Evaluation of glymphatic system activity with the diffusion MR technique: diffusion tensor image analysis along the perivascular space (DTI-ALPS) in Alzheimer's disease cases

Targeting the brain's glymphatic pathway: A novel therapeutic approach for cerebral small vessel disease

Cerebral small vessel disease encompasses a group of neurological disorders characterized by injury to small blood vessels, often leading to stroke and dementia. Due to its diverse etiologies and complex pathological mechanisms, preventing and treating cerebral small vessel vasculopathy is challenging. Recent studies have shown that the glymphatic system plays a crucial role in interstitial solute clearance and the maintenance of brain homeostasis. Increasing evidence also suggests that dysfunction in glymphatic clearance is a key factor in the progression of cerebral small vessel disease. This review begins with a comprehensive introduction to the structure, function, and driving factors of the glymphatic system, highlighting its essential role in brain waste clearance. Afterwards, cerebral small vessel disease was reviewed from the perspective of the glymphatic system, after which the mechanisms underlying their correlation were summarized. Glymphatic dysfunction may lead to the accumulation of metabolic waste in the brain, thereby exacerbating the pathological processes associated with cerebral small vessel disease. The review also discussed the direct evidence of glymphatic dysfunction in patients and animal models exhibiting two subtypes of cerebral small vessel disease: arteriolosclerosis-related cerebral small vessel disease and amyloid-related cerebral small vessel disease. Diffusion tensor image analysis along the perivascular space is an important non-invasive tool for assessing the clearance function of the glymphatic system. However, the effectiveness of its parameters needs to be enhanced. Among various nervous system diseases, including cerebral small vessel disease, glymphatic failure may be a common final pathway toward dementia. Overall, this review summarizes prevention and treatment strategies that target glymphatic drainage and will offer valuable insight for developing novel treatments for cerebral small vessel disease.

Measuring glymphatic function: Assessing the toolkit

Glymphatic flow has been proposed to clear brain waste while we sleep. Cerebrospinal fluid moves from periarterial to perivenous spaces through the parenchyma, with subsequent cerebrospinal fluid drainage to dural lymphatics. Glymphatic disruption is associated with neurological conditions such as Alzheimer's disease and traumatic brain injury. Therefore, investigating its structure and function may improve understanding of pathophysiology. The recent controversy on whether glymphatic flow increases or decreases during sleep demonstrates that the glymphatic hypothesis remains contentious. However, discrepancies between different studies could be due to limitations of the specific techniques used and confounding factors. Here, we review the methods used to study glymphatic function and provide a toolkit from which researchers can choose. We conclude that tracer analysis has been useful, ex vivo techniques are unreliable, and in vivo imaging is still limited. Finally, we explore the potential for future methods and highlight the need for in vitro models, such as microfluidic devices, which may address technique limitations and enable progression of the field.

Functional abnormalities of the glymphatic system in cognitive disorders

Various pathological mechanisms represent distinct therapeutic targets for cognitive disorders, but a balance between clearance and production is essential for maintaining the stability of the brain's internal environment. Thus, the glymphatic system may represent a common pathway by which to address cognitive disorders. Using the established model of the glymphatic system as our foundation, this review disentangles and analyzes the components of its clearance mechanism, including the initial inflow of cerebrospinal fluid, the mixing of cerebrospinal fluid with interstitial fluid, and the outflow of the mixed fluid and the clearance. Each section summarizes evidence from experimental animal models and human studies, highlighting the normal physiological properties of key structures alongside their pathological manifestations in cognitive disorders. The same pathologic manifestations of different cognitive disorders appearing in the glymphatic system and the same upstream influences are main points of interest of this review. We conclude this article by discussing new findings and outlining the limitations identified in current research progress.

Age-related change of glymphatic function in normative children assessed using diffusion tensor imaging-analysis along the perivascular space

BACKGROUND

The glymphatic system, crucial for brain waste removal and homeostasis, has an underexplored developmental trajectory in children. This study describes changes in glymphatic function during childhood via diffusion tensor imaging-analysis along the perivascular space (DTI-ALPS).

METHODS

We retrospectively studied DTI MR images of 72 pediatric participants (mean age = 92.37 months; 0-19.8 years; 50 % females), all showing normal MRI findings from 2019 to 2022. Imaging utilized 3 T scanners with a DTI sequence of 21 diffusion-encoded gradients, focusing on the ALPS index to assess glymphatic function. Clinical outcomes were determined using the Pediatric Cerebral Performance Category Scale and medical records within two weeks post-MRI. Regions-of-interest on diffusion maps were selected manually, guided by fractional anisotropy maps, for automatic ALPS computation. Pearson correlation and multiple linear regression analyzed the relationship between ALPS indices, age, and clinical scores, with a paired t-test comparing bilateral ALPS indices. Significance was set at P < 0.05.

RESULTS

Significant positive correlations between age and both left (R = 0.510, P < 0.001) and right (R = 0.688, P < 0.001) DTI-ALPS indices were observed, indicating developmental changes in glymphatic function. Age alone significantly predicted the DTI-ALPS indices (left ALPS: adjusted R2 = 0.235; right ALPS: adjusted R2 = 0.460), underscoring its developmental trajectory. The study found no significant differences between left and right DTI-ALPS indices, suggesting symmetrical glymphatic function during childhood.

CONCLUSION

This study reveals developmental changes in the glymphatic system across childhood, demonstrating an age-related increase in glymphatic function and bilateral symmetry.

Glymphatic pathway dysfunction in severe obstructive sleep apnea: A meta-analysis

BACKGROUND

Obstructive sleep apnea (OSA), a sleep disorder, is associated with cognitive decline and is potentially linked to glymphatic system dysfunction. This meta-analysis investigates glymphatic function in severe OSA (apnea-hypopnea index ≥30) using the Diffusion Tensor Imaging Analysis along the Perivascular Space (DTI-ALPS) index.

METHODS

This study followed PRISMA guidelines for systematic reviews and meta-analyses. A comprehensive search of PubMed, Web of Science, Scopus, and Embase was conducted from inception to January 20, 2024. Studies investigating the ALPS index in OSA using DTI were included. Analyses included a random-effects meta-analysis, sensitivity analysis, meta-regression, publication bias evaluation (funnel plot, Egger's test, and Begg's test), and risk of bias assessment.

RESULTS

Systematic review identified four studies (137 patients with severe OSA and 170 healthy controls (HCs)). Pooled analysis revealed a significant reduction in the DTI-ALPS index in severe OSA patients compared to HCs (standardized mean difference: -0.95, 95 % CI: -1.46 to -0.44, p < 0.001), indicating impaired glymphatic function. Heterogeneity was moderate to high (I2 = 76.07 %), but sensitivity analyses confirmed robustness. Meta-regression analyses identified the sources of heterogeneity as the apnea-hypopnea index (β = -0.039, p = 0.009) and the Epworth Sleepiness Scale (β = -0.150, p = 0.032), with no effects observed for age or male ratio. Qualitative (funnel plot) and quantitative publication bias assessments (Egger's and Begg's tests) showed no significant bias, and risk of bias evaluations using the Newcastle-Ottawa Scale indicated high methodological quality across studies.

CONCLUSIONS

These findings suggest that severe OSA disrupts glymphatic activity. The DTI-ALPS index emerges as a promising tool for assessing glymphatic dysfunction in OSA.

Altered default mode network and glymphatic function in insomnia with depression: A multimodal MRI study

OBJECTIVES

This study aims to evaluate functional changes in the default mode network (DMN) and glymphatic system in individuals of chronic insomnia disorder (CID) with comorbid major depression disorder (MDD).

METHODS

A total of 112 CID patients and 56 healthy controls with good sleep (GS) were enrolled. CID patients were divided into were further divided into a CID-only group and a group with CID and comorbid MDD. Resting-state functional magnetic resonance imaging (rs-fMRI) assessed DMN dysfunction and its connectivity with external networks. To determine whether comorbid MDD exacerbated the decline in glymphatic function in patients with CID, the diffusion tensor imaging along the perivascular space (DTI-ALPS) index was calculated. Binary logistic regression identified key imaging features for diagnostic modeling.

RESULTS

Patients with CID and comorbid MDD exhibited significantly weakened functional connectivity within the DMN. In contrast, the key node posterior cingulate cortex(PCC) of the default mode network showed enhanced functional connectivity with brain regions outside the DMN, including middle cingulate cortex and supplementary motor area. Regarding the glymphatic system, the lower ALPS index in CID patients with comorbid MDD was lower than in CID patients, indicating reduced glymphatic function compared to those without depression. HAMD scores were significantly associated with bilateral Dyproj values (P < 0.001) and the functional connectivity values of PCC_L-SMA_L and TempP_L-PHC_L (P < 0.01). The diagnostic model developed based on these findings demonstrated high diagnostic efficacy for CID with comorbid MDD.

