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131.
132.
Kinematics of the heart: strain-rate imaging from time-resolved three-dimensional phase contrast MRI
Selskog P Heiberg E Ebbers T Wigström L Karlsson M 《IEEE transactions on medical imaging》2002,21(9):1105-1109
A four-dimensional mapping (three spatial dimensions + time) of myocardial strain-rate would help to describe the mechanical properties of the myocardium, which affect important physiological factors such as the pumping performance of the ventricles. Strain-rate represents the local instantaneous deformation of the myocardium and can be calculated from the spatial gradients of the velocity field. Strain-rate has previously been calculated using one-dimensional (ultrasound) or two-dimensional (2-D) magnetic resonance imaging) techniques. However, this assumes that myocardial motion only occurs in one direction or in one plane, respectively. This paper presents a method for calculation of the time-resolved three-dimensional (3-D) strain-rate tensor using velocity vector information in a 3-D spatial grid during the whole cardiac cycle. The strain-rate tensor provides full information of both magnitude and direction of the instantaneous deformation of the myocardium. A method for visualization of the full 3-D tensor is also suggested. The tensors are visualized using ellipsoids, which display the principal directions of strain-rate and the ratio between strain-rate magnitude in each direction. The presented method reveals the principal strain-rate directions without a priori knowledge of myocardial motion directions. 相似文献
133.
Ahrens O Buhrdorf A Hohlfeld D Tebje L Binder J 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(9):1321-1329
A recently introduced set up of capacitive micromachined ultrasonic transducers (cMUT) combines a conductive membrane above a structured sacrificial layer. All previous approaches either require an additional metallic electrode or do not possess a structured sacrificial layer and, consequently, may make exact adjustment of the membrane dimensions difficult. The present set ups are especially suited for the fabrication of cMUT with gap heights ranging between 50 nm and 2 /spl mu/m between the electrodes. Large gaps are a prerequisite to enabling sufficient deflections of the membrane and, therewith, to generating high pressure gradients. On the other hand, small gap sizes are desirable for detecting weak ultrasonic sources. This paper focuses on the fabrication process of cMUT to realize electrode separation above 500 nm and, in addition, on the manufacturing of cMUT with gaps below 500 nm. The successful realization has been proven by some basic experimental investigations. Finally, the fundamental equations of a frequently chosen simulation model are documented, as a number of ambiguities exist in the common literature. 相似文献
134.
Sundfeldt M Widmark M Wennerberg A Kärrholm J Johansson CB Carlsson LV 《Journal of materials science. Materials in medicine》2002,13(11):1037-1043
The addition of sodium fluoride to poly (methyl-methacrylate) (PMMA) bone cement may theoretically improve the fixation of joint replacement. This hypothesis was tested in an animal model using nine mature healthy lop-eared rabbits. A femoral prosthesis was inserted in both knees to resurface the patellofemoral articulation. The same acrylic cement, with and without sodium fluoride, was randomised between the two sides for prosthetic fixation. Two screw shaped implants machined from cured rods of either cement were also inserted bilaterally into the proximal tibia. Qualitative and quantitative histomorphometry of the bone tissue response surrounding the cement in the femur and the intact tibial implants revealed similar results regardless of sodium fluoride addition. Six weeks after surgery removal, torque did not significantly differ between the two sides. Our findings indicate that addition of sodium fluoride to PMMA has little effect on implant stability and bone remodeling in rabbits in the short-term. 相似文献
135.
Studies using both in vitro and in vivo techniques have repeatedly shown that endothelium-dependent vasodilation (EDV) is impaired in different forms of experimental
as well as human hypercholesterolemia. Clearly this impaired EDV can be reversed by lowering cholesterol levels by diet or
medical therapy. Competitive blocking of l-arginine, changes in nitric oxide synthase acitivity, increased release of endothelin-1, and inactivation of nitric oxide
due to superoxide ions all contribute to the impairment in EDV during dyslipidemia. The oxidation of low density lipoprotein,
with its compound lysophosphatidylcholine, plays a critical role in these events. However, data on the role of triglycerides
and fat-rich meals regarding EDV are not so consistent as data for cholesterol, although a view that the compositions of individual
fatty acids and antioxidants are of major importance is emerging. Thus, this review shows that while impaired FDV is a general
feature of hypercholesterolemia, the mechanisms involved and the therapeutic opportunities available still have to be investigated.
Furthermore, discrepancies regarding the role of triglycerides and fat content in food may be explained by divergent effects
of different fatty acids on the endothelium. 相似文献
136.
