Cerebrospinal fluid flow imaging by using phase-contrast MR technique

Four-dimensional flow MRI for quantitative assessment of cerebrospinal fluid dynamics: Status and opportunities

Neurological disorders can manifest with altered neurofluid dynamics in different compartments of the central nervous system. These include alterations in cerebral blood flow, cerebrospinal fluid (CSF) flow, and tissue biomechanics. Noninvasive quantitative assessment of neurofluid flow and tissue motion is feasible with phase contrast magnetic resonance imaging (PC MRI). While two-dimensional (2D) PC MRI is routinely utilized in research and clinical settings to assess flow dynamics through a single imaging slice, comprehensive neurofluid dynamic assessment can be limited or impractical. Recently, four-dimensional (4D) flow MRI (or time-resolved three-dimensional PC with three-directional velocity encoding) has emerged as a powerful extension of 2D PC, allowing for large volumetric coverage of fluid velocities at high spatiotemporal resolution within clinically reasonable scan times. Yet, most 4D flow studies have focused on blood flow imaging. Characterizing CSF flow dynamics with 4D flow (i.e., 4D CSF flow) is of high interest to understand normal brain and spine physiology, but also to study neurological disorders such as dysfunctional brain metabolite waste clearance, where CSF dynamics appear to play an important role. However, 4D CSF flow imaging is challenged by the long T1 time of CSF and slower velocities compared with blood flow, which can result in longer scan times from low flip angles and extended motion-sensitive gradients, hindering clinical adoption. In this work, we review the state of 4D CSF flow MRI including challenges, novel solutions from current research and ongoing needs, examples of clinical and research applications, and discuss an outlook on the future of 4D CSF flow.

Spinal cord motion and CSF flow in the cervical spine of 70 healthy participants

Pulsatile spinal cord and CSF velocities related to the cardiac cycle can be depicted by phase-contrast MRI. Among patients with spontaneous intracranial hypotension, we have recently described relevant differences compared with healthy controls in segment C2/C3. The method might be a promising tool to solve clinical and diagnostic ambiguities. Therefore, it is important to understand the physiological range and the effects of clinical and anatomical parameters in healthy volunteers. Within a prospective study, 3D T2-weighted MRI for spinal canal anatomy and cardiac-gated phase-contrast MRI adapted to CSF flow and spinal cord motion for time-resolved velocity data and derivatives were performed in 70 participants (age 20-79 years) in segments C2/C3 and C5/C6. Correlations were analyzed by multiple linear regression models; p < 0.01 was required to assume a significant impact of clinical or anatomical data quantified by the regression coefficient B. Data showed that in C2/C3, the CSF and spinal cord craniocaudal velocity ranges were 4.5 ± 0.9 and 0.55 ± 0.15 cm/s; the total displacements were 1.1 ± 0.3 and 0.07 ± 0.02 cm, respectively. The craniocaudal range of the CSF flow rate was 8.6 ± 2.4 mL/s; the CSF stroke volume was 2.1 ± 0.7 mL. In C5/C5, physiological narrowing of the spinal canal caused higher CSF velocity ranges and lower stroke volume (C5/C6 B = +1.64 cm/s, p < 0.001; B = -0.4 mL, p = 0.002, respectively). Aging correlated to lower spinal cord motion (e.g., B = -0.01 cm per 10 years of aging, p < 0.001). Increased diastolic blood pressure was associated with lower spinal cord motion and CSF flow parameters (e.g., C2/C3 CSF stroke volume B = -0.3 mL per 10 mmHg, p < 0.001). Males showed higher CSF flow and spinal cord motion (e.g., CSF stroke volume B = +0.5 mL, p < 0.001; total displacement spinal cord B = +0.016 cm, p = 0.002). We therefore propose to stratify data for age and sex and to adjust for diastolic blood pressure and segmental narrowing in future clinical studies.

Quantitative 23Na magnetic resonance imaging in the abdomen at 3 T

OBJECTIVES

To assess the feasibility of sodium-23 MRI for performing quantitative and non-invasive measurements of total sodium concentration (TSC) and relaxation in a variety of abdominal organs.

MATERIALS AND METHODS

Proton and sodium imaging of the abdomen was performed in 19 healthy volunteers using a 3D cones sequence and a sodium-tuned 4-rung transmit/receive body coil on a clinical 3 T system. The effects of B1 non-uniformity on TSC measurements were corrected using the double-angle method. The long-component of 23Na T2* relaxation time was measured using a series of variable echo-times.

RESULTS

The mean and standard deviation of TSC and long-component 23Na T2* values were calculated across the healthy volunteer group in the kidneys, cerebrospinal fluid (CSF), liver, gallbladder, spleen, aorta, and inferior vena cava.

DISCUSSION

Mean TSC values in the kidneys, liver, and spleen were similar to those reported using 23Na-MRI previously in the literature. Measurements in the CSF and gallbladder were lower, potentially due to the reduced spatial resolution achievable in a clinically acceptable scan time. Mean long-component 23Na T2* values were consistent with previous reports from the kidneys and CSF. Intra-population standard error was larger in smaller, fluid-filled structures due to fluid motion and partial volume effects.

A comprehensive review on ziconotide

Managing severe chronic pain is a challenging task, given the limited effectiveness of available pharmacological and non-pharmacological treatments. This issue continues to be a significant public health concern, requiring a substantial therapeutic response. Ziconotide, a synthetic peptide initially isolated from Conus magus in 1982 and approved by the US Food and Drug Administration and the European Medicines Agency in 2004, is the first-line intrathecal method for individuals experiencing severe chronic pain refractory to other therapeutic measures. Ziconotide produces powerful analgesia by blocking N-type calcium channels in the spinal cord, which inhibits the release of pain-relevant neurotransmitters from the central terminals of primary afferent neurons. However, despite possessing many favorable qualities, including the absence of tolerance development, respiratory depression, and withdrawal symptoms (largely due to the absence of a G-protein mediation mechanism), ziconotide's application is limited due to factors such as intrathecal administration and a narrow therapeutic window resulting from significant dose-related undesired effects of the central nervous system. This review aims to provide a comprehensive and clinically relevant summary of the literatures concerning the pharmacokinetics and metabolism of intrathecal ziconotide. It will also describe strategies intended to enhance clinical efficacy while reducing the incidence of side effects. Additionally, the review will explore the current efforts to refine the structure of ziconotide for better clinical outcomes. Lastly, it will prospect potential developments in the new class of selective N-type voltage-sensitive calcium-channel blockers.

An autologous duraplasty in situ technique in the treatment of Chiari malformation Type I: a prospective study

OBJECTIVE

Our study aims to prospectively compare an autologous duraplasty in situ technique (IS group) with the synthetic dural graft duraplasty (SDG group) to clarify the effectiveness and superiority of the former in the treatment of patients with Chiari malformation type 1 (CM-I).

METHOD

29 patients with CM-I were randomly assigned to either IS or SDG group. In both groups, a dissection from the occipital bone was performed. All procedures were performed by the same surgeon. The two duraplasty methods were compared in terms of surgical factors and complications. Data analysis was done for the baseline material, the neurological outcome and MRI-documented syrinx size at the 6 month follow-up.

RESULT

29 patients were enrolled in this study, 14 in the IS group and 15 in the SDG group. The results showed no significant difference in operation time (P = 0.916), amount of bleeding (P = 0.120), operation complications, hospitalization time (P = 0.854) and prognosis between the two groups. The hospitalization cost of IS group was 15,125 yuan less than that of SDG group (P < 0.05).

CONCLUSION

The autogenous duraplasty in situ technique is a novel, simple, effective and economical surgical management for patients with CM-I.

Diffusion magnetic resonance imaging of cerebrospinal fluid dynamics: Current techniques and future advancements

Cerebrospinal fluid (CSF) plays a critical role in metabolic waste clearance from the brain, requiring its circulation throughout various brain pathways, including the ventricular system, subarachnoid spaces, para-arterial spaces, interstitial spaces, and para-venous spaces. The complexity of CSF circulation has posed a challenge in obtaining noninvasive measurements of CSF dynamics. The assessment of CSF dynamics throughout its various circulatory pathways is possible using diffusion magnetic resonance imaging (MRI) with optimized sensitivity to incoherent water movement across the brain. This review presents an overview of both established and emerging diffusion MRI techniques designed to measure CSF dynamics and their potential clinical applications. The discussion offers insights into the optimization of diffusion MRI acquisition parameters to enhance the sensitivity and specificity of diffusion metrics on underlying CSF dynamics. Lastly, we emphasize the importance of cautious interpretations of diffusion-based imaging, especially when differentiating between tissue- and fluid-related changes or elucidating structural versus functional alterations.

Transcranial direct current stimulation alters cerebrospinal fluid-interstitial fluid exchange in mouse brain

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has gained prominence recently. Clinical studies have explored tDCS as an adjunct to neurologic disease rehabilitation, with evidence suggesting its potential in modulating brain clearance mechanisms. The glymphatic system, a proposed brain waste clearance system, posits that cerebrospinal fluid-interstitial fluid (CSF-ISF) exchange aids in efficient metabolic waste removal. While some studies have linked tDCS to astrocytic inositol trisphosphate (IP3)/Ca2+ signaling, the impact of tDCS on CSF-ISF exchange dynamics remains unclear.

HYPOTHESIS

tDCS influences the dynamics of CSF-ISF exchange through astrocytic IP3/Ca2+ signaling.

