Total cerebral blood flow and total brain perfusion in the general population: the Rotterdam Scan Study

Automated Quantification of Total Cerebral Blood Flow from Phase-Contrast MRI and Deep Learning

Knowledge of input blood to the brain, which is represented as total cerebral blood flow (tCBF), is important in evaluating brain health. Phase-contrast (PC) magnetic resonance imaging (MRI) enables blood velocity mapping, allowing for noninvasive measurements of tCBF. In the procedure, manual selection of brain-feeding arteries is an essential step, but is time-consuming and often subjective. Thus, the purpose of this work was to develop and validate a deep learning (DL)-based technique for automated tCBF quantifications. To enhance the DL segmentation performance on arterial blood vessels, in the preprocessing step magnitude and phase images of PC MRI were multiplied several times. Thereafter, a U-Net was trained on 218 images for three-class segmentation. Network performance was evaluated in terms of the Dice coefficient and the intersection-over-union (IoU) on 40 test images, and additionally, on externally acquired 20 datasets. Finally, tCBF was calculated from the DL-predicted vessel segmentation maps, and its accuracy was statistically assessed with the correlation of determination (R2), the intraclass correlation coefficient (ICC), paired t-tests, and Bland-Altman analysis, in comparison to manually derived values. Overall, the DL segmentation network provided accurate labeling of arterial blood vessels for both internal (Dice=0.92, IoU=0.86) and external (Dice=0.90, IoU=0.82) tests. Furthermore, statistical analyses for tCBF estimates revealed good agreement between automated versus manual quantifications in both internal (R2=0.85, ICC=0.91, p=0.52) and external (R2=0.88, ICC=0.93, p=0.88) test groups. The results suggest feasibility of a simple and automated protocol for quantifying tCBF from neck PC MRI and deep learning.

Effects of sleep quality on diurnal variation of brain volume in older adults: A retrospective cross-sectional study

AIM

Brain volume is influenced by several factors that can change throughout the day. In addition, most of these factors are influenced by sleep quality. This study investigated diurnal variation in brain volume and its relation to overnight sleep quality.

METHODS

We enrolled 1,003 healthy Koreans without any psychiatric disorders aged 60 years or older. We assessed sleep quality and average wake time using the Pittsburgh Sleep Quality Index, and divided sleep quality into good, moderate, and poor groups. We estimated the whole and regional brain volumes from three-dimensional T1-weighted brain MRI scans. We divided the interval between average wake-up time and MRI acquisition time (INT) into tertile groups: short (INT1), medium (INT2), and long (INT3).

RESULTS

Whole and regional brain volumes showed no significance with respect to INT. However, the `interaction between INT and sleep quality showed significance for whole brain, cerebral gray matter, and cerebrospinal fluid volumes (p < .05). The INT2 group showed significantly lower volumes of whole brain, whole gray matter, cerebral gray matter, cortical gray matter, subcortical gray matter, and cerebrospinal fluid than the INT1 and INT3 groups only in the individuals with good sleep quality.

CONCLUSION

Human brain volume changes significantly within a day associated with overnight sleep in the individuals with good sleep quality.

Chronic cerebral hypoperfusion: a critical feature in unravelling the etiology of vascular cognitive impairment

Vascular cognitive impairment (VCI) describes a wide spectrum of cognitive deficits related to cerebrovascular diseases. Although the loss of blood flow to cortical regions critically involved in cognitive processes must feature as the main driver of VCI, the underlying mechanisms and interactions with related disease processes remain to be fully elucidated. Recent clinical studies of cerebral blood flow measurements have supported the role of chronic cerebral hypoperfusion (CCH) as a major driver of the vascular pathology and clinical manifestations of VCI. Here we review the pathophysiological mechanisms as well as neuropathological changes of CCH. Potential interventional strategies for VCI are also reviewed. A deeper understanding of how CCH can lead to accumulation of VCI-associated pathology could potentially pave the way for early detection and development of disease-modifying therapies, thus allowing preventive interventions instead of symptomatic treatments.

Association of blood pressure with brain perfusion and structure: A population-based prospective study

PURPOSE

To explore the association of blood pressure (BP) measurements with cerebral blood flow (CBF) and brain structure in general population.

METHOD

This prospective study included 902 participants from Kailuan community. All participants underwent brain MRI and BP measurements. The association of BP indicators with CBF, brain tissue volume and white matter hyperintensity (WMH) volume were investigated. In addition, mediation analysis was used to determine whether significantly changed brain tissue volume explained associations between BP and CBF.

RESULTS

Elevated diastolic BP (DBP), but not systolic BP (SBP), was associated with lower CBF in the total brain (β [95 % CI]: -0.62 [-1.14, -0.10]), total gray matter (β [95 % CI]: -0.71 [-1.27, -0.14]), hippocampus (β [95 % CI]: -0.59 [-1.13, -0.05]), frontal (β [95 % CI]: -0.72 [-1.31, -0.13]), parietal (β [95 % CI]: -0.92 [-1.54, -0.3]), temporal (β [95 % CI]: -0.63 [-1.18, -0.08]), and occipital lobe (β [95 % CI]: -0.69 [-1.37, -0.01]). Higher SBP and DBP were associated with reduced total and regional brain tissue volume (all p < 0.05). Increased SBP and PP were associated with higher total and periventricular WMH volume (all p < 0.05). In addition, mediation analysis identified that significantly decreased brain volume did not mediate the associations of BP measurements and lower CBF in corresponding region (all p > 0.05).

CONCLUSIONS

Elevated BP level was associated with decreased total and regional CBF and brain tissue volume and increased WMH burden.

Multimodality neuroimaging in vascular mild cognitive impairment: A narrative review of current evidence

The vascular mild cognitive impairment (VaMCI) is generally accepted as the premonition stage of vascular dementia (VaD). However, most studies are focused mainly on VaD as a diagnosis in patients, thus neglecting the VaMCI stage. VaMCI stage, though, is easily diagnosed by vascular injuries and represents a high-risk period for the future decline of patients’ cognitive functions. The existing studies in China and abroad have found that magnetic resonance imaging technology can provide imaging markers related to the occurrence and development of VaMCI, which is an important tool for detecting the changes in microstructure and function of VaMCI patients. Nevertheless, most of the existing studies evaluate the information of a single modal image. Due to the different imaging principles, the data provided by a single modal image are limited. In contrast, multi-modal magnetic resonance imaging research can provide multiple comprehensive data such as tissue anatomy and function. Here, a narrative review of published articles on multimodality neuroimaging in VaMCI diagnosis was conducted，and the utilization of certain neuroimaging bio-markers in clinical applications was narrated. These markers include evaluation of vascular dysfunction before tissue damages and quantification of the extent of network connectivity disruption. We further provide recommendations for early detection, progress, prompt treatment response of VaMCI, as well as optimization of the personalized treatment plan.

Cerebral Small Vessel Disease-Related Dementia: More Questions Than Answers

Cerebral small vessel disease (CSVD) has emerged as a common factor driving age-dependent diseases, including stroke and dementia. CSVD-related dementia will affect a growing fraction of the aging population, requiring improved recognition, understanding, and treatments. This review describes evolving criteria and imaging biomarkers for the diagnosis of CSVD-related dementia. We describe diagnostic challenges, particularly in the context of mixed pathologies and the absence of highly effective biomarkers for CSVD-related dementia. We review evidence regarding CSVD as a risk factor for developing neurodegenerative disease and potential mechanisms by which CSVD leads to progressive brain injury. Finally, we summarize recent studies on the effects of major classes of cardiovascular medicines relevant to CSVD-related cognitive impairment. Although many key questions remain, the increased attention to CSVD has resulted in a sharper vision for what will be needed to meet the upcoming challenges imposed by this disease.

Relationships of Cerebral Perfusion With Gait Speed Across Systolic Blood Pressure Levels and Age: A Cohort Study

BACKGROUND

This study aimed to examine if the association of cerebral perfusion with gait speed differs across systolic blood pressure (SBP) and age.

METHODS

Cerebral perfusion was measured via arterial spin labeled (ASL)-MRI among community-dwelling adults aged 31-94 years in the population-based Mayo Clinic Study of Aging. Usual gait speed was assessed over 5.6 meters on an electronic mat. Sex- and body mass index (BMI)-adjusted linear regression models estimated cross-sectional gait speed associations with ASL and modifying effects of age and SBP using 3-way and 2-way interaction terms between continuous age, SBP, and ASL. Results report estimated differences in gait speed per standard deviation (SD) lower ASL for exemplar SBPs and ages.

RESULTS

Among 479 participants (mean age 67.6 years; 44% women; mean gait speed 1.17 m/s), ASL relations to gait speed varied by age (ASL-x-age interaction: p = .001) and SBP (ASL-x-SBP interaction: p = .009). At an SBP of 120 mmHg, each SD lower ASL was associated with a 0.04 m/s (95% confidence interval [CI]: 0.01, 0.07) slower gait speed at 65 years, 0.07 m/s (0.04, 0.10) at 75 years, and 0.09 m/s (0.05, 0.13) at 85 years. At an SBP of 140 mmHg, ASL associations with gait speed were attenuated to 0.01 (-0.01, 0.04), 0.04 (0.02, 0.06), and 0.06 (0.04, 0.09) m/s slower gait speed at ages 65, 75, and 85, respectively.

