Accepted Manuscripts

Technical Brief  
Mirunalini Thirugnanasambandam, Dan Siminescu, G. Patricia Escobar, Eugene A. Sprague, Beth Goins, Geoffrey Clarke, Haichao Han, Krysta Amezcua, Oluwaseun Adeyinka, Craig Goergen and Ender A. Finol
J Biomech Eng   doi: 10.1115/1.4040398
The objective of this work is to develop a protocol for future studies to evaluate the effects of drug-based therapies on the mechanics and inflammation in rodent models of AAA. The scope of the study is limited to the use of pentagalloyl glucose (PGG) for aneurysm treatment in the calcium chloride rat AAA model. Peak wall stress (PWS) and matrix metalloproteinase (MMP) activity, which are the biomechanical and biological markers of AAA growth and rupture, were evaluated over 4 weeks in untreated and treated (with PGG) groups. The AAA specimens were mechanically characterized by planar biaxial tensile testing and the data fitted to a 5-parameter nonlinear, hyperelastic, anisotropic Holzapfel-Gasser-Ogden material model, which was used to perform finite element analysis (FEA) to evaluate PWS. Our results demonstrated that there was a reduction in PWS between pre- and post-AAA induction FEA models in the treatment group compared to the untreated group using either animal-specific or average material properties. However, this reduction was not statistically significant. Conversely, there was a statistically significant reduction in MMP-activated fluorescent signal between pre- and post-AAA induction models in the treated group compared to the untreated group. Therefore, the primary contribution of this work is the quantification of the stabilizing effects of PGG using biomechanical and biological markers of AAA, thus indicating that PGG could be part of a new clinical treatment strategy that will require further investigation.
Nir Emuna, David Durban and Shmuel Osovski
J Biomech Eng   doi: 10.1115/1.4040400
Despite major advances made in modeling vascular tissue biomechanics, the predictive power of constitutive models is still limited by uncertainty of the input data. Specifically, key measurements, like the geometry of the stress-free (SF) state, involve a definite, sometimes non-negligible, degree of uncertainty. Here, we introduce a new approach for sensitivity analysis of vascular hyperelastic constitutive models to uncertainty in SF measurements. We have considered two vascular hyperelastic models: the phenomenological Fung model, and the structure-motivated Holzapfel-Gasser-Ogden model. Our results indicate up to 160% errors in the identified constitutive parameters for a 5% measurement uncertainty in the SF data. Relative margins of errors of up to 30% in the luminal pressure, 36% in the axial force, and over 200% in the stress predictions, were recorded for 10% uncertainties. These findings are relevant to the large body of studies involving experimentally based modeling and analysis of vascular tissues. The impact of uncertainties on calibrated constitutive parameters is significant in context of studies that use constitutive parameters to draw conclusions about the underlying microstructure of vascular tissues, their growth and remodeling processes, aging and disease states. The propagation of uncertainties into the predictions of biophysical parameters e.g. force, luminal pressure, and wall stresses, is of practical importance in the design and execution of clinical devices and interventions. Furthermore, insights provided by the present findings may lead to more robust parameters identification techniques, and serve as selection criteria in the trade-off between model complexity and sensitivity.
Mohammadreza Khani, Lucas Sass, Tao Xing, M. Keith Sharp, Olivier Balédent and Bryn Martin
J Biomech Eng   doi: 10.1115/1.4040401
Cerebrospinal fluid (CSF) dynamics are thought to play a vital role in central nervous system (CNS) physiology. The objective of the present study was to investigate the impact of spinal cord nerve roots (NR) on CSF dynamics. A subject-specific computational fluid dynamics (CFD) model of the complete spinal subarachnoid space (SSS) with and without anatomically realistic NR and non-uniform moving dura wall deformation was constructed. This CFD model allowed detailed investigation of the impact of NR on CSF velocities that is not possible in vivo using MRI or other non-invasive imaging methods. Results showed that NR altered CSF dynamics in terms of velocity field, steady-streaming and vortical structures. Vortices occurred in the cervical spine around NR during CSF flow reversal. The magnitude of steady-streaming CSF flow increased with NR, in particular within the cervical spine. This increase was located axially upstream and downstream of NR due to the interface of adjacent vortices that formed around NR.