Byström JU Hansson GA Rylander L Ohlsson K Källrot G Skerfving S 《Applied ergonomics》2002,33(1):63-74
The aim was to evaluate (1) the physical workload on neck and upper limb in computer-aided design (CAD) work; (2) the impact of two applications (PROFESSIONAL-CADAM and PRO/Engineering) and (3) two input devices (computer mouse and keyboard), as well as (4) sitting and standing work positions. Fifteen CAD operators were interviewed and examined physically. For nine subjects, the physical workload was measured: electromyography (EMG) of trapezius and forearm extensor muscles, inclinometry of the head, the upper back and upper arms, as well as wrist goniometry. The muscular load was low in CAD work, but the inter-individual variation was considerable. Neither the positions were extreme, nor the movements. The applications, per se, did not have a large impact on the workload, but because of the need for different input devices the effect was strong. Using a keyboard meant higher angular velocities than using a mouse. Hence, when choosing a new software, which requires mainly a mouse as input device, this has to be balanced against the risk of disorders. 相似文献
137.
Pedersen IB Laurberg P Arnfred T Knudsen N Jørgensen T Perrild H Ovesen L 《Computer methods and programs in biomedicine》2002,67(3):209-216
In Denmark an increase in iodine intake through salt iodization has been introduced in 1998. In parallel a program for surveyance of thyroid diseases in the population was developed as recommended by UNICEF and WHO. OBJECTIVE: To develop and evaluate a computer based system to identify and register new cases of hyper- and hypothyroidism in a well defined cohort, by linkage to diagnostic laboratory databases. DESIGN AND RESULTS: (1) Two sub cohorts for monitoring were defined (n=535,859), and evaluated to minimize loss of new cases. Collaboration was established with laboratories covering thyroid hormone analyses in the cohort; (2) a diagnostic algorithm was defined and evaluated against clinical practice; (3) evaluation of the laboratory methods employed by the four participating laboratories, to ensure they would reach the same diagnosis in a patient; (4) a register database was developed which used data imported from the laboratory databases to automatically identify previously unknown cases of hyper- and hypothyroidism and record diagnostic activity in the area. All parts of the registration were carefully evaluated. CONCLUSION: We describe for the first time a computer based system for prospective measuring the incidence rate of hyper- and hypothyroidism. The system is particularly useful for monitoring of iodine supplementation programmes. 相似文献
138.
Kamilla Klonowska Håkan Lennerstad Lars Lundberg Charlie Svahnberg 《Acta Informatica》2005,41(6):341-365
Clusters and distributed systems offer fault tolerance and high performance through load sharing. When all n computers are up and running, we would like the load to be evenly distributed among the computers. When one or more computers break down, the load on these computers must be redistributed to other computers in the system. The redistribution is determined by the recovery scheme. The recovery scheme is governed by a sequence of integers modulo n. Each sequence guarantees minimal load on the computer that has maximal load even when the most unfavorable combinations of computers go down. We calculate the best possible such recovery schemes for any number of crashed computers by an exhaustive search, where brute force testing is avoided by a mathematical reformulation of the problem and a branch-and-bound algorithm. The search nevertheless has a high complexity. Optimal sequences, and thus a corresponding optimal bound, are presented for a maximum of twenty one computers in the distributed system or cluster.Received: 26 May 2004, Published online: 14 March 2005 相似文献
139.
As the demand for empirical evidence for claims of improvements in software development and evolution has increased, the use of empirical methods such as case studies has grown. In case study methodology various types of triangulation is a commonly recommended technique for increasing validity. This study investigates a multiple data source case study with the objective of identifying whether more findings, trustworthier findings and other findings are made using multiple data source triangulation, than had a single data source been used. The case study investigated analyses key lead-time success factors for a software evolution project in a large organization developing eBusiness systems with high-availability high throughput transaction characteristics. By tracing each finding in that study to the individual evidences motivating the finding, it is suggested that a multiple data source explorative case study can have a higher validity than a single data source study. It is concluded that a careful case study design with multiple sources of evidence can result in not only better justified findings than a single data source study, but also other findings. Thus this study provides empirically derived evidence that a multiple data source case study is more trustworthy than a comparable single data source case study. 相似文献
140.
Marcus Fleck Alexander I. Lichtenstein Andrzej M. Ole Lars Hedin 《Journal of Superconductivity》1999,12(1):147-149
We investigate the consequences of an incommensurate magnetic order in doped La2–x
Sr
x
CuO4 using dynamical mean-field theory for the effective single-band model. The high-energy optical transitions are due to high-energy excitations across large Mott–Hubbard gap, while low-energy excitations involve a pseudogap induced by the local spin order. The latter lead to a strong drop in the scattering rate at low , in qualitative agreement with the experimental data. 相似文献