CONCLUSION

The destabilization of subsystems within the DMN may represent the neurological mechanism through which depression contributes to insomnia. Comorbid depressive disorders may exacerbate glymphatic dysfunction in patients with CID, highlighting the importance of early clinical intervention for depressive symptoms in insomnia disorder.

Glymphatic system dysfunction in adult ADHD: Relationship to cognitive performance

OBJECTIVES

While attention-deficit/hyperactivity disorder (ADHD) persists into adulthood, the relationship between glymphatic system function and cognitive performance in adult ADHD remains unclear. This study investigated the association between glymphatic system markers and cognitive outcomes in adults with ADHD.

METHODS

This case-control study includes 41 adults with ADHD and 108 age-matched healthy controls (HCs). Glymphatic function was evaluated using choroid plexus volume (CPV), diffusion tensor imaging along the perivascular space (DTI-ALPS) index and coupling between blood‑oxygen-level-dependent signals and cerebrospinal fluid signals (BOLD-CSF coupling). Cognitive performance was measured using standardized neuropsychological tests.

RESULTS

Compared with HCs, adults with ADHD exhibited significantly lower bilateral and whole-brain ALPS indices (P < 0.05). Although CPV was increased in the ADHD group, this difference did not reach statistical significance, and no significant differences were observed in BOLD-CSF coupling between the two groups. Furthermore, whole-brain ALPS indices were positively associated with visual memory performance (r = 0.422, P = 0.005), an effect that was more pronounced in the right hemisphere (r = 0.458, P = 0.002).

LIMITATIONS

The cross-sectional design limits causal inferences, and the effects of medication were not fully accounted for.

CONCLUSIONS

These findings identify an association between glymphatic dysfunction and cognitive impairment in adults with ADHD. The observed correlation suggests that alterations in glymphatic function may underlie ADHD-related cognitive deficits. Targeting these pathways could provide novel therapeutic opportunities in the management of adult ADHD.

Glymphatic Impairment Associated with Neurocognitive Dysfunction in Moyamoya Disease

Glymphatic system alterations have been proved to be associated with cognitive dysfunction in neurodegenerative diseases. The glymphatic pathway has not been elucidated in moyamoya disease (MMD), which was recognized as a chronic hypoperfusion model for neurodegenerative disease. Here, we aimed to investigate the glymphatic system activity and its relation with neurocognition, and associated hallmarks in MMD. We prospectively recruited 30 MMD patients and 30 matched healthy controls (HC). Participants underwent MRI and neurocognition evaluation. The glymphatic function was assessed by diffusion tensor image analysis along perivascular space (DTI-ALPS) index. Gray matter volume (GMV) and microstructural alterations were calculated. Neurodegenerative-related serum biomarkers were examined. The mediation effect of ALPS index in the associations between variables and neurocognition were further explored. A lower ALPS index was identified in patients with MMD (P < 0.001). The decreased ALPS index was significantly correlated with declined neurocognitive performance. Moreover, the reduced ALPS index was notably linked with lower total GMV% and deep GMV% (P < 0.01). Microstructural changes in the periventricular areas were detected and associated with ALPS index in MMD. Serum neurodegenerative biomarkers (ApoE, Aβ40, Aβ42, and Aβ42/Aβ40) were significantly elevated and related to ALPS index. Additionally, the ALPS index significantly mediated the associations of microstructural alterations and ApoE level with neurocognitive dysfunction. The ALPS index was notably lower MMD in patients, suggesting the utility as a marker of potential glymphatic dysfunction. The index acted as a significant mediator in neurocognitive dysfunction. These findings indicated that glymphatic impairment may interact with MMD-related pathophysiological processes.

Advances in neuroimaging of multiple sclerosis

PURPOSE OF REVIEW

To summarize recent advancements in understanding multiple sclerosis (MS) pathophysiology, predicting disease course, and monitoring treatment responses using MRI.

RECENT FINDINGS

Paramagnetic rim lesions (PRLs) are highly specific to MS and clinically relevant. Detected from the earliest disease phases, PRLs aid in distinguishing MS from other conditions, improving diagnostic accuracy. Moreover, PRLs are associated with more severe disability and measures of brain damage and may predict disease progression. Similarly, slowly expanding lesions (SELs) are associated with more severe disability and predict a more severe disease course. Disease-modifying therapies have limited effectiveness in reducing PRLs or SELs. Choroid plexus (CP) enlargement is associated with structural brain damage and clinical disability and predicts disease evolution. Enlarged perivascular spaces (ePVS) suggest microangiopathic changes rather than direct MS-related inflammation. Glymphatic dysfunction, evaluated using diffusion tensor image analysis along the perivascular space, emerges early in MS and correlates with disability, cognitive impairment, and structural brain damage. Aging and comorbidities exacerbate MS-related damage, complicating diagnosis and treatment. Emerging technologies, such as brain-age paradigms, aim to disentangle aging from MS-specific neurodegeneration.

SUMMARY

Advances in MRI have highlighted the clinical significance of chronic inflammation and glymphatic dysfunction as early contributors to MS progression as well as the interplay between aging, comorbidities and MS.

Investigating glymphatic function and bed nucleus of the stria terminalis-based functional connectivity in Parkinson's disease with and without depression

Glymphatic activity and the bed nucleus of the stria terminalis (BNST) have been implicated in the pathogenesis of Parkinson's disease (PD) with depression (PDD). This study aimed to investigate glymphatic function and BNST-based functional connectivity (FC) and potential biomarkers in PDD. The diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) index combined with BNST-based FC and support vector machine were applied to 24 PDD, 24 PD with non-depression (PDND), and 25 healthy controls. We found that (1) the DTI-ALPS indices (p < 0.001), the right BNST-based FC values (p < 0.001, FWE small volume correction) were significantly different among three groups; (2) the FC features in the right mPFC (mPFC_R), right MTG (MTG_R), and right ITG (ITG_R) can distinguish PDD from PDND; (3) the right BNST-based FC values, DTI-ALPS indices, and HAMD scores were correlated with each other (r = -0.620, p = 0.004; r = 0.651, p = 0.002; r = -0.53, p = 0.016). Impaired glymphatic function and altered BNST-based FC values are strongly associated with PD, and brain regions with differences in the right BNST-based FC values may serve as potential biomarkers for classifying clinical subtypes of PD. These findings provide new insights into the pathogenesis of depression in PD. This study protocol was registered on the Chinese Clinical Trial Registry (ChiCTR2000038411, September 22, 2020, https://www.chictr.org.cn/showproj.html?proj=56715 ).

Glymphatic dysfunction in relapsing-remitting multiple sclerosis and its association with brain structural damage and cognitive impairment

OBJECTIVE

To explore the glymphatic dysfunction in relapsing-remitting multiple sclerosis (RRMS) and its potential associations with brain structural damage, clinical disability, and cognitive impairment (Co-I).

METHODS

The study involved 70 patients with RRMS and 44 healthy controls. Neurological and MRI assessments were performed, and cognitive performance was assessed via the Brief Repeatable Battery of Neuropsychological Tests (BRB-N). To assess the glymphatic function, we calculated the choroid plexus volume (CPV) and diffusion tensor imaging along perivascular spaces (DTI-ALPS) index. Multivariable linear regression analyses were used to examine correlations between glymphatic dysfunction and MRI-derived brain damage metrics. Additionally, we utilised random forest analysis to identify predictors of Co-I and assessed the mediating role of DTI-ALPS.

RESULTS

Patients with RRMS, particularly those with Co-I, exhibited a low DTI-ALPS index and large CPV. A lower DTI-ALPS index was associated with longer disease duration, greater disability, larger lesion volume (LV), mean diffusivity (MD), and CPV, as well as lower fractional anisotropy (FA) (all FDR-p < 0.05). Moreover, DTI-ALPS mediated 27.21 % and 43.75 % of CPV effects on information processing speed and visuospatial memory, respectively. Random forest analysis indicated that lower education (relative importance [RI] = 100 %), higher CPV (RI = 95.8 %), lower DTI-ALPS index (RI = 80.7 %), higher MD (RI = 61.3 %), lower FA (RI = 60.5 %), older age (RI = 54.6 %), and higher EDSS score (RI = 45.4 %) are predictors of Co-I.

CONCLUSION

The study implied that glymphatic dysfunction may contribute to brain structural damage, clinical disability, and cognitive impairment in RRMS, indicating that glymphatic dysfunction may play a key role in the pathogenesis of RRMS.

Unchanged Early Diffusion Tensor Imaging Along Perivascular Space Index After Amyloid-Targeting Disease-Modifying Therapy in Alzheimer's Disease: A Preliminary Study

Purpose

No longitudinal imaging biomarkers have been validated to capture early glymphatic changes during disease-modifying therapy (DMT) for Alzheimer's disease (AD). This study investigated whether the diffusion tensor imaging along the perivascular space (DTI-ALPS) index can detect early treatment-related changes in participants with AD who initiate amyloid-targeting DMT.

