An asymmetric stent with low porosity patch across the intracranial aneurysm neck and high porosity elsewhere is designed to modify the flow to result in thrombogenesis and occlusion of the aneurysm and yet to reduce the possibility of also occluding adjacent perforator vessels. The purposes of this study are to evaluate the flow field induced by an asymmetric stent using both numerical and digital subtraction angiography (DSA) methods and to quantify the flow dynamics of an asymmetric stent in an in vivo aneurysm model. We created a vein-pouch aneurysm model on the canine carotid artery. An asymmetric stent was implanted at the aneurysm, with 25% porosity across the aneurysm neck and 80% porosity elsewhere. The aneurysm geometry, before and after stent implantation, was acquired using cone beam CT and reconstructed for computational fluid dynamics (CFD) analysis. Both steady-state and pulsatile flow conditions using the measured waveforms from the aneurysm model were studied. To reduce computational costs, we modeled the asymmetric stent effect by specifying a pressure drop over the layer across the aneurysm orifice where the low porosity patch was located. From the CFD results, we found the asymmetric stent reduced the inflow into the aneurysm by 51%, and appeared to create a stasis-like environment which favors thrombus formation. The DSA sequences also showed substantial flow reduction into the aneurysm. Asymmetric stents may be a viable image guided intervention for treating intracranial aneurysms with desired flow modification features.

Stenting may provide a new, less invasive therapeutic option for cerebral aneurysms. However, a conventional porous stent may be insufficient in modifying the blood flow for clinical aneurysms. We designed an asymmetric stent consisting of a low porosity patch welded onto a porous stent for an anterior cerebral artery aneurysm of a specific patient geometry to block the strong inflow jet. To evaluate the effect of the patch on aneurysmal flow dynamics, we "virtually" implanted it into the patient's aneurysm geometry and performed Computational Fluid Dynamics (CFD) analysis. The patch was computationally deformed to fit into the vessel lumen segmented from the patient CT reconstructions. After the flow calculations, a patch with the same design was fabricated using laser cutting techniques and welded onto a commercial porous stent, creating a patient-specific asymmetric stent. This stent was implanted into a phantom, which was imaged with X-ray angiography. The hemodynamics of untreated and stented aneurysms were compared both computationally and experimentally. It was found from CFD of the patient aneurysm that the asymmetric stent effectively blocked the strong inflow jet into the aneurysm and eliminated the flow impingement on the aneurysm wall at the dome. The impact zone with elevated wall shear stress was eliminated, the aneurysmal flow activity was substantially reduced, and the flow was considerably reduced. Experimental observations corresponded well qualitatively with the CFD results. The demonstrated asymmetric stent could lead to a new minimally invasive image guided intervention to reduce aneurysm growth and rupture.

MR-guided focused ultrasound (MRgFUS) is a non-invasive method by which tissue is ablated using ultrasound energy focused on a point. The procedure has proven effective for stationary targets (e.g. uterine fibroids) but has not yet been used for liver lesion treatment due to organ motion. We describe a method to compensate for organ motion to enable continuous application of ultrasound energy in the presence of target movement in the liver. The method involves tracking several salient features (typically blood vessels) in the vicinity of the target location. The location of the target point(s) themselves are updated using a thin plate spline (TPS) interpolation scheme. We demonstrate sub-pixel tracking accuracy on synthetic sequences and additionally show results on MRI sequences acquired on human subjects. Per-feature tracking times were measured to be 5.7ms with a standard deviation of 1.6ms, sufficient for real-time use.

The new Multi-View Reconstruction (MVR) method for generating 3D vascular images was evaluated experimentally. The MVR method requires only a few digital subtraction angiographic (DSA) projections to reconstruct the 3D model of the vessel object compared to 180 or more projections for standard CBCT. Full micro-CBCT datasets of a contrast filled carotid vessel phantom were obtained using a Microangiography (MA) detector. From these datasets, a few projections were selected for use in the MVR technique. Similar projection views were also obtained using a standard x-ray image intensifier (II) system. A comparison of the 2D views of the MVRs (MA and II derived) with reference micro-CBCT data, demonstrated best agreement with the MA MVRs, especially at the curved part of the phantom. Additionally, the full 3D MVRs were compared with the full micro-CBCT 3D reconstruction resulting for the phantom with the smallest diameter (0.75 mm) vessel, in a mean centerline deviation from the micro-CBCT derived reconstructions of 29 μm for the MA MVR and 48 μm for the II MVR. The comparison implies that an MVR may be substituted for a full micro-CBCT scan for evaluating vessel segments with consequent substantial savings in patient exposure and contrast media injection yet without substantial loss in 3D image content. If a high resolution system with MA detector is used, the improved resolution could be well suited for endovascular image guided interventions where visualization of only a small field of view (FOV) is required.

Purpose: The sensitivity of a new 3D Multi‐View Reconstruction (MVR) angiography technique to the projection angles used is evaluated by comparing 3D centerlines calculated from combinations of three projections acquired from two imaging systems with that from micro‐Cone Beam CT (μCBCT), which is taken as truth. Method and Materials: A 3D centerline of a contrast‐filled carotid vessel phantom was reconstructed from image data acquired using a custom‐made μCBCT system with a microangiographic (MA) detector (45 μm pixels, 4.5 cm field‐of‐view (FOV)). Projection images of the same phantom were also acquired using the MA and an image intensifier (II) detector system (120 μm pixels, 4.5 in FOV) on a C‐arm x‐ray unit. The MVR technique was used to compute 3D centerlines for 12 combinations of projection angles. Each 3D MVR centerline was aligned with the μCBCT “true” 3D centerline using a Procrustes technique, and a root‐mean‐square (RMS) deviation was calculated. Results: The average RMS deviation for the MA‐MVR centerlines is 25 μm with a standard deviation of 3 μm over the 12 different projection‐angle combinations, whereas the average RMS deviation for the II‐MVR centerlines is 41 μm with a standard deviation of 4 μm over these same combinations. The RMS deviation as a percent of the internal vessel diameter, 0.75 mm, is 3.3% for the MA and 5.5% for the II and appears to be independent of view selection. Conclusion: For the MVR technique, the improved resolution of the MA resulted in improved centerline determination compared to the II system. For both detectors, the selection of a particular projection set had little effect on the RMS centerline deviation. The low RMS deviations for both detectors indicate that the MVR technique can provide accurate 3D centerlines. (Partial support from NIH Grants R01‐NS43924, R01‐EB02873, R01‐HL52567, R01‐EB02916, and Toshiba Medical Systems Corporation).