The Effects of Free Breathing on Cerebral Venous Flow: A Real-Time Phase Contrast MRI Study in Healthy Adults.

Quantifying the effects of free breathing on cerebral venous flow is crucial for understanding cerebral circulation mechanisms and clinical applications. Unlike conventional cine phase-contrast MRI sequences (CINE-PC), real-time phase-contrast MRI sequences (RT-PC) can provide a continuous beat-to-beat flow signal that makes it possible to quantify the effect of breathing on cerebral venous flow. In this study, we examined 28 healthy human participants, comprising of 14 males and 14 females. Blood flows in the right/left internal jugular veins in the extracranial plane and the superior sagittal sinus (SSS) and straight sinus in the intercranial plane were quantified using CINE-PC and RT-PC. The first objective of this study was to determine the accuracy of RT-PC in quantifying cerebral venous flow, relative to CINE-PC. The second, and main objective, was to quantify the effect of free breathing on cerebral venous flow, using a time-domain multiparameter analysis method. Our results showed that RT-PC can accurately quantify cerebral venous flow with a 2 × 2 mm2 spatial resolution and 75 ms/image time resolution. The mean flow rate, amplitude, stroke volume, and cardiac period of cerebral veins were significantly higher from the mid-end phase of expiration to the mid-end phase of inspiration. Breathing affected the mean flow rates in the jugular veins more than those in the SSS and straight sinus. Furthermore, the effects of free breathing on the flow rate of the left and right jugular veins were not synchronous. These new findings provide a useful reference for better understanding the mechanisms of cerebral circulation.

Assessment of neurofluid dynamics in relation to clinical improvement after tap-test: pilot study.

PURPOSE: Idiopathic Normal pressure hydrocephalus (iNPH) is an under-diagnosed in elderly patients but none of the diagnostic tests are currently sufficiently sensitive or specific. The objective of this study was to analyze the dynamics of neurofluids by PC-MRI in relation to clinical evolution as measured using the iNPH grading scale after tap-test. METHOD: We prospectively included patients with suspected iNPH. All these patients underwent PCMRI to assess craniospinal hemohydrodynamics with analysis of the stroke volume of the cephalospinal fluid (CSF) within the Sylvius' aqueduct, within the high cervical subarachnoid spaces and the arteriovenous stroke volume. By this means, we calculated a compliance index. Morphological analysis was carried out using the DESH score. The infusion test was measuring the resistance to CSF flow. We analysed all these parameters according to the clinical improvement of the patients. RESULTS: 23 patients were included. Compliance index assessed by PC-MRI was significantly higher in the group of patients with improvement > 10% (p = 0.015). CONCLUSIONS: Our study highlights the importance of investigating arteriovenous and CSF interactions in iNPH. This involves understanding the physiological and pathophysiological mechanisms related to the circulation of neurofluids. The analysis of the interactions of these neurofluids allows for a comprehensive understanding of the system.

Eye Tracking Post Processing to Detect Visual Artifacts and Quantify Visual Attention under Cognitive Task Activity during fMRI.

Determining visual attention during cognitive tasks using activation MRI remains challenging. This study aimed to develop a new eye-tracking (ET) post-processing platform to enhance data accuracy, validate the feasibility of subsequent ET-fMRI applications, and provide tool support. Sixteen volunteers aged 18 to 20 were exposed to a visual temporal paradigm with changing images of objects and faces in various locations while their eye movements were recorded using an MRI-compatible ET system. The results indicate that the accuracy of the data significantly improved after post-processing. Participants generally maintained their visual attention on the screen, with mean gaze positions ranging from 89.1% to 99.9%. In cognitive tasks, the gaze positions showed adherence to instructions, with means ranging from 46.2% to 50%. Temporal consistency assessments indicated prolonged visual tasks can lead to decreased attention during certain tasks. The proposed methodology effectively identified and quantified visual artifacts and losses, providing a precise measure of visual attention. This study offers a robust framework for future work integrating filtered eye-tracking data with fMRI analyses, supporting cognitive neuroscience research.

Familiarization with Mixed Reality for Individuals with Autism Spectrum Disorder: An Eye Tracking Study.