Methods

Thirteen participants with AD (mean age, 72 years; 8 women) who initiated lecanemab therapy prospectively underwent DTI at baseline and three months. Projection and association fiber regions of interest, predefined in the HCP-1065 atlas, were inversely warped to the native space with vector-aware linear and non-linear registration, enabling a fully automated DTI-ALPS index calculation. Within-participant variances were obtained from 23 healthy volunteers in the OASIS dataset and used to set an equivalence margin of ±0.05 and determine a required sample size of 13. The primary end-point was equivalence of pre- and post-treatment DTI-ALPS indices (a two one-sided test; one-sided α = 0.05). Second, a paired t-test was used to assess the changes. The intraclass correlation coefficients (ICCs) of the DTI-ALPS indices were also evaluated in identical machine environments and between different environments.

Results

Baseline and three-month DTI-ALPS indices were 1.515 and 1.513, respectively. The mean change was 0.002 (90% confidence interval: -0.049, +0.045), entirely within the pre-specified margin; both one-sided p-values were < 0.05, confirming statistical equivalence. A paired t-test showed no significant difference (p = 0.94). Automated processing yielded perfect within-platform reproducibility (ICC = 1.00) and excellent cross-platform reliability (ICC = 0.99).

Conclusion

The DTI-ALPS index, an imaging metric associated with glymphatic activity, did not change during the first three months of lecanemab therapy. Although this finding suggests that glymphatic alterations may not be detectable early after treatment initiation, larger cohorts and longer follow-up periods are required to clarify the temporal relationship between DTI-ALPS index dynamics and therapeutic effects.

Advances in Diagnostic Imaging of the Glial Lymphatic System in Alzheimer's Disease

The glial lymphatic system (GLS) is responsible for removing metabolic waste and aberrantly deposited substances from brain by exchanging materials with interstitial fluid (ISF), thereby maintaining cerebral homeostasis. Dysfunction in this system can result in the abnormal accumulation of amyloid-beta (Aβ) and tau proteins, leading to cognitive impairments. Recent advancements in neuroimaging have enhanced the evaluation of GLS function, forming a vital component of Alzheimer's disease (AD) diagnostics. This article offers a comprehensive overview of the imaging performance of various methods used to visualize the glial lymphatic system in Alzheimer's disease (AD), highlighting their respective advantages and limitations.

Sleep disturbances are related to glymphatic dysfunction in blepharospasm

Research has shown a close relationship between sleep and glymphatic function, with impaired glymphatic function potentially contributing to sleep problems in a bidirectional way. However, its role in sleep disturbances associated with dystonia remains unknown. This cross-sectional study aimed to investigate whether glymphatic function is impaired in dystonia and to explore its relationship with sleep disturbances. We conducted structural magnetic resonance imaging and diffusion tensor imaging (DTI) on two large cohorts: patients with blepharospasm (BSP, n = 45) and cervical dystonia (CD, n = 43), alongside age- and sex-matched healthy controls (HCs). Anxiety, depression, and sleep quality were evaluated using the Hamilton Anxiety Scale (HAMA), Hamilton Depression Scale (HAMD), and Pittsburgh Sleep Quality Index (PSQI), respectively. Analysis along the perivascular space (DTI-ALPS) index and choroid plexus volume (CPV) was used to assess glymphatic function in these participants. Patients with BSP and CD had higher HAMA, HAMD, and PSQI scores than those of HCs. Patients with BSP exhibited a lower DTI-ALPS index and larger CPV than those of HCs, while no significant differences were found between CD and HCs. In BSP and CD, PSQI scores positively correlated with HAMA and HAMD scores and negatively with the DTI-ALPS index in BSP. Multivariate analysis identified the DTI-ALPS index as a dependent predictive factor of the PSQI in patients with BSP. Our findings suggest that glymphatic function varies across types of focal dystonia, with glymphatic dysfunction potentially playing an important role in the pathogenesis of sleep disturbances in BSP.

Atrial fibrillation catheter ablation, brain glymphatic function, and cognitive performance

BACKGROUND AND AIMS

It remains unknown whether the brain glymphatic system, which is driven by the heartbeat-driven pulsation of arteries and is responsible for cerebral waste clearance, is impaired in atrial fibrillation (AF) and mediates cognitive dysfunction related to AF. The aim of this study was to assess brain glymphatic alterations in AF, their role in cognitive function, and whether catheter ablation can improve glymphatic activity.

METHODS

In this case-control and prospective before-and-after study, patients with AF and healthy controls (HCs) were enrolled. Participants underwent brain magnetic resonance imaging and a comprehensive neuropsychological battery. Glymphatic activity was quantified by diffusion tensor image analysis along the perivascular space (DTI-ALPS) index. Magnetic resonance imaging was repeated after surgery in patients who underwent ablation.

RESULTS

Overall, 87 patients with AF and 44 HCs were enrolled. Compared with HCs, patients with AF had a lower ALPS index (P = .016). Nonparoxysmal AF patients showed lower ALPS index than both HCs (P = .002) and paroxysmal AF patients (P = .044). A lower ALPS index was associated with worse scores of Trail Making Test, Digit Symbol Substitution Test, Digit Span Test, and Stroop Colour and Word Test (all P < .05). Mediation analyses revealed that glymphatic activity was a mediator between AF and cognitive decline. Among the 50 patients who underwent ablation therapy, DTI-ALPS index was improved after surgery (P = .015).

CONCLUSIONS

Brain glymphatic function measured by DTI-ALPS index was impaired in patients with AF, mediates the association between AF and cognitive decline, and was improved after ablation therapy.

Cerebral small vessel disease: The impact of glymphopathy and sleep disorders

The glymphatic system, a vital brain perivascular network for waste clearance, hinges on the functionality of the aquaporin 4 (AQP4) water channel. Alarmingly, AQP4 single nucleotide polymorphisms (SNPs) are linked to impaired glymphatic clearance, or glymphopathy, which contributes to sleep disturbances and various age-related neurodegenerative diseases. Despite the critical role of glymphopathy and sleep disturbances in cerebral small vessel disease (CSVD) - a silent precursor to age-related neurodegenerative disorders - their interplay remains underexplored. CSVD is a major cause of stroke and dementia, yet its pathogenesis is not fully understood. Emerging evidence implicates glymphopathy and sleep disorders as pivotal factors in age-related CSVD, exacerbating the condition by hindering waste removal and compromising blood-brain barrier (BBB) integrity. Advanced imaging techniques promise to enhance diagnosis and monitoring, while lifestyle modifications and personalised medicine present promising treatment avenues. This narrative review underscores the need for a multidisciplinary approach to understanding glymphopathy and sleep disorders in CSVD. By exploring their roles, emphasising the necessity for longitudinal studies, and discussing potential therapeutic interventions, this paper aims to pave the way for new research and therapeutic directions in CSVD management.

Glymphatic system dysfunction and its impact on seizure severity, cognitive function, and affective symptoms in patients with generalized tonic-clonic seizures alone

BACKGROUND

Generalized tonic-clonic seizures alone (GTCS alone) represent a distinct idiopathic epilepsy syndrome. Glymphatic system (GS) dysfunction-a brain-wide perivascular clearance pathway-has been proposed as a contributing mechanism in epilepsy and its related comorbidities.

OBJECTIVE

To assess GS function in patients with GTCS alone using the Analysis Along the Perivascular Space (ALPS) index derived from diffusion spectrum imaging (DSI), and to explore its associations with clinical, cognitive, and emotional measures.

METHODS

A total of 101 patients with GTCS alone and 76 demographically matched healthy controls underwent DSI. The ALPS index was calculated and correlated with scores from standardized assessments, including the National Hospital Seizure Severity Scale (NHS3), Epileptic Discharge Index (EDI), Montreal Cognitive Assessment (MoCA), Kilifi Stigma Scale for Epilepsy (KSSE), and Hamilton Depression Rating Scale (HAMD).

RESULTS

Patients with GTCS alone had lower ALPS indices compared to healthy controls (1.43 vs. 1.52, p < 0.01). Among patients, the ALPS index positively correlated with MoCA scores (r = 0.30, p = 0.002) and negatively correlated with age (r = -0.22, p = 0.030), NHS3 (r = -0.27, p = 0.007), KSSE (r = -0.21, p = 0.038), and HAMD (r = -0.20, p = 0.042). The ALPS index was lower in patients with higher antiseizure medication loads (1.36 vs. 1.44, p = 0.042) and elevated EDI values (1.39 vs. 1.45, p = 0.039).

