Gouthami Chintalapani

Hemodynamics at the ostium of cerebral aneurysms with relation to post-treatment changes by a virtual flow diverter: A computational fluid dynamics study

Computational fluid dynamics (CFD) techniques have been refined for modeling the hemodynamics in cerebral aneurysms. Recent interest has focused on understanding hemodynamic changes by treatment with a flow diverter (FD), i.e. a stent with a dense metal mesh which is placed across the ostium to divert the majority of flow away from the aneurysm. Potential complications include remnant inflow jets but, more seriously, aneurysm hemorrhage. For optimization of treatment outcome, a better understanding of the effects caused by the FD would be beneficial. In particular, pressure and velocity distributions at the aneurysm ostium are of interest, as they will be directly affected by the FD which in turn will influence post-treatment hemodynamics inside the aneurysm. Here, we report the results of a CFD study investigating the relationship between pre-treatment and post-treatment velocities, pressures and wall shear stresses (WSS) in the aneurysm with corresponding hemodynamic conditions at the aneurysm ostium prior to treatment. The study was carried out using a dedicated CFD prototype which allows modeling the effects of a virtual FD integrated into patient-specific geometries utilizing Darcys law. Velocities and WSS were reduced in all cases post FD treatment, pressure increased in one case. Heterogeneous distributions of the velocity magnitude were found at the ostium with focal maxima indicating potential risk zones for remnant inflow jets into the aneurysms. Pressures at the ostium correlated with pressure changes inside the aneurysm which could become a pre-treatment indicator for the evaluation of the suitability of a particular aneurysm for FD treatment.

Towards Clinical Application of a Laplace Operator-Based Region of Interest Reconstruction Algorithm in C-Arm CT

It is known that a reduction of the field-of-view in 3-D X-ray imaging is proportional to a reduction in radiation dose. The resulting truncation, however, is incompatible with conventional reconstruction algorithms. Recently, a novel method for region of interest reconstruction that uses neither prior knowledge nor extrapolation has been published, named approximated truncation robust algorithm for computed tomography (ATRACT). It is based on a decomposition of the standard ramp filter into a 2-D Laplace filtering and a 2-D Radon-based residual filtering step. In this paper, we present two variants of the original ATRACT. One is based on expressing the residual filter as an efficient 2-D convolution with an analytically derived kernel. The second variant is to apply ATRACT in 1-D to further reduce computational complexity. The proposed algorithms were evaluated by using a reconstruction benchmark, as well as two clinical data sets. The results are encouraging since the proposed algorithms achieve a speed-up factor of up to 245 compared to the 2-D Radon-based ATRACT. Reconstructions of high accuracy are obtained, e.g., even real-data reconstruction in the presence of severe truncation achieve a relative root mean square error of as little as 0.92% with respect to nontruncated data.

Metal coverage ratio of pipeline embolization device for treatment of unruptured aneurysms: Reality check.

Background and purpose The metal coverage ratio (MCR) of a flow diverter influences the intra-aneurysmal hemodynamics; a high MCR will occlude an aneurysm early, while a low MCR may delay aneurysm occlusion. The true MCR of a pipeline embolization device (PED) could be lower due to oversize, device deformation, or aneurysm location. In this study deviation of the true MCR from the nominal MCR is assessed and whether their difference affects aneurysm occlusion rate is determined. Methods A total of 40 consecutive patients, each of them treated by one PED for their aneurysms at the internal carotid artery (ICA), were retrospectively analyzed. The DynaCT images of these deployed PEDs were used to determine their true dimensions and estimate three MCRs (local, mean, and nominal). These data were compared in two groups of patients who had different aneurysm outcomes at six months. Results The difference in the local MCR between two groups is small, but statistically significant (24.5% vs 21.6%, p = 05). The local MCR is consistently lower than the nominal MCRs (23.2% vs 30.2%, p < 0.001); however, the difference between the mean and local MCRs is small (23.9% vs 23.2%). Conclusions An expectation that a PED can achieve a MCR of 30% may not be reasonable. Device oversize and deformation during deployment lower the local MCR by 5–7%. A lowered MCR affects the aneurysm occlusion rate at six months.

