MEDICINAL RESEARCH REVIEWS, Issue 4 2002
Christos A. Kontogiorgis
Abstract This article evaluates the quantitative structure-activity relationships (QSAR) of nitric oxide (NO) radical donors and nitric oxide synthases (NOS) inhibitors, using the C-QSAR program of Biobyte. Furoxans, triazines, amidoximes, tetrazoles, imidazoles and N,,2-nitroarylamino acid analogues were included in this survey. In nine out of seventeen cases, the clog P plays a significant part in the QSAR of the NO radical donors and of the NOS inhibition. Many of the compounds must be interacting with a hydrophobic space in a non-specific way. In some cases molecular refractivity CMR/MR as well as sterimol parameters (B1 and L) are important. Electronic effects, with the exception of the Hammett's constant , and the Swain,Lupton parameter F, are not found to govern the biological activity. Stereochemical and electronic features are also found to be important. Indicator variables were used after the best model was found to account for the usual structural features. © 2002 Wiley Periodicals, Inc. Med Res Rev, 22, No. 4, 385,418, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/med.10012 [source]

Diagnostic evaluation of developmental delay/mental retardation: An overview

AMERICAN JOURNAL OF MEDICAL GENETICS, Issue 1 2003
Agatino Battaglia
Abstract Mental retardation (MR) is one of the few clinically important disorders for which the etiopathogenesis is still poorly understood. It is a condition of great concern for public health and society. MR is currently defined as a significant impairment of cognitive and adaptive functions, with onset before age 18 years. It may become evident during infancy or early childhood as developmental delay (DD), but it is best diagnosed during the school years. MR is estimated to occur in 1,10% of the population, and research on its etiology has always been a challenge in medicine. The etiopathogenesis encompasses so many different entities that the attending physician can sometimes feel a "virtual panic," starting a wide-range diagnostic evaluation. The Consensus Conference of the American College of Medical Genetics has recently established guidelines regarding the evaluation of patients with MR [Curry et al., 1997], emphasizing the high diagnostic utility of cytogenetic studies and neuroimaging in certain clinical settings. However, since then there has been substantial progress in molecular cytogenetics and neuroimaging techniques, the use of which has allowed recognition and definition of new disorders, thus increasing the diagnostic yield. This review will focus on the most appropriate investigations shown to be, at present, necessary to define the etiology of DD/MR, in the context of recommendations for the clinical evaluation of the patient with undiagnosed MR. © 2003 Wiley-Liss, Inc. [source]

Synthesis of 2-Fluoro N10 -Substituted Acridones and Their Cytotoxicity Studies in Sensitive and Resistant Cancer Cell Lines and Their DNA Intercalation Studies

ARCHIV DER PHARMAZIE, Issue 11 2009
Yergeri C. Mayur
Abstract A series of 2-fluoro N10 -substituted acridone derivatives with varying alkyl side chain length with propyl, butyl substitution, and a tertiary amine group at the terminal end of the alkyl side chain were synthesized and screened against cancer cell lines SW 1573, SW 1573 2R 160 (P-gp substrate) which are non-small lung cancer cell lines, MCF-7, MCF-7/MR (BCRP substrate) are breast cancer cell lines, 2008 WT, 2008MRP1, 2008MRP2, 2008MRP3 are ovarian cancer cell lines, and human embryo kidney cell lines like HEK293, HEK293 MRP4, and HEK293 MRP5i. The propyl-series compounds showed lipophilicity in the range of 1.93 to 4.40 and the butyl series in the range of 2.37 to 4.78. The compounds 4, 7, and 8 showed good cytotoxicity against the 60 human cancer cell line panel of the National Cancer Institute, USA. The compounds 14 and 15 showed a better cytotoxicity in most of the cancer cell lines compared to other compounds tested. The DNA-binding properties of the compounds were evaluated based on their affinity or intercalation with CT-DNA measured with absorption titration. The compound 11 bearing planar tricyclic ring linked with a butyl methylpiperazino side chain showed the highest binding affinity with a binding constant (Ki) of 10.38×10 M,1. Evaluation of the compounds in cell lines with an overexpression of various multidrug resistance-related protein (MRP), P-glycoprotein (P-gp), or Breast Cancer Resistance Protein (BCRP) showed that all compounds are not substrates for any of these transporters. [source]

