Brain volumetrics to investigate aging and the principal forms of degenerative cognitive decline: a brief review

Hippocampal subfield volume in older adults with and without mild cognitive impairment: Effects of worry and cognitive reappraisal

Studies have confirmed that anxiety, especially worry and rumination, are associated with increased risk for cognitive decline, including Alzheimer's disease and related dementias (ADRD). Hippocampal atrophy is a hallmark of ADRD. We investigated the association between hippocampus and its subfield volumes and late-life global anxiety, worry, and rumination, and emotion regulation strategies. We recruited 110 participants with varying worry severity who underwent magnetic resonance imaging and clinical interviews. We conducted cross-sectional regression analysis between each subfield and anxiety, worry, rumination, reappraisal, and suppression while adjusting for age, sex, race, education, cumulative illness burden, stress, neuroticism, and intracranial volume. We imputed missing data and corrected for multiple comparisons across regions. Greater worry was associated with smaller subiculum volume, whereas greater use of reappraisal was associated with larger subiculum and CA1 volume. Greater worry may be detrimental to the hippocampus and to subfields involved in early ADRD pathology. Use of reappraisal appears protective of hippocampal structure. Worry and reappraisal may be modifiable targets for ADRD prevention.

Head CT: Toward Making Full Use of the Information the X-Rays Give

Although clinical head CT images are typically interpreted qualitatively, automated methods applied to routine clinical head CTs enable quantitative assessment of brain volume, brain parenchymal fraction, brain radiodensity, and brain radiomass. These metrics gain clinical meaning when viewed relative to a reference database and expressed as quantile regression values. Quantitative imaging data can aid in objective reporting and in the identification of outliers, with possible diagnostic implications. The comparison to a reference database necessitates standardization of head CT imaging parameters and protocols. Future research is needed to learn the effects of virtual monochromatic imaging on the quantitative characteristics of head CT images.

Are Anxiety Disorders Associated with Accelerated Aging? A Focus on Neuroprogression

Anxiety disorders (AnxDs) are highly prevalent throughout the lifespan, with detrimental effects on daily-life functioning, somatic health, and quality of life. An emerging perspective suggested that AnxDs may be associated with accelerated aging. In this paper, we explored the association between AnxDs and hallmarks of accelerated aging, with a specific focus on neuroprogression. We reviewed animal and human findings that suggest an overlap between processes of impaired neurogenesis, neurodegeneration, structural, functional, molecular, and cellular modifications in AnxDs, and aging. Although this research is at an early stage, our review suggests a link between anxiety and accelerated aging across multiple processes involved in neuroprogression. Brain structural and functional changes that accompany normal aging were more pronounced in subjects with AnxDs than in coevals without AnxDs, including reduced grey matter density, white matter alterations, impaired functional connectivity of large-scale brain networks, and poorer cognitive performance. Similarly, molecular correlates of brain aging, including telomere shortening, Aβ accumulation, and immune-inflammatory and oxidative/nitrosative stress, were overrepresented in anxious subjects. No conclusions about causality or directionality between anxiety and accelerated aging can be drawn. Potential mechanisms of this association, limitations of the current research, and implications for treatments and future studies are discussed.

Brain Structure in Neuropsychologically Defined Subgroups of Schizophrenia and Psychotic Bipolar Disorder

BACKGROUND

Neuropsychological impairment is heterogeneous in psychosis. The association of intracranial volume (ICV) and total brain volume (TBV) with cognition suggests brain structure abnormalities in psychosis will covary with the severity of cognitive impairment. We tested the following hypotheses: (1) brain structure abnormalities will be more extensive in neuropsychologically impaired psychosis patients; (2) psychosis patients with premorbid cognitive limitations will show evidence of hypoplasia (ie, smaller ICV); and (3) psychosis patients with evidence of cognitive decline will demonstrate atrophy (ie, smaller TBV, but normal ICV).

