Whole brain analysis of T2* weighted baseline FMRI signal in dementia

Astrocytes amplify neurovascular coupling to sustained activation of neocortex in awake mice

Functional hyperemia occurs when enhanced neuronal activity signals to increase local cerebral blood flow (CBF) to satisfy regional energy demand. Ca²⁺ elevation in astrocytes can drive arteriole dilation to increase CBF, yet affirmative evidence for the necessity of astrocytes in functional hyperemia in vivo is lacking. In awake mice, we discovered that functional hyperemia is bimodal with a distinct early and late component whereby arteriole dilation progresses as sensory stimulation is sustained. Clamping astrocyte Ca²⁺ signaling in vivo by expressing a plasma membrane Ca²⁺ ATPase (CalEx) reduces sustained but not brief sensory-evoked arteriole dilation. Elevating astrocyte free Ca²⁺ using chemogenetics selectively augments sustained hyperemia. Antagonizing NMDA-receptors or epoxyeicosatrienoic acid production reduces only the late component of functional hyperemia, leaving brief increases in CBF to sensory stimulation intact. We propose that a fundamental role of astrocyte Ca²⁺ is to amplify functional hyperemia when neuronal activation is prolonged.

Research on BOLD-fMRI Data Denoising Based on Bayesian Estimation and Adaptive Wavelet Threshold

The acquisition of functional magnetic resonance imaging (fMRI) images of blood oxygen level-dependent (BOLD) effect and the signals to be analyzed is based on weak changes in the magnetic field caused by small changes in blood oxygen physiological levels, which are weak signals and complex in noise. In order to model and analyze the pathological and hemodynamic parameters of BOLD-fMRI images effectively, it is urgent to use effective signal analysis techniques to reduce the interference of noise and artifacts. In this paper, the noise characteristics of functional magnetic resonance imaging and the traditional signal denoising methods are analyzed. The Bayesian decision criterion takes into account the probability of the total occurrence of all kinds of references and the loss caused by misjudgment and has strong discriminability. So, an improved adaptive wavelet threshold denoising method based on Bayesian estimation is proposed. By using the correlation characteristics of multiscale wavelet coefficients, the corresponding wavelet components of useful signals and noises are processed differently; while retaining useful frequency information, the noise is weakened to the greatest extent. The new adaptive threshold wavelet denoising method based on Bayesian estimation is applied to the actual experiment, and the results of OEF (oxygen extraction fraction) are optimized. A series of simulation experiments are carried out to verify the effectiveness of the proposed method.

Quantitative susceptibility mapping in β-Amyloid PET-stratified patients with dementia and healthy controls - A hybrid PET/MRI study

PURPOSE

Post-mortem and in-vivo MRI data suggest an accumulation of iron in the brain of Alzheimer's disease (AD) patients. The majority of studies in clinically diagnosed AD patients found an increase of iron-sensitive MRI signals in the putamen. As the clinical diagnosis shows only a moderate sensitivity, Aβ-PET was used to further stratify patients with the clinical diagnosis of AD. Aim of this exploratory study was to examine whether Aβ-positive (AD) and Aβ-negative (non-AD) patients differ in their regional magnetic susceptibility compared to healthy controls (HCs) and whether regional susceptibility values correlate with mini mental state examination (MMSE) scores or global Aβ-load.

METHODS

We retrospectively analyzed [¹¹C]PiB PET/MRI data of 11 HCs, 16 AD and 10 non-AD patients. We used quantitative susceptibility mapping (QSM) as iron-sensitive MRI signal measured at the 3 T PET/MR scanner. Global cerebral Aβ-load was determined by composite [¹¹C]PiB SUV ratios.

RESULTS

Compared to HCs, AD patients showed higher QSM values in putamen (0.049 ± 0.033 vs. 0.002 ± 0.031; p = 0.006), while non-AD patients showed lower QSM values in caudate nucleus (0.003 ± 0.027 vs. 0.051 ± 0.039; p = 0.006). There was a trend towards a significant correlation between putaminal QSM and MMSE values (ρ=-0.340, p = 0.053). In AD patients, global Aβ-load and putaminal QSM values were significantly correlated (ρ=-0.574, p = 0.020).

