Arterial Spin Labeling MRI Research Articles

Association between white matter hyperintensities and altered cerebral blood flow in maintenance hemodialysis patients: a longitudinal study

ObjectivesTo explore changes in cerebral blood flow (CBF) and white matter in hemodialysis patients.MethodsThirty-three hemodialysis patients who underwent two brain MRI at an interval of three years and 33 age- and sex-matched healthy controls (HC) underwent structural and arterial spin-labeling MRI examinations. Intergroup differences in CBF in the gray matter, white matter, and whole matter, and regional white matter hyperintensities (WMH) were analyzed. Based on the changes in CBF between the baseline and follow-up groups, the hemodialysis patients were divided into two subgroups: an increased CBF group and a decreased CBF group. Differences in CBF and WMH between the subgroups and HC were analyzed.ResultsPatients undergoing hemodialysis exhibited increased cerebral watershed (CW) WMH, deep WMH, and periventricular WMH (P < 0.01). The CBF of patients with decreased CBF was higher than that of HC at baseline (,P < 0.01) and lower than that of HC at follow-up (P < 0.01). Compared with the increased CBF group, obvious development of deep WMH was found in the decreased CBF group for the gray matter, white matter, and whole matter (P < 0.01).ConclusionsWMH in hemodialysis patients were distributed in the deep white matter, periventricular white matter and CW, and progressed with the extension of hemodialysis duration. CBF in hemodialysis patients could manifest as both increased and decreased, and WMH in patients with decreased CBF developed severely with prolongation of hemodialysis duration.Advances in knowledgeThese findings provide a basis for exploring neuropathological changes of hemodialysis patients.

Feasibility of high-resolution perfusion imaging using arterial spin labeling MRI at 3 Tesla.

Cerebral blood flow (CBF) is a critical physiological parameter of brain health, and it can be non-invasively measured with arterial spin labeling (ASL) MRI. In this study, we evaluated and optimized whole-brain, high-resolution ASL as an alternative to the low-resolution ASL employed in the routine assessment of CBF in both healthy participants and patients. Two high-resolution protocols (i.e., pCASL and FAIR-Q2TIPS (PASL) with 2 mm isotropic voxels) were compared to a default clinical pCASL protocol (3.4 × 3.4 × 4 mm 3), all of whom had an acquisition time of ≈ 5 min. We assessed the impact of high-resolution acquisition on reducing partial voluming and improving sensitivity to the perfusion signal, and evaluated the effectiveness of z-deblurring on the ASL data. We compared the quality of whole-brain ASL acquired using three available head coils with differing number of receive channels (i.e., 20, 32, and 64ch). We found that using higher coil counts (32 and 64ch coils as compared to 20ch) offers improved signal-to-noise ratio (SNR) and acceleration capabilities that are beneficial for ASL imaging at 3 Tesla (3 T). The inherent reduction in partial voluming effects with higher resolution acquisitions improves the resolving power of perfusion without impacting the sensitivity. In conclusion, our results suggest that high-resolution ASL (2 to 2.5 mm isotropic voxels) has the potential to become a new standard for perfusion imaging at 3 T and increase its adoption into clinical research and cognitive neuroscience applications.

T1 mapping combined with arterial spin labeling MRI to identify renal injury in patients with liver cirrhosis.

We investigated the capability and imaging criteria of T1 mapping and arterial spin labeling (ASL) MRI to identify renal injury in patients with liver cirrhosis. We recruited 27 patients with cirrhosis and normal renal function (cirrhosis-NR), 10 with cirrhosis and renal dysfunction (cirrhosis-RD) and 23 normal controls (NCs). All participants were examined via renal T1 mapping and ASL imaging. Renal blood flow (RBF) derived from ASL was measured from the renal cortex, and T1 values were measured from the renal parenchyma (cortex and medulla). MRI parameters were compared between groups. Diagnostic performances for detecting renal impairment were statistically analyzed. Cortical T1 (cT1) and medullary T1 (mT1) were significantly lower in the NCs than in the cirrhosis-NR group. The cortical RBF showed no significant changes between the NCs and cirrhosis-NR group but was markedly decreased in the cirrhosis-RD group. The areas under the curve (AUCs) for discriminating cirrhosis-NR from NCs were 0.883 and 0.826 by cT1 and mT1, respectively. Cortical RBF identified cirrhosis-RD with AUC of 0.978, and correlated with serum creatinine (r = -0.334) and the estimated glomerular filtration rate (r = 0.483). A classification and regression tree based on cortical RBF and cT1 achieved 85% accuracy in detecting renal impairment in the cirrhosis. Renal T1 values might be sensitive predictors of early renal impairment in patients with cirrhosis-NR. RBF enabled quantifying renal perfusion impairment in patients with cirrhosis-RD. The diagnostic algorithm based on cortical RBF and T1 values allowed detecting renal injury during cirrhosis.

