Cerebrospinal fluid dynamics

The classical cerebrospinal fluid (CSF) circulation theory has been accepted as an established theory of CSF physiology. It describes bulk CSF flow from production site to absorption site. However, much controversy remains regarding the basic CSF physiology and the mechanisms behind the development of hydrocephalus. In the recent observations made using advanced magnetic resonance imaging (MRI) technique, namely, the time spatial inversion pulse (Time-SLIP) method, CSF was used as internal CSF tracer to trace true CSF movement. Observation of the CSF dynamics using this method reveals aspects of CSF dynamics that are different from those of classical CSF circulation theory. Cerebrospinal fluid shows pulsation but does not show bulk flow from production site to absorption site, a theory that was built upon externally injected tracer studies. Observation of the exogeneous tracer studies were true but misinterpreted. Causes of misinterpretations are the differences between results obtained using the true CSF tracer and exogenous tracers. A better understanding of the real CSF physiology can be significant for the advancement of medical sciences in the future. Revisiting CSF flow physiology is a necessary step toward this goal

Dynamics of respiratory and cardiac CSF motion revealed with real-time simultaneous multi-slice EPI velocity phase contrast imaging

Cerebrospinal fluid (CSF) dynamics have been mostly studied with cardiac-gated phase contrast MRI combining signal from many cardiac cycles to create cine-phase sampling of one time averaged cardiac cycle. The relative effects of cardiac and respiratory changes on CSF movement are not well understood. There is possible respiration driven movement of CSF in ventricles, cisterns, and subarachnoid spaces which has not been characterized with velocity measurements. To date, commonly used cine-phase contrast techniques of velocity imaging inherently cannot detect respiratory velocity changes since cardiac gated data acquired over several minutes randomizes respiratory phase contributions. We have developed an extremely fast, real-time and quantitative MRI technique to image CSF velocity in simultaneous multi-slice (SMS) echo planar imaging (EPI) acquisitions of 3 or 6 slice levels simultaneously over 30 seconds and observe 3D spatial distributions of CSF velocity. Measurements were made in 10 subjects utilizing a respiratory belt to record respiratory phases and visual cues to instruct subjects on breathing rates. A protocol is able to measure velocity within regions of brain and basal cisterns covered with 24 axial slices in 4 minutes, repeated for 3 velocity directions. These measurements were performed throughout the whole brain, rather than in selected line regions so that a global view of CSF dynamics could be visualized. Observations of cardiac and breathing-driven CSF dynamics show bidirectional respiratory motion occurs primarily along the central axis through the basal cisterns and intraventricular passageways and to a lesser extent in the peripheral Sylvian fissure with little CSF motion present in subarachnoid spaces. During inspiration phase, there is upward (inferior to superior direction) CSF movement into the cranial cavity and into the lateral ventricles and a reversed direction in expiration phase

Identifying Respiration-Related Aliasing Artifacts in the Rodent Resting-State fMRI

Resting-state functional magnetic resonance imaging (rs-fMRI) combined with optogenetics and electrophysiological/calcium recordings in animal models is becoming a popular platform to investigate brain dynamics under specific neurological states. Physiological noise originating from the cardiac and respiration signal is the dominant interference in human rs-fMRI and extensive efforts have been made to reduce these artifacts from the human data. In animal fMRI studies, physiological noise sources including the respiratory and cardiorespiratory artifacts to the rs-fMRI signal fluctuation have typically been less investigated. In this article, we demonstrate evidence of aliasing effects into the low-frequency rs-fMRI signal fluctuation mainly due to respiration-induced B0 offsets in anesthetized rats. This aliased signal was examined by systematically altering the fMRI sampling rate, i.e., the time of repetition (TR), in free-breathing conditions and by adjusting the rate of ventilation. Anesthetized rats under ventilation showed a significantly narrower frequency bandwidth of the aliasing effect than free-breathing animals. It was found that the aliasing effect could be further reduced in ventilated animals with a muscle relaxant. This work elucidates the respiration-related aliasing effects on the rs-fMRI signal fluctuation from anesthetized rats, indicating non-negligible physiological noise needed to be taken care of in both awake and anesthetized animal rs-fMRI studies

Where are we? : The anatomy of the murine cortical meninges revisited for intravital imaging, immunology, and clearance of waste from the brain

Rapid progress is being made in understanding the roles of the cerebral meninges in the maintenance of normal brain function, in immune surveillance, and as a site of disease. Most basic research on the meninges and the neural brain is now done on mice, major attractions being the availability of reporter mice with fluorescent cells, and of a huge range of antibodies useful for immunocytochemistry and the characterization of isolated cells. In addition, two-photon microscopy through the unperforated calvaria allows intravital imaging of the undisturbed meninges with sub-micron resolution. The anatomy of the dorsal meninges of the mouse (and, indeed, of all mammals) differs considerably from that shown in many published diagrams: over cortical convexities, the outer layer, the dura, is usually thicker than the inner layer, the leptomeninx, and both layers are richly vascularized and innervated, and communicate with the lymphatic system. A membrane barrier separates them and, in disease, inflammation can be localized to one layer or the other, so experimentalists must be able to identify the compartment they are studying. Here, we present current knowledge of the functional anatomy of the meninges, particularly as it appears in intravital imaging, and review their role as a gateway between the brain, blood, and lymphatics, drawing on information that is scattered among works on different pathologies

Análisis anatomorradiológico de la circulación del líquido cefalorraquídeo con técnicas de imagen de última generación

[ES]El conocimiento de la anatomía y de la cavidades encefálicas que alojan al líquido cefalorraquídeo esta ampliamente establecido, sin embargo las nuevas técnicas de diagnóstico por imagen nos aportan una mejor interpretación de la anatomía, más real y completa, y que mediante el uso de nuevas aplicaciones informáticas que nos complementan, conseguimos una extensión de la información con reconstrucciones en 3D y en 4D que superan las formas de representación habituales. Además, el empleo de nuevas secuencias de resonancia magnética nos incluyen la posibilidad de extraer datos funcionales, tanto cualitativos y cuantitativos, que nos caracterizan la circulación del líquido cefalorraquídeo a través de los espacios ventriculares y subaracnoideos. Para la realización de este trabajo hemos contado con la valoración de 478 pacientes procedentes del Hospital Virgen de la Concha de Zamora, del Hospital Clínico Universitario de Valladolid y del Hospital Universitario de Salamanca sobre los que se realizaron tanto diferentes procedimientos diagnósticos basados en ecografía trasfontanelar, tomografía computarizada y resonancia magnética. Como principal finalidad, se ha tratado de conseguir una revisión exhaustiva de la anatomía de las cavidades encefálicas y de las vías de distribución del líquido cefalorraquídeo, según las aportaciones que pueden ofrecer las técnicas de imagen de última generación, definiendo los aspectos morfológicos y analizando cómo estos procedimientos permiten conocer los diferentes mecanismos de formación del fluido cerebroespinal, su fisiología y especialmente el desarrollo de su dinámica. Hemos tratado de caracterizar el desplazamiento a través de los diferentes segmentos y conocer el tipo de movimiento que se realiza desde los puntos de formación hasta alcanzar las porciones más distales de los espacios subaracnoideos. Además se busca definir la semiología, los signos y los hallazgos radiológicos que podemos interpretar mediante estas técnicas de exploración y que son determinantes para el diagnóstico de las diferentes entidades patológicas que surgen como causa o como consecuencia de alteraciones en determinadas localizaciones