CONCLUSIONS

These data indicate that AD and non-AD patients may show different cerebral iron pathologies which might be detectable by QSM MRI, and might be linked to neurodegeneration. Overall, the data encourage further investigations in well-defined patient cohorts to clarify the value of QSM/magnetic susceptibility in the course of neurodegenerative diseases and its potential as diagnostic biomarker.

A positive influence of basal ganglia iron concentration on implicit sequence learning

Iron homeostasis is important for maintaining normal physiological brain functioning. In two independent samples, we investigate the link between iron concentration in the basal ganglia (BG) and implicit sequence learning (ISL). In Study 1, we used quantitative susceptibility mapping and task-related fMRI to examine associations among regional iron concentration measurements, brain activation, and ISL in younger and older adults. In Study 2, we examined the link between brain iron and ISL using a metric derived from fMRI in an age-homogenous sample of older adults. Three main findings were obtained. First, BG iron concentration was positively related to ISL in both studies. Second, ISL was robust for both younger and older adults, and performance-related activation was found in fronto-striatal regions across both age groups. Third, BG iron was positively linked to task-related BOLD signal in fronto-striatal regions. This is the first study investigating the relationship among brain iron accumulation, functional brain activation, and ISL, and the results suggest that higher brain iron concentration may be linked to better neurocognitive functioning in this particular task.

Changes in brain activity after weight loss

OBJECTIVES

The importance of the regulatory role of the brain in directing glucose homeostasis, energy homeostasis, eating behaviour, weight control and obesity is increasingly recognized. Brain activity in (sub)cortical neuronal networks involved in homeostatic control and hedonic responses is generally increased in persons with obesity. Currently, it is not known if these functional changes can be affected by dieting. The aim of the current study was to investigate whether prolonged fasting and/or weight loss influences neuronal brain activity in obese persons.

METHODS

Fourteen participants with obesity were included (two male participants and 12 female participants, body mass index 35.2 ± 1.2 kg m-2). Whole-brain resting-state functional magnetic resonance imaging was performed after an overnight fast, after a prolonged 48-h fast and after an 8-week weight loss intervention.

RESULTS

An 8-week weight loss intervention decreased BOLD signal in areas of the brain involved in salience, sensory motor and executive control. BOLD signal in these areas correlated with leptin levels and body mass index.

CONCLUSIONS

Weight loss decreased activity in brain areas involved in feeding behaviour and reward processing. These results indicate that these obesity-associated alterations in neuronal activity are related to excessive body weight and might change after weight loss.

Quantitative Susceptibility Mapping of Amyloid-β Aggregates in Alzheimer's Disease with 7T MR

BACKGROUND

PET imaging is an established technique to detect cerebral amyloid-β (Aβ) plaques in vivo. Some preclinical and postmortem data report an accumulation of redox-active iron near Aβ plaques. Quantitative susceptibility mapping (QSM) at high-field MRI enables iron deposits to be depicted with high spatial resolution.

OBJECTIVE

Aim of this study was to examine whether iron and Aβ plaque accumulation is related and thus, whether 7T MRI might be an additive diagnostic tool to Aβ PET imaging.

METHODS

Postmortem human Alzheimer's disease (AD) and healthy control (HC) frontal gray matter (GM) was imaged with 7T MRI which resulted in T1 maps and QSM. Aβ plaque load was determined by histopathology. In vivo, 10 Aβ PET-positive AD patients (74.1±6.0a) and 10 Aβ PET-negative HCs (67.1±4.4a) underwent 7T MR examination and QSM maps were analyzed. Severity of cognitive deficits was determined by MMSE.

RESULTS

Postmortem, the susceptibility of Aβ plaque-containing GM were higher than those of Aβ plaque-free GM (0.011±0.002 versus - 0.008±0.003 ppm, p < 0.001). In vivo, only the bilateral globus pallidus showed significantly higher susceptibility in AD patients compared to HCs (right: 0.277±0.018 versus - 0.009±0.009 ppm; left: 0.293±0.014 versus - 0.007±0.012 ppm, p < 0.0001). The pallidal QSM values were negatively correlated with those of the MMSE (r = - 0.69, p = 0.001).