Ferris M. Pfeiffer, Suzanne Burgoyne, Heather Hunt and Johannas Strobel
J Biomech Eng   doi: 10.1115/1.4040399
Innovation arises from creativity. "Thinking outside the box" has long been seen as a necessary precursor to innovation and invention in engineering. However, creativity is rarely part of traditional engineering curricula. In 2015, our group began to explore integrating theatre-based creativity methods into bioengineering capstone design. Evaluation of student outcomes was encouraging, so we continued to develop the course in 2016 and 2017. As we worked to refine the pedagogical process, we discovered tensions (real or perceived) between providing academic rigor and allowing students to embrace their creativity; for instance, we experienced some resistance from engineering faculty and students towards adopting methods they viewed as "artsy" or lacking academic rigor. Here, we discuss the tensions we observed, offer potential ways to mitigate such tensions, and begin to consider how to expand on our successes.
Rotem Halevi, Ashraf Hamdan, Gil Marom, Karin Lavon, Sagit Ben Zekry, Ehud Raanani and Rami Haj-Ali
J Biomech Eng   doi: 10.1115/1.4040338
Calcific aortic valve disease (CAVD) is a progressive disease in which minerals accumulate in the tissue of the aortic valve cusps, stiffening them and preventing valve opening and closing. The process of valve calcification was found to be similar to that of bone formation including cell differentiation to osteoblast-like cells. Studies have shown the contribution of high strains to calcification initiation and growth process acceleration. In this paper, a new calcification growth mechano-biology model is proposed. The model aims to explain the unique shape of the calcification and other disease characteristics. The calcification process was divided into two stages: Calcification initiation and calcification growth. The initiation locations were based on previously published findings and a reverse calcification technique (RCT), which uses computed tomography (CT) scans of patients to reveal the calcification initiation point. The calcification growth process was simulated by a finite element model (FEM) of one aortic valve cusp loaded with cyclic loading. Similar to Wolff's law, describing bone response to stress, our model uses strains to drive calcification formation. The simulation grows calcification from its initiation point to its full typical stenotic shape. Study results showed that the model was able to reproduce the typical calcification growth pattern and shape, suggesting that strain is the main driving force behind calcification progression. The simulation also sheds light on other disease characteristics, such as calcification growth acceleration as the disease progresses, as well as sensitivity to hypertension.
TOPICS: Valves, Biology, Diseases, Shapes, Finite element model, Simulation, Bone, Minerals, Stress, Biological tissues, Computerized tomography, Osteoblasts
Paola Tasso, Anastasios Raptis, Miltiadis Matsagkas, Maurizio Lodi Rizzini, Diego Gallo, Michalis Xenos and Umberto Morbiducci
J Biomech Eng   doi: 10.1115/1.4040337
Endovascular aneurysm repair (EVAR) has disseminated rapidly as an alternative to open surgical repair for the treatment of abdominal aortic aneurysms (AAAs), because of its reduced invasiveness, low mortality and morbidity rate. The effectiveness of the endovascular devices used in EVAR is always at question as postoperative adverse events can lead to re-intervention or to a possible fatal scenario for the circulatory system. Motivated by the assessment of the risks related to thrombus formation, here the impact of two different commercial endovascular grafts on local hemodynamics is explored through 20 image-based computational hemodynamic models of EVAR-treated patients (N=10 per each endograft model). Hemodynamic features, susceptible to promote thrombus formation, such as flow separation and recirculation, are quantitatively assessed and compared with the local hemodynamics established in image-based infrarenal abdominal aortic models of healthy subjects (N=10). The hemodynamic analysis is complemented by a geometrical characterization of the EVAR-induced reshaping of the infrarenal abdominal aortic vascular region. The findings of this study indicate that: (1) the clinically observed propensity to thrombus formation in devices used in EVAR strategies can be explained in terms of local hemodynamics by means of image-based computational hemodynamics approach; (2) reportedly pro-thrombotic hemodynamic structures are strongly correlated with the geometry of the aortoiliac tract postoperatively. In perspective, our study suggests that future clinical follow up studies could include a geometric analysis of the region of the implant, monitoring shape variations that can lead to hemodynamic disturbances of clinical significance.
