PURPOSE: The purpose of this study was the simulation of the implantation of intrastromal corneal-ring segments for patients with keratoconus. The aim of the study was the prediction of the corneal curvature recovery after this intervention. METHODS: Seven patients with keratoconus diagnosed and treated by implantation of intrastromal corneal-ring segments were enrolled in the study. The 3D geometry of the cornea of each patient was obtained from its specific topography and a hyperelastic model was assumed to characterize its mechanical behavior. To simulate the intervention, the intrastromal corneal-ring segments were modeled and placed at the same location at which they were placed in the surgery. The finite element method was then used to obtain a simulation of the deformation of the cornea after the ring segment insertion. Finally, the predicted curvature was compared with the real curvature after the intervention. RESULTS: The simulation of the ring segment insertion was validated comparing the curvature change with the data after the surgery. Results showed a flattening of the cornea which was in consonance with the real improvement of the corneal curvature. The mean difference obtained was of 0.74 mm using properties of healthy corneas. CONCLUSIONS: For the first time, a patient-specific model of the cornea has been used to predict the outcomes of the surgery after the intrastromal corneal-ring segments implantation in real patients.
- MeSH
- Finite Element Analysis MeSH
- Biomechanical Phenomena MeSH
- Keratoconus surgery MeSH
- Humans MeSH
- Mechanical Phenomena * MeSH
- Patient-Specific Modeling * MeSH
- Prostheses and Implants * MeSH
- Cornea surgery MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
In vivo linear penetration in total hip arthroplasty (THA) exhibits similar values for 28mm and 32mm femoral head diameter with considerable variations between and within the studies. It indicates factors other than femoral head diameter influence polyethylene wear. This study is intended to test the effect of patient׳s individual geometry of musculoskeletal system, acetabular cup orientation, and radius of femoral head on wear. Variation in patient׳s musculoskeletal geometry and acetabular cup placement is evaluated in two groups of patients implanted with 28mm and 32mm THA heads. Linear wear rate estimated by mathematical model is 0.165-0.185mm/year and 0.157-0.205mm/year for 28 and 32mm THA heads, respectively. Simulations show little influence femoral head size has on the estimated annual wear rate. Predicted annual linear wear depends mostly on the abduction angle of the acetabular cup and individual geometry of the musculoskeletal system of the hip, with the latter having the greatest affect on variation in linear wear rate.
- MeSH
- Acetabulum anatomy & histology physiology MeSH
- Femur Head anatomy & histology physiology MeSH
- Muscle, Skeletal anatomy & histology physiology MeSH
- Hip Prosthesis * MeSH
- Middle Aged MeSH
- Humans MeSH
- Arthroplasty, Replacement, Hip * MeSH
- Patient-Specific Modeling MeSH
- Polyethylene MeSH
- Aged MeSH
- Check Tag
- Middle Aged MeSH
- Humans MeSH
- Male MeSH
- Aged MeSH
- Female MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
In many biomechanical problems, the availability of a suitable model for the wrapping of muscles when undergoing movement is essential for the estimation of forces produced on and by the body during motion. This is an important factor in the Osteoporotic Virtual Physiological Human project which is investigating the likelihood of fracture for osteoporotic patients undertaking a variety of movements. The weakening of their skeletons makes them particularly vulnerable to bone fracture caused by excessive loading being placed on the bones, even in simple everyday tasks. This paper provides an overview of a novel volumetric model that describes muscle wrapping around bones and other muscles during movement, and which includes a consideration of how the orientations of the muscle fibres change during the motion. The method can calculate the form of wrapping of a muscle of medium size and visualize the outcome within tenths of seconds on commodity hardware, while conserving muscle volume. This makes the method suitable not only for educational biomedical software, but also for clinical applications used to identify weak muscles that should be strengthened during rehabilitation or to identify bone stresses in order to estimate the risk of fractures.
- Publication type
- Journal Article MeSH
Purpose: To investigate the effect of patient specific vessel cooling on head and neck hyperthermia treatment planning (HTP). Methods and materials: Twelve patients undergoing radiotherapy were scanned using computed tomography (CT), magnetic resonance imaging (MRI) and contrast enhanced MR angiography (CEMRA). 3D patient models were constructed using the CT and MRI data. The arterial vessel tree was constructed from the MRA images using the 'graph-cut' method, combining information from Frangi vesselness filtering and region growing, and the results were validated against manually placed markers in/outside the vessels. Patient specific HTP was performed and the change in thermal distribution prediction caused by arterial cooling was evaluated by adding discrete vasculature (DIVA) modeling to the Pennes bioheat equation (PBHE). Results: Inclusion of arterial cooling showed a relevant impact, i.e., DIVA modeling predicts a decreased treatment quality by on average 0.19 °C (T90), 0.32 °C (T50) and 0.35 °C (T20) that is robust against variations in the inflow blood rate (|ΔT| < 0.01 °C). In three cases, where the major vessels transverse target volume, notable drops (|ΔT| > 0.5 °C) were observed. Conclusion: Addition of patient-specific DIVA into the thermal modeling can significantly change predicted treatment quality. In cases where clinically detectable vessels pass the heated region, we advise to perform DIVA modeling.
