INTRODUCTION: Micro level finite element (μFE) models of trabecular bone have a variety of possib... more INTRODUCTION: Micro level finite element (μFE) models of trabecular bone have a variety of possible applications that include understanding fracture mechanism in normal and osteoporotic bone and examining the mechanical response of bone to implants. Previous investigators used images or CT attenuations of real bone samples to develop μFE models. This involves: generating images of a bone sample using, for example, μ-CT; converting CT attenuations to elastic moduli; and mapping elastic moduli to 3D finite elements. The computational models created using these methods can only represent the samples used in their construction and any possible variations due to factors such as anatomical site, sex, age or degree of osteoporosity cannot be included without additional sample collection and processing. To authenticate any hypothesis it is essential to consider a wide range of samples with different characteristics. It is a colossal task to generate 3D μFE models from real samples for this ...
References: [1] Kolipaka, Proc Joint Annual Meeting ISMRM-ESMRMB 2010 [2] Holzapfel, Ann Biomed E... more References: [1] Kolipaka, Proc Joint Annual Meeting ISMRM-ESMRMB 2010 [2] Holzapfel, Ann Biomed Eng 2002; 30: 753-767 Summary: Hooke’s law states that the strain in a linearly elastic material is proportional to the applied load. Magnetic Resonance Elastography (MRE) uses this principle to deduce tissue stiffness by measuring the deformation created by externally generated waves, albeit using more complicated algorithms. Computational modelling can be used to demonstrate the feasibility of arterial MRE by showing the disruption of shear waves through a healthy vessel and an idealised fibrous and lipid plaque.
Apparent (macro level) stiffness directionality (anisotropy) of trabecular bone has received cons... more Apparent (macro level) stiffness directionality (anisotropy) of trabecular bone has received considerable attention in previous reseach, which has also identified ‘bone response to mechanical forces’ as the cause. Anisotropy of cortical bone stiffness has received relatively little attention. The effect of increased porosity (due to age or disease) on the directionality of cortical bone stiffness has not been considered before. To address these issues the present study evaluated the variation of orthotropic elastic constants of cortical bone from the female anterior femoral midshaft. Micro-finite-element (μFE) analysis of bone samples from 27 female donors (age 53.4 ±23.6) were conducted to quantify the elastic constants at the periosteal and endosteal aspects. The ratio of canal volume to tissue volume (Ca.V/TV), analogous to porosity, was found to be the most significant predictor (r = 0.958) of the elastic constants. As would be expected stiffness decreases with increasing Ca.V/T...
Assessment of the rupture risk of plaque is commonly made via imaging of the lumen reduction. How... more Assessment of the rupture risk of plaque is commonly made via imaging of the lumen reduction. However it is known that this is an imperfect criterion and that other features, such as plaque stiffness, may be more relevant. Magnetic Resonance Elastography (MRE) estimates the stiffness of tissues using inversion algorithms applied to the displacement of the tissue, measured in response to the induction of a shear wave from an external actuator. An idealised diseased vessel, embedded in an arbitrary tissue, was created to simulate the application of MRE to atherosclerotic plaque. The behaviour of shear waves propagating through an atherosclerotic plaque with development of the stenosis and lipid pool size was investigated. There is a local increase in wave displacement and decrease in wavelength, through a plaque containing a lipid pool compared to a purely fibrotic plaque. The amplitude of the wave through the lipid increases with lipid pool volume. This suggests that shear waves used...
The clinical assessment of the rupture risk of atherosclerotic plaque is made by imaging the redu... more The clinical assessment of the rupture risk of atherosclerotic plaque is made by imaging the reduction of the lumen; via ultrasound or angiography. It is known that this is an imperfect criterion and that other characteristics of the plaque, such as the change in mechanical properties, may be more relevant. Magnetic Resonance Elastography (MRE) is a novel imaging technique that measures tissue stiffness. Magnetic resonance imaging measures the tissue displacement in response to harmonic shear waves excited on the surface of the body by a vibrating actuator. The images of wave propagation are transformed into an image of stiffness using an inversion algorithm. A steady state analysis was conducted on a simulation of MRE shear waves propagating through an idealised atherosclerotic plaque. The variation of the 2D complex wave response was investigated with regards to stenosis size, lipid pool size and excitation frequency. The detectability of small lipid pools was shown to increase wi...
