43 research outputs found
Biomechanics of Contemporary Implants and Prosthesis: Modeling, Experiments, and Clinical Application
Modern medicine is now more oriented towards patient-based treatments. Taking into account individual biological features allows for increasing the quality of the healing process. Opportunities for modern hardware and software allow not only the complex behavior of implants and prostheses to be simulated, but also take into account any peculiarities of the patient. Moreover, the development of additive manufacturing expands the opportunities for materials. Technical limits for composite materials, biomaterials, and metamaterials are decreasing. On the other hand, there is a need for more detailed analyses of biomechanics research. A deeper understanding of the technological processes of implants, and the mechanobiological interactions of implants and organisms will potentially allow us to raise the level of medical treatment. Modern trends of the biomechanics of contemporary implants and prostheses, including experimental and mathematical modeling and clinical application, are discussed in this book
Nuevo enfoque morfométrico para el estudio de la biomecánica y adaptación de los homininos del Plio-Pleistoceno
Tesis inédita de la Universidad Complutense de Madrid, Facultad de Geografía e Historia, leída el 06-10-2021En la presente tesis doctoral titulada “Nuevo enfoque morfométrico para el estudio dela biomecánica y adaptación de los homininos del Plio-Pleistoceno” se presenta una nueva metodología para el análisis de los huesos largos de grandes simios a partir del uso de modelos tridimensionales, haciendo especial hincapié en la interpretación biomecánica de los restos fósiles relativos a especies de nuestra familia evolutiva. Los recientes hallazgos de nuevas especies fósiles humanas han puesto de manifiesto la gran complejidad de nuestra historia evolutiva y las dificultades que entraña su interpretación. Añadido a esto, el estudio de los huesos largos (húmero, radio, cúbito, fémur, tibia y fíbula) de especies homininas anteriores a la nuestra resulta especialmente problemático por una serie de razones entre las que destaca la obtención de información a partir de restos de pequeño tamaño que, en ocasiones, aparecen muy fragmentados en los yacimientos. Asimismo, existen otro tipo de limitaciones que afectan al estudio de la morfología y biomecánica de los huesos largos, entre las que se encuentran la baja integridad del registro fósil y la escasez de restos postcraneales, la dificultad para delimitar los factores que influyen en la morfología de los huesos y que, por lo tanto, pueden mermar la estimación del vínculo existente entre morfología y función, y el uso de muestras comparativas que incluyen un número muy limitado de grupos y morfologías. Esta tesis doctoral tiene como objetivo principal el desarrollo de un nuevo enfoque morfométrico para el estudio de la biomecánica y adaptación de los homininos del Plio-Pleistoceno apoyado en una caracterización muy detallada de la morfologíaexterna de los huesos largos y la implementación de modelos de clasificación de alta precisión...In the present doctoral thesis entitled "A new morphometric approach to the study of Plio-Pleistocene hominin biomechanics and adaptation" a new 3D methodology for the analysis of great ape long bones with special emphasis on the biomechanical interpretation of human fossil remains is introduced. Recent findings of human fossil specimens and taxa have revealed the great complexity of our evolutionary history and the difficulties involved in its comprehension and interpretation. Moreover, the study of hominin long bone remains (humerus, radius, ulna, femur, tibia, fibula) in Palaeoanthropologyis particularly problematic due to the difficulties involved in the analysis of fragmentary skeletal elements that in many occasions are merely represented by small diaphyseal portions. On top of that, there are several additional limitations that affect our ability to study fossil long bone morphology and draw biomechanical inferences, such as the scarcity and poor integrity of the fossil record; the delimitation of the factors that influence morphology and that might diminish the link between bone morphologyand function; and the widespread use of limited modern reference samples that encompass low degrees of interspecific variability. The main objective of the present research is the development of a new morphometric approach to the study of Plio-Pleistocene hominin biomechanics and adaptation that relies on the detailed quantitative characterisation of the external long bone morphology and the implementation of powerful classification methods...Fac. de Geografía e HistoriaTRUEunpu
Surgical planning model generation by extracting important feature sets in mandibular reconstruction
医師は医学知識と経験を駆使して医療行為を遂行しており, その判断基準が明確になれば手術手技の体系化に繋がると考えられる. これまでに下顎骨再建計画を対象として, 多クラス分類に対応したLasso解列挙を提案したが, 特徴量組の探索に要する計算量が大きい点が課題であった. 本研究では, 頻出特徴量を優先的に選出する多クラス分類問題に対応したLasso解列挙アルゴリズムを提案し, 可読性の高い低次元特徴量群に基づく手術計画モデルの生成を試みた. 232の手術計画例を対象とした実験により, 従来の約76%の計算時間で医師の手術計画を90%以上の正解率で再現する5次元の特徴量組を抽出したので報告する.Because implicit medical knowledge and experience are used to perform medical treatment, such decisions must be clarified when systematizing surgical procedures. We proposed the enumaration of Lasso solutions corresponding to multiple classes in mandibular reconstruction, but the calculation amount required to search feature sets was large. In this study, we propose the enumeration of Lasso solutions algorithm for multi-class classification that preferentioally selects frequently features. Experiments showed that the 5-dimensional feature set which can correctly estimate more than 90% of surgeons' plans with 76% calculation time compared to the previous methods
U-Net based deep convolutional neural network models for liver segmentation from CT scan images
Liver segmentation is a critical task for diagnosis, treatment and follow-up processes of liver cancer. Computed Tomography (CT) scans are the common medical image modality for the segmentation task. Liver segmentation is considered a very hard task for many reasons. Medical images are limited for researchers. Liver shape is changing based on the patient position during the CT scan process, and varies from patient to another based on the health conditions. Liver and other organs, for example heart, stomach, and pancreas, share similar gray scale range in CT images. Liver treatment using surgery operations is very critical because liver contains significant amount of blood and the position of liver is very close to critical organs like heart, lungs, stomach, and crucial blood veins. Therefore the accuracy of segmentation is critical to define liver and tumors shape and position especially when the treatment surgery conducted using radio frequency heating or cryoablation needles.
