Cartilage Deformation Measured by MRI Image Segmentation Validates MRI-Based Modeling Results

2008 ◽  
Author(s):  
Kenneth J. Fischer ◽  
Alexander J. Waller ◽  
Mehmet Bilgen ◽  
E. Bruce Toby ◽  
Manuela Kunz ◽  
...  
Keyword(s):  
Contact Pressure ◽  
Joint Mechanics ◽  
Normal Contact ◽  
Non Invasive ◽  
Pressure Distributions ◽  
Healthy Cartilage ◽  
Mri Scans ◽  
Normal Contact Pressure ◽  
The Relationship

The onset of arthritis is clearly associated with abnormal joint kinematics and contact pressures [1]. Yet our understanding of in vivo joint mechanics is still limited. In order to elucidate the relationship between joint mechanics and arthritis we must increase our knowledge of normal contact pressure distributions that help maintain healthy cartilage and abnormal contact pressure distributions that lead to arthritis. MRI-based modeling is a non-invasive means of determining joint mechanics in vivo, by combining information from MRI scans of joints with and without active functional loading.

Non-Invasive Molecular Imaging of Shear Stress-Induced Endothelial Activation and Atherosclerotic Plaque Vulnerability

2012 ◽  
Author(s):  
K. Van der Heiden ◽  
H. C. Groen ◽  
P. C. Evans ◽  
L. Speelman ◽  
F. Gijsen ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Atherosclerotic Lesion ◽  
Oscillatory Shear ◽  
Lesion Development ◽  
Non Invasive ◽  
Oscillatory Shear Stress ◽  
The Relationship ◽  
Atherosclerotic Lesion Development

Atherosclerosis is a lipid- and inflammation driven disease of the larger arteries and is found at specific locations in the arterial tree, i.e. at branches and bends where endothelial cells are exposed to low and low, oscillatory shear stress. Shear stress, the frictional force acting on the endothelial cells as a result of the blood flow, affects endothelial physiology. It determines the location of atherosclerotic lesion development as low and low, oscillatory shear stress induce pro-inflammatory transcription factors but reduce expression and/or activity of anti-inflammatory transcription factors in endothelial cells, rendering the vascular wall vulnerable for inflammation. Consequently, in the presence of atherosclerotic risk factors, such as hypercholesterolemia and diabetes, atherosclerotic lesion development can occur. Although the relationship between low and low, oscillatory shear stress and the prevalence of atherosclerosis has been recognized for several decades, insight into the mechanisms underlying this relationship is still incomplete. The correlation between shear stress and endothelial inflammation was demonstrated by in vitro experiments, in which cultured endothelial cells were exposed to specific flow profiles, and confirmed in vivo by gene expression pattern studies at atherosclerosis-susceptible sites. However, the relationship was not substantiated by direct causal in vivo evidence. Therefore, we developed a method to change the local shear stress field in mice in vivo and studied its effect on the endothelial molecular pathways and resulting atherosclerotic plaque formation. Moreover it allowed us to develop non-invasive molecular imaging strategies to detect vulnerable plaques.

The relationship between myocardial and hepatic T2 and T2* at 1.5T and 3T MRI in normal and iron-overloaded patients

2017 ◽  
Vol 59 (3) ◽  
pp. 355-362 ◽  
Author(s):  
Supika Kritsaneepaiboon ◽  
Natee Ina ◽  
Thirachit Chotsampancharoen ◽  
Supaporn Roymanee ◽  
Sirichai Cheewatanakornkul
Keyword(s):  
Iron Concentration ◽  
Liver Iron ◽  
3T Mri ◽  
Non Invasive ◽  
Asymptomatic Patients ◽  
Mri Scans ◽  
Magnetic Resonance Imaging Mri ◽  
Relationship Of ◽  
The Relationship ◽  
Best Fit