METHODS

In this study, we administered tDCS (0.1 mA for 10 min) to C57BL/6N mice anesthetized with ketamine-xylazine (KX). The anode was positioned on the cranial bone above the cortex, and the cathode was inserted into the neck. Following tDCS, we directly assessed brain fluid dynamics by injecting biotinylated dextran amine (BDA) as a CSF tracer into the cisterna magna (CM). The brain was then extracted after either 30 or 60 min and fixed. After 24 h, the sectioned brain slices were stained with Alexa 594-conjugated streptavidin (SA) to visualize BDA using immunohistochemistry. We conducted Electroencephalography (EEG) recordings and aquaporin 4 (AQP4)/CD31 immunostaining to investigate the underlying mechanisms of tDCS. Additionally, we monitored the efflux of Evans blue, injected into the cisterna magna, using cervical lymph node imaging. Some experiments were subsequently repeated with inositol trisphosphate receptor type 2 (IP3R2) knockout (KO) mice.

RESULTS

Post-tDCS, we observed an increased CSF tracer influx, indicating a modulation of CSF-ISF exchange by tDCS. Additionally, tDCS appeared to enhance the brain's metabolic waste efflux. EEG recordings showed an increase in delta wave post-tDCS. But no significant change in AQP4 expression was detected 30 min post-tDCS. Besides, we found no alteration in CSF-ISF exchange and delta wave activity in IP3R2 KO mice after tDCS.

CONCLUSION

Our findings suggest that tDCS augments the glymphatic system's influx and efflux. Through astrocytic IP3/Ca2+ signaling, tDCS was found to modify the delta wave, which correlates positively with brain clearance. This study underscores the potential of tDCS in modulating brain metabolic waste clearance.

Influence of body weight, age, and sex on cerebrospinal fluid peak flow velocity in dogs without neurological disorders

BACKGROUND

Changes in the brain can affect the flow velocity of cerebrospinal fluid (CSF). In humans, the flow velocity of CSF is not only altered by disease but also by age and sex. Such influences are not known in dogs.

HYPOTHESIS

Peak flow velocity of CSF in dogs is associated with body weight, age, and sex.

ANIMALS

Peak flow velocity of CSF was measured in 32 client-owned dogs of different breeds, age, and sex.

METHODS

Peak flow velocity of CSF was determined by phase-contrast magnetic resonance imaging (PC-MRI) at the mesencephalic aqueduct, foramen magnum (FM), and second cervical vertebral body (C2). Dogs were grouped according to body weight, age, and sex. Flow velocity of CSF was compared between groups using linear regression models.

RESULTS

Dogs with body weight >20 kg had higher CSF peak velocity compared with dogs <10 kg within the ventral and dorsal subarachnoid space (SAS) at the FM (P = .02 and P = .01, respectively), as well as in the ventral and dorsal SAS at C2 (P = .005 and P = .005, respectively). Dogs ≤2 years of age had significantly higher CSF peak flow velocity at the ventral SAS of the FM (P = .05). Females had significantly lower CSF peak flow velocity within the ventral SAS of FM (P = .04).

CONCLUSION

Body weight, age, and sex influence CSF peak flow velocity in dogs. These factors need to be considered in dogs when CSF flow is quantitatively assessed.

Quantitative Magnetic Resonance Cerebral Spinal Fluid Flow Properties and Executive Function Cognitive Outcomes in Congenital Heart Disease

Cerebrospinal fluid (CSF) circulation has recently been shown to be important in nutrient distribution, waste removal, and neurogenesis. Increased CSF volumes are frequently observed in congenital heart disease (CHD) and are associated with neurodevelopmental deficits. This suggests prolonged perturbation to the CSF system and possible interference to its homeostatic function, which may contribute to the neurodevelopmental deficits in CHD. CSF flow has yet to be studied in CHD patients, but the pulsatile flow of CSF throughout the brain is driven mainly by cardiopulmonary circulation. Given the underlying heart defects in CHD, the cardiopulmonary circulatory mechanisms in CHD might be impaired with resultant perturbation on the CSF circulation. In this study, we determine whether CSF flow, using MRI measurements of static and dynamic pulsatile flow, is abnormal in youths with CHD compared to healthy controls in relation to executive cognitive function. CSF flow measurements were obtained on a total of 58 child and young adult participants (CHD=20, healthy controls = 38). The CSF flow was measured across the lumen of the Aqueduct of Sylvius using cardiac-gated phase-contrast MRI at 3.0T. Static pulsatility was characterized as anterograde and retrograde peak velocities, mean velocity, velocity variance measurements, and dynamic pulsatility calculated as each participant's CSF flow deviation from the study cohort's consensus flow measured with root mean squared deviation (RMSD) were obtained. The participants had neurocognitive assessments for executive function with focus on inhibition, cognitive flexibility, and working memory domains. The CHD group demonstrated greater dynamic pulsatility (higher overall flow RMSD over the entire CSF flow cycle) compared to controls (p=0.0353), with no difference detected in static pulsatility measures. However, lower static CSF flow pulsatility (anterograde peak velocity: p=0.0323) and lower dynamic CSF flow pulsatility (RMSD: p=0.0181) predicted poor inhibitory executive function outcome. Taken together, while the whole CHD group exhibited higher dynamic CSF flow pulsatility compared to controls, the subset of CHD subjects with relatively reduced static and dynamic CSF flow pulsatility had the worst executive functioning, specifically the inhibition domain. These findings suggest that altered CSF flow pulsatility may be central to not only brain compensatory mechanisms but can also drive cognitive impairment in CHD. Further studies are needed to investigate possible mechanistic etiologies of aberrant CSF pulsatility (i.e. primary cardiac hemodynamic disturbances, intrinsic brain vascular stiffness, altered visco-elastic properties of tissue, or glial-lymphatic disturbances), which can result in acquired small vessel brain injury (including microbleeds and white matter hyperintensities).

Measurement of changes in cerebrospinal fluid pulsation after traumatic brain injury using echo-planar imaging-based functional MRI

Traumatic brain injury (TBI) is a major public health concern worldwide, with a high incidence and a significant impact on morbidity and mortality. The alteration of cerebrospinal fluid (CSF) dynamics after TBI is a well-known phenomenon; however, the underlying mechanisms and their implications for cognitive function are not fully understood. In this study, we propose a new approach to studying the alteration of CSF dynamics in TBI patients. Our approach involves using conventional echo-planar imaging-based functional MRI with no additional scan, allowing for simultaneous assessment of functional CSF dynamics and blood oxygen level-dependent-based functional brain activities. We utilized two previously suggested indices of (i) CSFpulse, and (ii) correlation between global brain activity and CSF inflow. Using CSFpulse, we demonstrated a significant decrease in CSF pulsation following TBI (p < 0.05), which was consistent with previous studies. Furthermore, we confirmed that the decrease in CSF pulsation was most prominent in the early months after TBI, which could be explained by ependymal ciliary loss, intracranial pressure increment, or aquaporin-4 dysregulation. We also observed a decreasing trend in the correlation between global brain activity and CSF inflow in TBI patients (p < 0.05). Our findings suggest that the decreased CSF pulsation after TBI could lead to the accumulation of toxic substances in the brain and an adverse effect on brain function. Further longitudinal studies with larger sample sizes, TBI biomarker data, and various demographic information are needed to investigate the association between cognitive decline and CSF dynamics after TBI. Overall, this study sheds light on the potential role of altered CSF dynamics in TBI-induced neurologic symptoms and may contribute to the development of novel therapeutic interventions.

John T, Estes AM, Schultz RT, Hazlett HC, Dager SR, Botteron KN, Styner M, Piven J, Shen MD. Enlarged Perivascular Spaces in Infancy and Autism Diagnosis, Cerebrospinal Fluid Volume, and Later Sleep Problems

Importance

Perivascular spaces (PVS) and cerebrospinal fluid (CSF) are essential components of the glymphatic system, regulating brain homeostasis and clearing neural waste throughout the lifespan. Enlarged PVS have been implicated in neurological disorders and sleep problems in adults, and excessive CSF volume has been reported in infants who develop autism. Enlarged PVS have not been sufficiently studied longitudinally in infancy or in relation to autism outcomes or CSF volume.

Objective

To examine whether enlarged PVS are more prevalent in infants who develop autism compared with controls and whether they are associated with trajectories of extra-axial CSF volume (EA-CSF) and sleep problems in later childhood.

Design, Setting, and Participants

This prospective, longitudinal cohort study used data from the Infant Brain Imaging Study. Magnetic resonance images were acquired at ages 6, 12, and 24 months (2007-2017), with sleep questionnaires performed between ages 7 and 12 years (starting in 2018). Data were collected at 4 sites in North Carolina, Missouri, Pennsylvania, and Washington. Data were analyzed from March 2021 through August 2022.

Exposure

PVS (ie, fluid-filled channels that surround blood vessels in the brain) that are enlarged (ie, visible on magnetic resonance imaging).

Main Outcomes and Measures

Outcomes of interest were enlarged PVS and EA-CSF volume from 6 to 24 months, autism diagnosis at 24 months, sleep problems between ages 7 and 12 years.

Results

A total of 311 infants (197 [63.3%] male) were included: 47 infants at high familial likelihood for autism (ie, having an older sibling with autism) who were diagnosed with autism at age 24 months, 180 high likelihood infants not diagnosed with autism, and 84 low likelihood control infants not diagnosed with autism. Sleep measures at school-age were available for 109 participants. Of infants who developed autism, 21 (44.7%) had enlarged PVS at 24 months compared with 48 infants (26.7%) in the high likelihood but no autism diagnosis group (P = .02) and 22 infants in the control group (26.2%) (P = .03). Across all groups, enlarged PVS at 24 months was associated with greater EA-CSF volume from ages 6 to 24 months (β = 4.64; 95% CI, 0.58-8.72; P = .002) and more frequent night wakings at school-age (F = 7.76; η2 = 0.08; P = .006).