Effect of a four-week oral Phe administration on neural activation and cerebral blood flow in adults with early-treated phenylketonuria

BackgroundPhenylketonuria (PKU) is a rare inborn error of metabolism characterized by impaired catabolism of the amino acid phenylalanine (Phe) into tyrosine. Cross-sectional studies suggest slight alterations in cognitive performance and neural activation in adults with early-treated PKU. The influence of high Phe levels on brain function in adulthood, however, remains insufficiently studied. Therefore, we aimed to explore the effect of a four-week period of oral Phe administration − simulating a controlled discontinuation of Phe restriction and raising Phe to an off-diet scenario − on working memory-related neural activation and cerebral blood flow (CBF). MethodsWe conducted a randomized, placebo-controlled, double-blind, crossover, non-inferiority trial to assess the effect of a high Phe load on working memory-related neural activation and CBF in early-treated adults with classical PKU. Twenty-seven patients with early-treated classical PKU were included and underwent functional magnetic resonance imaging (fMRI) of the working memory network and arterial spin labeling (ASL) MRI to assess CBF before and after a four-week intervention with Phe and placebo. At each of the four study visits, fMRI working memory task performance (reaction time and accuracy) and plasma Phe, tyrosine, and tryptophan levels were obtained. Additionally, cerebral Phe was determined by 1H-MR spectroscopy. ResultsPlasma Phe and cerebral Phe were significantly increased after the Phe intervention. However, no significant effect of Phe compared to placebo was found on neural activation and CBF. Regarding fMRI task performance, a significant impact of the Phe intervention on 1-back reaction time was observed with slower reaction times following the Phe intervention, whereas 3-back reaction time and accuracy did not differ following the Phe intervention compared to the placebo intervention. ConclusionResults from this present trial simulating a four-week discontinuation of the Phe-restricted diet showed that a high Phe load did not uniformly affect neural markers and cognition in a statistically significant manner. These results further contribute to the discussion on safe Phe levels during adulthood and suggest that a four-week discontinuation of Phe-restricted diet does not demonstrate significant changes in brain function.

Diffuse glioma molecular profiling with arterial spin labeling and dynamic susceptibility contrast perfusion MRI: A comparative study.

Evaluation of molecular markers (IDH, pTERT, 1p/19q codeletion, and MGMT) in adult diffuse gliomas is crucial for accurate diagnosis and optimal treatment planning. Dynamic Susceptibility Contrast (DSC) and Arterial Spin Labeling (ASL) perfusion MRI techniques have both shown good performance in classifying molecular markers, however, their performance has not been compared side-by-side. Pretreatment MRI data from 90 patients diagnosed with diffuse glioma (54 men/36 female, 53.1±15.5 years, grades 2-4) were retrospectively analyzed. DSC-derived normalized cerebral blood flow/volume (nCBF/nCBV) and ASL-derived nCBF in tumor and perifocal edema were analyzed in patients with available IDH-mutation (n = 67), pTERT-mutation (n = 39), 1p/19q codeletion (n = 33), and MGMT promoter methylation (n = 31) status. Cross-validated uni- and multivariate logistic regression models assessed perfusion parameters' performance in molecular marker detection. ASL and DSC perfusion parameters in tumor and edema distinguished IDH-wildtype (wt) and pTERT-wt tumors from mutated ones. Univariate classification performance was comparable for ASL-nCBF and DSC-nCBV in IDH (maximum AUROCC 0.82 and 0.83, respectively) and pTERT (maximum AUROCC 0.70 and 0.81, respectively) status differentiation. The multivariate approach improved IDH (DSC-nCBV AUROCC 0.89) and pTERT (ASL-nCBF AUROCC 0.8 and DSC-nCBV AUROCC 0.86) classification. However, ASL and DSC parameters could not differentiate 1p/19q codeletion or MGMT promoter methylation status. Positive correlations were found between ASL-nCBF and DSC-nCBV/-nCBF in tumor and edema. ASL is a viable gadolinium-free replacement for DSC for molecular characterization of adult diffuse gliomas.

