Quantitative susceptibility mapping of striatum in children and adults, and its association with working memory performance

Assessing brain iron and its relationship to cognition and comorbidity in children with ADHD with quantitative susceptibility mapping (QSM)

BACKGROUND

Quantitative susceptibility mapping (QSM) is a neuroimaging technique that detects local changes in magnetic susceptibility induced by brain iron. Brain iron and the dopaminergic system are linked since iron is an important cofactor for dopamine synthesis. ADHD is associated with dysregulation of dopaminergic transmission. Therefore, we applied QSM on subcortical structures, to study potential alterations in brain iron and its impact on cognition and mental health in children with ADHD.

METHODS

3 Tesla QSM-data of 111 participants (nADHD= 58, mean age: 13.2 (0.63); nControls=53, mean age: 13.2 (0.51)) were analyzed. Subcortical regional brain iron values were extracted. ANOVAs examined group differences for each region of interest. For dimensional approaches, Pearson correlation analysis was performed across the cohort examining the association with symptoms, mental health, and cognition.

RESULTS

No significant differences were found in iron susceptibility between ADHD and control, between persistent and remitted ADHD, or between medication use. An unexpected finding was that children with internalising disorder had significantly higher iron susceptibility, but the result did not survive multiple comparison corrections. Higher brain iron was associated with sustained attention, but not on inhibition, IQ, and working memory.

CONCLUSION

This is the first study addressing brain iron susceptibility and its association with comorbidities and cognition in ADHD. Alterations in brain iron may not account for the full diagnosis of ADHD but may be an indicator of internalising problems in children. Alterations in brain iron content in children were linked to detrimental sustained attention and may represent developmental variation in cognition.

Mechanistic insights and emerging therapeutic stratagems for Alzheimer's disease

Alzheimer's disease (AD), a multi-factorial neurodegenerative disorder has affected over 30 million individuals globally and these numbers are expected to increase in the coming decades. Current therapeutic interventions are largely ineffective as they focus on a single target. Development of an effective drug therapy requires a deep understanding of the various factors influencing the onset and progression of the disease. Aging and genetic factors exert a major influence on the development of AD. Other factors like post-viral infections, iron overload, gut dysbiosis, and vascular dysfunction also exacerbate the onset and progression of AD. Further, post-translational modifications in tau, DRP1, CREB, and p65 proteins increase the disease severity through triggering mitochondrial dysfunction, synaptic loss, and differential interaction of amyloid beta with different receptors leading to impaired intracellular signalling. With advancements in neuroscience tools, new inter-relations that aggravate AD are being discovered including pre-existing diseases and exposure to other pathogens. Simultaneously, new therapeutic strategies involving modulation of gene expression through targeted delivery or modulation with light, harnessing the immune response to promote clearance of amyloid deposits, introduction of stem cells and extracellular vesicles to replace the destroyed neurons, exploring new therapeutic molecules from plant, marine and biological sources delivered in the free state or through nanoparticles and use of non-pharmacological interventions like music, transcranial stimulation and yoga. Polypharmacology approaches involving combination of therapeutic agents are also under active investigation for superior therapeutic outcomes. This review elaborates on various disease-causing factors, their underlying mechanisms, the inter-play between different disease-causing players, and emerging therapeutic options including those under clinical trials, for treatment of AD. The challenges involved in AD therapy and the way forward have also been discussed.

Multivariate and regional age-related change in basal ganglia iron in neonates

In the perinatal period, reward and cognitive systems begin trajectories, influencing later psychiatric risk. The basal ganglia is important for reward and cognitive processing but early development has not been fully characterized. To assess age-related development, we used a measure of basal ganglia physiology, specifically brain tissue iron, obtained from nT2* signal in resting-state functional magnetic resonance imaging (rsfMRI), associated with dopaminergic processing. We used data from the Developing Human Connectome Project (n = 464) to assess how moving from the prenatal to the postnatal environment affects rsfMRI nT2*, modeling gestational and postnatal age separately for basal ganglia subregions in linear models. We did not find associations with tissue iron and gestational age [range: 24.29-42.29] but found positive associations with postnatal age [range:0-17.14] in the pallidum and putamen, but not the caudate. We tested if there was an interaction between preterm birth and postnatal age, finding early preterm infants (GA < 35 wk) had higher iron levels and changed less over time. To assess multivariate change, we used support vector regression to predict age from voxel-wise-nT2* maps. We could predict postnatal but not gestational age when maps were residualized for the other age term. This provides evidence subregions differentially change with postnatal experience and preterm birth may disrupt trajectories.

Developmental coupling of brain iron and intrinsic activity in infants during the first 150 days

Brain iron is vital for core neurodevelopmental processes including myelination and neurotransmitter synthesis and, accordingly, iron accumulates in the brain with age. However, little is known about the association between brain iron and neural functioning and how they evolve with age in early infancy. This study investigated brain iron in 48 healthy infants (22 females) aged 64.00 ± 33.28 days by estimating R2 * relaxometry from multi-echo functional MRI (fMRI). Linked independent component analysis was performed to examine the association between iron deposition and spontaneous neural activity, as measured by the amplitude of low frequency fluctuations (ALFF) by interrogating shared component loadings across modalities. Further, findings were validated in an independent dataset (n = 45, 24 females, 77.93 ± 26.18 days). The analysis revealed developmental coupling between the global R2 * and ALFF within the default mode network (DMN). Furthermore, we observed that this coupling effect significantly increased with age (r = 0.78, p = 9.2e-11). Our results highlight the importance of iron-neural coupling during early development and suggest that the neural maturation of the DMN may correspond to growth in distributed brain iron.

