Roger Bouzerar

Value of phase contrast magnetic resonance imaging for investigation of cerebral hydrodynamics

OBJECTIVE Phase Contrast Magnetic Resonance Imaging (PCMRI) is a noninvasive technique that can be used to quantify variations of flow during the cardiac cycle. PCMRI allows investigations of blood flow dynamics in the main arteries and veins of the brain but also the dynamics of cerebrospinal fluid. These cerebral flow investigations provide a description of the regulation mechanisms of intracranial pressure during the cardiac cycle. The objective of this paper is to describe the contribution of this technique in diseases related to disorders of cerebral hydrodynamics in the light of 5 clinical cases. METHOD Flow measurements were performed using PCMRI sequences on a 1.5 Tesla MR imager in 4 patients with symptomatic ventricular dilation and 1 patient with a syringomyelic cavity. RESULTS Flow quantification in these 5 patients, representative of the diseases mainly concerned by cerebral hydrodynamics, is useful to guide the indication for ventricular shunting in patients with hydrocephalus, to demonstrate obstruction of the cerebral aqueduct, to demonstrate recirculation of ventricular CSF after ventriculostomy and to characterize the dynamic features of CSF inside a spinal cavity. CONCLUSION PCMRI, now available to neurosurgeons, is complementary to morphological MR and provides quantitative information on cerebral hydrodynamics. This information is mainly used to confirm alteration of CSF flow in the cerebral and spinal compartments. PCMRI is also a functional tool to better understand the pathophysiology of hydrocephalus and syringomyelia.

Hepatic vascular flow measurements by phase contrast MRI and doppler echography: A comparative and reproducibility study

To directly compare and study the variability of parameters related to hepatic blood flow measurements using 3 T phase‐contrast magnetic resonance imaging (PC‐MRI) and Doppler ultrasound (US).

Relationship between cerebrospinal fluid flow, ventricles morphology, and DTI properties in internal capsules: differences between Alzheimer's disease and normal-pressure hydrocephalus.

Background Normal-pressure hydrocephalus (NPH) and Alzheimers disease (AD) have some similar clinical features and both involve white matter and cerebrospinal fluid (CSF) disorders. Purpose To compare putative relationships between ventricular morphology, CSF flow, and white matter diffusion in AD and NPH. Material and Methods Thirty patients (18 with AD and 12 with suspected NPH) were included in the study. All patients underwent a 3-Tesla MRI scan, which included phase-contrast MRI of the aqueduct (to assess the aqueductal CSF stroke volume) and a DTI session (to calculate the fractional anisotropy [FA] and apparent diffusion coefficient [ADC]) in the internal capsules). Results FA was correlated with ventricular volume in the suspected NPH population (P < 0.001; rs = 0.88), whereas the ADC was highly correlated with the aqueductal CSF stroke volume in AD (P < 0.001; rs = 0.79). Conclusion Although AD and NPH both involve CSF disorders, the two diseases do not have the same impact on the internal capsules. The magnitude of the ADC is related to the aqueductal CSF stroke volume in AD, whereas FA is related to ventricular volume in NPH.

Measurement of choroid plexus perfusion using dynamic susceptibility MR imaging: capillary permeability and age-related changes.

IntroductionThe cerebrospinal fluid (CSF) plays a major role in the physiology of the central nervous system. The continuous turnover of CSF is mainly attributed to the highly vascularized choroid plexus (CP) located in the cerebral ventricles which represent a complex interface between blood and CSF. We propose a method for evaluating CP functionality in vivo using perfusion MR imaging and establish the age-related changes of associated parameters.MethodsFifteen patients with small intracranial tumors were retrospectively studied. MR Imaging was performed on a 3T MR Scanner. Gradient-echo echo planar images were acquired after bolus injection of gadolinium-based contrast agent (CA). The software developed used the combined T1- and T2-effects. The decomposition of the relaxivity signals enables the calculation of the CP capillary permeability (K2). The relative cerebral blood volume (rCBV), mean transit time (MTT), and signal slope decrease (SSD) were also calculated.ResultsThe mean permeability K2 of the extracted CP was 0.033+/−0.18 s-1. K2 and SSD significantly decreased with subject’s age whereas MTT significantly increased with subject’s age. No significant correlation was found for age-related changes in rCBV and rCBF.ConclusionThe decrease in CP permeability is in line with the age-related changes in CSF secretion observed in animals. The MTT increase indicates significant structural changes corroborated by microscopy studies in animals or humans. Overall, DSC MR-perfusion enables an in vivo evaluation of the hemodynamic state of CP. Clinical applications such as neurodegenerative diseases could be considered thanks to specific functional studies of CP.