Conclusions and Relevance

These findings suggest that enlarged PVS emerged between ages 12 and 24 months in infants who developed autism. These results add to a growing body of evidence that, along with excessive CSF volume and sleep dysfunction, the glymphatic system could be dysregulated in infants who develop autism.

Decoupling Between Brain Activity and Cerebrospinal Fluid Movement in Neurological Disorders

Recent research has identified a link between the global mean signal of resting-state functional MRI (fMRI) and macro-scale cerebrospinal fluid movement, indicating the potential link between this resting-state dynamic and brain waste clearance. Consistent with this notion, the strength of this coupling has been associated with multiple neurodegenerative disease pathologies, especially the build-up of toxic proteins. This article aimed to review the latest advancements in this research area, emphasizing studies on spontaneous global brain activity that is tightly linked to the global mean resting-state fMRI signal, and aimed to discuss potential mechanisms through which this activity and associated physiological modulations might affect brain waste clearance. The available evidence supports the presence of a highly organized global brain activity that is linked to arousal and memory systems. This global brain dynamic, along with its associated physiological modulations, has the potential to influence brain waste clearance through multiple pathways through multiple pathways. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 3.

Low b-value Diffusion Tensor Imaging to Analyze the Dynamics of Cerebrospinal Fluid: Resolving Intravoxel Pseudorandom Motion into Ordered and Disordered Motions

PURPOSE

Analysis of cerebrospinal fluid (CSF) dynamics may be beneficial for understanding the mechanisms and diagnosis of several neurological diseases. Low b-value diffusion tensor imaging (low-b DTI) is useful for observing the slow and complex motion of the CSF. Theoretically, a mathematical framework suggests that low-b DTI provides the variance of the pseudorandom motion of the CSF. Furthermore, low-b DTI could provide comprehensive information on fluid dynamics. Accordingly, we proposed an analysis technique that resolves intravoxel pseudorandom motion into ordered (linear) and disordered (random) motions based on the mathematical framework.

METHODS

The proposed analysis technique helps measure low-b DTI with multiple diffusion times and linearly fits its mean diffusivity (MD) with the diffusion time to obtain two parameters, double-slope Vv and y-intersect Dr, which represent the variance of the velocity distribution of linear motion and the diffusion coefficient of random motion, respectively. Seven healthy subjects were scanned to evaluate the proposed technique and investigate fluid dynamics in several representative ROIs.

RESULTS

The obtained data showed the validity of the technique, repeatability, and consistency across the subjects in ROIs, such as the lateral ventricle (LV), third ventricle (3V), fourth ventricle (4V), and Sylvian fissure (SF). The obtained parameters Vv and Dr highlighted different characteristics of fluid dynamics in the representative ROIs: low Vv and low Dr in the LV, high Vv and moderate Dr in the 3V, and moderate Vv and moderate Dr in the 4V and SF.

CONCLUSION

The proposed analysis technique will facilitate a comprehensive investigation of the complex dynamics of the CSF using resolved parameters representing ordered and disordered motions.

Cerebral Spinal Fluid Volumetrics and Paralimbic Predictors of Executive Dysfunction in Congenital Heart Disease: A Machine Learning Approach Informing Mechanistic Insights

The relationship between increased cerebral spinal fluid (CSF) ventricular compartments, structural and microstructural dysmaturation, and executive function in patients with congenital heart disease (CHD) is unknown. Here, we leverage a novel machine-learning data-driven technique to delineate interrelationships between CSF ventricular volume, structural and microstructural alterations, clinical risk factors, and sub-domains of executive dysfunction in adolescent CHD patients. We trained random forest regression models to predict measures of executive function (EF) from the NIH Toolbox, the Delis-Kaplan Executive Function System (D-KEFS), and the Behavior Rating Inventory of Executive Function (BRIEF) and across three subdomains of EF - mental flexibility, working memory, and inhibition. We estimated the best parameters for the random forest algorithm via a randomized grid search of parameters using 10-fold cross-validation on the training set only. The best parameters were then used to fit the model on the full training set and validated on the test set. Algorithm performance was measured using root-mean squared-error (RMSE). As predictors, we included patient clinical variables, perioperative clinical measures, microstructural white matter (diffusion tensor imaging- DTI), and structural volumes (volumetric magnetic resonance imaging- MRI). Structural white matter was measured using along-tract diffusivity measures of 13 inter-hemispheric and cortico-association fibers. Structural volumes were measured using FreeSurfer and manual segmentation of key structures. Variable importance was measured by the average Gini-impurity of each feature across all decision trees in which that feature is present in the model, and functional ontology mapping (FOM) was used to measure the degree of overlap in feature importance for each EF subdomain and across subdomains. We found that CSF structural properties (including increased lateral ventricular volume and reduced choroid plexus volumes) in conjunction with proximate cortical projection and paralimbic-related association white matter tracts that straddle the lateral ventricles and distal paralimbic-related subcortical structures (basal ganglia, hippocampus, cerebellum) are predictive of two-specific subdomains of executive dysfunction in CHD patients: cognitive flexibility and inhibition. These findings in conjunction with combined RF models that incorporated clinical risk factors, highlighted important clinical risk factors, including the presence of microbleeds, altered vessel volume, and delayed PDA closure, suggesting that CSF-interstitial fluid clearance, vascular pulsatility, and glymphatic microfluid dynamics may be pathways that are impaired in CHD, providing mechanistic information about the relationship between CSF and executive dysfunction.

Depiction of detailed surgical anatomy and CSF flow information using a single MRI technique

We describe a novel MRI sequence (T2 SPACE) capable of demonstrating detailed structural anatomy and functional CSF flow information simultaneously. While traditionally, a variety of sequences are utilised for this purpose, we have highlighted the advantages of this technique over traditional approaches, using example of a patient with CSF loculation in prepontine/suprasellar cistern, causing third ventricular compression and hydrocephalus. The sequence depicted the surgical anatomy by showing the web/cyst wall as well as CSF flow entering the cyst potentially causing increased pressure.

Clinicoradiologic Risk Stratification and Outcome Assessment in Symptomatic Intracranial Arachnoid Cyst Managed Over Fifteen Years

BACKGROUND

Arachnoid cysts (ACs) are developmental anomalies formed by splitting the arachnoid membrane's layers. ACs contribute around 2% of all intracranial space-occupying lesions. ACs are more prevalent in children. Because of varied clinical presentation, there has been a constant need for clinicoradiologic risk stratification with a possible role in outcome prediction. The present study describes the management strategies and outcomes in symptomatic intracranial ACs.

METHODS

All biopsy-proven symptomatic patients who underwent surgical management over last 15 years were included in this study (January 2008-December 2022), while those with non-conclusive biopsies were excluded. Patients presenting with acute deterioration were managed in the emergency department with or without cerebrospinal fluid diversion and decompression of the AC. The microsurgical or endoscopic approach was the preferred surgical modality. Postoperative clinicoradiologic improvement was evaluated at 3 months follow-up visit.

RESULTS

A total of 108 patients were analyzed in this retrospective observational study. The median age of the patients was 27.5 years (range, 1 to 76 years). Headache was the most typical clinical presentation. Supratentorial ACs (n = 59, 54.6%) were higher than the infratentorial ACs (n = 49, 45.4%). Forty-seven patients belonged to the pediatric age group (<18 years), and seizure was their presenting complaint. In this observational study, there was no statistical difference in operative duration between microsurgical technique versus endoscopic decompression (P= 0.23).

CONCLUSIONS

ACs are uncommon brain lesions having a broad spectrum of symptoms. The location and clinical presentation of ACs decide the preferred surgical approach. Individuals in high-risk groups must be treated on priority to achieve long-term relief of symptoms.

The Reissner fiber under tension in vivo shows dynamic interaction with ciliated cells contacting the cerebrospinal fluid

The Reissner fiber (RF) is an acellular thread positioned in the midline of the central canal that aggregates thanks to the beating of numerous cilia from ependymal radial glial cells (ERGs) generating flow in the central canal of the spinal cord. RF together with cerebrospinal fluid (CSF)-contacting neurons (CSF-cNs) form an axial sensory system detecting curvature. How RF, CSF-cNs and the multitude of motile cilia from ERGs interact in vivo appears critical for maintenance of RF and sensory functions of CSF-cNs to keep a straight body axis, but is not well-understood. Using in vivo imaging in larval zebrafish, we show that RF is under tension and resonates dorsoventrally. Focal RF ablations trigger retraction and relaxation of the fiber's cut ends, with larger retraction speeds for rostral ablations. We built a mechanical model that estimates RF stress diffusion coefficient D at 5 mm2/s and reveals that tension builds up rostrally along the fiber. After RF ablation, spontaneous CSF-cN activity decreased and ciliary motility changed, suggesting physical interactions between RF and cilia projecting into the central canal. We observed that motile cilia were caudally-tilted and frequently interacted with RF. We propose that the numerous ependymal motile monocilia contribute to RF's heterogenous tension via weak interactions. Our work demonstrates that under tension, the Reissner fiber dynamically interacts with motile cilia generating CSF flow and spinal sensory neurons.