CONCLUSION

Poorer cerebral perfusion is associated with clinically meaningful slower gait speeds, particularly with older age, while higher perfusion markedly attenuates age differences in gait speed.

Subclinical liver traits are associated with structural and hemodynamic brain imaging markers

BACKGROUND & AIMS

Impaired liver function affects brain health and therefore understanding potential mechanisms for subclinical liver disease is essential. We assessed the liver-brain associations using liver measures with brain imaging markers, and cognitive measures in the general population.

METHODS

Within the population-based Rotterdam Study, liver serum and imaging measures (ultrasound and transient elastography), metabolic dysfunction-associated fatty liver disease (MAFLD), non-alcoholic fatty liver disease (NAFLD) and fibrosis phenotypes, and brain structure were determined in 3493 non-demented and stroke-free participants in 2009-2014. This resulted in subgroups of n = 3493 for MAFLD (mean age 69 ± 9 years, 56% ♀), n = 2938 for NAFLD (mean age 70 ± 9 years, 56% ♀) and n = 2252 for fibrosis (mean age 65 ± 7 years, 54% ♀). Imaging markers of small vessel disease and neurodegeneration, cerebral blood flow (CBF) and brain perfusion (BP) were acquired from brain MRI (1.5-tesla). General cognitive function was assessed by Mini-Mental State Examination and the g-factor. Multiple linear and logistic regression models were used for liver-brain associations and adjusted for age, sex, intracranial volume, cardiovascular risk factors and alcohol use.

RESULTS

Higher gamma-glutamyltransferase (GGT) levels were significantly associated with smaller total brain volume (TBV, standardized mean difference (SMD), -0.02, 95% confidence interval (CI) (-0.03 to -0.01); p = 8.4·10^-4 ), grey matter volumes, and lower CBF and BP. Liver serum measures were not related to small vessel disease markers, nor to white matter microstructural integrity or general cognition. Participants with ultrasound-based liver steatosis had a higher fractional anisotropy (FA, SMD 0.11, 95% CI (0.04 to 0.17), p = 1.5·10^-3 ) and lower CBF and BP. MAFLD and NAFLD phenotypes were associated with alterations in white matter microstructural integrity (NAFLD ~ FA, SMD 0.14, 95% CI (0.07 to 0.22), p = 1.6·10^-4 ; NAFLD ~ mean diffusivity, SMD -0.12, 95% CI (-0.18 to -0.05), p = 4.7·10^-4 ) and also with lower CBF and BP (MAFLD ~ CBF, SMD -0.13, 95% CI (-0.20 to -0.06), p = 3.1·10^-4 ; MAFLD ~ BP, SMD -0.12, 95% CI (-0.20 to -0.05), p = 1.6·10^-3 ). Furthermore, fibrosis phenotypes were related to TBV, grey and white matter volumes.

CONCLUSIONS

Presence of liver steatosis, fibrosis and elevated serum GGT are associated with structural and hemodynamic brain markers in a population-based cross-sectional setting. Understanding the hepatic role in brain changes can target modifiable factors and prevent brain dysfunction.

This is Your Brain, and This is Your Brain on Atrial Fibrillation: The Roles of Cardiac Malperfusion Events and Vascular Dysfunction in Cognitive Impairment

AF is an independent and strong predictor of long-term cognitive decline. However, the mechanism for this cognitive decline is difficult to define and likely multifactorial, leading to many different hypotheses. Examples include macro- or microvascular stroke events, biochemical changes to the blood-brain barrier related to anticoagulation, or hypo-hyperperfusion events. This review explores and discusses the hypothesis that AF contributes to cognitive decline and dementia through hypo-hyperperfusion events occurring during cardiac arrhythmias. We briefly explain several brain perfusion imaging techniques and further examine the novel findings associated with changes in brain perfusion in patients with AF. Finally, we discuss the implications and areas requiring more research to further understand and treat patients with cognitive decline related to AF.

Imputation models and error analysis for phase contrast MR cerebral blood flow measurements

Cerebral blood flow (CBF) supports brain metabolism. Diseases impair CBF, and pharmacological agents modulate CBF. Many techniques measure CBF, but phase contrast (PC) MR imaging through the four arteries supplying the brain is rapid and robust. However, technician error, patient motion, or tortuous vessels degrade quality of the measurements of the internal carotid (ICA) or vertebral (VA) arteries. We hypothesized that total CBF could be imputed from measurements in subsets of these 4 feeding vessels without excessive penalties in accuracy. We analyzed PC MR imaging from 129 patients, artificially excluded 1 or more vessels to simulate degraded imaging quality, and developed models of imputation for the missing data. Our models performed well when at least one ICA was measured, and resulted in R ² values of 0.998-0.990, normalized root mean squared error values of 0.044-0.105, and intra-class correlation coefficient of 0.982-0.935. Thus, these models were comparable or superior to the test-retest variability in CBF measured by PC MR imaging. Our imputation models allow retrospective correction for corrupted blood vessel measurements when measuring CBF and guide prospective CBF acquisitions.

Increase in Cerebral Blood Flow After Catheter Ablation of Atrial Fibrillation

BACKGROUND

Recent studies have found that atrial fibrillation (AF) is a risk factor for cognitive impairment. Brain hypoperfusion is hypothesized as an underlying mechanism of cognitive decline in AF patients.

OBJECTIVES

This study sought to assess changes in cerebral blood flow (CBF) and brain volume after catheter ablation of AF.

METHODS

Patients undergoing catheter ablation of AF were enrolled in this prospective study. AF patients being treated with pharmaceuticals alone served as a control group. Brain magnetic resonance imaging was performed before and 6 months after catheter ablation. CBF was assessed by 2-dimensional phase-contrast magnetic resonance angiography. Brain volume and bilateral hippocampal volume were measured using FreeSurfer software.

RESULTS

Of the 57 study patients (age 64 ± 11 years; 45 men; paroxysmal AF: n = 22; nonparoxysmal AF: n = 35), 48 patients were freed from tachyarrhythmia recurrence beyond a 3-month blanking period. Changes in CBF and brain perfusion over 6 months were significantly greater in the study patients than control (CBF: 39.26 vs -34.86 mL; P = 0.01, ANCOVA; brain perfusion: 3.78 vs -3.02 mL/100 mL/min; P = 0.009, ANCOVA), while changes in total brain volume and bilateral hippocampal volume were similar between 2 groups (total brain volume: 2.57 vs -2.15 mL; P = 0.32, ANCOVA; bilateral hippocampal volume: 0.03 vs 0.04 mL; P = 0.8, ANCOVA). Nonparoxysmal AF at baseline was an independent predictor of an increase in CBF of >32.6 mL/min.

CONCLUSIONS

Catheter ablation of AF has favorable effects on CBF, particularly in nonparoxysmal AF. Our results may partially explain the association between cognitive decline and AF.

Sympathoexcitatory Responses to Isometric Handgrip Exercise Are Associated With White Matter Hyperintensities in Middle-Aged and Older Adults

Vascular dysfunction may occur prior to declines in cognitive function and accumulation of neuropathology. White matter hyperintensities (WMH) develop due to cerebral ischemia and elevated blood pressure in midlife. The purpose of this study was to evaluate associations between cardiovascular and cerebrovascular responses to sympathoexcitatory stimuli and WMH burden in cognitively unimpaired middle-aged and older adults. Sixty-eight adults (age = 63 ± 4y, men = 20, women = 48) participated in this study. Participants completed isometric handgrip exercise (IHG) exercise at 40% of maximal voluntary contraction until fatigue followed by a 90s period of post-exercise ischemia. Heart rate (HR), mean arterial pressure (MAP), middle cerebral artery blood velocity (MCAv), and end-tidal CO₂ were continuously measured throughout the protocol. Cerebrovascular resistance index (CVRi) was calculated as MAP/MCAv. WMH lesion volume and intracranial volume (ICV) were measured using a FLAIR and T1 scan on a 3T MRI scanner, respectively. WMH fraction was calculated as (WMH lesion volume/ICV)*100 and cubic root transformed. Multiple linear regressions were used to determine the association between cardiovascular and cerebrovascular responses to IHG exercise and post-exercise ischemia and WMH fraction. Multiple linear regression models were adjusted for age, sex, apolipoprotein ε4 status, and total work performed during IHG exercise. During IHG exercise, there were significant increases from baseline in HR (25 ± 12%), MAP (27 ± 11%), MCAv (5 ± 10%), and CVRi (22 ± 17%; P < 0.001 for all). During post-exercise ischemia, HR (8 ± 7%), MAP (22 ± 9%), and CVRi (23 ± 16%) remained elevated (P < 0.001) while MCAv (0 ± 10%) was not different compared to baseline. There was an inverse association between the percent change in HR (r = −0.42, P = 0.002), MAP (r = −0.41, P = 0.002), and CVRi (r = −0.31, P = 0.045), but not MCAv (r = 0.19, P = 0.971) in response to IHG exercise and WMH fraction. There were no associations between responses to post-exercise ischemia and WMH fraction. Lower sympathoexcitatory responses to IHG exercise are associated with greater WMH burden in middle-aged to older adults. These findings suggest that individuals who demonstrate smaller increases in HR, MAP, and CVRi in response to sympathoexcitatory stress have greater WMH burden.