CONCLUSIONS

Glymphatic function is impaired in patients with GTCS alone, as indicated by reduced ALPS indices. These indices are associated with seizure severity, cognitive impairment, depressive symptoms, and perceived stigma. The ALPS index may serve as a noninvasive imaging biomarker of disease burden and a novel tool for understanding pathophysiological mechanisms in GTCS alone.

Diffusion Tensor Image Analysis Along the Perivascular Space in Former Professional Athletes with Repetitive Mild Traumatic Brain Injury History

RATIONALE AND OBJECTIVES

The long-term changes in the glymphatic system of former professional athletes exposed to repetitive mild traumatic brain injuries remain poorly understood. This study aimed to use diffusion tensor image analysis along the perivascular space (DTI-ALPS) to evaluate the glymphatic system activity and correlate the ALPS index with neuropsychiatric symptoms in former professional athletes.

MATERIALS AND METHODS

30 former professional athletes and 24 age- and sex-matched controls underwent DTI with 3 T magnetic resonance imaging, and neuropsychiatric tests were performed in the athlete group.

RESULTS

The ALPS index (mean, right, and left) in the athlete group was compared to that in controls, and correlations with clinical variables were analyzed. The mean, right, and left ALPS indices in the athlete group were significantly lower than those of the control group (mean: 1.49±0.12 vs. 1.61±0.16, cohen's d=0.847, p<0.01; right: 1.51±0.12 vs. 1.61±0.16, cohen's d=0.722, p=0.01; and left: 1.47±0.15 vs. 1.60±0.20, cohen's d=0.765, p<0.01). The mean and right ALPS indices were positively correlated with the Wisconsin Card Sorting Test performance in the athlete group (mean: r=0.41, p=0.04; right: r=0.43, p=0.03; not significant after Bonferroni correction).

CONCLUSION

A lower ALPS index in former professional athletes may be associated with impairments in cognitive function, reflected in glymphatic dysfunction.

Characterization of the glymphatic system and early-phase β-amyloid imaging in Alzheimer's disease: A simultaneous PET/MR study

Early-phase Aβ imaging can detect cerebral perfusion deficits, while glymphatic dysfunction is a key event in neurodegenerative diseases, including Alzheimer's disease (AD). However, their relationship within the AD continuum remains unclear. This study aimed to evaluate the role of the glymphatic system (diffusion tensor image analysis along the perivascular space, DTI-ALPS) and early-phase Aβ imaging in cognitive impairment using simultaneous PET/MR in healthy control (HC), Prodromal AD (PAD), and AD. It also examines the interaction between baseline amyloid (Aβ) burden and vascular burden in perfusion impairment and glymphatic dysfunction. AD patients showed lower SUVr of early-phase Aβ in the bilateral hippocampus, parahippocampal, and caudate (all P < 0.05), indicating perfusion deficits in these regions. Compared to HC, a lower mean ALPS-index was found in the AD and PAD groups (P < 0.001), suggesting that glymphatic dysfunction is an early event in AD. The mean ALPS-index was positively correlated with early-phase Aβ uptake in the bilateral hippocampus, parahippocampal, caudate, and thalamus (all P < 0.001). Mediation analysis revealed that the ALPS-index plays a crucial mediating role between perfusion deficits and cognitive impairment. Baseline Aβ burden and early-phase Aβ perfusion deficits affected the ALPS-index with the mediation of vascular burden (PVS or WMH), while early-phase Aβ perfusion also directly influenced the ALPS-index. In conclusion, this study highlights the role of glymphatic dysfunction and cerebral perfusion deficits in the AD continuum, emphasizing their necessity as early pathological markers. These findings provide imaging evidence for early diagnosis and personalized management of AD.

MR Imaging of Neurofluids in the Developing Brain

The different fluid compartments in the developing brain work together to facilitate the delivery of nutrients, neurotransmitters, and neuromodulators. The cerebrospinal fluid and interstitial fluid are essential for clearing macromolecules from the brain, a process that involves the recently discovered meningeal lymphatics. Disruptions in these interactions can hinder normal brain development. Additionally, alterations in systemic fluid dynamics may contribute to neurologic complications, highlighting the need for a more holistic approach to understanding and treating neurologic diseases. MR imaging techniques show potential for detecting these pathologic processes in pediatric neurologic disorders.

Gadolinium-Based Imaging and the Study of Neurofluid Dynamics

Gadolinium-based MR imaging has significantly advanced our understanding of neurofluid dynamics within the brain and spinal cord. Both intrathecal and intravenous MR imaging techniques hold promise for identifying surrogate markers of altered neurofluid dynamics in the brain. These insights can shed light on the pathophysiology of various neurologic disorders and aid in developing improved treatment strategies.

Coupling analysis of diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) with abnormal cerebral blood flow in methamphetamine-dependent patients and its application in machine-learning-based classification

BACKGROUND

Diffusion tensor imaging (DTI) analysis along the perivascular space (ALPS) index is currently widely employed to evaluate the neurophysiological activity in various neuropsychiatric disorders. However, there remains a scarcity of studies assessing the DTI-ALPS index in individuals with methamphetamine (MA) dependence. Recent studies on animals have demonstrated a significant correlation between glymphatic activity and alterations in cerebral blood flow (CBF). Hence, investigating the DTI-ALPS index and its coupling with CBF could yield novel insights for MA-dependent patients.

METHODS

In this study, we employed DTI and arterial spin labeling to investigate the ALPS index and CBF in 46 MA-dependent patients and 46 control subjects. By using DTI-ALPS, we evaluated a comprehensive diffusivity parameter that encompasses contributions from both the perivascular spaces and fiber tracts. Furthermore, a two-sample t-test was employed to assess inter-group differences. Partial correlation analysis was used to evaluate the correlations of the ALPS index with age, clinical parameters, and CBF, respectively. In addition, a causal mediation analysis was conducted to explore whether CBF mediates the causal relationship between MA-related clinical characteristics and the ALPS index. Finally, a support vector machine (SVM) was trained by the ALPS-related features and CBF features for the purpose of distinguishing MA-dependent subjects from control subjects.

RESULTS

Compared to the control group, the MA-dependent group presented a decreased ALPS index, particularly in the right hemisphere. Moreover, increased diffusivities were observed along the projection fibers in the right Y-axis and the association fibers in the right Z-axis, while the AI of the diffusivity along the Z-axis association fibers decreased in patients with MA dependence. The study observed a tight coupling between the ALPS index and CBF in MA-dependent patients, and revealed significant positive correlations between the ALPS index and CBF in specific brain regions, including the right precentral sulcus, right anterior transverse collateral sulcus, left postcentral sulcus, left superior parietal lobule, left superior occipital sulcus and transverse occipital sulcus, and right temporal pole. The causal mediation analysis suggested that CBF partially mediated the alteration of the ALPS index induced by the duration of MA consumption in MA-dependent patients. Additionally, CBF/ALPS ratio was lower in the MA-dependent group compared to the controls group. An SVM trained with the ALPS-related indicators and CBF indicators achieved classification accuracy, sensitivity, specificity, and kappa values of 93.31 % ± 5.72 %, 91.56 % ± 9.14 %, 95.05 % ± 7.91 % and 86.60 % ± 11.44 %, respectively, for identifying patients with MA dependence.

CONCLUSIONS

The study identified abnormal ALPS index, which has the potential to be a meaningful imaging marker for MA-dependent patients. The findings emphasized the strong coupling between the ALPS index and CBF in MA-dependent individuals, providing indirect imaging references for future research on the relationship between the glymphatic system and CBF. Moreover, the abnormal ALPS-related features and CBF features hold promise as valuable features for developing highly effective classification models.

Effects of sleep on the glymphatic functioning and multimodal human brain network affecting memory in older adults

Understanding how sleep affects the glymphatic system and human brain networks is crucial for elucidating the neurophysiological mechanism underpinning aging-related memory declines. We analyzed a multimodal dataset collected through magnetic resonance imaging (MRI) and polysomnographic recording from 72 older adults. A proxy of the glymphatic functioning was obtained from the Diffusion Tensor Image Analysis along the Perivascular Space (DTI-ALPS) index. Structural and functional brain networks were constructed based on MRI data, and coupling between the two networks (SC-FC coupling) was also calculated. Correlation analyses revealed that DTI-ALPS was negatively correlated with sleep quality measures [e.g., Pittsburgh Sleep Quality Index (PSQI) and apnea-hypopnea index]. Regarding human brain networks, DTI-ALPS was associated with the strength of both functional connectivity (FC) and structural connectivity (SC) involving regions such as the middle temporal gyrus and parahippocampal gyrus, as well as with the SC-FC coupling of rich-club connections. Furthermore, we found that DTI-ALPS positively mediated the association between sleep quality and rich-club SC-FC coupling. The rich-club SC-FC coupling further mediated the association between DTI-ALPS and memory function in good sleepers but not in poor sleepers. The results suggest a disrupted glymphatic-brain relationship in poor sleepers, which underlies memory decline. Our findings add important evidence that sleep quality affects cognitive health through the underlying neural relationships and the interplay between the glymphatic system and multimodal brain networks.