Mixed Reality (MR) technology is experiencing significant growth in the industrial and healthcare sectors. The headset HoloLens 2 displays virtual objects (in the form of holograms) in the user's environment in real-time. Individuals with Autism Spectrum Disorder (ASD) exhibit, according to the DSM-5, persistent deficits in communication and social interaction, as well as a different sensitivity compared to neurotypical (NT) individuals. This study aims to propose a method for familiarizing eleven individuals with severe ASD with the HoloLens 2 headset and the use of MR technology through a tutorial. The secondary objective is to obtain quantitative learning indicators in MR, such as execution speed and eye tracking (ET), by comparing individuals with ASD to neurotypical individuals. We observed that 81.81% of individuals with ASD successfully familiarized themselves with MR after several sessions. Furthermore, the visual activity of individuals with ASD did not differ from that of neurotypical individuals when they successfully familiarized themselves. This study thus offers new perspectives on skill acquisition indicators useful for supporting neurodevelopmental disorders. It contributes to a better understanding of the neural mechanisms underlying learning in MR for individuals with ASD.

Use of real-time phase-contrast MRI to quantify the effect of spontaneous breathing on the cerebral arteries.

Quantification of the effect of breathing on the cerebral circulation provides a better mechanistic understanding of the brain's circulatory system and is important in the early diagnosis of certain neurological diseases. However, conventional cine phase-contrast (CINE-PC) MRI cannot be used in this field of study because it only provides an average cardiac cycle flow curve reconstructed from multiple cardiac cycles. Unlike CINE-PC, phase-contrast echo-planar imaging (EPI-PC) can be used to quantify the blood flow rate in "real-time" and thus assess the effect of breathing on blood flow. Here, we first used post-processing software (developed in-house) to determine the feasibility of quantifying cerebral arterial blood flow with EPI-PC (relative to CINE-PC) in 16 participants. In a second step, we developed a new time-domain method for quantifying the intensity and the phase shift of the effects of breathing on the mean flow rate, stroke volume, cardiac period and amplitude of cerebral blood flow (in 10 participants). Our results showed that EPI-PC can quantify cerebral arterial blood flow rate with much the same degree of accuracy as CINE-PC but is more strongly influenced by differences in magnetic susceptibility. We found that breathing affected the mean flow rate, stroke volume and cardiac period of cerebral arterial blood flow.

Efficacy of benzodiazepines and related drugs in patients over 75 years of age and impact on cognition.

BACKGROUND: In France, despite the known risks, the use of benzodiazepines and related (BZD) is excessive, particularly in older populations. Over the age of 70, 1 person in 2 uses BZD on a long-term basis (more than 3 years), whereas it is recommended not to exceed 12 weeks. To compensate for the numerous undesirable effects and to maintain a positive benefit-risk balance, these treatments must be very effective and improve significantly the quality of life. AIMS: This study aims to determine whether the efficacy of BZD outweighs their adverse effects in older population. METHODS: In a population of 109 patients with cognitive impairment and hospitalized in Saint-Quentin (France), we recorded the use of BZD and medical background. Neuropsychological and geriatric assessments allowed cognitive and thymic evaluation. RESULTS: In our cohort of 109 patients, 50% of the subjects were BZD + and 78% were women. Patients in the BZD + group were no longer anxious but had poorer cognitive and executive performance than controls. DISCUSSION: Long-term treatment of anxiety in patients aged 75 and over with BZD appears to be effective. The deleterious impact of BZD on cognition has been demonstrated. CONCLUSIONS: These results tend to consider non-medicinal therapies as serious alternatives to BZD for treating anxiety in the older population.

Diffusion and Flow MR Imaging to Investigate Hydrocephalus Patients Before and After Endoscopic Third Ventriculostomy.

INTRODUCTION: In patients with noncommunicating hydrocephalus, dilation of the ventricles stresses white matter fibers and alters the cerebral blood flow (CBF) and cerebrospinal fluid (CSF) dynamics. The purpose of this work was to investigate, non-invasively, how endoscopic third ventriculostomy (ETV) impacts white matter, CSF oscillations, and CBF. METHODS: Eleven patients presenting with chronic headaches and noncommunicating hydrocephalus due to aqueductal stenosis were treated by ETV. Phase Contrast-MRI (PCMRI) and Diffusion Tensor Imaging (DTI) were performed before and after surgery to evaluate CSF and CBF as well as white matter stresses in the Corpus Callosum (CC) and Corona Radiata (CR). ETV success was confirmed by quantification of the CSF oscillations through the aperture in the third ventricle. RESULTS: All patients improved after surgery. CSF stroke volume was five times greater than normal ventricular stroke volume. Decrease in cervical CSF oscillations and increase in CBF were observed after ETV. In CR, fiber anisotropy decreased, while water diffusion increased. In CC, anisotropy did not vary, while water diffusion also increased. CONCLUSION: Even if static ICP typically do not increase, CSF and blood flow are impacted. PCMRI and DTI can provide useful information to help neurosurgeons select patients with good chance to improve after ETV.

