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

Back to Bernoulli: a simple formula for trans-stenotic pressure gradients and retrospective estimation of flow rates in cerebral venous disease

BACKGROUND

Venous sinus stenosis can be associated with cerebrovascular disorders. Understanding the role of blood flow disturbances in these disorders is often hampered by the lack of patient-specific flow rates. Our goal was to demonstrate the impact of this by predicting individual flow rates retrospectively from routine manometry and angiography.

METHODS

Ten cases, spanning a range of stenosis severities and pressure gradients, were selected from a cohort of patients who had undergone venous stenting for pulsatile tinnitus. Lumen geometries were digitally segmented from CT venograms. A simplified Bernoulli formula was derived to estimate individual cycle-average flow rates from clinical pressure gradients and minimum lumen cross-section areas. High-fidelity pulsatile computational fluid dynamics (CFD) simulations were performed to compare predictions of flow disturbances using generic versus individual flow rates, and to validate the Bernoulli formula.

RESULTS

Individual flow rates derived from the Bernoulli formula deviated by up to 47% from the assumed generic flow rate, resulting in substantial differences in CFD predictions of post-stenotic flow instabilities. Pressure gradients estimated by the simplified Bernoulli formula were, however, highly predictive of pressure gradients from the full CFD simulations (R2=0.95; slope=0.98, 95% CI 0.88 to 1.09).

CONCLUSIONS

A simple Bernoulli formula can predict CFD-estimated trans-stenotic pressure gradients in realistic venous geometries. As demonstrated here, this may be used to recover individual flow rates from routine-but-invasive clinical measurements; however, it also suggests a simpler path towards non-invasive estimation of trans-stenotic pressure gradients that may avoid some of the challenges associated with 4D flow MRI approaches.

Cerebral Sinus Hemodynamics in Adults Revealed by 4D Flow MRI

BACKGROUND

The hemodynamics of the cerebral sinuses play a vital role in understanding blood flow-related diseases, yet the hemodynamics of the cerebral sinuses in normal adults remains an unresolved issue.

PURPOSE

To evaluate hemodynamics in the cerebral sinus of adults using 4-dimensional flow MRI (4D Flow MRI).

STUDY TYPE

Cross-sectional.

POPULATION

Ninety-nine healthy volunteers (mean age, 42.88 ± 13.16 years old; females/males, 55/44).

FIELD STRENGTH/SEQUENCE

3 T/4D Flow MRI.

ASSESSMENT

The blood flow velocity, average blood flow rate (Q), and vortexes at the superior sagittal sinus (SSS), straight sinus (STS), transverse sinus, sigmoid sinus, and jugular bulb of each volunteer were evaluated by two independent neuroradiologists. The relationship between the total cerebral Q and sex and age was also assessed. Twelve volunteers underwent two scans within a month.

STATISTICAL TESTS

The intraclass correlation coefficient (ICC) evaluated the inter-observer agreement. Blood flow parameters among volunteers were compared by the independent-sample t-test or Mann-Whitney U test. The multiple linear regression equation was used to evaluate the relationship between total cerebral Q and age and sex. P < 0.05 indicated statistical significance.

RESULTS

The test-retest and interobserver reliability of average velocity and Q were moderate to high (ICC: 0.54-0.99). Cerebral sinus velocity varied by segment and cardiac cycle. The SSS's velocity and Q increased downstream and Q near torcular herophili was 3.5 times that through the STS. The total cerebral Q decreased by 0.06 mL/s per year (β = -0.06 ± 0.013) and was sex-independent within the group. Vortexes were found in 12.12%, 8.9%, and 59.8% of torcular herophili, transverse-sigmoid junction, and jugular bulb, respectively, and were related to higher upstream flow.

DATA CONCLUSION

Cerebral sinuses could be measured visually and quantitatively in vivo by 4D Flow MRI, providing a basis for future research on pulsating tinnitus, multiple sclerosis, and other related diseases.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.