- MeSH
- Blood Vessels anatomy & histology diagnostic imaging MeSH
- Hyperthermia, Induced * MeSH
- Humans MeSH
- Magnetic Resonance Imaging MeSH
- Head and Neck Neoplasms blood supply diagnostic imaging therapy MeSH
- Therapy, Computer-Assisted MeSH
- Tomography, X-Ray Computed MeSH
- Patient-Specific Modeling * MeSH
- Feasibility Studies MeSH
- Temperature MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
With the recent advances in computer-aided technologies and their breach into the medical field, there can be seen more and more successful outcomes, especially in the files of reconstructive prosthetic surgery. With the application of advanced tools for reconstruction of complex shape such as human anatomy, it allowed accurate and fast design of complex implants as a substitution for deformed or damaged regions in the field of maxillofacial surgery. Design, in compliance with application of additive manufacturing (AM) technologies, is starting to gain more recognition as a tool for fast and accurate delivery of patient-specific 3D implants. This paper present a case study where such 3D technologies are used to design and fabricate a patient-specific mandibular implant. Tools for design of complex anatomical surfaces, such as mandible are presented and demonstrated in this paper. As the verification stage, AM technologies are used for visual inspection and surgical procedure planning of the designed 3D model of the mandibular implant.
- MeSH
- Printing, Three-Dimensional MeSH
- Computer-Aided Design * MeSH
- Prosthesis Implantation methods instrumentation MeSH
- Humans MeSH
- Mandibular Prosthesis Implantation * MeSH
- Mandibular Prosthesis * MeSH
- Mandible MeSH
- Mandibular Diseases therapy MeSH
- Imaging, Three-Dimensional MeSH
- Check Tag
- Humans MeSH
The paper deals with the impact of chosen geometric and material factors on maximal stresses in carotid atherosclerotic plaque calculated using patient-specific finite element models. These stresses are believed to be decisive for the plaque vulnerability but all applied models suffer from inaccuracy of input data, especially when obtained in vivo only. One hundred computational models based on ex vivo MRI are used to investigate the impact of wall thickness, MRI slice thickness, lipid core and fibrous tissue stiffness, and media anisotropy on the calculated peak plaque and peak cap stresses. The investigated factors are taken as continuous in the range based on published experimental results, only the impact of anisotropy is evaluated by comparison with a corresponding isotropic model. Design of Experiment concept is applied to assess the statistical significance of these investigated factors representing uncertainties in the input data of the model. The results show that consideration of realistic properties of arterial wall in the model is decisive for the stress evaluation; assignment of properties of fibrous tissue even to media and adventitia layers as done in some studies may induce up to eightfold overestimation of peak stress. The impact of MRI slice thickness may play a key role when local thin fibrous cap is present. Anisotropy of media layer is insignificant, and the stiffness of fibrous tissue and lipid core may become significant in some combinations.
- MeSH
- Finite Element Analysis MeSH
- Carotid Arteries diagnostic imaging pathology MeSH
- Plaque, Atherosclerotic diagnostic imaging pathology MeSH
- Biomechanical Phenomena MeSH
- Humans MeSH
- Magnetic Resonance Imaging MeSH
- Mechanical Phenomena * MeSH
- Models, Cardiovascular MeSH
- Patient-Specific Modeling * MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Background: Hip fractures are a major cause for disability in patients. They require immediate attention as they could otherwise cause death. Hip fractures are almost always treated with surgery by implantation. Implants are of various types accounting for the many variations in hip fractures. Objectives: This paper presents the design and analysis of a hip implant using Finite element analysis. Fracture conditions are determined and the optimal design of the implant is obtained for improving healthcare and patient safety. Methods: Anthropometric parameters of the human femur bone are collected from a particular age group. These are then used to obtain a CAD model of the bone using CATIA. The standard Charnley hip implant, used in total hip replacement surgery is also modeled. The proposed models are analyzed using ANSYS software by assigning appropriate material properties to the bone and implant. The stress distribution is observed when loads corresponding to normal gait conditions are applied. The load at which fracture occurs is then determined experimentally. Results: Based on the analysis results of the modeled bone, the implant is optimized by varying the base cross section, the bio-materials used, and the design parameters so that, its stress response mimics that of the actual bone. It is found that the model no 2 as in Table 6 with head diameter 28mm, neck diameter 10mm, neck angle 128 degrees has minimum strain at the neck region with a value of 0.65 and is found to be suitable for implant design. Results show that initiation of fracture in the implant occurs at 2000N and complete fracture occurs at 2400N. Conclusions: The 3D models are very useful in simulation of bone fractures and internal fixations with implants. In this work, the hip joint and implant model, developed in CATIA software, help to understand how these structures adapt to external forces disturbances [15]. This will help the doctors to chose the optimal implant for a particular patient. This leads to greater accuracy and patient specificity.