Gestational and postnatal age associations for striatal tissue iron deposition in early infancy

Striatal development is crucial for later motor, cognitive, and reward behavior, but age-related change in striatal physiology during the neonatal period remains understudied. An MRI-based measure of tissue iron deposition, T2*, is a non-invasive way to probe striatal physiology neonatally, linked to dopaminergic processing and cognition in children and adults. Striatal subregions have distinct functions that may come online at different time periods in early life. To identify if there are critical periods before or after birth, we measured if striatal iron accrued with gestational age at birth [range= 34.57-41.85 weeks] or postnatal age at scan [range= 5-64 days], using MRI to probe the T2* signal in N = 83 neonates in three striatal subregions. We found iron increased with postnatal age in the pallidum and putamen but not the caudate. No significant relationship between iron and gestational age was observed. Using a subset of infants scanned at preschool age (N = 26), we show distributions of iron shift between time points. In infants, the pallidum had the least iron of the three regions but had the most by preschool age. Together, this provides evidence of distinct change for striatal subregions, a possible differentiation between motor and cognitive systems, identifying a mechanism that may impact future trajectories.

Gestational and postnatal age associations for striatal tissue iron deposition in early infancy

Striatal development is crucial for later motor, cognitive, and reward behavior, but age-related change in striatal physiology during the neonatal period remains understudied. An MRI-based measure of tissue iron deposition, T2*, is a non-invasive way to probe striatal physiology neonatally, linked to dopaminergic processing and cognition in children and adults. Striatal subregions have distinct functions that may come online at different time periods in early life. To identify if there are critical periods before or after birth, we measured if striatal iron accrued with gestational age at birth [range=34.57-41.85 weeks] or postnatal age at scan [range=5-64 days], using MRI to probe the T2* signal in N=83 neonates in three striatal subregions. We found iron increased with postnatal age in the pallidum and putamen but not the caudate. No significant relationship between iron and gestational age was observed. Using a subset of infants scanned at preschool age (N=26), we show distributions of iron shift between timepoints. In infants, the pallidum had the least iron of the three regions but had the most by preschool age. Together, this provides evidence of distinct change for striatal subregions, a possible differentiation between motor and cognitive systems, identifying a mechanism that may impact future trajectories.

Highlights

Neonatal striatal tissue iron can be measured using the T2* signal from rsfMRInT2* changed with postnatal age in the pallidum and putamen but not in the caudatenT2* did not change with gestational age in any of the three regionsPatterns of iron deposition (nT2*) among regions shift from infancy to preschool.

Cognition and brain iron deposition in whole grey matter regions and hippocampal subfields

Regional brain iron accumulation is observed in many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, and is associated with cognitive decline. We explored associations between age, cognition and iron content in grey matter regions and hippocampal subfields in 380 participants of the Aberdeen children of the 1950s cohort and their first-generation relatives (aged 26-72 years). Participants underwent cognitive assessment at the time of MRI scanning. Quantitative susceptibility mapping of these MRI data was used to assess iron content in grey matter regions and in hippocampal subfields. Principle component analysis was performed on cognitive test scores to create a general cognition score. Spline analysis was used with the Akaike information criterion to determine if order 1, 2 or 3 natural splines were optimal for assessing non-linear relationships between regional iron and age. Multivariate linear models were used to assess associations between regional iron and cognition. Higher iron correlated with older age in the left putamen across all ages and in the right putamen of only participants over 58. Whereas a decrease in iron with older age was observed in the right thalamus and left pallidum across all ages. Right amygdala iron levels were associated with poorer general cognition scores and poorer immediate recall scores. Iron was not associated with any measures of cognitive performance in other regions of interest. Our results suggest that, whilst iron in some regions was associated with cognitive performance, there is an overall lack of association between regional iron content and cognitive ability in cognitively healthy individuals.

High cortical iron is associated with the disruption of white matter tracts supporting cognitive function in healthy older adults

Aging is associated with brain iron accumulation, which has been linked to cognitive decline. However, how brain iron affects the structure and function of cognitive brain networks remains unclear. Here, we explored the possibility that iron load in gray matter is associated with disruption of white matter (WM) microstructure within a network supporting cognitive function, in a cohort of 95 cognitively normal older adults (age range: 60-86). Functional magnetic resonance imaging was used to localize a set of brain regions involved in working memory and diffusion tensor imaging based probabilistic tractography was used to identify a network of WM tracts connecting the functionally defined regions. Brain iron concentration within these regions was evaluated using quantitative susceptibility mapping and microstructural properties were assessed within the identified tracts using neurite orientation dispersion and density imaging. Results indicated that high brain iron concentration was associated with low neurite density (ND) within the task-relevant WM network. Further, regional associations were observed such that brain iron in cortical regions was linked with lower ND in neighboring but not distant WM tracts. Our results provide novel evidence suggesting that age-related increases in brain iron concentration are associated with the disruption of WM tracts supporting cognitive function in normal aging.

Voxel-Based Intraclass Correlation Coefficient to Evaluate the Inter-Scanner Reproducibility of Quantitative Susceptibility Mapping over the Deep Gray Matter Structure at 3.0T MR

BACKGROUND

The Quantitative susceptibility mapping (QSM) technique can be used to quantitatively evaluate the cerebral iron deposition of the deep gray matter structure (DGM) in clinical practice. However, it could be significantly important to assess the reproducibility of the susceptibility values at different magnetic resonance (MR) scanners before the QSM technique can be widely used in clinical applications.