Background Cardiac and liver iron assessment using magnetic resonance imaging (MRI) is non-invasive and used as a preclinical “endpoint” in asymptomatic patients and for serial iron measurements in iron-overloaded patients. Purpose To compare iron measurements between hepatic and myocardial T2* and T2 at 1.5T and 3T MRI in normal and iron-overloaded patients. Material and Methods The T2 and T2* values from the regions of interest (ROIs) at mid-left ventricle and mid-hepatic slices were evaluated by 1.5T and 3T MRI scans for healthy and iron-overloaded patients. Results For iron-overloaded patients, the myocardial T2 (1.5T) and myocardial T2 (3T) values were 60.3 ms (range = 56.2–64.8 ms) and 55 ms (range = 51.6–60.1 ms) (ρ = 0.3679) while the myocardial T2* (3T) 20.5 ms (range = 18.4–25.9 ms) was shorter than the myocardial T2* (1.5T) 35.9 ms (range = 31.4–39.5 ms) (ρ = 0.6454). The hepatic T2 at 1.5T and 3T were 19.1 ms (range = 14.8–27.9 ms) and 15.5 ms (14.6–20.4 ms) (ρ = 0.9444) and the hepatic T2* at 1.5T and 3T were 2.7 ms (range = 1.8–5.6 ms) and 1.8 ms (range = 1.1–2.9 ms) (ρ = 0.9826). The line of best fit exhibiting the linearity of the hepatic T2* (1.5T) and hepatic T2* (3T) had a slope of 2 and an intercept of –0.387 ms (R = 0.984). Conclusion Our study found myocardial T2 (1.5T) nearly equal to T2 (3T) with myocardial T2* (3T) 1.75 shorter than myocardial T2* (1.5T). The relationship of hepatic T2* (1.5T) and hepatic T2* (3T) was linear with T2* (1.5T) approximately double to T2* (3T) in iron-overloaded patients. This linear relationship between hepatic T2* (1.5T) and hepatic T2 (3T) could be an alternative method for estimating liver iron concentration (LIC) from 3T.

Conditions for Sticking Friction between Aluminium Alloy AA6060 and Tool Steel in Hot Forming

2011 ◽  
Vol 491 ◽  
pp. 121-128 ◽  
Author(s):  
F. Widerøe ◽  
T. Welo
Keyword(s):  
Aluminium Alloy ◽  
Contact Pressure ◽  
Tool Steel ◽  
Contrast Material ◽  
Stick Slip ◽  
Normal Contact ◽  
Bulk Forming ◽  
Instantaneous Temperature ◽  
Normal Contact Pressure ◽  
Rotational Method

The frictional conditions between an aluminium AA6060 alloy and tool steel in hot bulk forming have been investigated. The compressive-rotational method for frictional measurements, presented herein, represents an innovative approach for defining the thermo-mechanical conditions required for sticking friction at the interface between the two metals. Aluminium disks with inserted contrast material were subjected to a variety of pressures and rotated at one end at temperatures ranging from 250 °C to 500 °C. Visual inspection of the surfaces in combination with sectioning of the deformed disks formed a method for studying how different factors affect a stick-slip criterion in metal forming. It was found that the normal contact pressure required for sticking to occur was strongly dependent on the instantaneous temperature. When comparing the normal contact pressureqwith the characteristic shear strengthkof the aluminium alloy,q/k> 0.6 yielded sticking friction for temperatures above 300 °C, while a ratio of 0.7 was required for the lower temperatures.

Physics-Based Flexible Tire Model Integrated With LuGre Tire Friction for Transient Braking and Cornering Analysis

2016 ◽  
Vol 11 (3) ◽  
Author(s):  
Hiroki Yamashita ◽  
Paramsothy Jayakumar ◽  
Hiroyuki Sugiyama
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Friction Model ◽  
Distributed Parameter ◽  
Force Model ◽  
Tire Model ◽  
Normal Contact ◽  
Contact Patch ◽  
Normal Contact Pressure ◽  
Tire Friction

In transient vehicle maneuvers, structural tire deformation due to the large load transfer causes abrupt change in normal contact pressure and slip distribution over the contact patch, and it has a dominant effect on characterizing the transient braking and cornering forces including the history-dependent friction-induced hysteresis effect. To account for the dynamic coupling of structural tire deformations and the transient tire friction behavior, a physics-based flexible tire model is developed using the laminated composite shell element based on the absolute nodal coordinate formulation and the distributed parameter LuGre tire friction model. In particular, a numerical procedure to integrate the distributed parameter LuGre tire friction model into the finite-element based spatial flexible tire model is proposed. To this end, the spatially discretized form of the LuGre tire friction model is derived and integrated into the finite-element tire model such that change in the normal contact pressure and slip distributions over the contact patch predicted by the deformable tire model enters into the spatially discretized LuGre tire friction model to predict the transient shear contact stress distribution. By doing so, the structural tire deformation and the LuGre tire friction force model are dynamically coupled in the final form of the equations, and these equations are integrated simultaneously forward in time at every time step. The tire model developed is experimentally validated and several numerical examples for hard braking and cornering simulation are presented to demonstrate capabilities of the physics-based flexible tire model developed in this study.

