that this was related to the matching of successful task performance and task difficulty across patient and control groups. Following previous proposals, task-induced deactivations were suggested to underlie a shifting of attentional focus from monitoring of the self and the environment (through attenuation of these activities) to external, goal-directed behaviour.

PET network abnormalities and cognitive decline in patients with mild cognitive impairment

Temporoparietal and posterior cingulate metabolism deficits characterize patients with Alzheimer's disease (AD). A H(2)(15)O resting PET scan covariance pattern, derived by using multivariate techniques, was previously shown to discriminate 17 mild AD patients from 16 healthy controls. This AD covariance pattern revealed hypoperfusion in bilateral inferior parietal lobule and cingulate; and left middle frontal, inferior frontal, precentral, and supramarginal gyri. The AD pattern also revealed hyperperfusion in bilateral insula, lingual gyri, and cuneus; left fusiform and superior occipital gyri; and right parahippocampal gyrus and pulvinar. In an independent sample of 23 outpatients with mild cognitive impairment (MCI) followed at 6-month intervals, the AD pattern score was evaluated as a predictor of cognitive decline. In this MCI sample, an H2(15)O resting PET scan was carried out at baseline. Mean duration of follow-up was 48.8 (SD 15.5) months, during which time six of 23 MCI patients converted to AD. In generalized estimating equations (GEE) analyses, controlling for age, sex, education, and baseline neuropsychological scores, increased AD pattern score was associated with greater decline in each neuropsychological test score over time (Mini Mental State Exam, Selective Reminding Test delayed recall, Animal Naming, WAIS-R digit symbol; Ps<0.01-0.001). In summary, a resting PET covariance pattern previously reported to discriminate AD patients from control subjects was applied prospectively to an independent sample of MCI patients and found to predict cognitive decline. Independent replication in larger samples is needed before clinical application can be considered.

Fatale familiäre Insomnie

Fatal familial insomnia (FFI) is a hereditary prion disease caused by a mutation in codon 178 of the prion protein gene PRNP on chromosome 20. It is characterized by disturbed night sleep, resulting in daily vigilance perturbations and a variety of other neurological symptoms. We present the case of a 46-year-old woman deteriorating despite immunosuppressive treatment which was initiated suspecting cerebral vasculitis as the cause of her progressive neurological symptoms. The correct diagnosis was established only post mortem. Based on the case presented here, we discuss typical clinical symptoms and imaging findings. In particular, we outline how modern diagnostic methods such as positron emission tomography with [(15)O]H(2)O and [(18)F]FDG and single photon emission computed tomography can add valuable information to results from conventionally performed imaging techniques and genetic testing.

CSF tau protein and FDG PET in patients with aging-associated cognitive decline and Alzheimer's disease

INTRODUCTION

In Alzheimer's disease (AD), accelerated neurofibrillary tangle formation occurs which is associated with increased tau protein release into the cerebrospinal fluid (CSF). Recent studies found significantly increased CSF tau already in patients at risk of developing AD, indicating its potential as a biochemical marker of AD. Cerebral glucose metabolism is reduced in frontotemporoparietal and cingulate cortices in patients with mild AD. However, few studies have investigated CSF tau protein and cerebral glucose metabolism changes in patients at risk to develop AD.

METHODS

48 patients with AD, 88 patients with aging-associated cognitive decline (AACD), and 39 healthy controls were included. In all participants, CSF levels of tau were determined by ELISA at baseline and compared between the diagnostic groups. 14 AACD patients and 14 controls underwent (18)F-fluorodeoxyglucose positron emission tomography (FDG PET).

RESULTS

AD patients showed the highest CSF tau levels compared with AACD patients and controls. AACD patients had significantly higher tau levels than the controls but lower than the AD patients. AACD patients were characterized by reduced glucose metabolism in bilateral middle temporal cortex, left posterior cingulate cortex, right angular gyrus, and right precuneus compared with controls.

