Quantitative Evaluation of Normal Aqueductal Cerebrospinal Fluid Flow Using Phase-Contrast Cine MRI According to Age and Sex

Clinical magnetic resonance imaging evaluation of glymphatic function

The glymphatic system is a system of specialized perivascular spaces in the brain that facilitates removal of toxic waste solutes from the brain. Evaluation of glymphatic system function by means of magnetic resonance imaging (MRI) has thus far been largely focused on rodents because of the limitations of intrathecal delivery of gadolinium-based contrast agents to humans. This review discusses MRI methods that can be employed clinically for glymphatic-related measurements intended for early diagnosis, prevention, and the treatment of various neurological conditions. Although glymphatic system-based MRI research is in its early stages, recent studies have identified promising noninvasive MRI markers associated with glymphatic system alterations in neurological diseases. However, further optimization in data acquisition, validation, and modeling are needed to investigate the glymphatic system within the clinical setting.

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.

CSF and venous blood flow from childhood to adulthood studied by real-time phase-contrast MRI

PURPOSE

In vivo measurements of CSF and venous flow using real-time phase-contrast (RT-PC) MRI facilitate new insights into the dynamics and physiology of both fluid systems. In clinical practice, however, use of RT-PC MRI is still limited. Because many forms of hydrocephalus manifest in infancy and childhood, it is a prerequisite to investigate normal flow parameters during this period to assess pathologies of CSF circulation. This study aims to establish reference values of CSF and venous flow in healthy subjects using RT-PC MRI and to determine their age dependency.

METHODS

RT-PC MRI was performed in 44 healthy volunteers (20 females, age 5-40 years). CSF flow was quantified at the aqueduct (Aqd), cervical (C3) and lumbar (L3) spinal levels. Venous flow measurements comprised epidural veins, internal jugular veins and inferior vena cava. Parameters analyzed were peak velocity, net flow, pulsatility, and area of region of interest (ROI).

STATISTICAL TESTS

linear regression, student's t-test and analysis of variance (ANOVA).

RESULTS

In adults volunteers, no significant changes in flow parameters were observed. In contrast, pediatric subjects exhibited a significant age-dependent decrease of CSF net flow and pulsatility in Aqd, C3 and L3. Several venous flow parameters decreased significantly over age at C3 and changed more variably at L3.

CONCLUSION

Flow parameters varies depending on anatomical location and age. We established changes of brain and spinal fluid dynamics over an age range from 5-40 years. The application of RT-PC MRI in clinical care may improve our understanding of CSF flow pathology in individual patients.

Pulsatility analysis of the circle of Willis

Purpose

To evaluate the phenomenological significance of cerebral blood pulsatility imaging in aging research.

Methods

N = 38 subjects from 20 to 72 years of age (24 females) were imaged with ultrafast MRI with a sampling rate of 100 ms and simultaneous acquisition of pulse oximetry data. Of these, 28 subjects had acceptable MRI and pulse data, with 16 subjects between 20 and 28 years of age, and 12 subjects between 61 and 72 years of age. Pulse amplitude in the circle of Willis was assessed with the recently developed method of analytic phase projection to extract blood volume waveforms.

Results

Arteries in the circle of Willis showed pulsatility in the MRI for both the young and old age groups. Pulse amplitude in the circle of Willis significantly increased with age (p = 0.01) but was independent of gender, heart rate, and head motion during MRI.

Discussion and conclusion

Increased pulse wave amplitude in the circle of Willis in the elderly suggests a phenomenological significance of cerebral blood pulsatility imaging in aging research. The physiologic origin of increased pulse amplitude (increased pulse pressure vs. change in arterial morphology vs. re-shaping of pulse waveforms caused by the heart, and possible interaction with cerebrospinal fluid pulsatility) requires further investigation.

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.