CONCLUSION

The postmortem study revealed significant susceptibility differences between the Aβ plaque-containing and Aβ plaque-free GM, whereas in vivo only the QSM values of the globus pallidus differed significantly between AD and HC group. The pallidal QSM values correlated with the severity of cognitive deficits. These findings encourage efforts to optimize the 7T-QSM methodology.

Brain activity and connectivity changes in response to nutritive natural sugars, non-nutritive natural sugar replacements and artificial sweeteners

INTRODUCTION

The brain plays an important regulatory role in directing energy homeostasis and eating behavior. The increased ingestion of sugars and sweeteners over the last decades makes investigating the effects of these substances on the regulatory function of the brain of particular interest. We investigated whole brain functional response to the ingestion of nutrient shakes sweetened with either the nutritive natural sugars glucose and fructose, the low- nutritive natural sugar replacement allulose or the non-nutritive artificial sweetener sucralose.

METHODS

Twenty healthy, normal weight, adult males underwent functional MRI on four separate visits. In a double-blind randomized study setup, participants received shakes sweetened with glucose, fructose, allulose or sucralose. Resting state functional MRI was performed before and after ingestion. Changes in Blood Oxygen Level Dependent (BOLD) signal, functional network connectivity and voxel based connectivity by Eigenvector Centrality Mapping (ECM) were measured.

RESULTS

Glucose and fructose led to significant decreased BOLD signal in the cingulate cortex, insula and the basal ganglia. Glucose led to a significant increase in eigen vector centrality throughout the brain and a significant decrease in eigen vector centrality in the midbrain. Sucralose and allulose had no effect on BOLD signal or network connectivity but sucralose did lead to a significant increase in eigen vector centrality values in the cingulate cortex, central gyri and temporal lobe.

DISCUSSION

Taken together our findings show that even in a shake containing fat and protein, the type of sweetener can affect brain responses and might thus affect reward and satiety responses and feeding behavior. The sweet taste without the corresponding energy content of the non-nutritive sweeteners appeared to have only small effects on the brain. Indicating that the while ingestion of nutritive sugars could have a strong effect on feeding behavior, both in a satiety aspect as well as rewarding aspects, non-nutritive sweeteners appear to not have these effects.

TRIAL REGISTRATION

This study is registered at clinicaltrials.gov under number NCT02745730.

Altered functional brain networks in amnestic mild cognitive impairment: a resting-state fMRI study

Amnestic mild cognitive impairment MCI (aMCI) has a high progression to Alzheimer's disease (AD). Recently, resting-state functional MRI (RS-fMRI) has been increasingly utilized in studying the pathogenesis of aMCI, especially in resting-state networks (RSNs). In the current study, we aimed to explore abnormal RSNs related to memory deficits in aMCI patients compared to the aged-matched healthy control group using RS-fMRI techniques. Firstly, we used ALFF (amplitude of low-frequency fluctuation) method to define the regions of interest (ROIs) which exhibited significant changes in aMCI compared with the control group. Then, we divided these ROIs into different networks in line with prior studies. The aim of this study is to explore the functional connectivity between these ROIs within networks and also to investigate the connectivity between networks. Comparing aMCI to the control group, our results showed that 1) the hippocampus (HIPP) had decreased FC with the medial prefrontal cortex (mPFC) and inferior parietal lobe (IPL), and the mPFC showed increased connectivity to IPL in the default mode network; 2) the thalamus showed decreased FC with the putamen and HIPP, and the HIPP showed increased connectivity to the putamen in the limbic system; 3) the supplementary motor area had decreased FC with the middle temporal gyrus and increased FC with the superior parietal lobe in the sensorimotor network; 4) increased connectivity between the lingual gyrus and middle occipital gyrus in the visual network; and 5) the DMN has reduced inter-network connectivities with the SMN and VN. These findings indicated that functional brain networks involved in cognition such as episodic memory, sensorimotor and visual cognition in aMCI were altered, and provided a new sight in understanding the important subtype of aMCI.

Can transverse relaxation rates in deep gray matter be approximated from functional and T2-weighted FLAIR scans for relative brain iron quantification?

