A general kinetic model for quantitative perfusion imaging with arterial spin labeling

Assessment of renal insufficiency in patients with renal artery stenosis by multiparametric magnetic resonance imaging

OBJECTIVES

To evaluate the function of kidneys with renal artery stenosis using multiparametric magnetic resonance imaging, assess the diagnostic efficacy of multiparametric magnetic resonance imaging for single kidney dysfunction.

MATERIALS AND METHODS

Renal multiparametric magnetic resonance imaging was performed on 62 patients with RAS using the Philips Ingenia CX 3.0 T MRI machine. The scanning sequences included arterial spin labeling, phase contrast MRI, diffusion weighted imaging, T1 mapping, and blood oxygen level-dependent MRI. All patients underwent radionuclide renal dynamic imaging, and the glomerular filtration rate (GFR) was calculated to determine renal function. Individual kidneys from renal artery stenosis patients were classified into normal (GFR ≥ 30) and reduced (GFR < 30) groups and the ability of the uni- and multi-variate logistic regression model to predict the group was determined.

RESULTS

MR parameters demonstrated considerable diagnostic efficacy for single kidney dysfunction, with AUC range of 0.597- 0.864. The strongest predictor was mean renal artery blood flow. The sensitivity and specificity were 0.93 and 0.69AUC was 0.864. The strongest predictors of the renal microstructure were cortical apparent diffusion coeffecient and T1 value, with ROC AUCs of 0.756 and 0.741, sensitivities of 0.875 and 0.689, and specificities of 0.537 and 0.731. Multiparametric MRI combined with the values of cortical renal blood flow and cortical T1 exhibited the highest diagnostic efficacy, with an AUC of 0.92, and sensitivity of 0.919, and specificity of 0.743.

CONCLUSION

Multiparametric magnetic resonance imaging can effectively detect the single renal dysfunction of kidneys with renal artery stenosis, which holds promise for the diagnosis and prognosis of patients with renal artery stenosis.

Hybrid Multidelay PCASL Acquired With Time-Encoded and Variable-TR Schemes for the Assessment of Cerebral Perfusion in Moyamoya Disease

Multidelay arterial spin labeling (ASL) MRI requires balancing temporal information with signal-to-noise ratio (SNR). A hybrid scheme combines the high SNR of time-encoded pseudo-continuous ASL (PCASL) with the temporal flexibility of variable-TR PCASL. The purpose of the present study was to assess the SNR and quantitative performance of the hybrid scheme by comparing it to time-encoded and variable-TR schemes for evaluating cerebral perfusion in patients with moyamoya disease. Twenty patients with moyamoya disease (8 men and 12 women, 27.6 ± 22.7 years) were scanned with 3 T MRI system. Variable-TR PCASL with 12 delays (vTR12), time-encoded PCASL with seven delays (TEnc7), and hybrid PCASL with 12 (4 × 3) delays (Hyb12) were obtained. Hyb12 and vTR12 were configured with nearly identical label duration (LD) and postlabeling delay (PLD) settings. For TEnc7, it was balanced so that the maximum LD + PLD time is the same. Time-corrected SNR (SNRt), cerebral blood flow (CBF), and arterial transit time (ATT) were measured in vascular territories within gray matter. The three parameters were compared using the Friedman's matched test, followed by the Dunn's multiple comparison test. Correlations were evaluated with Pearson's correlation, and agreement was assessed by Bland-Altman plot analysis and intraclass correlation coefficient (ICC). The SNRt of Hyb12 (4.67 ± 1.97) was significantly higher than that of vTR12 (3.27 ± 1.37, p < 0.0001) and TEnc7 (3.52 ± 1.32, p < 0.0001). The CBF of Hyb12 (49.9 ± 13.7 mL/100 g/min) was significantly lower than that of vTR12 (54.9 ± 15.4 mL/100 g/min, p < 0.0001) and TEnc7 (57.5 ± 15.9 mL/100 g/min, p < 0.0001). The ATT of Hyb12 (1240 ± 430 ms) was significantly shorter than that of vTR12 (1474 ± 419 ms, p < 0.0001) and TEnc7 (1402 ± 333 ms, p < 0.0001). CBF and ATT measurements from Hyb12 showed strong correlations and good agreement with the other two schemes. The hybrid scheme offers higher SNRt than both time-encoded and variable-TR schemes, which may improve the accuracy of cerebral perfusion assessment in patients with cerebral artery occlusive diseases, where delayed blood flow is a concern.

Alterations in magnetic susceptibility correlate with higher cerebral blood flow in the right amygdala of patients with major depressive disorder

BACKGROUND

The amygdala plays a crucial role in emotion processing and is a key target for understanding the mechanisms underlying major depressive disorder (MDD). This study aimed to investigate the magnetic susceptibility of the amygdala in MDD and examine its association with structural and cerebral blood flow (CBF) changes.

METHODS

A total of 158 individuals were included in the study, comprising 86 patients with MDD and 72 healthy controls. Depression severity was assessed using Hamilton Depression Rating Scale. Quantitative susceptibility mapping (QSM), T1-weighted, and arterial spin labeling scans were conducted to measure amygdala magnetic susceptibility, volume, and CBF, respectively. Group differences were compared, and associations between susceptibility, volume, and CBF were examined.

RESULTS

The median susceptibility of the amygdala was significantly higher in MDD patients than in controls (all p < 0.01). In the MDD group, increased QSM value in the right amygdala was associated with higher CBF (r = 0.28, p = 0.01), whereas no significant correlation was found between QSM value and volume (p = 0.76). Increased QSM value in the right amygdala was associated with worse depressed mood (r = 0.30, p < 0.01).

LIMITATION

Retrospective cross-sectional study conducted at a single center.

CONCLUSION

The magnetic susceptibility of the amygdala was higher in MDD patients with than in controls. QSM changes in the right amygdala correlated with increased CBF and worse depressed mood, indicating both microstructural and functional alterations. Our results encourage further use of the QSM technique in the elucidation of MDD pathophysiology.

Neurovascular coupling alterations in cerebral small vessel disease: A multi-delayed ASL and fMRI perspective on cognitive impairment

BACKGROUND

To explore the alteration of neurovascular coupling (NVC), relationships between neuroimaging metrics with clinical assessments, and classification metrics in cerebral small vessel disease (CSVD).

METHODS

Participants were grouped into healthy control, CSVD with normal cognition, and CSVD with cognition impairment according to CSVD scales and Montreal Cognitive Assessment. Cerebral blood flow (CBF) adjusted for arterial transit time and dynamic/static amplitude of low-frequency fluctuation (dALFF, ALFF) were combined to evaluate NVC and to determine intergroup differences. Partial Spearman Correlation between measures from abnormal brain areas and scores of clinical assessments were operated. Multivariate pattern analysis was applied to determine the most effective classification metrics among groups.

RESULTS

Cross-voxel correlation was lower in CSVD compared to healthy control. Abnormal brain regions were presented mainly in sensorimotor cortex, limbic/paralimbic system, and basal ganglia in CSVD. Notably, correlations between clinical assessment scores and NVC-related metrics in these areas were significant before correction. CBF/ALFF ratio exhibited superior classification performance between healthy control and CSVD with normal cognition, while a combination of dALFF and CBF effectively differentiated between CSVD patients with normal and impaired cognition.

CONCLUSIONS

Our investigation finds neurovascular decoupling using ATT-corrected CBF, dALFF and ALFF, as well as suggests effective classification metrics in CSVD with/without cognition impairment, potentially improving diagnostic and therapeutic strategies.

Evaluation of Neurovascular Coupling in Early-Onset and Late-Onset Epilepsy of Unknown Etiology

BACKGROUND

Previous studies have shown neurovascular coupling (NVC) dysfunction in epilepsy, suggesting its role in the pathological mechanisms. However, it remains unclear whether NVC abnormalities exist in epilepsy of unknown etiology (EU).

PURPOSE

To integrate multiparametric MRI to assess NVC and its relationship with cognition in early-onset and late-onset EU patients.

STUDY TYPE

Prospective.

POPULATION

Ninety-six EU patients (46 early-onset, M/F = 20/26; 50 late-onset, M/F = 29/21) and 60 healthy controls (HCs, M/F = 25/35).

FIELD STRENGTH/SEQUENCE

3.0 T, resting-state gradient echo-planar imaging, pseudo-continuous arterial spin labeling (pc-ASL), and T1-weighted brain volume sequence.

ASSESSMENT

Functional MRI data were analyzed to assess intrinsic brain activity including amplitude of low-frequency fluctuations (ALFF), fractional ALFF (fALFF), regional homogeneity (ReHo), and functional connectivity strength (FCS), while pc-ASL provided cerebral blood flow (CBF) measurements. Coupling correlation coefficients and ratios of CBF to neural activity were calculated to evaluate global and regional NVC.

STATISTICAL TESTS

Two-sample t-test, Analysis of Variance, Kruskal-Wallis test, Chi-square test, Analysis of Covariance, family-wise error/Bonferroni correction, partial correlation analyses. Statistical significance was defined as P < 0.05.

RESULTS

Whole-brain analysis revealed increased ALFF values in both patient groups' left precentral and postcentral gyri. Both patient groups had lower global NVC coefficients than HCs, with reduced CBF-ALFF (0.28 vs. 0.30), CBF-fALFF (0.43 vs. 0.45), and CBF-ReHo (0.40 vs. 0.41) in early-onset patients, and lower CBF-fALFF (0.38 vs. 0.45) and CBF-ReHo (0.32 vs. 0.41) in late-onset patients. Regional analysis showed significantly decreased CBF/ALFF ratios in the left precentral and postcentral gyri (T = 3.85 to 5.33). Reduced global NVC in early-onset patients was significantly associated with poorer executive function (r = 0.323), while global coupling in late-onset patients was negatively correlated with disease duration (r = -0.348 to -0.426).