In the literature, convolutional neural networks (CNN) have achieved very high accuracy on liver segmentation and the U-Net model is considered the state-of-the-art for the medical image segmentation task. Many researchers have developed CNN models based on U-Net and stacked U-Nets with/without bridged connections. However, CNN models need significant number of labeled samples for training and validation which is not commonly available in the case of liver CT images. The process of generating manual annotated masks for the training samples are time consuming and need involvement of expert clinical doctors. Data augmentation has thus been widely used in boosting the sample size for model training.
Using rotation with steps of 15o and horizontal and vertical flipping as augmentation techniques, the lack of dataset and training samples issue is solved. The choice of rotation and flipping because in the real life situations, most of the CT scans recorded while the while patient lies on face down or with 45o, 60o,90o on right side according to the location of the tumor. Nonetheless, such process has brought up a new issue for liver segmentation. For example, due to the augmentation operations of rotation and flipping, the trained model detected part of the heart as a liver when it is on the wrong side of the body.
The first part of this research conducted an extensive experimental study of U-Net based model in terms of deeper and wider, and variant bridging and skip-connections in order to give recommendation for using U-Net based models. Top-down and bottom-up approaches were used to construct variations of deeper models, whilst two, three, and four stacked U-Nets were applied to construct the wider U-Net models. The variation of the skip connections between two and three U-Nets are the key factors in the study. The proposed model used 2 bridged U-Nets with three extra skip connections between the U-Nets to overcome the flipping issue. A new loss function based on minimizing the distance between the center of mass between the predicted blobs has also enhanced the liver segmentation accuracy. Finally, the deep-supervision concept was integrated with the new loss functions where the total loss was calculated as the sum of weighted loss functions over each weighted deeply supervision. It has achieved a segmentation accuracy of up to 90%.
The proposed model of 2 bridged U-Nets with compound skip-connections and specific number of levels, layers, filters, and image size has increased the accuracy of liver segmentation to ~90% whereas the original U-Net and bridged nets have recorded a segmentation accuracy of ~85%. Although applying extra deeply supervised layers and weighted compound of dice coefficient and centroid loss functions solved the flipping issue with ~93%, there is still a room for improving the accuracy by applying some image enhancement as pre-processing stage
Case series of breast fillers and how things may go wrong: radiology point of view
INTRODUCTION: Breast augmentation is a procedure opted by women to overcome sagging
breast due to breastfeeding or aging as well as small breast size. Recent years have shown the
emergence of a variety of injectable materials on market as breast fillers. These injectable
breast fillers have swiftly gained popularity among women, considering the minimal
invasiveness of the procedure, nullifying the need for terrifying surgery. Little do they know
that the procedure may pose detrimental complications, while visualization of breast
parenchyma infiltrated by these fillers is also deemed substandard; posing diagnostic
challenges. We present a case series of three patients with prior history of hyaluronic acid and
collagen breast injections.
REPORT: The first patient is a 37-year-old lady who presented to casualty with worsening
shortness of breath, non-productive cough, central chest pain; associated with fever and chills
for 2-weeks duration. The second patient is a 34-year-old lady who complained of cough, fever
and haemoptysis; associated with shortness of breath for 1-week duration. CT in these cases
revealed non thrombotic wedge-shaped peripheral air-space densities.
The third patient is a 37‐year‐old female with right breast pain, swelling and redness for 2-
weeks duration. Previous collagen breast injection performed 1 year ago had impeded
sonographic visualization of the breast parenchyma. MRI breasts showed multiple non-
enhancing round and oval shaped lesions exhibiting fat intensity.