Image Analysis Techniques for In Vivo Quantification of Cerebrospinal Fluid Flow

Over the last decade, there has been a tremendously increased interest in understanding the neurophysiology of cerebrospinal fluid (CSF) flow, which plays a crucial role in clearing metabolic waste from the brain. This growing interest was largely initiated by two significant discoveries: the glymphatic system (a pathway for solute exchange between interstitial fluid deep within the brain and the CSF surrounding the brain) and meningeal lymphatic vessels (lymphatic vessels in the layer of tissue surrounding the brain that drain CSF). These two CSF systems work in unison, and their disruption has been implicated in several neurological disorders including Alzheimer's disease, stoke, and traumatic brain injury. Here, we present experimental techniques for in vivo quantification of CSF flow via direct imaging of fluorescent microspheres injected into the CSF. We discuss detailed image processing methods, including registration and masking of stagnant particles, to improve the quality of measurements. We provide guidance for quantifying CSF flow through particle tracking and offer tips for optimizing the process. Additionally, we describe techniques for measuring changes in arterial diameter, which is an hypothesized CSF pumping mechanism. Finally, we outline how these same techniques can be applied to cervical lymphatic vessels, which collect fluid downstream from meningeal lymphatic vessels. We anticipate that these fluid mechanical techniques will prove valuable for future quantitative studies aimed at understanding mechanisms of CSF transport and disruption, as well as for other complex biophysical systems.

Syringomyelia Associated with Chiari 1 Malformation in Adults: Positive Outcome Predictors after Posterior Fossa Decompression with Duraplasty

BACKGROUND

Syringomyelia (Syr) in patients with Chiari 1 malformation (CM1) may be attributable to abnormal dynamics of cerebrospinal fluid (CSF) in the upper cervical segment; fourth ventricle enlargement has been reported in association with a worse clinical and radiological presentation, independently of the posterior fossa volume. In this study, we analyzed presurgery hydrodynamic markers to evaluate if their changes could be associated with clinical and radiological improvement after posterior fossa decompression and duraplasty (PFDD). As a primary endpoint, we aimed to correlate improvement in the fourth ventricle area with positive clinical outcomes.

METHODS

In total, in this study, we enrolled 36 consecutive adults with Syr and CM1 who were followed by a multidisciplinary team. All the patients were prospectively evaluated with clinical scales and neuroimaging, including CSF flow, the fourth ventricle area, and the Vaquero Index by using a phase-contrast MRI before (T0) and after surgical treatment (T1-Tlast, with a range of 12-108 months). The CSF flow at the craniocervical junction (CCJ), the fourth ventricle area, and the Vaquero Index changes were statistically analyzed and compared to the clinical and quality of life improvement after surgery. The good outcome prediction ability of presurgical radiological variables was tested.

RESULTS

Surgery was associated with positive clinical and radiological outcomes in more than 90% of cases. The fourth ventricle area significantly reduced after surgery (T0-Tlast, p = 0.0093), but no significant associations with clinical improvement were found. The presurgical presence of CSF flow at the CCJ was able to predict a good outcome (AUC = 0.68, 95% CI 0.50-0.87 and LH+ = 2.1, IC 95% 1.16-3.07) and was also significantly associated with post-surgical pain relief (rho = 0.61 and p = 0.0144).

CONCLUSIONS

Presurgery CSF flow at the CCJ is proposed as a radiological marker with the ability to predict a positive outcome after PFDD in adults with syringomyelia and CM1. Measurements of the fourth ventricle area could be useful additional information for evaluating surgical long-term follow-up; further experience on larger cohorts is required to better define the prognostic yield of this radiological parameter.

Editorial Comment: Estimation of venous sinus pressure drop in patients with idiopathic intracranial hypertension using 4D-flow MRI

KEY POINTS

• Work-energy equation using 4D-flow MRI is a promising technique for non-invasive estimation of trans-stenotic pressure drop in patients with idiopathic intracranial hypertension.• Additional research with larger and multicentric prospective cohorts is needed to validate the results, along with improvement of the segmentation process with automated techniques and shortening of scanning times to allow for practical clinical use.

Population Pharmacokinetic Analysis of Rifampicin in Plasma, Cerebrospinal Fluid, and Brain Extracellular Fluid in South African Children with Tuberculous Meningitis

Limited knowledge is available on the pharmacokinetics of rifampicin in children with tuberculous meningitis (TBM) and its penetration into brain tissue, which is the site of infection. In this analysis, we characterize the distribution of rifampicin in cerebrospinal fluid (CSF), lumbar (LCSF) and ventricular (VCSF), and brain extracellular fluid (ECF). Children with TBM were included in this pharmacokinetic analysis. Sparse plasma, LCSF, and VCSF samples were collected opportunistically, as clinically indicated. Brain ECF was sampled using microdialysis (MD). Rifampicin was quantified with liquid chromatography with tandem mass spectrometry in all samples, and 25-desacetyl rifampicin in the plasma samples. The data were interpreted with nonlinear mixed-effects modeling, with the CSF and brain ECF modeled as "effect compartments." Data were available from 61 children, with median (min-max) age of 2 (0.3 to 10) years and weight of 11.0 (4.8 to 49.0) kg. A one-compartment model for parent and metabolite with first-order absorption and elimination via saturable hepatic clearance described the data well. Allometric scaling, maturation, and auto-induction of clearance were included. The pseudopartition coefficient between plasma and LCSF/VCSF was ~5%, while the value for ECF was only ~0.5%, possibly reflecting low recovery of rifampicin using MD. The equilibration half-life between plasma and LCSF/VCSF was ~4 h and between plasma and ECF ~2 h. Our study confirms previous reports showing that rifampicin concentrations in the LCSF are lower than in plasma and provides novel knowledge about rifampicin in the VCSF and the brain tissue. Despite MD being semiquantitative because the relative recovery cannot be quantified, our study presents a proof-of-concept that rifampicin reaches the brain tissue and that MD is an attractive technique to study site-of-disease pharmacokinetics in TBM.

Management of Adult Chiari I Patients Based on CSF Flow Magnetic Resonance Imaging: Experience of Two Neurosurgical Centers

BACKGROUND AND STUDY AIMS

 Chiari malformation type 1 (CM1) is one of the most discussed neurosurgical disorders. No consensus exists how to manage adult CM1 patients. We aimed to evaluate all adult CM1 patients consecutively managed at our institutions and discuss our approach based on the phase-contrast (PC) magnetic resonance imaging (MRI).

PATIENTS AND METHODS

 The medical charts of adult patients diagnosed with CM1 at two referral neurosurgical centers between 2010 and 2017 were reviewed. The patients were either managed conservatively or surgically. We evaluated the patients clinically with the Chicago Chiari Outcome Scale (CCOS). The radiologic diagnosis was based on both craniocervical and PC-MRI.

RESULTS

 Ninety adult CM1 patients were managed conservatively. Conservative treatment failed in 5 of these 90 patients. Seventy-two patients (including those 5 patients who did not benefit from conservative treatment) underwent posterior fossa decompression with duraplasty. Eighty-five patients (94.4%) from the conservative group and 61 patients (84.7%) from the surgical group were treated successfully. An aqueductal stroke volume (ASV) value of 12 µL was found as the cutoff value for surgical candidates. A strong positive correlation between the increase in ASV values and clinical improvement was observed.

CONCLUSIONS

 PC-MRI can help in the management and follow-up of adult CM1 patients. Conservative management is possible in selected symptomatic CM1 patients with a high ASV (ASV > 15 µL). Surgery should be considered in patients with an ASV ≤ 12 µL. CM1 patients with ASV ≤12 to >15 μL require close follow-up. Long-standing symptoms, severe sleep apnea, symptoms influencing functionality, and syrinx are factors that affected outcomes negatively.

Characterising spinal cerebrospinal fluid flow in the pig with phase-contrast magnetic resonance imaging

BACKGROUND

Detecting changes in pulsatile cerebrospinal fluid (CSF) flow may assist clinical management decisions, but spinal CSF flow is relatively understudied. Traumatic spinal cord injuries (SCI) often cause spinal cord swelling and subarachnoid space (SAS) obstruction, potentially causing pulsatile CSF flow changes. Pigs are emerging as a favoured large animal SCI model; therefore, the aim of this study was to characterise CSF flow along the healthy pig spine.

METHODS

Phase-contrast magnetic resonance images (PC-MRI), retrospectively cardiac gated, were acquired for fourteen laterally recumbent, anaesthetised and ventilated, female domestic pigs (22-29 kg). Axial images were obtained at C2/C3, T8/T9, T11/T12 and L1/L2. Dorsal and ventral SAS regions of interest (ROI) were manually segmented. CSF flow and velocity were determined throughout a cardiac cycle. Linear mixed-effects models, with post-hoc comparisons, were used to identify differences in peak systolic/diastolic flow, and maximum velocity (cranial/caudal), across spinal levels and dorsal/ventral SAS. Velocity wave speed from C2/C3 to L1/L2 was calculated.

RESULTS

PC-MRI data were obtained for 11/14 animals. Pulsatile CSF flow was observed at all spinal levels. Peak systolic flow was greater at C2/C3 (dorsal: - 0.32 ± 0.14 mL/s, ventral: - 0.15 ± 0.13 mL/s) than T8/T9 dorsally (- 0.04 ± 0.03 mL/s; p < 0.001), but not different ventrally (- 0.08 ± 0.08 mL/s; p = 0.275), and no difference between thoracolumbar levels (p > 0.05). Peak diastolic flow was greater at C2/C3 (0.29 ± 0.08 mL/s) compared to T8/T9 (0.03 ± 0.03 mL/s, p < 0.001) dorsally, but not different ventrally (p = 1.000). Cranial and caudal maximum velocity at C2/C3 were greater than thoracolumbar levels dorsally (p < 0.001), and T8/T9 and L1/L2 ventrally (p = 0.022). Diastolic velocity wave speed was 1.41 ± 0.39 m/s dorsally and 1.22 ± 0.21 m/s ventrally, and systolic velocity wave speed was 1.02 ± 0.25 m/s dorsally and 0.91 ± 0.22 m/s ventrally.