METHODS

One hundred thirty-one individuals with psychosis and 97 healthy subjects underwent structural magnetic resonance imaging and neuropsychological testing. Patients were divided into neuropsychologically normal and impaired groups. Impaired patients were further subdivided into deteriorated and compromised groups if estimated premorbid intellect was average or below average, respectively. ICV and TBV were compared across groups. Localized brain volumes were qualitatively examined using voxel-based morphometry.

RESULTS

Compared to healthy subjects, neuropsychologically impaired patients exhibited smaller TBV, reduced grey matter volume in frontal, temporal, and subcortical brain regions, and widespread white matter volume loss. Neuropsychologically compromised patients had smaller ICV relative to healthy subjects, and neuropsychologically normal and deteriorated patient groups, but relatively normal TBV. Deteriorated patients exhibited smaller TBV compared to healthy subjects, but relatively normal ICV. Unexpectedly, TBV, adjusted for ICV, was reduced in neuropsychologically normal patients.

CONCLUSIONS

Patients with long-standing cognitive limitations exhibit evidence of early cerebral hypoplasia, whereas neuropsychologically normal and deteriorated patients show evidence of brain tissue loss consistent with progression or later cerebral dysmaturation.

High-Dimensional Medial Lobe Morphometry: An Automated MRI Biomarker for the New AD Diagnostic Criteria

Introduction. Medial temporal lobe atrophy assessment via magnetic resonance imaging (MRI) has been proposed in recent criteria as an in vivo diagnostic biomarker of Alzheimer's disease (AD). However, practical application of these criteria in a clinical setting will require automated MRI analysis techniques. To this end, we wished to validate our automated, high-dimensional morphometry technique to the hypothetical prediction of future clinical status from baseline data in a cohort of subjects in a large, multicentric setting, compared to currently known clinical status for these subjects. Materials and Methods. The study group consisted of 214 controls, 371 mild cognitive impairment (147 having progressed to probable AD and 224 stable), and 181 probable AD from the Alzheimer's Disease Neuroimaging Initiative, with data acquired on 58 different 1.5 T scanners. We measured the sensitivity and specificity of our technique in a hierarchical fashion, first testing the effect of intensity standardization, then between different volumes of interest, and finally its generalizability for a large, multicentric cohort. Results. We obtained 73.2% prediction accuracy with 79.5% sensitivity for the prediction of MCI progression to clinically probable AD. The positive predictive value was 81.6% for MCI progressing on average within 1.5 (0.3 s.d.) year. Conclusion. With high accuracy, the technique's ability to identify discriminant medial temporal lobe atrophy has been demonstrated in a large, multicentric environment. It is suitable as an aid for clinical diagnostic of AD.

Vitamin D and brain volumetric changes: Systematic review and meta-analysis

Vitamin D has multiple functions in the nervous system. Our objective was to systematically review and quantitatively synthesize evidence on the location and nature of brain morphometric changes linked to vitamin D depletion or repletion. A Medline search was conducted in February 2014, without limit of date and language restriction, using the MeSH terms "Vitamin D" OR "Ergocalciferols" combined with "Brain Mapping" OR "Magnetic Resonance Imaging" OR "Tomography, X-ray Computed" OR "Tomography, Emission-Computed, Single-Photon" OR "Positron-Emission Tomography" OR "Nuclear Medicine" OR "Radionucleide Imaging". Of the 376 selected studies, nine observational studies - two animal and seven human studies - met the selection criteria. The number of participants ranged from 20 to 333 (40-79% female). Three studies were eligible for fixed-effects meta-analysis of bias-corrected effect size of the difference in lateral ventricle volume between cases with vitamin D depletion and controls. Results showed that vitamin D depletion was associated with lower brain volume, specifically larger lateral ventricles. The pooled effect size was 1.01 [95% CI: 0.62; 1.41], a 'large' effect size indicating that the ventricle volume was 1.01 SD higher with vitamin D depletion. Results on brain subvolumes were mixed, and indicated that brain atrophy with vitamin D depletion could be explained not by temporal lobe atrophy but rather by loss of matter at the cranial vertex, possibly in the precuneus cortex. In conclusion, despite increasing evidence arguing for an action of vitamin D in the brain, data is sparse regarding brain morphological changes related to vitamin D depletion. The retrieved association between vitamin D depletion and brain atrophy provides a scientific base for vitamin D replacement trials.