OBJECTIVE

To assess the reproducibility of susceptibility value of the deep gray matter structure (DGM) at two different MR systems with the same magnetic strength.

METHODS

Raw data of 21 normal subjects (M/F = 7/14, median age 29 (21, 63) years) were acquired from a 3D multi-echo enhanced gradient recalled echo sequence at two different 3.0T MR systems, and STI software was used to reconstruct the magnetic susceptibility images. Brain structural images were used to be coregistered with magnitude images to generate normalized parameters and normalized susceptibility images. Voxel-based intraclass correlation coefficient (VB-ICC) was used to evaluate the reproducibility of susceptibility value of DGM at different 3.0T MR systems.

RESULTS

DGM with ICC > 0.75 located in the bilateral posterior putamen and globus pallidus, bilateral red nuclei and left dental nucleus. DGM with 0.6 < ICC < 0.75 mainly located in the bilateral anterior putamen and globus pallidus, the margin of the bilateral red nuclei, right dental nucleus and the margin of the left dental nucleus. DGM with 0.4 < ICC < 0.6 located in anterior parts of the bilateral putamen, bilateral globus pallidus and substantia nigra, the margin of the bilateral dental nuclei and the inferior part of right dental nucleus.

CONCLUSION

DGM presented regional dependent reproducibility of susceptibility value at two different 3.0T MR system based on VB-ICC analysis.

Ironsmith: An Automated Pipeline for QSM-based Data Analyses

Quantitative susceptibility mapping (QSM) is an MRI-based, computational method for anatomically localizing and measuring concentrations of specific biomarkers in tissue such as iron. Growing research suggests QSM is a viable method for evaluating the impact of iron overload in neurological disorders and on cognitive performance in aging. Several software toolboxes are currently available to reconstruct QSM maps from 3D GRE MR Images. However, few if any software packages currently exist that offer fully automated pipelines for QSM-based data analyses: from DICOM images to region-of-interest (ROI) based QSM values. Even less QSM-based software exist that offer quality control measures for evaluating the QSM output. Here, we address these gaps in the field by introducing and demonstrating the reliability and external validity of Ironsmith; an open-source, fully automated pipeline for creating and processing QSM maps, extracting QSM values from subcortical and cortical brain regions (89 ROIs) and evaluating the quality of QSM data using SNR measures and assessment of outlier regions on phase images. Ironsmith also features automatic filtering of QSM outlier values and precise CSF-only QSM reference masks that minimize partial volume effects. Testing of Ironsmith revealed excellent intra- and inter-rater reliability. Finally, external validity of Ironsmith was demonstrated via an anatomically selective relationship between motor performance and Ironsmith-derived QSM values in motor cortex. In sum, Ironsmith provides a freely-available, reliable, turn-key pipeline for QSM-based data analyses to support research on the impact of brain iron in aging and neurodegenerative disease.

Analysis of deep grey nuclei susceptibility in early childhood: a quantitative susceptibility mapping and R2* study at 3 Tesla

Purpose

Aging is the most significant determinant for brain iron accumulation in the deep grey matter. Data on brain iron evolution during brain maturation in early childhood are limited. The purpose of this study was to investigate age-related iron deposition in the deep grey matter in children using quantitative susceptibility (QSM) and R2* mapping.

Methods

We evaluated brain MRI scans of 74 children (age 6–154 months, mean 40 months). A multi-echo gradient-echo sequence obtained at 3 Tesla was used for the QSM and R2* calculation. Susceptibility of the pallidum, head of caudate nucleus, and putamen was correlated with age and compared between sexes.

Results

Susceptibility changes in all three nuclei correlated with age (correlation coefficients for QSM/R2*: globus pallidus 0.955/0.882, caudate nucleus 0.76/0.65, and putamen 0.643/0.611). During the first 2 years, the R2* values increased more rapidly than the QSM values, indicating a combined effect of iron deposition and myelination, followed by a likely dominating effect of iron deposition. There was no significant gender difference.

Conclusion

QSM and R2* can monitor myelin maturation processes and iron accumulation in the deep grey nuclei of the brain in early life and may be a promising tool for the detection of deviations of this normal process. Susceptibility in the deep nuclei is almost similar early after birth and increases more quickly in the pallidum. The combined use of QSM and R2* analysis is beneficial.

Substantia nigra iron affects functional connectivity networks modifying working memory performance in younger adults

Brain iron affects working memory (WM) but the impact of iron content in deep grey matter nuclei on WM networks is unknown. We aimed to test whether deep grey matter nuclei iron concentration can affect resting-state functional connectivity (rsFC) within brain networks modifying WM performance. An N-back WM paradigm was applied in a hundred healthy younger adults. The participants then underwent a resting-state functional magnetic resonance imaging (fMRI) for brain network analysis and quantitative susceptibility mapping (QSM) imaging for assessment of deep grey matter nuclei iron concentration. Higher substantia nigra (SN) iron concentration was associated with lower rsFC between SN and brain regions of the temporal/frontal lobe but with better WM performance after controlling for age, gender and education. A follow-up mediation analysis also indicated that functional connectivity may mediate the link between SN iron and WM performance. Our results suggest that high SN iron concentration may affect communication between the SN and temporal/frontal lobe and is associated with strengthened WM performance in younger adults.

