Computational Simulations for Aortic Coarctation: Representative Results From a Sampling of Patients

Treatments for coarctation of the aorta (CoA) can alleviate blood pressure (BP) gradients(D), but long-term morbidity still exists that can be explained by altered indices of hemodynamics and biomechanics. We introduce a technique to increase our understanding of these indices for CoA under resting and nonresting conditions, quantify their contribution to morbidity, and evaluate treatment options. Patient-specific computational fluid dynamics (CFD) models were created from imaging and BP data for one normal and four CoA patients (moderate native CoA: D12 mmHg, severe native CoA: D25 mmHg and postoperative end-to-end and end-to-side patients: D0 mmHg). Simulations incorporated vessel deformation, downstream vascular resistance and compliance. Indices including cyclic strain, time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were quantified. Simulations replicated resting BP and blood flow data. BP during simulated exercise for the normal patient matched reported values. Greatest exercise-induced increases in systolic BP and mean and peak DBP occurred for the moderate native CoA patient (SBP: 115 to 154 mmHg; mean and peak DBP: 31 and 73 mmHg). Cyclic strain was elevated proximal to the coarctation for native CoA patients, but reduced throughout the aorta after treatment. A greater percentage of vessels was exposed to subnormal TAWSS or elevated OSI for CoA patients. Local patterns of these indices reported to correlate with atherosclerosis in normal patients were accentuated by CoA. These results apply CFD to a range of CoA patients for the first time and provide the foundation for future progress in this area

TrauMAP - Integrating Anatomical and Physiological Simulation (Dissertation Proposal)

In trauma, many injuries impact anatomical structures, which may in turn affect physiological processes - not only those processes within the structure, but also ones occurring in physical proximity to them. Our goal with this research is to model mechanical interactions of different body systems and their impingement on underlying physiological processes. We are particularly concerned with pathological situations in which body system functions that normally do not interact become dependent as a result of mechanical behavior. Towards that end, the proposed TRAUMAP system (Trauma Modeling of Anatomy and Physiology) consists of three modules: (1) a hypothesis generator for suggesting possible structural changes that result from the direct injuries sustained; (2) an information source for responding to operator querying about anatomical structures, physiological processes, and pathophysiological processes; and (3) a continuous system simulator for simulating and illustrating anatomical and physiological changes in three dimensions. Models that can capture such changes may serve as an infrastructure for more detailed modeling and benefit surgical planning, surgical training, and general medical education, enabling students to visualize better, in an interactive environment, certain basic anatomical and physiological dependencies

Aortic Coarctation: Recent Developments in Experimental and Computational Methods to Assess Treatments for this Simple Condition

Coarctation of the aorta (CoA) is often considered a relatively simple disease, but long-term outcomes suggest otherwise as life expectancies are decades less than in the average population and substantial morbidity often exists. What follows is an expanded version of collective work conducted by the authors\u27 and numerous collaborators that was presented at the 1st International Conference on Computational Simulation in Congenital Heart Disease pertaining to recent advances for CoA. The work begins by focusing on what is known about blood flow, pressure and indices of wall shear stress (WSS) in patients with normal vascular anatomy from both clinical imaging and the use of computational fluid dynamics (CFD) techniques. Hemodynamic alterations observed in CFD studies from untreated CoA patients and those undergoing surgical or interventional treatment are subsequently discussed. The impact of surgical approach, stent design and valve morphology are also presented for these patient populations. Finally, recent work from a representative experimental animal model of CoA that may offer insight into proposed mechanisms of long-term morbidity in CoA is presented

Virtual interactive musculoskeletal system (VIMS) in orthopaedic research, education and clinical patient care

