Sex and age-related differences in cerebral blood flow investigated using pseudo-continuous arterial spin labeling magnetic resonance imaging

Quantitative transport mapping of multi-delay arterial spin labeling MRI detects early blood perfusion alterations in Alzheimer's disease

BACKGROUND

Quantitative transport mapping (QTM) of blood velocity, based on the transport equation has been demonstrated higher accuracy and sensitivity of perfusion quantification than the traditional Kety's method-based cerebral blood flow (CBF). This study aimed to investigate the associations between QTM velocity and cognitive function in Alzheimer's disease (AD) using multiple post-labeling delay arterial spin labeling (ASL) MRI.

METHODS

A total of 128 subjects (21 normal controls (NC), 80 patients with mild cognitive impairment (MCI), and 27 AD) were recruited prospectively. All participants underwent MRI examination and neuropsychological evaluation. QTM velocity and traditional CBF maps were computed from multiple delay ASL. Regional quantitative perfusion measurements were performed and compared to study group differences. We tested the hypothesis that cognition declines with reduced cerebral blood perfusion with consideration of age and gender effects.

RESULTS

In cortical gray matter (GM) and the hippocampus, QTM velocity and CBF showed decreased values in the AD group compared to NC and MCI groups; QTM velocity, but not CBF, showed a significant difference between MCI and NC groups. QTM velocity and CBF showed values decreasing with age; QTM velocity, but not CBF, showed a significant gender difference between male and female. QTM velocity and CBF in the hippocampus were positively correlated with cognition, including global cognition, memory, executive function, and language function.

CONCLUSION

This study demonstrated an increased sensitivity of QTM velocity as compared with the traditional Kety's method-based CBF. Specifically, we observed only in QTM velocity, reduced perfusion velocity in GM and the hippocampus in MCI compared with NC. Both QTM velocity and CBF demonstrated a reduction in AD vs. controls. Decreased QTM velocity and CBF in the hippocampus were correlated with poor cognitive measures. These findings suggest QTM velocity as potential biomarker for early AD blood perfusion alterations and it could provide an avenue for early intervention of AD.

Study on the Relationship between Cerebral Blood Perfusion, Neuronal Cytokines and Cognitive Function in Patients with Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a common neurodegenerative disorder characterized by the progressive emergence of multiple cognitive deficits. Early diagnosis is of great significance for the intervention and treatment of AD. The objective of this study is to explore the relationship between cerebral blood perfusion, neuronal cytokines and cognitive function in patients with AD.

METHODS

AD patients admitted to the 903 Hospital of the People's Liberation Army Joint Logistics Support Force from June 2020 to January 2023 were retrospectively selected as the study objects, and 65 healthy people who underwent physical examination during the same period were included in the control group. Subjects in both groups underwent 3.0 T magnetic resonance imaging (MRI) to observe their cerebral blood perfusion parameters. The level of cognitive function in both groups was assessed using the Montreal Cognitive Assessment (MoCA). Venous blood was collected from both groups, and the serum levels of brain-derived neuronal factor (BDNF) and glial cell-derived neurotrophic factor (GDNF) were measured by enzyme-linked immunosorbent assay (ELISA). The correlation of serum BDNF and GDNF levels with cerebral blood perfusion parameters and MoCA score in the AD group was analyzed using Spearman analysis.

RESULTS

The cerebral blood flow signal intensity of the left frontal lobe, right frontal lobe, left temporal lobe, right temporal lobe, left parietal lobe, right parietal lobe, left occipital lobe, and right occipital lobe of the observation group was significantly lower than that of the control group (p < 0.001). The visuospatial, executive functions, naming, attention, language function, abstract generalization ability, memory ability, orientation, and total MoCA scale scores were significantly lower than those of the control group (p < 0.001). The serum levels of BDNF and GDNF in the observation group were significantly lower than those in the control group (p < 0.001). The results of Spearman analysis showed that cerebral blood perfusion parameters of the left frontal lobe, right frontal lobe, left temporal lobe, right temporal lobe, left parietal lobe, right parietal lobe, left occipital lobe, and right occipital lobe were positively correlated with cognitive function scores in AD patients, serum BDNF and GDNF levels were positively correlated with cognitive function scores in AD patients, and the correlation was statistically significant (p < 0.05).

CONCLUSION

In AD patients, blood perfusion parameters and serum BDNF and GDNF levels were significantly lower than those of healthy people. Cerebral blood perfusion parameters of the left frontal lobe, right frontal lobe, left temporal lobe, right temporal lobe, left parietal lobe, right parietal lobe, left occipital lobe, and right occipital lobe, and BDNF and GDNF levels were positively correlated with cognitive function scores in AD patients.

The time constant of the cerebral arterial bed: exploring age-related implications

The time constant of the cerebral arterial bed (τ) represents an estimation of the  transit time of flow from the point of insonation at the level of the middle cerebral artery to the arteriolar-capillary boundary, during a cardiac cycle. This study assessed differences in τ among healthy volunteers across different age groups. Simultaneous recordings of transcranial Doppler cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP) were performed on two groups: young volunteers (below 30 years of age), and older volunteers (above 40 years of age). τ was estimated using mathematical transformation of ABP and CBFV pulse waveforms. 77 healthy volunteers [52 in the young group, and 25 in the old group] were included. Pulse amplitude of ABP was higher [16.7 (14.6-19.4) mmHg] in older volunteers as compared to younger ones [12.5 (10.9-14.4) mm Hg; p < 0.001]. CBFV was lower in older volunteers [59 (50-66) cm/s] as compared to younger ones [72 (63-78) cm/s p < 0.001]. τ was longer in the younger volunteers [217 (168-237) ms] as compared to the older volunteers [183 (149-211) ms; p = 0.004]. τ significantly decreased with age (rS =  - 0.27; p = 0.018). τ is potentially an integrative marker of the changes occurring in cerebral vasculature, as it encompasses the interplay between changes in compliance and resistance that occur with age.