Application of quantitative MRI for brain tissue segmentation at 1.5 T and 3.0 T field strengths

BACKGROUND

Brain tissue segmentation of white matter (WM), grey matter (GM), and cerebrospinal fluid (CSF) are important in neuroradiological applications. Quantitative Mri (qMRI) allows segmentation based on physical tissue properties, and the dependencies on MR scanner settings are removed. Brain tissue groups into clusters in the three dimensional space formed by the qMRI parameters R1, R2 and PD, and partial volume voxels are intermediate in this space. The qMRI parameters, however, depend on the main magnetic field strength. Therefore, longitudinal studies can be seriously limited by system upgrades. The aim of this work was to apply one recently described brain tissue segmentation method, based on qMRI, at both 1.5 T and 3.0 T field strengths, and to investigate similarities and differences.

METHODS

In vivo qMRI measurements were performed on 10 healthy subjects using both 1.5 T and 3.0 T MR scanners. The brain tissue segmentation method was applied for both 1.5 T and 3.0 T and volumes of WM, GM, CSF and brain parenchymal fraction (BPF) were calculated on both field strengths. Repeatability was calculated for each scanner and a General Linear Model was used to examine the effect of field strength. Voxel-wise t-tests were also performed to evaluate regional differences.

RESULTS

Statistically significant differences were found between 1.5 T and 3.0 T for WM, GM, CSF and BPF (p<0.001). Analyses of main effects showed that WM was underestimated, while GM and CSF were overestimated on 1.5 T compared to 3.0 T. The mean differences between 1.5 T and 3.0 T were -66 mL WM, 40 mL GM, 29 mL CSF and -1.99% BPF. Voxel-wise t-tests revealed regional differences of WM and GM in deep brain structures, cerebellum and brain stem.

CONCLUSIONS

Most of the brain was identically classified at the two field strengths, although some regional differences were observed.

Cognitive reserve in granulin-related frontotemporal dementia: from preclinical to clinical stages

Objective

Consistent with the cognitive reserve hypothesis, higher education and occupation attainments may help persons with neurodegenerative dementias to better withstand neuropathology before developing cognitive impairment. We tested here the cognitive reserve hypothesis in patients with frontotemporal dementia (FTD), with or without pathogenetic granulin mutations (GRN+ and GRN-), and in presymptomatic GRN mutation carriers (aGRN+).

Methods

Education and occupation attainments were assessed and combined to define Reserve Index (RI) in 32 FTD patients, i.e. 12 GRN+ and 20 GRN-, and in 17 aGRN+. Changes in functional connectivity were estimated by resting state fMRI, focusing on the salience network (SN), executive network (EN) and bilateral frontoparietal networks (FPNs). Cognitive status was measured by FTD-modified Clinical Dementia Rating Scale.

Results

In FTD patients higher level of premorbid cognitive reserve was associated with reduced connectivity within the SN and the EN. EN was more involved in FTD patients without GRN mutations, while SN was more affected in GRN pathology. In aGRN+, cognitive reserve was associated with reduced SN.

Conclusions

This study suggests that cognitive reserve modulates functional connectivity in patients with FTD, even in monogenic disease. In GRN inherited FTD, cognitive reserve mechanisms operate even in presymptomatic to clinical stages.

