Biomedical Imaging and Computational Modeling in Biomechanics

Cervical smear screening is the most popular method used for the detection of cervical cancer in its early stages. The most eminent screening test is the Pap smear, which is based on the staining of cervical cells, using the technique that was first introduced by George Papanicolaou (Science 1942). With this screening technique, precancerous conditions and abnormal changes in cells that may develop into cancer are recognized. The widespread use of this test in developed countries has significantly reduced the incidence and mortality of invasive cervical cancer. In the last years, many methods have been appeared in the literature, which aim at the automated determination of the cytoplasm and the nucleus in these images. In this context, sophisticated image processing techniques and feature extraction and classification methods have been developed by several researchers, in order to derive useful conclusions for the characterization of the contents of the Pap smear images. In this work, an overview of the published techniques related to cervical smear screening is presented, in order to provide an integrated essay of the state of the art methods in the specific scientific field. Special focus has been paid on two main concepts with great research interest: the cell image segmentation and the classification techniques proposed for the characterization Pap smear images.

The primary mechanical function of bones is to provide rigid levers for muscles to pull against and to remain as light as possible to allow for efficient locomotion. To accomplish this function, bones must adapt their shape and architecture efficiently. Bone tissue during skeletal growth and development continuously adjusts its mass and architecture to changing mechanical environments.

The trabecular structure in bone is the result of a dynamic remodeling process controlled by mechanical loads.

In this study, the process of adaptive bone remodeling is investigated mathematically and simulated by a finite element model. Bone tissue is described as continuous material with variable mass density. Topology optimization and cellular automata models are adopted with the aim to characterize the osteocytes located within the bone as sensors of mechanical signals.

An implemented optimization process provides structures resembling actual trabecular architectures and aligning them with the actual principal stress orientation. Two cost indices are derived from the structural optimization task of simultaneously minimizing the weight and maximizing the stiffness of the investigated domain. A trabecular architecture characterized by the highest structural efficiency is showed as result of the proposed optimal control process.

The abnormalities in the shape and orientation of the femoral head and neck or the acetabulum are important morphological characteristics of femoroacetabular impingement (FAI). Concerns exist about the effect of damaged cartilage on the kinematics of the affected hip joint. The current study is aiming to track the motion of a femur bearing a cam deformity, with healthy or damaged articular cartilage. This may prove useful in understanding the changes occurring in a hip joint with cam-type FAI, as arthritis develops and progresses. A three-dimensional (3D) model of the left hip joint of a male patient diagnosed with FAI was obtained from pre-operative Computerised Tomography (CT) data using density segmentation techniques in Mimics 13.1 (Materialise NV). The kinematics of FAI was analysed in Abaqus 6.9 (Simulia Dassault Systems) using a finite element method. The translation and rotation parameters were defined in a single step for each one of three cases: healthy cartilage, 2mm (one-sided thinning) and 4mm (two-sided thinning) worn-out articular cartilage. As the acetabulum and femur came into contact, the penetrations were detected and the contact constraints were applied according to the penalty constraint enforcement method. The results of the analysis showed that thinning of the cartilage at the hip joint adversely affects impingement, as range of motion was decreased with progressive thinning of the articular cartilage.

Developments in medical imaging and finite element analysis techniques have made it possible to conduct personalized studies on patients. The field of medical implants is especially benefitting from these advancements, where patient specific geometries can be created and analyzed. The present work is focused on using image based techniques for construction of solid models of human knee joints for finite element analysis. Accurate 3D solid models of the human cadaveric knee joint are developed based on a sequence of high resolution MRI images obtained from a Siemens 7T machine. The approach involves identification of various components of the knee joint such as the femur, tibia, femoral and tibial cartilage, and menisci of the tibio-femoral knee joint; construction of a 3D model; smoothing the geometries; meshing of geometry; and then performing finite element analysis. The focus of the present work is on understanding the effect of menisci on the stress and strain distribution in the knee joint. Availability of such image based modeling and analysis methods would help in designing effective meniscal implants.