Using digital pathology to analyze the murine cerebrovasculature

Research on the cerebrovasculature may provide insights into brain health and disease. Immunohistochemical staining is one way to visualize blood vessels, and digital pathology has the potential to revolutionize the measurement of blood vessel parameters. These tools provide opportunities for translational mouse model research. However, mouse brain tissue presents a formidable set of technical challenges, including potentially high background staining and cross-reactivity of endogenous IgG. Formalin-fixed paraffin-embedded (FFPE) and fixed frozen sections, both of which are widely used, may require different methods. In this study, we optimized blood vessel staining in mouse brain tissue, testing both FFPE and frozen fixed sections. A panel of immunohistochemical blood vessel markers were tested (including CD31, CD34, collagen IV, DP71, and VWF), to evaluate their suitability for digital pathological analysis. Collagen IV provided the best immunostaining results in both FFPE and frozen fixed murine brain sections, with highly-specific staining of large and small blood vessels and low background staining. Subsequent analysis of collagen IV-stained sections showed region and sex-specific differences in vessel density and vessel wall thickness. We conclude that digital pathology provides a useful tool for relatively unbiased analysis of the murine cerebrovasculature, provided proper protein markers are used.

Quantitative transport mapping of multi-delay arterial spin labeling MRI detects early blood perfusion alteration in Alzheimer's disease

Background

Quantitative transport mapping (QTM) of blood velocity, based on the transport equation has been demonstrated higher accuracy and sensitivity of perfusion quantification than the traditional Kety's method-based blood flow (Kety flow). This study aimed to investigate the associations between QTM velocity and cognitive function in Alzheimer's disease (AD) using multiple post-labeling delay arterial spin labeling (ASL) MRI.

Methods

A total of 128 subjects (21 normal controls (NC), 80 patients with mild cognitive impairment (MCI), and 27 AD) were recruited prospectively. All participants underwent MRI examination and neuropsychological evaluation. QTM velocity and traditional Kety flow maps were computed from multiple delay ASL. Regional quantitative perfusion measurements were performed and compared to study group differences. We tested the hypothesis that cognition declines with reduced cerebral blood flow with consideration of age and gender effects.

Results

In cortical gray matter (GM) and the hippocampus, QTM velocity and Kety flow showed decreased values in AD group compared to NC and MCI groups; QTM velocity, but not Kety flow, showed a significant difference between MCI and NC groups. QTM velocity and Kety flow showed values decreasing with age; QTM velocity, but not Kety flow, showed a significant gender difference between male and female. QTM velocity and Kety flow in the hippocampus were positively correlated with cognition, including global cognition, memory, executive function, and language function.

Conclusion

This study demonstrated an increased sensitivity of QTM velocity as compared with the traditional Kety flow. Specifically, we observed only in QTM velocity, reduced perfusion velocity in GM and the hippocampus in MCI compared with NC. Both QTM velocity and Kety flow demonstrated reduction in AD vs controls. Decreased QTM velocity and Kety flow in the hippocampus were correlated with cognitive measures. These findings suggest QTM velocity as an improved biomarker for early AD blood flow alterations.

Uncovering Sex-Specific Epigenetic Regulatory Mechanism Involving H3k9me2 in Neural Inflammation, Damage, and Recovery in the Internal Carotid Artery Occlusion Mouse Model

Cerebral ischemic stroke is one of the foremost global causes of death and disability. Due to inadequate knowledge in its sequential disease mechanisms, therapeutic efforts to mitigate acute ischemia-induced brain injury are limited. Recent studies have implicated epigenetic mechanisms, mostly histone lysine acetylation/deacetylation, in ischemia-induced neural damage and death. However, the role of lysine methylation/demethylation, another prevalent epigenetic mechanism in cerebral ischemia has not undergone comprehensive investigation, except a few recent reports, including those from our research cohort. Considering the impact of sex on post-stroke outcomes, we studied both male and female mice to elucidate molecular details using our recently developed Internal Carotid Artery Occlusion (ICAO) model, which induces mild to moderate cerebral ischemia, primarily affecting the striatum and ventral hippocampus. Here, we demonstrate for the first time that female mice exhibit faster recovery than male mice following ICAO, evaluated through neurological deficit score and motor coordination assessment. Furthermore, our investigation unveiled that dysregulated histone lysine demethylases (KDMs), particularly kdm4b/jmjd2b are responsible for the sex-specific variance in the modulation of inflammatory genes. Building upon our prior reportage blocking KDMs by DMOG (Dimethyloxalylglycine) and thus preventing the attenuation in H3k9me2 reduced the post-ICAO transcript levels of the inflammatory molecules and neural damage, our present study delved into investigating the differential role of H3k9me2 in the regulation of pro-inflammatory genes in female vis-à-vis male mice underlying ICAO-induced neural damage and recovery. Overall, our results reveal the important role of epigenetic mark H3k9me2 in mediating sex-specific sequential events in inflammatory response, elicited post-ICAO.

Subject-specific timing adaption in time-encoded arterial spin labeling imaging

OBJECTIVES

One challenge in arterial spin labeling (ASL) is the high variability of arterial transit times (ATT), which causes associated arterial transit delay (ATD) artifacts. In patients with pathological changes, these artifacts occur when post-labeling delay (PLD) and bolus durations are not optimally matched to the subject, resulting in difficult quantification of cerebral blood flow (CBF) and ATT. This is also true for the free lunch approach in Hadamard-encoded pseudocontinuous ASL (H-pCASL).

MATERIAL AND METHODS

Five healthy volunteers were scanned with a 3 T MR-system. pCASL-subbolus timing was adjusted individually by the developed adaptive Walsh-ordered pCASL sequence and an automatic feedback algorithm. The quantification results for CBF and ATT and the respective standard deviations were compared with results obtained using recommended timings and intentionally suboptimal timings.