Role of Histogram Features on Arterial Spin Labeling Perfusion Magnetic Resonance Imaging in Identifying Isocitrate Dehydrogenase Genotypes and Glioma Malignancies.

To explore the use of histogram features on noninvasive arterial spin labeling (ASL) perfusion magnetic resonance imaging (MRI) in differentiating isocitrate dehydrogenase mutant-type (IDH-mut) from isocitrate dehydrogenase wild-type (IDH-wt) gliomas, and lower-grade gliomas (LGGs) from glioblastomas. This retrospective study included 131 patients who underwent ASL MRI and anatomic MRI. Cerebral blood flow (CBF) maps were calculated, from which 10 histogram features describing the CBF distribution were extracted within the tumor region. Correlation analysis was performed to determine the correlations between histogram features as well as tumor grades and IDH genotypes. The independent t-test and Fisher's exact test were used to determine differences in the extracted histogram features, age at diagnosis, and sex in different glioma subtypes. Multivariate binary logistic regression analysis was performed, and diagnostic performances were evaluated with the receiver operating characteristic curves. CBF histogram features were significantly correlated with tumor grades and IDH genotypes. These features can effectively differentiate LGGs from glioblastomas, and IDH-mut from IDH-wt gliomas. The area under the receiving operating characteristic curve of the model calculated using combined CBF 30th percentile and age at diagnosis in differentiating LGGs from glioblastomas was 0.73. Integrating age at diagnosis and CBF 10th percentile could be more effective in differentiating IDH-mut from IDH-wt gliomas. Furthermore, the combined model had a better area under the receiving operating characteristic curve at 0.856 (sensitivity: 84.4%, specificity: 82.9%). The histogram features on ASL were significantly correlated with tumor grade and IDH genotypes. Moreover, the use of these features could effectively differentiate glioma subtypes. The combined application of age at diagnosis and perfusion histogram features resulted in a more comprehensive identification of tumor subtypes. Therefore, ASL can be a noninvasive tool for the pre-surgical evaluation of gliomas.

A mixed loss joint approach-based deep learning strategy to enhance SNR and resolution of arterial spin labelling MRI

A mixed loss joint approach-based deep learning strategy to enhance SNR and resolution of arterial spin labelling MRI

Cerebral perfusion differences are linked to executive function performance in very preterm-born children and adolescents

Children and adolescents born very preterm are at risk of cognitive impairment, particularly affecting executive functions. To date, the neural correlates of these cognitive differences are not yet fully understood, although converging evidence points to a pattern of structural and functional brain alterations, including reduced brain volumes, altered connectivity, and altered brain activation patterns. In very preterm neonates, alterations in brain perfusion have also been reported, but the extent to which these perfusion alterations persist into later childhood is not yet known. This study evaluated global and regional brain perfusion, measured with arterial spin labelling (ASL) MRI, in 26 very preterm children and adolescents and 34 term-born peers. Perfusion was compared between groups and relative to executive function (EF) scores, derived from an extensive EF battery assessing working memory, cognitive flexibility, and planning. Very preterm children and adolescents showed regions of altered perfusion, some of which were also related to EF scores. Most of these regions were located in the right hemisphere and included regions like the thalamus and hippocampus, which are known to play a role in executive functioning and can be affected by prematurity. In addition, perfusion decreased with age during adolescence and showed a significant interaction between birth status and sex, such that very preterm girls showed lower perfusion than term-born girls, but this trend was not seen in boys. Taken together, our results indicate a regionally altered perfusion in very preterm children and adolescents, with age and sex related changes during adolescence.

Focal tDCS of auditory cortex in chronic tinnitus: A randomized controlled mechanistic trial