CONCLUSION

In conclusion, our findings reflect and confirm the clinical judgment of an incipient neurodegenerative disorder in a considerable portion of AACD patients. In patients with AACD, CSF tau levels and cerebral glucose metabolism show an altered pattern comparable with that found in AD and thus may facilitate early diagnosis.

Locus ceruleus degeneration promotes Alzheimer pathogenesis in amyloid precursor protein 23 transgenic mice

Locus ceruleus (LC) degeneration and loss of cortical noradrenergic innervation occur early in Alzheimer's disease (AD). Although this has been known for several decades, the contribution of LC degeneration to AD pathogenesis remains unclear. We induced LC degeneration with N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (dsp4) in amyloid precursor protein 23 (APP23) transgenic mice with a low amyloid load. Then 6 months later the LC projection areas showed a robust elevation of glial inflammation along with augmented amyloid plaque deposits. Moreover, neurodegeneration and neuronal loss significantly increased. Importantly, the paraventricular thalamus, a nonprojection area, remained unaffected. Radial arm maze and social partner recognition tests revealed increased memory deficits while high-resolution magnetic resonance imaging-guided micro-positron emission tomography demonstrated reduced cerebral glucose metabolism, disturbed neuronal integrity, and attenuated acetylcholinesterase activity. Nontransgenic mice with LC degeneration were devoid of these alterations. Our data demonstrate that the degeneration of LC affects morphology, metabolism, and function of amyloid plaque-containing higher brain regions in APP23 mice. We postulate that LC degeneration substantially contributes to AD development.

Magnetic resonance and PET studies in the early diagnosis of Alzheimer's disease

The demographics of aging identify an immediate need for the early diagnosis and development of dementia prevention strategies. Recent neuropathological studies have pointed to the early involvement of the hippocampus and entorhinal cortex in the progression of Alzheimer's disease in the brain. In particular, these studies have implicated tau-related pathology as an important cause of neuronal death. In addition, there is a large body of evidence showing that beta-amyloid, which has a predilection for the neocortex, is also involved early in the course of the disease and may also have toxic effects on cells. In vivo cerebrospinal fluid studies have shown that markers for these brain changes have a diagnostic value for Alzheimer's disease and that some measures also provide diagnostic specificity for Alzheimer's disease. Structural and metabolic imaging studies demonstrate brain changes in impaired and at-risk individuals. While currently available magnetic resonance and positron emission tomography techniques are not by themselves specific for the pathologic features of Alzheimer's disease, there are patterns of change that have been useful for the early diagnosis. As such, both prediction and longitudinal imaging studies demonstrate a capacity to recognize abnormalities that relate to future Alzheimer's disease and most recently to future mild cognitive impairment. This review highlights cross-sectional, prediction, and longitudinal magnetic resonance and positron emission tomography imaging studies and attempts to put into perspective their utility for the early diagnosis of Alzheimer's disease, and for their utility to provide diagnostic specificity. It is concluded that there is considerable promise for an early and specific diagnosis for Alzheimer's disease by combining information from imaging and biomarker modalities.

Human gene therapy and imaging in neurological diseases

Molecular imaging aims to assess non-invasively disease-specific biological and molecular processes in animal models and humans in vivo. Apart from precise anatomical localisation and quantification, the most intriguing advantage of such imaging is the opportunity it provides to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Further, molecular imaging can be used to address basic scientific questions, e.g. transcriptional regulation, signal transduction or protein/protein interaction, and will be essential in developing treatment strategies based on gene therapy. Most importantly, molecular imaging is a key technology in translational research, helping to develop experimental protocols which may later be applied to human patients. Over the past 20 years, imaging based on positron emission tomography (PET) and magnetic resonance imaging (MRI) has been employed for the assessment and "phenotyping" of various neurological diseases, including cerebral ischaemia, neurodegeneration and brain gliomas. While in the past neuro-anatomical studies had to be performed post mortem, molecular imaging has ushered in the era of in vivo functional neuro-anatomy by allowing neuroscience to image structure, function, metabolism and molecular processes of the central nervous system in vivo in both health and disease. Recently, PET and MRI have been successfully utilised together in the non-invasive assessment of gene transfer and gene therapy in humans. To assess the efficiency of gene transfer, the same markers are being used in animals and humans, and have been applied for phenotyping human disease. Here, we review the imaging hallmarks of focal and disseminated neurological diseases, such as cerebral ischaemia, neurodegeneration and glioblastoma multiforme, as well as the attempts to translate gene therapy's experimental knowledge into clinical applications and the way in which this process is being promoted through the use of novel imaging approaches.