A Phase-Contrast MRI Study of Acute and Chronic Hydrodynamic Alterations after Hydrocephalus Induced by Subarachnoid Hemorrhage

To determine acute intracranial hydrodynamic changes after subarachnoid hemorrhage (SAH) via phase‐contrast MRI (PC‐MRI) analysis of the CSF stroke volume in the aqueduct (SVaq) and the foramen magnum (SVfm).

Dynamics of hydrocephalus: a physical approach

As brain ventricles lose their ability to regulate the cerebrospinal fluid (CSF) pressure, serious brain conditions collectively named hydrocephalus can appear. By modelling ventricular dynamics with the laws of physics, dynamical instabilities are evidenced, caused by either CSF transport dysregulations or abnormal properties of the elasticity of the ependyma. We show that these instabilities would lead, in most cases, to dilation of the ventricles, establishing a close connection to hydrocephalus, or in some other cases to a ventricular contraction as observed in the slit ventricle syndrome. Signs seem to indicate the possibility of phase transitions occurring as a result of these instabilities, which might have important clinical consequences, such as the inability to recover a healthy state. Even so, our dynamical approach could allow the development of a unified view of these complex intracranial conditions along with a classification that might be clinically relevant.

Insights into cerebrospinal fluid and cerebral blood flows in infants and young children

This study investigates the craniospinal flows of blood and cerebrospinal fluid using phase-contrast magnetic resonance imaging (MRI) on 23 control neonates and infants (5 d-68 mo old). Mean arterial cerebral blood flow increased with age of infant from 180 mL/min after birth to 1330 mL/min around 6 years of age. This corresponds to 51 mL/min/100 g and 95 mL/min/100 g, respectively. Cervical cerebrospinal fluid stroke volume increased from 38 × 10–3 mL to 752 × 10–3 mL per cardiac cycle. After arterial systolic blood inflow, we observed a delay of the venous outflow that was always preceded by cerebrospinal fluid flushing out through the spinal canal. These results highlighted the importance of compliance of the spinal compartment and the interaction of blood and cerebrospinal fluid dynamics. The capacity of the spinal compartment to receive intracranial cerebrospinal fluid in presence of fontanels was demonstrated. We provide reference values to understand the physiology of cerebrospinal fluid and cerebral blood.

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.

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.

Physical Phantom of Craniospinal Hydrodynamics

INTRODUCTION Inside the craniospinal system, blood, and cerebrospinal fluid (CSF) interactions occurring through volume exchanges are still not well understood. We built a physical model of this global hydrodynamic system. The main objective was to study, in controlled conditions, CSF-blood interactions to better understand the phenomenon underlying pathogenesis of hydrocephalus. MATERIALS AND METHODS A structure representing the cranium is connected to the spinal channel. The cranium is divided into compartments mimicking anatomical regions such as ventricles or aqueduct cerebri. Resistive and compliant characteristics of blood and CSF compartments can be assessed or measured using pressure and flow sensors incorporated in the model. An arterial blood flow input is generated by a programmable pump. Flows and pressures inside the system are simultaneously recorded. RESULTS Preliminary results show that the model can mimic venous and CSF flows in response to arterial pressure input. Pulse waveforms and volume flows were measured and confirmed that they partially replicated the data previously obtained with phase-contrast magnetic resonance imaging. The phantom shows that CSF oscillations directly result from arteriovenous flow, and intracranial pressure measurements show that the model obeys an exponential relationship between pressure and intracranial volume expansion. CONCLUSION The phantom will be useful to investigate the hydrodynamic hypotheses underlying development of hydrocephalus.