GPU-based interactive visualization framework for ultrasound datasets

COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 1 2009
Sukhyun Lim
Abstract Ultrasound imaging is widely used in medical areas. By transmitting ultrasound signals into the human body, their echoed signals can be rendered to represent the shape of internal organs. Although its image quality is inferior to that of CT or MR, ultrasound is widely used for its speed and reasonable cost. Volume rendering techniques provide methods for rendering the 3D volume dataset intuitively. We present a visualization framework for ultrasound datasets that uses programmable graphics hardware. For this, we convert ultrasound coordinates into Cartesian form. In ultrasound datasets, however, since physical storage and representation space is different, we apply different sampling intervals adaptively for each ray. In addition, we exploit multiple filtered datasets in order to reduce noise. By our method, we can determine the adequate filter size without considering the filter size. As a result, our approach enables interactive volume rendering for ultrasound datasets, using a consumer-level PC. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Prospects for diffusion enhancement of signal and resolution in magnetic resonance microscopy

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003
Charles H. Pennington
Abstract The prospects for and practical requirements of the "diffusion enhancement of signal and resolution" (DESIRE) scheme proposed by Lauterbur as a method to enhance the sensitivity, spatial resolution, and contrast in magnetic resonance (MR) microscopy and localized MR spectroscopy is assessed. The method, which still has not been implemented, promises signal enhancements of 1,2 orders of magnitude in imaging or localized spectroscopy on the scale of ,10 microns and requires magnetic field gradient strengths (,10 T/m) that are not unreasonable. I emphasize the development of an understanding of the physical principles involved in this unfamiliar, "real-space" imaging method. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 71,79, 2003. [source]

Design of an MR-compatible piezoelectric actuator for MR elastography

CONCEPTS IN MAGNETIC RESONANCE, Issue 4 2002
Kai Uffmann
Abstract Magnetic Resonance (MR) elastography is a method for measuring tissue elasticity via phase images acquired with an MR scanner. The propagation of periodic mechanical waves through the tissue can be captured by means of a modified phase contrast sequence. These waves are generated with a mechanical oscillator (actuator) and coupled into the tissue through the skin. The actuator must be capable of generating a sinusoidal excitation with excellent phase and amplitude stability, while not disturbing the MR imaging process. In this work, an actuator based on a piezoelectric principle was developed. Based on the imaging evaluation of several material samples, the housing for the piezoelectric ceramic was constructed of aluminum. Smaller parts of the housing were manufactured from brass and titanium to fulfill the mechanical constraints. A lever was used to transfer the oscillation generated by the piezoelectric ceramic to the point of excitation. The lever amplifies the piezoelectric motion, allowing for a more compact design. Three different lever designs were characterized by an acceleration sensor both outside and inside the magnet. It was shown that the rigidity of the lever, as determined by its material and form, was decisive in determining the resonant frequency of the system and therefore the maximum practical frequency of operation. It was also shown that the motion of the oscillator is unaffected by the electromagnetic fields of the MR imager. The final design can be placed directly in the magnet bore within a few centimeters of the tissue volume to be imaged without generating significant artifacts. An amplitude range of 0,1 mm in the frequency range from 0 to over 300 Hz was achieved, sufficient for performing most MR elastography applications. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 239,254, 2002 [source]

Novel software architecture for rapid development of magnetic resonance applications

