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Relationship between morphology and hemodynamics of intracranial aneurysms: A preliminary study1Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China, 2Department of Interventional Neuroradiology, Beijing Neurosurgical Institute and Beijing Tiantan Hospital, Capital Medical University, Beijing, China, 3Department of Radiology, University of Washington, Seattle, WA, United States
Synopsis
In this study, the purpose was to investigate the relationship between morphology and hemodynamics of IA. Flowavg-APA and Flowmax-IA was positive correlated with IA size and was negatively correlated with mWT. Flowavg-APA was positive correlated with IA size when excluding mWT dependence. And no indices were correlated with mWT when excluding IA size dependence. As blood flows into IA, the volume of aneurysm is enlarged, resulting in the reduction of WT. IA size correlated stronger with blood flow than mWT. This study suggests that mWT and hemodynamics may provide additional information other than size, thus improve current IA risk standard.
Introduction
Intracranial aneurysm (IA) are dilatations of cerebral arteries1, and subarachnoid hemorrhage caused by rupture of IA is fatal2, resulting in a mortality of around 50%3. Morphology, such as IA size and wall thickness (WT), were considered as imaging bio-markers of IA rupture risk 4-5, and previous studies reported that hemodynamics also played an important role in pathophysiology of IA6. However, the relationship between morphology and hemodynamics is still unclear. Therefore, the purpose of this study was to investigate the relationship between morphological indices and hemodynamic parameters of IA.Methods
Study Population: 35 patients (8 males and 27 females, age range: 16 ~ 77 years) with IA diagnosed by DSA were included in this study. All subjects were approved by the local ethics committee and gave written informed consent.
MR Protocol: All MRI scan were performed on a 3.0T MRI scanner (Philips Achieva, Best, Netherlands) with a 32-channel head coil. For morphology evaluation, T1-weighted volumetric isotropic turbo spin echo acquisition (T1-VISTA) was utilized in this study. Scan parameters were: TR/TE = 700/30 ms, FOV = 160 x 160 x 54 mm3, voxel size =0.6 x 0.6 x 0.6 mm3. Furthermore, 4D-flow MRI was used for hemodynamic evaluation. Scan parameters were: TR/TE = 8.0/3.6 ms, FOV = 160 x 160 x 30 mm3, voxel size = 1 x 1 x 1 mm3, VENC = 120 cm/s.
Data Analysis: IA size, defined by maximum diameter of IA lumen, and minimum wall thickness (mWT), were measured from both DSA and BB-MRI images. Maximum through-plane velocity (VAPA, cm/s) in adjacent parent artery (APA) and maximum through-plane velocity (VIA, cm/s) within aneurysm were defined at the time index when peak velocity appears. Average blood flow in APA (Flowavg-APA, ml/s), and maximum blood flow in IA (Flowmax-IA, ml/s) were automatically measured in GTFlow, version 2.2.15 (GyroTools, Zurich, Switzerland). Furthermore, pulsatility index (PI) in APA was calculated as follows:PI=( Vpeak-Vvalley)/Vmean where Vpeak/Vvalley/Vmean are peak/valley/mean value of through-plane velocity (cm/s) over all time indices in one cardiac cycle.
Statistical analysis: All statistical analysis were conducted by MedCalc (MedCalc Software, Mariakerke, Belgium). Variables are denoted as mean ± standard deviation (SD) as appropriate. The difference of aneurysm size measurements between DSA and BB-MRI was evaluated by Mann-Whitney U test and intra-class coefficient (ICC). In order to investigate the relationship between morphological indices, such as IA size and mWT, and hemodynamic parameters, such as VAPA, VIA, Flowavg-APA, Flowmax-IA. Linear regression analysis was performed. Additionally, multiple linear regression analysis (partial correlation) was used by analysis of covariance. The level of statistical significance was set at p < 0.05.
Results
Mann-Whitney U test indicated that there is no difference in aneurysm size measurements between DSA and BB-MRI, as shown in Table.1. Table.2 showed that Flowavg-APA and Flowmax-IA was positive correlated with IA size, and Flowavg-APA was positive correlated with IA size when excluding mWT dependence, as shown in Table.2. Table.3 showed that Flowmax-IA and Flowavg-APA was negatively correlated with mWT, and no hemodynamic indices were correlated with mWT when excluding IA size dependence. Figure.1 showed examples of patients with small (Fig.1a-1b) and giant (Fig.1c-1d) IA, respectively. We can see that giant IA has thinner wall thickness and larger average blood flow in APA than the small one.Discussion and Conclusion
In this study, we assessed the relationship between morphology indices, such as IA size and mWT, and hemodynamic parameters. As blood flows into IA, the volume of aneurysm is enlarged, resulting in the reduction of WT. Partial correlation results illustrated that IA size correlated stronger with blood flow than mWT, which is probably because of the limited variation of mWT among this population. BB-MRI, benefit from its high resolution, can be used to provide more detailed information, such as IA size and WT, and its reliability of morphological measurements has been validated by DSA in this study. Furthermore, 4D-flow MRI can provide more versatile depiction of hemodynamics than other imaging techniques. This study suggests that mWT and hemodynamics may provide additional information of aneurysm instability other than IA size, thus improve current IA risk evaluation standard.Acknowledgements
No acknowledgement found.References
1. Bonneville F et al. Neuroimaging Clinics of North America, 2006, 16(3):371.
2. Juhana Frösen et al. Translational Stroke Research 2014; 5(3):347-356.
3. Van G J. Lancet, 2001, 357(9259):886-886.
4. Wiebers DO et al. Lancet 2003; 362: 103–110.
5. Sakurai K et al. J Neuroradiol 2013;40(1):19-28.
6. Nixon A M et al. Journal of Neurosurgery, 2010, 112(6):1240.
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