Quantitative MRI susceptibility mapping reveals cortical signatures of changes in iron, calcium and zinc in malformations of cortical development in children with drug-resistant epilepsy

OBJECTIVE

Malformations of cortical development (MCD), including focal cortical dysplasia (FCD), are the most common cause of drug-resistant focal epilepsy in children. Histopathological lesion characterisation demonstrates abnormal cell types and lamination, alterations in myelin (typically co-localised with iron), and sometimes calcification. Quantitative susceptibility mapping (QSM) is an emerging MRI technique that measures tissue magnetic susceptibility (χ) reflecting it's mineral composition. We used QSM to investigate abnormal tissue composition in a group of children with focal epilepsy with comparison to effective transverse relaxation rate (R2*) and Synchrotron radiation X-ray fluorescence (SRXRF) elemental maps. Our primary hypothesis was that reductions in χ would be found in FCD lesions, resulting from alterations in their iron and calcium content. We also evaluated deep grey matter nuclei for changes in χ with age.

METHODS

QSM and R2* maps were calculated for 40 paediatric patients with suspected MCD (18 histologically confirmed) and 17 age-matched controls. Patients' sub-groups were defined based on concordant electro-clinical or histopathology data. Quantitative investigation of QSM and R2* was performed within lesions, using a surface-based approach with comparison to homologous regions, and within deep brain regions using a voxel-based approach with regional values modelled with age and epilepsy as covariates. Synchrotron radiation X-ray fluorescence (SRXRF) was performed on brain tissue resected from 4 patients to map changes in iron, calcium and zinc and relate them to MRI parameters.

RESULTS

Compared to fluid-attenuated inversion recovery (FLAIR) or T1-weighted imaging, QSM improved lesion conspicuity in 5% of patients. In patients with well-localised lesions, quantitative profiling demonstrated decreased χ, but not R2*, across cortical depth with respect to the homologous regions. Contra-lateral homologous regions additionally exhibited increased χ at 2-3 mm cortical depth that was absent in lesions. The iron decrease measured by the SRXRF in FCDIIb lesions was in agreement with myelin reduction observed by Luxol Fast Blue histochemical staining. SRXRF analysis in two FCDIIb tissue samples showed increased zinc and calcium in one patient, and decreased iron in the brain region exhibiting low χ and high R2* in both patients. QSM revealed expected age-related changes in the striatum nuclei, substantia nigra, sub-thalamic and red nucleus.

CONCLUSION

QSM non-invasively revealed cortical/sub-cortical tissue alterations in MCD lesions and in particular that χ changes in FCDIIb lesions were consistent with reduced iron, co-localised with low myelin and increased calcium and zinc content. These findings suggest that measurements of cortical χ could be used to characterise tissue properties non-invasively in epilepsy lesions.

R2* and quantitative susceptibility mapping in deep gray matter of 498 healthy controls from 5 to 90 years

Putative MRI markers of iron in deep gray matter have demonstrated age related changes during discrete periods of healthy childhood or adulthood, but few studies have included subjects across the lifespan. This study reports both transverse relaxation rate (R2*) and quantitative susceptibility mapping (QSM) of four primary deep gray matter regions (thalamus, putamen, caudate, and globus pallidus) in 498 healthy individuals aged 5–90 years. In the caudate, putamen, and globus pallidus, increases of QSM and R2* were steepest during childhood continuing gradually throughout adulthood, except caudate susceptibility which reached a plateau in the late 30s. The thalamus had a unique profile with steeper changes of R2* (reflecting additive effects of myelin and iron) than QSM during childhood, both reaching a plateau in the mid‐30s to early 40s and decreasing thereafter. There were no hemispheric or sex differences for any region. Notably, both R2* and QSM values showed more inter‐subject variability with increasing age from 5 to 90 years, potentially reflecting a common starting point in iron/myelination during childhood that diverges as a result of lifestyle and genetic factors that accumulate with age.

Healthy dietary intake moderates the effects of age on brain iron concentration and working memory performance

Age-related brain iron accumulation is linked with oxidative stress, neurodegeneration and cognitive decline. Certain nutrients can reduce brain iron concentration in animal models, however, this association is not well established in humans. Moreover, it remains unknown if nutrition can moderate the effects of age on brain iron concentration and/or cognition. Here, we explored these issues in a sample of 73 healthy older adults (61-86 years old), while controlling for several factors such as age, gender, years of education, physical fitness and alcohol-intake. Quantitative susceptibility mapping was used for assessment of brain iron concentration and participants performed an N-Back paradigm to evaluate working memory performance. Nutritional-intake was assessed via a validated questionnaire. Nutrients were grouped into nutrition factors based on previous literature and factor analysis. One factor, comprised of vitamin E, lysine, DHA omega-3 and LA omega-6 PUFA, representing food groups such as nuts, healthy oils and fish, moderated the effects of age on both brain iron concentration and working memory performance, suggesting that these nutrients may slow the rate of brain iron accumulation and working memory declines in aging.

Investigation of the association between cerebral iron content and myelin content in normative aging using quantitative magnetic resonance neuroimaging

Myelin loss and iron accumulation are cardinal features of aging and various neurodegenerative diseases. Oligodendrocytes incorporate iron as a metabolic substrate for myelin synthesis and maintenance. An emerging hypothesis in Alzheimer’s disease research suggests that myelin breakdown releases substantial stores of iron that may accumulate, leading to further myelin breakdown and neurodegeneration. We assessed associations between iron content and myelin content in critical brain regions using quantitative magnetic resonance imaging (MRI) on a cohort of cognitively unimpaired adults ranging in age from 21 to 94 years. We measured whole-brain myelin water fraction (MWF), a surrogate of myelin content, using multicomponent relaxometry, and whole-brain iron content using susceptibility weighted imaging in all individuals. MWF was negatively associated with iron content in most brain regions evaluated indicating that lower myelin content corresponds to higher iron content. Moreover, iron content was significantly higher with advanced age in most structures, with men exhibiting a trend towards higher iron content as compared to women. Finally, relationship between MWF and age, in all brain regions investigated, suggests that brain myelination continues until middle age, followed by degeneration at older ages. This work establishes a foundation for further investigations of the etiology and sequelae of myelin breakdown and iron accumulation in neurodegeneration and may lead to new imaging markers for disease progression and treatment.