Compliance of the cerebrospinal space: comparison of three methods.

BACKGROUND: Cerebrospinal compliance describes the ability of the cerebrospinal space to buffer changes in volume. Diminished compliance is associated with increased risk of potentially threatening increases in intracranial pressure (ICP) when changes in cerebrospinal volume occur. However, despite various methods of estimation proposed so far, compliance is seldom used in clinical practice. This study aimed to compare three measures of cerebrospinal compliance. METHODS: ICP recordings from 36 normal-pressure hydrocephalus patients who underwent infusion tests with parallel recording of transcranial Doppler blood flow velocity were retrospectively analysed. Three methods were used to calculate compliance estimates during changes in the mean ICP induced by infusion of fluid into the cerebrospinal fluid space: (a) based on Marmarou's model of cerebrospinal fluid dynamics (CCSF), (b) based on the evaluation of changes in cerebral arterial blood volume (CCaBV), and (c) based on the amplitudes of peaks P1 and P2 of ICP pulse waveform (CP1/P2). RESULTS: Increase in ICP caused a significant decrease in all compliance estimates (p < 0.0001). Time courses of compliance estimators were strongly positively correlated with each other (group-averaged Spearman correlation coefficients: 0.94 [0.88-0.97] for CCSF vs. CCaBV, 0.77 [0.63-0.91] for CCSF vs. CP1/P2, and 0.68 [0.48-0.91] for CCaBV vs. CP1/P2). CONCLUSIONS: Indirect methods, CCaBV and CP1/P2, allow for the assessment of relative changes in cerebrospinal compliance and produce results exhibiting good correlation with the direct method of volumetric manipulation. This opens the possibility of monitoring relative changes in compliance continuously.

Early assessment of lateralization and sex influences on the microstructure of the white matter corticospinal tract in healthy term neonates.

We assessed the sex and the lateralization differences in the corticospinal tract (CST) during the early postnatal period. Twenty-five healthy term neonates (13 girls, aged 39.2 ± 1.2 weeks, and 12 boys aged 38.6 ± 3.0 weeks) underwent Diffusion Tensor Imaging (DTI). Fiber tracking was performed to extract bilaterally the CST pathways and to quantify the parallel (E1 ) and perpendicular (E23 ) diffusions, the apparent diffusion coefficient (ADC), and fractional anisotropy (FA). The measurements were performed on the entire CST fibers and on four segments: base of the pons (CST-Po), cerebral peduncles (CST-CP), posterior limb of the internal capsule (CST-PLIC), and corona-radiata (CST-CR). Significantly higher E1 , lower E23, and higher FA in the right compared to the left were noted in the CST-PLIC of the girls. Significantly lower E23 and lower ADC with higher FA in the right compared to left were observed in the CST-CP of the boys. Moreover, the CST-PLIC of the boys had significantly higher E1 in the right compared to the left. There was a significant increase in left CST E1 of boys when compared with girls. Girls had a significantly lower E1 , lower E23 and, lower ADC in the left CST-CP compared with boys. In addition, girls had a significantly lower E23 and higher FA in the right CST-PLIC compared with boys. Sex differences and lateralization in structure-based segments of the CST were found in healthy term infants during early postnatal period. These findings are vital to understanding motor development of healthy term born neonates to better interpret newborn infants with abnormal neurodevelopment.

Total cerebrovascular blood flow and whole brain perfusion in children sedated using propofol with or without ketamine at induction: An investigation with 2D-Cine PC and ASL.