TOPICS: Maintenance, Computational fluid dynamics, Hemodynamics, Aneurysms, Thrombosis, Shapes, Surgery, Cardiovascular system, Flow separation, Geometry
Anita Singh, Dawn Ferry and Susan Mills
J Biomech Eng   doi: 10.1115/1.4040359
This study reports our experience of developing a series of biomedical engineering (BME) courses having active and experiential learning components in an interdisciplinary learning environment. In the first course, BME465:Biomechanics, students were immersed in a simulation lab setting involving mannequins that are currently used for teaching in the School of Nursing. Each team identified possible technological challenges directly related to the biomechanics of the mannequin and presented an improvement overcoming the challenge. This approach of exposing engineering students to a problem in a clinical learning environment enhanced the adaptive and experiential learning capabilities of the course. In the following semester, through BME448:Medical Devices, engineering students were partnered with nursing students and exposed to simulation scenarios and real-world clinical settings. They were required to identify three unmet needs in the real-world clinical settings and propose a viable engineering solution. This approach helped students to understand and employ real-world applications of engineering principles in problem solving while being exposed to an interdisciplinary collaborative environment. A final step was for engineering students to execute their proposed solution from either BME465/BME448 courses by undertaking it as their capstone senior design project (ENGR401-402). Overall, the inclusion of clinical immersions in interdisciplinary teams in a series of courses not only allowed the integration of active and experiential learning in continuity but also offered engineers more practice of their profession, adaptive expertise and an understanding of roles and expertise of other professionals involved in enhancement of healthcare and patient safety.
TOPICS: Biomedical engineering, Education, Students, Engineering students, Biomechanics, Simulation, Teams, Safety, Engineers, Design, Engineering systems and industry applications, Medical devices, Health care, Teaching
Jessica Buice, Amanda Esquivel and Christopher Andrecovich
J Biomech Eng   doi: 10.1115/1.4040311
Mild traumatic brain injuries (mTBIs), or concussions, can result from head acceleration during sports. Wearable sensors like the GForceTrackerTM (GFT) can monitor an athlete's head acceleration during play. The purpose of this study was to evaluate the accuracy of the GFT for use in boys' and girls' lacrosse. The GFT was mounted to either lacrosse goggles or a helmet. The assembly was fit to a Hybrid III headform instrumented with sensors and impacted multiple times at different velocities and locations. Measurements of peak linear acceleration and angular velocity were obtained from both systems and compared. It was found that a large percent error between the GFT and headform system existed for linear acceleration (29% for goggles and 123% for helmet) and angular velocity (48% for goggles and 17% for helmet). This error was substantially reduced when correction equations were applied based on impact location (3-14% for goggles and 3-11% for helmet). Our study has shown that the GFT does not accurately calculate linear acceleration or angular velocity at the CG of the head; however, reasonable error can be achieved by correcting data based on impact location.
TOPICS: Sensors, Eye protection, Errors, Sports, Traumatic brain injury, Manufacturing
Benjamin B. Wheatley, Gregory M. Odegard, Kenton Kaufman and Tammy L. Haut Donahue
J Biomech Eng   doi: 10.1115/1.4040318
Clinical treatments of skeletal muscle weakness are hindered by a lack of an approach to evaluate individual muscle force. Intramuscular pressure (IMP) has shown a correlation to muscle force in vivo, but patient to patient and muscle to muscle variability results in difficulty of utilizing IMP to estimate muscle force. The goal of this work was to develop a finite element model of whole skeletal muscle which can predict IMP under passive and active conditions to further investigate the mechanisms of IMP variability. A previously validated hyper-visco-poroelastic constitutive approach was modified to incorporate muscle activation through an inhomogeneous geometry. Model parameters were optimized to fit model stress to experimental data, and the resulting model fluid pressurization data were utilized for validation. Model fitting was excellent (RMSE <1.5 kPa for passive and active conditions), and IMP predictive capability was strong for both passive (RMSE 3.5 mmHg) and active (RMSE 10 mmHg at in vivo lengths) conditions. Additionally, model fluid pressure was affected by length under isometric conditions, as increases in stretch yielded decreases in fluid pressurization following a contraction, resulting from counteracting Poisson effects. Model pressure also varied spatially, with the highest gradients located near aponeuroses. These findings may explain variability of in vivo IMP measurements in the clinic, and thus help reduce this variability in future studies. Further development of this model to include isotonic contractions and muscle weakness would greatly benefit this work.