PET Imaging of Neurofluids

Following a brief review of brain neurofluid pathways and the general PET technique, we introduce PET imaging of cerebrospinal fluid and interstitial fluid dynamics. Our summary includes both our published and unpublished observations on the modeling of PET imaging for neurofluid quantification in aging, Alzheimer's disease, and in the presence of amyloid lesions. We identify the limitations of PET imaging and point to validations and potential future directions.

Altered Clearance in Alzheimer's Disease and Cerebral Amyloid Angiopathy

With our focus on Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA), the authors herein provided a comprehensive overview of impaired amyloid beta and tau clearance pathways observed through advanced neuroimaging techniques such as dynamic contrast-enhanced MR imaging, arterial spin labeling, phase contrast MR imaging, PET, and functional MR imaging. The findings suggest the role of impaired degradation clearance, blood-brain barrier clearance, perivascular clearance, glymphatic system clearance, and cerebrospinal fluid dynamics in AD and CAA pathogenesis.

U-Net-Based Prediction of Cerebrospinal Fluid Distribution and Ventricular Reflux Grading

Previous work indicates evidence that cerebrospinal fluid (CSF) plays a crucial role in brain waste clearance processes and that altered flow patterns are associated with various diseases of the central nervous system. In this study, we investigate the potential of deep learning to predict the distribution in human brain of a gadolinium-based CSF contrast agent (tracer) administered intrathecal. For this, T1-weighted magnetic resonance imaging (MRI) scans taken at multiple time points before and after injection were utilized. We propose a U-net-based supervised learning model to predict pixel-wise signal increase at its peak after 24 h. Performance is evaluated based on different tracer distribution stages provided during training, including predictions from baseline scans taken before injection. Our findings show that training with imaging data from only the first 2-h postinjection yields tracer flow predictions comparable to models trained with additional later-stage scans. Validation against ventricular reflux gradings from neuroradiologists confirmed alignment with expert evaluations. These results demonstrate that deep learning-based methods for CSF flow prediction deserve more attention, as minimizing MR imaging without compromising clinical analysis could enhance efficiency, improve patient well-being and lower healthcare costs.

Emerging non-invasive MRI techniques for glymphatic system assessment in neurodegenerative disease

The discovery of the glymphatic system has revolutionized our understanding of brain physiology, particularly in waste clearance and fluid dynamics within the central nervous system. This pathway, essential for nutrient distribution and waste removal, operates predominantly during sleep and has been implicated in neurodegenerative diseases like Alzheimer's and Parkinson's. Recent advances in non-invasive MRI techniques, including diffusion tensor imaging along the perivascular space (DTI-ALPS), perivascular space (PVS) analysis, and free water (FW) indices, have improved our ability to study glymphatic function and its alterations in disease states. This review discusses the glymphatic system's ultrastructure, physiology, and the latest imaging methods to assess this critical pathway. We highlight how these non-invasive MRI techniques can enhance the understanding of glymphatic function in health and disease, with a focus on neurodegenerative conditions. By integrating insights from current research, this review underscores the diagnostic and therapeutic implications of glymphatic dysfunction. Understanding these mechanisms can pave the way for novel strategies to enhance waste clearance and improve neurological health, offering potential benefits for early diagnosis and intervention in neurodegenerative diseases.

Updated imaging markers in cerebral amyloid angiopathy: What radiologists need to know

Cerebral amyloid angiopathy (CAA) is an age-related small vessel disease pathologically characterized by the progressive accumulation of amyloid-beta (Aβ) peptide in cerebrovascular walls, affecting both cortical and leptomeningeal vessels. Amyloid deposition results in fragile vessels, which may lead to lobar intracerebral hemorrhage (ICH) and cognitive impairment. To evaluate the probability and severity of CAA, the imaging markers depicted on CT and MRI techniques are crucial, as brain pathological examination is highly invasive. Although the Boston criteria have established diagnostic value and have been updated to version 2.0, due to an aging population, the patients with CAA should also be assessed for their risk of future ICH or cognitive impairment. Furthermore, an increased awareness of CAA is essential when introducing anticoagulants for infarct in elderly patients or anti-amyloid antibodies for Alzheimer's disease, as these may worsen CAA-related hemorrhagic lesions. However, the radiological literature on CAA has not been comprehensively updated. Here, we review the imaging markers of CAA and clinical significance. We also discuss the clinical and imaging characteristics of CAA-related inflammation, amyloid-related imaging abnormalities, and iatrogenic-CAA.

Alterations of Glymphatic System Before and After Shunt Surgery in Patients With Idiopathic Normal Pressure Hydrocephalus: A Longitudinal Study

AIMS

This study aimed to assess the glymphatic dysfunction in idiopathic normal pressure hydrocephalus (iNPH) patients and its recovery post-shunt surgery using diffusion tensor image analysis along perivascular spaces (DTI-ALPS).

METHODS

Thirty-five iNPH patients and forty healthy controls (HC) underwent MRI scans and neuropsychological assessments at baseline. A follow-up study, conducted three months post-shunt surgery, included fifteen iNPH patients. The DTI-ALPS index was calculated to assess the glymphatic system status. Group differences were evaluated using the Mann-Whitney U test, while the paired Wilcoxon signed-rank test was employed to compare pre-operative and post-operative ALPS indices. Multiple linear regression was utilized to analyze the association between changes in the ALPS index (ΔALPS) and alterations in clinical scores.

RESULTS

Baseline examinations disclosed iNPH patients had a lower ALPS index than HC (p < 0.0001). We found a significantly increased ALPS index at 3 months after surgery compared to baseline (p < 0.0001). Positive correlations between theΔALPS and the increments of MMSE score (ΔMMSE) were found in all iNPH patients. Baseline age and ΔALPS emerged as significant predictors of ΔMMSE, with the model explaining 68.13% of the variance (R2 = 0.6813).

CONCLUSION

Glymphatic function in iNPH was enhanced following shunt surgery, which positively impacted cognitive recovery. The DTI-ALPS index may serve as a useful predictor of shunting efficacy in iNPH patients.

Decreased brain interstitial fluid dynamics is associated with risk of Alzheimer's disease-related cognitive decline

BACKGROUND

Diffusion-tensor image analysis along the perivascular space (ALPS) index that has the potential to reflect brain interstitial fluid (ISF) dynamics may predict the development of Alzheimer's Disease (AD). We aimed to study whether brain ISF dynamics indicated by the ALPS index relate to AD dementia diagnosis and AD-related changes.

METHODS

This study included a discovery cohort (n = 180) and a validation cohort (n = 127), which were composed of cognitively normal, subjective memory concern, mild cognitive impairment, and AD dementia subjects. All participants underwent brain magnetic resonance imaging examination and neuropsychological evaluation. The diffusivities and diffusion-tensor image analysis along the perivascular space (ALPS) were calculated. The support vector machine (SVM) model for AD dementia diagnosis was built in the discovery cohort and validated in the validation cohort. Linear mixed-effects models were used to evaluate the association between the ALPS and cognitive decline. Cox regression models were used to evaluate the association between the ALPS and the risk of AD dementia.

RESULTS

There was a lower median ALPS index in the AD dementia group compared to other groups (all P < 0.05) for both cohorts. The SVM model for AD dementia diagnosis produced an AUC of 0.802 in the discovery cohort (P < 0.001) and 0.783 in the external validation cohort (P < 0.001). Higher ALPS levels were associated with less cognitive decline (P < 0.001). Moreover, lower baseline ALPS had a greater risk of converting to AD dementia (P = 0.014).

CONCLUSIONS

The SVM model based on diffusivities and ALPS was effective for AD dementia diagnosis, and higher ALPS levels are associated with a lower risk of AD-related changes. These findings suggest that ALPS may provide a useful AD progression or treatment biomarker.

Altered Clearance and Amyloid-Related Imaging Abnormalities

Amyloid-related imaging abnormalities (ARIA) are parenchymal edema/effusion and hemorrhage that occur as side effects of immunotherapies targeting beta-amyloid for patients with Alzheimer's disease (AD). The mechanism of ARIA remains unclear but is thought to be due to loss of vascular integrity secondary to overwhelming perivascular clearance pathways, worsening of cerebral amyloid angiopathy (CAA), removal of amyloid from the vessel wall, and initiation of a local immune response. Further imaging and neuropathological studies may help further inform the mechanism of ARIA and its relationship to underlying AD and CAA pathology.

Diffusion Tensor Imaging in Neurofluids

In this review article, we describe the development and application of diffusion-based MR imaging methods for studying glymphatic physiology. Fluid exchange and solute transport are the 2 key components of the glymphatic system. Here we describe the use of low b-value imaging, free water fraction imaging, and diffusion time sensitization to leverage cerebral spinal fluid, as well as interstitial fluid motion in the parenchyma. We also describe multiple b-value diffusion imaging to better delineate diffusion components within the brain. Finally, we touch upon newer approaches that use advanced models of the diffusion signal, including high b-value imaging.