RESULTS

The algorithm individually adjusted the pCASL-subbolus PLD for each subject within the range of recommended timing for healthy subjects, with a mean intra-subject adjustment deviation of 47.15 ms for single-shot and 44.5 ms for segmented acquisition in three repetitions.

DISCUSSION

A first positive assessment of the results was performed on healthy volunteers. The extent to which the results can be transferred to patients and are of benefit must be investigated in follow-up studies.

Cerebral Microvascular Perfusion Assessed in Elderly Adults by Spin-Echo Dynamic Susceptibility Contrast MRI at 7 Tesla

Perfusion measures of the total vasculature are commonly derived with gradient-echo (GE) dynamic susceptibility contrast (DSC) MR images, which are acquired during the early passes of a contrast agent. Alternatively, spin-echo (SE) DSC can be used to achieve specific sensitivity to the capillary signal. For an improved contrast-to-noise ratio, ultra-high-field MRI makes this technique more appealing to study cerebral microvascular physiology. Therefore, this study assessed the applicability of SE-DSC MRI at 7 T. Forty-one elderly adults underwent 7 T MRI using a multi-slice SE-EPI DSC sequence. The cerebral blood volume (CBV) and cerebral blood flow (CBF) were determined in the cortical grey matter (CGM) and white matter (WM) and compared to values from the literature. The relation of CBV and CBF with age and sex was investigated. Higher CBV and CBF values were found in CGM compared to WM, whereby the CGM-to-WM ratios depended on the amount of largest vessels excluded from the analysis. CBF was negatively associated with age in the CGM, while no significant association was found with CBV. Both CBV and CBF were higher in women compared to men in both CGM and WM. The current study verifies the possibility of quantifying cerebral microvascular perfusion with SE-DSC MRI at 7 T.

MRI Assessment of Cerebral White Matter Microvascular Hemodynamics Across the Adult Lifespan

BACKGROUND

Changes in cerebral hemodynamics with aging are important for understanding age-related variation in neuronal health. While many prior studies have focused on gray matter, less is known regarding white matter due in part to measurement challenges related to the lower vascular density in white matter.

PURPOSE

To investigate the impact of age and sex on white matter hemodynamics in a Human Connectome Project in Aging (HCP-A) cohort using tract-based spatial statistics (TBSS).

STUDY TYPE

Retrospective cross-sectional.

POPULATION

Six hundred seventy-eight typically aging individuals (381 female), aged 36-100 years.

FIELD STRENGTH/SEQUENCE

Multi-delay pseudo-continuous arterial spin labeling (ASL) and diffusion-weighted pulsed-gradient spin-echo echo planar imaging sequences at 3.0 T.

ASSESSMENT

A skeleton of mean fractional anisotropy (FA) was produced using TBSS. This skeleton was used to project ASL-derived cerebral blood flow (CBF) and arterial transit time (ATT) measures onto white matter tracts.

STATISTICAL TESTS

General linear models were applied to white matter FA, CBF, and ATT maps, while covarying for age and sex. Threshold-free cluster enhancement multiple comparisons correction was performed for the effects of age and sex, thresholded at PFWE  < 0.05. CBF, ATT, and FA were compared between sex for each tract using analysis of covariance, with multiple comparisons correction for the number of tracts at PFDR  < 0.05.

RESULTS

Significantly lower white matter CBF and significantly prolonged white matter ATTs were associated with older age. These effects were widespread across tracts for ATT. Significant (PFDR  < 0.05) sex differences in ATT were observed across all tracts, and significant sex differences in CBF were observed in all tracts except the bilateral uncinate fasciculus. Females demonstrated significantly higher CBF compared to males across the lifespan. Few tracts demonstrated significant sex differences in FA.

DATA CONCLUSION

This study identified significant sex- and age-associated differences in white matter hemodynamics across tracts.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 3.

Assessing cerebrovascular reactivity (CVR) in rhesus macaques (Macaca mulatta) using a hypercapnic challenge and pseudo-continuous arterial spin labeling (pCASL)

Cerebrovascular reactivity (CVR) is a measure of cerebral small vessels' ability to respond to changes in metabolic demand and can be quantified using magnetic resonance imaging (MRI) coupled with a vasoactive stimulus. Reduced CVR occurs with neurodegeneration and is associated with cognitive decline. While commonly measured in humans, few studies have evaluated CVR in animal models. Herein, we describe methods to induce hypercapnia in rhesus macaques (Macaca mulatta) under gas anesthesia to measure cerebral blood flow (CBF) and CVR using pseudo-continuous arterial spin labeling (pCASL). Fifteen (13 M, 2 F) adult rhesus macaques underwent pCASL imaging that included a baseline segment (100% O2) followed by a hypercapnic challenge (isoflurane anesthesia with 5% CO2, 95% O2 mixed gas). Relative hypercapnia was defined as an end-tidal CO2 (ETCO2) ≥5 mmHg above baseline ETCO2. The mean ETCO2 during the baseline segment of the pCASL sequence was 34 mmHg (range: 23-48 mmHg). During this segment, mean whole-brain CBF was 51.48 ml/100g/min (range: 21.47-77.23 ml/100g/min). Significant increases (p<0.0001) in ETCO2 were seen upon inspiration of the mixed gas (5% CO2, 95% O2). The mean increase in ETCO2 was 8.5 mmHg and corresponded with a mean increase in CBF of 37.1% (p<0.0001). The mean CVR measured was 4.3%/mmHg. No anesthetic complications occurred as a result of the CO2 challenge. Our methods were effective at inducing a state of relative hypercapnia that corresponds with a detectable increase in whole brain CBF using pCASL MRI. Using these methods, a CO2 challenge can be performed in conjunction with pCASL imaging to evaluate CBF and CVR in rhesus macaques. The measured CVR in rhesus macaques is comparable to human CVR highlighting the translational utility of rhesus macaques in neuroscience research. These methods present a feasible means to measure CVR in comparative models of neurodegeneration and cerebrovascular dysfunction.