CONCLUSIONS

In anaesthetised and ventilated domestic pigs, spinal CSF has lower pulsatile flow and slower velocity wave propagation, compared to humans. This study provides baseline CSF flow at spinal levels relevant for future SCI research in this animal model.

Novel developments in non-contrast enhanced MRI of the perivascular clearance system: What are the possibilities for Alzheimer's disease research?

The cerebral waste clearance system (i.e, glymphatic or intramural periarterial drainage) works through a network of perivascular spaces (PVS). Dysfunction of this system likely contributes to aggregation of Amyloid-β and subsequent toxic plaques in Alzheimer's disease (AD). A promising, non-invasive technique to study this system is MRI, though applications in dementia are still scarce. This review focusses on recent non-contrast enhanced (non-CE) MRI techniques which determine and visualise physiological aspects of the clearance system at multiple levels, i.e., cerebrospinal fluid flow, PVS-flow and interstitial fluid movement. Furthermore, various MRI studies focussing on aspects of the clearance system which are relevant to AD are discussed, such as studies on ageing, sleep alterations, and cognitive decline. Additionally, the complementary function of non-CE to CE methods is elaborated upon. We conclude that non-CE studies have great potential to determine which parts of the waste clearance system are affected by AD and in which stages of cognitive impairment dysfunction of this system occurs, which could allow future clinical trials to target these specific mechanisms.

MR Protocols for Paediatric Neurosurgical Common Conditions: An Update Guide for Neurosurgeons

The biggest challenge for clinicians and surgeons when it comes to radiological examinations is the ability to request the right modalities and to understand the strengths and limitations of each modality. This is particularly important in paediatric neurosciences where despite magnetic resonance imaging (MRI) being the main imaging modality, there are several protocols, technical limitations of specific scanners and issues related to sedation that need to be taken into account. In this chapter, we describe a simple approach for six common neurosurgical conditions to guide the paediatric neurosurgeons in requesting the right MR protocol and understanding the rationale of it.Paediatric neuro-oncology, epilepsy and neck/skull base protocols are discussed elsewhere in this book and therefore will not be a focus in this chapter (Bernasconi et al., Epilepsia 60:1054-68, 2019; D'Arco et al., Neuroradiology 64:1081-100; 2022; Avula et al., Childs Nerv Syst 37:2497-508; 2021).

CSF Dynamics: Implications for Hydrocephalus and Glymphatic Clearance

Beyond its neuroprotective role, CSF functions to rid the brain of toxic waste products through glymphatic clearance. Disturbances in the circulation of CSF and glymphatic exchange are common among those experiencing HCP syndrome, which often results from SAH. Normally, the secretion of CSF follows a two-step process, including filtration of plasma followed by the introduction of ions, bicarbonate, and water. Arachnoid granulations are the main site of CSF absorption, although there are other influencing factors that affect this process. The pathway through which CSF is through to flow is from its site of secretion, at the choroid plexus, to its site of absorption. However, the CSF flow dynamics are influenced by the cardiovascular system and interactions between CSF and CNS anatomy. One, two, and three-dimensional models are currently methods researchers use to predict and describe CSF flow, both under normal and pathological conditions. They are, however, not without their limitations. "Rest-of-body" models, which consider whole-body compartments, may be more effective for understanding the disruption to CSF flow due to hemorrhages and hydrocephalus. Specifically, SAH is thought to prevent CSF flow into the basal cistern and paravascular spaces. It is also more subject to backflow, caused by the presence of coagulation cascade products. In regard to the fluid dynamics of CSF, scar tissue, red blood cells, and protein content resulting from SAH may contribute to increased viscosity, decreased vessel diameter, and increased vessel resistance. Outside of its direct influence on CSF flow, SAH may result in one or both forms of hydrocephalus, including noncommunicating (obstructive) and communicating (nonobstructive) HCP. Imaging modalities such as PC-MRI, Time-SLIP, and CFD model, a mathematical model relying on PC-MRI data, are commonly used to better understand CSF flow. While PC-MRI utilizes phase shift data to ultimately determine CSF speed and flow, Time-SLIP compares signals generated by CSF to background signals to characterizes complex fluid dynamics. Currently, there are gaps in sufficient CSF flow models and imaging modalities. A prospective area of study includes generation of models that consider "rest-of-body" compartments and elements like arterial pulse waves, respiratory waves, posture, and jugular venous posture. Going forward, imaging modalities should work to focus more on patients in nature in order to appropriately assess how CSF flow is disrupted in SAH and HCP.

Influence of the area of the aqueduct and region of interest on quantification of stroke volume in healthy volunteers using phase-contrast cine magnetic resonance imaging

Background

Phase-contrast cine magnetic resonance imaging (PC-MRI) has been used to measure cerebrospinal fluid (CSF) flow dynamics, but the influence of the area of the aqueduct and region of interest (ROI) on quantification of stroke volume (SV) has not been assessed.

Purpose

To assess the influence of the area of the ROI in quantifying the aqueductal SV measured with PC-MRI within the cerebral aqueduct.

Material and Methods

Nine healthy volunteers (mean age = 29.6 years) were enrolled in the study, and brain MRI examinations were performed on a 3.0-T system. Quantitative analysis of the aqueductal CSF flow was performed using manual ROI placement. ROIs were separately drawn for each of the 12 phases of the cardiac cycle, and changes in aqueduct size during the cardiac cycle were determined. The SV was calculated using 12 different aqueductal ROIs and compared with the SV calculated using a fixed ROI size.

Results

There was variation in the size of the aqueduct during the cardiac cycle. In addition, the measured SV increased with a greater area of the ROI. A significant difference in the calculated SVs with the 12 variable ROIs was observed compared with that using a fixed ROI throughout the cardiac cycle.

Conclusion

To establish reliable reference values for the SV in future studies, a variable ROI should be considered.

Accuracy of MRI derived cerebral aqueduct flow parameters in the diagnosis of idiopathic normal pressure hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is a potentially reversible cause of dementia-like symptoms among the elderly. Current diagnostic guidelines for iNPH rely on clinical manifestations and ventricular morphology, which often lack accuracy. While magnetic resonance imaging (MRI) CSF flowmetry of the cerebral aqueduct provides a noninvasive aid to differential diagnosis, previous studies suffered from small sample sizes. This study compares the accuracy of different CSF flow parameters for iNPH diagnosis in a general patient population. From 2016 to 2018, a total of 216 subjects over 60 years of age were retrospectively enrolled, including 38 patients with iNPH and 178 patients with non-iNPH neurological conditions. All participants received phase-contrast MRI (PC-MRI) CSF flowmetry, with measurements performed independently by two radiologists. Flow parameters of iNPH and non-iNPH groups were compared along with their diagnostic accuracy. Absolute stroke volume (ABSV), forward flow, backward flow, mean flux and peak velocity were significantly higher in iNPH patients (P < 0.001, P < 0.001, P < 0.001, P = 0.008, P = 0.038, respectively). Backward flow had the highest diagnostic accuracy, followed by ABSV and forward flow. Net caudocranial aqueductal flow was observed in both groups, but with greater volume in the iNPH group. PC-MRI provides a non-invasive method of CSF flowmetry across the cerebral aqueduct and may aid in iNPH diagnosis. ABSV and its component flow values may provide better accuracy in identifying iNPH than other parameters.

Cerebrospinal fluid dynamics along the optic nerve

The cerebrospinal fluid (CSF) plays an important role in delivering nutrients and eliminating the metabolic wastes of the central nervous system. An interrupted CSF flow could cause disorders of the brain and eyes such as Alzheimer's disease and glaucoma. This review provides an overview of the anatomy and flow pathways of the CSF system with an emphasis on the optic nerve. Imaging technologies used for visualizing the CSF dynamics and the anatomic structures associated with CSF circulation have been highlighted. Recent advances in the use of computational models to predict CSF flow patterns have been introduced. Open questions and potential mechanisms underlying CSF circulation at the optic nerves have also been discussed.

Quantifying cerebrospinal fluid dynamics: A review of human neuroimaging contributions to CSF physiology and neurodegenerative disease

Cerebrospinal fluid (CSF), predominantly produced in the ventricles and circulating throughout the brain and spinal cord, is a key protective mechanism of the central nervous system (CNS). Physical cushioning, nutrient delivery, metabolic waste, including protein clearance, are key functions of the CSF in humans. CSF volume and flow dynamics regulate intracranial pressure and are fundamental to diagnosing disorders including normal pressure hydrocephalus, intracranial hypotension, CSF leaks, and possibly Alzheimer's disease (AD). The ability of CSF to clear normal and pathological proteins, such as amyloid-beta (Aβ), tau, alpha synuclein and others, implicates it production, circulation, and composition, in many neuropathologies. Several neuroimaging modalities have been developed to probe CSF fluid dynamics and better relate CSF volume and flow to anatomy and clinical conditions. Approaches include 2-photon microscopic techniques, MRI (tracer-based, gadolinium contrast, endogenous phase-contrast), and dynamic positron emission tomography (PET) using existing approved radiotracers. Here, we discuss CSF flow neuroimaging, from animal models to recent clinical-research advances, summarizing current endeavors to quantify and map CSF flow with implications towards pathophysiology, new biomarkers, and treatments of neurological diseases.