Widespread and prolonged pain may reduce brain clearance capacity only via sleep impairment: Evidence from participants with knee pain

The brain is key in the pain-sleep relationship, and sleep is needed for glymphatic clearance. However, no studies have examined how pain relates to the glymphatic system (GS). Characterizing the GS alongside sleep quality in well-characterized pain samples is essential for advancing this understanding. Non-invasive MRI techniques, such as Diffusion Tensor Imaging-Analysis aLong the Perivascular Space (DTI-ALPS), are particularly valuable as they are approved for humans. Although the relationship between the DTI-ALPS index and the GS is primarily deductive, the index may be a proxy for waste clearance capacity in deep white matter. Its sensitivity to interstitial space changes-known to be modulated by norepinephrine-offers a unique opportunity to investigate how sleep impairment and chronic pain regulation affect specific components of brain waste clearance. We thus fitted two longitudinal models linking pain, sleep quality and the DTI-ALPS index. We hypothesized that variations in pain characteristics would predict DTI-ALPS index changes, either directly or mediated by sleep quality changes. Alternatively, we hypothesized that variations in sleep quality would predict changes in pain characteristics via DTI-ALPS index modifications. Knee pain participants (n=87) completed an MRI and self-reported measures of pain and sleep impairment at baseline and two years later. We only found evidence supporting that more widespread and longer pain at baseline significantly influenced decreases in the DTI-ALPS index in the left hemisphere through increased sleep impairment two years later (p=0.039, corrected). PERSPECTIVE: Findings highlight the need for research on the relationship between pain and sleep quality and its implications for brain health.

Impact of enlarged perivascular spaces in the basal ganglia on gait in cerebral small vessel disease

BACKGROUND

Gait disturbance is a prevalent characteristic of cerebral small vessel disease (CSVD), yet the underlying mechanisms remain largely unclear.

AIMES

To test the hypothesis that enlarged perivascular spaces in the basal ganglia (BG-EPVS) are related to gait performance in individuals with CSVD and the elderly.

METHODS

This cross-sectional study included 138 CSVD patients and 62 healthy elderly controls who underwent quantitative gait analysis. Neuroimaging markers, including BG-EPVS, white matter hyperintensities (WMH), lacunes, and cerebral microbleeds (CMB), were assessed using MRI. Principal component analysis (PCA) was used to reduce the dimensionality of multiple gait indicators. Linear regression models were employed to examine the relationship between BG-EPVS and the principal component values of gait performance, with WMH as a potential mediator.

RESULTS

Compared to healthy controls, CSVD patients exhibited significantly prolonged stance and double-support phases, shortened swing phase, reduced gait speed, increased step width, and decreased stride length and step height (p < 0.05 for all comparisons). Higher BG-EPVS grades were independently associated with poorer gait performance in both CSVD patients (p = 0.012) and all subjects (p = 0.001), even after adjusting for other CSVD markers. WMH partially mediated the relationship between BG-EPVS and gait performance, accounting for 18.2% of the total effect in CSVD patients and 24.9% of the total effects in all subjects.

CONCLUSION

BG-EPVS is independently associated with gait disturbances in both CSVD patients and the elderly. These findings underscore the importance of early gait assessment in the aging population. Further longitudinal research is needed to confirm these associations.

Neurologic symptoms as a hallmark of glymphatic alteration in recovered patients with COVID-19

BACKGROUND

The glymphatic system is a glial-based perivascular network that facilitates the clearance of metabolic waste from the brain. Dysfunction of the glymphatic system, along with neurological symptoms such as cognitive deficits and olfactory dysfunction, has been reported in patients with coronavirus disease (COVID-19). However, the link between these neurological symptoms and alterations in the glymphatic system remains unclear. In this study, we aimed to evaluate magnetic resonance imaging (MRI)-based measures of the glymphatic system in patients recovered from COVID-19 with and without neurological symptoms.

METHODS

This study included 89 patients who recovered from respiratory infections, of whom 71 had confirmed COVID-19 (20 experienced anosmia and 41 had cognitive symptoms). Three MRI-based measures were quantified and compared: the dilated perivascular spaces (dPVS), free water (FW) fraction, and diffusion tensor image analysis along the perivascular spaces (DTI-ALPS). A partial correlation network was used to assess the relationships between COVID-19 infection, neurological symptoms, and glymphatic measures.

RESULTS

COVID-19 patients with anosmia had increased FW in the left orbitofrontal area compared to those without anosmia (mean difference: 0.01, p = 0.48), while patients with cognitive symptoms showed decreased left-sided DTI-ALPS (mean difference: 0.06, p = 0.40). Neurological symptoms mediate the relationship between COVID-19 and glymphatic system measures.

CONCLUSIONS

Our findings imply that neurological symptoms accompanied by COVID-19 are linked to distinct alterations in the glymphatic system, suggesting a potential association between neuroinvasion and neuroinflammatory processes related to COVID-19.

Analysis of the glymphatic system function in high-grade glioma patients using diffusion tensor imaging along perivascular spaces

OBJECTIVES

This study seeks to determine if patients with high-grade glioma (HGG) demonstrate glymphatic system (GS) impairments using Diffusion Tensor Imaging Along Perivascular Spaces (DTI-ALPS). Additionally, it aims to examine the factors affecting GS performance and their implications for HGG prognosis.

METHODS

The study enrolled fifty HGG patients alongside fifty age- and sex-matched healthy individuals. Each participant underwent diffusion tensor imaging with a Philips 3.0T MRI scanner to assess and compute the ALPS index within perivascular spaces. Variables such as gender, grade, location, volume, peritumoral edema volume, mass-edema index (peritumoral edema volume/tumor volume) and ALPS index were recorded. The Student's t-test and rank sum test compared the ALPS indices between HGG patients and healthy controls to evaluate hemispheric differences. Linear and multivariate Cox regression analyses were utilized to discern factors influencing the ALPS index and to establish independent prognostic markers for HGG, respectively.

RESULTS

The ALPS indices in both hemispheres were significantly lower in HGG patients, with the ipsilateral hemisphere exhibiting further reduced levels than the contralateral (P < 0.001). In comparisons involving tumor and edema volumes, no significant variations were observed between the hemispheres within HGG patients harboring larger tumors (P = 0.079) or lesser edema volumes (P = 0.24). A decrease in postoperative ALPS indices compared to preoperative figures was noted (P < 0.001). Univariate linear regression indicated a negative relationship between the ipsilateral ALPS index and peritumoral edema volume (P = 0.0392). Kaplan-Meier analysis demonstrated shorter survival times in patients with lower ALPS indices. Moreover, multivariate Cox regression highlighted tumor grade (HR = 1.548, P = 0.023) and ipsilateral ALPS index (HR = 0.040, P = 0.003) as crucial prognostic indicators.

CONCLUSION

In patients with HGG, there is impaired GS function in both hemispheres of the brain. Additionally, the impaired GS function in the tumor-side hemisphere is associated with tumor-associated edema. Following surgery, further damage to GS function is observed in both hemispheres of the brain in HGG patients. Poor GS function in the tumor-side hemisphere is correlated with a worse prognosis in HGG patients.

Association between movement impairments and glymphatic system dysfunction in spastic diplegic cerebral palsy using DTI-ALPS

BACKGROUND

The role of the glymphatic system in occult cerebral palsy (CP) remains unclear. In this study, glymphatic system function and its association with motor impairment in occult CP patients was investigated using diffusion tensor image analysis along the perivascular space (DTI-ALPS).

METHODS

This retrospective study used DTI to calculate the diffusivity values along the x-, y-, and z-axes in 27 occult CP patients and 27 matched controls. A correlation analysis the ALPS index, derived from perivascular, projection, and association fibres, and with the Gross Motor Function Classification (GMFSC) grade was performed.

RESULTS

We found significant differences in the ALPS index between occult CP patients and healthy controls (HCs). The ALPS index of the lateral hemisphere was lower in occult CP patients than in HCs (left: 1.51 ± 0.20 vs. 1.68 ± 0.24, p = 0.011; right: 1.51 ± 0.20 vs. 1.65 ± 0.24, p = 0.019). Correlation analysis revealed a negative correlation between the ALPS index in the lateral hemisphere and the GMFSC grade (left: r = -0.61, p = 0.004; right: r = -0.48, p = 0.015).

CONCLUSION

Our findings show that occult CP patients have reduced ALPS indices, suggesting glymphatic system dysfunction. Lower ALPS indices were associated with higher motor function grades, indicating a potential link between glymphatic system dysfunction and motor impairment in CP patients.

