Associations between morphology and hemodynamics of intracranial aneurysms based on 4D flow and black-blood magnetic resonance imaging

Abstract

Background: Previous studies have hypothesized that intracranial aneurysm (IA) morphology interacts with hemodynamic conditions. Magnetic resonance imaging (MRI) provides a single image modality solution for both morphological and hemodynamic measurements for IA. This study aimed to explore the interaction between the morphology and hemodynamics of IA using black-blood MRI (BB-MRI) and 4D flow MRI.

Methods: A total of 97 patients with unruptured IA were recruited for this study. The IA size, size ratio (SR), and minimum wall thickness (mWT) were measured using BB-MRI. Velocity, blood flow, pulsatility index (PI), and wall shear stress (WSS) were measured with 4D flow MRI. The relationship between hemodynamic parameters and morphological indices was investigated by linear regression analysis and unpaired two-sample t-test. To determine the independent interaction, multiple linear regression analysis was further performed.

Results: The findings showed that mWT was negatively correlated with IA size (r=-0.665, P<0.001). Maximum blood flow in IA (Flow_IA) was positively correlated with IA size (r=0.458, P<0.001). The average WSS (WSS_avg) was negatively correlated with IA size (r=-0.650, P<0.001). The relationships remained the same after the multivariate analysis was adjusted for hemodynamic, morphologic, and demographic confounding factors. The WSS_avg was positively correlated with mWT (r=0.528, P<0.001). In the unpaired two-sample t-test, mWT, WSS_avg, and Flow_IA were statistically significantly associated with the size and SR of IAs.

Conclusions: There is potential for BB-MRI and 4D flow MRI to provide morphological and hemodynamic information regarding IA. Blood flow, WSS, and mWT may serve as non-invasive biomarkers for IA assessments, and may contribute to a more comprehensive understanding of the mechanism of IA.

Keywords: 4D flow magnetic resonance imaging (4D flow MRI); Intracranial aneurysm (IA); black-blood magnetic resonance imaging (BB-MRI).

Figure 1

Measurement of IA size using BB-MRI. IA size was defined as the largest of three measurements. IA, intracranial aneurysm; BB-MRI, black-blood magnetic resonance imaging.

Figure 2

Illustration of 4D flow data analysis using dedicated software in different IA. Flow pattern visualization of the (A,B) APA and (C,D) IA were performed by streamlines, and hemodynamic measurements within contours were conducted in a defined cross-sectional plane of the APA and IA. APA, adjacent parent artery; IA, intracranial aneurysm.

Figure 3

Illustration of hemodynamic and morphological parameter measurements. All hemodynamic measurements were implemented at the peak systolic phase. Cut-planes were created in the largest cross-sectional plane of APA and IA containing the maximum velocity vector. Maximum through-plane velocity in the APA (V_APA, cm/s) and maximum blood flow in the APA (Flow_APA, mL/s) were automatically measured. Maximum through-plane velocity in the IA (V_IA, cm/s), maximum blood flow in the IA (Flow_IA, mL/s), and average WSS of the IA (WSS_avg) were also automatically measured. In the meantime, mWT was also measured in the same geometry from BB-MRI. APA, adjacent parent artery; IA, intracranial aneurysm; mWT, minimum wall thickness; WSS, wall shear stress.

Figure 4

Scatter plots illustrating the relationship between morphological indices and hemodynamic parameters. (A) mWT was negatively correlated with IA size; (B) maximum Flow_IA was positively correlated with IA size; (C) WSS_avg was negatively correlated with IA size; (D) WSS_avg was positively correlated with mWT. mWT, minimum wall thickness; WSS, wall shear stress.

Figure 5

(A) The relationship (A) between IA diameter (abscissa) and 7 features (ordinate) and (B) between IA size ratio (abscissa) and 7 features (ordinate). For each feature, patients were separated into two subgroups based on the feature. Mean IA diameter, mean IA size ratio (SR), and 95% CI are shown for all subgroups. Vertical dashed lines show the mean IA diameter and mean IA SR from 72 patients. Two sample t-test. *, P<0.05; **, P<0.01. IA, intracranial aneurysm.

Figure 6

Two representative cases of IA. Example of a patient with: (A,B) IA size =8.74 mm, mWT =0.82 mm, maximum Flow_IA =5.866 mL/s, WSS_avg =0.447 N/m², and another patient with (C,D) IA size =20.4 mm, mWT =0.66 mm, Flow_IA =13.548 mL/s, WSS_avg =0.056 N/m². The giant IA has a thinner wall thickness, smaller WSS, and faster maximum blood flow than the small IA. IA, intracranial aneurysm; mWT, minimum wall thickness; WSS, wall shear stress.