TOPICS: Stress, Modeling, Pressure, Muscle, Fluids, Fluid pressure, Finite element model, Fittings, Geometry
Maziar Aghvami, John Brunski, Ustun Serdar Tulu, Chih-Hao Chen and Jill Helms
J Biomech Eng   doi: 10.1115/1.4040312
With the introduction of high-speed cutting tools, clinicians have recognized the potential for thermal damage to the material being cut. Here, we developed a mathematical model of heat transfer caused by drilling bones of different densities, and validated it with respect to experimentally measured temperatures in bone. We then coupled these computational results with a biological assessment of cell death following osteotomy site preparation. Parameters under clinical control, e.g., drill diameter, rotational speed, and irrigation, along with patient-specific variables such as bone density were evaluated in order to understand their contributions to thermal damage. Predictions from our models provide insights into temperatures and thresholds that cause osteocyte death and that can ultimately compromise stability of an implant.
TOPICS: Drilling, Bone, Damage, Temperature, Heat transfer, Irrigation (Agriculture), Drills (Tools), Cutting tools, Site preparation (Construction), Density, Stability
Expert View  
Cherie Avent, Ayesha Boyce, Lakeita Servance, Lizanne DeStefano, Robert M. Nerem and Manu Platt
J Biomech Eng   doi: 10.1115/1.4040310
Enriching science experiences and competencies for underrepresented students during high school years is crucial to increasing their entry into the science pipeline and to improving their preparedness for success in college and STEM careers. The purpose of this article is to describe the implementation of Project ENGAGES, a high school STEM year-long research program for African-American students, mentored by graduate students and postdoctoral researchers at Georgia Tech. It aims to provide an authentic research experience and expose student to the possibility and benefits of attaining an advanced degree and careers in STEM fields. Initial program outcomes include student reported satisfaction with research experience, improved technical skill development, increased curiosity and interest in STEM careers. Additionally, students indicated increases in college readiness, research skill development, and exposure to STEM careers as a result of interactions with faculty advisors and graduate student mentors, along with laboratory assignments. Lessons learned and potential pitfalls and barriers to acceptance are also discussed.
TOPICS: Biomedical engineering, Students, Graduate students, Science, technology, engineering, and mathematics, Emergency preparedness, Performance, Pipelines, Mentoring, Competencies
Alireza Noamani, Albert Vette, Richard Preuss, Milos R. Popovic and Hossein Rouhani
J Biomech Eng   doi: 10.1115/1.4040247
Kinetics assessment of the human head-arms-trunk (HAT) complex using a multi-segment model is required for clinical evaluation of several pathological conditions. Inaccuracies in body segment parameters (BSPs) is a major source of uncertainty in the estimation of the joint moments associated with the multi-segment HAT. Given the large inter-subject variability, there is currently no comprehensive database for the estimation of BSPs for the HAT. We propose a nonlinear, multi-step, optimization-based, non-invasive method for estimating individual-specific BSPs and calculating joint moments in a multi-segment HAT model. Eleven non-disabled individuals participated in a trunk-bending experiment, and their body motion was recorded using cameras and a force plate. A seven-segment model of the HAT was reconstructed for each participant. An initial guess of the BSPs was obtained by individual-specific scaling of the BSPs calculated from the Male Visible Human images. The inter-segmental moments were calculated using both bottom-up and top-down inverse dynamics approaches. Our proposed method adjusted the scaled BSPs and centre of pressure offsets to estimate optimal individual-specific BSPs that minimize the difference between the moments obtained by top-down and bottom-up inverse dynamics approaches. Our results indicate that the proposed method reduced the error in the net joint moment estimation by 77.59% (average among participants). Our proposed method enables accurate estimation of individual-specific BSPs and, consequently, accurate assessment of the three-dimensional kinetics of a multi-segment HAT model.