ObjectiveThe goal of this pilot study was to understand how focal transcranial direct current stimulation (tDCS) targeting auditory cortex changes brain function in chronic tinnitus using magnetic resonance imaging (MRI). MethodsPeople with chronic tinnitus were randomized to active or sham tDCS on five consecutive days in this mechanistic trial (n = 10/group). Focal 4x1 tDCS (central anode, surround cathodes) targeted left auditory cortex, with single-blind 2 mA current during twenty-minute sessions. Arterial spin-labeled and blood oxygenation level dependent MRI occurred immediately before and after the first tDCS session, and tinnitus symptoms were measured starting one week before the first tDCS session and through four weeks after the final session. ResultsAcute increases in cerebral blood flow and functional connectivity were noted in auditory cortex after the first active tDCS session. Reduced tinnitus loudness ratings after the final tDCS session correlated with acute change in functional connectivity between an auditory network and mediodorsal thalamus and prefrontal cortex. Reduced tinnitus intrusiveness also correlated with acute change in connectivity between precuneus and an auditory network. ConclusionsFocal auditory-cortex tDCS can influence function in thalamus, auditory, and prefrontal cortex, which may associate with improved tinnitus. SignificanceWith future refinement, tDCS targeting auditory cortex could become a viable intervention for tinnitus.

Cerebral microcirculatory pulse wave propagation and pulse wave amplitude mapping in retrospectively gated MRI

To analyze cerebral arteriovenous pulse propagation and to generate phase-resolved pulse amplitude maps from a fast gradient-echo sequence offering flow-related enhancement (FREE). Brain MRI was performed using a balanced steady-state free precession sequence at 3T followed by retrospective k-space gating. The time interval of the pulse wave between anterior-, middle- and posterior cerebral artery territories and the superior sagittal sinus were calculated and compared between and older and younger groups within 24 healthy volunteers. Pulse amplitude maps were generated and compared to pseudo-Continuous Arterial Spin Labeling (pCASL) MRI maps by voxel-wise Pearson correlation, Sørensen-Dice maps and in regards to signal contrast. The arteriovenous delays between all vascular territories and the superior sagittal sinus were significantly shorter in the older age group (11 individuals, ≥ 31 years) ranging between 169 ± 112 and 246 ± 299 ms versus 286 ± 244 to 419 ± 299 ms in the younger age group (13 individuals) (P ≤ 0.04). The voxel-wise pulse wave amplitude values and perfusion-weighted pCASL values correlated significantly (Pearson-r = 0.33, P < 0.01). Mean Dice overlaps of high (gray) and low (white matter) regions were 73 ± 3% and 59 ± 5%. No differences in image contrast were seen in the whole brain and the white matter, but significantly higher mean contrast of 0.73 ± 0.23% in cortical gray matter in FREE-MRI compared to 0.52 ± 0.12% in pCASL-MRI (P = 0.01). The dynamic information of flow-related enhancement allows analysis of the cerebral pulse wave propagation potentially providing information about the (micro)circulation on a regional level. However, the pulse wave amplitude reveals weaknesses in comparison to true perfusion-weighting and could rather be used to calculate a pulsatility index.

Deeply Accelerated Arterial Spin Labeling Perfusion MRI for Measuring Cerebral Blood Flow and Arterial Transit Time.

Cerebral blood flow (CBF) indicates both vascular integrity and brain function. Regional CBF can be non-invasively measured with arterial spin labeling (ASL) perfusion MRI. By repeating the same ASL MRI sequence several times, each with a different post-labeling delay (PLD), another important neurovascular index, the arterial transit time (ATT) can be estimated by fitting the acquired ASL signal to a kinetic model. This process however faces two challenges: one is the multiplicatively prolonged scan time, making it impractically for clinical use due to the escalated risk of motions; the other is the reduced signal-to-noise-ratio (SNR) in the long PLD scans due to the T1 decay of the labeled spins. Increasing SNR needs more repetitions which will further increase the total scan time. Currently, there lacks a way to accurately estimate ATT from a parsimonious number of PLDs. In this paper, we proposed a deep learning-based algorithm to reduce the number of PLDs and to accurately estimate ATT and CBF. Two separate deep networks were trained: one is designed to estimate CBF and ATT from ASL data with a single PLD; the other is to estimate CBF and ATT from ASL data with two PLDs. The models were trained and tested using the large Human Connectome Project multiple-PLD ASL MRI. Performance of the DL-based approach was compared to the traditional full dataset-based data fitting approach. Our results showed that ATT and CBF can be reliably estimated using deep networks even with one PLD.