Thyroid Status and Brain Circulation: The Rotterdam Study

CONTEXT

Whether thyroid dysfunction is related to altered brain circulation in the general population remains unknown.

OBJECTIVE

We determined the association of thyroid hormones with different markers of brain circulation within community-dwelling elderly people.

METHODS

This was a population-based study of 3 subcohorts of the Rotterdam Study, starting in 1989, 2000, and 2006. A total of 5142 participants (mean age, 63.8 years; 55.4% women), underwent venipuncture to measure serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4). Between 2005 and 2015, all participants underwent phase-contrast brain magnetic resonance imaging to assess global brain perfusion (mL of blood flow/100 mL of brain/minute). Arteriolar retinal calibers were assessed using digitized images of stereoscopic fundus color transparencies in 3105 participants as markers of microcirculation. We investigated associations of TSH, FT4 with brain circulation measures using (non)linear regression models.

RESULTS

FT4 (in pmol/L) levels had an inverse U-shaped association with global brain perfusion, such that high and low levels of FT4 were associated with lower global brain perfusion than middle levels of FT4. The difference in global brain perfusion between high FT4 levels (25 pmol/L) and middle FT4 levels (FT4 = 15 pmol/L; P nonlinearity = .002) was up to -2.44 mL (95% CI -4.31; -0.56). Higher and lower levels of FT4, compared with middle FT4 levels, were associated with arteriolar retinal vessels (mean difference up to -2.46 µm, 95% CI -4.98; 0.05 for lower FT4).

CONCLUSION

These results suggest that thyroid dysfunction could lead to brain diseases such as stroke or dementia through suboptimal brain circulation that is potentially modifiable.

Why do humans undergo an adiposity rebound? Exploring links with the energetic costs of brain development in childhood using MRI-based 4D measures of total cerebral blood flow

Background

Individuals typically show a childhood nadir in adiposity termed the adiposity rebound (AR). The AR serves as an early predictor of obesity risk, with early rebounders often at increased risk; however, it is unclear why this phenomenon occurs, which could impede understandings of weight gain trajectories. The brain’s energy requirements account for a lifetime peak of 66% of the body’s resting metabolic expenditure during childhood, around the age of the AR, and relates inversely to weight gain, pointing to a potential energy trade-off between brain development and adiposity. However, no study has compared developmental trajectories of brain metabolism and adiposity in the same individuals, which would allow a preliminary test of a brain-AR link.

Methods

We used cubic splines and generalized additive models to compare age trajectories of previously collected MRI-based 4D flow measures of total cerebral blood flow (TCBF), a proxy for cerebral energy use, to the body mass index (BMI) in a cross-sectional sample of 82 healthy individuals (0–60 years). We restricted our AR analysis to pre-pubertal individuals (0–12 years, n = 42), predicting that peak TCBF would occur slightly after the BMI nadir, consistent with evidence that lowest BMI typically precedes the nadir in adiposity.

Results

TCBF and the BMI showed inverse trajectories throughout childhood, while the estimated age at peak TCBF (5.6 years) was close but slightly later than the estimated age of the BMI nadir (4.9 years).

Conclusions

The timing of peak TCBF in this sample points to a likely concordance between peak brain energetics and the nadir in adiposity. Inverse age trajectories between TCBF and BMI support the hypothesis that brain metabolism is a potentially important influence on early life adiposity. These findings also suggest that experiences influencing the pattern of childhood brain energy use could be important predictors of body composition trajectories.

Haemorheologic Enhancement of Cerebral Perfusion Improves Oxygen Supply and Reduces Aβ Plaques Deposition in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a consequence of complex interactions of age-related neurodegeneration and vascular-associated pathologies, affecting more than 44 million people worldwide. For the last decade, it has been suggested that chronic brain hypoperfusion and consequent hypoxia play a direct role in the pathogenesis of AD. However, current treatments of AD have not focused on restoring or improving microvascular perfusion. In a previous study, we showed that drag reducing polymers (DRP) enhance cerebral blood flow and tissue oxygenation. We hypothesised that haemorheologic enhancement of cerebral perfusion by DRP would be useful for treating Alzheimer's disease. We used double transgenic B6C3-Tg(APPswe, PSEN1dE9) 85Dbo/Mmjax AD mice. DRP or vehicle (saline) was i.v. injected every week starting at four months of age till 12 months of age (10 mice/group). In-vivo 2-photon laser scanning microscopy was used to evaluate amyloid plaques development, cerebral microcirculation, and tissue oxygen supply/metabolic status (NADH autofluorescence). The imaging sessions were repeated once a month till 12 months of age. Statistical analyses were done by independent Student's t-test or Kolmogorov-Smirnov tests where appropriate. Differences between groups and time were determined using a two-way repeated measures ANOVA analysis for multiple comparisons and post hoc testing using the Mann-Whitney U test. In the vehicle group, numerous plaques completely formed in the cortex by nine months of age. The development of plaques accumulation was accompanied by cerebral microcirculation disturbances, reduction in tissue oxygen supply and metabolic impairment (NADH increase). DRP mitigated microcirculation and tissue oxygen supply reduction - microvascular perfusion was 29.5 ± 5%, and tissue oxygen supply was 22 ± 4% higher than in the vehicle group (p < 0.05). In the DRP group, amyloid plaques deposition was substantially less than in the vehicle group (p < 0.05). Thus, rheological enhancement of blood flow by DRP is associated with reduced rate of beta amyloid plaques deposition in AD mice.

Comparison of cerebral blood flow in subjects with and without chronic obstructive pulmonary disease from the population-based Rotterdam Study

OBJECTIVES

Patients with chronic obstructive pulmonary disease (COPD) are at increased risk of cerebrovascular disease, which might be associated with decreases in cerebral blood flow. Since studies examining cerebral blood flow in COPD remain scarce and are limited by sample size, we aimed to study cerebral blood flow in participants with and without COPD.

DESIGN

Observational cohort study.

SETTING

Population-based Rotterdam Study.

PARTICIPANTS

4177 participants (age 68.0±8.5 years; 53% females) with and without COPD.

PREDICTOR VARIABLE

Spirometry and pulmonary diffusing capacity.

OUTCOME MEASURES

Cerebral blood flow by two-dimensional phase-contrast cerebral MRI.

RESULTS

Compared with subjects with normal spirometry (forced expiratory volume in 1 s (FEV₁)/forced vital capacity (FVC) ≥0.7 and FEV₁ ≥80%), multivariable adjusted cerebral blood flow (mL/min) was preserved in subjects with COPD Global initiative for Chronic Obstructive Lung Disease (GOLD1) (FEV₁/FVC <0.7 and FEV₁ ≥80%), but significantly lower in subjects with COPD GOLD2-3 (FEV₁/FVC <0.7 and FEV₁ <80%), even after adjustment for cardiovascular comorbidities. In sex-stratified analyses, this difference in cerebral blood flow was statistically significant in women but not in men. Cerebral blood flow was lowest in subjects with FEV₁, FVC and diffusion lung capacity for carbon monoxide % predicted values in the lowest quintile, even after adjustment for cardiovascular comorbidities and cardiac function.

CONCLUSION

We observed a lowered cerebral blood flow in subjects with COPD GOLD2-3.

Changes in cerebral arterial pulsatility and hippocampal volume: a transcranial doppler ultrasonography study

The physiological mechanisms of age-related cognitive decline remain unclear, in no small part due to the lack of longitudinal studies. Extant longitudinal studies focused on gross neuroanatomy and diffusion properties of the brain. We present herein a longitudinal analysis of changes in arterial pulsatility - a proxy for arterial stiffness - in two major cerebral arteries, middle cerebral and vertebral. We found that pulsatility increased in some participants over a relatively short period and these increases were associated with hippocampal shrinkage. Higher baseline pulsatility was associated with lower scores on a test of fluid intelligence at follow-up. This is the first longitudinal evidence of an association between increase in cerebral arterial stiffness over time and regional shrinkage.

Comparison of algorithms for estimating blood flow velocities in cerebral arteries based on the transport information of contrast agent: An in silico study

While many algorithms have been proposed to estimate blood flow velocities based on the transport information of contrast agent acquired by digital subtraction angiography (DSA), most relevant studies focused on a single vessel, leaving a question open as to whether the algorithms would be suitable for estimating blood flow velocities in arterial systems with complex topological structures. In this study, a one-dimensional (1-D) modeling method was developed to simulate the transport of contrast agent in cerebral arterial networks with various anatomical variations or having occlusive disease, thereby generating an in silico database for examining the accuracies of some typical algorithms (i.e., time-of-center of gravity (TCG), shifted least-squares (SLS), and cross correlation (CC) algorithms) that estimate blood flow velocity based on the concentration-time curves (CTCs) of contrast agent. The results showed that the TCG algorithm had the best performance in estimating blood flow velocities in most cerebral arteries, with the accuracy being only mildly affected by anatomical variations of the cerebral arterial network. Nevertheless, the presence of a stenosis of moderate to high severity in the internal carotid artery could considerably impair the accuracy of the TCG algorithm in estimating blood flow velocities in some cerebral arteries where the transport of contrast agent was disturbed by strong collateral flows. In summary, the study suggests that the TCG algorithm may offer a promising means for estimating blood flow velocities based on CTCs of contrast agent monitored in cerebral arteries, provided that the shapes of CTCs are not highly distorted by collateral flows.