DATA CONCLUSION

This study showed abnormal global and regional NVC in both early-onset and late-onset EU patients, emphasizing the potential role of NVC in the pathophysiological mechanisms of EU.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 1.

Quantitative multiple boli arterial spin labeling

PURPOSE

mbASL relies on the use of a series of adiabatic radio-frequency pulses to label successive boli of blood water. As the sequence is a hybrid of pCASL and PASL, it requires an appropriate kinetic model to accurately describe the signal for quantification purposes.

THEORY AND METHODS

Drawing on the Buxton standard kinetic model, we propose modifications to account for the multiple labeling pulses at variable delays. By varying the number of adiabatic pulses and the thickness of the inversion slab, we maximize SNR and demonstrate the hybrid nature of the sequence.

RESULTS

The mbASL kinetic model is used to produce mbASL cerebral blood flow maps, with average values for mice (110 ml/100 g/min) and rats (96 ml/100 g/min).

CONCLUSION

We have successfully quantified and validated the mbASL kinetic model and demonstrated that the resulting CBF values agree with the existing literature.

Agreement between early-phase amyloid-PET and pulsed arterial spin labeling in a memory clinic cohort

Relative cerebral blood flow (rCBF), assessed using pulsed arterial spin labeling (pASL) MRI, and the standardized uptake value ratio (SUVr) in early-phase amyloid-PET (ePET) are used as proxies for brain perfusion. These methods have the potential to streamline clinical workflows and reduce the burden on patients by eliminating the need for additional procedures. While both techniques have shown good agreement with the gold standard for glucose metabolism assessment, F-fluorodeoxyglucose-PET, a direct comparison between them has yet to be fully clarified. This retrospective study aimed to compare perfusion-like data from pASL (rCBF) and ePET (SUVr) in a memory clinic cohort. We included 46 subjects (69 ± 8 years; 37 women) from the Geneva Memory Center (cognitively impaired-CI n = 29; cognitively unimpaired-CU n = 17), with available pASL and ePET. We evaluated the association between rCBF and SUVr values across 18 cortical and subcortical regions using linear regression and the within-subject coefficient of variation (wsCV). Regional differences between CU and CI groups were assessed using linear regression model corrected for age. We observed significant association between rCBF and SUVr in precuneus (β = 0.69, wsCV = 16.9), angular gyrus (β = 0.64, wsCV = 19.4), and hippocampus (β = 0.23, wsCV = 16.1). Additionally, significant differences in rCBF between CU and CI were also observed in the posterior cingulate, precuneus, calcarine, hippocampus, and composite (p < 0.05), while SUVr showed significant differences only in the hippocampus. Our findings indicate weak to moderate local correlations between the two techniques. However, both exhibited differing regional perfusion levels in CU and CI groups, with rCBF showing more regional differences between cognitive stages in comparison with SUVr. KEY MESSAGES: rCBF is assessed through pASL MRI and SUVr through ePET, both serving as proxies of brain perfusion. Weak to moderate associations between rCBF and SUVr were found in a number of brain regions. rCBF and SUVr differences between cognitive stages were observed mostly in cortical and subcortical regions respectively. Both techniques were able to identify AD perfusion-like differences expected in cognitively impaired vs unimpaired.

MULti-TImepoint VElocity-selective Reconciled with Spatially-sElective (MULTIVERSE) ASL: Improving robustness to both shortened and prolonged arterial transit time

PURPOSE

To improve the quantification of existing multi-timepoint arterial spin labeling (ASL) methods in estimating cerebral blood flow (CBF) and arterial transit time (ATT) for a wider range of ATTs.

METHODS

MULti-TImepoint VElocity-selective Reconciled with Spatially-sElective (MULTIVERSE) ASL utilizes multi-delay pseudo-continuous (PC) ASL and velocity-selective (VS) ASL with spatially defined bolus, and joint fitting to estimate CBF and ATT. Numerical simulations were performed to evaluate the accuracy and precision of single-delay and multi-delay PCASL and VSASL, as well as the proposed MULTIVERSE ASL, in quantifying CBF and ATT across an extended range of ATTs. The CBF and ATT estimates between multi-delay PCASL, VSASL, and MULTIVERSE ASL were compared across healthy volunteers.

RESULTS

Numerical simulations showed that the utility of MULTIVERSE ASL improved the accuracy and precision over an extended ATT range of up to 4000 ms. In vivo scans from healthy subjects demonstrated that MULTIVERSE ASL led to reduced uncertainty in CBF and ATT quantification compared to multi-post-labeling delay PCASL while maintaining comparable repeatability.

CONCLUSION

This novel and straightforward approach improves the accuracy and precision of the fitted CBF and ATT over an extended range of ATT, which is not possible with existing ASL methods. Brain scans from healthy subjects demonstrated the feasibility and reliability of the technique, highlighting the clinical potential of ASL-based perfusion mapping in various altered physiological and pathological conditions.

Acute cerebral blood flow response to heavy cream ingestion in older adults: A non-randomized pilot study

BackgroundHypertension and the APOE4 allele are known risk factors for Alzheimer's disease (AD) and E4 carriers show different blood pressure (BP) and cognitive responses to high fat feeding.ObjectiveWe investigated the influence of these factors on global cerebral blood flow (CBF) and four regions of interest (ROIs) (angular gyrus, hippocampus, posterior cingulate, temporal lobe) using arterial spin labeling (ASL) MRI in fasting state and after ingestion of heavy cream in older adults.Methods29 adults (age in years 66.8 ± 4.1) underwent baseline and 1, 2, 3-h ASL MRI after ingestion of 100 mL heavy cream. We used pCASL MRI with background suppression to measure CBF in ml/100 g/min. Statistical analyses included mixed-effects modeling and Pearson correlation to ascertain whether CBF changed over time and how variables influenced results.ResultsGlobal CBF decreased at 1-, 2-, and 3-h post-heavy cream, compared to time 0 (overall change 7.11%, p < 0.01); recapitulated in 3 of 4 ROIs. Mean arterial pressure emerged as a predictive variable for both baseline and post-heavy cream CBF (β = -0.25, 95% CI = -0.39, -0.10, p = 0.002). Individuals with higher BP demonstrated reduced CBF, particularly in posterior cingulate and temporal lobe (β = -5.50, 95% CI = -9.9, -1.09; β = -6.28, 95% CI = -12.35, -0.21, respectively, both p < 0.05). Examination of correlations with BP and change scores revealed that this relationship was driven largely by E4 carriers.ConclusionsCBF decreased after ingestion of heavy cream, globally and in regions known to be important in AD, and this finding was driven by E4 carriers with higher BP.

"MR Fingerprinting for Imaging Brain Hemodynamics and Oxygenation"

Over the past decade, several studies have explored the potential of magnetic resonance fingerprinting (MRF) for the quantification of brain hemodynamics, oxygenation, and perfusion. Recent advances in simulation models and reconstruction frameworks have also significantly enhanced the accuracy of vascular parameter estimation. This review provides an overview of key vascular MRF studies, emphasizing advancements in geometrical models for vascular simulations, novel sequences, and state-of-the-art reconstruction techniques incorporating machine learning and deep learning algorithms. Both pre-clinical and clinical applications are discussed. Based on these findings, we outline future directions and development areas that need to be addressed to facilitate their clinical translation. EVIDENCE LEVEL: N/A. TECHNICAL EFFICACY: Stage 1.

Vasomotion loss precedes impaired cerebrovascular reactivity and microbleeds in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a cerebral small vessel disease in which amyloid-β accumulates in vessel walls. CAA is a leading cause of symptomatic lobar intracerebral haemorrhage and an important contributor to age-related cognitive decline. Recent work has suggested that vascular dysfunction may precede symptomatic stages of CAA, and that spontaneous slow oscillations in arteriolar diameter (termed vasomotion), important for amyloid-β clearance, may be impaired in CAA. To systematically study the progression of vascular dysfunction in CAA, we used the APP23 mouse model of amyloidosis, which is known to develop spontaneous cerebral microbleeds mimicking human CAA. Using in vivo 2-photon microscopy, we longitudinally imaged unanesthetized APP23 transgenic mice and wildtype (WT) littermates from 7 to 14 months of age, tracking amyloid-β accumulation and vasomotion in individual pial arterioles over time. MRI was used in separate groups of 12-, 18- and 24-month-old APP23 transgenic mice and WT littermates to detect microbleeds and to assess cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) with pseudo-continuous arterial spin labelling. We observed a significant decline in vasomotion with age in APP23 mice, while vasomotion remained unchanged in WT mice with age. This decline corresponded in timing to initial vascular amyloid-β deposition (∼8-10 months of age), although it was more strongly correlated with age than with vascular amyloid-β burden in individual arterioles. Declines in vasomotion preceded the development of MRI-visible microbleeds and the loss of smooth muscle actin in arterioles, both of which were observed in the majority of APP23 mice by 18 months of age. Additionally, CBF and evoked CVR were intact in APP23 mice at 12 months of age, but significantly lower in APP23 mice by 24 months of age. Our findings suggest that a decline in spontaneous vasomotion is an early, potentially pre-symptomatic, manifestation of CAA and vascular dysfunction, and a possible future treatment target.

Leveraging deep learning for improving parameter extraction from perfusion MR images: A narrative review

BACKGROUND

Perfusion magnetic resonance imaging (MRI) is a non-invasive technique essential for assessing tissue microcirculation and perfusion dynamics. Various perfusion MRI techniques like Dynamic Contrast-Enhanced (DCE), Dynamic Susceptibility Contrast (DSC), Arterial Spin Labeling (ASL), and Intravoxel Incoherent Motion (IVIM) provide critical insights into physiological and pathological processes. However, traditional methods for quantifying perfusion parameters are time-consuming, often prone to variability, and limited by noise and complex tissue dynamics. Recent advancements in artificial intelligence (AI), particularly in deep learning (DL), offer potential solutions to these challenges. DL algorithms can process large datasets efficiently, providing faster, more accurate parameter extraction with reduced subjectivity.