Functional connectivity of the fusiform gyrus during a face-matching task in subjects with mild cognitive impairment

Cognitive function requires a high level of functional interaction between regions of a network supporting cognition. Assuming that brain activation changes denote an advanced state of disease progression, changes in functional connectivity may precede changes in brain activation. The objective of this study was to investigate changes in functional connectivity of the right middle fusiform gyrus (FG) in subjects with mild cognitive impairment (MCI) during performance of a face-matching task. The right middle FG is a key area for processing face stimuli. Brain activity was measured using functional MRI. There were 16 MCI subjects and 19 age-matched healthy controls. The linear correlation coefficient was utilized as a measure of functional connectivity between the right middle FG and all other voxels in the brain. There were no statistical differences found in task performance or activation between groups. The right middle FG of the healthy control and MCI groups showed strong bilateral positive linear correlation with the visual cortex, inferior and superior parietal lobules, dorsolateral prefrontal cortex (DLPFC) and anterior cingulate. The healthy controls showed higher positive linear correlation of the right middle FG to the visual cortex, parietal lobes and right DLPFC than the MCI group, whereas the latter had higher positive linear correlation in the left cuneus. In the healthy controls, the right middle FG had negative linear correlation with right medial frontal gyrus and superior temporal gyrus and with left inferior parietal lobule (IPL), angular gyrus, superior frontal gyrus and anterior cingulate gyrus, but the MCI group had negative linear correlation with the left IPL, angular gyrus, precuneus, anterior cingulate, and to right middle temporal gyrus and posterior cingulate gyrus. In the negatively linearly correlated regions, the MCI group had reduced functional connectivity to the frontal areas, right superior temporal gyrus and left IPL. Different regions of the cuneus and IPL had increased functional connectivity in either group. The putative presence of Alzheimer's disease neuropathology in MCI affects functional connectivity from the right middle FG to the visual areas and medial frontal areas. In addition, higher linear correlation in the MCI group in the parietal lobe may indicate the initial appearance of compensatory processes. The results demonstrate that functional connectivity can be an effective marker for the detection of changes in brain function in MCI subjects.

Molecular, structural, and functional characterization of Alzheimer's disease: evidence for a relationship between default activity, amyloid, and memory

Alzheimer's disease (AD) and antecedent factors associated with AD were explored using amyloid imaging and unbiased measures of longitudinal atrophy in combination with reanalysis of previous metabolic and functional studies. In total, data from 764 participants were compared across five in vivo imaging methods. Convergence of effects was seen in posterior cortical regions, including posterior cingulate, retrosplenial, and lateral parietal cortex. These regions were active in default states in young adults and also showed amyloid deposition in older adults with AD. At early stages of AD progression, prominent atrophy and metabolic abnormalities emerged in these posterior cortical regions; atrophy in medial temporal regions was also observed. Event-related functional magnetic resonance imaging studies further revealed that these cortical regions are active during successful memory retrieval in young adults. One possibility is that lifetime cerebral metabolism associated with regionally specific default activity predisposes cortical regions to AD-related changes, including amyloid deposition, metabolic disruption, and atrophy. These cortical regions may be part of a network with the medial temporal lobe whose disruption contributes to memory impairment.