BACKGROUND: Multiple sedation regimes may be used to facilitate pediatric MRI scans. These regimes might affect cerebral blood flow and hemodynamics to varying degrees, particularly in children who may be vulnerable to anesthetic side effects. PURPOSE: To compare the effects of propofol monosedation solely (Pm group) vs. a combination of propofol and ketamine (KP group) on brain hemodynamics and perfusion. STUDY TYPE: Prospective double-blind randomized trial. FIELD STRENGTH/SEQUENCES: 1.5T and 3T. 2D-Cine phase contrast (2D-Cine PC) and pseudocontinuous arterial spin labeling (ASL). POPULATION: Children aged from 3 months to 10 years referred for MRI with deep sedation were randomized into either the KP or the Pm group. Perfusion images were acquired with ASL followed by single-slice 2D-Cine PC acquired between the cervical vertebra C2 and C3. ASSESSMENT: Average whole-brain perfusion (WBP ml.min-1 .100 ml-1 ) was extracted from the ASL perfusion maps and total cerebrovascular blood flow (CVF) was quantified by bilaterally summing the flow in the vertebral and the internal carotid arteries. The CVF values were converted to units of ml.min-1 .100 g-1 to calculate the tissue CVF100g (ml.min-1 .100 g-1 ). Images were assessed by a neuroradiologist and data from n = 81 (ASL) and n = 55 (PC) cases with no apparent pathology were entered into the analysis. STATISTICAL TESTS: Multivariate analysis of covariance was performed to compare drug sedation effects on WBP, CVF, and CVF100g . RESULTS: No significant difference in arterial flow was observed (P = 0.57), but the KP group showed significantly higher WBP than the Pm group, covarying for scanner and age (P = 0.003). A correlation analysis showed a significant positive correlation between mean WBP (ml.min-1 .100 g-1 ) and mean CVF100g . DATA CONCLUSION: The KP group showed higher perfusion but no significant difference in vascular flow compared with the Pm group. WBP and CVF100g correlated significantly, but ASL appeared to have more susceptibility to perfusion differences arising from the different sedation regimes. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2019;50:1433-1440.

Quantification of blood flow in the superior ophthalmic vein using phase contrast magnetic resonance imaging.

Phase contrast magnetic resonance imaging (PC MRI), a validated, non-invasive technique for measuring intracranial blood and cerebrospinal flows, has been recently applied to studies of blood flow of the ophthalmic artery (OA). This study evaluated PC-MRI's ability to quantify blood flow in the superior ophthalmic vein (SOV). We analyzed with 3 T PC MRI the blood flow in the SOV in 11 healthy subjects and, for comparison purpose, in the OA. Segmentation software was used to analyze the PC images and quantify the variation in blood flow over the cardiac cycle in each of the vessels. The anatomy of the orbital veins was also assessed. We were able to measure the blood flow in 19 SOV; the mean ±â€¯standard deviation (SD) SOV flow was 9.13 ±â€¯7.10 mL/min with a mean ±â€¯SD variation of flow during cardiac cycle of 8.45 ±â€¯4.90 mL/min. The mean ±â€¯SD flow in the OA was 12.83 ±â€¯8.36 mL/min. The SOV was constantly present, with a mean cross-sectional area of 2.43 mm2. A medium and an inferior ophthalmic veins were found in 5 and 3 orbits, respectively. In conclusion, PC MRI is able to measure SOV as well as OA flows. To the best of our knowledge, the present study is the first to provide quantitative SOV blood flow values using PC MRI. Investigations of hydrocephalus, intracranial hypertension and even glaucoma might be facilitated by the application of this quantitative imaging modality.

Influence of principal component analysis acceleration factor on velocity measurement in 2D and 4D PC-MRI.

OBJECTIVE: The objective of the study was to determine how to optimize 2D and 4D phase-contrast magnetic resonance imaging (PC-MRI) acquisitions to acquire flow velocities in millimetric vessels. In particular, we search for the best compromise between acquisition time and accuracy and assess the influence of the principal component analysis (PCA). MATERIALS AND METHODS: 2D and 4D PC-MRI measurements are conducted within two in vitro vessel phantoms: a Y-bifurcation phantom, the branches of which range from 2 to 5 mm in diameter, and a physiological subject-specific phantom of the carotid bifurcation. The same sequences are applied in vivo in carotid vasculature. RESULTS: For a vessel oriented in the axial direction, both 2D and axial 4D PC-MRI provided accuracy measurements regardless of the k-t PCA factor, while the acquisition time is reduced by a factor 6 for k-t PCA maximum value. The in vivo measurements show that the proposed sequences are adequate to acquire 2D and 4D velocity fields in millimetric vessels and with clinically realistic time durations. CONCLUSION: The study shows the feasibility of conducting fast, high-resolution PC-MRI flow measurements in millimetric vessels and that it is worth maximizing the k-t PCA factor to reduce the acquisition time in the case of 2D and 4D axial acquisitions.