Validation of early‐frame 18F‐FDG PET for CBF quantification: Comparison to simultaneous eASL measurements in memory patients

AbstractBackgroundThis study aimed to validate early [18F]‐FDG (eFDG) imaging for the quantification of cerebral blood flow (CBF), enabling dual‐marker imaging of perfusion and metabolism with a single tracer.Method19 participants with memory concerns underwent simultaneous [18F]‐FDG PET and multi delay pseudo‐continuous arterial spin labeling (eASL) MR imaging on a hybrid 3T PET/MRI scanner. eFDG‐CBF maps were generated from the first 30s, 60s, 120s and 300s after injection, and measurements were compared to ASL‐CBF using voxel‐wise cross correlation and concordance correlation for 7 regions derived from the MNI‐structural atlas.ResultHighest voxel‐wise cross‐correlation to ASL‐CBF maps were reported for 300s (5 min) eFDG (r = 0.77).Concordance correlation (CC) values were strong in all ROIs, ranging from (CC = 0.88) to (CC = 0.65) in temporal and occipital regions respectively. Mean of measurements in all ROIs were in good agreement between eFDG and ASL CBF maps, with a reported voxel‐wise mean absolute error of ±6.73 ml/100g/min between two maps.ConclusionBy simultaneous measurement of hemodynamics across modalities with a TOF‐enabled PET/MRI, we were able to demonstrate that eFDG PET is a reliable measure in mapping CBF based on strong inter‐modality correlation with ASL‐CBF, irrespective of pathophysiological variations in memory patients.

Associations between glymphatic function and BBB water exchange rate and perfusion in a Latinx cohort

AbstractBackgroundThe glymphatic system is thought to clear waste products from the brain by facilitating the exchange of interstitial fluid (ISF) with cerebrospinal fluid (CSF) through aquaporin‐4 (AQP4) water channels present in astrocyte endfeet. A recent non‐invasive MRI method, diffusion tensor image analysis along the perivascular space (DTI‐ALPS), has been proposed for evaluating brain clearance function and has shown reduced glymphatic function in various neurological disorders such as Alzheimer’s disease. However, the role of microvascular perfusion and blood‐brain barrier (BBB) permeability in the glymphatic system remains unclear. In this study, we used a novel diffusion‐prepared arterial spin labeling (DP‐ASL) MRI technique to measure BBB water exchange rate (kw) and cerebral blood flow (CBF) and studied their relationships with the DTI‐ALPS score.Method44 Latinx subjects (20 male; age = 65.6±5.6 years) were recruited from the USC MarkVCID study. Imaging parameters for DP‐ASL were: resolution = 3.5×3.5×8mm3, 10 slices, scan time 10 mins. kw was calculated from the ratio of intra‐ and extra‐vascular perfusion signals with total‐general‐variation (TGV) regularized single‐pass approximation (SPA) modeling and CBF was calculated from PLD = 1800ms data using one‐compartment Kety model. kw and CBF maps were normalized into the MNI space and regional analysis was performed in the frontal/temporal/parietal lobe, and subcortical regions. Association between ALPS score and CBF/kw values were studied by linear regressions. P&lt;0.05 was considered as significant.ResultFig.1 shows kw and CBF maps from three representative subjects with increasing ALPS scores (top to bottom). ALPS was significantly correlated with kw in MTL (β = 1.7e‐3,P = 0.04) and a positive trend was observed between ALPS and whole brain average kw (P = 0.11). While significant correlations were found between ALPS and CBF in multiple brain regions including frontal lobe (β = 7e‐3,P = 0.009), temporal lobe (β = 7e‐3,P = 0.002), parietal lobe (β = 4e‐3,P = 0.03), MTL (β = 8e‐3,P = 0.03), ACC (β = 6e‐3,P = 0.005), PCC (β = 4e‐3,P = 0.02), precuneus (β = 4e‐3,P = 0.04) and whole brain (β = 8e‐3,P = 0.01). Fig.2 shows scatter plots of ALPS versus kw (A) and CBF in MTL and whole brain, respectively.ConclusionThis is the first study in Latinx population demonstrating positive correlations between ALPS score and both CBF and kw, suggesting a possible involvement of blood flow and BBB water exchange rate in the glymphatic system.