Fully automatic diagnostic system for early- and late-onset mild Alzheimer’s disease using FDG PET and 3D-SSP

PURPOSE

The purpose of this study was to design a fully automatic computer-assisted diagnostic system for early- and late-onset mild Alzheimer's disease (AD).

METHODS

Glucose metabolic images were obtained from mild AD patients and normal controls using positron emission tomography (PET) and( 18)F-fluorodeoxyglucose (FDG). Two groups of 20 mild AD patients with different ages of onset were examined. A fully automatic diagnostic system using the statistical brain mapping method was established from the early-onset (EO) and late-onset (LO) groups, with mean ages of 59.1 and 70.9 years and mean MMSE scores of 23.3 and 22.8, respectively. Aged-matched normal subjects were used as controls. We compared the diagnostic performance of visual inspection of conventional axial FDG PET images by experts and beginners with that of our fully automatic diagnostic system in another 15 EO and 15 LO AD patients (mean age 58.4 and 71.7, mean MMSE 23.6 and 23.1, respectively) and 30 age-matched normal controls. A receiver operating characteristic (ROC) analysis was performed to compare data.

RESULTS

The diagnostic performance of the automatic diagnostic system was comparable with that of visual inspection by experts. The area under the ROC curve for the automatic diagnostic system was 0.967 for EO AD patients and 0.878 for LO AD patients. The mean area under the ROC curve for visual inspection by experts was 0.863 and 0.881 for the EO and LO AD patients, respectively. The mean area under the ROC curve for visual inspection by beginners was 0.828 and 0.717, respectively.

CONCLUSION

The fully automatic diagnostic system for EO and LO AD was able to perform at a similar diagnostic level to visual inspection of conventional axial images by experts.

Self-reported fatigue common among optimally treated HIV patients: no correlation with cerebral FDG-PET scanning abnormalities

OBJECTIVE

It was the aim of this study to determine the prevalence and severity of fatigue among optimally treated HIV patients and to investigate the potential association with systemic inflammation and abnormalities of the distribution of cerebral glucose metabolism.

METHODS

A cohort of HIV patients (n = 95), known to be HIV positive for 5 years, on anti-retroviral therapy for a minimum of 3 years and with CD4 counts above 0.2 x 10(9) cells/l, completed a validated fatigue inventory, and plasma was analysed for pro-inflammatory markers including tumour necrosis factor-alpha, interleukin 6 and soluble urokinase receptor (suPAR) levels. The distribution of the regional cerebral metabolic rate of glucose was measured in a sub-group of patients suffering from severe fatigue (n = 9) and a group with no fatigue (n = 7) using fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET) scanning.

RESULTS

Fifteen percent suffered from severe fatigue, but no association with pro-inflammatory markers was found. About 50% of the FDG-PET-scanned patients showed minor abnormalities in the relative cerebral metabolic rate of glucose. These abnormalities were not associated with fatigue but tended to correlate with a short HIV history (p = 0.058), a low CD4 nadir (p = 0.082) and elevated tumour necrosis factor-alpha levels (p = 0.074).

CONCLUSION

Fatigue is common among optimally treated HIV patients. FDG-PET-described signs of imminent neurodegeneration among HIV patients who had a low CD4 nadir may illustrate an aspect of HIV neuropathogenicity.

Lack of age-related increase of mitochondrial DNA amount in brain, skeletal muscle and human heart