Alterations in iron concentration in certain deep gray matter regions are known to occur in aging and several clinical conditions. In vivo measurements of R₂^∗ transverse relaxation rates and quantitative susceptibility mapping (QSM) have been shown to be strongly correlated with iron concentration in tissue, but their calculation requires the acquisition of a multi-echo gradient recalled echo sequence (MGRE). In the current study, we examined the feasibility of approximating R₂^∗ rates using metrics derived from fMRI-EPI and T₂-weighted FLAIR images, which are widely available. In a sample of 40 healthy subjects, we obtained these metrics (v_EPI and v_FLAIR), as well as R₂^∗ rates and QSM estimates, and found significant correlations between v_EPI and v_FLAIR and R₂^∗ rates in several subcortical gray matter regions known to accumulate iron, but not in a control corticospinal white matter region. These relationships were preserved after referencing v_EPI and v_FLAIR with respect to the values in the control region. Effect sizes (above 0.5 for some of the regions, particularly the largest ones) were calculated and put in relation to those of the correlation between QSM and R₂^∗ rates. We propose that the metrics described here may be applied, possibly in a retrospective fashion, to analyze datasets with available EPI or T₂-weighted FLAIR scans (and lacking a MGRE sequence), to devise new hypotheses regarding links between iron concentration in brain tissue and other variables of interest.

Structural and functional connectivity in traumatic brain injury

Traumatic brain injury survivors often experience cognitive deficits and neuropsychiatric symptoms. However, the neurobiological mechanisms underlying specific impairments are not fully understood. Advances in neuroimaging techniques (such as diffusion tensor imaging and functional MRI) have given us new insights on structural and functional connectivity patterns of the human brain in both health and disease. The connectome derived from connectivity maps reflects the entire constellation of distributed brain networks. Using these powerful neuroimaging approaches, changes at the microstructural level can be detected through regional and global properties of neuronal networks. Here we will review recent developments in the study of brain network abnormalities in traumatic brain injury, mainly focusing on structural and functional connectivity. Some connectomic studies have provided interesting insights into the neurological dysfunction that occurs following traumatic brain injury. These techniques could eventually be helpful in developing imaging biomarkers of cognitive and neurobehavioral sequelae, as well as predicting outcome and prognosis.

Frequency-dependent changes in the amplitude of low-frequency fluctuations in subcortical ischemic vascular disease (SIVD): a resting-state fMRI study

Resting-state functional magnetic resonance imaging (RS-fMRI) allowed researchers to detect intrinsic brain activity during rest and has been considered an analytical tool for evaluation of dementia. Previously, subcortical ischemic vascular disease (SIVD) has been found decreased amplitude low-frequency fluctuations (ALFF) in a widely frequency range (0.01-0.08Hz) in the bilateral precuneus and increased ALFF values in the bilateral anterior cingulate cortex (ACC), left insula and hippocampus, which showed significant correlations with the cognitive performance. In this study we analyzed the ALFF of 30 patients with SIVD in two different frequency bands (slow-5: 0.01-0.027Hz; slow-4: 0.027-0.073Hz). In the slow-5 band, SIVD patients compared with controls exhibited significant higher ALFF in the bilateral anterior cingulate cortex, right putamen and right supplementary motor area, while lower ALFF in the right precuneus and right angular gyrus. A close correlation was found between the ALFF value of the right angular gyrus and ADL scores. In the slow-4 band, SIVD patients only exhibited increased ALFF in the bilateral anterior cingulate cortex, right putamen, left fusiform gyrus, and no correlation with cognitive scores was found. Our data demonstrate that SIVD patients have widespread abnormal intrinsic neural oscillations, which are dependent on specific frequency bands. ALFF of right angular gyrus at slow-5 band is more specific for SIVD and may be a useful tool to help SIVD diagnosis.