Estimating cerebral venous oxygenation in human fetuses with ventriculomegaly using quantitative susceptibility mapping

RATIONALE AND OBJECTIVES

The goal of this study was to estimate venous blood oxygen saturation (SvO2) in the superior sagittal sinus (SSS) in fetal brains with ventriculomegaly (VM) using quantitative susceptibility mapping (QSM).

MATERIALS AND METHODS

A radiofrequency spoiled gradient echo sequence was used to evaluate data on 19 fetuses with VM (gestational age(GA): median = 29.9 weeks (range 23 to 37.3 weeks)) and 20 healthy fetuses (GA: median = 30.9 (range 22.7 to 38.7 weeks)) at 1.5 T. Susceptibility weighted images encompassing the entire fetal brain were acquired within 1 min. An iterative, geometry constraint-based thresholded k-space division algorithm was used for generating QSM data of the fetal brain. The venous oxygen saturation was calculated using the magnetic susceptibility of the SSS obtained from the QSM data. Mixed-model analysis of variance and interobserver variability assessment were used to analyze the results.

RESULTS

The median SvO2 values in the entire VM cohort as well as for second and third trimester fetuses (with interquartile range) were: 67.8% (63.2%, 73.6%), 73.1% (69.1%, 77.3%) and 63.8% (59.4%, 68.1%), respectively. The corresponding median SvO2 value in the healthy control group was: 65.3% (58.3%, 68.2%), 67.5% (61.7%, 69.2%) and 60.8% (53.6%, 68.2%), respectively. However, the difference of SvO2 between VM and control groups was not significant at the p = 0.05 level (p = 0.076). The SvO2 was found decreasing significantly with GA in the healthy control group (p < 0.05).

CONCLUSIONS

We report for the first time the estimation of cerebral SvO2 in human fetuses with VM using QSM. This measure of oxygen saturation might be beneficial in assessing and monitoring the metabolic status of the fetus in various clinical conditions.

Elevated neuroinflammation contributes to the deleterious impact of iron overload on brain function in aging

Intracellular iron is essential for many neurobiological mechanisms. However, at high concentrations, iron may induce oxidative stress and inflammation. Brain iron overload has been shown in various neurodegenerative disorders and in normal aging. Elevated brain iron in old age may trigger brain dysfunction and concomitant cognitive decline. However, the exact mechanism underlying the deleterious impact of iron on brain function in aging is unknown. Here, we investigated the role of iron on brain function across the adult lifespan from 187 healthy participants (20-79 years old, 99 women) who underwent fMRI scanning while performing a working-memory n-back task. Iron content was quantified using R2* relaxometry, whereas neuroinflammation was estimated using myo-inositol measured by magnetic resonance spectroscopy. Striatal iron increased non-linearly with age, with linear increases at both ends of adulthood. Whereas higher frontostriatal activity was related to better memory performance independent of age, the link between brain activity and iron differed across age groups. Higher striatal iron was linked to greater frontostriatal activity in younger, but reduced activity in older adults. Further mediation analysis revealed that, after age 40, iron provided unique and shared contributions with neuroinflammation to brain activations, such that neuroinflammation partly mediated brain-iron associations. These findings promote a novel mechanistic understanding of how iron may exert deleterious effects on brain function and cognition with advancing age.

The impact of brain iron accumulation on cognition: A systematic review

Iron is involved in many processes in the brain including, myelin generation, mitochondrial function, synthesis of ATP and DNA and the cycling of neurotransmitters. Disruption of normal iron homeostasis can result in iron accumulation in the brain, which in turn can partake in interactions which amplify oxidative damage. The development of MRI techniques for quantifying brain iron has allowed for the characterisation of the impact that brain iron has on cognition and neurodegeneration. This review uses a systematic approach to collate and evaluate the current literature which explores the relationship between brain iron and cognition. The following databases were searched in keeping with a predetermined inclusion criterion: Embase Ovid, PubMed and PsychInfo (from inception to 31st March 2020). The included studies were assessed for study characteristics and quality and their results were extracted and summarised. This review identified 41 human studies of varying design, which statistically assessed the relationship between brain iron and cognition. The most consistently reported interactions were in the Caudate nuclei, where increasing iron correlated poorer memory and general cognitive performance in adulthood. There were also consistent reports of a correlation between increased Hippocampal and Thalamic iron and poorer memory performance, as well as, between iron in the Putamen and Globus Pallidus and general cognition. We conclude that there is consistent evidence that brain iron is detrimental to cognitive health, however, more longitudinal studies will be required to fully understand this relationship and to determine whether iron occurs as a primary cause or secondary effect of cognitive decline.