CONCEPTS IN MAGNETIC RESONANCE, Issue 3 2002
Josef Debbins
Abstract As the pace of clinical magnetic resonance (MR) procedures grows, the need for an MR scanner software platform on which developers can rapidly prototype, validate, and produce product applications becomes paramount. A software architecture has been developed for a commercial MR scanner that employs state of the art software technologies including Java, C++, DICOM, XML, and so forth. This system permits graphical (drag and drop) assembly of applications built on simple processing building blocks, including pulse sequences, a user interface, reconstruction and postprocessing, and database control. The application developer (researcher or commercial) can assemble these building blocks to create custom applications. The developer can also write source code directly to create new building blocks and add these to the collection of components, which can be distributed worldwide over the internet. The application software and its components are developed in Java, which assures platform portability across any host computer that supports a Java Virtual Machine. The downloaded executable portion of the application is executed in compiled C++ code, which assures mission-critical real-time execution during fast MR acquisition and data processing on dedicated embedded hardware that supports C or C++. This combination permits flexible and rapid MR application development across virtually any combination of computer configurations and operating systems, and yet it allows for very high performance execution on actual scanner hardware. Applications, including prescan, are inherently real-time enabled and can be aggregated and customized to form "superapplications," wherein one or more applications work with another to accomplish the clinical objective with a very high transition speed between applications. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 216,237, 2002 [source]

CMR2009: 10.01: Imaging tumor necrosis with the second-generation, folate-specific ultrasmall paramagnetic iron oxide (USPIO) P1133 with magnetic resonance (MR) imaging in a transgenic mouse model for breast cancer

CONTRAST MEDIA & MOLECULAR IMAGING, Issue 6 2009
D. Golovko
No abstract is available for this article. [source]

MR determination of glomerular filtration rate in subjects with solitary kidneys in comparison to clinical standards of renal function: feasibility and preliminary report,

CONTRAST MEDIA & MOLECULAR IMAGING, Issue 2 2009
Richard W. Katzberg
Abstract This study was conducted to demonstrate the feasibility of quantifying single kidney glomerular filtration rate (skGFR) by magnetic resonance (MR) by comparison to the clinical estimates of GFR in volunteer subjects with a single kidney. Seven IRB-approved subjects with a solitary kidney, stable serum creatinine (SCr) and a 24,h creatinine clearance (CrCl) volunteered to undergo an MR examination that determined renal extraction fraction (EF) with a breathhold inversion recovery echo planar pulse sequence and renal blood flow with a velocity encoded phase imaging sequence. The product of EF and blood flow determines GFR. These values were compared with the 24,h CrCl, estimated GFR by the modification of diet in renal disease (MDRD) regression analysis and the Cockroft,Gault (CG) determination of CrCl. The mean and standard deviation of differences between the MR GFR, MDRD and CG vs the 24,h CrCl were 12.3,±,35.7, ,8.9,±,18.5 and 1.2,±,19.6, respectively. The Student t -test showed that none of the mean differences were statistically significant between techniques. This clinical investigation shows that MR can be used for skGFR determination in human subjects with comparable values to those derived from clinically used serum-based GFR estimation techniques. Copyright © 2009 John Wiley & Sons, Ltd. [source]

MR imaging in assessing cardiovascular interventions and myocardial injury

CONTRAST MEDIA & MOLECULAR IMAGING, Issue 1 2007
Alexis Jacquier
Abstract Performing an MR-guided endovascular intervention requires (1) real-time tracking and guidance of catheters/guide wires to the target, (2) high-resolution images of the target and its surroundings in order to define the extent of the target, (3) performing a therapeutic procedure (delivery of stent or injection of gene or cells) and (4) evaluating the outcome of the therapeutic procedure. The combination of X-ray and MR imaging (XMR) in a single suite was designed for new interventional procedures. MR contrast media can be used to delineate myocardial infarcts and microvascular obstruction, thereby defining the target for local delivery of therapeutic agents under MR-guidance. Iron particles, or gadolinium- or dysprosium-chelates are mixed with the soluble injectates or stem cells in order to track intramyocardial delivery and distribution. Preliminary results show that genes encoded for vascular endothelial and fibroblast growth factor and cells are effective in promoting angiogenesis, arteriogenesis, perfusion and LV function. Angiogenic growth factors, genes and cells administered under MR-guided minimally invasive catheter-based procedures will open up new avenues in treating end-stage ischemic heart disease. The optimum dose of the therapeutic agents, delivery devices and real-time imaging techniques to guide the delivery are currently the subject of ongoing research. The aim of this review is to (1) provide an updated review of experiences using MR imaging to guide transcatheter therapy, (2) address the potential of cardiovascular magnetic resonance (MR) imaging and MR contrast media in assessing myocardial injury at a molecular level and labeling cells and (3) illustrate the applicability of the non-invasive MR imaging in the field of angiogenic therapies through recent clinical and experimental publications. Copyright © 2007 John Wiley & Sons, Ltd. [source]