- MeSH
- Anthropometry methods MeSH
- Hip Fractures * surgery therapy MeSH
- Humans MeSH
- Musculoskeletal System * anatomy & histology surgery injuries MeSH
- Orthopedic Procedures methods instrumentation trends MeSH
- Computers MeSH
- Prostheses and Implants * MeSH
- Statistics as Topic MeSH
- Imaging, Three-Dimensional * methods instrumentation utilization MeSH
- Check Tag
- Humans MeSH
During the minimally-invasive liver surgery, only the partial surface view of the liver is usually provided to the surgeon via the laparoscopic camera. Therefore, it is necessary to estimate the actual position of the internal structures such as tumors and vessels from the pre-operative images. Nevertheless, such task can be highly challenging since during the intervention, the abdominal organs undergo important deformations due to the pneumoperitoneum, respiratory and cardiac motion and the interaction with the surgical tools. Therefore, a reliable automatic system for intra-operative guidance requires fast and reliable registration of the pre- and intra-operative data. In this paper we present a complete pipeline for the registration of pre-operative patient-specific image data to the sparse and incomplete intra-operative data. While the intra-operative data is represented by a point cloud extracted from the stereo-endoscopic images, the pre-operative data is used to reconstruct a biomechanical model which is necessary for accurate estimation of the position of the internal structures, considering the actual deformations. This model takes into account the patient-specific liver anatomy composed of parenchyma, vascularization and capsule, and is enriched with anatomical boundary conditions transferred from an atlas. The registration process employs the iterative closest point technique together with a penalty-based method. We perform a quantitative assessment based on the evaluation of the target registration error on synthetic data as well as a qualitative assessment on real patient data. We demonstrate that the proposed registration method provides good results in terms of both accuracy and robustness w.r.t. the quality of the intra-operative data.
- MeSH
- Surgery, Computer-Assisted instrumentation methods MeSH
- Adult MeSH
- Fibula blood supply transplantation MeSH
- Mandibular Fractures diagnostic imaging etiology surgery MeSH
- Bone Plates MeSH
- Humans MeSH
- Mandible blood supply diagnostic imaging surgery MeSH
- Computer Simulation MeSH
- Patient-Specific Modeling MeSH
- Mandibular Reconstruction methods MeSH
- Reoperation MeSH
- Free Tissue Flaps blood supply MeSH
- Imaging, Three-Dimensional MeSH
- Check Tag
- Adult MeSH
- Humans MeSH
- Male MeSH
- Publication type
- Letter MeSH
- Case Reports MeSH
Physiologically realistic results are the aim of every blood flow simulation. This is not different in aorto-coronary bypasses where the properties of the coronary circulation may significantly affect the relevance of the performed simulations. By considering three patient-specific bypass geometries, the present article focuses on two aspects of the coronary blood flow - its phasic flow pattern and its behaviour affected by blood rheology. For the phasic flow property, a multiscale modelling approach is chosen as a means to assess the ability of five different types of coronary boundary conditions (mean arterial pressure, Windkessel model and three lumped parameter models) to attain realistic coronary haemodynamics. From the analysed variants of boundary conditions, the best option in terms of physiological characteristics and its potential for use in patient-based simulations, is utilised to account for the effect of shear-dependent viscosity on the resulting haemodynamics and wall shear stress stimulation. Aside from the Newtonian model, the blood rheology is approximated by two non-Newtonian models in order to determine whether the choice of a viscosity model is important in simulations involving coronary circulation. A comprehensive analysis of obtained results demonstrated notable superiority of all lumped parameter models, especially in comparison to the constant outlet pressure, which regardless of bypass type gave overestimated and physiologically misleading results. In terms of rheology, it was noted that blood in undamaged coronary arteries behaves as a Newtonian fluid, whereas in vessels with atypical lumen geometry, such as that of anastomosis or stenosis, its shear-thinning behaviour should not be ignored.
- MeSH
- Hemodynamics * MeSH
- Coronary Vessels * surgery MeSH
- Coronary Circulation MeSH
- Humans MeSH
- Stress, Mechanical MeSH
- Models, Cardiovascular MeSH
- Computer Simulation MeSH
- Blood Flow Velocity MeSH
- Viscosity MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