Anthropomorphic Model of Intrathecal Cerebrospinal Fluid Dynamics Within the Spinal Subarachnoid Space: Spinal Cord Nerve Roots Increase Steady-Streaming.

Cerebrospinal fluid (CSF) dynamics are thought to play a vital role in central nervous system (CNS) physiology. The objective of this study was to investigate the impact of spinal cord (SC) nerve roots (NR) on CSF dynamics. A subject-specific computational fluid dynamics (CFD) model of the complete spinal subarachnoid space (SSS) with and without anatomically realistic NR and nonuniform moving dura wall deformation was constructed. This CFD model allowed detailed investigation of the impact of NR on CSF velocities that is not possible in vivo using magnetic resonance imaging (MRI) or other noninvasive imaging methods. Results showed that NR altered CSF dynamics in terms of velocity field, steady-streaming, and vortical structures. Vortices occurred in the cervical spine around NR during CSF flow reversal. The magnitude of steady-streaming CSF flow increased with NR, in particular within the cervical spine. This increase was located axially upstream and downstream of NR due to the interface of adjacent vortices that formed around NR.

Numerical Cerebrospinal System Modeling in Fluid-Structure Interaction.

OBJECTIVE: Cerebrospinal fluid (CSF) stroke volume in the aqueduct is widely used to evaluate CSF dynamics disorders. In a healthy population, aqueduct stroke volume represents around 10% of the spinal stroke volume while intracranial subarachnoid space stroke volume represents 90%. The amplitude of the CSF oscillations through the different compartments of the cerebrospinal system is a function of the geometry and the compliances of each compartment, but we suspect that it could also be impacted be the cardiac cycle frequency. To study this CSF distribution, we have developed a numerical model of the cerebrospinal system taking into account cerebral ventricles, intracranial subarachnoid spaces, spinal canal and brain tissue in fluid-structure interactions. MATERIALS AND METHODS: A numerical fluid-structure interaction model is implemented using a finite-element method library to model the cerebrospinal system and its interaction with the brain based on fluid mechanics equations and linear elasticity equations coupled in a monolithic formulation. The model geometry, simplified in a first approach, is designed in accordance with realistic volume ratios of the different compartments: a thin tube is used to mimic the high flow resistance of the aqueduct. CSF velocity and pressure and brain displacements are obtained as simulation results, and CSF flow and stroke volume are calculated from these results. RESULTS: Simulation results show a significant variability of aqueduct stroke volume and intracranial subarachnoid space stroke volume in the physiological range of cardiac frequencies. CONCLUSIONS: Fluid-structure interactions are numerous in the cerebrospinal system and difficult to understand in the rigid skull. The presented model highlights significant variations of stroke volumes under cardiac frequency variations only.

Mathematical Modelling of CSF Pulsatile Flow in Aqueduct Cerebri.

OBJECTIVE: The phase-contrast MRI technique permits the non-invasive assessment of CSF movements in cerebrospinal fluid cavities of the central nervous system. Of particular interest is pulsatile cerebrospinal fluid (CSF) flow through the aqueduct cerebri. It is allegedly increased in hydrocephalus, having potential diagnostic value, although not all scientific reports contain unequivocally positive conclusions. METHODS: For the mathematical simulation of CSF flow, we used a computational model of cerebrospinal blood/fluid circulation designed by a former student as his PhD project. With this model, cerebral blood flow and CSF may be simulated in various vessels using a system of non-linear differential equations as time-varying signals. RESULTS: The amplitude of CSF flow seems to be positively related to the amplitude of pulse waveforms of intracranial pressure (ICP) in situations where mean ICP increases, such as during simulated infusion tests and following step increases of resistance to CSF outflow. An additional positive association between the pulse amplitude of ICP and CSF flow can be seen during simulated increases in the amplitude of arterial pulses (without changes in mean arterial pressure, MAP). The opposite effect can be observed during step increases in the resistance of the aqueduct cerebri and with decreasing elasticity of the system, where the CSF flow amplitude and the ICP pulse amplitude are related inversely. Vasodilatation caused by both gradual decreases in MAP and by increases in PaCO2 provokes an elevation in the observed amplitude of pulsatile CSF flow. CONCLUSIONS: Preliminary results indicate that the pulsations of CSF flow may carry information about both CSF-circulatory and cerebral vasogenic components. In most cases, the pulsations of CSF flow are positively related to the pulse amplitudes of both arterial pressure and ICP and to a degree of cerebrovascular dilatation.