During the ageing process, an increase of mitochondrial DNA (mtDNA) deletions and other mutations have been reported. These structural alterations of mtDNA are assumed to cause a reduction in the respiratory chain activity and may contribute to the ageing process. Therefore, the question arises if the accumulation of deleted mtDNA is compensated in vivo by an increase of mtDNA synthesis via a feedback mechanism. We designed two human mtDNA-specific oligonucleotide probes for quantitative mtDNA analysis of 5 different tissues from 50 individuals aged from 8 weeks to 93 years. The amount of mtDNA was approximately 1.1 +/- 0.5% (4617 +/- 2099 copies) in the caudate nucleus, 1.0 +/- 0.5% (4198 +/- 2099 copies) in the frontal lobe cortex, 0.3 +/- 0.2% (1259 +/- 840 copies) in the cerebellar cortex, 1.0 +/- 0.4% (4198 +/- 1679 copies) in skeletal muscle and 2.2+/-1.3% (9235 +/- 5457 copies) in heart muscle. We did not observe any significant change in the absolute copy number during ageing in five different tissues, and therefore, found no evidence for the postulated feedback mechanism. Our study indicates that mtDNA copy number is tissue-specific and depends on the energy demand of the tissue.

Decomposition of metabolic brain clusters in the frontal variant of frontotemporal dementia

Previous studies that measured brain activity in frontotemporal dementia (FTD) used univariate analyses, examining each region of interest separately. We explored in a multicenter European research program the principal brain clusters characterized by a common variability in cerebral metabolism in FTD. Seventy patients with frontal variant (fv) FTD were selected according to international clinical recommendations; principal component analysis (PCA) was performed on FDG-PET metabolic images, looking for covariance clusters in this large population. A first metabolic cluster included most of the lateral and medial prefrontal cortex, bilaterally; PC1 scores correlated with performances on memory and executive neuropsychological tasks. Moreover, FDG-PET images in fv-FTD were further characterized by a metabolic covariance in two clusters comprising the subcallosal medial frontal region, the temporal pole, medial temporal structures and the striatum, separately in the left and in the right hemisphere. The study provides original data-driven arguments for metabolic involvement of separate brain clusters in the rostral limbic system, corresponding to pathological poles differentially affected in each FTD patient.

Mapping of temporal and parietal cortex in progressive nonfluent aphasia and Alzheimer's disease using chemical shift imaging, voxel-based morphometry and positron emission tomography

Little and controversial evidence is available from neuroimaging studies in progressive nonfluent aphasia (PNA). The goal of this study was to combine information from different imaging modalities in PNA compared with Alzheimer's disease (AD). Chemical shift imaging (CSI), voxel-based morphometry (VBM) and fluorodeoxyglucose positron emission tomography (FDG-PET) were used in 5 PNA, 10 AD patients and 10 normal subjects. Group comparisons revealed left anterior lateral temporal abnormalities (BA20/21) in PNA using CSI, VBM and PET in comparison to normal subjects. AD patients showed more limited hypometabolism within the same area. In addition left lateral parietal (BA40) abnormalities were demonstrated in our PNA as well as our AD group using PET and VBM (AD group only). Combining information from all imaging modalities on a single case basis revealed pathology within the left anterior lateral temporal and lateral parietal lobe both in PNA and AD. PNA and AD patients differed significantly, however, with respect to the frequency of medial temporal lobe and posterior cingulate/precuneus involvement. Although our results might not be generalizable to all subgroups of PNA, we conclude that medial temporal and posterior cingulate/precuneus cortex pathology as assessed by CSI and VBM or PET distinguish PNA from AD, whereas lateral temporal and parietal areas are involved in both conditions.

Visual rating of medial temporal lobe metabolism in mild cognitive impairment and Alzheimer's disease using FDG-PET

PURPOSE

This study was designed to examine the utility of visual inspection of medial temporal lobe (MTL) metabolism in the diagnosis of mild cognitive impairment (MCI) and Alzheimer's disease (AD) using FDG-PET scans.

METHODS

Seventy-five subjects [27 normal controls (NL), 26 MCI, and 22 AD] with FDG-PET and MRI scans were included in this study. We developed a four-point visual rating scale to evaluate the presence and severity of MTL hypometabolism on FDG-PET scans. The visual MTL ratings were compared with quantitative glucose metabolic rate (MR(glc)) data extracted using regions of interest (ROIs) from the MRI-coregistered PET scans of all subjects. A standard rating evaluation of neocortical hypometabolism was also completed. Logistic regressions were used to determine and compare the diagnostic accuracy of the MTL and cortical ratings.

