Background: The proximity of transverse sinus stenosis (TSS) to inner ear structures and the temporal bone makes it a substantial cause of pulsatile tinnitus (PT). Treatment typically involves venous sinus stenting. This study investigates the hemodynamic stressors in TSS patients with PT along the pulse-transmitting temporal bone area and evaluates its treatment effects. Methods: Four patients with idiopathic intracranial hypertension, PT, and TSS, and four control patients were imaged using MR venography (MRV) and flat panel CT (FP-CT). Patient-specific blood flow simulations were conducted using boundary conditions based on quantitative MR angiography before and after VSS. Catheter-based trans-stenotic pressure gradient measurements were used to validate the simulation results. Results: The prediction of pressure gradients was close to catheter-based measurements using FP-CT-based segmentations (absolute deviation of 0.35 mm Hg) and is superior to MRV-based reconstructions (absolute deviation of 6.9 mm Hg). In TSS patients, the sinus temporal bone contact areas revealed notably higher time-averaged wall shear stress by 47±22% and velocity values by 41±18% compared with the sinus brain side. The relative residence time decreased by 57±58%. After stenting, the hemodynamic parameters dropped at the temporal side and throughout the sigmoid sinus. Almost all control patient hemodynamics remained lower than post-interventional results. Conclusion: Our simulations based on patient-specific flows highly predicts pressure gradients across the stenosis. Flow conditions in TSS reveal flow jet formation and high shear rates at the temporal bone, potentially causing sound transmission. The treatment reduces these stressors, demonstrating its targeted therapeutic effect.

Background/Objectives: Intracranial arteriovenous malformations (AVMs) exhibit a complex vasculature characterized by a locally occurring tangled nidus connecting the arterial and venous system bypassing the capillary network. Clinically available imaging modalities may not give sufficient spatial or temporal resolution. Adequate 3D models of large vascular areas and a detailed blood flow analysis of the nidus including the surrounding vessels are not available yet. Methods: Three representative AVM cases containing multimodal image data (3D rotational angiography, magnetic resonance angiography, magnetic resonance venography, and phase-contrast quantitative magnetic resonance imaging) are investigated. Image segmentation results in partial 3D models of the different vascular segments, which are merged into large-scale neurovascular models. Subsequently, image-based blood flow simulations are conducted based on the segmented models using patient-specific flow measurements as boundary conditions. Results: The segmentation results provide comprehensive 3D models of the overall arteriovenous morphology including realistic nidus vessels. The qualitative results of the hemodynamic simulations show realistic flow behavior in the complex vasculature. Feeding arteries exhibit increased wall shear stress (WSS) and higher flow velocities in two cases compared to contralateral vessels. In addition, feeding arteries are exposed to higher overall WSS with increased value variation between individual vessels (20.1 Pa ± 17.3 Pa) compared to the draining veins having a 62% lower WSS (8.9 Pa ± 5.9 Pa). Blood flow distribution is dragged towards the dominating circulation side feeding the nidus for all the cases quantified by the volume flow direction changes in the posterior communicating arteries. Conclusions: This multimodal study demonstrates the feasibility of the presented workflow to acquire detailed blood flow predictions in large-scale AVM models based on complex image data. The hemodynamic models serve as a base for endovascular treatment modeling influencing flow patterns in distally located vasculatures.

Due to their effect on aneurysm hemodynamics, flow diverters (FD) have become a routine endovascular therapy for intracranial aneurysms. Since over- and undersizing affect the device’s hemodynamic abilities, selecting the correct device diameter and accurately simulating FD placement can improve patient-specific outcomes. The purpose of this study was to validate the accuracy of virtual flow diverter deployments in the novel Derivo^® 2 device. We retrospectively analyzed blood flows in ten FD placements for which 3D DSA datasets were available pre- and post-intervention. All patients were treated with a second-generation FD Derivo^® 2 (Acandis GmbH, Pforzheim, Germany) and post-interventional datasets were compared to virtual FD deployment at the implanted position for implanted stent length, stent diameters, and curvature analysis using ANKYRAS (Galgo Medical, Barcelona, Spain). Image-based blood flow simulations of pre- and post-interventional configurations were conducted. The mean length of implanted FD was 32.61 (±11.18 mm). Overall, ANKYRAS prediction was good with an average deviation of 8.4% (±5.8%) with a mean absolute difference in stent length of 3.13 mm. There was a difference of 0.24 mm in stent diameter amplitude toward ANKYRAS simulation. In vessels exhibiting a high degree of curvature, however, relevant differences between simulated and real-patient data were observed. The intrasaccular blood flow activity represented by the wall shear stress was qualitatively reduced in all cases. Inflow velocity decreased and the pulsatility over the cardiac cycle was weakened. Virtual stenting is an accurate tool for FD positioning, which may help facilitate flow FDs’ individualization and assess their hemodynamic impact. Challenges posed by complex vessel anatomy and high curvatures must be addressed.