Hip prosthetic implants represent a consolidated and successful solution to restore functional gait in patients affected by a wide range of disease including osteoarthritis degeneration processes, cancer effects, osteoporosis, traumatic injuries. While at the beginning of the worldwide dissemination of this joint replacement methodology the target patients were mainly part of a quite old population, characterized by moderate physical activity and only asking for restoring of an acceptable quality of life and of functional gait and standing, the scenario significantly changed along the years. Nowadays, hip implants are also used to treat young and active patients; moreover, the amount of expected life years is more and more increasing; and, last but not least, the average body mass of western populations is increasing as well. As an overall consequence of the above changes, hip implants need to be highly performing: they have to cope with many years of repetitive high stresses not only due to regular locomotor daily activities but also to sports, excessive loading, wear and ageing effects. It is thus of extremely relevance for Researchers, Industry, Health Authorities and Users, to gain deeper and deeper knowledge of mechanical properties and performance of hip prosthesis components, and behavior of the musculo-skeletal system which hosts the implant. Potentially dangerous conditions should be clearly identified and investigated so as to prevent implant structural failure, being implant revision highly demanding for patients and health structures in terms of worsening of health status and increase of overall assistance costs. The present chapter investigates the potentialities of research studies in the field of hip implants biomechanics which rely on a synergy between FE modeling and experimental mechanical fatigue tests and whose main goal is to infer about related risks. An example of the implemented methodology is described, and few practical applications are reported, analyzed and commented from clinical, biomechanical and regulatory point of view.

In orthopedic surgery, to decide upon intervention and how it can be optimized, surgeons usually rely on subjective analysis of medical images of the patient, obtained from computed tomography, magnetic resonance imaging, ultrasound or other techniques. Recent advancements in computational performance, image analysis and in silico modeling techniques have started to revolutionize clinical practice through the development of quantitative tools, including patient specific models aiming at improving clinical diagnosis and surgical treatment. Anatomical and surgical landmarks as well as features extraction can be automated allowing for the creation of general or patient specific models based on statistical shape models. Preoperative virtual planning and rapid prototyping tools allow the implementation of customized surgical solutions in real clinical environments. In the present chapter we discuss the applications of some of these techniques in orthopedics and present new computer-aided tools that can take us from image analysis to customized surgical treatment.

High resolution techniques are being increasingly applied to image or measure biomaterial properties. Data interpretations from these measurements have to be performed carefully to extract meaningful information. Two aspects become significant when such techniques are used in a complementary manner. Firstly, the measurements have to be performed using a homotopic methodology such that property correlations or ‘data fusion’ considers the same material volume. Secondly, appropriate mathematical models must be applied to interpret the data in terms of material properties since the high resolution technique seldom measure the properties directly. In this paper, we have described the application of scanning acoustic and scanning electron microscopy to measure the mechanical and the compositional properties of primary tooth dentin using a homotopic methodology. We have then utilized a homogenization technique in order to understand the variation in the measured elastic moduli.

X-ray microtomography is a miniaturized form of traditional axial computerized tomography that allows three dimensional investigations on small radiopaque objects, with an high resolution (about 5–μm), in a non-invasive and non-destructive way.

Compared with the conventional electronical and microscopical techniques that produce only bidimensional images, microCT is used to obtain a three dimensional analysis of a sample with no need to cut and no need of particular chemical treatments at all.

Therefore, X-ray 3D microtomography may satisfy the ideal requirements of 3D microscopy:

This justifies the application of this innovative technique not only in medicine and odontostomatology, but also in biomedical engineering, material science, biology, electronic, geology, archeology, petroleum and semiconductors industries.

In this section of the book will be showed different possibilities of microtomographic applications in biomedical field:

Patient-specific simulations will become in the not so distant future a “de facto” standard in surgical planning and diagnostic. Nowadays, in-silico simulations have the power to explore in detail a system close to its “in-vivo” conditions, and to report values difficult or impossible to characterize due to physical or ethical constraints. The objective of this chapter is to present two applications of patient-specific simulations for heart valves: In Application 1, a coupled 3D-1D of a mechanical heart valve is shown. In application 2, a structural patient-specific study for percutaneous valve implantations is presented.

The aim of this paper was to analyze the viscous flow around different kayak design models, allowing computing hydrodynamic drag force through numerical simulations. The simulations were based on Finite volume method of discretization. Numerical simulations were performed on three different kayak models, corresponding to kayak design evolution of K1 Vanquish M Nelo^TM models (M.A.R. Kayaks Lda, Portugal). The numerical simulations were performed only for the outer shell section of the kayak hull geometry, assumed to be submerged in still water. For a speed of 5.0m/s, it can be observed that the pressure of the bow is larger, and the pressure of the stern is smaller, and variation of pressure of the middle is relatively small. The main results suggest that the evolution from Vanquish I to Vanquish III was succeeded, as shown by the reduction of hydrodynamic drag over the three models studied. In the design of Kayak, one can optimize the shape of the outer surface by combining the pressure and shear stress distribution of the shell.