Endovascular Recanalization in Acute Ischemic Stroke Using the Solitaire FR Revascularization Device with Adjunctive C-Arm CT Imaging

SUMMARY: In this clinical report, we examined a single-center experience by using the Solitaire FR Revascularization Device in the treatment of acute ischemic stroke in which there was poor initial visualization of the occluded arterial branches by using biplanar cerebral angiography. In all cases, adjunctive C-arm CT was used during the deployment of the thrombectomy device to gain additional information regarding device placement and expansion. Outcome measures included the extent of reperfusion, posttreatment changes in NIHSS scores, posttreatment TICI scores, cerebral hemorrhage, and survival. Clot removal with successful arterial recanalization was achieved in 15/18 cases (83.3%) with TICI scores of 2b/3 in all patients who had initial recanalization. The NIHSS score improved, on average, from 19 pretreatment to 11 posttreatment, and 72% of patients survived. In cases of acute stroke in which there is little information available regarding the positioning and deployment of a retrievable stent during mechanical thrombectomy, the use of C-arm CT may provide more information about device placement across an area of thrombus.

The Added Value of Volume-of-Interest C-Arm CT Imaging during Endovascular Treatment of Intracranial Aneurysms

VOI C-arm CT images were obtained in 28 patients undergoing endovascular treatment of intracranial aneurysms and the VOI images were reconstructed by using a novel prototype reconstruction algorithm to minimize truncation artifacts from double collimation. The reconstruction accuracy of VOI C-arm CT images was assessed quantitatively by comparing them with the full-head noncollimated images. Quality of VOI C-arm CT images was comparable with that of the standard Feldkamp, Davis, and Kress reconstruction of noncollimated C-arm CT images. The authors conclude that VOI imaging allows multiple 3D C-arm CT acquisitions and provides information related to device expansion, parent wall apposition, and neck coverage during the procedure, with very low additional radiation exposure to the patient. BACKGROUND AND PURPOSE: Successful endovascular treatment of intracranial aneurysms requires understanding the exact relationship of implanted devices to the aneurysm, parent artery, and other branch vessels during the treatment. Intraprocedural C-arm CT imaging has been shown to provide such information. However, its repeated use is limited due to increasing radiation exposure to the patient. The goal of this study was to evaluate a new volume-of-interest C-arm CT imaging technique, which would provide device-specific information through multiple 3D acquisitions of only the region of interest, thus reducing cumulative radiation exposure to the patient. MATERIALS AND METHODS: VOI C-arm CT images were obtained in 28 patients undergoing endovascular treatment of intracranial aneurysms. VOI images were acquired with the x-ray source collimated around the deployed device, both horizontally and vertically. The images were reconstructed by using a novel prototype robust reconstruction algorithm to minimize truncation artifacts from double collimation. The reconstruction accuracy of VOI C-arm CT images was assessed quantitatively by comparing them with the full-head noncollimated images. RESULTS: Quantitative analysis showed that the quality of VOI C-arm CT images is comparable with that of the standard Feldkamp, Davis, and Kress reconstruction of noncollimated C-arm CT images (correlation coefficient = 0.96 and structural similarity index = 0.92). Furthermore, 91.5% reduction in dose-area product was achieved with VOI imaging compared with the full-head acquisition. CONCLUSIONS: VOI imaging allows multiple 3D C-arm CT acquisitions and provides information related to device expansion, parent wall apposition, and neck coverage during the procedure, with very low additional radiation exposure to the patient.