AIM

This paper reviews the state-of-the-art DL-based techniques applied to perfusion MRI, considering DCE, DSC, ASL and IVIM acquisitions, focusing on their advantages, challenges, and potential clinical applications.

MAIN FINDINGS

DL-driven methods promise significant improvements over conventional approaches, addressing limitations like noise, manual intervention, and inter-observer variability. Deep learning techniques such as convolutional neural networks (CNNs), recurrent neural networks (RNNs), and generative adversarial networks (GANs) are particularly valuable in handling spatial and temporal data, enhancing image quality, and facilitating precise parameter extraction.

CONCLUSIONS

These innovations could revolutionize diagnostic accuracy and treatment planning, offering a new frontier in perfusion MRI by integrating DL with traditional imaging methods. As the demand for precise, efficient imaging grows, DL's role in perfusion MRI could significantly improve clinical outcomes, making personalized treatment a more realistic goal.

Multi-delay arterial spin labeling using a variable repetition time scheme in Moyamoya disease: Comparison with single-delay arterial spin labeling

PURPOSE

To present a multi-delay arterial spin labeling (ASL) protocol that obtains the cerebral blood flow (CBF) considering the arterial transit time (ATT), and to assess the correlations with an iodine-123-N-isopropyl-p-iodoamphetamine single-photon emission computed tomography (123I-IMP SPECT) reference standard between multi-delay ASL and single-delay ASL in patients with Moyamoya disease.

METHOD

We retrospectively analyzed the images of 23 patients with Moyamoya disease (4-73 years, 5 men, 18 women), each of whom was imaged with 10-delay ASL using the variable repetition time (TR) scheme, single-delay ASL, and SPECT. Pearson correlation coefficients were calculated between the CBF values of each ASL and SPECT in the three divisions of the ATT, which we categorized as fast, normal, and slow regions. The threshold for statistical significance was set atP<0.05.

RESULTS

The CBF measured by multi-delay ASL and single-delay ASL were positively correlated with that measured by SPECT, with correlation coefficients of 0.6701 and 0.5637, respectively (P < 0.001). In the fast, normal, and slow ATT divisions, the correlation coefficients between the CBF measured by multi-delay ASL and that measured by SPECT were 0.6745, 0.7055, and 0.6746, respectively. Similarly, the correlations between the CBF measured by single-delay ASL and that measured by SPECT were 0.3811, 0.5090 and 0.6178, respectively.

CONCLUSIONS

Multi-delay ASL using the variable TR scheme showed a higher correlation with 123I-IMP SPECT than single-delay ASL for measuring the CBF. The variable TR scheme potentially improved the quantification of CBF on ASL imaging.

New physiological insights using multi-TE ASL MRI measuring blood-brain barrier water exchange after caffeine intake

OBJECTIVES

Caffeine, a known neurostimulant and adenosine antagonist, affects brain physiology by decreasing cerebral blood flow. It interacts with adenosine receptors to induce vasoconstriction, potentially disrupting brain homeostasis. However, the impact of caffeine on blood-brain barrier (BBB) permeability to water remains underexplored. This study investigated the water exchange via the BBB in a perturbed physiological condition caused by caffeine ingestion, using the multiple echo time (multi-TE) arterial spin labeling (ASL) technique.

MATERIAL AND METHODS

Ten healthy, regular coffee drinkers (age = 31 ± 9 years, 3 females) were scanned to acquire five measurements before and six measurements after caffeine ingestion. Data were analyzed with a multi-TE two-compartment model to estimate exchange time (Tex), serving as a proxy for BBB permeability to water. Additionally, cerebral blood flow (CBF), arterial transit time (ATT), and intravoxel transit time (ITT) were investigated.

RESULTS

Following caffeine intake, mean gray matter CBF showed a significant time-dependent decrease (P < 0.01). In contrast, Tex, ATT, and ITT did not exhibit significant time-dependent change. However, a non-significant decreasing trend was observed for Tex and ITT, respectively, while ATT showed an increasing trend over time.

DISCUSSION

The observed decreasing trend in Tex after caffeine ingestion suggests a potential increase in water flux across the BBB, which may represent a compensatory mechanism to maintain brain homeostasis in response to the caffeine-induced reduction in CBF. Further studies with larger sample sizes are needed to validate and expand upon these findings.

Age and gender-related patterns of arterial transit time and cerebral blood flow in healthy adults

Normal aging has been associated with increased arterial transit time (ATT) and reduced cerebral blood flow (CBF). However, age-related patterns of ATT and CBF and their relationship remain unclear. This is partly due to the lengthy scan times required for ATT measurements, which caused previous age-related CBF studies to not fully account for transit time. In this work, we aimed to elucidate age-related ATT and ATT-corrected CBF patterns. We examined 131 healthy subjects aged 19 to 82 years old using two pseudo-continuous arterial spin labeling (PCASL) MRI scans: one to measure fast low-resolution ATT maps with five post-labeling delays and the other to measure high-resolution perfusion-weighted maps with a single post-labeling delay. Both ATT and perfusion-weighed maps were applied with vessel suppression. We found that ATT increases with age in the frontal, temporoparietal, and occipital regions, with a more pronounced elongation in males compared to females in the middle temporal gyrus. ATT-corrected CBF decreases with age in several brain regions, including the anterior cingulate, insula, posterior cingulate, angular, precuneus, supramarginal, frontal, parietal, superior and middle temporal, occipital, and cerebellar regions, while remaining stable in the inferior temporal and subcortical regions. In contrast, without ATT correction, we detected artifactual decreases in the inferior temporal and precentral regions. These findings suggest that ATT provides valuable and independent insights into microvascular deficits and should be incorporated into CBF measurements for studies involving aging populations.

Developmental Mismatch Across Brain Modalities in Young Children

Background: Brain development during the preschool period is complex and extensive and underlies ongoing behavioral and cognitive maturation. Increasing understanding of typical brain maturation during this time is critical to early identification of atypical development and could inform treatments and interventions. Previous studies have suggested mismatches between brain structural and functional development in later childhood and adolescence. The current study aimed to delineate the developmental matches and mismatches between brain measures from multiple magnetic resonance imaging modalities in young children. Methods: Brain volume, cortical thickness, fractional anisotropy, cerebral blood flow (CBF), amplitude of low-frequency fluctuations (ALFF), regional homogeneity (ReHo), and eigenvector centrality mapping (ECM) were included. Multi-modal neuroimages for 159 datasets from 67 typically developing preschoolers (2.0-7.6 years old) were collected and analyzed. Results: Functional measures (CBF, ECM, ReHo, ALFF) had similar developmental trajectories across regions, whereas development trajectories for brain volumes and cortical thickness were more heterogeneous. Furthermore, within individuals, brain volumes and cortical thickness were very good at predicting individual scans from prior longitudinal scans. Conclusions: These findings provide a more detailed characterization of the complex interplay of different types of brain development in the early years, laying the foundation for future studies on the impact of environmental factors and neurodevelopmental disorders on the development matches/mismatches patterns between brain areas and modalities.

High resolution multi-delay arterial spin labeling with self-supervised deep learning denoising for pediatric choroid plexus perfusion MRI

Choroid plexus (CP) is an important brain structure that produces cerebrospinal fluid (CSF). CP perfusion has been studied using multi-delay arterial spin labeling (MD-ASL) in adults but not in pediatric populations due to the challenge of small CP size in children. Here we present a high resolution (iso2 mm) MDASL protocol with 10-minute scan time and performed test-retest scans on 21 typically developing children aged 8 to 17 years. We further proposed a Transformer-based deep learning (DL) model with k-space weighted image average (KWIA) denoised images as reference for training the model. The performance of the model was evaluated by the SNR, bias and repeatability of the fitted perfusion parameters of the CP and gray matter. The proposed method was compared to several benchmark methods including KWIA, joint denoising and reconstruction with total generalized variation (TGV) regularization, as well as another self-supervised method termed Noise2Void. The results show that the proposed Transformer model with KWIA reference can effectively denoise multi-delay ASL images, not only improving the SNR for perfusion images of each delay, but also improving the SNR for the fitted perfusion maps for visualizing and quantifying CP perfusion in children. This may facilitate the use of MDASL in neurodevelopmental studies to characterize the development of CP and glymphatic system.

Cerebrovascular Reactivity Mapping in Brain Tumors Based on a Breath-Hold Task Using Arterial Spin Labeling

Hemodynamic measurements such as cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) can provide useful information for the diagnosis and characterization of brain tumors. Previous work showed that arterial spin labeling (ASL) in combination with vasoactive stimulation enabled simultaneous non-invasive evaluation of both parameters, however this approach had not been previously tested in tumors. The aim of this work was to investigate the application of this technique, using a pseudo-continuous ASL (PCASL) sequence combined with breath-holding at 3 T, to measure CBF and CVR in high-grade gliomas and metastatic lesions, and to explore differences across tumoral-peritumoral regions and tumor types. To that end, 27 patients with brain tumor were studied. Baseline CBF and CVR were measured in tumor, edema, and gray matter (GM) volumes-of-interest (VOIs). Peritumoral ipsilateral ring-shaped VOIs were also generated and mirrored to the contralateral hemisphere. Differences in baseline CBF and CVR were evaluated between contralateral and ipsilateral GM, contralateral and ipsilateral peritumoral rings, and among VOIs and tumor types. CBF in the tumor was higher in grade 4 gliomas than metastases. In grade 4 gliomas, edema had lower CBF than the tumor and contralateral GM. CVR values were different between grade 3 and grade 4 gliomas, and between grade 4 and metastases. CVR values in the tumor were lower compared to the contralateral GM. Differences in CVR between contralateral and ipsilateral-ring VOIs were also found in grade 4 gliomas, presumably suggesting tumor infiltration within the peritumoral tissue. A cut-off value for CVR of 27.9%-signal-change is suggested to differentiate between grade 3 and grade 4 gliomas (specificity = 83.3%, sensitivity = 70.6%). In conclusion, CBF and CVR mapping with ASL offered insights into the perilesional environment that could help to detect infiltrative disease, particularly in grade 4 gliomas. CVR emerged as a potential biomarker to differentiate between grade 3 and grade 4 gliomas.