Brain Iron Assessment after Ferumoxytol-enhanced MRI in Children and Young Adults with Arteriovenous Malformations: A Case-Control Study

Background Iron oxide nanoparticles are an alternative contrast agent for MRI. Gadolinium deposition has raised safety concerns, but it is unknown whether ferumoxytol administration also deposits in the brain. Purpose To investigate whether there are signal intensity changes in the brain at multiecho gradient imaging following ferumoxytol exposure in children and young adults. Materials and Methods This retrospective case-control study included children and young adults, matched for age and sex, with brain arteriovenous malformations who received at least one dose of ferumoxytol from January 2014 to January 2018. In participants who underwent at least two brain MRI examinations (subgroup), the first and last available examinations were analyzed. Regions of interests were placed around deep gray structures on quantitative susceptibility mapping and R2* images. Mean susceptibility and R2* values of regions of interests were recorded. Measurements were assessed by linear regression analyses: a between-group comparison of ferumoxytol-exposed and unexposed participants and a within-group (subgroup) comparison before and after exposure. Results Seventeen participants (mean age ± standard deviation, 13 years ± 5; nine male) were in the ferumoxytol-exposed (case) group, 21 (mean age, 14 years ± 5; 11 male) were in the control group, and nine (mean age, 12 years ± 6; four male) were in the subgroup. The mean number of ferumoxytol administrations was 2 ± 1 (range, one to four). Mean susceptibility (in parts per million [ppm]) and R2* (in inverse seconds [sec^-1]) values of the dentate (case participants: 0.06 ppm ± 0.04 and 23.87 sec^-1 ± 4.13; control participants: 0.02 ppm ± 0.03 and 21.7 sec^-1 ± 5.26), substantia nigrae (case participants: 0.08 ppm ± 0.06 and 27.46 sec^-1 ± 5.58; control participants: 0.04 ppm ± 0.05 and 24.96 sec^-1 ± 5.3), globus pallidi (case participants: 0.14 ppm ± 0.05 and 30.75 sec^-1 ± 5.14; control participants: 0.08 ppm ± 0.07 and 28.82 sec^-1 ± 6.62), putamina (case participants: 0.03 ppm ± 0.02 and 20.63 sec^-1 ± 2.44; control participants: 0.02 ppm ± 0.02 and 19.65 sec^-1 ± 3.6), caudate (case participants: -0.1 ppm ± 0.04 and 18.21 sec^-1 ± 3.1; control participants: -0.06 ppm ± 0.05 and 18.83 sec^-1 ± 3.32), and thalami (case participants: 0 ppm ± 0.03 and 16.49 sec^-1 ± 3.6; control participants: 0.02 ppm ± 0.02 and 18.38 sec^-1 ± 2.09) did not differ between groups (susceptibility, P = .21; R2*, P = .24). For the subgroup, the mean interval between the first and last ferumoxytol administration was 14 months ± 8 (range, 1-25 months). Mean susceptibility and R2* values of the dentate (first MRI: 0.06 ppm ± 0.05 and 25.78 sec^-1 ± 5.9; last MRI: 0.06 ppm ± 0.02 and 25.55 sec^-1 ± 4.71), substantia nigrae (first MRI: 0.06 ppm ± 0.06 and 28.26 sec^-1 ± 9.56; last MRI: 0.07 ppm ± 0.06 and 25.65 sec^-1 ± 6.37), globus pallidi (first MRI: 0.13 ppm ± 0.07 and 27.53 sec^-1 ± 8.88; last MRI: 0.14 ppm ± 0.06 and 29.78 sec^-1 ± 6.54), putamina (first MRI: 0.03 ppm ± 0.03 and 19.78 sec^-1 ± 3.51; last MRI: 0.03 ppm ± 0.02 and 19.73 sec^-1 ± 3.01), caudate (first MRI: -0.09 ppm ± 0.05 and 21.38 sec^-1 ± 4.72; last MRI: -0.1 ppm ± 0.05 and 18.75 sec^-1 ± 2.68), and thalami (first MRI: 0.01 ppm ± 0.02 and 17.65 sec^-1 ± 5.16; last MRI: 0 ppm ± 0.02 and 15.32 sec^-1 ± 2.49) did not differ between the first and last MRI examinations (susceptibility, P = .95; R2*, P = .54). Conclusion No overall significant differences were found in susceptibility and R2* values of deep gray structures to suggest retained iron in the brain between ferumoxytol-exposed and unexposed children and young adults with arteriovenous malformations and in those exposed to ferumoxytol over time. © RSNA, 2020.

Cortical iron disrupts functional connectivity networks supporting working memory performance in older adults

Excessive brain iron negatively affects working memory and related processes but the impact of cortical iron on task-relevant, cortical brain networks is unknown. We hypothesized that high cortical iron concentration may disrupt functional circuitry within cortical networks supporting working memory performance. Fifty-five healthy older adults completed an N-Back working memory paradigm while functional magnetic resonance imaging (fMRI) was performed. Participants also underwent quantitative susceptibility mapping (QSM) imaging for assessment of non-heme brain iron concentration. Additionally, pseudo continuous arterial spin labeling scans were obtained to control for potential contributions of cerebral blood volume and structural brain images were used to control for contributions of brain volume. Task performance was positively correlated with strength of task-based functional connectivity (tFC) between brain regions of the frontoparietal working memory network. However, higher cortical iron concentration was associated with lower tFC within this frontoparietal network and with poorer working memory performance after controlling for both cerebral blood flow and brain volume. Our results suggest that high cortical iron concentration disrupts communication within frontoparietal networks supporting working memory and is associated with reduced working memory performance in older adults.

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.

Quantitative susceptibility mapping (QSM) evaluation of infantile neuroaxonal dystrophy

We present the first case of twins with infantile neuroaxonal dystrophy evaluating brain iron deposition using quantitative susceptibility mapping (QSM). A 6-year-old boy who was normal at birth had psychomotor regression and hypotonia from 2-years-old. Brain MRI showed low intensity areas in globus pallidus (GP) and substantia nigra (SN) on T ₂* weighted imaging. QSM values of GP and SN were 0.19 and 0.29 ppm, respectively. His twin brother showed almost the same imaging findings. Follow-up MRI revealed increase of QSM value in GP and SN.