Evaluation of C-arm CT metal artifact reduction algorithm during intra-aneurysmal coil embolization: Assessment of brain parenchyma, stents and flow-diverters

PURPOSE Flat panel C-arm CT images acquired in the interventional suite provide valuable information regarding brain parenchyma, vasculature, and device status during the procedure. However, these images often suffer from severe streak artifacts due to the presence of metallic objects such as coils. These artifacts limit the capability to make diagnostic inferences and thus need to be reduced for better image interpretation. The main purpose of this paper is to systematically evaluate the accuracy of one such C-arm CT based metal artifact reduction (MAR) algorithm and to demonstrate its usage in both stent and flow diverter assisted coil embolization procedures. METHODS C-arm CT images routinely acquired in 24 patients during coil embolization procedure (stent-assisted (12) and flow-diverter assisted (12)) were included in this study in a retrospective fashion. These images were reconstructed without and with MAR algorithm on an offline workstation and compared using quantitative image analysis metrics. This analysis was carried out to assess the improvements in both brain parenchyma and device visibility with MAR algorithm. Further, ground truth reference images from phantom experiments and clinical data were used for accurate assessment. RESULTS Quantitative image analysis of brain parenchyma showed uniform distribution of grayscale values and reduced image noise after MAR correction. The line profile plot analysis of device profile in both phantom and clinical data demonstrated improved device visibility with MAR correction. CONCLUSIONS MAR algorithm successfully reduced streak artifacts from coil embolization in all cases, thus allowing more accurate assessment of devices and adjacent brain parenchyma.

Development of a recalcitrant, large clot burden, bifurcation occlusion model for mechanical thrombectomy

OBJECTIVE Stroke is a major cause of disability and death in adults. Several large randomized clinical trials have shown the significant benefit of mechanical thrombectomy with modern stent retrievers in the treatment of large-vessel occlusions. However, large clots located at bifurcations remain challenging to treat. An in vivo model of these recalcitrant clots needs to be developed to test future generations of devices. METHODS Autologous blood was drawn from anesthetized swine via a femoral sheath. Blood was then mixed with thrombin, calcium chloride, and saline, and injected into silicone tubing to form cylindrical clots in the standard fashion. Matured clots were then delivered in an unfragmented fashion directly into the distal extracranial vasculature, at branch points where vessel sizes mimic the human middle cerebral artery, by using Penumbra aspiration tubing and the Penumbra ACE68 reperfusion catheter. RESULTS A total of 5 adult swine were used to develop the model. The techniques evolved during experiments in the first 3 animals, and the last 2 were used to establish the final model. In these 2 swine, a total of 8 autologous clots, 15-20 mm, were injected directly into 8 distal extracranial vessels at branch points to mimic a bifurcation occlusion in a human. All clots were delivered directly at a distal bifurcation or trifurcation in an unfragmented fashion to cause an occlusion. Ten revascularization attempts were made, and none of the branch-point occlusions were fully revascularized on the first attempt. CONCLUSIONS Using novel large-bore distal access catheters, large unfragmented clots can be delivered into distal extracranial vessels in a swine occlusion model. The model mimics the clinical situation of a recalcitrant bifurcation occlusion and will be valuable in the study of next-generation stroke devices and in training settings.

P-005 Evaluation of an Automatic Detection and Segmentation Tool for Flow Diverters (Pipeline™ Embolization Device) from C-arm CT Images