Traumatic brain injury, neuroimaging, and neurodegeneration

Depending on severity, traumatic brain injury (TBI) induces immediate neuropathological effects that in the mildest form may be transient but as severity increases results in neural damage and degeneration. The first phase of neural degeneration is explainable by the primary acute and secondary neuropathological effects initiated by the injury; however, neuroimaging studies demonstrate a prolonged period of pathological changes that progressively occur even during the chronic phase. This review examines how neuroimaging may be used in TBI to understand (1) the dynamic changes that occur in brain development relevant to understanding the effects of TBI and how these relate to developmental stage when the brain is injured, (2) how TBI interferes with age-typical brain development and the effects of aging thereafter, and (3) how TBI results in greater frontotemporolimbic damage, results in cerebral atrophy, and is more disruptive to white matter neural connectivity. Neuroimaging quantification in TBI demonstrates degenerative effects from brain injury over time. An adverse synergistic influence of TBI with aging may predispose the brain injured individual for the development of neuropsychiatric and neurodegenerative disorders long after surviving the brain injury.

Brain tissue modifications induced by cholinergic therapy in Alzheimer's disease

A previous preliminary investigation based on a novel MRI approach to map anatomical connectivity revealed areas of increased connectivity in Alzheimer's disease (AD) but not in mild cognitive impairment patients. This prompted the hypothesis tested here, that these areas might reflect phenomena of brain plasticity driven by acetylcholinesterase inhibitors (AChEIs). Thirty-eight patients with probable AD (19 under medication with AChEIs and 19 drug-naïve) were recruited together with 11 healthy controls. All subjects had MRI scanning at 3T, including volumetric and diffusion-weighted scans. Probabilistic tractography was used to initiate streamlines from all parenchymal voxels, and anatomical connectivity maps (ACMs) were obtained by counting, among the total number of streamlines initiated, the fraction passing through each brain voxel. After normalization into standard space, ACMs were used to test for between-group comparisons, and for interactions between the exposure to AChEIs and global level of cognition. Patients with AD had reduced ACM values in the fornix, cingulum, and supramarginal gyri. The ACM value was strongly associated with the AChEI dosage-x-duration product in the anterior limb (non-motor pathway) of the internal capsule. Tractography from this region identified the anterior thalamic radiation as the main white matter (WM) tract passing through it. The reduced connectivity in WM bundles connecting the hippocampi with the rest of the brain (fornix/cingulum) suggests a possible mechanism for the spread of AD pathology. An intriguing explanation for the interaction between AChEIs and ACM is related to the mechanisms of brain plasticity, partially driven by neurotrophic properties of acetylcholine replacement.

Quantitative magnetization transfer provides information complementary to grey matter atrophy in Alzheimer's disease brains

Preliminary studies, based on a region-of-interest approach, suggest that quantitative magnetization transfer (qMT), an extension of magnetization transfer imaging, provides complementary information to conventional magnetic resonance imaging (MRI) in the characterisation of Alzheimer's disease (AD). The aim of this study was to extend these findings to the whole brain, using a voxel-wise approach. We recruited 19AD patients and 11 healthy subjects (HS). All subjects had an MRI acquisition at 3.0T including a T(1)-weighted volume, 12 MT-weighted volumes for qMT, and data for computing T(1) and B(1) maps. The T(1)-weighted volumes were processed to yield grey matter (GM) volumetric maps, while the other sequences were used to compute qMT parametric maps of the whole brain. qMT maps were warped to standard space and smoothed, and subsequently compared between groups. Of all the qMT parameters considered, only the forward exchange rate, RM(0)(B), showed significant group differences. These images were therefore retained for the multimodal statistical analysis, designed to locate brain regions of RM(0)(B) differences between AD and HS groups, adjusting for local GM atrophy. Widespread areas of reduced RM(0)(B) were found in AD patients, mainly located in the hippocampus, in the temporal lobe, in the posterior cingulate and in the parietal cortex. These results indicate that, among qMT parameters, RM(0)(B) is the most sensitive to AD pathology. This quantity is altered in the hippocampus of patients with AD (as found by previous works) but also in other brain areas, that PET studies have highlighted as involved with both, reduced glucose metabolism and amyloid β deposition. RM(0)(B) might reflect, through the measurement of the efficiency of MT exchange, some information with a specific pathological counterpart. Given previous evidence of a strict relationship between RM(0)(B) and intracellular pH, an intriguing speculation is that our findings might reflect metabolic changes related to mitochondrial dysfunction, which has been proposed as a contributor to neurodegeneration in AD.