Application of Gap Element Method to Wheel/Rail Contact Problem Based on V-5

2013 ◽  
Vol 344 ◽  
pp. 46-54
Author(s):  
Jun Jie Zhong ◽  
Bing Wu ◽  
Ze Feng Wen ◽  
Xin Zhao ◽  
Xue Song Jin
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Two Dimensions ◽  
Vector Form ◽  
Normal Contact ◽  
Large Rotation ◽  
Gap Element ◽  
Normal Contact Pressure ◽  
Rolling Wheel ◽  
Element Method

The vector form intrinsic finite element (V-5) method and the gap element method are combined to solve the static wheel/rail contact in two-dimensions in this paper to obtain the wheel/rail normal contact pressure, which would be compared with the normal contact pressure of ABAQUS and Hertz theory. The results showed that the contact pressure distribution of V-5 was consistent with ABAQUS and Hertzs, and the mechanical behavior of contact area was reasonable under the circumstance of different axle loads. Besides, it also verified the feasibility of adopting gap elements method to solve the static wheel/rail contact on the basis of vector form finite element method, which with the superiority of large rotation and large deformation, and laid the foundation of rolling wheel-rail contact behavior analysis.

scholarly journals Expression and methylation status of LAMA2 are associated with the invasiveness of nonfunctioning PitNET

2019 ◽  
Vol 10 ◽  
pp. 204201881882129 ◽  
Author(s):  
Ruo-Qiang Wang ◽  
Yu-Long Lan ◽  
Jia-Cheng Lou ◽  
Yi-Zhu Lyu ◽  
Yu-Chao Hao ◽  
...  
Keyword(s):  
Western Blotting ◽  
Promoter Methylation ◽  
Methylation Status ◽  
Xenograft Model ◽  
Invasive Group ◽  
Non Invasive ◽  
Protein Functions ◽  
Methylation Patterns ◽  
The Relationship

The laminin subunit alpha 2 (LAMA2) gene encodes an alpha 2 chain, which constitutes one of the subunits of laminin 2 (merosin) and laminin 4 (s-merosin). In the current study, we investigated the relationship between LAMA2 promoter methylation status and the invasiveness of clinically nonfunctioning pituitary adenomas (PitNETs). Specimens from patients with nonfunctioning PitNET were classified into three groups according to preoperative computed tomography (CT)/magnetic resonance imaging findings: a normal group ( n = 6), non-invasive group ( n = 11) and invasive group ( n = 6). LAMA2 expression was assessed using quantitative real-time polymerase chain reaction (RT-qPCR) and western blotting, and the methylation status of the LAMA2 promoter region was observed using sodium bisulfite sequencing. Furthermore, 5-aza-2-deoxycytidine was used to explore the relationship between decreased LAMA expression and methylation in PitNET cells. According to the RT-qPCR and western blotting results, LAMA2 expression was downregulated in invasive PitNET, while the methylation of the LAMA2 promoter was increased. Methylation of the LAMA2 promoter decreased the expression of LAMA2. Thus, changes in LAMA2 expression due to promoter methylation were inversely correlated with the invasiveness of PitNET and the protein functions as a tumor suppressor. In addition, overexpression and demethylation of LAMA2 suppressed the invasion of PitNET cells, partially by exerting effects on the PTEN-PI3K/AKT signaling pathway and matrix metalloproteinase-9 (MMP-9). Furthermore, a xenograft model was also generated, and LAMA2 overexpression significantly suppressed tumor growth in vivo. Thus, LAMA2 expression and methylation patterns might be used as biomarkers to predict the prognosis of patients with PitNET.

Contact Analysis for Joint Interfaces of Machine Tools Based on a 3-D Anisotropic Asperity Model

2011 ◽  
Vol 189-193 ◽  
pp. 114-120 ◽  
Author(s):  
Hai Tao Liu ◽  
Wan Hua Zhao ◽  
Jun Zhang
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Contact Stiffness ◽  
Contact Analysis ◽  
Joint Interface ◽  
Average Height ◽  
Exponential Relationship ◽  
Normal Contact ◽  
Normal Deformation ◽  
Normal Contact Pressure

In this paper, a 3-D contact model for anisotropic rough surfaces based on 3-D statistically measurements is established and finite element contact analysis is conducted. The average height of the asperity (h), the average summit distances between two neighboring peaks of asperities (Sx and Sy) are selected as the characterized parameters of the rough surface. Finite element simulation results show that the normal contact pressure has an exponential relation with the normal deformation and an exact linear relationship between the normal deformation and the real contact pressure of the surfaces is obtained. At last, the normal contact stiffness of the joint interface is obtained empirically with the exponential relationship assumption.

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