Purpose In addition to stent-assisted coiling, endovascular treatment of intracranial aneurysms using flow diverters, like the Pipeline™ Embolization Device (PED), has become a viable treatment option. Visualization of the device after deployment or during routine follow-up imaging is important to assess expansion and vessel wall apposition. Currently, PEDs are visually assessed from 3D C-arm CT images because of their limited visibility under 2D fluoroscopy. However, tedious post-processing is required to segment the device from the surrounding bony anatomy to better visualise the deployment. The main objective of this study is to report preliminary results of prototype software that automatically detects and segments PEDs from C-arm CT images. Materials and methods C-arm CT images from 15 patients with internal carotid artery (ICA) aneurysms that underwent endovascular treatment with PEDs were evaluated using prototype software (Flow Diverter Detection Prototype, Siemens AG, Forchheim, Germany). PEDs were deployed in the right cavernous ICA (n = 7), right supraclinoid ICA (n = 2), left cavernous ICA (n = 3), and left supraclinoid ICA (n = 2). C-arm CT images (Syngo Inspace 3D 5s DSA, Siemens AG, Forchheim, Germany) were obtained immediately after deployment or during follow-up angiography as part of the routine imaging for device assessment. The software was applied to the native mask reconstructed around the PED using a sharp kernel with a matrix size of 512 × 512 × 512 voxels and a voxel size of 0.11–0.16 mm3. The software requires the operator to use one click to automatically segment the PED.The segmentation results were analyzed qualitatively. Quality of segmentation was rated based on the following: 0 – software failed to detect PED, 1 – software detected PED with additional bony contamination that required additional cropping, 2 – software automatically detected PED without any need for additional post-processing. Results Software automatically segmented the PED in all fifteen datasets. Six datasets were given a rating of 2. Nine datasets were given a rating of 1, indicating small parts of bone were still included in the segmentation. This did not limit the visualization of the device and can be cropped out with minor post-processing. The average time needed to automatically segment the PED was 20.39 ± 3.5 seconds. Conclusions The prototype software was able to identify and segment the PED in all cases. Hence, automatic detection of PED from C-arm CT images is feasible. This tool can provide fast visualization of the flow diverters in 3D to assess device expansion and vessel wall apposition. Abstract P-005 Figure 1 Disclosures M. Jagani: 5; C; Siemens Medical Solutions USA, Inc. P. Chinnadurai: 5; C; Siemens Medical Solutions USA, Inc. G. Chintalapani: 5; C; Siemens Medical Solutions USA, Inc.. H. Shaltoni: None. H. Morsi: None. M. Mawad: None.

PREDICTION OF OPTIMAL DEPLOYMENT ANGLE FOR TAVR: FEASIBILITY OF CT ANGIOGRAPHY AND NON–CONTRAST DYNACT IMAGE REGISTRATION BASED APPROACH AND ITS POTENTIAL IMPLICATION ON LIMITING CONTRAST VOLUME

Prediction of an optimal C–arm angle that aligns the coronary sinuses for valve deployment is critical during TAVR. Current solutions derive the deployment angle from multiple angiograms, reconstruction of multi–slice CT (MSCT) or C–arm CT rotational angiography (CTRA). We evaluated a method

Fast acquisition cone-beam computed tomography: initial experience with a 10 s protocol

Background Cone-beam computed tomography (CBCT) facilitates the acquisition of cross-sectional imaging in angiography suites using a rotational C-arm and digital flat panel detectors. The applications are numerous, including evaluation of implanted devices and localization of cerebrovascular lesions. We present and validate the clinical utility of an alternative fast CBCT acquisition protocol in the context of neurovascular device imaging. Methods Contrast-enhanced (CE)-CBCT images were acquired using a new 10 s protocol in a phantom head model, swine model, and in patients. The acquisition parameters of both the 10 s and 20 s protocols were exactly the same, except for fewer projections (250 projections in 10 s vs 500 projections in 20 s), resulting in reduced scan time. Image quality was measured quantitatively in a controlled phantom study and qualitatively by blinded reviewers. The latter was performed to assess the image quality of the 10 s protocol pertinent to the device visibility and its apposition to the parent artery. Results 10 s CBCT images were comparable to 20 s CBCT in both phantom and animal studies. Of the 25 patient images, the reviewers agreed that they were able to discern the flow diverter struts and assess the apposition in all images. The overall rating for all 10 s images was 4.28 on a 5-point scale. No images were rated as less than 3, which was the average diagnostic quality. The ratings were concordant across three blinded reviewers (κ=0.411). Additionally, contrast and spatial resolution between 10 s and 20 s images were similar in non-human models. Conclusions CBCT images of neurovascular devices can be obtained successfully using a 10 s acquisition protocol. In addition, the 10 s protocol offers faster acquisition, thus allowing its use in awake patients and with an added advantage of lower radiation and contrast dose.