Altered cerebrovascular reactivity velocity in mild cognitive impairment and Alzheimer's disease

Interindividual variation in neurovascular reserve and its relationship with cognitive performance is not well understood in imaging in neurodegeneration. We assessed the neurovascular reserve in amnestic mild cognitive impairment (aMCI) and Alzheimer's dementia (AD). Twenty-eight healthy controls (HC), 15 aMCI, and 20 AD patients underwent blood oxygen level-dependent imaging for 9 minutes, breathing alternatively air and 7% carbon dioxide mixture. The data were parcellated into 88 anatomic regions, and carbon dioxide regressors accounting for different washin and washout velocities were fitted to regional average blood oxygen level-dependent signals. Velocity of cerebrovascular reactivity (CVR) was analyzed and correlated with cognitive scores. aMCI and AD patients had significantly slower response than HC (mean time to reach 90% of peak: HC 33 seconds, aMCI and AD 59 seconds). CVR velocity correlated with Mini Mental State Examination in 35 of 88 brain regions (p = 0.019, corrected for multiple comparisons), including 10 regions of the default-mode network, an effect modulated by age. This easily applicable protocol yielded a practical assessment of CVR in cognitive decline.

Ex vivo T2 relaxation: associations with age-related neuropathology and cognition

The transverse relaxation time constant, T(2), is sensitive to brain tissue's free water content and the presence of paramagnetic materials such as iron. In this study, ex vivo magnetic resonance imaging was used to investigate alterations in T(2) related to Alzheimer's disease (AD) pathology and other types of neuropathology common in old age, as well as the relationship between T(2) alterations and cognition. Cerebral hemispheres were obtained from 371 deceased older adults. Using fast spin-echo imaging with multiple echo times, T(2) maps were produced and warped to a study-specific template. Hemispheres underwent neuropathologic examination for identification of AD pathology and other common age-related neuropathologies. Voxelwise linear regression was carried out to detect regions of pathology-related T(2) alterations and, in separate analyses, regions in which T(2) alterations were linked to antemortem cognitive performance. AD pathology was associated with T(2) prolongation in white matter of all lobes and T(2) shortening in the basal ganglia and insula. Gross infarcts were associated with T(2) prolongation in white matter of all lobes, and in the thalamus and basal ganglia. Hippocampal sclerosis was associated with T(2) prolongation in the hippocampus and white matter of the temporal lobe. After controlling for neuropathology, T(2) prolongation in the frontal lobe white matter was associated with lower performance in the episodic, semantic, and working memory domains. In addition, voxelwise analysis of in vivo and ex vivo T(2) values indicated a positive relationship between the two, though further investigation is necessary to accurately translate findings of the present study to the in vivo case.

The role of hippocampal iron concentration and hippocampal volume in age-related differences in memory

The goal of this study was to examine the relationships between 2 age-sensitive indices of brain integrity--volume and iron concentration--and the associated age differences in memory performance. In 113 healthy adults (age 19-83 years), we measured the volume and estimated iron concentration in the hippocampus (HC), caudate nucleus (Cd), and primary visual cortex (VC) in vivo with T2* relaxation times, and assessed memory performance with multiple tests. We applied structural equation modeling to evaluate the contribution of individual differences in 2 indices of integrity, volume and T2*, to age-related memory variance. The results show that in healthy adults, age differences in memory can be explained in part by individual differences in HC volume that in turn are associated with differences in HC iron concentration. Lower memory scores were linked to smaller HC and higher HC iron concentration. No such associations were noted for Cd and VC. We conclude that the association between age-related declines in memory and reduced hippocampal volume may reflect the impact of oxidative stress related to increase in free iron concentration. Longitudinal follow-up is needed to test whether altered iron homeostasis in the HC is an early marker for age-related cognitive decline.

What can we learn from T2* maps of the cortex?

Studies have shown that T2* contrast can reveal features of cortical anatomy. However, understanding the relationship between T2* contrast and the underlying cyto- and myelo-architecture is not an easy task, given the number of confounds, such as myelin, iron, blood vessels and structure orientation. Moreover, it is difficult to obtain reliable T2* measurements in the cortex due to its thin and folded geometry and the presence of artifacts. This review addresses issues associated with T2* mapping in the human cortex. After describing the theory behind T2* relaxation, a list of practical steps is proposed to reliably acquire and process T2* data and then map these values within the cortex using surface-based analysis. The last section addresses the question: "What can we gain from T2* cortical mapping?", with particular emphasis on Brodmann mapping.