Detectability of white matter cerebral blood flow using arterial spin labeling MRI in patients with sickle cell disease: Relevance of flow territory, bolus arrival time and hematocrit

Sickle cell disease (SCD) is the most common genetic blood disorder, characterized by red cell hemolysis, anemia, and corresponding increased compensatory cerebral blood flow (CBF). SCD patients are at high risk for cerebral infarcts and CBF quantification is likely critical to assess infarct risk. Infarcts primarily localize to white matter (WM), yet arterial spin labeling (ASL) MRI, the most common non-invasive CBF approach, has poor WM CBF sensitivity owing to low WM CBF and long WM bolus arrival time (BAT). We hypothesize that anemia, and associated cerebral hyperemia, in SCD leads to improved WM detection with ASL. We performed 3-Tesla multi-delay pulsed ASL in SCD (n = 35; age = 30.5 ± 8.3 years) and control (n = 15; age = 28.7 ± 4.5 years) participants and applied t-tests at each inversion time within different flow territories, and determined which regions were significantly above noise floor (criteria: one-sided p < 0.05). Total WM CBF-weighted signal was primarily detectable outside of borderzone regions in SCD (CBF = 17.7 [range = 12.9-25.0] mL/100 g/min), but was largely unphysiological in control (CBF = 8.1 [range = 7.6-9.9)] mL/100 g/min) participants. WM BAT was reduced in SCD versus control participants (ΔBAT = 37 [range = 46-70] ms) and BAT directly correlated with hematocrit (Spearman's-ρ = 0.62; p < 0.001). Findings support the feasibility of WM CBF quantification using ASL in SCD participants for appropriately parameterized protocols.

A Test-Retest Study of Single- and Multi-Delay pCASL for Choroid Plexus Perfusion Imaging in Healthy Subjects Aged 19 to 87 Years

There is a growing interest in the choroid plexus (ChP) due to its critical role in cerebrospinal fluid (CSF) production and its involvement in neurodegenerative and cerebrovascular diseases. However, comprehensive studies comparing the accuracy and reliability of single- and multi-PLD (post-labeling delay) arterial spin labeling (ASL) techniques, specifically in relation to the ChP, remain limited. This study systematically evaluated the test-retest reliability and quantification accuracy of cerebral blood flow (CBF) measurements, focusing on the ChP, using single-delay and multi-delay 3D gradient-and-spin echo (GRASE) pseudo-continuous ASL (pCASL) on 28 subjects (aged 19 to 87 years, 14 males/14 females) at 3.0 tesla. Both single-delay (2 s) and 5-PLD (0.5 - 2.5 s) pCASL scans were repeated approximately one week apart with a spatial resolution of 2.5 × 2.5 × 3 mm³. Voxel-wise and regional CBF and arterial transit time (ATT) measurements were compared to assess test-retest reliability, with a particular focus on ChP perfusion changes with age. In this study, 12.15 % of ChP voxels exhibited ATTs longer than 2 s, potentially leading to a significant underestimation of CBF using single-delay ASL. Multi-delay ASL showed improved accuracy in estimating CBF values for the ChP compared to single-delay ASL when ATT > PLD. Additionally, ChP volume (mean ± std = 1.72± 0.85 ml) increased (p < 0.01) and ChP perfusion (43.07±14.18 mL/100 g/min) decreased (p = 0.04) with age. These findings underscore the robustness of multi-delay ASL with model-fitting quantification in assessing ChP perfusion, making it the preferred method for accurate CBF and ATT estimation, particularly in regions with prolonged transit time such as ChP.

Acute psilocybin and ketanserin effects on cerebral blood flow: 5-HT2AR neuromodulation in healthy humans

Psilocin, the active metabolite of psilocybin, is a psychedelic and agonist at the serotonin 2A receptor (5-HT2AR) that has shown positive therapeutic effects for brain disorders such as depression. To elucidate the brain effects of psilocybin, we directly compared the acute effects of 5-HT2AR agonist (psilocybin) and antagonist (ketanserin) on cerebral blood flow (CBF) using pseudo-continuous arterial spin labeling magnetic resonance imaging (MRI) in a single-blind, cross-over study in 28 healthy participants. We evaluated associations between plasma psilocin level (PPL) or subjective drug intensity (SDI) and CBF. We also evaluated drug effects on internal carotid artery (ICA) diameter using time-of-flight MRI angiography. PPL and SDI were significantly negatively associated with regional and global CBF (∼11.6% at peak drug effect, p < 0.0001). CBF did not significantly change following ketanserin (2.3%, p = 0.35). Psilocybin induced a significantly greater decrease in CBF compared to ketanserin in the parietal cortex (pFWER < 0.0001). ICA diameter was significantly decreased following psilocybin (10.5%, p < 0.0001) but not ketanserin (-0.02%, p = 0.99). Our data support an asymmetric 5-HT2AR modulatory effect on CBF and provide the first in vivo human evidence that psilocybin constricts the ICA, which has important implications for understanding the neurophysiological mechanisms underlying its acute effects.

PINNing cerebral blood flow: analysis of perfusion MRI in infants using physics-informed neural networks

Arterial spin labelling (ASL) magnetic resonance imaging (MRI) enables cerebral perfusion measurement, which is crucial in detecting and managing neurological issues in infants born prematurely or after perinatal complications. However, cerebral blood flow (CBF) estimation in infants using ASL remains challenging due to the complex interplay of network physiology, involving dynamic interactions between cardiac output and cerebral perfusion, as well as issues with parameter uncertainty and data noise. We propose a new spatial uncertainty-based physics-informed neural network (PINN), SUPINN, to estimate CBF and other parameters from infant ASL data. SUPINN employs a multi-branch architecture to concurrently estimate regional and global model parameters across multiple voxels. It computes regional spatial uncertainties to weigh the signal. SUPINN can reliably estimate CBF (relative error - 0.3 ± 71.7 ), bolus arrival time (AT) ( 30.5 ± 257.8 ) , and blood longitudinal relaxation time ( T 1 b ) (-4.4 ± 28.9), surpassing parameter estimates performed using least squares or standard PINNs. Furthermore, SUPINN produces physiologically plausible spatially smooth CBF and AT maps. Our study demonstrates the successful modification of PINNs for accurate multi-parameter perfusion estimation from noisy and limited ASL data in infants. Frameworks like SUPINN have the potential to advance our understanding of the complex cardio-brain network physiology, aiding in the detection and management of diseases. Source code is provided at: https://github.com/cgalaz01/supinn.

A novel model to quantify blood transit time in cerebral arteries using ASL-based 4D magnetic resonance angiography with example clinical application in moyamoya disease

Angiography is critical for visualizing cerebral blood flow in intracranial steno-occlusive diseases. Current 4D magnetic resonance angiography (MRA) techniques primarily focus on macrovascular structures, yet few have quantified hemodynamic timing. This study introduces a novel model to estimate macrovascular arterial transit time (mATT) derived from arterial spin labeling (ASL)-based 4D-MRA. We provide examples of our method that visualize mATT differences throughout the brain of patients with intracranial steno-occlusive disease (moyamoya), as well as changes in mATT resulting from the cerebrovascular reactivity response to an acetazolamide (ACZ) injection. Furthermore, we present a method that projects sparse arterial signals into a 3D native brain-region atlas space and correlates regional mATT with other hemodynamic parameters of interest, such as tissue transit time and cerebrovascular reactivity. This approach offers a non-invasive, quantitative assessment of macrovascular dynamics, with potential to enhance understanding of large-vessel and tissue-level hemodynamics and augment monitoring of treatment outcomes in steno-occlusive disease patients. Furthermore, it sets the stage for more in-depth investigations of the macrovascular contribution to brain hemodynamics.

High-Fidelity MRI Assessment of Cerebral Perfusion in Healthy Neonates Less Than 1 Week of Age

BACKGROUND

Perfusion imaging of the brain has important clinical applications in detecting neurological abnormalities in neonates. However, such tools have not been available to date. Although arterial-spin-labeling (ASL) MRI is a powerful noninvasive tool to measure perfusion, its application in neonates has encountered obstacles related to low signal-to-noise ratio (SNR), large-vessel contaminations, and lack of technical development studies.

PURPOSE

To systematically develop and optimize ASL perfusion MRI in healthy neonates under 1 week of age.

STUDY TYPE

Prospective.

SUBJECTS

Thirty-two healthy term neonates (19 female; postnatal age 1.9 ± 0.7 days).

FIELD STRENGTH/SEQUENCE

3.0 T; T2-weighted half-Fourier single-shot turbo-spin-echo (HASTE) imaging, single-delay and multi-delay 3D gradient-and-spin-echo (GRASE) large-vessel-suppression pseudo-continuous ASL (LVS-pCASL).

ASSESSMENT

Three studies were conducted. First, an LVS-pCASL MRI sequence was developed to suppress large-vessel spurious signals in neonatal pCASL. Second, multiple post-labeling delays (PLDs) LVS-pCASL were employed to simultaneously estimate normative cerebral blood flow (CBF) and arterial transit time (ATT) in neonates. Third, an enhanced background-suppression (BS) scheme was developed to increase the SNR of neonatal pCASL.

STATISTICAL TESTS

Repeated measure analysis-of-variance, paired t-test, spatial intraclass-correlation-coefficient (ICC), and voxel-wise coefficient-of-variation (CoV). P-value <0.05 was considered significant.