The ability to combine physiology and engineering analyses with computer sciences has opened the door to the possibility of creating the "Virtual Human" reality. This paper presents a broad foundation for a full-featured biomechanical simulator for the human musculoskeletal system physiology. This simulation technology unites the expertise in biomechanical analysis and graphic modeling to investigate joint and connective tissue mechanics at the structural level and to visualize the results in both static and animated forms together with the model. Adaptable anatomical models including prosthetic implants and fracture fixation devices and a robust computational infrastructure for static, kinematic, kinetic, and stress analyses under varying boundary and loading conditions are incorporated on a common platform, the VIMS (Virtual Interactive Musculoskeletal System). Within this software system, a manageable database containing long bone dimensions, connective tissue material properties and a library of skeletal joint system functional activities and loading conditions are also available and they can easily be modified, updated and expanded. Application software is also available to allow end-users to perform biomechanical analyses interactively. Examples using these models and the computational algorithms in a virtual laboratory environment are used to demonstrate the utility of these unique database and simulation technology. This integrated system, model library and database will impact on orthopaedic education, basic research, device development and application, and clinical patient care related to musculoskeletal joint system reconstruction, trauma management, and rehabilitation

Custom software for the 3D printing of patient specific plate bending templates in pelvic fracture repair.

The purpose of this work is to reduce the operative time and blood loss incurred during open reduction and internal fixation (ORIF) of traumatic pelvic injuries through the creation of patient specific bending templates for reconstruction plates. These templates are 3D printed in a resin capable of being sterilized and taken into the operating room so that bending may be performed by the surgeon before the patient is opened or by another team member in parallel with the surgeon. A novel software extension was created in 3D modeling software to allow a surgeon to individually position screws on a pelvic model to create a virtual plate. The software constrains the locations of placed screws so that the virtual plate is dimensionally identical to common reconstruction plates. The user is then able to export a bending template that includes the section of the pelvis the virtual plate was located on as well as screw location landmarks. The user can then flash sterilize the template and use it intraoperatively to obtain a plate that is accurately bent to the patient’s anatomy and the surgeon’s specifications. We produced a bending template representative of the most complex plating location on the pelvis, the posterior wall. A surgeon then accurately bent reconstruction plate to match the bending template, proving that the software produced a dimensionally accurate output. Other work has shown that the pre-bending of plates can shorten operative time, reduce blood loss, and allow for less invasive procedures. However, methods currently available for pre-bending patient specific plates involve the lengthy process of printing the patient’s pelvis and then a lengthy sterilization process of the implant itself. Our method allows the template to be printed and processed in as little as 3 hours and sterilized by autoclave in less than 10 minutes. Further work needs to be done to evaluate how the process works when used in a patient case, to statistically prove that our method reduces operative time and blood loss, and show that plates bent using our method are similar between all members of the surgical team

Biomechanical Stress and Strain Analysis of Mandibular Human Region from Computed Tomography to Custom Implant Development

Currently computational tools are helping and improving the processes and testing procedures in several areas of knowledge. Computed tomography (CT) is a diagnostic tool already consolidated and now beginning to be used as a tool for something even more innovative, creating biomodels. Biomodels are anatomical physical copies of human organs and tissues that are used for diagnosis and surgical planning. The use of tomographic images in the creation of biomodels has been arousing great interest in the medical and bioengineering area. In addition to creating biomodels by computed tomography it is also possible, using this process, to create mathematical models to perform computer simulations and analyses of regions of interest. This paper discusses the creation of a biomodel of the skull-mandibular region of a patient from CT for study and evaluation of efforts in the area of the temporomandibular joint (TMJ) aiming at the design and development of a TMJ custom prosthesis. The evaluation of efforts in the TMJ region due to the forces of mastication was made using the finite element method and the results were corroborated by comparison with mandibular models studied in similar works