Seasonality of cognitive function in the general population: the Rotterdam Study

Seasonal variation in cognitive function and underlying cerebral hemodynamics in humans has been suggested, but not consistently shown in previous studies. We assessed cognitive function in 10,276 participants from the population-based Rotterdam Study, aged 45 years and older without dementia, at baseline and at subsequent visits between 1999 and 2016. Seasonality of five cognitive test scores and of a summary measure of global cognition were determined, as well as of brain perfusion. Using linkage with medical records, we also examined whether a seasonal variation was present in clinical diagnoses of dementia. We found a seasonal variation of global cognition (0.05 standard deviations [95% confidence interval: 0.02–0.08]), the Stroop reading task, the Purdue Pegboard test, and of the delayed world learning test, with the best performance in summer months. In line with these findings, there were fewer dementia diagnoses of dementia in spring and summer than in winter and fall. We found no seasonal variation in brain perfusion. These findings support seasonality of cognition, albeit not explained by brain perfusion.

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.

Arterial Spin Labeling Imaging Assessment of Cerebrovascular Reactivity in Hypertensive Small Vessel Disease

Objective: Cerebrovascular reactivity (CVR) represents the phenomenon where cerebral vessels dilate or constrict in response to vasoactive stimuli. CVR impairment may contribute to brain injury due to cerebral small vessel disease (SVD). We aimed to determine the CVR in hypertensive intracerebral hemorrhage (ICH) and to identify its vascular dysfunction.

Methods: A total of 21 patients with spontaneous hypertensive ICH (strictly deep or mixed deep and lobar hemorrhages, mean age 62.5 ± 11.3 years) and 10 control subjects (mean age 66.1 ± 6.0 years) were enrolled for CVR measurement at least 3 months after the symptomatic ICH event. Each participant underwent a brain MRI study, and CVR was calculated as the cerebral blood flow (CBF) reduction using arterial spin labeling (ASL) between baseline and 10 min after an intravenous dipyridamole injection (0.57 mg/kg). Traditional MRI markers for SVD were also evaluated, including cerebral microbleed, white matter hyperintensity, lacune, and MRI-visible enlarged perivascular space, which were used to determine the total small vessel disease score.

Results: Compared to control subjects, hypertensive ICH patients showed reduced CVR in the basal ganglia (CBF reduction 22.4 ± 22.7% vs. 41.7 ± 18.3, p = 0.026), the frontal lobe (15.1 ± 11.9 vs. 26.6 ± 9.9, p = 0.013), and the temporal lobe (14.7 ± 11.1 vs. 26.2 ± 10.0, p = 0.010). These differences remained significant in multivariable models after adjusting for age and sex. Within ICH groups, the CBF reduction in the basal ganglia was significantly correlated with the total small vessel disease score (R = 0.58, p = 0.006), but not with individual MRI markers.

Conclusion: Patients with advanced hypertensive SVD demonstrated impaired vasoconstriction after dipyridamole challenge in the basal ganglia and the frontal and temporal lobes. Our findings provide safe approaches for whole-brain CVR mapping in SVD and identify a potential physiological basis for vascular dysfunction in hypertensive SVD.

Impact of age and cyclooxygenase inhibition on the hemodynamic response to acute cognitive challenges

Structural and functional changes in the cerebral vasculature occur with advancing age, which may lead to impaired neurovascular coupling (NVC) and cognitive decline. Cyclooxygenase (COX) inhibition abolishes age-related differences in cerebrovascular reactivity, but it is unclear if COX inhibition impacts NVC. The purpose of this study was to examine the influence of aging on NVC before and after COX inhibition. Twenty-three young (age = 25 ± 4 yr) and 21 older (age = 64 ± 5 yr) adults completed two levels of difficulty of the Stroop and n-back tests before and after COX inhibition. Middle cerebral artery blood velocity (MCAv) was measured using transcranial Doppler ultrasound and mean arterial blood pressure (MAP) was measured using a finger cuff. Hemodynamic variables were measured at rest and in response to cognitive challenges. During the Stroop test, older adults demonstrated a greater increase in MCAv (young: 2.2 ± 6.8% vs. older: 5.9 ± 5.8%; P = 0.030) and MAP (young: 2.0 ± 4.9% vs. older: 4.8 ± 4.9%; P = 0.036) compared with young adults. There were no age-related differences during the n-back test. COX inhibition reduced MCAv by 30% in young and 26% in older adults (P < 0.001 for both). During COX inhibition, there were no age-related differences in the percent change in MCAv or MAP in response to the cognitive tests. Our results show that older adults require greater increases in MCAv and MAP during a test of executive function compared with young adults and that any age-related differences in NVC were abolished during COX inhibition. Collectively, this suggests that aging is associated with greater NVC necessary to accomplish a cognitive task.

Common Carotid Artery Volume Flow: A Comparison Study between Ultrasound Vector Flow Imaging and Phase Contrast Magnetic Resonance Imaging

Volume flow estimation in the common carotid artery (CCA) can assess the absolute hemodynamic effect of a carotid stenosis. The aim of this study was to compare a commercial vector flow imaging (VFI) setup against the reference method magnetic resonance phase contrast angiography (MRA) for volume flow estimation in the CCA. Ten healthy volunteers were scanned with VFI and MRA over the CCA. VFI had an improved precision of 19.2% compared to MRA of 31.9% (p = 0.061). VFI estimated significantly lower volume flow than MRA (mean difference: 63.2 mL/min, p = 0.017), whilst the correlation between VFI and MRA was strong (R² = 0.81, p < 0.0001). A Bland–Altman plot indicated a systematic bias. After bias correction, the percentage error was reduced from 41.0% to 25.2%. This study indicated that a VFI setup for volume flow estimation is precise and strongly correlated to MRA volume flow estimation, and after correcting for the systematic bias, VFI and MRA become interchangeable.

Reduced parenchymal cerebral blood flow is associated with greater progression of brain atrophy: The SMART-MR study

Global cerebral hypoperfusion may be involved in the aetiology of brain atrophy; however, long-term longitudinal studies on this relationship are lacking. We examined whether reduced cerebral blood flow was associated with greater progression of brain atrophy. Data of 1165 patients (61 ± 10 years) from the SMART-MR study, a prospective cohort study of patients with arterial disease, were used of whom 689 participated after 4 years and 297 again after 12 years. Attrition was substantial. Total brain volume and total cerebral blood flow were obtained from magnetic resonance imaging scans and expressed as brain parenchymal fraction (BPF) and parenchymal cerebral blood flow (pCBF). Mean decrease in BPF per year was 0.22% total intracranial volume (95% CI: -0.23 to -0.21). Mean decrease in pCBF per year was 0.24 ml/min per 100 ml brain volume (95% CI: -0.29 to -0.20). Using linear mixed models, lower pCBF at baseline was associated with a greater decrease in BPF over time (p = 0.01). Lower baseline BPF, however, was not associated with a greater decrease in pCBF (p = 0.43). These findings indicate that reduced cerebral blood flow is associated with greater progression of brain atrophy and provide further support for a role of cerebral blood flow in the process of neurodegeneration.

Intracranial baroreflex is attenuated in an ovine model of renovascular hypertension

We have previously shown that elevations in intracranial pressure (ICP) within physiological ranges in normotensive animals increase arterial pressure; termed the intracranial baroreflex. Hypertension is associated with alterations in reflexes which maintain arterial pressure however, whether the intracranial baroreflex is altered is not known. Hence, in the present study, we tested the hypothesis that in hypertension, physiological increases in ICP would not be accompanied with an increase in arterial pressure. Renovascular hypertension was associated with no change in heart rate, renal blood flow or ICP levels compared to the normotensive group. ICV infusion of saline produced a ramped increase in ICP of 20 ± 1 mmHg. This was accompanied by an increase in arterial pressure (16 ± 2 mmHg) and a significant decrease in renal vascular conductance. ICV infusion of saline in the hypertensive group also increased ICP (19 ± 2 mmHg). However, the increase in arterial pressure was significantly attenuated in the hypertensive group (5 ± 2 mmHg). Ganglionic blockade abolished the increase in arterial pressure in both groups to increased ICP. Our data indicates that physiological increases in ICP lead to increases in arterial pressure in normotensive animals but this is severely attenuated in renovascular hypertension.

Age-related normative changes in cerebral perfusion: Data from The Irish Longitudinal Study on Ageing (TILDA)

OBJECTIVE

To establish normative reference values for total grey matter cerebral blood flow (CBF_GM) measured using pseudo-continuous arterial spin labelling (pCASL) MRI in a large cohort of community-dwelling adults aged 54 years and older.