RESULTS

LVS-pCASL reduced spurious ASL signals, making the CBF images more homogenous and significantly reducing the temporal variation of CBF measurements by 58.0% when compared to the standard pCASL. Multi-PLD ASL yielded ATT and CBF maps showing a longer ATT and lower CBF in the white matter relative to the gray matter. The highest CBF was observed in basal ganglia and thalamus (10.4 ± 1.9 mL/100 g/min). Enhanced BS resulted in significantly higher test-retest reproducibility (ICC = 0.90 ± 0.04, CoV = 8.4 ± 1.2%) when compared to regular BS (ICC = 0.59 ± 0.12, CoV = 23.6 ± 3.8%).

DATA CONCLUSION

We devised an ASL method that can generate whole-brain CBF images in 4 minutes with a test-retest image ICC of 0.9. This technique holds potential for studying neonatal brain diseases involving perfusion abnormalities.

PLAIN LANGUAGE SUMMARY

MR imaging of cerebral blood flow in neonates remains a challenge due to low blood flow rates and confounding factors from large blood vessels. This study systematically developed an advanced MRI technique to enhance the reliability of perfusion measurements in neonates. The proposed method reduced signal artifacts from large blood vessels and improved the signal-to-noise ratio of brain perfusion images. With this approach, whole-brain neonatal perfusion can be measured in 4 minutes with excellent reproducibility. This technique may provide a useful tool for studying neonatal brain maturation and detecting perfusion abnormalities in diseases.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

Association between carotid artery hemodynamics and neurovascular coupling in cerebral small vessel disease: an exploratory study

Background

Recent studies have linked disrupted cerebral hemodynamics, including pulsatility index (PI) and wall shear stress (WSS), with neuroimaging features of cerebral small vessel disease (CSVD). Cerebral neurovascular coupling (NVC) dysfunction is an important pathophysiological mechanism of CSVD. However, evidence linking the features of carotid artery hemodynamics to cerebral NVC is still lacking.

Objective

This study is aimed to explore the impact of PI and WSS on NVC and cognitive performance in CSVD patients using neuroimaging.

Methods

This study included 52 CSVD patients and 41 healthy controls. Carotid artery PI and WSS were measured using 4D flow magnetic resonance imaging (MRI). NVC was assessed through voxel-wise correlations between cerebral blood flow and the amplitude of low-frequency fluctuations. Multiple linear regression was used to investigate correlations between them.

Results

CSVD patients showed elevated PI in the C2 and C4 segments of the internal carotid artery and reduced WSS in the common carotid artery compared to controls. NVC measurements were significantly diminished in CSVD patients. Multiple linear regression analysis indicated significant correlations between reduced WSS and impaired NVC as well as between reduced PI and impaired NVC, but not between PI, WSS, and cognitive scores.

Conclusion

Reduced WSS and PI in CSVD patients are associated with impaired NVC. These findings provide insights into the mechanisms underlying CSVD and suggest that hemodynamic abnormalities may serve as indicators of neurovascular dysfunction in early-stage CSVD.

Stochastic variational inference improves quantification of multiple timepoint arterial spin labelling perfusion MRI

Multiple-timepoint arterial spin labelling MRI is a non-invasive imaging technique that permits measurement of both cerebral blood flow and arterial transit time, the latter of which is an emerging biomarker of interest for cerebrovascular health. Quantification of arterial spin labelling data is challenging due to the low signal to noise ratio and non-linear tracer kinetics of this technique. In this work, we introduce a new quantification method called SSVB that addresses limitations in existing methods and demonstrate its performance using simulations and acquisition data. Simulations showed that the method is more accurate, particularly for estimating arterial transit time, and more robust to noise than existing techniques. On high spatial resolution data acquired at 3 T, the method produced less noisy parameter maps than the comparator method and captured greater variation in arterial transit time on a cross-sectional cohort.

Quantitative mapping of renal oxygen consumption using pseudo-continuous arterial spin labeling and quantitative susceptibility mapping in humans

PURPOSE

To propose a new method for quantitatively mapping the renal metabolic rate of oxygen (RMRO2) and to evaluate the proposed method using a caffeine challenge.

THEORY AND METHODS

Pseudo-continuous arterial spin labeling (pCASL) and QSM sequences were used to obtain MR images in the kidney. Six healthy volunteers were scanned on caffeine and control days. The pCASL and QSM images were registered using DICOM information and rigid translation. The Fick principle was applied to estimate RMRO2. The results on caffeine and control days were compared to evaluate the capability of the proposed method to estimate renal oxygen consumption. A paired t-test was used to assess the statistical significance.

RESULTS

Estimated renal blood flow (RBF), QSM, and RMRO2 maps were consistent with those reported in the literature. RMRO2 values were higher than the cerebral metabolic rate of oxygen (CMRO2) and were significantly reduced on the caffeine days compared to the control days, consistent with findings from non-MRI literature.

CONCLUSION

The feasibility of measuring renal oxygen consumption using pCASL and QSM images was demonstrated. To the best of our knowledge, this work provides quantitative maps of renal oxygen consumption in humans for the first time. The results were consistent with the literature, including the statistically significant reduction in renal oxygen consumption with caffeine challenge. These findings suggest the potential utility of our technique in measuring renal oxygen consumption noninvasively, especially for patients with complications associated with contrast agents.

Multiparametric functional MRI of the kidneys - evaluation of test-retest repeatability and effects of different manual and automatic image analysis strategies

Multiparametric MRI is a promising technique for noninvasive structural and functional imaging of the kidneys that is gaining increasing importance in clinical research. Still, there are no standardized recommendations for analyzing the acquired images and there is a need to further evaluate the accuracy and repeatability of currently recommended MRI parameters. The aim of the study was to evaluate the test-retest repeatability of functional renal MRI parameters using different image analysis strategies.Ten healthy volunteers were examined twice with a multiparametric renal MRI protocol including arterial spin labeling (ASL), diffusion-weighted imaging (DWI) with intravoxel incoherent motion (IVIM), blood-oxygen-dependent (BOLD) imaging, T1 and T2 mapping, and volumetry with an interval of one week. The quantitative results of both kidneys were determined by manual organ segmentation, ROI analysis, and automatic segmentation based on the nnUNet framework. Test-retest repeatability of each parameter was computed using the within-subject coefficient of variance (wCV) and the intraclass coefficient (ICC). Segmentation accuracy and inter-reader agreement were evaluated using the dice score.Structural tissue parameters (T1, T2) showed wCV (%) between 4 and 11 and an ICC between 0.2 and 0.8. Functional parameters (ASL, BOLD and DWI) showed wCV (%) between 3 and 38 and an ICC between 0.0 and 0.7. The highest variances between test-retest scans were observed in perfusion measurements with ASL and IVIM (wCV: 17-37%). Quantitative analysis of the cortex and medulla showed a better repeatability when acquired using manual segmentation compared to ROI-based image analysis. Comparable repeatability was achieved with manual and automatic segmentation of the total kidney.Reasonable repeatability was achieved for all MR parameters. Structural MR parameters showed better repeatability compared to functional parameters. ROI-based image analysis showed overall lower repeatability compared to manual segmentation. Comparable repeatability to manual segmentation as well as acceptable segmentation accuracy could be achieved with automatic segmentation. · Reasonable test-retest repeatability can be achieved with multiparametric MRI of the kidneys.. · Image analysis based on manual segmentation of the cortex and medulla showed overall better repeatability compared to ROI-based analysis.. · Automatic segmentation of kidney volume showed similar repeatability of quantitative image analysis compared to manual segmentation.. · Liang C, Loster I, Ursprung S et al. Multiparametric functional MRI of the kidneys - evaluation of test-retest repeatability and effects of different manual and automatic image analysis strategies. Fortschr Röntgenstr 2024; DOI 10.1055/a-2480-4885.

Arterial spin labelling perfusion MRI analysis for the Human Connectome Project Lifespan Ageing and Development studies

The Human Connectome Project Lifespan studies cover the Development (5-21) and Aging (36-100+) phases of life. Arterial spin labelling (ASL) was included in the imaging protocol, resulting in one of the largest datasets collected to-date of high spatial resolution multiple delay ASL covering 3,000 subjects. The HCP-ASL minimal processing pipeline was developed specifically for this dataset to pre-process the image data and produce perfusion estimates in both volumetric and surface template space, though quality control is not performed. Applied to the whole dataset, the outputs of the pipeline revealed significant and expected differences in perfusion between the Development and Ageing cohorts. Visual inspection of the group average surface maps showed that cortical perfusion often followed cortical areal boundaries, suggesting differential regulation of cerebral perfusion within brain areas at rest. Group average maps of arterial transit time also showed differential transit times in core and watershed areas of the cerebral cortex, which are useful for interpreting haemodynamics of functional MRI images. The pre-processed dataset will provide a valuable resource for understanding haemodynamics across the human lifespan.

Cerebral blood flow alterations measured by ASL-MRI as a predictor of vascular dementia in small vessel ischemic disease

BACKGROUND

Cerebral small vessel ischemic disease (SVID) as a common age-related morbidity is the key mechanism of vascular cognitive impairment (VCI). This study uses Cerebral blood flow (CBF) measured by pseudo-continuous ASL MRI in SVID patients with and without cognitive impairment to differentiate VCI from normal aging.

MATERIALS AND METHODS

In this cross-sectional study, 74 SVID patients, including 35 with diagnosed VCI and 39 without cognitive impairment (control) underwent pCASL-MRI in the resting state. ROI-based approach pre-processing, denoising techniques, and correction for partial volume effects were performed. Regional CBF was compared between severe cognitive impairment (SCI), mild cognitive impairment (MCI), and SVID patients without cognitive impairment.