Clinical and brain volumetric correlates of decreased DTI-ALPS, suggestive of local glymphatic dysfunction, in iRBD

Glymphatic alterations may underlie neurodegeneration in alpha-synucleinopathies. Reduced Diffusion-Tensor Imaging ALong the Perivascular Space (DTI-ALPS), a proxy of perivascular glymphatic activity, has been scarcely studied in isolated REM sleep behaviour disorder (iRBD), a prodromal synucleinopathy stage. Furthermore, its associations with clinical symptoms and brain structural abnormalities remain unexplored. We assessed the DTI-ALPS in sixty-two patients with iRBD and twenty-three healthy controls (HC), exploring its associations with clinical symptoms, cortical thickness and brain volumetric data. iRBD patients exhibited a lower DTI-ALPS and poorer odor identification, semantic fluency and processing speed relative to HC. The DTI-ALPS positively correlated with cognitive performance, olfactory function and amygdalar, hippocampal, brainstem and diencephalic volumes, and negatively with age in iRBD. Perivascular glymphatic activity is compromised in iRBD and is associated with brain atrophy and clinical risk factors of progression to alpha-synucleinopathies, supporting the potential of the DTI-ALPS index as an early imaging neurodegeneration marker.

Relationship between cerebrospinal fluid circulation markers, brain degeneration, and cognitive impairment in cerebral amyloid angiopathy

Objectives

To investigate whether cerebrospinal fluid (CSF) circulation markers alter in patients with probable cerebral amyloid angiopathy (pCAA) and whether they are associated with brain degeneration and cognitive impairment.

Methods

We screened pCAA patients from the ADNI3 database according to the Boston 2.0 Criteria. Fifty-two patients with cognitive impairment (26 pCAA; 26 age-sex-matched non-pCAA) and 26 age-sex-matched cognitively normal control (NC) were included in this study. All participants underwent neurological MRI and cognitive assessments. Choroid plexus (ChP) was segmented using a deep learning-based method and its volume was extracted. Diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) was used to assess perivenous fluid mobility. AD pathological markers (Aβ and tau) were assessed using positron emission tomography. Brain parenchymal damage markers included white matter hyperintensities (WMH) volume and brain atrophy ratio. All markers were compared among the three groups. Correlations among the ChP volume, DTI-ALPS index, parenchymal damage markers, and cognitive scales were analyzed in the pCAA group.

Results

The three groups exhibited significant differences in cognitive scores, AD biomarkers, and imaging markers. Post hoc analyses showed that patients with pCAA had significantly higher WMH volume, higher Aβ and tau deposition, and lower DTI-ALPS compared to NC. However, no difference in ChPs volume was found among the groups. Controlling for age, sex, and vascular risk factors, partial correlation analyses showed a significant negative correlation between the DTI-ALPS and WMH volume fraction (r = -0.606, p = 0.002). ChP volume was significantly associated with the Montreal cognitive assessment score (r = -0.492, p = 0.028).

Conclusion

CSF circulation markers were associated with elevated WMH burden and cognitive impairments in probable CAA.

Parkinson's disease with possible REM sleep behavior disorder correlated with more severe glymphatic system dysfunction

This study aimed to evaluate the glymphatic system activity in Parkinson's disease (PD) with and without rapid eye movement sleep behavior disorder (RBD) using the diffusion tensor image analysis along the perivascular space (DTI-ALPS) methods. Overall, 91 patients with PD and 33 healthy controls were recruited. PD patients were divided into PD-RBD (n = 55) and PD-nRBD (n = 36) groups according to RBD scales. The ALPS-index and enlarged perivascular spaces (EPVS) scores were calculated. PD-RBD group exhibited lower ALPS-index than PD-nRBD and controls after controlling for the effect of age (p = 0.018 and p = 0.001). PD-RBD group showed higher UPDRS part I and HAMD score than those in PD-nRBD group. RBD symptom was independently correlated with ALPS-index in PD (β = -0.259, p = 0.014). In conclusion, PD with possible RBD correlated with more severe glymphatic system dysfunction and non-motor symptoms than those in PD without RBD.

Assessing neonatal brain glymphatic system development using diffusion tensor imaging along the perivascular space and choroid plexus volume

PURPOSE

Neonatal brain development constitutes a critical period of structural and functional maturation underpinning sensory, motor, and cognitive capacities. The glymphatic system-a cerebral waste clearance network-remains poorly understood in neonates. We investigated non-invasive magnetic resonance imaging (MRI) biomarkers of glymphatic system and their developmental correlates in neonates.

METHODS

In 117 neonates undergoing high-resolution T1-weighted and diffusion MRI, we quantified two glymphatic metrics: (1) diffusion tensor imaging along the perivascular space (DTI-ALPS) index, reflecting perivascular fluid dynamics; (2) choroid plexus (CP) volume, a cerebrospinal fluid (CSF) production marker. Associations with postmenstrual age (PMA) at MRI scan, gestational age (GA), birth weight (BW), and sex were analyzed using covariate-adjusted models.

RESULTS

Preterm neonates displayed significantly reduced DTI-ALPS indices versus term neonates (total index: 1.01 vs. 1.05, P = 0.002), with reductions persisting after adjustment (P < 0.05). CP volumes showed right-dominant pre-adjustment differences (preterm: 0.33 vs. term: 0.39, P = 0.039) that attenuated post-adjustment (P = 0.348). DTI-ALPS indices demonstrated transient correlations with PMA/GA/BW in unadjusted analyses (P < 0.05), whereas CP volumes maintained robust PMA associations post-adjustment in all neonates (P = 0.037) and term subgroup (P = 0.013). No significant effects of sex on both metrics were observed.

CONCLUSION

Our findings reveal prematurity-associated delays in glymphatic maturation, rather than biological sex. The persistent PMA-CP volume relationship suggests developmental regulation of CSF production, while attenuated DTI-ALPS correlations highlight covariate-mediated effects. These glymphatic metrics show potential for monitoring neurodevelopmental trajectories, though longitudinal validation is required to establish their clinical utility in neonatal care.

CLINICAL TRIAL NUMBER

Not applicable.

Clinical Neuroimaging Over the Last Decade: Achievements and What Lies Ahead

ABSTRACT

The past decade has witnessed notable advancements in clinical neuroimaging facilitated by technological innovations and significant scientific discoveries. In conjunction with Investigative Radiology's 60th anniversary, this review examines key contributions from the past 10 years, emphasizing the journal's most accessed articles and their impact on clinical practice and research. Advances in imaging technologies, including photon-counting computed tomography, and innovations in low-field and high-field magnetic resonance imaging systems have expanded diagnostic capabilities. Progress in the development and translation of contrast media and rapid quantitative imaging techniques has further improved diagnostic accuracy. Additionally, the integration of advanced data analysis methods, particularly deep learning and medical informatics, has improved image interpretation and operational efficiency. Beyond technological developments, this review highlights basic neuroscience findings, such as the discovery and characterization of the glymphatic system. These insights have provided a deeper understanding of central nervous system physiology and pathology, bridging the gap between research and clinical applications. This review integrates these advancements to provide an overview of the progress and ongoing challenges in clinical neuroimaging, offering insights into its current state and potential future directions within the broader field of radiology.

Vascular Contribution to Cerebral Waste Clearance Affected by Aging or Diabetes

Background: The brain's vascular system has recently been shown to provide an important efflux pathway for cerebral waste clearance (CWC). However, little is known about the influence of aging or diabetes on the CWC. The aim of the current study is to investigate the vasculature contribution to CWC under aging and diabetic conditions. Methods: Male Wistar rats under aging and diabetic conditions were evaluated using dynamic intra-cisterna superparamagnetic iron oxide-enhanced susceptibility-weighted imaging (SPIO-SWI). Theoretical analysis of the expected signal intensity using SPIO-SWI was compared with the corresponding dynamic in vivo images. Quantitative susceptibility mapping (QSM) was used to evaluate the iron-based tracer concentration in the venous system. Results: Our data demonstrated that the theoretical analysis predicted the dynamic changes in the signal intensity after SPIO infusion. The distinct hyperintense signals due to the lower concentration of the SPIO over time in cerebrospinal fluid (CSF) and meningeal lymphatic (ML) vessels likely represented the CWC through various efflux pathways, including cerebral vascular and ML vessels. The QSM analysis further revealed reduced CWC from the vasculature in both the aged and diabetic groups compared to the younger group. Conclusions: Our results demonstrated that SPIO-SWI can quantitatively evaluate the CWC efflux contributions from cerebral vascular vessels under aging or diabetic conditions.