Lumbar cerebrospinal fluid-to-brain extracellular fluid surrogacy is context-specific: insights from LeiCNS-PK3.0 simulations

Predicting brain pharmacokinetics is critical for central nervous system (CNS) drug development yet difficult due to ethical restrictions of human brain sampling. CNS pharmacokinetic (PK) profiles are often altered in CNS diseases due to disease-specific pathophysiology. We previously published a comprehensive CNS physiologically-based PK (PBPK) model that predicted the PK profiles of small drugs at brain and cerebrospinal fluid compartments. Here, we improved this model with brain non-specific binding and pH effect on drug ionization and passive transport. We refer to this improved model as Leiden CNS PBPK predictor V3.0 (LeiCNS-PK3.0). LeiCNS-PK3.0 predicted the unbound drug concentrations of brain ECF and CSF compartments in rats and humans with less than two-fold error. We then applied LeiCNS-PK3.0 to study the effect of altered cerebrospinal fluid (CSF) dynamics, CSF volume and flow, on brain extracellular fluid (ECF) pharmacokinetics. The effect of altered CSF dynamics was simulated using LeiCNS-PK3.0 for six drugs and the resulting drug exposure at brain ECF and lumbar CSF were compared. Simulation results showed that altered CSF dynamics changed the CSF PK profiles, but not the brain ECF profiles, irrespective of the drug's physicochemical properties. Our analysis supports the notion that lumbar CSF drug concentration is not an accurate surrogate of brain ECF, particularly in CNS diseases. Systems approaches account for multiple levels of CNS complexity and are better suited to predict brain PK.

Hemodynamic Changes in the Sigmoid Sinus of Patients With Pulsatile Tinnitus Induced by Sigmoid Sinus Wall Anomalies

OBJECTIVE

This study is to investigate the hemodynamic changes of pulsatile tinnitus (PT) patients induced by sigmoid sinus wall anomalies (SSWA).

STUDY DESIGN

Prospective study.

SETTING

Tertiary referral university hospital.

PATIENTS

Fifteen unilateral PT patients with SSWA identified on computed tomography images and surgery and 15 age-, sex-, and body mass index-matched healthy volunteers underwent velocity-encoded, cine magnetic resonance imaging.

INTERVENTION

Hemodynamic data in sigmoid sinus were obtained from velocity-encoded, cine magnetic resonance imaging, and compared between PT patients and controls.

MAIN OUTCOME MEASURES

Heart rate was recorded. Cross-sectional area (CSA), peak positive velocity (PPV), average positive flow volume per beat (APFV/beat), average flow volume per beat (AFV/beat), peak negative velocity (PNV), and average negative flow volume per beat (ANFV/beat) were measured. Average flow volume per minute (AFV/min), average positive flow volume per minute (APFV/min), average negative flow volume per minute (ANFV/min), average positive velocity (APV), average negative velocity (ANV), and regurgitation fraction (RF) were calculated.

RESULTS

APV at PT side of patients was 13.4 ± 3.3 cm/s, which was significantly slower than that at corresponding side of controls (15.8 ± 2.6 cm/s). PNV and RF at PT side of patients were 21.0 ± 15.4 cm/s and 2.4% respectively, which were significantly higher than those values at corresponding side of controls (both of them were 0). HR, CSA, PPV, APFV/beat, APFV/min, AFV/beat, AFV/min, ANV, ANFV/beat, and ANFV/min were 69.8 ± 9.4 beat/min, 48.4 ± 17 mm, 31.4 ± 5.9 cm/s, 5.4 ± 1.8 ml/beat, 373.9 ± 117.7 ml/min, 5.1 ± 2.0 ml/beat, 352.0 ± 134.6 ml/min, 2 (0-4.9) cm/s, 1 (0-2.7) ml/beat, and 4.1 (0-141.3) ml/min at PT side of patients, and 67.4 ± 7.8 beat/min, 38.2 ± 18 mm, 29.9 ± 3.9 cm/s, 5.3 ± 2.0 ml/beat, 350.3 ± 125.3 ml/min, 5.1 ± 1.9 ml/beat, 340.5 ± 117.9 ml/min, 0 (0-2.1) cm/s, 0 (0-0.8) ml/beat, and 0 (0-55.4) ml/min at corresponding side of controls. These hemodynamics were not significantly different between groups.