BACKGROUND

Quantitative assessment of CBF_GM may provide an imaging biomarker for the early detection of those at risk of neurodegenerative diseases, such as Alzheimer's and dementia. However, the use of this method to differentiate normal age-related decline in CBF_GM from pathological reduction has been hampered by the lack of reference values for cerebral perfusion.

METHODS

The study cohort comprised a subset of wave 3 (2014-2015) participants from The Irish Longitudinal Study on Ageing (TILDA), a large-scale prospective cohort study of individuals aged 50 and over. Of 4309 participants attending for health centre assessment, 578 individuals returned for 3T multi-parametric MRI brain examinations. In total, CBF_GM data acquired from 468 subjects using pCASL-MRI were included in this analysis. Normative values were estimated using Generalised Additive Models for Location Shape and Scale (GAMLSS) and are presented as percentiles, means and standard deviations.

RESULTS

The mean age of the cohort was 68.2 ± 6.9 years and 51.7% were female. Mean CBF_GM for the cohort was 36.5 ± 8.2 ml/100 g/min. CBF_GM decreased by 0.2 ml/100 g/min for each year increase in age (95% CI = -0.3, -0.1; p ≤ 0.001) and was 3.1 ml/100 g/min higher in females (95% CI = 1.6, 4.5; p ≤ 0.001).

CONCLUSIONS

This study is by far the largest single-site study focused on an elderly community-dwelling cohort to present normative reference values for CBF_GM measured at 3T using pCASL-MRI. Significant age- and sex-related differences exist in CBF_GM.

The interplay of blood flow and temperature in regional hyperthermia: a mathematical approach

In recent decades, hyperthermia has been used to raise oxygenation levels in tumours undergoing other therapeutic modalities, of which radiotherapy is the most prominent one. It has been hypothesized that oxygenation increases would come from improved blood flow associated with vasodilation. However, no test has determined whether this is a relevant assumption or other mechanisms might be acting. Additionally, since hyperthermia and radiotherapy are not usually co-administered, the crucial question arises as to how temperature and perfusion in tumours will change during and after hyperthermia. Overall, it would seem necessary to find a research framework that clarifies the current knowledge, delimits the scope of the different effects and guides future research. Here, we propose a simple mathematical model to account for temperature and perfusion dynamics in brain tumours subjected to regional hyperthermia. Our results indicate that tumours in well-perfused organs like the brain might only reach therapeutic temperatures if their vasculature is highly disrupted. Furthermore, the characteristic times of return to normal temperature levels are markedly shorter than those required to deliver adjuvant radiotherapy. According to this, a mechanistic coupling of perfusion and temperature would not explain any major oxygenation boost in brain tumours immediately after hyperthermia.

Long-term effects of adjuvant treatment for breast cancer on carotid plaques and brain perfusion

Purpose

Breast cancer treatment has been associated with vascular pathology. It is unclear if such treatment is also associated with long-term cerebrovascular changes. We studied the association between radiotherapy and chemotherapy with carotid pathology and brain perfusion in breast cancer survivors.

Methods

We included 173 breast cancer survivors exposed to radiotherapy and chemotherapy, assessed ± 21.2 years after cancer diagnosis, and 346 age-matched cancer-free women (1:2) selected from the population-based Rotterdam Study. Outcome measures were carotid plaque score, intima-media thickness (IMT), total cerebral blood flow (tCBF), and brain perfusion. Additionally, we investigated the association between inclusion of the carotid artery in the radiation field (no/small/large part), tumor location, and these outcome measures within cancer survivors.

Results

Cancer survivors had lower tCBF (− 19.6 ml/min, 95%CI − 37.3;− 1.9) and brain perfusion (− 2.5 ml/min per 100 ml, 95%CI − 4.3;− 0.7) than cancer-free women. No statistically significant group differences were observed regarding plaque score or IMT. Among cancer survivors, a large versus a small part of the carotid artery in the radiation field was associated with a higher IMT (0.05, 95%CI0.01;0.09). Also, survivors with a right-sided tumor had lower left carotid plaque score (− 0.31, 95%CI − 0.60;− 0.02) and higher brain perfusion (3.5 ml/min per 100 ml, 95%CI 0.7;6.2) than those with a left-sided tumor.

Conclusions

On average two decades post-diagnosis, breast cancer survivors had lower tCBF and brain perfusion than cancer-free women. Also, survivors with a larger area of the carotid artery within the radiation field had a larger IMT. Future studies should confirm if these cerebrovascular changes underlie the frequently observed cognitive problems in cancer survivors.

Relationship between white matter hyperintensities and chronic kidney disease in patients with acute lacunar stroke

BACKGROUND AND PURPOSE

Previous studies have revealed a relationship between chronic kidney disease (CKD) and white matter hyperintensities (WMH). However, studies on the WMH and CKD in acute stroke patients are rare, and the conclusion is consistent. Our study aimed to investigate the relationship between the severity of WMH and CKD in acute lacunar infarction patients.

METHODS

Consecutive acute lacunar infarction patients were recruited in this cross-sectional study. All patients were divided into two groups according to the severity of periventricular WMH (PVWMH) and deep WMH (DWMH). We dichotomized the severity of WMH (PVWMH and DWMH, separately) into mild group (Fazekas scores 0-1) and moderate-severe group (Fazekas scores 2-3). Estimated glomerular filtration rate (eGFR), proteinuria, vascular risk factors, and clinical features were compared between these two groups. Multivariable logistic regression analysis was used to investigate the association between the severity of WMH and risk factors.

RESULTS

A total of 993 acute lacunar infarction patients aged 25-95 years were enrolled. The proportions of participants presenting moderate-severe group PVWMH and DWMH were 46.6% and 38.6%, respectively. Patients with moderate-severe PVWMH had higher age (P < 0.001) and higher incidence of stroke history (P < 0.001) than those in mild group. The level of serum creatinine and the presence of CKD were significantly higher while the eGFR was significantly lower in patients with moderate-severe PVWMH than those with mild PVWMH. Patients with moderate-severe DWMH (n = 383) also had higher age (P < 0.001) and often had a history of stroke (P < 0.001). But the association between the severity of DWMH and eGFR was not found. Multivariable logistic regression analyses showed stage 2 CKD and stage 3 CKD were independently associated with moderate-severe PVWMH, but not DWMH.

CONCLUSIONS

Our study demonstrates that CKD was independently associated with moderate-severe PVWMH in patients with acute lacunar infarction, but not DWMH. PVWMH and DWMH may have distinct pathophysiology.

Carotid Intima-Media Thickness and Markers of Brain Health in a Biracial Middle-Aged Cohort: CARDIA Brain MRI Sub-study

BACKGROUND

We investigated whether carotid intima-media thickness is associated with measures of cerebral blood flow (CBF), white matter hyperintensities, and brain volume in a biracial cohort of middle-aged individuals.

METHODS

We performed a cross-sectional cohort study based on data from a multicenter, population-based study Coronary Artery Risk Development in Young Adults. Using linear and logistic regression, we estimated the association of the composite intima-media thickness measured in three segments of carotid arteries (common carotid artery, carotid artery bulb, and internal carotid artery) with volume (cm3) and CBF (mL/100 g/min) in the total brain and gray matter as well as volume of white matter hyperintensities (cm3).

RESULTS

In the analysis, 461 participants (54% women, 34% African Americans) were included. Greater intima-media thickness was associated with lower CBF in gray matter (β=-1.36; p = .04) and total brain (β=-1.26; p = .04), adjusting for age, sex, race, education, and total brain volume. The associations became statistically nonsignificant after further controlling for cardiovascular risk factors. Intima-media thickness was not associated with volumes of total brain, gray matter, and white matter hyperintensities.

CONCLUSIONS

This study suggests that lower CBF in middle age is associated with markers of atherosclerosis in the carotid arteries. This association may reflect early long-term exposure to traditional cardiovascular risk factors. Early intervention on atherosclerotic risk factors may modulate the trajectory of CBF as people age and develop brain pathology.

Uncontrolled hypertension associates with subclinical cerebrovascular health globally: a multimodal imaging study

OBJECTIVES

The study aimed to analyze the association between hypertension control and subclinical cerebrovascular health using a comprehensive multimodal imaging approach.

METHODS

The study included 200 hypertensive older males without previous cardiovascular diseases. Clinic blood pressure (BP) was measured using a standard approach. Cerebrovascular health was evaluated using magnetic resonance imaging in the following four aspects: Intracranial atherosclerosis as determined by vessel wall imaging; Vascular rarefaction (defined as less discernible vessels on angiography) was evaluated using a custom-developed technique. Cerebral blood flow (CBF) and white matter hyperintensity (WMH) were assessed using arterial spin-labeling imaging and fluid-attenuated inversion recovery imaging, respectively.

RESULTS

A total of 189 subjects had MRI scans. The mean age was 64.9 (± 7.2) years. For intracranial atherosclerosis, there was a significant association between uncontrolled hypertension and presence of intracranial plaque. When systolic and diastolic BP were analyzed separately, the association remained significant for both. For vascular rarefaction, uncontrolled hypertension was associated with less discernible vessel branches or shorter vessel length on angiography. Further analysis revealed that this is due to uncontrolled diastolic BP, but not uncontrolled systolic BP. There was an association between uncontrolled hypertension and reduced CBF, which was also mainly driven by uncontrolled diastolic BP. We also found that uncontrolled diastolic BP, but not uncontrolled systolic BP, was associated with increased WMH volume.