A window into the brain: multimodal MRI assessment of vascular cognitive impairment

Vascular cognitive impairment (VCI) encompasses a diverse range of syndromes, including mild cognitive impairment and vascular dementia (VaD), primarily attributed to cerebrovascular lesions and vascular risk factors. Its prevalence ranks second only to Alzheimer's disease (AD) in neuro diseases. The advancement of medical imaging technology, particularly magnetic resonance imaging (MRI), has enabled the early detection of structural, functional, metabolic, and cerebral connectivity alterations in individuals with VCI. This paper examines the utility of multimodal MRI in evaluating structural changes in the cerebral cortex, integrity of white matter fiber tracts, alterations in the blood-brain barrier (BBB) and glymphatic system (GS) activity, alteration of neurovascular coupling function, assessment of brain connectivity, and assessment of metabolic changes in patients with VCI.

Impaired glymphatic function in autoimmune glial fibrillary acidic protein astrocytopathy: a prospective analysis

BACKGROUND

To evaluate the glymphatic dysfunction and its association with disease severity in autoimmune glial fibrillary acidic protein astrocytopathy (A-GFAP-A) patients, and to determine its clinical predictors.

METHODS

A total of 20 A-GFAP-A patients and 20 healthy controls (HC) were included. All participants underwent magnetic resonance imaging, and glymphatic function was assessed using the diffusion tensor imaging along the perivascular space (DTI-ALPS) index. Modified Rankin Scale (mRS) scores were recorded at baseline and 4 weeks post-immunotherapy. Multiple linear regression analysis was conducted to identify independent predictors of short-term prognosis.

RESULTS

The baseline DTI-ALPS index was significantly lower in A-GFAP-A patients compared to HC (mean ± SD: 1.50 ± 0.06 vs. 1.62 ± 0.04 [CI -0.16, -0.08], p = 0.003), after adjusting for confounding factors. Four weeks after immunotherapy, the DTI-ALPS index significantly increased (mean ± SD: 1.52 ± 0.14 vs. 1.59 ± 0.17 [CI 0.01, 0.14], p = 0.037). A significant negative correlation was observed between the residuals of the baseline DTI-ALPS index and the baseline mRS scores (r = -0.50 [CI -0.77, -0.07], p = 0.025). The baseline DTI-ALPS index was identified as an independent predictor of short-term prognosis (coefficient = -3.43 [CI -6.68, -0.04], p = 0.048).

CONCLUSIONS

This study indicates that A-GFAP-A patients exhibit significant glymphatic dysfunction, as detected by the DTI-ALPS index, which is related to the severity of the disease. The DTI-ALPS index may serve as a biomarker for monitoring disease progression and as a predictor of short-term prognosis in A-GFAP-A patients.

Exploring glymphatic system alterations in iRBD and Parkinson's disease using automated DTI-ALPS analysis

Diffusion tensor image analysis along the perivascular space (DTI-ALPS) is a potential non-invasive marker of glymphatic function that typically relies on manual region of interest (ROI) placement. This study compared ALPS indices in treatment-naïve, de novo diagnosed patients with Parkinson's disease (PD), patients with isolated REM behavior disorder (iRBD), and healthy controls using both manual and automatic approaches to the ROI selection used in ALPS-index calculation. ALPS indices were analyzed bilaterally and correlated with clinical severity (MDS-UPDRS) and nigrostriatal denervation (DAT-SPECT). ANCOVA revealed significant inter-group differences using both manual (p = 0.018) and automatic (p = 0.002) ROI selection methods. The automatic ROI selection approach showed significantly lower ALPS indices in PD compared to controls (p = 0.001) and iRBD (p = 0.009). ALPS indices correlated with symptom severity and nigrostriatal denervation. These findings underscore the reliability of the automatic ROI placement approach for ALPS index calculation and may indicate early glymphatic alterations in Parkinson's disease.

Glymphatic dysfunction in moyamoya disease: The influence of arterial stenosis and ventricular enlargement

The glymphatic system is a vascular-dependent network, involving cerebrospinal fluid circulation, that facilitates waste clearance from the brain. Although glymphatic dysfunction has been implicated in various neurologic diseases, its influencing factors are still not fully understood. We aimed to evaluate glymphatic clearance in moyamoya disease (MMD) and explore its associations with arterial stenosis and ventricular size. Patients with MMD and healthy controls were prospectively recruited to undergo multi-modal MRI scans. Patients were divided into three subgroups based on initial symptoms: hemorrhagic, ischemic, and other. We used diffusion tensor image analysis along the perivascular space (DTI-ALPS) index, magnetic resonance angiography, 3D T1-weighted images to evaluate glymphatic clearance, arterial stenosis and ventricular size. The relationships between arterial stenosis, ventricular size, and ALPS index were analyzed using multivariable linear regression analyses. Compared to controls (n = 39), patients (n = 55) exhibited reduced ALPS index (p < 0.001) and increased volumes of the lateral ventricles (p < 0.001), third ventricle (p < 0.001) and fourth ventricle (p = 0.013). In MMD, arterial stenosis (standardized β=-0.283, p = 0.013), lateral ventricular volume (standardized β=-0.504, p < 0.001), and their interaction (standardized β=-0.606, p < 0.001) were all significantly associated with the ALPS index in multivariable analysis. Among the three subgroups, hemorrhagic subgroup had the lowest ALPS index (p = 0.085) and the largest lateral ventricular volume (p = 0.013). Our findings demonstrated that enlarged lateral ventricles were associated with decreased ALPS index, both alone and synergistically with arterial stenosis, and the reduced ALPS index and ventricular enlargement would be exacerbated in hemorrhagic MMD. This evidence provides new insights into the mechanisms underlying glymphatic impairment in MMD.

Poor glymphatic function is associated with mild cognitive impairment and its progression to Alzheimer's disease: A DTI-ALPS study

BACKGROUND

We aimed to explore the association between ALPS index and both risks of MCI from cognitively normal (CN) and incident AD progressed from MCI, as well as potential mediating factors.

METHODS

This study included 519 adults including 253 (48.75 %) CN and 266 (51.25 %) MCI participants from Alzheimer's Disease Neuroimaging Initiative. Glymphatic function (assessed by along the perivascular space [ALPS] index) was measured by diffusion tensor image at baseline. Neurobiomarkers (Aβ and tau from CSF, plasma and PET) and cognitive functions were served as mediators. Data were analyzed using Cox and Laplace regression and mediation analysis.

RESULTS

During follow-up (median 3.6 years, interquartile range [IQR]: 2.0-4.9 years), 30 (11.86 %) participants developed MCI in the CN cohort and 73 (27.4 %) participants progressed to AD in the MCI cohort. The hazard ratios (95 % confidence intervals [CIs]) of the higher ALPS index was 0.605 (0.386-0.948) for MCI and 0.501 (0.356-0.706) for AD. In addition, participants with high ALPS index had 3.837 and 3.466 years prolonged onset of MCI and AD, separately. Aβ in choroid plexus (17.1 %), tau in cortex [Inferiortemporal (21.1 %), Middletemporal (AV1451:17.0 %, FTP:15.5 %), Superiortemporal(7.7 %), Meta_temporal (AV1451:17.5 %, FTP:16.6 %)], and executive function (14.1 %) mediated the association between ALPS and MCI-AD progression.

CONCLUSION

High ALPS index decreases MCI risk and delays MCI progression to AD by approximately 3.5 years. Aβ in choroid plexus, tau in cortex, and executive function may partially mediate the MCI-AD progression in relation to ALPS index.

Diffusion along Perivascular Spaces as a Marker for Glymphatic System Impairment in Huntington's Disease

BACKGROUND

The aim was to investigate if glymphatic function is impaired in patients with Huntington's disease (HD) and its clinical relevance.

METHODS

Forty-nine subjects carrying mutant Huntingtin (mHTT), comprising 35 manifest (mHD) and 14 pre-manifest (PreHD), and 35 healthy controls (HC) were recruited in this study. The diffusion along perivascular spaces (ALPS) index and the percentage of perivascular space in the basal ganglia (pPVS_BG) were obtained in different groups. The discrimination effects of ALPS index were detected using receiver operating characteristic (ROC) analysis, and the correlations of ALPS index with clinical features of HD were further analyzed.

RESULTS

ALPS index was decreased in mHTT carriers compared to HCs, and it was lower in mHD compared to PreHD patients. ROC analysis showed that the ALPS index could discriminate mHTT from HC (AUC [area under the curve] = 0.903), mHD from PreHD (AUC = 0.886), and PreHD from controls (AUC = 0.755). Lower ALPS index correlated with greater disease burden, severity of the disease, lager pPVS_BG, and lower brain volume and thickness of cortices. Regression analysis showed that ALPS index could predict the performance of motor and cognitive functions. Mediation analysis revealed that ALPS partially mediated the effects of CAG repeat and age on the cognitive decline in HD.

CONCLUSIONS

This study demonstrated that the impairment of the glymphatic system, especially in the paraventricular white matter and BG, was correlated with the clinical manifestations, disease burden, and brain structural changes in mHTT carriers. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.