Regional cortical hypoperfusion observed in elderly adults prior to development of mild cognitive impairment

AbstractBackgroundCardiovascular disease is associated with increased risk of developing mild cognitive impairment (MCI) and Alzheimer’s disease (AD), although the underlying mechanisms are not well understood. While it has been theorised that cerebral hypoperfusion caused by heart failure may directly lead to the formation of amyloid plaques and neurofibrillary tangles characteristic of AD, it has also been suggested that decreased perfusion occurs later in disease progression. We used arterial spin labelling (ASL) MRI to compare cerebral blood flow (CBF) between cognitively unimpaired elderly individuals who would remain cognitively stable and those who would later develop MCI to determine if hypoperfusion is detectable at a preclinical stage.Methods647 cognitively normal elderly participants with ASL and structural T1‐weighted MRI were selected from the Vallecas Project cohort, a single‐centre longitudinal study currently in its 12th year of annual follow‐up. 586 participants remained cognitively stable (CS) while 61 participants developed MCI over the course of the study. Cortical CBF maps derived from ASL images at the visit before MCI diagnosis were analysed in a voxelwise comparison with CS individuals, with age, sex, and total intracranial volume as covariates.ResultsCBF was significantly lower in the right insular cortex in future MCI converters than CS individuals (p&lt;0.05, family‐wise error (FWE) corrected). Hypoperfusion was also significant in the anterior corpus callosum in future converters.ConclusionCerebral hypoperfusion, as measured by ASL, can already be observed in individuals before the onset of clinical symptoms.

Blood‐brain barrier permeability measured with arterial spin labeling as potential cerebrovascular biomarker over the lifespan

AbstractBackgroundBlood‐brain barrier (BBB) dysfunction is considered a hallmark of Alzheimer’s disease (AD), making non‐invasive imaging of BBB with arterial spin labeling (ASL) MRI a potential imaging biomarker (BBB‐ASL). However, the normal BBB development over the lifespan is unknown. Here, we created population‐based BBB‐ASL permeability reference maps, and aimed to investigate associations between BBB‐ASL, chronological age, and biological cerebrovascular age – expressed as white matter hyperintensities (WMH) volume.MethodCognitively‐unimpaired (CU) participants were included from Center for Lifespan Changes in Brain and Cognition (LCBC) (n = 28, age 58.9±16.1y) and University of Singapore (n = 30, age 55.8±6.1y). The Singapore cohort is known to be vascularly compromised and thus expected to have early cerebrovascular pathology in the form of WMH. Multi‐echo, multi‐post‐labeling‐delay pseudo‐continuous ASL images were acquired at two identical Siemens 3T scanners and analyzed with ExploreASL. Gray matter (GM) BBB water time‐of‐exchange (Tex) was quantified with and without partial‐volume correction (PVC). For Singapore data, WMH were segmented on 3D FLAIR. Linear regression models were used to investigate associations of Tex with age and WMH volume, with and without covarying for sex and site.ResultBoth site population‐averages (Figure 1) show similar Tex patterns, with slightly higher posterior variability in the Singapore data. GM Tex was negatively associated with age (Figure 2A) irrespective of PVC, and after covarying for sex and site (Table 1). GM Tex was also negatively associated with WMH volume (β = ‐0.005, p = 0.012), although the association became non‐significant if both PVC and sex and site corrections were applied (β = ‐0.005, p = 0.068).ConclusionOur findings support the hypothesis of increased BBB permeability with aging and there are signs of association with increased cerebrovascular age assessed with WMH volume. We aim to further increase our sample size and also investigate associations with other AD biomarkers.

Investigating the impact of APOE4 genotype on the association between cerebral blood flow and haematological properties in mid‐life adults

AbstractBackgroundCarriership of the apolipoprotein ε4 (APOE4) allele confers a heightened risk for the development of Alzheimer’s disease (AD). Cerebral blood flow (CBF) is decreased in prodromal and established AD, however findings in the preclinical stage are mixed, with some studies reporting increases. CBF can be impacted by many factors including the haematocrit. We investigated in a cohort at risk of developing AD how haematological variables relate to CBF and if this relationship is differentially moderated by APOE4.Method375 participants from the PREVENT‐Dementia study underwent arterial spin labelling (ASL) and structural 3Tesla MRI. ASL data were analysed using BASIL/FSL and structural scans with SPM12. CBF maps were corrected for partial volume effects. A vascular territory mask with nine territories, the middle, proximal and distal branches of the anterior, middle and posterior cerebral arteries (ACA, MCA, PCA) was used for region‐of‐interest analysis and registered to the native ASL space. Regional gray matter (GM) CBF values were harmonised using COMBAT. Linear regression was used to examine differences between APOE4 carriers and non‐carriers controlling for age, sex and years of education. Associations between haematological properties and CBF were examined with Pearson’s correlations. Differential relationships between CBF, haematocrit, and measures of red blood cell size and shape (distribution width (RDW) and mean corpuscular volume (MCV)) were investigated by including interaction terms of APOE4 and haematological variables in the models.ResultAPOE4 carriers had significantly higher CBF in the proximal MCA (t = 2.54, p = 0.01). Across all subjects, RDW and MCV were not associated with GM CBF, though several significant interactions were observed between APOE4 and RDW in predicting CBF (Figure 1). Haematocrit was associated with GM CBF (ρ = ‐0.19, p &lt; 0.01). No significant interactions were seen between APOE4 and haematocrit or MCV in predicting CBF.ConclusionThe variability of the size and shapes of erythrocytes was differentially associated with CBF between APOE4 carriers and non‐carriers suggesting a different response to morphological erythrocyte alterations. This could further relate to underlying factors such as inflammation, which is associated with a higher RDW. Such associations should be examined in further studies.