Cerebrospinal Fluid and Cerebral Blood Flows in Idiopathic Intracranial Hypertension.

OBJECTIVES: Cerebrospinal fluid (CSF) and blood flows have a strong relationship during a cardiac cycle. Idiopathic intracranial hypertension (IIH) is a pathology that seems to present hemodynamic and hydrodynamic disturbance. The aim of this study was to establish CSF and blood interaction in IIH. MATERIAL AND METHODS: We retrospectively studied cerebral hydrodynamic and hemodynamic flows by phase-contrast MRI (PCMRI) in 13 IIH subjects (according Dandy's criteria) and 16 controls. We analyzed arterial peak flow, pulsatility index, and resistive index in arterial and venous compartments (PFart, PIart, RIart, PFvein, PIvein, RIvein) and measured arteriovenous and CSF peak flow and stroke volume (PFav, SVVASC, PFCSF, SVCSF). RESULTS: We found no significant difference between IIH and control groups in arterial and venous parameters. Arteriovenous flow analysis showed higher PFav and SVVASC in the IIH group than in the control group (respectively 369 ± 27 mL/min and 286 ± 47 mL/min, p = 0.02; and 1085 ± 265 µL/cardiac cycle and 801 ± 226 µL/cardiac cycle, p = 0.007). PFCSF and SVCSF were higher in the IIH group than in the control group (respectively 206 ± 50 mL/min and 126.6 ± 24.8 mL/min, p = 0.04; and 570 ± 190 µL/cardiac cycle and 430 ± 100 µL/cardiac cycle, p = 0.0007). CONCLUSION: Although no significant change was found in arterial and venous flows, we showed that a small phase shift of venous outflow might cause an increase in the arteriovenous pulsatility and an increasing brain expansion during the cardiac cycle. This arteriovenous flow increase would result in an increase of CSF flushing through the foramen magnum and an increased ICP.

Ventriculomegaly in the Elderly: Who Needs a Shunt? A MRI Study on 90 Patients.

OBJECTIVE: In the case of ventriculomegaly in the elderly, it is often difficult to differentiate between communicating chronic hydrocephalus (CCH) and brain atrophy. The aim of this study is to describe the MRI criteria of CCH, defined by a symptomatic patient with ventriculomegaly and that improved after shunt placement. MATERIALS AND METHODS: Magnetic resonance imaging was prospectively evaluated in 90 patients with ventriculomegaly. Patients were classified into three groups: patients without clinical signs of CCH (control, n = 47), patients with CCH treated by shunt placement with clinical improvement (responders, n = 36), and patients with CCH treated using a shunt without clinical improvement (nonresponders, n = 7). MRI parameters of the two groups of interest (responders vs. controls) were compared. RESULTS: Compared with controls, Evans' index (p = 0.029), ventricular area (p < 0.01), and volume (p = 0.0001) were higher in the responders. In this group, the callosal angle was smaller (p ≤ 0.0001) and the aqueductal stroke volume (SVa) of CSF was higher (p ≤ 0.0001) than in controls. On the ROC curves, the optimal cut-off values for differentiating between responders and controls were a ventricular area >33.5 cm2, a callosal angle <90.8° and a SVa > 136.5 µL/R-R. In multivariate analysis, responders remained associated with SVa and callosal angle, with a c-statistic of 0.90 (95%CI, 0.83-0.98). CONCLUSION: On suspicion of CCH, a large ventricular area, a small callosal angle, and an increased aqueductal stroke volume are important MRI arguments that can be associated with the clinical evaluation and dynamic testing of CSF to confirm the indication for a shunt.

Heart rate and respiration influence on macroscopic blood and CSF flows.