RESULTS

For both MTL and cortical ratings, high intra- and inter-rater reliabilities were found (p values <0.001). The MTL rating was highly correlated with and yielded a diagnostic accuracy equivalent to the ROI MR(glc) measures (p values <0.001). The combination of MTL and cortical ratings significantly improved the diagnostic accuracy over the cortical rating alone, with 100% of AD, 77% of MCI, and 85% of NL cases being correctly identified.

CONCLUSION

This study shows that the visual rating of MTL hypometabolism on PET is reliable, yields a diagnostic accuracy equal to the quantitative ROI measures, and is clinically useful and more sensitive than cortical ratings for patients with MCI. We suggest this method be further evaluated for its potential in the early diagnosis of AD.

Understanding metamemory: neural correlates of the cognitive process and subjective level of confidence in recognition memory

An essential feature of human memory is the capacity to assess confidence in one's own memory performance, but the neural mechanisms underlying the process of determining confidence in memory performance have not yet been isolated. Using functional magnetic resonance imaging, we examined both the process of confidence assessment and the subjective level of high or low confidence expressed during this process. The comparison of confidence assessment to recognition showed greater relative activation during confidence assessment in medial and lateral parietal regions, which typically deactivate during cognitive tasks, previously described as part of the "default network". Furthermore, comparisons of high versus low confidence judgments revealed modulation of neural activity in the hippocampus, cingulate and other limbic regions, previously described as the Circuit of Papez. Our findings suggest that activity in two distinct networks of brain regions contribute to the subjective experience of "knowing you know" through memory monitoring processes and signaling subjective confidence level for recognition memory.

Pathological aging of the brain: an overview

The number of elderly people is increasing rapidly and, therefore, an increase in neurodegenerative and cerebrovascular disorders causing dementia is expected. Alzheimer disease (AD) is the most common cause of dementia. Vascular dementia, dementia with Lewy bodies, and frontotemporal dementia are the most frequent causes after AD, but a large proportion of patients have a combination of degenerative and vascular brain pathology. Characteristic magnetic resonance (MR) imaging findings can contribute to the identification of different diseases causing dementia. The MR imaging protocol should include axial T2-weighted images (T2-WI), axial fluid-attenuated inversion recovery (FLAIR) or proton density-weighted images, and axial gradient-echo T2*-weighted images, for the detection of cerebrovascular pathology. Structural neuroimaging in dementia is focused on detection of brain atrophy, especially in the medial temporal lobe, for which coronal high resolution T1-weighted images perpendicular to the long axis of the temporal lobe are extremely important. Single photon emission computed tomography and positron emission tomography may have added value in the diagnosis of dementia and may become more important in the future, due to the development of radioligands for in vivo detection of AD pathology. New functional MR techniques and serial volumetric imaging studies to identify subtle brain abnormalities may also provide surrogate markers for pathologic processes that occur in diseases causing dementia and, in conjunction with clinical evaluation, may enable a more rigorous and early diagnosis, approaching the accuracy of neuropathology.

Positron Emission Tomography Diagnosis of Alzheimer's Disease

Positron emission tomography (PET) imaging of [18F]-2-fluoro-2-deoxy-D-glucose (FDG) is accurate in the early detection of Alzheimer's disease (AD) and in the differentiation of AD from the other causes of dementia. FDG-PET imaging is available widely and performed easily. Different patterns of abnormality with the various causes of dementia are well described. Semiquantitative methods of image interpretation are available. Medicare covers FDG-PET imaging for the narrow indication of differentiation of possible AD from frontotemporal dementia.