TOPICS: Dynamics (Mechanics), Pressure, Optimization, Databases, Errors, Uncertainty
Laurel Kuxhaus and Karen L. Troy
J Biomech Eng   doi: 10.1115/1.4040293
Equipping engineering students for career success requires more than technical proficiency; mindset and contextual interpretation also matter. Entrepreneurial Mindset Learning (EML) is one framework that faculty can use to systematically enrich course projects to encourage development of these important career skills. We present the thought process behind enriching two biomechanics class projects to foster both the entrepreneurial mindset and technical proficiency in undergraduate engineering students. One project required students to analyze a court case surrounding vertebral fracture in an elderly woman diagnosed one year after a fall in an elevator. In addition to technical analysis, students had to make a recommendation about the likelihood that the injury occurred due to the fall, and contextualize the results within economic and societal terms - how much should the plaintiff sue for, and how could such injuries be prevented through design and regulation? The second project asked students to evaluate cervine cancellous bone as a suitable laboratory model for biomechanics research. In addition to technical analysis, students considered the value of cervine vertebrae as a laboratory model within the context of societal and economic benefits of ex-vivo animal models, including the relevant policy and regulatory issues. In both projects, implemented at different institutions with similar student demographics, students performed well and enjoyed the "real-world" nature of the projects, despite their frustrations with the open-ended nature of the questions posed. These, and similar projects can be further enhanced to foster entrepreneurial mindset in undergraduate engineering students without undue burden on the instructor.
TOPICS: Biomechanics, Bone, Students, Wounds, Undergraduate students, Elevators, Matter, Spinal fractures, Design, Engineering students
Jorge Barrios-Muriel, Francisco Romero, F.J. Alonso and D.R. Salgado
J Biomech Eng   doi: 10.1115/1.4040250
Nowadays, both usability and comfort play a key role in the development of medical and wearable products. When designing any device that is in contact with the human body, the mechanical behaviour of the embraced soft tissue must be known. The unavoidable displacement of the soft tissue during motion may lead to discomfort adn, thus, the withdrawal of the wearable product. This work presents a new methodology to design and test a wearable device based on the measurement of the dynamic skin strain field. Furthermore, from this field, the anatomical lines with minimum strain (Lines of non extension, LoNEs) are calculated to design the structural parts of the wearable device. Whith this new criteria, the resulting product is not only optimized to reduce the friction in skin-device interface, but fully personalized to the patient's morphology and motion. The methodology is applied to the design of an ankle-foot wearable orthosis for subjects with ankle dorsiflexors muscles weakness due to nervous system disorders. The results confirm that the use of LoNEs may benefit the design of products with a high interaction with the skin.
TOPICS: Design, Skin, Soft tissues, Biomedicine, Nervous system, Mechanical behavior, Displacement, Muscle, Orthotics, Friction
Yogesh Deepak Bansod, Takeo Matsumoto, Kazuaki Nagayama and Jiri Bursa
J Biomech Eng   doi: 10.1115/1.4040246
Mechanical interaction of cell with extracellular environment affects its function. The mechanisms by which mechanical stimuli are sensed and transduced into biochemical responses are still not well understood. Considering this, two finite element (FE) bendo-tensegrity models of a cell in different states are proposed with the aim to characterize cell deformation under different mechanical loading conditions: a suspended cell model elucidating the global response of cell in tensile test simulation and an adherent cell model explicating its local response in atomic force microscopy (AFM) indentation simulation. The force-elongation curve obtained from tensile test simulation lies within the range of experimentally obtained characteristics of smooth muscle cells (SMCs) and illustrates a non-linear increase in reaction force with cell stretching. The force-indentation curves obtained from indentation simulations lie within the range of experimentally obtained curves of embryonic stem cells (ESCs) and exhibit the influence of indentation site on the overall reaction force of cell. Simulation results have demonstrated that actin filaments (AFs) and microtubules (MTs) play a crucial role in the cell stiffness during stretching, whereas actin cortex (AC) along with actin bundles (ABs) and MTs are essential for the cell rigidity during indentation. The proposed models quantify the mechanical contribution of individual cytoskeletal components to cell mechanics and the deformation of nucleus under different mechanical loading conditions. These results can aid in better understanding of structure-function relationships in living cells.