Assessing pulsatile waveforms of paravascular cerebrospinal fluid dynamics using dynamic diffusion-weighted imaging (dDWI)

Cerebrospinal fluid (CSF) in the paravascular spaces of the surface arteries (sPVS) is a vital pathway in brain waste clearance. Arterial pulsations may be the driving force of the paravascular flow, but its pulsatile pattern remains poorly characterized, and no clinically practical method for measuring its dynamics in the human brain is available. In this work, we introduce an imaging and quantification framework for in-vivo non-invasive assessment of pulsatile fluid dynamics in the sPVS. It used dynamic Diffusion-Weighted Imaging (dDWI) at a lower b-values of 150s/mm² and retrospective gating to detect the slow flow of CSF while suppressing the fast flow of adjacent arterial blood. The waveform of CSF flow over a cardiac cycle was revealed by synchronizing the measurements with the heartbeat. A data-driven approach was developed to identify sPVS and allow automatic quantification of the whole-brain fluid waveforms. We applied dDWI to twenty-five participants aged 18–82 y/o. Results demonstrated that the fluid waveforms across the brain showed an explicit cardiac-cycle dependency, in good agreement with the vascular pumping hypothesis. Furthermore, the shape of the CSF waveforms closely resembled the pressure waveforms of the artery wall, suggesting that CSF dynamics is tightly related to artery wall mechanics. Finally, the CSF waveforms in aging participants revealed a strong age effect, with a significantly wider systolic peak observed in the older relative to younger participants. The peak widening may be associated with compromised vascular compliance and vessel wall stiffening in the older brain. Overall, the results demonstrate the feasibility, reproducibility, and sensitivity of dDWI for detecting sPVS fluid dynamics of the human brain. Our preliminary data suggest age-related alterations of the paravascular pumping. With an acquisition time of under six minutes, dDWI can be readily applied to study fluid dynamics in normal physiological conditions and cerebrovascular/neurodegenerative diseases.

Headache and Other Symptoms in Chiari Malformation Type I Are Associated with Cerebrospinal Fluid Flow Improvement After Decompression: A Two-Institutional Study

OBJECTIVE

Chiari malformation type I (CMI) is a common neurologic condition and surgery is the standard treatment. We aim to establish the cerebrospinal fluid (CSF) flow change as a potential objective indicator of surgical efficacy to improve symptoms.

METHODS

We performed a retrospective 2-center analysis of surgically treated patients with CMI. Qualitative CSF flow studies obtained preoperatively and postoperatively were analyzed by the neuroradiologist, seeking improvement in CSF flow. Symptom status, including headache and neck pain, were recorded.

RESULTS

Forty-nine patients were identified between 2010 and 2017. The average age was 36 years, with 47 females. After decompression, CSF flow was improved in 41 patients (group A) and unchanged in 8 (group B). Group A and B had a mean age of 34 and 42 years (P < 0.05) and an average tonsillar herniation of 8.3 and 8.5 mm (P = 0.40), respectively. Group A had improved clinical outcomes, compared with group B (P = 0.024), more specifically, in headache (50% vs. 37%), neck pain (66% vs. 33%), dizziness (78% vs. 50%), vision symptoms (84% vs. 80%), and weakness (100% vs. 66%), respectively. Group B had the only patient who did worse on clinical follow-up.

CONCLUSIONS

Patients with CMI often present with a constellation of symptoms. We showed a significant association between improved CSF flow after decompression and symptom alleviation. Further, our study suggests that the presence of improved CSF flow postoperatively could represent an objective indicator for improved patient outcomes.

Measurement of CSF pulsation from EPI-based human fMRI

It is recently discovered that the glymphatic system and meningeal lymphatic system are the primary routes for the clearance of brain waste products. The CSF flow is part of these systems, facilitating the clearance procedure. Nonetheless, the relationship between CSF flow and brain functional activity has been underexplored. To investigate CSF dynamics and functional brain activity simultaneously, recent studies have proposed a CSF inflow index measured on edge slices (CSFedge) of echo-planar imaging (EPI) based functional magnetic resonance imaging (fMRI), however, it lacks the quantitative aspect of the CSF pulsation. We proposed a new method for quantifying CSF pulsation (CSFpulse) based on an interslice CSF pulsation model in the 4^th ventricle of EPI-based fMRI. The proposed CSFpulse successfully detected the higher CSF flow during the resting state than the typical task states (visual and motor) (p<.05), which is consistent with previous studies based on phase contrast (PC) MRI and CSF volume MRI, while it was not detected in CSFedge based indices or baseline CSF signals in various regions of interest (ROIs). Moreover, CSFpulse demonstrated dynamic functional changes in CSF pulsation: it decreased during the activation-on blocks while it increased during the activation-off blocks. CSFpulse significantly correlated with stroke volume measured using PC MRI, a standard method for CSF pulsation quantification, under the same functional state, while CSFedge based indices or CSF ROIs showed no correlation with the PC MRI stroke volume. Lastly, the correlation of CSFpulse with global BOLD was weaker than that of CSFedge, suggesting that CSFpulse may reflect distinct CSF physiological information that is less affected by global BOLD effects. Based on these results, the proposed CSFpulse provides CSF pulsatility information more accurately in a quantitative manner than CSFedge based indices from the recent CSF studies or the conventional ROI-based analysis. In addition to the high correlation with PC MRI, CSFpulse is much faster than PC MRI and provides information of functional brain activations simultaneously, advantageous over PC MRI or CSF volume MRI. Accordingly, the suggested CSFpulse can be used for investigating intra-subject functional changes in BOLD and CSF pulsation simultaneously and inter-subject CSF pulsation variations based on conventional EPI-based fMRI, which warrants further investigation.

Conservative Treatment of Chiari Malformation Type I Based on the Phase-Contrast MRI: A Retrospective Study

BACKGROUND

The phase-contrast magnetic resonance image (PC-MRI) use is interestingly increased in diagnosis and follow-up patients with Chiari Type I Malformation (CM1). The current study aimed to elaborate the benefits of conservative treatment by evaluating consecutively treated adult patients with CM1 who were selected on basis of the PC-MRIs.

METHODS

Medical records of patients diagnosed with CM1 were retrospectively reviewed at two neurosurgical centers spanning eight years (2010-2017). Adult patients with CM1, who were treated conservatively and met study criteria, were selected to be the core sample for this study. Between-groups (benefited vs non-benefited) comparisons were performed to understand the factors that may affect the outcomes.

RESULTS

Ninety (68 females and 22 males) adult patients received conservative treatment for CM1. The mean age was 40.6. Headaches and pinprick loss were the most commonly recorded symptoms and clinical findings which were recorded in 58 (64.4%) and 31 (34.4%) patients, respectively. Eleven patients were presented with a syrinx. The mean aqueductal stroke volume (ASV) was 16.5 μl. The conservative treatment failed in treating five (5.6%) patients who underwent surgical intervention. The means of ASV in the benefited and non-benefited groups were 16.7 and 13.2 μl, respectively (p=0.004).

CONCLUSION

Conservative approaches (prescriptive medications, physical therapy, Pilates, and swimming) can improve the life quality of non-surgical candidate adult patients with CM1. Conservative treatment can be useful in selected patients with variably CM1 (ASV=16.7 μl). The presence of heavy sleep apnea or/and functional symptoms were prognostic factors that were affected the conservative treatment negatively.

The factors affecting the outcomes of conservative and surgical treatment of chiari i adult patients: a comparative retrospective study

BACKGROUND

The prognosis of the Chiari malformation type 1 (CM1) demonstrates a variant spectrum that varies from full recovery to complicated worse neurological disability.

OBJECTIVE

To investigate the factors affecting the outcomes of conservative and surgical treatment for CM1 by evaluating adult patients consecutively managed at our institutions.

MATERIALS AND METHODS

We retrospectively reviewed the medical records of patients diagnosed with CM1 at two reference neurosurgical centers for eight years (2010-2017). We selected all CM1 adult patients who managed conservatively or surgically as the core sample for this study. For clinical evaluation, we used a Chicago Chiari Outcome Scale (CCOS). For radiological assessment, we adopted both craniocervical and contrast-phase MRIs. We investigate factors such as age, sex, pretreatment symptoms, symptoms duration, and radiological findings in both groups.

RESULTS

Ninety patients were treated conservatively. After a progression, five of them were treated surgically later and included in a total of 72 patients who underwent decompressive surgery. We successfully managed 85 patients (94.4%) of the conservative group and 64 patients (88.9%) of the surgical group. We found that patients with aqueductal stroke volume (ASV) of 12 µl are surgical candidates. We observed a strong positive correlation between clinical improvement and the increase in ASV values.

CONCLUSIONS

ASV≤12 µl is a significant predictor for surgical intervention. The presence of heavy sleep apnea or/and functional symptoms, tonsillar herniation >13.4 mm on coronal images, low ASV, long symptom durations, and a syrinx are the independent prognostic factors that affected outcomes negatively.

The (extended) achondroplasia foramen magnum score has good observer reliability

BACKGROUND

Achondroplasia is the most common skeletal dysplasia. A significant complication is foramen magnum stenosis. When severe, compression of the spinal cord may result in sleep apnea, sudden respiratory arrest and death. To avoid complications, surgical decompression of the craniocervical junction is offered in at-risk cases. However, practice varies among centres. To standardize magnetic resonance (MR) reporting, the achondroplasia foramen magnum score was recently developed. The reliability of the score has not been assessed.

OBJECTIVE

To assess the interobserver reliability of the achondroplasia foramen magnum score.

MATERIALS AND METHODS

Base of skull imaging of children with achondroplasia under the care of Sheffield Children's Hospital was retrospectively and independently reviewed by four observers using the achondroplasia foramen magnum score. Two-way random-effects intraclass coefficient (ICC) was used to assess inter- and intra-observer reliability.

RESULTS

Forty-nine eligible cases and five controls were included. Of these, 10 were scored normal, 17 had a median score of 1 (mild narrowing), 11 had a median score of 2 (effacement of cerebral spinal fluid), 10 had a score of 3 (compression of cord) and 6 had a median score of 4 (cord myelopathic change). Interobserver ICC was 0.72 (95% confidence interval = 0.62-0.81). Intra-observer ICC ranged from 0.60 to 0.86. Reasons for reader disagreement included flow void artefact, subtle T2 cord signal and myelopathic T2 cord change disproportionate to canal narrowing.