Neurovascular coupling dysfunction of visual network organization in Parkinson's disease

Parkinson's disease (PD) has been showed perfusion and neural activity alterations in specific regions, such as the motor and visual networks; however, the clinical significance of coupling changes is still unknown. To identify how neurovascular coupling changes during the pathophysiology of PD, patients and healthy controls underwent multiparametric magnetic resonance imaging to measure neural activity organization of segregation and integration using amplitude of low-frequency fluctuation (ALFF) and functional connectivity strength (FCS), and measure vascular responses using cerebral blood flow (CBF). Neurovascular coupling was calculated as the global CBF-ALFF and CBF-FCS coupling and the regional CBF/ALFF and CBF/FCS ratio. Correlations and dynamic causal modeling was then used to evaluate relationships with disease-alterations to clinical variables and information flow. Neurovascular coupling was impaired in PD with decreased global CBF-ALFF and CBF-FCS coupling, as well as decreased CBF/ALFF in the parieto-occipital cortex (dorsal visual stream) and CBF/FCS in the temporo-occipital cortex (ventral visual stream); these decouplings were associated with motor and non-motor impairments. The distinctive patterns of neurovascular coupling alterations within the dorsal and ventral visual streams of the visual system could potentially provide additional understanding into the pathophysiological mechanisms of PD.

Global effects of aging on the hemodynamic response function in the human brain

In functional magnetic resonance imaging, the hemodynamic response function (HRF) is a transient, stereotypical response to local changes in cerebral hemodynamics and oxygen metabolism due to briefly (< 4 s) evoked neural activity. Accordingly, the HRF is often used as an impulse response with the assumption of linearity in data analysis. In cognitive aging studies, it has been very common to interpret differences in brain activation as age-related changes in neural activity. Contrary to this assumption, however, evidence has accrued that normal aging may also significantly affect the vasculature, thereby affecting cerebral hemodynamics and metabolism, confounding interpretation of fMRI aging studies. In this study, use was made of a multisensory stimulus to evoke the HRF in ~ 87% of cerebral cortex in cognitively intact adults with ages ranging from 22-75 years. The stimulus evokes both positive and negative HRFs, which were characterized using model-free parameters in native-space coordinates. Results showed significant age trends in HRF parameter distributions in terms of both amplitudes (e.g., peak amplitude and CNR) and temporal dynamics (e.g., full-width-at-half-maximum). This work sets the stage for using HRF methods as a biomarker for age-related pathology.

Associations between age, sex, APOE genotype, and regional vascular physiology in typically aging adults

Altered blood flow in the human brain is characteristic of typical aging. However, numerous factors contribute to inter-individual variation in patterns of blood flow throughout the lifespan. To better understand the mechanisms behind such variation, we studied how sex and APOE genotype, a primary genetic risk factor for Alzheimer's disease (AD), influence associations between age and brain perfusion measures. We conducted a cross-sectional study of 562 participants from the Human Connectome Project - Aging (36 to >90 years of age). We found widespread associations between age and vascular parameters, where increasing age was associated with regional decreases in cerebral blood flow (CBF) and increases in arterial transit time (ATT). When grouped by sex and APOE genotype, interactions between group and age demonstrated that females had relatively greater CBF and lower ATT compared to males. Females carrying the APOEε4 allele showed the strongest association between CBF decline and ATT incline with age. This demonstrates that sex and genetic risk for AD modulate age-associated patterns of cerebral perfusion measures.

Normative cerebral microvascular blood flow waveform morphology assessed with diffuse correlation spectroscopy

Microvascular cerebral blood flow exhibits pulsatility at the cardiac frequency that carries valuable information about cerebrovascular health. This study used diffuse correlation spectroscopy to quantify normative features of these waveforms in a cohort of thirty healthy adults. We demonstrate they are sensitive to changes in vascular tone, as indicated by pronounced morphological changes with hypercapnia. Further, we observe significant sex-based differences in waveform morphology, with females exhibiting higher flow, greater area-under-the-curve, and lower pulsatility. Finally, we quantify normative values for cerebral critical closing pressure, i.e., the minimum pressure required to maintain flow in a given vascular region.

Evidence of An Association Between Cerebral Blood Flow and Microstructural Integrity in Normative Aging Using a Holistic MRI Approach

BACKGROUND

Cerebral tissue integrity decline and cerebral blood flow (CBF) alteration are major aspects of motor and cognitive dysfunctions and neurodegeneration. However, little is known about the association between blood flow and brain microstructural integrity, especially in normal aging.

PURPOSE

To assess the association between CBF and cerebral microstructural integrity.

STUDY TYPE

Cross sectional.

POPULATION

A total of 94 cognitively unimpaired adults (mean age 50.7 years, age range between 22 and 88 years, 56 Men).

FIELD STRENGTH/SEQUENCE

A 3 T; pseudo-continuous arterial spin labeling (pCASL), diffusion tensor imaging (DTI), Bayesian Monte Carlo analysis of multicomponent driven equilibrium steady-state observation of T1 and T2 (BMC-mcDESPOT).

ASSESSMENT

Lobar associations between CBF derived from pCASL, and longitudinal relaxation rate (R1 ), transverse relaxation rate (R2 ) and myelin water fraction (MWF) derived from BMC-mcDESPOT, or radial diffusivity (RD), axial diffusivity (AxD), mean diffusivity (MD) and fractional anisotropy (FA) derived from DTI were assessed.