Diagnostic value of FDG-PET and HMPAO-SPET in patients with mild dementia and mild cognitive impairment: metabolic index and perfusion index

OBJECTIVE

The diagnostic potential of F-18-2-fluoro-2-deoxy-D-glucose positron emission tomography (PET) and technetium-99m hexamethylpropylene amine oxime single-photon emission tomography (SPET) in early detection and differential diagnosis of early dementia was evaluated including a comparison of metabolic and perfusion indices (PI).

METHODS

Twenty-four patients with initial clinical suspicion of beginning dementia were examined, 12 of them with mild cognitive impairment. All patients underwent SPET and PET within 2 weeks. Data were compared with the final clinical diagnosis at follow-up - 9 with Alzheimer's disease (AD), 1 with frontotemporal dementia, 1 with vascular dementia (VD), 7 with mixed type of dementia (MIX) and 6 without any type of dementia. Metabolic indices (MI) and PI were compared with each other. The regional cerebral blood flow difference (rCBFdiff) calculated as local uptake difference between the right and left hemisphere was measured for patients with VD and MIX.

RESULTS

PET showed higher sensitivity and specificity in identifying the different types of early dementia (44--91 and 78--89%, respectively) than SPET (11--64 and 79--89%, respectively), especially in detecting AD (sensitivity 44%, specificity 83%) and MIX (sensitivity 71%, specificity 78%). Especially in patients with mild cognitive impairment, PET was the superior imaging modality for predicting dementia. Using PET, dementia could be excluded in all patients who did not develop dementia during the follow-up. In all patients, a weak correlation between PI and MI was observed (rho=0.64, p<0.002). The rCBFdiff in patients with VD and MIX ranged from 7 to 37%.

CONCLUSION

In this study on patients with initial suspicion of beginning dementia who underwent both imaging modalities, PET and SPET, PET was the superior imaging method, especially in the detection of early AD or MIX.

Cognitive aging and Alzheimer's disease

Cognitive aging and clinically probable Alzheimer's disease can be discriminated by means of clinical and neuropsychological testing, and structural and functional imaging techniques. Research at the level of cognitive brain systems and at the molecular level provides exciting new insights into the relation between aging and neurodegeneration. The advances at the clinical and at the basic research levels are necessary if we wish to meet the formidable challenge that the increasing prevalence of Alzheimer's disease poses to the medical community.

Voxel-based assessment of spinal tap test-induced regional cerebral blood flow changes in normal pressure hydrocephalus

OBJECTIVE

Normal pressure hydrocephalus (NPH) is a cause of dementia that may be amended by medical intervention. Its diagnosis is therefore of major importance and the establishment of response criteria to cerebrospinal fluid (CSF) shunting is essential. One of these criteria is the clinical response to spinal tap. The accuracy of the spinal tap test could potentially be improved by adding neuroimaging of regional cerebral blood flow (rCBF) changes to the response criteria. Statistical parametric mapping (SPM) is a voxel-based method of image analysis that may be used to statistically assess the significance of rCBF changes. The objective of this study was to evaluate, by SPM, spinal tap test-induced rCBF changes in patients with NPH syndrome.

METHODS

Forty patients with NPH syndrome underwent hexamethylpropylene amine oxime (HMPAO) brain single photon emission computed tomography (SPECT) before and after a spinal tap test (1-day split-dose protocol). The differences in rCBF between these pairs of scans were analysed by SPM in the whole group and between subgroups divided according to gait improvement at the spinal tap test.

RESULTS

In the whole group of patients, there was no statistical difference between pre- and post-spinal tap SPECT images. SPM analysis of patients grouped as a function of their clinical response to the spinal tap test revealed a significant post-spinal tap rCBF increase in the bilateral dorsolateral frontal and left mesiotemporal cortex in clinically responding compared with non-responding patients.

CONCLUSION

According to SPM analysis, gait improvement at the spinal tap test in patients with NPH syndrome is associated with an rCBF increase localized in the bilateral dorsolateral frontal and left mesiotemporal cortex.