CONCLUSION

The achondroplasia foramen magnum score has good interobserver reliability. Imaging features leading to interobserver disagreement have been identified. Further research is required to prospectively validate the score against clinical outcomes.

Ultra-long-TE arterial spin labeling reveals rapid and brain-wide blood-to-CSF water transport in humans

The study of brain clearance mechanisms is an active area of research. While we know that the cerebrospinal fluid (CSF) plays a central role in one of the main existing clearance pathways, the exact processes for the secretion of CSF and the removal of waste products from tissue are under debate. CSF is thought to be created by the exchange of water and ions from the blood, which is believed to mainly occur in the choroid plexus. This exchange has not been thoroughly studied in vivo.

We propose a modified arterial spin labeling (ASL) MRI sequence and image analysis to track blood water as it is transported to the CSF, and to characterize its exchange from blood to CSF. We acquired six pseudo-continuous ASL sequences with varying labeling duration (LD) and post-labeling delay (PLD) and a segmented 3D-GRASE readout with a long echo train (8 echo times (TE)) which allowed separation of the very long-T₂ CSF signal. ASL signal was observed at long TEs (793 ms and higher), indicating presence of labeled water transported from blood to CSF. This signal appeared both in the CSF proximal to the choroid plexus and in the subarachnoid space surrounding the cortex. ASL signal was separated into its blood, gray matter and CSF components by fitting a triexponential function with T₂s taken from literature. A two-compartment dynamic model was introduced to describe the exchange of water through time and TE. From this, a water exchange time from the blood to the CSF (T_bl->CSF) was mapped, with an order of magnitude of approximately 60 s.

Simultaneous Exercise and Cognitive Training in Virtual Reality Phase 2 Pilot Study: Impact on Brain Health and Cognition in Older Adults

Background:

Aerobic exercise and environmental enrichment have been shown to enhance brain function. Virtual reality (VR) is a promising method for combining these activities in a meaningful and ecologically valid way.

Objective:

The purpose of this Phase 2 pilot study was to calculate relative change and effect sizes to assess the impact of simultaneous exercise and cognitive training in VR on brain health and cognition in older adults.

Methods:

Twelve cognitively normal older adults (64.7±8.8 years old, 8 female) participated in a 12-week intervention, 3 sessions/week for 25–50 minutes/session at 50–80% HR_max. Participants cycled on a custom-built stationary exercise bike while wearing a VR head-mounted display and navigating novel virtual environments to train spatial memory. Brain and cognitive changes were assessed using MRI imaging and a cognitive battery.

Results:

Medium effect size (ES) improvements in cerebral flow and brain structure were observed. Pulsatility, a measure of peripheral vascular resistance, decreased 10.5% (ES(d) = 0.47). Total grey matter volume increased 0.73% (ES(r) = 0.38), while thickness of the superior parietal lobule, a region associated with spatial orientation, increased 0.44% (ES(r) = 0.30). Visual memory discrimination related to pattern separation showed a large improvement of 68% (ES(η_p²) = 0.43). Cognitive flexibility (Trail Making Test B) (ES(r) = 0.42) and response inhibition (ES(W) = 0.54) showed medium improvements of 14% and 34%, respectively.

Conclusions:

Twelve weeks of simultaneous exercise and cognitive training in VR elicits positive changes in brain volume, vascular resistance, memory, and executive function with moderate-to-large effect sizes in our pilot study.

Decreased CSF Dynamics in Treatment-Naive Patients with Essential Hypertension: A Study with Phase-Contrast Cine MR Imaging

BACKGROUND AND PURPOSE

Arterial sclerosis resulting from hypertension slows CSF transportation in the perivascular spaces, showing the intrinsic relationship between the CSF and the blood vasculature. However, the exact effect of hypertension on human CSF flow dynamics remains unclear. The present study aimed to evaluate CSF flow dynamics in treatment-naive patients with essential hypertension using phase-contrast cine MR imaging.

MATERIALS AND METHODS

The study included 60 never-treated patients with essential hypertension and 60 subjects without symptomatic atherosclerosis. CSF flow parameters, such as forward flow volume, forward peak velocity, reverse flow volume, reverse peak velocity, average flow, and net flow volume, were measured with phase-contrast cine MR imaging. Differences between the 2 groups were assessed to determine the independent determinants of these CSF flow parameters.

RESULTS

Forward flow volume, forward peak velocity, reverse flow volume, reverse peak velocity, and average flow in the patients with hypertension significantly decreased (all, P < .05). Increasing systolic blood pressure was significantly associated with lower forward flow volume (β = -0.44 mL/mL/mm Hg; 95% CI, -0.83 to -0.06 mL/mL/mm Hg), forward peak velocity (β = -0.50 cm/s/mm Hg; 95% CI, -0.88 to -0.12 cm/s/mm Hg), reverse flow volume (β = -0.61 mL/mL/mm Hg; 95% CI, -0.97 to -0.26 mL/mL/mm Hg), reverse peak velocity (β = -0.55 cm/s/mm Hg; 95% CI, -0.91-0.18 cm/s/mm Hg), and average flow (β = -0.50 mL/min/mm Hg; 95% CI, -0.93 to -0.08 mL/min/mm Hg).

CONCLUSIONS

The CSF flow dynamics in patients with hypertension are decreased, and increasing systolic blood pressure is strongly associated with lower CSF flow dynamics.

Papilledema: A review of etiology, pathophysiology, diagnosis, and management

Papilledema is optic nerve head edema secondary to raised intracranial pressure (ICP). It is distinct from other causes of optic disk edema in that visual function is usually normal in the acute phase. Papilledema is caused by transmission of elevated ICP to the subarachnoid space surrounding the optic nerve that hinders axoplasmic transport within ganglion cell axons. There is ongoing controversy as to whether axoplasmic flow stasis is produced by physical compression of axons or microvascular ischemia. The most common cause of papilledema, especially in patients under the age of 50, is idiopathic intracranial hypertension (IIH); however, conditions that decrease cerebrospinal fluid (CSF) outflow by either causing CSF derangements or mechanically blocking CSF outflow channels, and rarely conditions that increase CSF production, can be the culprit. When papilledema is suspected clinically, blood pressure should be measured, and pseudopapilledema should be ruled out. Magnetic resonance imaging of the brain and orbits with venography sequences is the preferred neuroimaging modality that should be performed next to look for indirect imaging signs of increased ICP and to rule out nonidiopathic causes. Lumbar puncture with measurement of opening pressure and evaluation of CSF composition should then be performed. In patients not in a typical demographic group for IIH, further investigations should be conducted to assess for underlying causes of increased ICP. Magnetic resonance imaging of the neck and spine, magnetic resonance angiography of the brain, computed tomography of the chest, complete blood count, and creatinine testing should be able to identify most secondary causes of intracranial hypertension. Treatment for patients with papilledema should be targeted toward the underlying etiology. Most patients with IIH respond to weight loss and oral acetazolamide. For patients with decreased central acuity and constricted visual fields at presentation, as well as patients who do not respond to treatment with acetazolamide, surgical treatments should be considered, with ventriculoperitoneal shunting being the typical procedure of choice.

Absence of CSF flow within the cerebral aqueduct in spontaneous intracranial hypotension: a report of two cases

Spontaneous intracranial hypotension (SIH) is a potentially debilitating condition resulting from a low cerebrospinal fluid (CSF) volume secondary to spinal CSF leakage. Characteristic clinical and radiological imaging findings are helpful in diagnosis. Herein, we present and discuss the magnetic resonance imaging (MRI) and CSF flow study of two patients with SIH and no CSF flow within the cerebral aqueduct, which is extremely rare in the literature.

Assessment of Cerebrospinal Fluid Hydrodynamics Using Magnetic Resonance Imaging in Postcraniospinal Surgery Patients

Objective Aim of this study is to evaluate the effect of craniospinal interventions on cerebrospinal fluid (CSF) flow hydrodynamics and study the correlation of postoperative changes in flow alteration with clinical outcome.

Materials and Methods Fifty patients who underwent various craniospinal procedures were studied using conventional and phase-contrast magnetic resonance imaging (PCMRI) protocol. CSF flow quantification was performed at cerebral aqueduct, foramen magnum, C2–3, and D12–L1 vertebral levels with site showing maximal alteration of CSF flow dynamics considered as the region of interest. Velocity encoding was kept at 20 cm/s. Patients with pathology atcraniovertebral junction were considered separately (group I) from others (group II) due to different flow dynamics. Follow-up scans were performed after an interval of 1 month for temporal evaluation of changes in CSF flow dynamics.

Results Patients in both groups showed a significant change in peak CSF velocity postoperatively (mean change of 1.34 cm/s in group I and 0.28 cm/s in group II) with bidirectional improvement in flow on cine-phase-contrast qualitative images. Regional pain (82%) and headache (46%) were seen in most of the patients preoperatively. Postoperatively clinical symptoms improved in 59.5%, static in 26.2%, and worsened in 14.3%. In both the groups, an improvement in clinical symptomatology had significant correlation with mean changes in peak CSF velocity postoperatively ( p = 0.04 in both groups).

Conclusion PCMRI can effectively evaluate changes in CSF flow noninvasively both pre- and postoperatively. This may have potential role in determining clinical outcome and prognosis of patients undergoing procedures in craniospinal axis.

Interlayer dural split technique for Chiari I malformation treatment in adult-Technical note

OBJECTIVE

To present an alternative surgical technique in treating cases of Chiari I Malformation with mild-to-moderate syringomyelia after decompressive suboccipital craniectomy: incising only the outer layer of the dura mater, then dissecting it from the inner layer without opening the latter.