STATISTICAL TESTS

Multiple linear regression models were used using the mean region of interest (ROI) values for MWF, R1 , R2 , FA, MD, RD, or AxD as the dependent variable and CBF, age, age2 , and sex as the independent variables. A two-sided P value of <0.05 defined statistical significance.

RESULTS

R1 , R2 , MWF, FA, MD, RD, and AxD parameters were associated with CBF in most of the cerebral regions evaluated. Specifically, higher CBF values were significantly associated with higher FA, MWF, R1 and R2 , or lower MD, RD and AxD values.

DATA CONCLUSION

These findings suggest that cerebral tissue microstructure may be impacted by global brain perfusion, adding further evidence to the intimate relationship between cerebral blood supply and cerebral tissue integrity.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 4.

Cerebral blood flow and cerebrovascular resistance across the adult lifespan: A multimodality approach

Cerebral blood flow (CBF) decreases across the adult lifespan; however, more studies are needed to understand the underlying mechanisms. This study measured CBF and cerebrovascular resistance (CVR) using a multimodality approach in 185 healthy adults (21-80 years). Color-coded duplex ultrasonography and phase-contrast MRI were used to measure CBF, CBF velocity, and vessel diameters of the internal carotid (ICA) and vertebral arteries (VA). MRI arterial spin labeling was used to measure brain perfusion. Transcranial Doppler was used to measure CBF velocity at the middle cerebral artery. Structural MRI was used to measure brain volume. CBF was presented as total blood flow (mL/min) and normalized CBF (nCBF, mL/100g/min). Mean arterial pressure was measured to calculate CVR. Age was associated with decreased CBF by ∼3.5 mL/min/year and nCBF by ∼0.19 mL/100g/min/year across the methods. CVR increased by ∼0.011 mmHg/mL/100g/min/year. Blood flow velocities in ICA and VA decreased with age ranging from 0.07-0.15 cm/s/year, while the vessel diameters remained similar among age groups. These findings suggest that age-related decreases in CBF can be attributed mainly to decreases in blood flow velocity in the large cerebral arteries and that increased CVR likely reflects the presence of cerebral vasoconstrictions in the small cerebral arterioles and/or capillaries.

Cerebral blood flow regulates iron overload in the cerebral nuclei of hemodialysis patients with anemia

Hemodialysis patients exhibit anemia-related cerebral hyperperfusion and iron deposition (ID). However, the mechanisms underlying the pathology of cerebral ID are not clear. We investigated the role of cerebral blood flow (CBF) in the pathophysiology of cerebral ID in hemodialysis patients with anemia. This study recruited 33 hemodialysis patients with anemia and thirty-three healthy controls (HCs). All the subjects underwent quantitative susceptibility mapping (QSM) and arterial spin labeling (ASL) to measure ID and CBF in the cerebral nuclei. Furthermore, we evaluated lacunar infarction (LI), cerebral microbleeds, and total white matter hyperintensity volume (TWMHV). Hemodialysis patients with anemia showed significantly higher ID and CBF in some nuclei compared to the HCs after adjusting for age, sex, and total intracranial volume (TIV) [P < 0.05, false discovery rate (FDR) corrected]. CBF showed a positive correlation with ID in both patients and HCs after adjustments for age, gender, and TIV (P < 0.05, FDR corrected). Serum phosphorus, calcium, TWMHV, hypertension, and dialysis duration were independently associated with ID (P < 0.05). Hemoglobin, serum phosphorus, and LI were independently associated with CBF (P < 0.05). Mediation analysis demonstrated that CBF mediated the effects between hemoglobin and ID. Our study demonstrated that CBF mediated aberrant cerebral ID in hemodialysis patients with anemia.

Associations between everyday activities and arterial spin labeling-derived cerebral blood flow: A longitudinal study in community-dwelling elderly volunteers

Cerebral blood flow (CBF) is critical for brain metabolism and function. Age-related changes in CBF are associated with increased risk of neurocognitive disorders and vascular events such as stroke. Identifying correlates and positive modifiers of age-related changes in CBF before the emergence of incipient clinical decline may inform public health advice and clinical practice. Former research has been inconclusive regarding the association between regular physical activity and CBF, and there is a lack of studies on the association between level of everyday activities and CBF, in older adults. To investigate these relationships, 118 healthy community-dwelling adults (65-89 years) underwent pseudo-continuous arterial spin labeling (ASL) MRI, neurocognitive, physical, and activity assessments at baseline. Eighty-six participants completed a follow-up ASL MRI, on average 506 (SD = 113) days after the baseline scan. Cross-sectional analysis revealed credible evidence for positive associations between time spent on low intensity physical activity and CBF in multiple cortical and subcortical regions, time spent on moderate to vigorous intensity physical activity and accumbens CBF, participation in social activity and CBF in multiple cortical regions, and between reading and thalamic CBF, indicating higher regional CBF in more active adults. Longitudinal analysis revealed anecdotal evidence for an interaction between time and baseline level of gardening on occipital and parietal CBF, and baseline reading on pallidum CBF, indicating more change in CBF in adults with lower level of activity. The findings support that malleable lifestyle factors contribute to healthy brain aging, with relevance for public health guidelines.

Parsing neurobiological heterogeneity of the clinical high-risk state for psychosis: A pseudo-continuous arterial spin labelling study

Introduction

The impact of the clinical high-risk for psychosis (CHR-P) construct is dependent on accurately predicting outcomes. Individuals with brief limited intermittent psychotic symptoms (BLIPS) have higher risk of developing a first episode of psychosis (FEP) compared to individuals with attenuated psychotic symptoms (APS). Supplementing subgroup stratification with information from candidate biomarkers based on neurobiological parameters, such as resting-state, regional cerebral blood flow (rCBF), may help refine risk estimates. Based on previous evidence, we hypothesized that individuals with BLIPS would exhibit increased rCBF compared to APS in key regions linked to dopaminergic pathways.