Frequency-dependent changes in the amplitude of low-frequency fluctuations in amnestic mild cognitive impairment: a resting-state fMRI study

Here we utilized resting-state functional magnetic resonance imaging (R-fMRI) to measure the amplitude of low-frequency fluctuations (ALFF) and fractional ALFF (fALFF) in 24 patients with amnestic mild cognitive impairment (aMCI) and 24 age- and sex-matched healthy controls. Two different frequency bands (slow-5: 0.01-0.027 Hz; slow-4: 0.027-0.073 Hz) were analyzed. We showed that there were widespread differences in ALFF/fALFF between the two bands in many brain regions, predominantly including the medial prefrontal cortex (MPFC), posterior cingulate cortex/precuneus (PCC/PCu), basal ganglia, and hippocampus/parahippocampal gyrus (PHG). Compared to controls, the aMCI patients had decreased ALFF/fALFF values in the PCC/PCu, MPFC, hippocampus/PHG, basal ganglia, and prefrontal regions, and increased ALFF/fALFF values mainly in several occipital and temporal regions. Specifically, we observed that the ALFF/fALFF abnormalities in the PCC/PCu, PHG, and several occipital regions were greater in the slow-5 band than in the slow-4 band. Finally, our results of functional analysis were not significantly influenced by the gray matter loss in the MCI patients, suggesting that the results reflect functional differences between groups. Together, our data suggest that aMCI patients have widespread abnormalities in intrinsic brain activity, and the abnormalities depend on the studied frequency bands of R-fMRI data.

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

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

Acupuncture mobilizes the brain's default mode and its anti-correlated network in healthy subjects

Previous work has shown that acupuncture stimulation evokes deactivation of a limbic-paralimbic-neocortical network (LPNN) as well as activation of somatosensory brain regions. This study explores the activity and functional connectivity of these regions during acupuncture vs. tactile stimulation and vs. acupuncture associated with inadvertent sharp pain. Acupuncture during 201 scans and tactile stimulation during 74 scans for comparison at acupoints LI4, ST36 and LV3 was monitored with fMRI and psychophysical response in 48 healthy subjects. Clusters of deactivated regions in the medial prefrontal, medial parietal and medial temporal lobes as well as activated regions in the sensorimotor and a few paralimbic structures can be identified during acupuncture by general linear model analysis and seed-based cross correlation analysis. Importantly, these clusters showed virtual identity with the default mode network and the anti-correlated task-positive network in response to stimulation. In addition, the amygdala and hypothalamus, structures not routinely reported in the default mode literature, were frequently involved in acupuncture. When acupuncture induced sharp pain, the deactivation was attenuated or became activated instead. Tactile stimulation induced greater activation of the somatosensory regions but less extensive deactivation of the LPNN. These results indicate that the deactivation of the LPNN during acupuncture cannot be completely explained by the demand of attention that is commonly proposed in the default mode literature. Our results suggest that acupuncture mobilizes the anti-correlated functional networks of the brain to mediate its actions, and that the effect is dependent on the psychophysical response.

Understanding White Matter Disease

Most strokes are covert and observed incidentally on brain scans, but their presence increases risk of overt stroke and dementia. Amyloid angiopathy, associated with Alzheimer Disease (AD) causes stroke, and when even small strokes coexist with AD, they lower the threshold for dementia. Diffuse ischemic white matter disease impairs executive functioning, information processing speed, and gait. Neuroimaging techniques, such as tissue segmentation, Diffusion Tensor Imaging, MR Spectroscopy, functional MRI and amyloid PET, probe microstructural integrity, molecular biology, and activation patterns, providing new insights into brain-behavior relationships. MR-pathological studies of periventricular hyperintensity (leukoaraiosis) in aging and dementia reveal arteriolar tortuosity, reduced vessel density, and occlusive venous collagenosis which causes venous insufficiency and vasogenic edema. Activated microglia, oligodendroglial apoptosis, clasmatodendritic astrocytosis, and upregulated hypoxia-markers are seen on immunohistochemistry. Further research is needed to understand and treat this chronic subcortical vascular disease, which is epidemic in our aging population.