RESULTS

Total and regional CBF values in the thalamus, left cortex, hippocampus, post cingulate cortex, precuneus, insula, putamen, and middle temporal lobe was lower in VCI compared to SVID, also in SCI compared MCI group. There was a linear correlation between the Mini-Mental State Examination (MMSE) z score and CBF in the thalamus region in SVID participants and between the MMSE z score and CBF in the medial temporal region in MCI participants. The medial temporal atrophy )MTA( z score was significantly correlated with CBF values in the hippocampus and medial temporal regions in SCI and MCI also a significant correlation was seen between total CBF and Fazekas score.

CONCLUSION

Due to the growing prevalence of dementia and the role of CBF as a predictive biomarker, ASL-MRI as a non-invasive method can be easily added to diagnostic tools of cognitive impairment in individuals with SVID to recognize the initiation of vascular cognitive impairment.

High-resolution perfusion imaging in rodents using pCASL at 9.4 T

Adequate perfusion is critical for maintaining normal brain function and aberrations thereof are hallmarks of many diseases. Pseudo-Continuous Arterial Spin Labeling (pCASL) MRI enables noninvasive quantitative perfusion mapping without contrast agent injection and with a higher signal-to-noise ratio (SNR) than alternative methods. Despite its great potential, pCASL remains challenging, unstable, and relatively low-resolution in rodents - especially in mice - thereby limiting the investigation of perfusion properties in many transgenic or other relevant rodent models of disease. Here, we address this gap by developing a novel experimental setup for high-resolution pCASL imaging in mice and combining it with the enhanced SNR of cryogenic probes. We show that our new experimental setup allows for optimal positioning of the carotids within the cryogenic coil, rendering labeling reproducible. With the proposed methodology, we managed to increase the spatial resolution of pCASL perfusion images by a factor of 15 in mice; a factor of 6 in rats is gained compared to the state of the art just by virtue of the cryogenic coil. We also show that the improved pCASL perfusion imaging allows much better delineation of specific brain areas, both in healthy animals as well as in rat and mouse models of stroke. Our results bode well for future high-definition pCASL perfusion imaging in rodents.

POINTER Study Group. The POINTER Imaging baseline cohort: Associations between multimodal neuroimaging biomarkers, cardiovascular health, and cognition

INTRODUCTION

The U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER) is evaluating lifestyle interventions in older adults at risk for cognitive decline and dementia. Here we characterize the baseline data set of the POINTER Imaging ancillary study.

METHODS

Participants underwent health and cognitive assessments and neuroimaging with multimodal positron emission tomography (PET) (beta-amyloid [Aβ] and tau) and magnetic resonance imaging (MRI). Framingham risk score (FRS) was used to quantify cardiovascular disease (CVD) risk.

RESULTS

A total of 1052 participants (31% from underrepresented ethnoracial groups) were enrolled. Compared to Aβ-, Aβ+ (29%) participants were older, had higher apolipoprotein E (APOE) ε4 carriage rate and white matter hyperintensity volume, and greater temporal tau. FRS was related to MRI measures, but not AD biomarkers. FRS and tau had independent effects on cognition.

DISCUSSION

In this heterogenous, at-risk cohort, CVD risk was related to more abnormal brain structure and poorer cognition, representing a putative non-AD (Alzheimer's disease) pathway to brain injury and cognitive decline.

HIGHLIGHTS

·The U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER) cohort is enriched for cardiovascular disease (CVD) and poor lifestyle ·POINTER Imaging collected multimodal neuroimaging data in this unique, at-risk cohort ·Amyloid burden was related to age, apolipoprotein E (APOE) ε4 carriage, and measures of disease progression ·Associations between amyloid and tau, and tau and cognition, were relatively weak ·CVD risk and tau pathology were independently related to memory.

Non-invasive MRI of blood-cerebrospinal fluid-barrier function in a mouse model of Alzheimer's disease: a potential biomarker of early pathology

BACKGROUND

Choroid plexus (CP) or blood-cerebrospinal fluid-barrier (BCSFB) is a unique functional tissue which lines the brain's fluid-filled ventricles, with a crucial role in CSF production and clearance. BCSFB dysfunction is thought to contribute to toxic protein build-up in neurodegenerative disorders, including Alzheimer's disease (AD). However, the dynamics of this process remain unknown, mainly due to the paucity of in-vivo methods for assessing CP function.

METHODS

We harness recent developments in Arterial Spin Labelling MRI to measure water delivery across the BCSFB as a proxy for CP function, as well as cerebral blood flow (CBF), at different stages of AD in the widely used triple transgenic mouse model (3xTg), with ages between 8 and 32 weeks. We further compared the MRI results with Y-maze behaviour testing, and histologically validated the expected pathological changes, which recapitulate both amyloid and tau deposition.

RESULTS

Total BCSFB-mediated water delivery is significantly higher in 3xTg mice (> 50%) from 8 weeks (preclinical stage), an increase which is not explained by differences in ventricular volumes, while tissue parameters such as CBF and T1 are not different between groups at all ages. Behaviour differences between the groups were observed starting at 20 weeks, especially in terms of locomotion, with 3xTg animals showing a significantly smaller number of arm entries in the Y-maze.

CONCLUSIONS

Our work strongly suggests the involvement of CP in the early stages of AD, before the onset of symptoms and behavioural changes, providing a potential biomarker of pathology.

Trial of the cerebral perfusion response to sodium nitrite infusion in patients with acute subarachnoid haemorrhage using arterial spin labelling MRI

Aneurysmal subarachnoid haemorrhage (SAH) is a devastating subset of stroke. One of the major determinants of outcome is an evolving multifactorial injury occurring in the first 72 hours, known as early brain injury. Reduced nitric oxide (NO) bioavailability and an associated disruption to cerebral perfusion is believed to play an important role in this process. We sought to explore this relationship, by examining the effect on cerebral perfusion of the in vivo manipulation of NO levels using an exogenous NO donor (sodium nitrite). We performed a double blind placebo controlled randomised experimental medicine study of the cerebral perfusion response to sodium nitrite infusion during the early brain injury period in 15 low grade (World Federation of Neurosurgeons grade 1-2) SAH patients. Patients were randomly assigned to receive sodium nitrite at 10 mcg/kg/min or saline placebo. Assessment occurred following endovascular aneurysm occlusion, mean time after ictus 66h (range 34-90h). Cerebral perfusion was quantified before infusion commencement and after 3 hours, using multi-post labelling delay (multi-PLD) vessel encoded pseudocontinuous arterial spin labelling (VEPCASL) magnetic resonance imaging (MRI). Administration of sodium nitrite was associated with a significant increase in average grey matter cerebral perfusion. Group level voxelwise analysis identified that increased perfusion occurred within regions of the brain known to exhibit enhanced vulnerability to injury. These findings highlight the role of impaired NO bioavailability in the pathophysiology of early brain injury.

Higher Validity, Lower Radiation: A New Ictal Single-Photon Emission Computed Tomography Framework

OBJECTIVE

To assess whether arterial spin labeling perfusion images of healthy controls can enhance ictal single-photon emission computed tomography analysis and whether the acquisition of the interictal image can be omitted.

METHODS

We developed 2 pipelines: The first uses ictal and interictal images and compares these to single-photon emission computed tomography and arterial spin labeling of healthy controls. The second pipeline uses only the ictal image and the analogous healthy controls. Both pipelines were compared to the gold standard analysis and evaluated on data of individuals with epilepsy who underwent ictal single-photon emission computed tomography imaging during presurgical evaluation between 2010 and 2022. Fifty healthy controls prospectively underwent arterial spin labeling imaging. The correspondence between the detected hyperperfusion and the postoperative resection cavity or the presumably affected lobe was assessed using Dice score and mean Euclidean distance. Additionally, the outcomes of the pipelines were automatically assigned to 1 of 5 concordance categories.

RESULTS

Inclusion criteria were met by 43 individuals who underwent epilepsy surgery and by 73 non-surgical individuals with epilepsy. Compared to the gold standard analysis, both pipelines resulted in significantly higher Dice scores and lower mean distances (p < 0.05). The combination of both provided localizing results in 85/116 cases, compared to 54/116 generated by the current gold standard analysis and the ictal image alone produced localizing results in 60/116 (52%) cases.

INTERPRETATION

We propose a new ictal single-photon emission computed tomography protocol; it finds relevantly more ictal hyperperfusion, and halves the radiation dose in about half of the individuals. ANN NEUROL 2024;96:1160-1173.

Automated Quality Evaluation Index for Arterial Spin Labeling Derived Cerebral Blood Flow Maps

BACKGROUND

Arterial spin labeling (ASL) derived cerebral blood flow (CBF) maps are prone to artifacts and noise that can degrade image quality.

PURPOSE

To develop an automated and objective quality evaluation index (QEI) for ASL CBF maps.

STUDY TYPE

Retrospective.

POPULATION

Data from N = 221 adults, including patients with Alzheimer's disease (AD), Parkinson's disease, and traumatic brain injury.

FIELD STRENGTH/SEQUENCE

Pulsed or pseudocontinuous ASL acquired at 3 T using non-background suppressed 2D gradient-echo echoplanar imaging or background suppressed 3D spiral spin-echo readouts.

ASSESSMENT

The QEI was developed using N = 101 2D CBF maps rated as unacceptable, poor, average, or excellent by two neuroradiologists and validated by 1) leave-one-out cross validation, 2) assessing if CBF reproducibility in N = 53 cognitively normal adults correlates inversely with QEI, 3) if iterative discarding of low QEI data improves the Cohen's d effect size for CBF differences between preclinical AD (N = 27) and controls (N = 53), 4) comparing the QEI with manual ratings for N = 50 3D CBF maps, and 5) comparing the QEI with another automated quality metric.

STATISTICAL TESTS

Inter-rater reliability and manual vs. automated QEI were quantified using Pearson's correlation. P < 0.05 was considered significant.