Methods

Data from four studies were combined using ComBat (to account for between-study differences) to analyse rCBF in 150 age- and sex-matched subjects (n = 30 healthy controls [HCs], n = 80 APS, n = 20 BLIPS and n = 20 FEP). Global gray matter (GM) rCBF was examined in addition to region-of-interest (ROI) analyses in bilateral/left/right frontal cortex, hippocampus and striatum. Group differences were assessed using general linear models: (i) alone; (ii) with global GM rCBF as a covariate; (iii) with global GM rCBF and smoking status as covariates. Significance was set at p < 0.05.

Results

Whole-brain voxel-wise analyses and Bayesian ROI analyses were also conducted. No significant group differences were found in global [F(3,143) = 1,41, p = 0.24], bilateral frontal cortex [F(3,143) = 1.01, p = 0.39], hippocampus [F(3,143) = 0.63, p = 0.60] or striatum [F(3,143) = 0.52, p = 0.57] rCBF. Similar null findings were observed in lateralized ROIs (p > 0.05). All results were robust to addition of covariates (p > 0.05). No significant clusters were identified in whole-brain voxel-wise analyses (p > 0.05FWE). Weak-to-moderate evidence was found for an absence of rCBF differences between APS and BLIPS in Bayesian ROI analyses.

Conclusion

On this evidence, APS and BLIPS are unlikely to be neurobiologically distinct. Due to this and the weak-to-moderate evidence for the null hypothesis, future research should investigate larger samples of APS and BLIPS through collaboration across large-scale international consortia.

Cerebral blood flow in striatum is increased by partial dopamine agonism in initially antipsychotic-naïve patients with psychosis

BACKGROUND

Resting cerebral blood flow (rCBF) in striatum and thalamus is increased in medicated patients with psychosis, but whether this is caused by treatment or illness pathology is unclear. Specifically, effects of partial dopamine agonism, sex, and clinical correlates on rCBF are sparsely investigated. We therefore assessed rCBF in antipsychotic-naïve psychosis patients before and after aripiprazole monotherapy and related findings to sex and symptom improvement.

METHODS

We assessed rCBF with the pseudo-Continuous Arterial Spin Labeling (PCASL) sequence in 49 first-episode patients (22.6 ± 5.2 years, 58% females) and 50 healthy controls (HCs) (22.3 ± 4.4 years, 63% females) at baseline and in 29 patients and 49 HCs after six weeks. RCBF in striatum and thalamus was estimated with a region-of-interest (ROI) approach. Psychopathology was assessed with the positive and negative syndrome scale.

RESULTS

Baseline rCBF in striatum and thalamus was not altered in the combined patient group compared with HCs, but female patients had lower striatal rCBF compared with male patients (p = 0.009). Treatment with a partial dopamine agonist increased rCBF significantly in striatum (p = 0.006) in the whole patient group, but not significantly in thalamus. Baseline rCBF in nucleus accumbens was negatively associated with improvement in positive symptoms (p = 0.046), but baseline perfusion in whole striatum and thalamus was not related to treatment outcome.

CONCLUSIONS

The findings suggest that striatal perfusion is increased by partial dopamine agonism and decreased in female patients prior to first treatment. This underlines the importance of treatment effects and sex differences when investigating the neurobiology of psychosis.

[Influence of bronchopulmonary dysplasia on cerebral blood flow in preterm infants: a prospective study based on arterial spin labeling]

OBJECTIVES

To investigate local cerebral blood perfusion in preterm infants with bronchopulmonary dysplasia (BPD) based on cerebral blood flow (CBF) values of arterial spin labeling (ASL).

METHODS

A prospective study was conducted on 90 preterm infants with a gestational age of <32 weeks and a birth weight of <1 500 g who were born in the Department of Obstetrics and admitted to the Department of Neonatology in the Third Affiliated Hospital of Zhengzhou University from August 2021 to June 2022. All of the infants underwent cranial MRI and ASL at the corrected gestational age of 35-40 weeks. According to the presence or absence of BPD, they were divided into a BPD group with 45 infants and a non-BPD group with 45 infants. The two groups were compared in terms of the CBF values of the same regions of interest (frontal lobe, temporal lobe, parietal lobe, occipital lobe, thalamus, and basal ganglia) on ASL image.

RESULTS

Compared with the non-BPD group, the BPD group had a significantly lower 1-minute Apgar score, a significantly longer duration of assisted ventilation, and a significantly higher incidence rate of fetal distress (P<0.05). After control for the confounding factors such as corrected age and age at the time of cranial MRI by multiple linear regression analysis, compared with the non-BPD group, the BPD group still had higher CBF values of the frontal lobe, temporal lobe, parietal lobe, occipital lobe, basal ganglia, and thalamus at both sides (P<0.05).

CONCLUSIONS

BPD can increase cerebral blood perfusion in preterm infants, which might be associated with hypoxia and a long duration of assisted ventilation in the early stage.