TOPICS: Finite element analysis, Tensegrity, Simulation, Deformation, Atomic force microscopy, Stiffness, Surface mount components, Stem cells, Antilock braking systems, Cellular mechanics, Elongation, Biological cells, Muscle, Simulation results
Technical Brief  
Fatemeh Farhadi, Muhammad Faraz, Marabelle Heng and Shane Johnson
J Biomech Eng   doi: 10.1115/1.4040248
Osteoarthritis sufferers commonly have first metatarsophalangeal joint problems in which articular surfaces are changed permanently due to fatigue. Therefore, medical devices for early diagnosis would increase the opportunity for prevention of disease progression. In previous studies on stiffness of the 1st MTPJ many details, although functionally of great importance, have not been fully considered including: design and size of the device, tribology consideration and errors from device. Therefore, the motivation of our research was to enhance the device design by reducing the size of the device, and device design was enhanced by minimizing measurement errors through development of a new ergonomic left and right foot instrument located medial to the 1st MTPJ (instead of beneath the foot). The 1st MTPJ stiffness (N.mm/ kg. radian) measurement was taken on 28 subjects with two replicates per subject by the same tester. The 1st MTPJ stiffness ranged from 3.49 to 14.42 N.mm/ kg. radian with the mean (SD) value of 8.28 (3.15) N.mm/ kg. radian for the left feet and 3.91 to 11.90 N.mm/ kg. radian with the mean (SD) value of 7.65 (2.07) N.mm/ kg. radian for the right feet. Reliability evaluation was measured using Intraclass Correlation Coefficient and described an excellent reliability between two tests.
TOPICS: Testing, Stiffness, Design, Reliability, Errors, Diseases, Instrumentation, Medical devices, Fatigue, Tribology, Osteoarthritis
Subhomoy Chatterjee, Sabine Kobylinski and Bikramjit Basu
J Biomech Eng   doi: 10.1115/1.4040249
Innovated acetabular shell designs of total hip replacement have been found to be better than the conventional hemispherical design in terms of component stability. In this study, the impact of shell design (conventional, finned, spiked and combined design) and liner material on the biomechanical response of periprosthetic bone has been analysed through finite element method. Two different liner materials: HDPE-20%HA-20%Al2O3 and highly cross linked ultrahigh molecular weight polyethylene (HC-UHMWPE) were used. The subject parameters included bone condition and bodyweight. Physiologically relevant load cases of a gait cycle were considered. The deviation of mechanical condition of the periprosthetic bone due to implantation was least for the finned shell design. No significant deviation was observed at the bone region adjacent to the spikes and the fins. This study recommends the use of the finned design, particularly for weaker bone conditions. For stronger bones, the combined design may also be recommended for higher stability. The use of HC-UHMWPE liner was found to be better for convensional shell design. However, closer biomechanical environment was found for both the liner materials in case of other shell designs. Overall, the study establishes the biomechanical response of pre-clinically tested liner materials together with new shell design for different subject conditions.
TOPICS: Biomechanics, Bone, Design, Finite element analysis, Modeling, Shells, Stability, Stress, Finite element methods, Cycles, Fins, Molecular weight, Hip joint prostheses
Ravi Patel, Andriy Noshchenko, R. Dana Carpenter, Todd Baldini, Carl Frick, Vikas V. Patel and Christopher Yakacki
J Biomech Eng   doi: 10.1115/1.4040252
Current implant materials and designs used in spinal fusion show high rates of subsidence. There is currently a need for a method to predict the mechanical properties of the endplate using clinically available tools. The purpose of this study was to develop a predictive model of the mechanical properties of the vertebral endplate at a scale relevant to the evaluation of current medical implant designs and materials. Twenty vertebrae (10 L1 and 10 L2) from 10 cadavers were studied using dual-energy x-ray absorptiometry (DEXA) to define bone status (normal, osteopenic, or osteoporotic) and CT to study endplate thickness (µm), density (mg/mm3), and mineral density of underlying trabecular bone (mg/mm3) at discrete sites. Apparent Oliver-Pharr modulus, stiffness, maximum tolerable pressure, and Brinell hardness were measured at each site using a 3mm spherical indenter. Predictive models were built for each measured property using various measures obtained from CT and demographic data. Stiffness showed a strong correlation between the predictive model and experimental values (r=.85), a polynomial model for Brinell Hardness had a stronger predictive ability compared to the linear model (r=.82), and the modulus model showed weak predictive ability (r=.44), likely due the low indentation depth and the inability to image the endplate at that depth (~0.15mm). Osteoporosis and osteopenia were found to be the largest confounders of the measured properties, decreasing them by approximately 50%. It was confirmed that vertebral endplate mechanical properties could be predicted using CT and demographic indices.