Model-free group analysis shows altered BOLD FMRI networks in dementia

FMRI research in Alzheimer's disease (AD) and mild cognitive impairment (MCI) typically is aimed at determining regional changes in brain function, most commonly by creating a model of the expected BOLD-response and estimating its magnitude using a general linear model (GLM) analysis. This crucially depends on the suitability of the temporal assumptions of the model and on assumptions about normality of group distributions. Exploratory data analysis techniques such as independent component analysis (ICA) do not depend on these assumptions and are able to detect unknown, yet structured spatiotemporal processes in neuroimaging data. Tensorial probabilistic ICA (T-PICA) is a model free technique that can be used for analyzing multiple subjects and groups, extracting signals of interest (components) in the spatial, temporal, and also subject domain of FMRI data. We applied T-PICA and model-based GLM to study FMRI signal during face encoding in 18 AD, 28 MCI patients, and 41 healthy elderly controls. T-PICA showed activation in regions associated with motor, visual, and cognitive processing, and deactivation in the default mode network. Six networks showed a significantly decreased response in patients. For two networks the T-PICA technique was significantly more sensitive to detect group differences than the standard model-based technique. We conclude that T-PICA is a promising tool to identify and detect differences in (de)activated brain networks in elderly controls and dementia patients. The technique is more sensitive than the commonly applied model-based method. Consistent with other research, we show that networks of activation and deactivation show decreased reactivity in dementia.

Discriminating accuracy of medial temporal lobe volumetry and fMRI in mild cognitive impairment

We investigated structural and functional changes in the medial temporal lobe (MTL) using magnetic resonance imaging (MRI) and compared the discriminative power of these measures with neuropsychological testing in mild cognitive impairment (MCI) and Alzheimer's disease (AD). Functional MRI (fMRI) was performed in 21 elderly controls, 14 MCI subjects, and 15 mild AD patients during encoding and cued retrieval of word-picture pairs. A region-of-interest-based approach in SPM2 was used to extract the extent of hippocampal activation. The volumes of the hippocampus and entorhinal cortex (EC) were manually outlined from anatomical MR images. Discriminant analyses were conducted to assess the ability of hippocampal fMRI, MTL volumetry, and neuropsychological measures to classify subjects into clinical groups. Entorhinal but not hippocampal volumes differed significantly between the control and MCI subjects. Both entorhinal and hippocampal volumes differed between MCI and AD patients. There were no significant differences in the extent of hippocampal fMRI activation during encoding or retrieval between the groups. Entorhinal volume was the best discriminator with a discriminating accuracy of 85.7% between controls and MCI, 86.2% between MCI and AD, and 97.2% between controls and AD. Delayed recall of a wordlist classified the subjects, second best, with a discriminating accuracy of 81.8% between controls and MCI, 75% between MCI and AD and 93.5% between controls and AD. The accuracy of hippocampal volumetry ranged from 42.9 to 69.4%, and hippocampal fMRI activation during encoding and retrieval had a classification accuracy of only 41.4-57.7% between the groups. Our results suggest that evaluation of entorhinal atrophy, in addition to the prevailing diagnostic criteria, seems promising in the identification of prodromal AD. Future technical improvements may improve the utilization of hippocampal fMRI for early diagnostic purposes.

Assessment of functional development in normal infant brain using arterial spin labeled perfusion MRI

Arterial spin labeled (ASL) perfusion MRI provides a noninvasive approach for longitudinal imaging of regional brain function in infants. In the present study, continuous ASL (CASL) perfusion MRI was carried out in normally developing 7- and 13-month-old infants while asleep without sedation. The 13-month infant group showed an increase (P<0.05) of relative CBF in frontal regions as compared to the 7-month group using a region of interest based analysis. Using a machine-learning algorithm to automatically classify the relative CBF maps of the two infant groups, a significant (P<0.05, permutation testing) regional CBF increase was found in the hippocampi, anterior cingulate, amygdalae, occipital lobes, and auditory cortex in the 13-month-old infants. These results are consistent with current understanding of infant brain development and demonstrate the feasibility of using perfusion MRI to noninvasively monitor developing brain function.