RESULTS

The correlation between QEI and manual ratings (R = 0.83, CI: 0.76-0.88) was similar (P = 0.56) to inter-rater correlation (R = 0.81, CI: 0.73-0.87) for the 2D data. CBF reproducibility correlated negatively (R = -0.74, CI: -0.84 to -0.59) with QEI. The effect size comparing patients and controls improved (R = 0.72, CI: 0.59-0.82) as low QEI data was discarded iteratively. The correlation between QEI and manual ratings (R = 0.86, CI: 0.77-0.92) of 3D ASL was similar (P = 0.09) to inter-rater correlation (R = 0.78, CI: 0.64-0.87). The QEI correlated (R = 0.87, CI: 0.77-0.92) significantly better with manual ratings than did an existing approach (R = 0.54, CI: 0.30-0.72).

DATA CONCLUSION

Automated QEI performed similarly to manual ratings and can provide scalable ASL quality control.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

Age-related decline in blood-brain barrier function is more pronounced in males than females in parietal and temporal regions

The blood-brain barrier (BBB) plays a pivotal role in protecting the central nervous system (CNS), and shielding it from potential harmful entities. A natural decline of BBB function with aging has been reported in both animal and human studies, which may contribute to cognitive decline and neurodegenerative disorders. Limited data also suggest that being female may be associated with protective effects on BBB function. Here, we investigated age and sex-dependent trajectories of perfusion and BBB water exchange rate (kw) across the lifespan in 186 cognitively normal participants spanning the ages of 8-92 years old, using a non-invasive diffusion-prepared pseudo-continuous arterial spin labeling (DP-pCASL) MRI technique. We found that the pattern of BBB kw decline with aging varies across brain regions. Moreover, results from our DP-pCASL technique revealed a remarkable decline in BBB kw beginning in the early 60 s, which was more pronounced in males. In addition, we observed sex differences in parietal and temporal regions. Our findings provide in vivo results demonstrating sex differences in the decline of BBB function with aging, which may serve as a foundation for future investigations into perfusion and BBB function in neurodegenerative and other brain disorders.

Inhibiting Ca2+ channels in Alzheimer's disease model mice relaxes pericytes, improves cerebral blood flow and reduces immune cell stalling and hypoxia

Early in Alzheimer's disease (AD), pericytes constrict capillaries, increasing their hydraulic resistance and trapping of immune cells and, thus, decreasing cerebral blood flow (CBF). Therapeutic approaches to attenuate pericyte-mediated constriction in AD are lacking. Here, using in vivo two-photon imaging with laser Doppler and speckle flowmetry and magnetic resonance imaging, we show that Ca2+ entry via L-type voltage-gated calcium channels (CaVs) controls the contractile tone of pericytes. In AD model mice, we identifed pericytes throughout the capillary bed as key drivers of an immune reactive oxygen species (ROS)-evoked and pericyte intracellular calcium concentration ([Ca2+]i)-mediated decrease in microvascular flow. Blocking CaVs with nimodipine early in disease progression improved CBF, reduced leukocyte stalling at pericyte somata and attenuated brain hypoxia. Amyloid β (Aβ)-evoked pericyte contraction in human cortical tissue was also greatly reduced by CaV block. Lowering pericyte [Ca2+]i early in AD may, thus, offer a therapeutic strategy to enhance brain energy supply and possibly cognitive function in AD.

Quantifying myocardial perfusion during MR-guided interventions without exogenous contrast agents: intra-arterial spin labeling

PURPOSE

To test intra-arterial spin labeling (iASL) using active guiding catheters for myocardial perfusion measurements during magnetic resonance (MR)-guided interventions in a pig study.

METHODS

In this work, a single-loop radiofrequency (RF) coil at the tip of a 6F active coronary catheter was used as a transmit coil for local spin labeling. The transmit magnetic RF field (B1) of the coil and the labeling efficiency were determined, and iASL was tested in two pigs after the catheter was engaged in the aortic root, the ostium of the left coronary artery (LCA) under MR-guidance. The iASL effect was assessed by the signal difference between spin-labeling On and control (spin-labeling OFF) images, and in a cross-correlation between ON/Off states of spin-labeling a binary labeling paradigm. In addition, quantitative myocardial perfusion was calculated from the iASL experiments.

RESULTS

The maximum B1 in the vicinity of the catheter coil was 2.1 µT. A strong local labeling effect with a labeling efficiency of 0.45 was achieved with iASL both in vitro and in vivo. In both pigs, the proximal myocardial segments supplied by the LCA showed significant labelling effect up to distances of 60 mm from the aortic root with a relative signal difference of (3.14 ± 2.89)% in the first and (3.50 ± 1.25)% in the second animal. The mean correlation coefficients were R = 0.63 ± 0.22 and 0.42 ± 0.16, respectively. The corresponding computed myocardial perfusion values in this region of the myocardium were similar to those obtained with contrast perfusion methods ((1.2 ± 1.1) mL/min/g and (0.8 ± 0.6) mL/min/g).

CONCLUSION

The proposed iASL method demonstrates the feasibility of selective myocardial perfusion measurements during MR-guided coronary interventions, which with further technical improvements may provide an alternative to exogenous contrast-based perfusion. Due to the invasive nature of the iASL method, it can potentially be used in concert with MRI-guided coronary angioplasty.

A timeline study on vascular co-morbidity induced cerebral endothelial dysfunction assessed by perfusion MRI

Endothelial dysfunction is considered a key element in the early pathogenesis of neurodegenerative disorders. Dysfunction of the cerebral endothelial cells can result in dysregulation of cerebral perfusion and disruption of the Blood Brain Barrier (BBB), leading to brain damage, neurodegeneration and cognitive decline. It has been shown that the presence of modifiable risk factors exacerbates endothelial dysfunction. This study primarily aimed to identify which among various perfusion MRI methodologies could be effectively utilized to non-invasively identify early pathological alterations as a result of endothelial dysfunction. We compared these perfusion MRI measurements to invasive immunohistochemistry to detect early pathological alterations in the cerebral vasculature of a rat model of multiple cardiovascular co-morbidities (the ZSF1 Obese rat) at several stages of the cerebrovascular pathology. We observed cerebral hyperperfusion, expressed by increased Cerebral Blood Flow (CBF) and increased BBB permeability in the ZSF1 Obese rats, at an early stage of disease development. The increase in CBF observed with Arterial Spin Labeling (ASL) was lost during later stages of disease progression. These findings are in line with recent clinical findings in early stages of Alzheimer's disease (AD), that also show early increases in CBF.

Comparison of Myocardial Blood Flow Quantification Models for Double ECG Gating Arterial Spin Labeling MRI: Reproducibility Assessment

BACKGROUND

Arterial spin labeling (ASL) allows non-invasive quantification of myocardial blood flow (MBF). Double-ECG gating (DG) ASL is more robust to heart rate variability than single-ECG gating (SG), but its reproducibility requires further investigation. Moreover, the existence of multiple quantification models hinders its application. Frequency-offset-corrected-inversion (FOCI) pulses provide sharper edge profiles than hyperbolic-secant (HS), which could benefit myocardial ASL.

PURPOSE

To assess the performance of MBF quantification models for DG compared to SG ASL, to evaluate their reproducibility and to compare the effects of HS and FOCI pulses.

STUDY TYPE

Prospective.

SUBJECTS

Sixteen subjects (27 ± 8 years).

FIELD STRENGTH/SEQUENCE

1.5 T/DG and SG flow-sensitive alternating inversion recovery ASL.

ASSESSMENT

Three models for DG MBF quantification were compared using Monte Carlo simulations and in vivo experiments. Two models used a fitting approach (one using only a single label and control image pair per fit, the other using all available image pairs), while the third model used a T1 correction approach. Slice profile simulations were conducted for HS and FOCI pulses with varying B0 and B1. Temporal signal-to-noise ratio (tSNR) was computed for different acquisition/quantification strategies and inversion pulses. The number of images that minimized MBF error was investigated in the model with highest tSNR. Intra and intersession reproducibility were assessed in 10 subjects.

STATISTICAL TESTS

Within-subject coefficient of variation, analysis of variance. P-value <0.05 was considered significant.

RESULTS

MBF was not different across acquisition/quantification strategies (P = 0.27) nor pulses (P = 0.9). DG MBF quantification models exhibited significantly higher tSNR and superior reproducibility, particularly for the fitting model using multiple images (tSNR was 3.46 ± 2.18 in vivo and 3.32 ± 1.16 in simulations, respectively; wsCV = 16%). Reducing the number of ASL pairs to 13/15 did not increase MBF error (minimum = 0.22 mL/g/min).

DATA CONCLUSION

Reproducibility of MBF was better for DG than SG acquisitions, especially when employing a fitting model.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 1.

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

BACKGROUND

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

PURPOSE

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

STUDY TYPE

Retrospective cross-sectional.

POPULATION

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

FIELD STRENGTH/SEQUENCE

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

ASSESSMENT

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

STATISTICAL TESTS

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

RESULTS

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

DATA CONCLUSION

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

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 3.

Efficient 3D cone trajectory design for improved combined angiographic and perfusion imaging using arterial spin labeling

PURPOSE

To improve the spatial resolution and repeatability of a non-contrast MRI technique for simultaneous time resolved 3D angiography and perfusion imaging by developing an efficient 3D cone trajectory design.

METHODS

A novel parameterized 3D cone trajectory design incorporating the 3D golden angle was integrated into 4D combined angiography and perfusion using radial imaging and arterial spin labeling (CAPRIA) to achieve higher spatial resolution and sampling efficiency for both dynamic angiography and perfusion imaging with flexible spatiotemporal resolution. Numerical simulations and physical phantom scanning were used to optimize the cone design. Eight healthy volunteers were scanned to compare the original radial trajectory in 4D CAPRIA with our newly designed cone trajectory. A locally low rank reconstruction method was used to leverage the complementary k-space sampling across time.