Spatiotemporal variations of magnetic susceptibility in the deep gray matter nuclei from 1 month to 6 years: A quantitative susceptibility mapping study

BACKGROUND

Quantitative susceptibility mapping (QSM) is emerging as a technique that quantifies the paramagnetic nonheme iron in brain tissue. Brain iron quantification during early development provides insights into the underlying mechanism of brain maturation.

PURPOSE

To quantify the spatiotemporal variations of brain iron-related magnetic susceptibility in deep gray matter nuclei during early development by using QSM.

STUDY TYPE

Retrospective.

SUBJECTS

Eighty-seven infants and children aged 1 month to 6 years.

FIELD STRENGTH/SEQUENCE

Enhanced T₂ *-weighted angiography using a 3D gradient-echo sequence at 3.0T.

ASSESSMENT

QSM was calculated by modified sophisticated harmonic artifact reduction for phase data and sparse linear equations and sparse least squares-based algorithm. Means of susceptibility in deep gray matter nuclei (caudate nucleus, putamen, globus pallidus, thalamus) relative to that in splenium of corpus callosum were measured.

STATISTICAL TESTS

Relationships of mean susceptibility with age and referenced iron concentration were tested by Pearson correlation. Differences of mean susceptibility between the selected nuclei in each age group were compared by one-way analysis of variance (ANOVA) and Fisher's Linear Significant Difference (LSD) test.

RESULTS

Positive correlations of susceptibility with both referenced iron concentration and age were found (P < 0.0001); particularly, globus pallidus showed the highest correlation with age (correlation coefficient, 0.882; slope, 1.203; P < 0.001) and greatest susceptibility (P < 0.05) among the selected nuclei.

DATA CONCLUSION

QSM allows the feasible quantification of iron deposition in deep gray matter nuclei in infants and young children, which exhibited gradual accumulation at different speeds. The fastest and highest iron accumulation was observed in the globus pallidus with increasing age during early development.

LEVEL OF EVIDENCE

4 Technical Efficacy:Stage 2 J. Magn. Reson. Imaging 2018.

A robust multi-scale approach to quantitative susceptibility mapping

Quantitative Susceptibility Mapping (QSM), best known as a surrogate for tissue iron content, is becoming a highly relevant MRI contrast for monitoring cellular and vascular status in aging, addiction, traumatic brain injury and, in general, a wide range of neurological disorders. In this study we present a new Bayesian QSM algorithm, named Multi-Scale Dipole Inversion (MSDI), which builds on the nonlinear Morphology-Enabled Dipole Inversion (nMEDI) framework, incorporating three additional features: (i) improved implementation of Laplace's equation to reduce the influence of background fields through variable harmonic filtering and subsequent deconvolution, (ii) improved error control through dynamic phase-reliability compensation across spatial scales, and (iii) scalewise use of the morphological prior. More generally, this new pre-conditioned QSM formalism aims to reduce the impact of dipole-incompatible fields and measurement errors such as flow effects, poor signal-to-noise ratio or other data inconsistencies that can lead to streaking and shadowing artefacts. In terms of performance, MSDI is the first algorithm to rank in the top-10 for all metrics evaluated in the 2016 QSM Reconstruction Challenge. It also demonstrated lower variance than nMEDI and more stable behaviour in scan-rescan reproducibility experiments for different MRI acquisitions at 3 and 7 Tesla. In the present work, we also explored new forms of susceptibility MRI contrast making explicit use of the differential information across spatial scales. Specifically, we show MSDI-derived examples of: (i) enhanced anatomical detail with susceptibility inversions from short-range dipole fields (hereby referred to as High-Pass Susceptibility Mapping or HPSM), (ii) high specificity to venous-blood susceptibilities for highly regularised HPSM (making a case for MSDI-based Venography or VenoMSDI), (iii) improved tissue specificity (and possibly statistical conditioning) for Macroscopic-Vessel Suppressed Susceptibility Mapping (MVSSM), and (iv) high spatial specificity and definition for HPSM-based Susceptibility-Weighted Imaging (HPSM-SWI) and related intensity projections.

Developmental variation in regional brain iron and its relation to cognitive functions in childhood

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We examine relationship of brain iron and cognition in childhood and adolescence.

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Estimates of iron in basal ganglia and hippocampus from R2* relaxometry.

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Age-related increase in non-heme iron content was observed in multiple brain areas.

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Greater iron content was indicative of improved cognitive ability.

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Non-heme iron appears to play a critical role in neural and cognitive development.

Non-heme iron is a vital metabolic cofactor for many core processes of brain development including myelination, dendritogenesis, and neurotransmitter synthesis, and accumulates in the brain with age. However, little is known about development-related differences in brain iron and its association with emerging cognitive abilities during formative years. In this study, we estimated brain iron via R2* relaxometry in children ages 7–16 (N = 57; 38 females) and examined its relation to age-related differences in cognitive ability. As we hypothesized, age correlated positively with iron content in the hippocampus and across subregions of the basal ganglia. The magnitude of age differences in iron content differed between regions such that the largest effects were observed in basal ganglia subregions: globus pallidus, substantia nigra, caudate nucleus, and putamen, as compared to values obtained for the hippocampus and red nucleus. We did not observe sex or hemispheric differences in iron content. Notably, greater brain iron content was associated with both faster processing speed and higher general intelligence, and shared 21.4% of the age-related improvement in processing speed and 12.5% of the improvement in general intelligence. These results suggest that non-heme iron plays a central neurobiological role in the development of critical cognitive abilities during childhood.