Blood‐brain barrier permeability measured with arterial spin labeling as potential cerebrovascular biomarker over the lifespan

AbstractBackgroundBlood‐brain barrier (BBB) dysfunction is considered a hallmark of Alzheimer’s disease (AD), making non‐invasive imaging of BBB with arterial spin labeling (ASL) MRI a potential imaging biomarker (BBB‐ASL). However, the normal BBB development over the lifespan is unknown. Here, we created population‐based BBB‐ASL permeability reference maps, and aimed to investigate associations between BBB‐ASL, chronological age, and biological cerebrovascular age – expressed as white matter hyperintensities (WMH) volume.MethodCognitively‐unimpaired (CU) participants were included from Center for Lifespan Changes in Brain and Cognition (LCBC) (n = 28, age 58.9±16.1y) and University of Singapore (n = 30, age 55.8±6.1y). The Singapore cohort is known to be vascularly compromised and thus expected to have early cerebrovascular pathology in the form of WMH. Multi‐echo, multi‐post‐labeling‐delay pseudo‐continuous ASL images were acquired at two identical Siemens 3T scanners and analyzed with ExploreASL. Gray matter (GM) BBB water time‐of‐exchange (Tex) was quantified with and without partial‐volume correction (PVC). For Singapore data, WMH were segmented on 3D FLAIR. Linear regression models were used to investigate associations of Tex with age and WMH volume, with and without covarying for sex and site.ResultBoth site population‐averages (Figure 1) show similar Tex patterns, with slightly higher posterior variability in the Singapore data. GM Tex was negatively associated with age (Figure 2A) irrespective of PVC, and after covarying for sex and site (Table 1). GM Tex was also negatively associated with WMH volume (ß = ‐0.005, p = 0.012), although the association became non‐significant if both PVC and sex and site corrections were applied (ß = ‐0.005, p = 0.068).ConclusionOur findings support the hypothesis of increased BBB permeability with aging and there are signs of association with increased cerebrovascular age assessed with WMH volume. We aim to further increase our sample size and also investigate associations with other AD biomarkers.

Regional cortical hypoperfusion observed in elderly adults prior to development of mild cognitive impairment

AbstractBackgroundCardiovascular disease is associated with increased risk of developing mild cognitive impairment (MCI) and Alzheimer’s disease (AD), although the underlying mechanisms are not well understood. While it has been theorised that cerebral hypoperfusion caused by heart failure may directly lead to the formation of amyloid plaques and neurofibrillary tangles characteristic of AD, it has also been suggested that decreased perfusion occurs later in disease progression. We used arterial spin labelling (ASL) MRI to compare cerebral blood flow (CBF) between cognitively unimpaired elderly individuals who would remain cognitively stable and those who would later develop MCI to determine if hypoperfusion is detectable at a preclinical stage.Method647 cognitively normal elderly participants with ASL and structural T1‐weighted MRI were selected from the Vallecas Project cohort, a single‐centre longitudinal study currently in its 12th year of annual follow‐up. 586 participants remained cognitively stable (CS) while 61 participants developed MCI over the course of the study. Cortical CBF maps derived from ASL images at the visit before MCI diagnosis were analysed in a voxelwise comparison with CS individuals, with age, sex, and total intracranial volume as covariates.ResultCBF was significantly lower in the right insular cortex in future MCI converters than CS individuals (p&lt;0.05, family‐wise error (FWE) corrected). Hypoperfusion was also significant in the anterior corpus callosum in future converters.ConclusionCerebral hypoperfusion, as measured by ASL, can already be observed in individuals before the onset of clinical symptoms.