Frailty and functional brain connectivity (FBC) in older adults with mild cognitive impairment (MCI): baseline results from the SYNERGIC Trial

Functional brain connectivity (FBC), or areas that are anatomically separate but temporally synchronized in their activation, represent a sensitive biomarker for monitoring dementia progression. It is unclear whether frailty is associated with FBC in those at higher risk of progression to dementia (e.g., mild cognitive impairment -MCI-) and if sex plays a role. We used baseline data from the SYNERGIC trial, including participants with MCI that received brain MRI. In this cross-sectional analyses (n = 100), we measured frailty using a deficit accumulation frailty index. Using the CONN toolbox, we assessed FBC of networks and regions of interest across the entire connectome. We used Pearson's correlation to investigate the relationship between FBC and frailty index in the full sample and by sex. We also divided the full sample and each sex into tertiles based upon their frailty index score and then assessed between-tertile differences in FBC. The full sample (cluster: size = 291 p-FDR < 0.05) and males (cluster: size = 993 and 451 p-FDR < 0.01) demonstrated that increasing (stronger) connectivity between the right hippocampus and clusters in the temporal gyrus was positively correlated with increasing (worse) frailty. Males also demonstrated between-tertile differences in right hippocampus connectivity to clusters in the lateral occipital cortex (cluster: size = 289 p-FDR < 0.05). Regardless of frailty status, females demonstrated stronger within-network connectivity of the Default-Mode (p = 0.024). Our results suggest that increasing (worse) frailty was associated with increasing (stronger) connectivity between regions not typically linked, which may reflect a compensation tactic by the plastic brain. Furthermore, the relationship between the two variables appears to differ by sex. Our results may help elucidate why specific individuals progress to a dementia syndrome. NCT02808676. https://www.clinicaltrials.gov/ct2/show/NCT02808676.

Altered neurovascular coupling in children with idiopathic generalized epilepsy

AIMS

Alterations in neuronal activity and cerebral hemodynamics have been reported in idiopathic generalized epilepsy (IGE) patients, possibly resulting in neurovascular decoupling; however, no neuroimaging evidence confirmed this disruption. This study aimed to investigate the possible presence of neurovascular decoupling and its clinical implications in childhood IGE using resting-state fMRI and arterial spin labeling imaging.

METHODS

IGE patients and healthy participants underwent resting-state fMRI and arterial spin labeling imaging to calculate degree centrality (DC) and cerebral blood flow (CBF), respectively. Across-voxel CBF-DC correlations were analyzed to evaluate the neurovascular coupling within the whole gray matter, and the regional coupling of brain region was assessed with the CBF/DC ratio.

RESULTS

The study included 26 children with IGE and 35 sex- and age-matched healthy controls (HCs). Compared with the HCs, the IGE group presented lower across-voxel CBF-DC correlations, higher CBF/DC ratio in the right posterior cingulate cortex/precuneus, middle frontal gyrus, and medial frontal gyrus (MFG), and lower ratio in the left inferior frontal gyrus. The increased CBF/DC ratio in the right MFG was correlated with lower performance intelligence quotient scores in the IGE group.

CONCLUSION

Children with IGE present altered neurovascular coupling, associated with lower performance intelligence quotient scores. The study shed a new insight into the pathophysiology of epilepsy and provided potential imaging biomarkers of cognitive performances in children with IGE.

Cerebral metabolic rate of oxygen (CMRO2) changes measured with simultaneous tDCS-MRI in healthy adults

BACKGROUND

Transcranial direct current stimulation (tDCS) is a safe and well-tolerated noninvasive technique used for cortical excitability modulation. tDCS has been extensively investigated for its clinical applications; however further understanding of its underlying in-vivo physiological mechanisms remains a fundamental focus of current research.

OBJECTIVES

We investigated the simultaneous effects of tDCS on cerebral blood flow (CBF), venous blood oxygenation (Yv) and cerebral metabolic rate of oxygen (CMRO2) using simultaneous MRI in healthy adults to provide a reference frame for its neurobiological mechanisms.

METHODS

Twenty-three healthy participants (age = 35.6 ± 15.0 years old, 10 males) completed a simultaneous tDCS-MRI session in a 3 T scanner fitted with a 64-channels head coil. A MR-compatible tDCS device was used to acquire CBF, Yv and CMRO2 at three time points: pre-, during- and post- 15 minutes of 2.0 mA tDCS on left anodal dorsolateral prefrontal cortex.

RESULTS

During tDCS, CBF significantly increased (57.10 ± 8.33 mL/100g/min) from baseline (53.67 ± 7.75 mL/100g/min; p < 0.0001) and remained elevated in post-tDCS (56.79 ± 8.70 mL/100g/min). Venous blood oxygenation levels measured in pre-tDCS (60.71 ± 4.12 %) did not significantly change across the three timepoints. The resulting CMRO2 significantly increased by 5.9 % during-tDCS (175.68 ± 30.78 µmol/100g/min) compared to pre-tDCS (165.84 ± 25.32 µmol/100g/min; p = 0.0015), maintaining increased levels in post-tDCS (176.86 ± 28.58 µmol/100g/min).

CONCLUSIONS

tDCS has immediate effects on neuronal excitability, as measured by increased cerebral blood supply and oxygen consumption supporting increased neuronal firing. These findings provide a standard range of CBF and CMRO2 changes due to tDCS in healthy adults that may be incorporated in clinical studies to evaluate its therapeutic potential.

Cerebral blood flow network differences correlated with cognitive impairment in mild traumatic brain injury

Purpose

To examine whether the cerebral blood flow (CBF) and CBF connectivity differences are sex-specific and whether these differences are correlated with cognitive impairment in mTBI.

Methods

Resting-state perfusion magnetic resonance imaging was performed in 40 patients with acute mTBI and 40 healthy controls by using pseudocontinuous arterial spin labeling within 14 days following injury. The differences in normalized CBF were first compared and CBF connectivity of the brain regions with significant CBF differences were compared next. The association between the normalized CBF and CBF connectivity differences and cognitive function were further investigated.

Results

Men patients had lower normalized CBF in the frontal gyrus, temporal gyrus and hippocampus and decreased negative CBF connectivity between brain regions including the hippocampus, temporal gyrus, postcentral gyrus and lenticular nucleus, putamen, compared with men controls. Women patients had lower normalized CBF in the frontal gyrus, however had higher normalized CBF in the temporal gyrus and hippocampus, compared with women controls. Additionally, women patients showed increased positive CBF connectivity between the seed region of interest (ROI) of the right inferior temporal gyrus and temporal gyrus and frontal gyrus, and had increased positive CBF connectivity between the seed ROI of the right hippocampus and the temporal gyrus. Furthermore, men patients had higher CBF in the right middle temporal gyrus and left precentral gyrus than women patients.