TOPICS: Mechanical properties, Computerized tomography, Lumbar spine, Stiffness, Osteoporosis, Bone, Density, Pressure, X-rays, Biomedicine, Polynomials, Spinal fusion, Minerals
Deva Chan, Andrew K. Knutsen, Yuan-Chiao Lu, Sarah H Yang, Elizabeth Magrath, Wen-Tung Wang, Philip V Bayly, John A. Butman and Dzung L. Pham
J Biomech Eng   doi: 10.1115/1.4040230
Understanding of in vivo brain biomechanical behavior is critical in the study of traumatic brain injury (TBI) mechanisms and prevention. Using tagged magnetic resonance imaging, we measured spatiotemporal brain deformations in 34 healthy human volunteers under mild angular accelerations of the head. Two-dimensional Lagrangian strains were examined throughout the brain in each subject. Strain metrics peaked shortly after contact with a padded stop, corresponding to the inertial response of the brain after head deceleration. Maximum shear strain of at least 3% was experienced at peak deformation by an area fraction (median ± standard error) of 23.5% ± 1.8% of cortical gray matter, 15.9% ± 1.4% of white matter, and 4.0% ± 1.5% of deep gray matter. Cortical gray matter strains were greater in the temporal cortex on the side of the initial contact with the padded stop and also in the contralateral temporal, frontal, and parietal cortex. These tissue-level deformations from a population of healthy volunteers provide the first in vivo measurements of full-volume brain deformation in response to known kinematics. Although strains differed in different tissue type and cortical lobes, no significant differences between male and female head accelerations or strain metrics were found. These cumulative results highlight important kinematic features of the brain's mechanical response and can be used to facilitate the evaluation of computational simulations of TBI.
TOPICS: Deformation, Magnetic resonance imaging, Brain, Matter, Biological tissues, Kinematics, Engineering simulation, Simulation, Biomechanics, Shear (Mechanics), Errors, Spatiotemporal phenomena, Traumatic brain injury
Soroush Heidari Pahlavian, John Oshinski, Xiaodong Zhong, Francis Loth and Rouzbeh Amini
J Biomech Eng   doi: 10.1115/1.4040227
Intrinsic cardiac-induced deformation of brain tissue is thought to be important in the pathophysiology of various neurological disorders. In this study, we evaluated the feasibility of utilizing displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) to quantify two-dimensional neural tissue strain using cardiac-driven brain pulsations. We examined eight adult healthy volunteers with an electrocardiogram-gated spiral DENSE sequence performed at the mid-sagittal plane on a 3 Tesla MRI scanner. Displacement, pixel-wise trajectories, and principal strains were determined in seven regions of interest: the brain stem, cerebellum, corpus callosum, and four cerebral lobes. Quantification of small neural tissue motion and strain along with their spatial and temporal variations in different brain regions was found to be feasible using DENSE. The medial and inferior brain structures (brain stem, cerebellum, and corpus callosum) had significantly larger motion and strain compared to structures located more peripherally. The brain stem had the largest peak mean displacement (187 ± 50 µm, mean ± SD). The largest mean principal strains in compression and extension were observed in the brain stem (0.38 ± 0.08) and the corpus callosum (0.37 ± 0.08), respectively. Up to 0.1% difference was observed in strain measurements due to interscan variabilities. This study showed that DENSE can quantify regional variations in brain tissue motion and strain and has the potential to be utilized as a tool to evaluate the changes in brain tissue dynamics resulting from alterations in biomechanical stresses and tissue properties.
TOPICS: Echoes, Biological tissues, Magnetic resonance imaging, Brain, Displacement, Encryption, Strain measurement, Nervous system, Compression, Dynamics (Mechanics), Deformation, Stress, Biomechanics

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