CONCLUSION

APV, PNV, and RF changes take place in SSWA patients, which may be associated with the occurrence of PT and have the potential value to improve accurate etiological diagnosis and predict treatment success.

Quantification of cerebrospinal fluid flow in dogs by cardiac-gated phase-contrast magnetic resonance imaging

BACKGROUND

Cerebrospinal fluid (CSF) flow in disease has been investigated with two-dimensional (2D) phase-contrast magnetic resonance imaging (PC-MRI) in humans. Despite similar diseases occurring in dogs, PC-MRI is not routinely performed and CSF flow and its association with diseases is poorly understood.

OBJECTIVES

To adapt 2D and four-dimensional (4D) PC-MRI to dogs and to apply them in a group of neurologically healthy dogs.

ANIMALS

Six adult Beagle dogs of a research colony.

METHODS

Prospective, experimental study. Sequences were first optimized on a phantom mimicking small CSF spaces and low velocity flow. Then, 4D PC-MRI and 2D PC-MRI at the level of the mesencephalic aqueduct, foramen magnum (FM), and cervical spine were performed.

RESULTS

CSF displayed a bidirectional flow pattern on 2D PC-MRI at each location. Mean peak velocity (and range) in cm/s was 0.92 (0.51-2.08) within the mesencephalic aqueduct, 1.84 (0.89-2.73) and 1.17 (0.75-1.8) in the ventral and dorsal subarachnoid space (SAS) at the FM, and 2.03 (range 1.1-3.0) and 1.27 (range 0.96-1.82) within the ventral and dorsal SAS of the cervical spine. With 4D PC-MRI, flow velocities of >3 cm/s were visualized in the phantom, but no flow data were obtained in dogs.

CONCLUSION

Peak flow velocities were measured with 2D PC-MRI at all 3 locations and slower velocities were recorded in healthy Beagle dogs compared to humans. These values serve as baseline for future applications. The current technical settings did not allow measurement of CSF flow in Beagle dogs by 4D PC-MRI.

In cervical spondylotic myelopathy spinal cord motion is focally increased at the level of stenosis: a controlled cross-sectional study

STUDY DESIGN

Level-, age-, and gender-matched controlled cross-sectional cohort study.

OBJECTIVES

To investigate alterations of spinal cord (SC) motion within cervical spondylotic myelopathy (CSM) across the cervical spinal segments and its relation to cerebrospinal fluid (CSF)-flow, anatomic conditions, and clinical parameters.

SETTING

University Hospital Balgrist, Zurich, Switzerland.

METHODS

Overall, 12 patients suffering from CSM at level C5 and 12 controls underwent cardiac-gated 2D phase-contrast-MRI at level C2 and C5 and standard MRI sequences. Parameters of interest: Velocity measurements of SC and CSF (area under the curve = total displacement (normalization for duration of the heart cycle), total displacement ratio (C5/C2; intraindividual normalization for confounders)), spinal canal diameters, clinical motor- and sensory scores, and performance measures.

RESULTS

Interrater reliability was excellent for SC motion at both levels and for CSF flow at C2, but not reliable for CSF flow at C5. Within controls, SC motion at C2 positively correlated with SC motion at C5 (p = 0.000); this correlation diminished in patients (p = 0.860). SC total displacement ratio was significantly increased in patients (p = 0.029) and correlated with clinical impairment (p = 0.017). Morphometric measures of the extent of stenosis were not related to SC motion or clinical symptoms.

CONCLUSION

The findings revealed physiological interactions of CSF flow and SC motion across the cervical spine in healthy controls while being diminished in CSM patients. Findings of focally increased SC motion at the level of stenosis were related to clinical impairment and might be promising as a diagnostic and prognostic marker in CSM.

SPONSORSHIP

CRPP Neurorehab of the University of Zurich, Switzerland.