CONCLUSIONS

Uncontrolled hypertension was associated with subclinical cerebrovascular injury globally, with both small and medium-to-large arteries being affected.

KEY POINTS

• In this study, we leveraged the advantage of a series of cutting-edge MR imaging and analysis techniques and found uncontrolled hypertension is associated with subclinical globally compromised cerebrovascular health. • The detrimental consequences of uncontrolled BP affect not only the small vessels but also the medium-to-large arteries, and uncontrolled systolic and diastolic BP are both independently associated with certain types of cerebrovascular injury. • Our data suggest that cerebrovascular health is impaired globally in uncontrolled hypertension before the onset of stroke.

Role of deep medullary veins in pathogenesis of lacunes: Longitudinal observations from the CIRCLE study

Our purpose is to assess the role of deep medullary veins in pathogenesis of lacunes in patients with cerebral small vessel disease (cSVD). We included patients with baseline and 2.5-year follow-up MRI in CIRCLE study. Susceptibility Weighted Imaging-Phase images were used to evaluate deep medullary veins based on a brain region-based visual score, and T2-Fluid-Attenuated-Inversion-Recovery images were used to evaluate lacunes. Cerebral blood flow and microstructural parameters in white matter hyperintensities and normal appearing white matter were also analyzed. A total of 203 cSVD patients were analyzed and 101 (49.8%) patients had baseline lacunes. Among them, 64 patients had follow-up MRI, including 16 (25.0%) with new lacunes. The patients' deep medullary veins median score was 9 (7-12). At baseline, high deep medullary veins score was independently associated with the presence of lacunes after adjusting for age, diabetes mellitus, white matter hyperintensities volume and cerebral blood flow or white matter microstructural parameters (all p < 0.001). Longitudinally, high deep medullary veins score was independently associated with new lacunes after adjusting for gender (p < 0.001). The association was also independent of white matter hyperintensities volumes, cerebral blood flow or white matter microstructural parameters (all p < 0.05). Our results suggest that deep medullary veins disruption might be involved in pathogenesis of lacunes.

Designing and comparing optimized pseudo-continuous Arterial Spin Labeling protocols for measurement of cerebral blood flow

Arterial Spin Labeling (ASL) is a non-invasive, non-contrast, perfusion imaging technique which is inherently SNR limited. It is, therefore, important to carefully design scan protocols to ensure accurate measurements. Many pseudo-continuous ASL (PCASL) protocol designs have been proposed for measuring cerebral blood flow (CBF), but it has not yet been demonstrated which design offers the most accurate and repeatable CBF measurements. In this study, a wide range of literature PCASL protocols were first optimized for CBF accuracy and then compared using Monte Carlo simulations and in vivo experiments. The protocols included single-delay, sequential and time-encoded multi-timepoint protocols, and several novel protocol designs, which are hybrids of time-encoded and sequential multi-timepoint protocols. It was found that several multi-timepoint protocols produced more confident, accurate, and repeatable CBF estimates than the single-delay protocol, while also generating maps of arterial transit time. Of the literature protocols, the time-encoded protocol with T₁-adjusted label durations gave the most confident and accurate CBF estimates in vivo (16% and 40% better than single-delay), while the sequential multi-timepoint protocol was the most repeatable (20% more repeatable than single-delay). One of the novel hybrid protocols, Hybrid_T1-adj, was found to produce the most confident, accurate and repeatable CBF estimates out of all the protocols tested in both simulations and in vivo (24%, 47%, and 28% more confident, accurate, and repeatable than single-delay in vivo). The Hybrid_T1-adj protocol makes use of the best aspects of both time-encoded and sequential multi-timepoint protocols and should be a useful tool for accurately and efficiently measuring CBF.

Intracranial Large Artery Abnormalities and Association With Cerebral Small Vessel Disease in CADASIL

Background and objective: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited systemic arteriopathy, the classic feature of which is small vessel lesions. Studies on intracranial large arteries in CADASIL are not common. We aim to evaluate intracranial large arteries, describing the characteristics of large arteries in CADASIL and their association with cerebral small vessel associated lesions.

Methods: Consecutive CADASIL patients from a single-center prospective cohort were analyzed. Brain magnetic resonance imaging and magnetic resonance angiography were performed to assess the intracranial large arteries and cerebral small vessels associated lesions' neuroimaging.

Results: The study included 37 CADASIL patients. Of the patients, 28 of them (75.7%) had intracranial large artery abnormalities. Eighteen (48.6%) had congenital variations such as fenestration, vertebral artery (VA) hypoplasia and agenesis, or common trunk and fetus posterior cerebral artery. Seventeen (45.9%) had acquired anomalies such as arterial stenosis, prolongation, or tortuosity (seven of them had both congenital and acquired anomalies). CADASIL patients with anterior circulation middle cerebral artery (MCA) or internal cerebral artery (ICA) severe stenosis were more likely to have ipsilateral asymmetric white matter hyper-density (WMH) distribution. Patients with posterior circulation VA hypoplasia had a higher prevalence of posterior subcortical zone dominant WMH distribution.

Conclusion: CADASIL patients can demonstrate various intracranial large artery abnormalities which might influence the development of microangiopathy. Assessment of great vessels seems essential in CADASIL.

Global Brain Perfusion and the Risk of Transient Ischemic Attack and Ischemic Stroke: The Rotterdam Study

Background

The role of subtle disturbances of brain perfusion in the risk of transient ischemic attack (TIA) or ischemic stroke remains unknown. We examined the association between global brain perfusion and risk of TIA and ischemic stroke in the general population.

Methods and Results

Between 2005 and 2015, 5289 stroke‐free participants (mean age, 64.3 years; 55.6% women) from the Rotterdam Study underwent phase‐contrast brain magnetic resonance imaging at baseline to assess global brain perfusion. These participants were followed for incident TIA or ischemic stroke until January 1, 2016. We investigated associations between global brain perfusion (mL of blood flow/100 mL of brain/min) and risk of TIA and ischemic stroke using Cox regression models with adjustment for age, sex, and cardiovascular risk factors. Additionally, we investigated whether associations were modified by retinal vessel calibers, small and large vessel disease, blood pressure, and heart rate. During a median follow‐up of 7.2 years (36 103 person‐years), 137 participants suffered a TIA and another 108 an ischemic stroke. We found that lower global brain perfusion was associated with a higher risk of TIA, but not with the risk of ischemic stroke (adjusted hazard ratio, 95% CI, per standard deviation decrease of global brain perfusion: 1.29, 1.07–1.55 for TIA and adjusted hazard ratio of 1.06, 0.87–1.30 for ischemic stroke). Across strata of wider arteriolar retinal calibers, lower brain perfusion was more prominently associated with TIA, but not with ischemic stroke.

Conclusions

In a community‐dwelling population, impaired global brain perfusion increased the risk of TIA, but not of ischemic stroke.

Alterations of the Whole Cerebral Blood Flow in Patients With Different Total Cerebral Small Vessel Disease Burden

Background

Cerebral small vessel disease (CSVD) is a common age-related vascular disease of the brain associated with slowly accumulating tissue damage. At present, total CSVD burden score is a commonly used method to evaluate the severity of the disease.

Purpose

To observe whether global and regional cerebral perfusion is related to total CSVD score and to explore global and regional cerebral blood flow (CBF) changes in patients with different degrees of CSVD.

Methods

We collected 130 subjects with different total burden score of CSVD (0 point: 33 subjects, 1 point: 39 subjects, 2 points: 24 subjects, 3 points: 24 subjects, 4 points: 10 subjects). Total CSVD burden score was evaluated by clinically routine sequences (T2WI, T2-FLAIR, T1WI, DWI, and SWAN sequence). Global and regional CBF were calculated and correlation analysis was used to investigate the relationship between total CSVD score and CBF of the whole brain and several brain regions.

Results

The analysis results showed that there was a negative correlation between total CSVD burden score and global CBF (r = −0.33, p = 0.001). Total CSVD burden score also had moderately negative correlations with CBF of almost all the brain regions.

Conclusion

CSVD is a disease that affects the whole brain. With the increase of total CSVD burden score, the global and regional CBF decreased. The CSVD total burden score could be used to evaluate the overall condition of brain perfusion.

Hemodynamic Significance of Middle Cerebral Artery Stenosis Associated With the Severity of Ipsilateral White Matter Changes

Background: Previous studies conflicted in the association between intracranial atherosclerotic stenosis (ICAS) and the severity of white matter changes (WMC).

Aims: We aimed to investigate the relationships between the severity of luminal stenosis and the hemodynamic significance of middle cerebral artery (MCA) stenosis, and the severity of ipsilateral WMC.