PATIENTS AND METHODS

We utilized this technique in a short series of three cases who were admitted to our department for mild symptoms such as intermittent headache and dissociated sensory loss in the upper limbs, caused by a Chiari Malformation Type I. The patients were placed in the sitting position. We performed a reduced median suboccipital craniectomy and resection of the posterior arch of C1 adapted to the level of tonsil descent, from a limited superior half to complete resection. Afterward, we incised the outer dural layer, while sparing the inner one. Using a fine dissector, we then split apart the outer and inner layers to the margin of the craniectomy. Through the transparency of the inner layer and the arachnoid, the cerebellum and the medulla were visible and pulsating. An autologous fascia duraplasty was then performed.

RESULTS

The postoperative course was favorable in all cases, the patients being discharged without any deficits and with complete symptom resolution. Follow-up at 3, 6, and 12 months after surgery revealed a significant reduction in brainstem compression and syringomyelia.

CONCLUSIONS

Interlayer dural split technique can be used effectively in treating symptomatic cases of type I Chiari malformation in adults, with mild-to-moderate syringomyelia. It is less invasive than opening the dura and possibly more effective than decompressive craniectomy and C1 laminectomy alone. This technique must be validated in a larger case-control series.

Communicating chronic hydrocephalus: A review

Formerly called normal pressure hydrocephalus, communicating chronic hydrocephalus (CCH) is a condition affecting 0.1 to 0.5% of patients over 60years of age. The pathophysiology of this disease is poorly understood, but a defect in cerebrospinal fluid (CSF) resorption appears to be commonly defined as the cause of the neurological disorders. The last important discovery is the description of the glymphatic system and its implication in CCH and CSF resorption. Comorbidities (Alzheimer's disease, microangiopathy, parkinsonism) are very frequent, and involve a diagnostic challenge. The clinical presentation is based on the Hakim and Adams triad, comprising gait disorders, mainly impairing walking, cognitive disorders, affecting executive functions, episodic memory, visuospatial cognition, and sphincter disorders as urinary incontinence (detrusor hyperactivity). The diagnosis is suspected through a set of arguments, combining the clinical presentation, the radiological data of the magnetic resonance imaging (MRI) showing a ventriculomegaly associated with signs of transependymomous resorption of the CSF and disappearance of the cortical sulci, and the clinical response to the depletion of CSF. In the presence of all these elements, or a strong clinical suspicion, the standard treatment will be of a permanent CSF shunt, using a ventriculoatrial or ventriculoperitoneal shunt. The effectiveness of this treatment defines the diagnosis. The clinical improvement is better when treatment occurs early after the onset of the disorders, reaching 75 to 90% of motor improvement.

Non-Invasive Evaluation of Cerebral Microvasculature Using Pre-Clinical MRI: Principles, Advantages and Limitations

Alterations to the cerebral microcirculation have been recognized to play a crucial role in the development of neurodegenerative disorders. However, the exact role of the microvascular alterations in the pathophysiological mechanisms often remains poorly understood. The early detection of changes in microcirculation and cerebral blood flow (CBF) can be used to get a better understanding of underlying disease mechanisms. This could be an important step towards the development of new treatment approaches. Animal models allow for the study of the disease mechanism at several stages of development, before the onset of clinical symptoms, and the verification with invasive imaging techniques. Specifically, pre-clinical magnetic resonance imaging (MRI) is an important tool for the development and validation of MRI sequences under clinically relevant conditions. This article reviews MRI strategies providing indirect non-invasive measurements of microvascular changes in the rodent brain that can be used for early detection and characterization of neurodegenerative disorders. The perfusion MRI techniques: Dynamic Contrast Enhanced (DCE), Dynamic Susceptibility Contrast Enhanced (DSC) and Arterial Spin Labeling (ASL), will be discussed, followed by less established imaging strategies used to analyze the cerebral microcirculation: Intravoxel Incoherent Motion (IVIM), Vascular Space Occupancy (VASO), Steady-State Susceptibility Contrast (SSC), Vessel size imaging, SAGE-based DSC, Phase Contrast Flow (PC) Quantitative Susceptibility Mapping (QSM) and quantitative Blood-Oxygenation-Level-Dependent (qBOLD). We will emphasize the advantages and limitations of each strategy, in particular on applications for high-field MRI in the rodent's brain.

Promoted Aggregation of Aβ on Lipid Bilayers in an Open Flowing System

Self-assembly of amyloid-β (Aβ) peptides in nonequilibrium, flowing conditions is associated with pathogenesis of Alzheimer's disease. We examined the role of biologically relevant, nonequilibrium, flowing conditions in the desorption, diffusion, and integration of Aβ-lipid assemblies at the membrane surface using a microchannel connected with microsyringes. A 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer was formed on a glass substrate and incubated in Aβ solution under either a quiescent condition (no flow) or flowing condition for 24 h. Although dot-like aggregates (<1 μm) comprising Aβ fibrils formed on the DMPC membrane under the quiescent condition, larger plaque-like aggregates formed under the flowing condition, suggesting that nonequilibrium continuous flow governs the cytotoxicity of Aβ species. We propose that Aβ adsorption on the membrane surface involves spontaneous desorption of Aβ-lipid to form self-assembling aggregates, with this accelerated by surface shear forces. These findings suggest that nonequilibrium, flowing conditions influence inter/intra-molecular Aβ-fibril formation to trigger formation of amyloid plaques.

Advanced Magnetic Resonance Imaging of the Skull Base

Magnetic resonance (MR) imaging is a crucial tool for evaluation of the skull base, enabling characterization of complex anatomy by utilizing multiple image contrasts. Recent technical MR advances have greatly enhanced radiologists' capability to diagnose skull base pathology and help direct management. In this paper, we will summarize cutting-edge clinical and emerging research MR techniques for the skull base, including high-resolution, phase-contrast, diffusion, perfusion, vascular, zero echo-time, elastography, spectroscopy, chemical exchange saturation transfer, PET/MR, ultra-high-field, and 3D visualization. For each imaging technique, we provide a high-level summary of underlying technical principles accompanied by relevant literature review and clinical imaging examples.

MRI CSF flowmetry in evaluation of different neurological diseases

Background

Phase contrast MR imaging is a rapid and non-invasive technique which is sensitive in diagnosis and follow-up of different neurological diseases that cause CSF flow abnormality. MRI CSF flowmetry will be currently assessed in different neurological diseases that may cause CSF flow abnormalities.

Results

This study includes 39 patients with their ages ranging from 1 to 65 years; they were referred from the neurology department, with nine individuals of matched age and sex as a control group. Based on clinical history and conventional MRI, patients were subdivided into five subgroups; normal pressure hydrocephalus (NPH), hydrocephalus, idiopathic intracranial hypertension (IIH), brain atrophy (BA), and Chiari malformation type I (CM-I). All patients and control were subjected to MRI CSF flowmetry evaluation with stress on peak diastolic velocity (PDV), peak systolic velocity (PSV), stroke volume (SV), and maximum velocity (Vmax). PDV, PSV, and SV were found significantly higher in NPH, CM-I, and hydrocephalus compared to control (4.2, 4.96, and 83.23 for NPH; 3.95, 4.93, and 37.38 for CM-I; and 4.2, 5.6, and 125 in hydrocephalus versus 2.11, 2.73, and 75.33 in control, respectively; P = 0.0004, 0.0008, and 0.0009 for NPH; 0.03, 0.003, and 0.06 for CM-I; and 0.0005, 0.0002, and 0.0003, respectively). On the other hand, patients with BA showed significantly lower values (1.37, 1.66, and 1.53, respectively) compared to control (P = 0.001, 0.001, and 0.004, respectively).

Conclusion

MRI CSF flowmetry provides an easy, accurate, and non-invasive method for diagnosis of different neurological diseases that cause CSF flow abnormality. Moreover, this diagnostic modality could be helpful in selecting the therapeutic option.

Phase-Contrast MRI: Physics, Techniques, and Clinical Applications

With phase-contrast imaging, the MRI signal is used to visualize and quantify velocity. This imaging modality relies on phase data, which are intrinsic to all MRI signals. With use of bipolar gradients, degrees of phase shift are encoded and in turn correlated directly with the velocity of protons. The acquisition of diagnostic-quality images requires selection of the correct imaging plane to ensure accurate measurement and selection of the encoding velocity and thus prevent aliasing and achieve the highest signal-to-noise ratio. Multiple applications of phase-contrast imaging are actively used in clinical practice. One of the most common clinical uses is in cardiac valvular flow imaging, at which the data are used to assess the severity of valvular disease and quantify the shunt fraction. In neurologic imaging, phase-contrast imaging can be used to measure the flow of cerebrospinal fluid. This measurement can aid in the diagnosis and direct management of normal pressure hydrocephalus or be used to evaluate the severity of stenosis, such as that in Chiari I malformations. At vascular analysis, phase-contrast imaging can be used to visualize arterial and venous flow, and this application is used most commonly in the brain. Three-dimensional imaging can yield highly detailed flow data in a technique referred to as four-dimensional flow. A more recently identified application is in MR elastography. Shear waves created by using an impulse device can be velocity encoded, and this velocity is directly proportional to the stiffness of the organ, or the shear modulus. This imaging modality is most commonly used in the liver for evaluation of cirrhosis and steatosis, although research on the assessment of other organs is being performed. Phase-contrast imaging is an important tool in the arsenal of MRI examinations and has many applications. Proper use of phase-contrast imaging requires an understanding of the many practical and technical factors and unique physics principles underlying the technique.^©RSNA, 2020.