Damage to the cingulum contributes to Alzheimer's disease pathophysiology by deafferentation mechanism

This study investigates the differential contribution of gray matter (GM) atrophy and deafferentation through white matter (WM) damage in the clinical progression of Alzheimer's disease (AD). Thirty-one patients with probable AD, 23 with amnestic mild cognitive impairment (a-MCI), and 14 healthy subjects underwent MRI scanning at 3T. Voxel-based morphometry was used to assess regional GM atrophy in AD and a-MCI patients. Diffusion tensor-MRI tractography was used to reconstruct the cingulum bilaterally, and to quantify, voxel-by-voxel, its fractional anisotropy (FA) and mean diffusivity (MD) (measures of microscopic WM integrity). Atrophy of the cinguli was also assessed by means of jacobian determinants (JD) of local transformations. In AD patients, four clusters of reduced GM were found nearby the cinguli, in the posterior (PCC) and anterior cingulate cortex, and in the hippocampal/parahippocampal areas. Widespread areas of reduced FA and increased MD were found in the cinguli of both, AD and a-MCI patients. A region of macroscopic atrophy was detectable in AD patients only. Strong associations were found between local GM densities in the four identified clusters, and measures of micro- and (to a lesser extent) macroscopic damage of patients' cinguli. Linear regression analyses revealed that MD in the cinguli predicts patients' measures of episodic memory in combination with GM density of hippocampal/parahippocampal areas, and measures of global cognition in combination with GM density of the PCC. This study indicates that brain deafferentation though the cingulum is likely to play a remarkable role in progressive development of cognitive impairment in AD.

Neuroanatomical correlates of cognitive reserve in Alzheimer disease

Cognitive reserve (CR), for which formal education represents a proxy index, has been claimed as a factor mitigating the clinical manifestations of Alzheimer disease (AD). The aim of this study was to assess the impact of formal education in modifying the relationship between cerebral grey matter (GM) damage and clinical manifestations in a large cohort of patients with AD or amnesic mild cognitive impairment (a-MCI). We recruited 22 patients with AD and 23 with a-MCI, and we classified them in subjects with high (HEL) or low educational level (LEL). All patients underwent a neuropsychological assessment and magnetic resonance imaging (MRI) scanning at 3T. T1-weighted volumes were analyzed, using voxel-based morphometry, for GM investigation. A 1-year clinical follow-up was available for part of the a-MCI patients. There were no between-groups differences in clinical features, memory, and language functions. Conversely, HEL subjects performed better in all tests assessing visuo-spatial abilities. GM volumes of LEL compared with HEL patients were reduced in the supramarginal gyrus bilaterally and in the right posterior cingulate/precuneus and frontal opercular cortex. Conversely, HEL compared with LEL patients showed reduced GM volumes in the entorhinal cortices and temporal poles, regions typically affected by AD pathology. These results remained unchanged when including in the analysis of only patients with clinically proven AD (AD and a-MCI converters). This study suggests that CR produces selective GM changes that mitigate the clinical impact of AD. Moreover, it supports the idea that CR is based on several "brain reserves" rather than on a generalized increase of brain plasticity.