The Use of Tactile Sensors in Oral and Maxillofacial Surgery: An Overview

Background: This overview aimed to characterize the type, development, and use of haptic technologies for maxillofacial surgical purposes. The work aim is to summarize and evaluate current advantages, drawbacks, and design choices of presented technologies for each field of application in order to address and promote future research as well as to provide a global view of the issue. Methods: Relevant manuscripts were searched electronically through Scopus, MEDLINE/PubMed, and Cochrane Library databases until 1 November 2022. Results: After analyzing the available literature, 31 articles regarding tactile sensors and interfaces, sensorized tools, haptic technologies, and integrated platforms in oral and maxillofacial surgery have been included. Moreover, a quality rating is provided for each article following appropriate evaluation metrics. Discussion: Many efforts have been made to overcome the technological limits of computed assistant diagnosis, surgery, and teaching. Nonetheless, a research gap is evident between dental/maxillofacial surgery and other specialties such as endovascular, laparoscopic, and microsurgery; especially for what concerns electrical and optical-based sensors for instrumented tools and sensorized tools for contact forces detection. The application of existing technologies is mainly focused on digital simulation purposes, and the integration into Computer Assisted Surgery (CAS) is far from being widely actuated. Virtual reality, increasingly adopted in various fields of surgery (e.g., sino-nasal, traumatology, implantology) showed interesting results and has the potential to revolutionize teaching and learning. A major concern regarding the actual state of the art is the absence of randomized control trials and the prevalence of case reports, retrospective cohorts, and experimental studies. Nonetheless, as the research is fast growing, we can expect to see many developments be incorporated into maxillofacial surgery practice, after adequate evaluation by the scientific community

Atrial fibrillation dynamics and ionic block effects in six heterogeneous human 3D virtual atria with distinct repolarization dynamics

Atrial fibrillation (AF) usually manifests as reentrant circuits propagating through the whole atria creating chaotic activation patterns. Little is yet known about how differences in electrophysiological and ionic properties between patients modulate reentrant patterns in AF. The goal of this study is to quantify how variability in action potential duration (APD) at different stages of repolarization determines AF dynamics and their modulation by ionic block using a set of virtual whole-atria human models. Six human whole-atria models are constructed based on the same anatomical structure and fiber orientation, but with different electrophysiological phenotypes. Membrane kinetics for each whole-atria model are selected with distinct APD characteristics at 20, 50, and 90% repolarization, from an experimentally calibrated population of human atrial action potential models, including AF remodeling and acetylcholine parasympathetic effects. Our simulations show that in all whole-atria models, reentrant circuits tend to organize around the pulmonary veins and the right atrial appendage, thus leading to higher dominant frequency (DF) and more organized activation in the left atrium than in the right atrium. Differences in APD in all phases of repolarization (not only APD90) yielded quantitative differences in fibrillation patterns with long APD associated with slower and more regular dynamics. Long APD50 and APD20 were associated with increased interatrial conduction block and interatrial differences in DF and organization index, creating reentry instability and self-termination in some cases. Specific inhibitions of IK1, INaK, or INa reduce DF and organization of the arrhythmia by enlarging wave meandering, reducing the number of secondary wavelets, and promoting interatrial block in all six virtual patients, especially for the phenotypes with short APD at 20, 50, and/or 90% repolarization. This suggests that therapies aiming at prolonging the early phase of repolarization might constitute effective antiarrhythmic strategies for the pharmacological management of AF. In summary, simulations report significant differences in atrial fibrillatory dynamics resulting from differences in APD at all phases of repolarization

Methods for Modeling and Predicting Mechanical Deformations of the Breast During Interventional Procedures

When doing high field (1.5T) magnetic resonance breast imaging, the use of compression plate during imaging after a contrast-agent injection may critically change the enhancement characteristics of the tumor, making the tracking of its boundaries very difficult. A new method for clinical breast biopsy is presented based on a deformable finite element model of the breast. The geometry of the model is constructed from MR data, and its mechanical properties are based on a non-linear material model. This method allows imaging the breast without compression before the procedure, then compressing the breast and using the finite element model to predict the tumor’s position. The axial breast contours and the segmented slices are ported to a custom-written MR-image contour analysis program, which generates a finite element model (FEM) input file readable by a commercial FEM software. A deformable silicon gel phantom was built to study the movements of an inclusion inside a deformable environment. The hyperelastic properties of the phantom materials were evaluated on an Instron Model 1331 mechanical testing machine. The phantom was placed in a custom-built pressure device, where a pressure plate caused a 14% (9.8mm) compression. The phantom was imaged in a 1.5T magnet (axial and coronal), in the undeformed and deformed states. An FEM of the phantom was built using the custom-written software from the MR data, and another FEM of the phantom was built using a commercial pre-processor from the phantom’s directly measured dimensions. The displacements of the inclusion center and its boundaries were calculated, both from the experimental and FEM results. The calculated displacements from both models are within 0.5mm of each other, and agree within 1.0mm with the experimental results. This difference is within the imaging error