BackgroundIntracranial fusiform aneurysms are complex and poorly characterized vascular lesions. High-resolution magnetic resonance imaging (HR-MRI) and computational morphological analysis may be used to characterize cerebral fusiform aneurysms.ObjectiveTo use advanced imaging and computational analysis to understand the unique pathophysiology, and determine possible underlying mechanisms of instability of cerebral fusiform aneurysms.MethodsPatients with unruptured intracranial aneurysms prospectively underwent imaging with 3T HR-MRI at diagnosis. Aneurysmal wall enhancement was objectively quantified using signal intensity after normalization of the contrast ratio (CR) with the pituitary stalk. Enhancement between saccular and fusiform aneurysms was compared, as well as enhancement characteristics of fusiform aneurysms. The presence of microhemorrhages in fusiform aneurysms was determined with quantitative susceptibility mapping (QSM). Three distinct types of fusiform aneurysms were analyzed with computational fluid dynamics (CFD) and finite element analysis (FEA).ResultsA total of 130 patients with 160 aneurysms underwent HR-MRI. 136 aneurysms were saccular and 24 were fusiform. Fusiform aneurysms had a significantly higher CR and diameter than saccular aneurysms. Enhancing fusiform aneurysms exhibited more enhancement of reference vessels than non-enhancing fusiform aneurysms. Ten fusiform aneurysms underwent QSM analysis, and five aneurysms showed microhemorrhages. Microhemorrhage-positive aneurysms had a larger volume, diameter, and greater enhancement than aneurysms without microhemorrhage. Three types of fusiform aneurysms exhibited different CFD and FEA patterns.ConclusionFusiform aneurysms exhibited more contrast enhancement than saccular aneurysms. Enhancing fusiform aneurysms had larger volume and diameter, more enhancement of reference vessels, and more often exhibited microhemorrhage than non-enhancing aneurysms. CFD and FEA suggest that various pathophysiological processes determine the formation and growth of fusiform aneurysms.
Biomechanical computational simulation of intracranial aneurysms has become a promising method for predicting features of instability leading to aneurysm growth and rupture. Hemodynamic analysis of aneurysm behavior has helped investigate the complex relationship between features of aneurysm shape, morphology, flow patterns, and the proliferation or degradation of the aneurysm wall. Finite element analysis paired with high-resolution vessel wall imaging can provide more insight into how exactly aneurysm morphology relates to wall behavior, and whether wall enhancement can describe this phenomenon. In a retrospective analysis of 23 unruptured aneurysms, finite element analysis was conducted using an isotropic, homogenous third order polynomial material model. Aneurysm wall enhancement was quantified on 2D multiplanar views, with 14 aneurysms classified as enhancing (CRstalk≥0.6) and nine classified as non-enhancing. Enhancing aneurysms had a significantly higher 95th percentile wall tension (μ = 0.77 N/cm) compared to non-enhancing aneurysms (μ = 0.42 N/cm, p < 0.001). Wall enhancement remained a significant predictor of wall tension while accounting for the effects of aneurysm size (p = 0.046). In a qualitative comparison, low wall tension areas concentrated around aneurysm blebs. Aneurysms with irregular morphologies may show increased areas of low wall tension. The biological implications of finite element analysis in intracranial aneurysms are still unclear but may provide further insights into the complex process of bleb formation and aneurysm rupture.
Background: The lack of safety clearance of several metallic breast implants in 7T(Tesla) poses a significant hurdle to standard clinical breast cancer care and research from reaping the benefits of ultra-high resolution MR imaging. A breast biopsy clip (Ultracor Twirl, Becton, Dickinson and Company, Vernon Hills, IL) composed of nitinol, was tested for safety and artifact susceptibility clearance in a 7T MRI scanner, using standardized procedures. This clearance is significant in henceforth allowing patients with this implant to be scanned in now FDA approved ultra-high-field MRI scanners of 7T or less for clinical and research purposes. Methods: Tests for magnetic susceptibility (torque and translational attraction), MRI-related heating, and artifacts were conducted as per standardized protocols. The torque and translational attraction tests evaluated the effects of magnetic force by the MRI to cause the clip to move and twist respectively. The heating test was conducted with customized MR parameters of short TR (repetition time) and maximum echo-train length, designed to induce temperature change. The artifact test using T1 weighted spin and gradient echo imaging sequences, evaluated potential localized signal loss that may result in misrepresentation of the imaged area. This may occur due to the presence of the metallic clip in the MR environment. Results: The torque and translational attraction tests respectively indicated that the MR environment did not induce any movement in the clip in eight orientations, with a deflection angle of 0 degrees. Results of the heating test indicated no significant temperature change of the clip. A temperature change of less than 0.45C° was observed in the phantom gel in both the absence and presence of the clip, which is well within the safety threshold (< 1°C). Results of the artifact test indicated a very small artifact, with the largest artifact cross-sectional area appearing on gradient echo images. Conclusion: These cumulative results indicate that the Ultracor Twirl breast biopsy clip is safe for imaging patients at 7T. Citation Format: William Dong, Kanchna Ramchandran, Adam Galloy, Marco A. Nino, Marla Kleingartner, Madhavan L. Raghavan, Sneha Phadke, Vincent A. Magnotta. Safety and artifact testing of a nitinol breast biopsy clip in an ultra-high resolution magnetic resonance imaging (MRI) environment [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-04-07.
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