KEYWORDS: Arteries, Magnetic resonance imaging, Scanning electron microscopy, Image segmentation, Independent component analysis, Image resolution, Hemodynamics, Aneurysms, Simulation of CCA and DLA aggregates, 3D image processing
Background: Hemodynamics is a driving factor behind remodeling of the cerebral vasculature, yet mechanisms of flowinduced remodeling remain incompletely understood. Studies employing serial imaging could help characterize hemodynamic-induced pathologic and physiologic remodeling of cerebral arteries. Methods: This preliminary study was performed us ing 4 mice. In 3, we induced flow-driven vascular remodeling in the Circle of Willis (CoW). This was done by ligation of the left common carotid artery (CCA), and the right external carot id and pterygopalatine arteries, which resulted in an increase of blood flow through the basilar artery and the right internal carotid artery. The remaining mouse was used as a wild-type control. In the 3 experimental mice, we performed 9.4 Tesla Magnetic Resonance Imaging (MRI) over a span of 3 months. 3D images were reconstructed for serial computational evaluation of gross morphological changes . These measurements were verified by the terminal vascular corrosion casting and scanning electron microscope imaging. Results: This study demonstrated the feasibility to distinguish and serially measure pathologic cerebral vascular changes in the mouse CoW, specifically in the anterior vasculature. We showed that these changes were characterized by compensatory arterial dilation and increased tortuosity on the anterior cerebral artery. From scanning electron microscope images, we also found that there was microscopic damage, akin to aneurysmal remodeling, at the right olfactory artery origin. Conclusions: MRI-based serial imaging has the potential to serially characterize gross morphological changes in the CoW in response to flow manipulation. In the future, combining this analysis with computational fluid dynamics simulations will help to define the hemodynamic environments corresponding to these and other pathologic remodeling changes in the mouse CoW.
Angiographic Parametric Imaging (API) is a quantitative image analysis method that uses a digital subtraction angiography (DSA) to characterize contrast media dynamics throughout vasculature. The parameters acquired through API may be used to assess the success of a neurovascular intervention such as the stenting or coiling of an aneurysm. This imaging tool requires manual contouring of the aneurysm sac and the surrounding vasculature, which is not realistic in an interventional suite. To address this challenge, we studied whether convolutional neural networks can carry out a three-class segmentation problem differentiating between the background, vasculature, and aneurysm sac in a DSA acquisition. Image data were retrospectively collected from patients being monitored or treated for cerebral aneurysms at Gates Vascular Institute. While VGG-16 and U-NET architecture were both investigated, a modified VGG architecture was developed and used. Network training was carried out over 100 epochs. Our training dataset comprised of 12000 DSA acquisitions. Our validation dataset comprised of 2000 DSA acquisitions. The Jaccard Index was above 0.74 for both classes. The Dice similarity coefficient was above 0.83 for both classes. Area under the ROC curve was above 0.72 for both classes. These results indicate good agreement between the ground-truth labels and the network predicted labels. Our network proved not sensitive to motion artifacts or the presence of skull in the image data. This work indicates the potential clinical utility of a convolutional neural network in the context of aneurysm detection in DSA for feature extraction using parametric imaging to support a clinical decision.
Purpose: Angiographic Parametric Imaging (API) based on Digital Subtraction Angiography (DSA) of Intracranial Aneurysms (IA) can provide parameters related to contrast flow. In this study we propose to investigate the use of a Deep Neural Network (DNN) to analyze API parameters to classify IAs as un-treated or treated, quantify the prediction accuracy, and compare its performance with the Naïve Bayes (NB) and K-Nearest Neighbor (KNN) algorithms. Materials and Methods: DSA scans were obtained from patients with un-treated and treated IAs. Three datasets were created based on treatment method: coiled, flow-diverted and combined. These scans were analyzed to provide API parameters for the IA and corresponding main artery. IA parameters were normalized to the main artery parameters. Data was augmented by adding Gaussian noise. The DNN, NB and KNN models were trained on API parameters and tested to classify aneurysms as un-treated or treated. This was performed on each dataset for both normalized and un-normalized data. Results: The DNN had an accuracy and ROC AUC of 72.4% and 0.80 respectively on un-normalized coiled data, 87.9% and 0.95 respectively on normalized coiled data, 73.9% and 0.79 respectively on un-normalized flow-diverted data, 85.3% and 0.80 respectively on normalized flow-diverted data, 62.9% and 0.64 respectively on un-normalized combined data, 64.8% and 0.73 respectively on normalized combined data. Conclusions: This study proves feasibility of using DNNs to classify IAs and make other clinical predictions using normalized API data with treatment methods separated, in addition to being more effective than other classifiers.
Purpose: The purpose of this study is to apply targeted Parametric Imaging on aneurysms to quantitatively investigate contrast flow changes at pre-, post-treatment and follow-up with outcome scoring. Methods: The angiograms for 50 patients were acquired, 25 treated with coil embolization and 25 treated using a flow diverter. API was performed by synthesizing the time density curve (TDC) at every pixel. Based on the TDCs, we calculated various parameters for the quantitative characterization of contrast flow through the vascular network and aneurysms and displayed them using color encoded maps. The parameters included were : Time to Peak (TTP), Mean Transit Time (MTT), Time of Arrival (TTA), Peak Height (PH) and Area Under the Curve (AUC). Two Regions of Interest (ROI) were manually marked over the aneurysm dome and the main artery. Average aneurysm parameter values were normalized to those values recorded in the main artery and recorded pre-/post-treatment and follow-up and compared to Raymond Roy scores and flow diverter stent scoring. Results: The normalized mean values were as follows (pre and post treatment): TTP (1.09+/-0.14, 1.55+/-1.36), MTT (1.07+/-0.23, 1.27+/-0.42), TTA (0.14+/-0.15, 0.26+/-0.23), PH (1.2+/-0.54, 0.95+/-0.83) and AUC (1.29+/-0.69, 1.44+/- 1.92). The neural network gave a validation accuracy of 0.8036 with a loss of 0.0927. A receiver operating characteristic curve with an AUC of 0.866 was obtained. Conclusions: API can quantitatively describe the flow in the aneurysm for initial investigation of the radiomics of intracranial aneurysms. It also shows a clear demarcation between pre and post treatment. Statistical modelling and a machine learning network is used to prove the success of our model.
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