Christian Herz, Nicolas Vergnet, Sijie Tian, Abdullah Aly, Matthew Jolley, Nathanael Tran, Gabriel Arenas, Andras Lasso, Nadav Schwartz, Kathleen O’Neill, Paul Yushkevich, Alison Pouch
PurposeDeformable medial modeling is an inverse skeletonization approach to representing anatomy in medical images, which can be used for statistical shape analysis and assessment of patient-specific anatomical features such as locally varying thickness. It involves deforming a pre-defined synthetic skeleton, or template, to anatomical structures of the same class. The lack of software for creating such skeletons has been a limitation to more widespread use of deformable medial modeling. Therefore, the objective of this work is to present an open-source user interface (UI) for the creation of synthetic skeletons for a range of medial modeling applications in medical imaging.ApproachA UI for interactive design of synthetic skeletons was implemented in 3D Slicer, an open-source medical image analysis application. The steps in synthetic skeleton design include importation and skeletonization of a 3D segmentation, followed by interactive 3D point placement and triangulation of the medial surface such that the desired branching configuration of the anatomical structure’s medial axis is achieved. Synthetic skeleton design was evaluated in five clinical applications. Compatibility of the synthetic skeletons with open-source software for deformable medial modeling was tested, and representational accuracy of the deformed medial models was evaluated.ResultsThree users designed synthetic skeletons of anatomies with various topologies: the placenta, aortic root wall, mitral valve, cardiac ventricles, and the uterus. The skeletons were compatible with skeleton-first and boundary-first software for deformable medial modeling. The fitted medial models achieved good representational accuracy with respect to the 3D segmentations from which the synthetic skeletons were generated.ConclusionsSynthetic skeleton design has been a practical challenge in leveraging deformable medial modeling for new clinical applications. This work demonstrates an open-source UI for user-friendly design of synthetic skeletons for anatomies with a wide range of topologies.
3D echocardiography (3DE) is the standard modality for visualizing heart valves and their surrounding anatomical structures. Commercial cardiovascular ultrasound systems commonly offer a set of parameters that allow clinical users to modify, in real time, visual aspects of the information contained in the echocardiogram. To our knowledge, there is currently no work that demonstrates if the methods currently used by commercial platforms are optimal. In addition, current platforms have limitations in adjusting the visibility of anatomical structures, such as reducing information that obstructs anatomical structures without removing essential clinical information. To overcome this, the present work proposes a new method for 3DE visualization based on “focus + context” (F+C), a concept which aims to present a detailed region of interest while preserving a less detailed overview of the surrounding context. The new method is intended to allow clinical users to modify parameter values differently within a certain region of interest, independently from the adjustment of contextual information. To validate this new method, a user study was conducted amongst clinical experts. As part of the user study, clinical experts adjusted parameters for five echocardiograms of patients with complete atrioventricular canal defect (CAVC) using both the method conventionally used by commercial platforms and the proposed method based on F+C. The results showed relevance for the F+C-based method to visualize 3DE of CAVC patients, where users chose significantly different parameter values with the F+C-based method.
Hypoplastic left heart syndrome is a severe congenital heart defect requiring surgical intervention shortly after birth. The surgery is complex and often leads to complications requiring additional surgeries. Understanding the relationship between the structure of the tricuspid valve and functional complications could lead to more powerful diagnostic and treatment options. Because the tricuspid valve does not have spherical topology, many traditional methods for creating boundary-based or skeleton-based shape models that require spherical parameterization of an object are not applicable unless individual leaflets are independently parameterized and then merged in a multi-object model. Instead we propose to create skeletal models (s-reps) of the entire tricuspid valve structure using a cylindrical parameterization. We modify a traditional cylindrical parameterization approach by adaptively changing angle sampling based on landmarks to produce anatomically relevant correspondence across a population of objects. From this we derive s-reps which yield an improved shape space and classification performance compared with previous approaches.
KEYWORDS: Process modeling, 3D modeling, Heart, Silicon, Pathology, Image segmentation, Data modeling, Ultrasonography, Surgery, Visual process modeling
Physical replicas of patient specific heart valve pathologies may improve clinicians’ ability to plan the optimal treatment for patients with complex valvular heart disease. Our previous work has demonstrated the ability to replicate patient pathology of the adult mitral valve (MV) in a dynamic environment [13]. Infant congenital heart defects present possibly the most challenging form of valvular disease, given the range of pathologies, the relative size of these valves compared to adult anatomy, and the rarity of congenital heart disease. Patient specific valve models could be particularly valuable for pediatric cardiologists and surgeons, as a means to both plan for and practice interventions. Our current goal is to assess our ability to apply our workflow to the more challenging case of the tricuspid valve (TV) presented in cases of hypoplastic left heart syndrome (HLHS). We explore the feasibility of adapting our previous workflow for creating dynamic silicone MV models for pre-surgical planning and simulation training, to developing 3D echocardiogram derived, patient specific TV models for use in a physical heart simulator. These models are intended for characterization of the TV, and exploration of the relationship between specific anatomical features and tricuspid regurgitation (TR) severity. The simulations may be relevant to pre-surgical planning of repair of the particularly complex and unique anatomical pathologies presented in children with HLHS.
PURPOSE: Patient-specific heart and valve models have shown promise as training and planning tools for heart surgery, but physically realistic valve models remain elusive. Available proprietary, simulation-focused heart valve models are generic adult mitral valves and do not allow for patient-specific modeling as may be needed for rare diseases such as congenitally abnormal valves. We propose creating silicone valve models from a 3D-printed plastic mold as a solution that can be adapted to any individual patient and heart valve at a fraction of the cost of direct 3D-printing using soft materials. METHODS: Leaflets of a pediatric mitral valve, a tricuspid valve in a patient with hypoplastic left heart syndrome, and a complete atrioventricular canal valve were segmented from ultrasound images. A custom software was developed to automatically generate molds for each valve based on the segmentation. These molds were 3D-printed and used to make silicone valve models. The models were designed with cylindrical rims of different sizes surrounding the leaflets, to show the outline of the valve and add rigidity. Pediatric cardiac surgeons practiced suturing on the models and evaluated them for use as surgical planning and training tools. RESULTS: Five out of six surgeons reported that the valve models would be very useful as training tools for cardiac surgery. In this first iteration of valve models, leaflets were felt to be unrealistically thick or stiff compared to real pediatric leaflets. A thin tube rim was preferred for valve flexibility. CONCLUSION: The valve models were well received and considered to be valuable and accessible tools for heart valve surgery training. Further improvements will be made based on surgeons’ feedback.
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