Investigating the impact of APOE4 genotype on the association between cerebral blood flow and haematological properties in mid‐life adults

AbstractBackgroundCarriership of the apolipoprotein ε4 (APOE4) allele confers a heightened risk for the development of Alzheimer’s disease (AD). Cerebral blood flow (CBF) is decreased in prodromal and established AD, however findings in the preclinical stage are mixed, with some studies reporting increases. CBF can be impacted by many factors including the haematocrit. We investigated in a cohort at risk of developing AD how haematological variables relate to CBF and if this relationship is differentially moderated by APOE4.Method375 participants from the PREVENT‐Dementia study underwent arterial spin labelling (ASL) and structural 3Tesla MRI. ASL data were analysed using BASIL/FSL and structural scans with SPM12. CBF maps were corrected for partial volume effects. A vascular territory mask with nine territories, the middle, proximal and distal branches of the anterior, middle and posterior cerebral arteries (ACA, MCA, PCA) was used for region‐of‐interest analysis and registered to the native ASL space. Regional gray matter (GM) CBF values were harmonised using COMBAT. Linear regression was used to examine differences between APOE4 carriers and non‐carriers controlling for age, sex and years of education. Associations between haematological properties and CBF were examined with Pearson’s correlations. Differential relationships between CBF, haematocrit, and measures of red blood cell size and shape (distribution width (RDW) and mean corpuscular volume (MCV)) were investigated by including interaction terms of APOE4 and haematological variables in the models.ResultAPOE4 carriers had significantly higher CBF in the proximal MCA (t = 2.54, p = 0.01). Across all subjects, RDW and MCV were not associated with GM CBF, though several significant interactions were observed between APOE4 and RDW in predicting CBF (Figure 1). Haematocrit was associated with GM CBF (ρ = ‐0.19, p &lt; 0.01). No significant interactions were seen between APOE4 and haematocrit or MCV in predicting CBF.ConclusionThe variability of the size and shapes of erythrocytes was differentially associated with CBF between APOE4 carriers and non‐carriers suggesting a different response to morphological erythrocyte alterations. This could further relate to underlying factors such as inflammation, which is associated with a higher RDW. Such associations should be examined in further studies.

Relationship between Arterial Transit Time and Framingham Risk Score in the U.S. POINTER lifestyle intervention trial

AbstractBackgroundThe U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER) is a two‐year randomized controlled trial designed to evaluate the effects of lifestyle interventions on older adults aged 60‐79 years. The POINTER Imaging ancillary study employs arterial spin labeling (ASL) magnetic resonance imaging (MRI) with two inversion times, enabling the mapping of arterial transit time (ATT) and the investigation of its relationship with dementia risk factors. This study examines the effect of the Framingham Risk Score (FRS) on ATT, which provides hemodynamic information on the cerebral vasculature.MethodA subset of POINTER Imaging participants (n = 134; F/M = 81/53; age = 68.1±5.1; FRS = 11.3±10.4) from two imaging sites underwent two ASL MRI scans during the baseline session. Two 3D Pulsed ASL scans were obtained with TI1 of 790ms and TI2 values of 2000ms or 2750ms, providing delay times (between labeling and imaging) of 1210ms or 1960ms. ATT, the time required for blood to travel from the neck to the tissue, was estimated in the range of 1210ms and 1960ms using a kinetic model (Figure 1). ATT maps were normalized to a standard space, and a voxel‐wise linear regression (ATT∼age+sex+log(FRS)) was performed on ATT maps in gray matter to assess the effect of FRS on ATT. To control false positives, clusters smaller than 1.4ml were removed based on a simulation with α = 0.05.ResultFigure 2 depicts three clusters found in the occipital, precuneus and frontal gray matter regions, all of which demonstrate a positive relationship between ATT and log(FRS). Participants with higher FRS exhibit prolonged mean ATT values in the clusters as shown in Figure 3. After stratifying into sex groups, both groups show the same direction.ConclusionAlthough the detectable range of ATT with two ASL scans was limited, the analysis suggests that an increased risk of cardiovascular disease, as quantified by the Framingham Risk Score, can serve as an indicator of potential cerebrovascular disease leading to prolonged ATT, which is associated with arterial stiffness, and vascular resistance. The clusters demonstrating the association between FRS and ATT are the brain regions that may have heightened vulnerability to vascular risk factors, according to previous studies.