Background Changes in blood volume in the intracranial arteries and the resulting oscillations of brain parenchyma have been presumed as main initiating factors of cerebrospinal fluid (CSF) pulsations. However, respiration has been recently supposed to influence CSF dynamics via thoracic pressure changes. Purpose To measure blood and CSF cervical flow and quantify the contribution of cardiac and respiratory cycles on the subsequent signal evolution. Material and Methods Sixteen volunteers were enrolled. All participant underwent two-dimensional fast field echo echo planar imaging (FFE-EPI). Regions of interest were placed on internal carotids, jugular veins, and rachidian canal to extract temporal profiles. Spectral analysis was performed to extract respiratory and cardiac frequencies. The contribution of respiration and cardiac activity was assessed to signal evolution by applying a multiple linear model. Results Mean respiratory frequency was 14.6 ± 3.9 cycles per min and mean heart rate was 66.8 ± 9 cycles per min. Cardiac contribution was higher than breathing for internal carotids, explaining 74.68% and 10.27% of the signal variance, respectively. For the jugular veins, respiratory component was higher than the cardiac one contributing 44.28% and 6.53% of the signal variance, respectively. For CSF, breathing and cardiac component contributed less than half of signal variance (12.61% and 23.23%, respectively). Conclusion Respiration and cardiac activity both influence fluid flow at the cervical level. Arterial inflow is driven by the cardiac pool whereas venous blood aspiration seems more due to thoracic pressure changes. CSF dynamics acts as a buffer between these two blood compartments.

Phase-shift between arterial flow and ICP pulse during infusion test.

BACKGROUND: The dynamic relationship between pulse waveform of intracranial pressure (ICP) and transcranial Doppler (TCD) cerebral blood flow velocity (CBFV) may contain information about cerebrospinal compliance. This study investigated the possibility by focusing on the phase shift between fundamental harmonics of CBFV and ICP. METHODS: Thirty-seven normal pressure hydrocephalus patients (20 men, mean age 58) underwent the cerebrospinal fluid (CSF) infusion tests. The infusion was performed via pre-implanted Ommaya reservoir. The TCD FV was recorded in the middle cerebral artery. Resulting continuous ICP and pressure-volume (PV) signals were analyzed by ICM+ software. RESULTS: In initial stage of the CSF infusion, the phase shift was negative (median value = -11°, range = +60 to -117). There was significant inverse association of phase shift with brain elasticity (R = -0.51; p = 0.0009). In all tests, phase shift consistently decreased during gradual elevation of ICP (p = 0.00001). Magnitude of decrease in phase shift was inversely related to the peak-to-peak amplitude of ICP pulse waveform at a baseline (R = -0.51; p = 0.001). CONCLUSIONS: Phase shift between fundamental harmonics of ICP and TCD waveforms decreases during elevation of ICP. This is caused by an increase of time delay between systolic peak of flow velocity wave and ICP pulse.

Effect of surgery on periventricular white matter in normal pressure hydrocephalus patients: comparison of two methods of DTI analysis.

BACKGROUND: Diffusion tensor imaging (DTI) is a useful tool for assessing changes that occur in microstructures. We have developed a novel method for region of interest (ROI) delineation in the assessment of DTI parameters in patients with normal pressure hydrocephalus (NPH). PURPOSE: To compare the standard method and our novel method in an evaluation of the impact of surgery on periventricular white matter in patients with NPH. MATERIAL AND METHODS: Ten patients with NPH underwent 3T magnetic resonance imaging (MRI; including 12-direction DTI sequences) before and after surgery. We recorded diffusion parameters (λi, the fractional anisotropy [FA], the apparent diffusion coefficient, and Dr) in the internal capsule (IC) and the body of the corpus callosum (BCC). Using the standard delineation technique, regions of interest (ROIs) were positioned according to anatomical and functional considerations and then filled with several sub-ROIs. The ROIs delineated with our novel technique (extracted as the six sub-ROIs with the lowest standard deviation for the FA) were arranged in two rows (medial and lateral), from the ventricle to the brain surface. RESULTS: The within-ROI homogeneity was higher with the novel method than with the conventional method (P<10(-4)). When the conventional delineation method was applied to the IC data, only λ2 was found to be significantly greater after surgery; in contrast, application of our novel method evidenced a significant decrease in FA and λ1 and a significant increase in λ2 (P<0.05). Both before and after surgery, the FA in the medial row of ROIs was greater than the FA in the lateral row (P<0.01). In the BCC, only λ2 and Dr varied significantly (when evaluated with the novel method). CONCLUSION: Our results show that use of a novel method of DTI data analysis may be more sensitive to local changes induced by surgical procedures. Furthermore, this novel method was able to detect the transmantle pressure gradient related to the regional stress distribution.