SUMMARY:Intracranial aneurysms are a common pathologic condition with a potential severe complication: rupture. Effective treatment options exist, neurosurgical clipping and endovascular techniques, but guidelines for treatment are unclear and focus mainly on patient age, aneurysm size, and localization. New criteria to define the risk of rupture are needed to refine these guidelines. One potential candidate is aneurysm wall motion, known to be associated with rupture but difficult to detect and quantify. We review what is known about the association between aneurysm wall motion and rupture, which structural changes may explain wall motion patterns, and available imaging techniques able to analyze wall motion.
Aneurysm wall motion has been reported to be associated with rupture. However, its quantification with medical imaging is challenging and should be based on experimental ground-truth to avoid misinterpretation of results. In this work a time-resolved CT angiography (4D-CTA) acquisition protocol is proposed to detect the pulsation of intracranial aneurysms with a low radiation dose. To acquire ground-truth data, the accuracy of volume pulsation detection and quantification in a silicone phantom was assessed by applying pressure sinusoidal waves of increasing amplitudes. These experiments were carried out using a test bench that could reproduce pulsatile waveforms similar to those inside the internal carotid arteries of human subjects. 4D-CTA acquisition parameters (mAs, kVp) were then selected to achieve reliable pulsation detection and quantification with the lowest radiation dose achievable. The resulting acquisition protocol was then used to image an anterior communicating artery aneurysm in a human subject. Data reveals that in a simplified in vitro setting 4D-CTA allows for an effective and reproducible method to detect and quantify aneurysm volume pulsation with an inferior limit as low as 3 mm3 and a background noise of 0.5–1 mm3. Aneurysm pulsation can be detected in vivo with a radiation dose approximating 1 mSv.
Ischemic Stroke is the most frequent type of stroke and is subject to many studies investigating prevention means. Avoiding the difficulties and ethical problems of experimental in-vivo research, in-vitro testing is a convenient way of studying in controlled conditions the morphological impact and mechanical aspects of emboli dynamics. This in-vitro study was performed with two realistic silicone aortic-arch phantoms submitted to physiological pulsatile flow conditions. In the in-vitro test bed, using automatic image tracking and analysis, it was made possible detecting and tracking artificial spherical emboli candidates circulating in the anatomic aortic-arch models under a realistic based-patient blood flow profile. The emboli trajectories as well as their repartition in the different supra-aortic branches are presented for the two aortic-arch geometries obtained from CT scans. Through a statistical analysis performed with several artificial emboli sizes, the experimental study shows that the repartition percentages of the emboli closely follow the flowrate repartition percentages for both aortic-arch models, suggesting that higher flowrates lead to higher concentrations of emboli in a given artery. Sets of human thrombi were also injected and the repartition percentages have been established, giving the same trend as for artificial emboli.
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