INTRODUCTION Computational modelling in orthopaedic biomechanics often uses continuum homogenised... more INTRODUCTION Computational modelling in orthopaedic biomechanics often uses continuum homogenised finite element models of the bone which require accurate definitions of its elastic properties. In this study the variation of the orthotropic elastic constants of cortical bone from the female anterior femoral midshaft were evaulated. Micro-finite-element (μFE) analysis of bone samples from 27 female donors aged between 20 – 87years were conducted to quantify the elastic constants at the periosteal and endosteal aspects. The variation of properties with age and canal volume to total volume (Ca.V/TV) were evaluated.
Ab stract— The clinical assessment of the rupture risk of atherosclerotic plaque is made by imagi... more Ab stract— The clinical assessment of the rupture risk of atherosclerotic plaque is made by imaging the reduction of the lumen; via ultrasound or angiography. It is known that this is an imperfect criterion and that other characteristics of the plaque, such as the change in mechanical properties, may be more relevant. Magnetic Resonance Elastography (MRE) is a novel imaging technique that measures tissue stiffness. Magnetic resonance imaging measures the tissue displacement in response to harmonic shear waves excited on the surface of the body by a vibrating actuator. The images of wave propagation are transformed into an image of stiffness using an inversion algorithm. A steady state analysis was conducted on a simulation of MRE shear waves propagating through an idealised atherosclerotic plaque. The variation of the 2D complex wave response was investigated with regards to stenosis size, lipid pool size and excitation frequency. The detectability of small lipid pools was shown to ...
The aim of the study is to investigate the biomechanical effects on the pelvis of the anterolater... more The aim of the study is to investigate the biomechanical effects on the pelvis of the anterolateral and posterolateral approaches at the time of hip arthroplasty. In particular the study investigates the change in stress distribution, and the change in muscle recruitment pattern following surgery. The study uses an advanced finite element model of the pelvis, in which the role of muscles and ligaments in determining the stress distribution in the pelvis is included. The model is altered for the posterolateral approach by excision of the external rotators. Different levels of gluteal damage for the anterolateral approach are modelled by excising in turn the anterior third, half, and two-thirds of the gluteus medius and minimus. Although attempt is generally made to repair gluteal damage at the time of surgery, it is clear the muscle volume will be compromised immediately after surgery. In support of previous clinical studies indicating an increased risk of limp, and pelvic tilt follo...
INTRODUCTION: Micro level finite element (μFE) models of trabecular bone have a variety of possib... more INTRODUCTION: Micro level finite element (μFE) models of trabecular bone have a variety of possible applications that include understanding fracture mechanism in normal and osteoporotic bone and examining the mechanical response of bone to implants. Previous investigators used images or CT attenuations of real bone samples to develop μFE models. This involves: generating images of a bone sample using, for example, μ-CT; converting CT attenuations to elastic moduli; and mapping elastic moduli to 3D finite elements. The computational models created using these methods can only represent the samples used in their construction and any possible variations due to factors such as anatomical site, sex, age or degree of osteoporosity cannot be included without additional sample collection and processing. To authenticate any hypothesis it is essential to consider a wide range of samples with different characteristics. It is a colossal task to generate 3D μFE models from real samples for this ...
References: [1] Kolipaka, Proc Joint Annual Meeting ISMRM-ESMRMB 2010 [2] Holzapfel, Ann Biomed E... more References: [1] Kolipaka, Proc Joint Annual Meeting ISMRM-ESMRMB 2010 [2] Holzapfel, Ann Biomed Eng 2002; 30: 753-767 Summary: Hooke’s law states that the strain in a linearly elastic material is proportional to the applied load. Magnetic Resonance Elastography (MRE) uses this principle to deduce tissue stiffness by measuring the deformation created by externally generated waves, albeit using more complicated algorithms. Computational modelling can be used to demonstrate the feasibility of arterial MRE by showing the disruption of shear waves through a healthy vessel and an idealised fibrous and lipid plaque.
Apparent (macro level) stiffness directionality (anisotropy) of trabecular bone has received cons... more Apparent (macro level) stiffness directionality (anisotropy) of trabecular bone has received considerable attention in previous reseach, which has also identified ‘bone response to mechanical forces’ as the cause. Anisotropy of cortical bone stiffness has received relatively little attention. The effect of increased porosity (due to age or disease) on the directionality of cortical bone stiffness has not been considered before. To address these issues the present study evaluated the variation of orthotropic elastic constants of cortical bone from the female anterior femoral midshaft. Micro-finite-element (μFE) analysis of bone samples from 27 female donors (age 53.4 ±23.6) were conducted to quantify the elastic constants at the periosteal and endosteal aspects. The ratio of canal volume to tissue volume (Ca.V/TV), analogous to porosity, was found to be the most significant predictor (r = 0.958) of the elastic constants. As would be expected stiffness decreases with increasing Ca.V/T...