CONCLUSION: Radiologists should be familiar with the potential risks and hazards as well
as limitations of imaging posed by breast fillers such that MRI is required as problem-solving
tool
Automatic Segmentation of the Mandible for Three-Dimensional Virtual Surgical Planning
Three-dimensional (3D) medical imaging techniques have a fundamental role in the field of oral and maxillofacial surgery (OMFS). 3D images are used to guide diagnosis, assess the severity of disease, for pre-operative planning, per-operative guidance and virtual surgical planning (VSP). In the field of oral cancer, where surgical resection requiring the partial removal of the mandible is a common treatment, resection surgery is often based on 3D VSP to accurately design a resection plan around tumor margins. In orthognathic surgery and dental implant surgery, 3D VSP is also extensively used to precisely guide mandibular surgery. Image segmentation from the radiography images of the head and neck, which is a process to create a 3D volume of the target tissue, is a useful tool to visualize the mandible and quantify geometric parameters. Studies have shown that 3D VSP requires accurate segmentation of the mandible, which is currently performed by medical technicians. Mandible segmentation was usually done manually, which is a time-consuming and poorly reproducible process. This thesis presents four algorithms for mandible segmentation from CT and CBCT and contributes to some novel ideas for the development of automatic mandible segmentation for 3D VSP. We implement the segmentation approaches on head and neck CT/CBCT datasets and then evaluate the performance. Experimental results show that our proposed approaches for mandible segmentation in CT/CBCT datasets exhibit high accuracy
Characterization of alar ligament on 3.0T MRI: a cross-sectional study in IIUM Medical Centre, Kuantan
INTRODUCTION: The main purpose of the study is to compare the normal anatomy of alar
ligament on MRI between male and female. The specific objectives are to assess the prevalence
of alar ligament visualized on MRI, to describe its characteristics in term of its course, shape and
signal homogeneity and to find differences in alar ligament signal intensity between male and
female. This study also aims to determine the association between the heights of respondents
with alar ligament signal intensity and dimensions.
MATERIALS & METHODS: 50 healthy volunteers were studied on 3.0T MR scanner
Siemens Magnetom Spectra using 2-mm proton density, T2 and fat-suppression sequences. Alar
ligament is depicted in 3 planes and the visualization and variability of the ligament courses,
shapes and signal intensity characteristics were determined. The alar ligament dimensions were
also measured.
RESULTS: Alar ligament was best depicted in coronal plane, followed by sagittal and axial
planes. The orientations were laterally ascending in most of the subjects (60%), predominantly
oval in shaped (54%) and 67% showed inhomogenous signal. No significant difference of alar
ligament signal intensity between male and female respondents. No significant association was
found between the heights of the respondents with alar ligament signal intensity and dimensions.
CONCLUSION: Employing a 3.0T MR scanner, the alar ligament is best portrayed on coronal
plane, followed by sagittal and axial planes. However, tremendous variability of alar ligament as
depicted in our data shows that caution needs to be exercised when evaluating alar ligament,
especially during circumstances of injury
The use of near infrared spectroscopy (NIRS) to measure vascular haemodynamics in human bone tissue in vivo
Rationale: Poor cardiovascular health is associated with reduced bone strength and increased risk of fragility fracture. However, direct measurement of intraosseous vascular health is difficult due to the density and mineral content of bone. The aim of this PhD project was to investigate the feasibility of near infrared spectroscopy (NIRS) for the investigation of vascular haemodynamics in human bone in vivo. NIRS provides inexpensive, non-invasive, safe, and real time data on changes in oxygenated and deoxygenated haemoglobin concentration at superficial anatomical sites. NIRS utilises a source optode of near infrared (NIR) light and detector optode that obtains representative data of the interactions of NIR photons with tissue. Method: A systematic review was performed identifying the current existing applications of NIRS (and similar technologies) for measuring human bone tissue in vivo. This review informed the development of an arterial occlusion protocol for obtaining haemodynamic measurements of the proximal tibia and lateral calf, including assessment of the protocol’s reliability. For thirty-six participants, NIRS results were also compared to alternative tests of bone haemodynamics involving dynamic contrast enhanced MRI (DCE-MRI), and measures of general bone health based on dual x-ray absorptiometry testing and blood markers of bone metabolism. Results: This thesis presents novel data demonstrating NIRS can obtain acceptably reliable markers of haemodynamics at the proximal tibia in vivo, comparable with reliability assessments of alternative modalities measuring intraosseous haemodynamics, and the use of NIRS for measuring muscle. Novel associations have been demonstrated between haemodynamic markers measured with NIRS and DCE-MRI, giving confidence NIRS truly represents bone haemodynamics. Increased NIRS markers of oxygen extraction during occlusion, and greater post-ischaemic vascular response to occlusion, were both associated with greater bone mineral density. Conclusion: As a feasibility study, this PhD project has demonstrated the potential for NIRS to contribute to research around the potential pathophysiological role of vascular dysfunction within bone tissue, but also the limitations and need for further development of NIRS technology.The Royal College of Radiologist