Backround: The flow characteristics of bifurcation aneurysms in the posterior communicating artery (PCOM) have rarely been studied. The likelihood of a complete PCOM aneurysm occlusion after endovascular treatment is reduced with the presence of a fetal posterior communicating artery (fPCOM). As a result, anatomical variations in PCOM aneurysms represent a major challenge for the endovascular treatment. This study addresses hemodynamic variations in PCOM aneurysms of either fetal or adult type. Methods: 3D-DSA data of 14 patients with bifurcation aneurysms located in the PCOM junction were collected. Nine patients presented with a fPCOM and five patients an adult PCOM (aPCOM). Patient-specific 3D models containing at least one bifurcation distal the aneurysm in the anterior circulation as well as the PCOM itself were extracted using image-based blood flow simulations. Seven hemodynamic parameters were calculated for all aneurysm models to characterize the intra-aneurysmal blood flow. The PCOM outflow was artificially varied to represent both fPCOM and aPCOM conditions for each model resulting in 28 simulations. Results: Fetal‑type PCOM showed higher intra‑aneurysmal mean velocity (median 0.09 vs. 0.06 m/s), maximum velocity (0.17 vs. 0.14 m/s), averaged wall shear stress (1.67 vs. 1.27 Pa), neck inflow rate (40.9 vs. 22.4 ml/min), and inflow concentration index (0.56 vs. 0.40), with lower pulsatility index (1.73 vs. 1.89). Those differences were significant whereas mean oscillatory shear index did not differ significantly. Conclusion: The presence of anatomical variations affects the hemodynamic parameters of PCOM bifurcation aneurysms. In particular, the presence of an fPCOM has an unfavorable effect on the intra-aneurysmal flow dynamics.

The use of 3D printing technology for medical applications is becoming increasingly popular. Recent stereolithography (SLA)-based printing methods allow the generation of complex structures with a high surface quality. This is particularly useful for applications in the neurovascular field, where sophisticated structures are involved. In this study patient-specific intracranial aneurysm models are extracted based on medical image data und printed as thin-walled vascular phantom models. For this purpose, two commercially available 3D printers are used to print flexible vascular models with three different silicone-like elastic resins (Ultracur3D FL 300, Prusament Flex80 and Formlabs Elastic 50A) of various Shore hardness. Three aneurysm models of different size and complexity are chosen. To evaluate the geometric accuracy of the flexible models, angiographic measurements are performed for an exemplary case and morphological parameters are extracted from the generated 3D models. The printed results demonstrate a successful generation of hollow aneurysm phantoms. There are dependencies regarding the print quality from the model to platform positioning for two materials. The quantitative geometric accuracy analysis shows notable differences between the materials. The extracted morphological parameter values for all materials show a mean decrease compared to the original reference model of aneurysm volume (4.5 %) and maximum diameter (1.0 %) as well as an increase of ostium area (6.0 %) and maximum height (4.9 %). However, Formlabs Elastic 50A in particular exhibits just slight reductions with respect to the reference model, with a mean decrease for all parameters of 5.7 % as well as no dependence on printing position and resulting artifacts. The study investigates the feasibility of using SLA-based 3D printing to generate realistic flexible aneurysm phantoms. In this context, the Formlabs Elastic 50A could be identified as potentially applicable for phantom creation in terms of reproducible quality and geometric validity.