Methods: In this cross-sectional study, patients with a recent ischemic stroke or transient ischemic attack and a 50–99% MCA-M1 stenosis in the Chinese Intracranial Atherosclerosis study cohort were analyzed. The post- to pre-stenotic signal intensity ratio (SIR) was obtained in time-of-flight MR angiography (MRA) to represent the hemodynamic significance of MCA-M1 stenosis, with a lower SIR indicating a hemodynamically more severe lesion. The severity of ipsilesional WMC was assessed by an age-related WMC (ARWMC) scale in T2-weighted fluid attenuated inversion recovery MR imaging. The relationships between the degree of MCA-M1 stenosis, SIR, and ipsilesional ARWMC scale were analyzed. The MCA-M1 lesion with a higher percentage of stenosis was chosen for analyses in patients with bilateral MCA-M1 stenoses.

Results: Among 180 subjects (mean age, 64 years), a lower SIR of MCA-M1 stenosis (Spearman correlation coefficient, −0.543; p < 0.001), but not the degree of stenosis (p = 0.93), was significantly linearly correlated with a higher ipsilateral ARWMC. Multivariate ordinal logistic regression identified older age (OR = 1.037; 95% CI, 1.008–1.066; p = 0.011) and lower SIR (OR = 0.010; 95% CI, 0.002–0.058; p < 0.001) as independent predictors for more severe ipsilateral WMC.

Conclusion: Patients with hemodynamically more severe ICAS are more likely to have more severe ipsilateral WMC. Longitudinal studies with sequential imaging exams may further reveal the impact of hemodynamic significance of ICAS on the development and progression of WMC.

Memory impairment in spontaneously hypertensive rats is associated with hippocampal hypoperfusion and hippocampal vascular dysfunction

We investigated the effect of chronic hypertension on hippocampal arterioles (HippAs) and hippocampal perfusion as underlying mechanisms of memory impairment, and how large artery stiffness relates to HippA remodeling. Using male spontaneously hypertensive rats (SHR) and normotensive Wistar rats (n = 12/group), long-term (LTM) and spatial memory were tested using object recognition and spontaneous alternation tasks. Hippocampal blood flow was measured via hydrogen clearance basally and during hypercapnia. Reactivity of isolated and pressurized HippAs to pressure and pharmacological activators and inhibitors was investigated. To determine large artery stiffness, distensibility and elastin content were measured in thoracic aorta. SHR had impaired LTM and spatial memory associated with decreased basal blood flow (68 ± 12 mL/100 g/min) vs. Wistar (111 ± 28 mL/100 g/min, p < 0.01) that increased during hypercapnia similarly between groups. Compared to Wistar, HippAs from SHR had increased tone at 60 mmHg (58 ± 9% vs. 37 ± 7%, p < 0.01), and decreased reactivity to small- and intermediate-conductance calcium-activated potassium (SK/IK) channel activation. HippAs in both groups were unaffected by NOS inhibition. Decreased elastin content correlated with increased stiffness in aorta of SHR that was associated with increased stiffness and hypertrophic remodeling of HippAs. Hippocampal vascular dysfunction during hypertension could potentiate memory deficits and may provide a therapeutic target to limit vascular cognitive impairment.

Predicting Global Cognitive Decline in the General Population Using the Disease State Index

Background

Identifying persons at risk for cognitive decline may aid in early detection of persons at risk of dementia and to select those that would benefit most from therapeutic or preventive measures for dementia.

Objective

In this study we aimed to validate whether cognitive decline in the general population can be predicted with multivariate data using a previously proposed supervised classification method: Disease State Index (DSI).

Methods

We included 2,542 participants, non-demented and without mild cognitive impairment at baseline, from the population-based Rotterdam Study (mean age 60.9 ± 9.1 years). Participants with significant global cognitive decline were defined as the 5% of participants with the largest cognitive decline per year. We trained DSI to predict occurrence of significant global cognitive decline using a large variety of baseline features, including magnetic resonance imaging (MRI) features, cardiovascular risk factors, APOE-ε4 allele carriership, gait features, education, and baseline cognitive function as predictors. The prediction performance was assessed as area under the receiver operating characteristic curve (AUC), using 500 repetitions of 2-fold cross-validation experiments, in which (a randomly selected) half of the data was used for training and the other half for testing.

Results

A mean AUC (95% confidence interval) for DSI prediction was 0.78 (0.77–0.79) using only age as input feature. When using all available features, a mean AUC of 0.77 (0.75–0.78) was obtained. Without age, and with age-corrected features and feature selection on MRI features, a mean AUC of 0.70 (0.63–0.76) was obtained, showing the potential of other features besides age.

Conclusion

The best performance in the prediction of global cognitive decline in the general population by DSI was obtained using only age as input feature. Other features showed potential, but did not improve prediction. Future studies should evaluate whether the performance could be improved by new features, e.g., longitudinal features, and other prediction methods.

Higher physiological vulnerability to hypoxic exposure with advancing age in the human brain

The aging brain is associated with atrophy along with functional and metabolic changes. In this study, we examined age-related changes in resting brain functions and the vulnerability of brain physiology to hypoxic exposure in humans in vivo. Brain functions were examined in 81 healthy humans (aged 18-62 years) by acquisitions of gray and white matter volumes, cerebral blood flow, cerebral oxygen consumption, and concentrations of lactate, N-acetylaspartate, and glutamate+glutamine using magnetic resonance imaging and spectroscopy. We observed impaired cerebral blood flow reactivity in response to inhalation of hypoxic air (p = 0.029) with advancing age along with decreased cerebral oxygen consumption (p = 0.036), and increased lactate concentration (p = 0.009), indicating tissue hypoxia and impaired metabolism. Diminished resilience to hypoxia and consequently increased vulnerability to metabolic stress could be a key part of declining brain health with age. Furthermore, we observed increased resting cerebral lactate concentration with advancing age (p = 0.007), which might reflect inhibited brain clearance of waste products.

Small vessel disease is associated with altered cerebrovascular pulsatility but not resting cerebral blood flow

Cerebral small vessel disease (SVD) contributes to 25% of ischemic strokes and 45% of dementias. We aimed to investigate the role of cerebral blood flow (CBF) and intracranial pulsatility in SVD. We scanned 60 patients with minor ischemic stroke, representing a range of white matter hyperintensities (WMH). We rated WMH and perivascular spaces (PVS) using semi-quantitative scales and measured WMH volume. We measured flow and pulsatility in the main cerebral vessels and cerebrospinal fluid (CSF) using phase-contrast MRI. We investigated the association between flow, pulsatility and SVD features. In 56/60 patients (40 male, 67.8±8.3 years) with complete data, median WMH volume was 10.7 mL (range 1.4-75.0 mL), representing median 0.77% (0.11-5.17%) of intracranial volume. Greater pulsatility index (PI) in venous sinuses was associated with larger WMH volume (e.g. superior sagittal sinus, β = 1.29, P < 0.01) and more basal ganglia PVS (e.g. odds ratio = 1.38, 95% confidence interval 1.06, 1.79, per 0.1 increase in superior sagittal sinus PI) independently of age, sex and blood pressure. CSF pulsatility and CBF were not associated with SVD features. Our results support a close association of SVD features with increased intracranial pulsatility rather than with low global CBF, and provide potential targets for mechanistic research, treatment and prevention of SVD.

Phase contrast mapping MRI measurements of global cerebral blood flow across different perfusion states - A direct comparison with 15O-H2O positron emission tomography using a hybrid PET/MR system

Phase-contrast mapping (PCM) magnetic resonance imaging (MRI) provides easy-access non-invasive quantification of global cerebral blood flow (gCBF) but its accuracy in altered perfusion states is not established. We aimed to compare paired PCM MRI and 15O-H2O positron emission tomography (PET) measurements of gCBF in different perfusion states in a single scanning session. Duplicate combined gCBF PCM-MRI and 15O-H2O PET measurements were performed in the resting condition, during hyperventilation and after acetazolamide administration (post-ACZ) using a 3T hybrid PET/MR system. A total of 62 paired gCBF measurements were acquired in 14 healthy young male volunteers. Average gCBF in resting state measured by PCM-MRI and 15O-H2O PET were 58.5 ± 10.7 and 38.6 ± 5.7 mL/100 g/min, respectively, during hyperventilation 33 ± 8.6 and 24.7 ± 5.8 mL/100 g/min, respectively, and post-ACZ 89.6 ± 27.1 and 57.3 ± 9.6 mL/100 g/min, respectively. On average, gCBF measured by PCM-MRI was 49% higher compared to 15O-H2O PET. A strong correlation between the two methods across all states was observed (R2 = 0.72, p < 0.001). Bland-Altman analysis suggested a perfusion dependent relative bias resulting in higher relative difference at higher CBF values. In conclusion, measurements of gCBF by PCM-MRI in healthy volunteers show a strong correlation with 15O-H2O PET, but are associated with a large and non-linear perfusion-dependent difference.

Migraine Genetic Variants Influence Cerebral Blood Flow

Objective

To investigate the association of migraine genetic variants with cerebral blood flow (CBF).

Background

Migraine is a common disorder with many genetic and non‐genetic factors affecting its occurrence. The exact pathophysiological mechanisms underlying the disease remain unclear, but are known to involve hemodynamic and vascular disruptions. Recent genome‐wide association studies have identified 44 genetic variants in 38 genetic loci that affect the risk of migraine, which provide the opportunity to further disentangle these mechanisms.