Functional differentiation between convergence and non-convergence zones of the striatum in children

Most cortical areas send projections to the striatum. In some parts of the striatum, the connections converge from several cortical areas. It is unknown whether the convergence and non-convergence zones of the striatum differ functionally. Here, we used diffusion-weighted magnetic resonance imaging and probabilistic fiber tracking to parcellate the striatum based on its connections to dorsolateral prefrontal, parietal and orbitofrontal cortices in two different datasets (children aged 6-7 years and adults). In both samples, quantitative susceptibility mapping (QSM) values were significantly correlated with working memory (WM) in convergence zones, but not in non-convergence zones. In children, this was also true for mean diffusivity, MD. The association of MD to WM specifically in the convergent zone was replicated in the Pediatric Imaging, Neurocognition, and Genetics (PING) dataset for 135 children aged 6-9 years. QSM data was not available in the PING dataset, and the association to QSM still needs to be replicated. These results suggest that connectivity-based segments of the striatum exhibit functionally different characteristics. The association between convergence zones and WM performance might relate to a role in integrating and coordinating activity in different cortical areas.

Ferrosenescence: The iron age of neurodegeneration?

Aging has been associated with iron retention in many cell types, including the neurons, promoting neurodegeneration by ferroptosis. Excess intracellular iron accelerates aging by damaging the DNA and blocking genomic repair systems, a process we define as ferrosenescence. Novel neuroimaging and proteomic techniques have pinpointed indicators of both iron retention and ferrosenescence, allowing for their early correction, potentially bringing prevention of neurodegenerative disorders within reach. In this review, we take a closer look at the early markers of iron dyshomeostasis in neurodegenerative disorders, focusing on preventive strategies based on nutritional and microbiome manipulations.

Characterizing Brain Iron Deposition in Patients with Subcortical Vascular Mild Cognitive Impairment Using Quantitative Susceptibility Mapping: A Potential Biomarker

The presence and pattern of iron accumulation in subcortical vascular mild cognitive impairment (svMCI) and their effects on cognition have rarely been investigated. We aimed to examine brain iron deposition in svMCI subjects using quantitative susceptibility mapping (QSM). Moreover, we aimed to investigate the correlation between brain iron deposition and the severity of cognitive impairment as indicated by z-scores. We recruited 20 subcortical ischemic vascular disease (SIVD) patients who fulfilled the criteria for svMCI. The control group comprised 19 SIVD patients without cognitive impairment. The SIVD and control groups were matched based on age, gender, and years of education. Both groups underwent QSM using a 3.0T MRI system. Susceptibility maps were reconstructed from in vivo data, which were acquired with a three-dimensional spoiled gradient recalled sequence. Then, regions of interest were drawn manually on the map of each subject. The inter-group differences of susceptibility values were explored in deep gray matter nuclei, including the bilateral pulvinar nucleus of the thalamus, head of caudate nucleus, globus pallidus, putamen, hippocampus, substantia nigra, and red nucleus. The correlations between regional iron deposition and composite z-score, memory z-score, language z-score, attention-executive z-score and visuospatial z-score were assessed using partial correlation analysis, with patient age and gender as covariates. Compared with the control, the svMCI group had elevated susceptibility values within the bilateral hippocampus and right putamen. Furthermore, the susceptibility value in the right hippocampus was negatively correlated with memory z-score and positively correlated with language z-score. The susceptibility value in the right putamen was negatively correlated with attention-executive z-score in the svMCI group. However, composite z-score were unrelated to susceptibility values. Our results suggest that brain iron deposition has clinical relevance as a biomarker for cognition. In addition, our results highlight the importance of iron deposition in understanding svMCI-associated cognitive deficits in addition to conventional MRI markers.

Methods for the computation of templates from quantitative magnetic susceptibility maps (QSM): Toward improved atlas- and voxel-based analyses (VBA)

PURPOSE

To develop and assess a method for the creation of templates for voxel-based analysis (VBA) and atlas-based approaches using quantitative magnetic susceptibility mapping (QSM).

MATERIALS AND METHODS

We studied four strategies for the creation of magnetic susceptibility brain templates, derived as successive extensions of the conventional template generation (CONV) based on only T₁ -weighted (T₁ w) images. One method that used only T₁ w images involved a minor improvement of CONV (U-CONV). One method used only magnetic susceptibility maps as input for template generation (DIRECT), and the other two used a linear combination of susceptibility and T₁ w images (HYBRID) and an algorithm that directly used both image modalities (MULTI), respectively. The strategies were evaluated in a group of N = 10 healthy human subjects and semiquantitatively assessed by three experienced raters. Template quality was compared statistically via worth estimates (WEs) obtained with a log-linear Bradley-Terry model.

RESULTS

The overall quality of the templates was better for strategies including both susceptibility and T₁ w contrast (MULTI: WE = 0.62; HYBRID: WE = 0.21), but the best method depended on the anatomical region of interest. While methods using only one modality resulted in lower WEs, lowest overall WEs were obtained when only T₁ w images were used (DIRECT: WE = 0.12; U-CONV: WE = 0.05).

CONCLUSION

Template generation strategies that employ only magnetic susceptibility contrast or both magnetic susceptibility and T₁ w contrast produce templates with the highest quality. The optimal approach depends on the anatomical structures of interest. The established approach of using only T₁ w images (CONV) results in reduced image quality compared to all other approaches studied.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1474-1484.