Conclusion

This study provides evidence of sex differences in both decreased and increased CBF and CBF connectivity and association with cognitive outcome in the acute stage after mTBI.

Resting-state BOLD functional connectivity depends on the heterogeneity of capillary transit times in the human brain A combined lesion and simulation study about the influence of blood flow response timing

Functional connectivity (FC) derived from blood oxygenation level dependent (BOLD) functional magnetic resonance imaging at rest (rs-fMRI), is commonly interpreted as indicator of neuronal connectivity. In a number of brain disorders, however, metabolic, vascular, and hemodynamic impairments can be expected to alter BOLD-FC independently from neuronal activity. By means of a neurovascular coupling (NVC) model of BOLD-FC, we recently demonstrated that aberrant timing of cerebral blood flow (CBF) responses may influence BOLD-FC. In the current work, we support and extend this finding by empirically linking BOLD-FC with capillary transit time heterogeneity (CTH), which we consider as an indicator of delayed and broadened CBF responses. We assessed 28 asymptomatic patients with unilateral high-grade internal carotid artery stenosis (ICAS) as a hemodynamic lesion model with largely preserved neurocognitive functioning and 27 age-matched healthy controls. For each participant, we obtained rs-fMRI, arterial spin labeling, and dynamic susceptibility contrast MRI to study the dependence of left-right homotopic BOLD-FC on local perfusion parameters. Additionally, we investigated the dependency of BOLD-FC on CBF response timing by detailed simulations. Homotopic BOLD-FC was negatively associated with increasing CTH differences between homotopic brain areas. This relation was more pronounced in asymptomatic ICAS patients even after controlling for baseline CBF and relative cerebral blood volume influences. These findings match simulation results that predict an influence of delayed and broadened CBF responses on BOLD-FC. Results demonstrate that increasing CTH differences between homotopic brain areas lead to BOLD-FC reductions. Simulations suggest that CTH increases correspond to broadened and delayed CBF responses to fluctuations in ongoing neuronal activity.

Contribution of Inflammation and Hypoperfusion to White Matter Hyperintensities-Related Cognitive Impairment

White matter hyperintensities (WMHs) of presumed vascular origin are one of the most important neuroimaging markers of cerebral small vessel disease (CSVD), which are closely associated with cognitive impairment. The aim of this study was to elucidate the pathogenesis of WMHs from the perspective of inflammation and hypoperfusion mechanisms. A total of 65 patients with WMHs and 65 healthy controls were enrolled in this study. Inflammatory markers measurements [hypersensitive C-reactive protein (hsCRP) and lipoprotein-associated phospholipase A2 (Lp-PLA2)], cognitive evaluation, and pseudocontinuous arterial spin labeling (PCASL) MRI scanning were performed in all the subjects. The multivariate logistic regression analysis showed that Lp-PLA2 was an independent risk factor for WMHs. Cerebral blood flow (CBF) in the whole brain, gray matter (GM), white matter (WM), left orbital medial frontal gyrus [MFG.L (orbital part)], left middle temporal gyrus (MTG.L), and right thalamus (Tha.R) in the patients was lower than those in the controls and CBF in the left triangular inferior frontal gyrus [IFG.L (triangular part)] was higher in the patients than in the controls. There was a significant correlation between Lp-PLA2 levels and CBF in the whole brain (R = -0.417, p < 0.001) and GM (R = -0.278, p = 0.025), but not in the WM in the patients. Moreover, CBF in the MFG.L (orbital part) and the Tha.R was, respectively, negatively associated with the trail making test (TMT) and the Stroop color word test (SCWT), suggesting the higher CBF, the better executive function. The CBF in the IFG.L (triangular part) was negatively correlated with attention scores in the Cambridge Cognitive Examination-Chinese Version (CAMCOG-C) subitems (R = -0.288, p = 0.020). Our results revealed the vascular inflammation roles in WMHs, which may through the regulation of CBF in the whole brain and GM. Additionally, CBF changes in different brain regions may imply a potential role in the modulation of cognitive function in different domains.

Characterization of Age-Related Differences in the Human Choroid Plexus Volume, Microstructural Integrity, and Blood Perfusion Using Multiparameter Magnetic Resonance Imaging

The choroid plexus (CP) is an important cerebral structure involved in cerebrospinal fluid production and transport of solutes into the brain. Recent studies have uncovered the involvement of the CP in neurological disorders such as Alzheimer's disease and multiple sclerosis. However, our understanding of human age-related microstructural and functional changes in the CP with aging and neuropathology is limited. In this cross-sectional study, we investigated age and sex differences in the CP structure and function using advanced quantitative magnetic resonance imaging methodology in a large cohort (n = 155) of cognitively unimpaired individuals over a wide age range between 21 and 94 years. Our analysis included volumetric measurements, relaxometry measures (T 1 and T 2), diffusion tensor imaging (DTI) measures of fractional anisotropy (FA) and mean diffusivity (MD), as well as measures of cerebral blood flow (CBF). Our results revealed that CP volume was increasing with advancing age. We conjecture that this novel observation is likely attributed to alterations in the CP microstructure or function as well as to ventriculomegaly. Indeed, we also found that CBF was lower with advanced age, while, consistent with previous studies, T 1, T 2 and MD were higher, and FA was lower with advanced age. We attribute these functional and microstructural differences to a deteriorated CP structural integrity with aging. Furthermore, our relaxometry and DTI measures were found to be associated with differences in blood perfusion revealing lower microstructural integrity with lower CBF. Finally, in agreement with literature, sex-related differences in MD and CBF were statistically significant. This work lays the foundation for ongoing investigation of the involvement of CP in neurodegeneration.