Assessment of the rupture risk of plaque is commonly made via imaging of the lumen reduction. How... more Assessment of the rupture risk of plaque is commonly made via imaging of the lumen reduction. However it is known that this is an imperfect criterion and that other features, such as plaque stiffness, may be more relevant. Magnetic Resonance Elastography (MRE) estimates the stiffness of tissues using inversion algorithms applied to the displacement of the tissue, measured in response to the induction of a shear wave from an external actuator. An idealised diseased vessel, embedded in an arbitrary tissue, was created to simulate the application of MRE to atherosclerotic plaque. The behaviour of shear waves propagating through an atherosclerotic plaque with development of the stenosis and lipid pool size was investigated. There is a local increase in wave displacement and decrease in wavelength, through a plaque containing a lipid pool compared to a purely fibrotic plaque. The amplitude of the wave through the lipid increases with lipid pool volume. This suggests that shear waves used...
The clinical assessment of the rupture risk of atherosclerotic plaque is made by imaging the redu... more The clinical assessment of the rupture risk of atherosclerotic plaque is made by imaging the reduction of the lumen; via ultrasound or angiography. It is known that this is an imperfect criterion and that other characteristics of the plaque, such as the change in mechanical properties, may be more relevant. Magnetic Resonance Elastography (MRE) is a novel imaging technique that measures tissue stiffness. Magnetic resonance imaging measures the tissue displacement in response to harmonic shear waves excited on the surface of the body by a vibrating actuator. The images of wave propagation are transformed into an image of stiffness using an inversion algorithm. A steady state analysis was conducted on a simulation of MRE shear waves propagating through an idealised atherosclerotic plaque. The variation of the 2D complex wave response was investigated with regards to stenosis size, lipid pool size and excitation frequency. The detectability of small lipid pools was shown to increase wi...
INTRODUCTION Computational modelling in orthopaedic biomechanics often uses continuum homogenised... more INTRODUCTION Computational modelling in orthopaedic biomechanics often uses continuum homogenised finite element models of the bone which require accurate definitions of its elastic properties. In this study the variation of the orthotropic elastic constants of cortical bone from the female anterior femoral midshaft were evaulated. Micro-finite-element (μFE) analysis of bone samples from 27 female donors aged between 20 – 87years were conducted to quantify the elastic constants at the periosteal and endosteal aspects. The variation of properties with age and canal volume to total volume (Ca.V/TV) were evaluated.
Ab stract— The clinical assessment of the rupture risk of atherosclerotic plaque is made by imagi... more Ab stract— The clinical assessment of the rupture risk of atherosclerotic plaque is made by imaging the reduction of the lumen; via ultrasound or angiography. It is known that this is an imperfect criterion and that other characteristics of the plaque, such as the change in mechanical properties, may be more relevant. Magnetic Resonance Elastography (MRE) is a novel imaging technique that measures tissue stiffness. Magnetic resonance imaging measures the tissue displacement in response to harmonic shear waves excited on the surface of the body by a vibrating actuator. The images of wave propagation are transformed into an image of stiffness using an inversion algorithm. A steady state analysis was conducted on a simulation of MRE shear waves propagating through an idealised atherosclerotic plaque. The variation of the 2D complex wave response was investigated with regards to stenosis size, lipid pool size and excitation frequency. The detectability of small lipid pools was shown to ...
The aim of the study is to investigate the biomechanical effects on the pelvis of the anterolater... more The aim of the study is to investigate the biomechanical effects on the pelvis of the anterolateral and posterolateral approaches at the time of hip arthroplasty. In particular the study investigates the change in stress distribution, and the change in muscle recruitment pattern following surgery. The study uses an advanced finite element model of the pelvis, in which the role of muscles and ligaments in determining the stress distribution in the pelvis is included. The model is altered for the posterolateral approach by excision of the external rotators. Different levels of gluteal damage for the anterolateral approach are modelled by excising in turn the anterior third, half, and two-thirds of the gluteus medius and minimus. Although attempt is generally made to repair gluteal damage at the time of surgery, it is clear the muscle volume will be compromised immediately after surgery. In support of previous clinical studies indicating an increased risk of limp, and pelvic tilt follo...
Uploads
Papers by Pankaj Pankaj