Methods

We included 4665 participants of the population‐based Rotterdam Study (mean age 65.0 ± 10.9 years, 55.6% women). Cross‐sectional area (mm²), flow velocity (mm/s), and blood flow (mL/min) were measured in both carotids and the basilar artery using 2‐dimensional phase‐contrast magnetic resonance imaging. We analyzed 43 previously identified migraine variants separately and calculated a genetic risk score (GRS). To assess the association with CBF, we used linear regression models adjusted for age, sex, and total brain volume. Hierarchical clustering was performed based on the associations with CBF measures and tissue enrichment.

Results

The rs67338227 risk allele was associated with higher flow velocity and smaller cross‐sectional area in the carotids (P_minimum = 3.7 × 10⁻⁸). Other variants were related to CBF with opposite directions of effect, but not significantly after multiple testing adjustments (P < 1.4 × 10⁻⁴). The migraine GRS was not associated with CBF after multiple testing corrections. Migraine risk variants were found to be enriched for flow in the basilar artery (λ = 2.39).

Conclusions

These findings show that genetic migraine risk is complexly associated with alterations in cerebral hemodynamics.

Brain Volumes and Longitudinal Cognitive Change: A Population-based Study

OBJECTIVE

To investigate the association of brain volumes, white matter lesion (WML) volumes, and lacunes, with cognitive decline in a population-based cohort of nondemented persons.

METHODS

Within the Rotterdam Study, 3624 participants underwent brain magnetic resonance imaging. Cognition was evaluated at baseline (2005 to 2009) and at the follow-up visit (2011 to 2013). We used a test battery that tapped into domains of executive function, information processing speed, motor speed, and memory. The volumetric measures assessed were total brain volume, lobar (gray matter and white matter) volumes, and hippocampal volumes. We also studied the association of WML volumes and lacunes with cognitive decline using linear regression models.

RESULTS

Total brain volume was associated with decline in global cognition, information processing, and motor speed (P<0.001) in analyses controlled for demographic and vascular factors. Specifically, smaller frontal and parietal lobes were associated with decline in information processing and motor speed, and smaller temporal and parietal lobes were associated with decline in general cognition and motor speed (P<0.001 for all tests). Total WML volume was associated with decline in executive function. Lobar WML volume, hippocampal volume, and lacunes were not associated with cognitive decline.

CONCLUSIONS

Lower brain volume is associated with subsequent cognitive decline. Although lower total brain volume was significantly associated with decline in global cognition, specific lobar volumes were associated with decline in certain cognitive domains.

Hemoglobin and anemia in relation to dementia risk and accompanying changes on brain MRI

Objective

To determine the long-term association of hemoglobin levels and anemia with risk of dementia, and explore underlying substrates on brain MRI in the general population.

Methods

Serum hemoglobin was measured in 12,305 participants without dementia of the population-based Rotterdam Study (mean age 64.6 years, 57.7% women). We determined risk of dementia and Alzheimer disease (AD) (until 2016) in relation to hemoglobin and anemia. Among 5,267 participants without dementia with brain MRI, we assessed hemoglobin in relation to vascular brain disease, structural connectivity, and global cerebral perfusion.

Results

During a mean follow-up of 12.1 years, 1,520 individuals developed dementia, 1,194 of whom had AD. We observed a U-shaped association between hemoglobin levels and dementia (p = 0.005), such that both low and high hemoglobin levels were associated with increased dementia risk (hazard ratio [95% confidence interval (CI)], lowest vs middle quintile 1.29 [1.09–1.52]; highest vs middle quintile 1.20 [1.00–1.44]). Overall prevalence of anemia was 6.1%, and anemia was associated with a 34% increased risk of dementia (95% CI 11%–62%) and 41% (15%–74%) for AD. Among individuals without dementia with brain MRI, similar U-shaped associations were seen of hemoglobin with white matter hyperintensity volume (p = 0.03), and structural connectivity (for mean diffusivity, p < 0.0001), but not with presence of cortical and lacunar infarcts. Cerebral microbleeds were more common with anemia. Hemoglobin levels inversely correlated to cerebral perfusion (p < 0.0001).

Conclusion

Low and high levels of hemoglobin are associated with an increased risk of dementia, including AD, which may relate to differences in white matter integrity and cerebral perfusion.

Characterizing a perfusion-based periventricular small vessel region of interest

The periventricular white matter (PVWM) is supplied by terminal distributions of small vessels and is particularly susceptible to developing white matter lesions (WML) associated with cerebral small vessel disease (CSVD). We obtained group-averaged cerebral blood flow (CBF) maps from Arterial Spin Labeled (ASL) perfusion MRI data obtained in 436 middle-aged (50.4 ± 3.5 years) subjects in the NHLBI CARDIA study and in 61 elderly (73.3 ± 6.9 years) cognitively normal subjects recruited from the Penn Alzheimer's Disease Center (ADC) and found that the lowest perfused brain voxels are located within the PVWM. We constructed a white matter periventricular small vessel (PSV) region of interest (ROI) by empirically thresholding the group averaged CARDIA CBF map at CBF < 15 ml/100 g/min. Thereafter we compared CBF in the PSV ROI and in the remaining white matter (RWM) with the location and volume of WML measured with Fluid Attenuated Inversion Recovery (FLAIR) MRI. WM CBF was lower within WML than outside WML voxels (p < <0.0001) in both the PSV and RWM ROIs, however this difference was much smaller (p < <0.0001) in the PSV ROI than in the RWM suggesting a more homogenous reduction of CBF in the PSV region. Normalized WML volumes were significantly higher in the PSV ROI than in the RWM and in the elderly cohort as compared to the middle-aged cohort (p < <0.0001). Additionally, the PSV ROI showed a significantly (p = .001) greater increase in lesion volume than the RWM in the elderly ADC cohort than the younger CARDIA cohort. Considerable intersubject variability in PSV CBF observed in both study cohorts likely represents biological variability that may be predictive of future WML and/or cognitive decline. In conclusion, a data-driven PSV ROI defined by voxels with low perfusion in middle age defines a region with homogeneously reduced CBF that is particularly susceptible to progressive ischemic injury in elderly controls. PSV CBF may provide a mechanistically specific biomarker of CSVD.

Different Relationship Between Systolic Blood Pressure and Cerebral Perfusion in Subjects With and Without Hypertension

Although there is an increasing agreement that hypertension is associated with cerebrovascular compromise, relationships between blood pressure (BP) and cerebral blood flow are not fully understood. It is not known what BP level, and consequently what therapeutic goal, is optimal for brain perfusion. Moreover, there is limited data on how BP affects hippocampal perfusion, a structure critically involved in memory. We conducted a cross-sectional (n=445) and longitudinal (n=185) study of adults and elderly without dementia or clinically apparent stroke, who underwent clinical examination and brain perfusion assessment (age 69.2±7.5 years, 62% women, 45% hypertensive). Linear models were used to test baseline BP-blood flow relationship and to examine how changes in BP influence changes in perfusion. In the entire group, systolic BP (SBP) was negatively related to cortical (β=-0.13, P=0.005) and hippocampal blood flow (β=-0.12, P=0.01). Notably, this negative relationship was apparent already in subjects without hypertension. Hypertensive subjects showed a quadratic relationship between SBP and hippocampal blood flow (β=-1.55, P=0.03): Perfusion was the highest in subjects with mid-range SBP around 125 mm Hg. Longitudinally, in hypertensive subjects perfusion increased with increased SBP at low baseline SBP but increased with decreased SBP at high baseline SBP. Cortical and hippocampal perfusion decrease with increasing SBP across the entire BP spectrum. However, in hypertension, there seems to be a window of mid-range SBP which maximizes perfusion.

Cerebral blood flow in bipolar disorder: A systematic review

BACKGROUND

Neuroimaging of cerebral blood flow (CBF) can inform our understanding of the pathophysiology of bipolar disorder (BD) as there is increasing support for the concept that BD is in part a vascular disease. Despite numerous studies examining CBF in BD, there has not yet been a review of the literature on the topic of CBF in BD.

METHODS

A systematic review of the literature on CBF in BD was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Studies included measured CBF by single-photon emission computerized tomography (SPECT), positron emission tomography (PET), arterial spin labelling (ASL) or perfusion weighted imaging (PWI) in a group of BD patients.

RESULTS

Thirty-three studies with a total of 508 subjects with BD and 538 controls were included (n = 15 SPECT; n = 8 PET; n = 7 ASL; n = 1 PWI; n = 2 other). The majority of studies in BD depression and mania reported widespread resting hypoperfusion in cingulate gyrus, frontal, and anterior temporal regions in comparison to healthy controls (HC). Findings in euthymic BD subjects and in symptomatically heterogeneous groups were less consistent. Studies that examined CBF responses to cognitive or emotional stimuli in BD subjects have reported hypoperfusion or different regions involved in comparison to HC.

LIMITATIONS

Important methodological heterogeneity between studies, and small number of subjects per study.

CONCLUSIONS

The most consistent findings to date are hypoperfusion in BD mood episodes, and hypoactive CBF responses to emotional or cognitive challenges. Future studies examining CBF are warranted, including prospective studies, studies examining CBF as a treatment target, and multimodal imaging studies.