RESULTS

The improved sampling in the periphery of k-space obtained with the optimized 3D cone trajectory resulted in improved spatial resolution compared with the radial trajectory in phantom scans. Improved vessel sharpness and perfusion visualization were also achieved in vivo. Less dephasing was observed in the angiograms because of the short TE of our cone trajectory and the improved k-space sampling efficiency also resulted in higher repeatability compared to the original radial approach.

CONCLUSION

The proposed 3D cone trajectory combined with 3D golden angle ordering resulted in improved spatial resolution and image quality for both angiography and perfusion imaging and could potentially benefit other applications that require an efficient sampling scheme with flexible spatial and temporal resolution.

Dose-Painting Proton Radiotherapy Guided by Functional MRI in Non-enhancing High-Grade Gliomas

AIMS

This study aimed to demonstrate the feasibility and evaluate the dosimetric effect and clinical impact of dose-painting proton radiotherapy (PRT) guided by functional MRI in non-enhancing high-grade gliomas (NE-HGGs).

MATERIALS AND METHODS

The 3D-ASL and T2 FLAIR MR images of ten patients with NE-HGGs before radiotherapy were studied retrospectively. The hyperintensity on T2 FLAIR was used to generate the planning target volume (PTV), and the high-perfusion volume on 3D-ASL (PTV-ASL) was used to generate the simultaneous integrated boost (SIB) volume. Each patient received pencil beam scanning PRT and photon intensity-modulated radiotherapy (IMRT). There were five plans in each modality: (1) Uniform plans (IMRT60 vs. PRT60): 60Gy in 30 fractions to the PTV. (2)-(5) SIB plans (IMRT72, 84, 96, 108 vs. PRT72, 84, 96, 108): Uniform plan plus additional dose boost to PTV-ASL in 30 fractions to 72, 84, 96, 108 Gy. The dosimetric differences between various plans were compared. The clinical effects of target volume and organs at risk (OARs) were assessed using biological models for both tumor control probability (TCP) and normal tissue complication probability (NTCP).

RESULTS

Compared with the IMRT plan, the D2 and D50 of the PRT plans with the same prescription dose increased by 1.27-4.12% and 0.64-2.01%, respectively; the R30 decreased by > 32%; the dose of brainstem and chiasma decreased by > 27% and >32%; and the dose of normal brain tissue (Br-PTV), optic nerves, eyeballs, lens, cochlea, spinal cord, and hippocampus decreased by > 50% (P < 0.05). The maximum necessary dose was 96GyE to achieve >98% TCP for PRT, and it was 84Gy to achieve >91% TCP for IMRT. The average NTCP of Br-PTV was 1.30% and 1.90% for PRT and IMRT at the maximum dose escalation, respectively. The NTCP values of the remaining OARs approached zero in all PRT plans.

CONCLUSION

The functional MRI-guided dose escalation using PRT is feasible while sparing the OARs constraints and demonstrates a potential clinical benefit by improving TCP with no or minimal increase in NCTP for tissues outside the PTV. This retrospective study suggested that the use of PRT-based SIB guided by functional MRI may represent a strategy to provide benefits for patients with NE-HGGs.

Real-time fMRI neurofeedback of the anterior insula using arterial spin labelling

Arterial spin labelling (ASL) is the only non-invasive technique that allows absolute quantification of perfusion and is increasingly used in brain activation studies. Contrary to the blood oxygen level-dependent (BOLD) effect ASL measures the cerebral blood flow (CBF) directly. However, the ASL signal has a lower signal-to-noise ratio (SNR), than the BOLD signal, which constrains its utilization in neurofeedback studies. If successful, ASL neurofeedback can be used to aid in the rehabilitation of health conditions with impaired blood flow, for example, stroke. We provide the first ASL-based neurofeedback study incorporating a double-blind, sham-controlled design. A pseudo-continuous ASL (pCASL) approach with background suppression and 3D GRASE readout was combined with a real-time post-processing pipeline. The real-time pipeline allows to monitor the ASL signal and provides real-time feedback on the neural activity to the subject. In total 41 healthy adults (19-56 years) divided into three groups underwent a neurofeedback-based emotion imagery training of the left anterior insula. Two groups differing only in the explicitness level of instruction received real training and a third group received sham feedback. Only those participants receiving real feedback with explicit instruction showed significantly higher absolute CBF values in the trained region during neurofeedback than participants receiving sham feedback. However, responder analyses of percent signal change values show no differences in activation between the three groups. Persisting limitations, such as the lower SNR, confounding effects of arterial transit time and partial volume effects still impact negatively the implementation of ASL neurofeedback.

Quantitative non-contrast perfusion MRI in the body using arterial spin labeling

Arterial spin labeling (ASL) is a non-invasive magnetic resonance imaging (MRI) method that enables the assessment and the quantification of perfusion without the need for an exogenous contrast agent. ASL was originally developed in the early 1990s to measure cerebral blood flow. The utility of ASL has since then broadened to encompass various organ systems, offering insights into physiological and pathological states. In this review article, we present a synopsis of ASL for quantitative non-contrast perfusion MRI, as a contribution to the special issue titled "Quantitative MRI-how to make it work in the body?" The article begins with an introduction to ASL principles, followed by different labeling strategies, such as pulsed, continuous, pseudo-continuous, and velocity-selective approaches, and their role in perfusion quantification. We proceed to address the technical challenges associated with ASL in the body and outline some of the innovative approaches devised to surmount these issues. Subsequently, we summarize potential clinical applications, challenges, and state-of-the-art ASL methods to quantify perfusion in some of the highly perfused organs in the thorax (lungs), abdomen (kidneys, liver, pancreas), and pelvis (placenta) of the human body. The article concludes by discussing future directions for successful translation of quantitative ASL in body imaging.

Recommendations for quantitative cerebral perfusion MRI using multi-timepoint arterial spin labeling: Acquisition, quantification, and clinical applications

Accurate assessment of cerebral perfusion is vital for understanding the hemodynamic processes involved in various neurological disorders and guiding clinical decision-making. This guidelines article provides a comprehensive overview of quantitative perfusion imaging of the brain using multi-timepoint arterial spin labeling (ASL), along with recommendations for its acquisition and quantification. A major benefit of acquiring ASL data with multiple label durations and/or post-labeling delays (PLDs) is being able to account for the effect of variable arterial transit time (ATT) on quantitative perfusion values and additionally visualize the spatial pattern of ATT itself, providing valuable clinical insights. Although multi-timepoint data can be acquired in the same scan time as single-PLD data with comparable perfusion measurement precision, its acquisition and postprocessing presents challenges beyond single-PLD ASL, impeding widespread adoption. Building upon the 2015 ASL consensus article, this work highlights the protocol distinctions specific to multi-timepoint ASL and provides robust recommendations for acquiring high-quality data. Additionally, we propose an extended quantification model based on the 2015 consensus model and discuss relevant postprocessing options to enhance the analysis of multi-timepoint ASL data. Furthermore, we review the potential clinical applications where multi-timepoint ASL is expected to offer significant benefits. This article is part of a series published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group, aiming to guide and inspire the advancement and utilization of ASL beyond the scope of the 2015 consensus article.

Water exchange across the blood-brain barrier and epilepsy: Review on pathophysiology and neuroimaging

The blood-brain barrier (BBB) is a barrier protecting the brain and a milieu of continuous exchanges between blood and brain. There is emerging evidence that the BBB plays a major role in epileptogenesis and drug-resistant epilepsy, through several mechanisms, such as water homeostasis dysregulation, overexpression of drug transporters, and inflammation. Studies have shown abnormal water homeostasis in epileptic tissue and altered aquaporin-4 water channel expression in animal epilepsy models. This review focuses on abnormal water exchange in epilepsy and describes recent non-invasive MRI methods of quantifying water exchange. PLAIN LANGUAGE SUMMARY: Abnormal exchange between blood and brain contribute to seizures and epilepsy. The authors describe why correct water balance is necessary for healthy brain functioning and how it is impacted in epilepsy. This review also presents recent MRI methods to measure water exchange in human brain. These measures would improve our understanding of factors leading to seizures.

Reproducibility of arterial spin labeling cerebral blood flow image processing: A report of the ISMRM open science initiative for perfusion imaging (OSIPI) and the ASL MRI challenge

PURPOSE

Arterial spin labeling (ASL) is a widely used contrast-free MRI method for assessing cerebral blood flow (CBF). Despite the generally adopted ASL acquisition guidelines, there is still wide variability in ASL analysis. We explored this variability through the ISMRM-OSIPI ASL-MRI Challenge, aiming to establish best practices for more reproducible ASL analysis.

METHODS

Eight teams analyzed the challenge data, which included a high-resolution T1-weighted anatomical image and 10 pseudo-continuous ASL datasets simulated using a digital reference object to generate ground-truth CBF values in normal and pathological states. We compared the accuracy of CBF quantification from each team's analysis to the ground truth across all voxels and within predefined brain regions. Reproducibility of CBF across analysis pipelines was assessed using the intra-class correlation coefficient (ICC), limits of agreement (LOA), and replicability of generating similar CBF estimates from different processing approaches.

RESULTS

Absolute errors in CBF estimates compared to ground-truth synthetic data ranged from 18.36 to 48.12 mL/100 g/min. Realistic motion incorporated into three datasets produced the largest absolute error and variability between teams, with the least agreement (ICC and LOA) with ground-truth results. Fifty percent of the submissions were replicated, and one produced three times larger CBF errors (46.59 mL/100 g/min) compared to submitted results.

CONCLUSIONS

Variability in CBF measurements, influenced by differences in image processing, especially to compensate for motion, highlights the significance of standardizing ASL analysis workflows. We provide a recommendation for ASL processing based on top-performing approaches as a step toward ASL standardization.