Unsupervised MRI segmentation of brain tissues using a local linear model and level set

Real-world magnetic resonance imaging of the brain is affected by intensity nonuniformity (INU) phenomena which makes it difficult to fully automate the segmentation process. This difficult task is accomplished in this work by using a new method with two original features: (1) each brain tissue class is locally modeled using a local linear region representative, which allows us to account for the INU in an implicit way and to more accurately position the region's boundaries; and (2) the region models are embedded in the level set framework, so that the spatial coherence of the segmentation can be controlled in a natural way. Our new method has been tested on the ground-truthed Internet Brain Segmentation Repository (IBSR) database and gave promising results, with Tanimoto indexes ranging from 0.61 to 0.79 for the classification of the white matter and from 0.72 to 0.84 for the gray matter. To our knowledge, this is the first time a region-based level set model has been used to perform the segmentation of real-world MRI brain scans with convincing results.

Evidence for retrochiasmatic tissue loss in Leber's hereditary optic neuropathy

Patients with Leber's hereditary optic neuropathy (LHON) have loss of central vision with severe damage of small-caliber fibers of the papillomacular bundle and optic nerve atrophy. The aim of this study was to define the presence and topographical distribution of brain grey matter (GM) and white matter (WM) injury in LHON patients using voxel-based morphometry (VBM). The correlation of such changes with neuro-ophthalmologic findings and measurements of peripapillary retinal nerve fiber layer (RNFL) thickness by optical coherence tomography (OCT) was also assessed. Dual-echo and fast-field echo scans were acquired from 12 LHON patients and 12 matched controls. VBM analysis was performed using SPM5 and an ANCOVA model. A complete neuro-ophthalmologic examination, including standardized automated Humphrey perimetry as well as average and temporal peripapillary RNFL thickness measurements were obtained in all the patients. Compared with controls, average peripapillary RNFL thickness was significantly decreased in LHON patients. LHON patients also had significant reduced GM volume in the bilateral primary visual cortex, and reduced WM volume in the optic chiasm, optic tract, and several areas located in the optic radiations (OR), bilaterally. Visual cortex and OR atrophy were significantly correlated with average and temporal peripapillary RNFL thickness (P < 0.001; r values ranging from 0.76 to 0.89). Brain damage in patients with LHON is not limited to the anterior visual pathways, but extends posteriorly to the OR and the primary visual cortex. Such a damage to the posterior parts of the visual pathways may be due either to trans-synaptic degeneration secondary to neuroaxonal damage in the retina and optic nerve or to local mitochondrial dysfunction.

Initial experience in using continuous arterial spin-labeled MR imaging for early detection of Alzheimer disease

BACKGROUND AND PURPOSE

MR imaging of the brain has significant potential in the early detection of neurodegenerative disorders such as AD. The purpose of this work was to determine if perfusion MR imaging can be used to separate AD from normal cognition in individual subjects. We investigated the diagnostic utility of perfusion MR imaging for early detection of AD compared with structural imaging.

MATERIALS AND METHODS

Data were analyzed from 32 participants in the institutional review board-approved CHS-CS: 19 cognitively healthy individuals and 13 with clinically adjudicated AD. All subjects underwent structural T1-weighted SGPR and CASL MR imaging. Four readers with varying experience separately rated each CASL and SPGR scan finding as normal or abnormal on the basis of standardized qualitative diagnostic criteria for observed perfusion abnormalities on CASL or volume loss on SPGR and rated the confidence in their evaluation.

RESULTS

Inter-rater reliability was superior in CASL (kappa = 0.7 in experienced readers) compared with SPGR (kappa = 0.17). CASL MR imaging had the highest sensitivity (85%) and accuracy (70%). Frontal lobe CASL findings increased sensitivity to 88% and accuracy to 79%. Fifty-seven percent of false-positive readings with CASL were in controls with cognitive decline or instability within 5 years. Three of the 4 readers revealed a statistically significant relationship between confidence and correct classification when using CASL.

CONCLUSIONS

Readers were able to separate individuals with mild AD from those with normal cognition with high sensitivity by using CASL but not volumetric MR imaging. This initial experience suggests that CASL MR imaging may be a useful technique for detecting AD.