The influence of Pb-ion irradiation on melt-textured YBa2Cu3Ox crystals

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2009
I. M. Obaidat
Abstract Melt-textured YBa2Cu3Ox crystals have been irradiated along the c -axis with 208Pb56+ ions corresponding to dose matching fields, B, = 0.5 T and B, = 2.0 T. Magnetization measurements were conducted along the ab plane of the samples. The strength of pinning sites was investigated by measuring magnetization hysterisis and the saturation remanent magnetization MR at several temperatures. We have found that the pinning strength was considerably enhanced after irradiation at both doses. Interestingly, the pinning strength at a Pb-ion irradiation which corresponds to the dose matching field B, = 0.5 T, was found to be significantly larger than that at the dose matching field B, = 2.0 T at all temperatures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Neural correlates of movement generation in the ,at-risk mental state'

ACTA PSYCHIATRICA SCANDINAVICA, Issue 4 2010
M. R. Broome
Broome MR, Matthiasson P, Fusar-Poli P, Woolley JB, Johns LC, Tabraham P, Bramon E, Valmaggia L, Williams SCR, Brammer MJ, Chitnis X, McGuire PK. Neural correlates of movement generation in the ,at-risk mental state'. Objective:, People with ,prodromal' symptoms have a very high risk of developing psychosis. We examined the neurocognitive basis of this vulnerability by using functional MRI to study subjects with an at-risk mental state (ARMS) while they performed a random movement generation task. Method:, Cross-sectional comparison of individuals with an ARMS (n = 17), patients with first episode schizophreniform psychosis (n = 10) and healthy volunteers (n = 15). Subjects were studied using functional MRI while they performed a random movement generation paradigm. Results:, During random movement generation, the ARMS group showed less activation in the left inferior parietal cortex than controls, but greater activation than in the first episode group. Conclusion:, The ARMS is associated with abnormalities of regional brain function that are qualitatively similar to those in patients who have recently presented with psychosis but less severe. [source]

Outcome of suicidal patients with schizophrenia: results from a naturalistic study

ACTA PSYCHIATRICA SCANDINAVICA, Issue 5 2010
R. Schennach-Wolff
Schennach-Wolff R, Jäger M, Seemüller F, Obermeier M, Schmauss M, Laux G, Pfeiffer H, Naber D, Schmidt LG, Gaebel W, Klosterkötter J, Heuser I, Maier W, Lemke MR, Rüther E, Klingberg S, Gastpar M, Möller H-J, Riedel M. Outcome of suicidal patients with schizophrenia: results from a naturalistic study. Objective:, Purpose was to assess suicidality before and at the time of admission in patients with schizophrenia and compare outcome differences. Method:, Biweekly PANSS (Positive and Negative Syndrome Scale), HAMD (Hamilton Depression Rating Scale) and UKU (Udvalg for Klinske Undersogelser Side Effect Rating Scale) ratings were evaluated in 339 in-patients with schizophrenic spectrum disorders. Response was defined as an initial 20% PANSS total score reduction at discharge, remission was defined according to the proposed consensus criteria by the Remission in Schizophrenia Working Group. Results:, Suicidal patients (22%) scored significantly higher on the PANSS negative subscore, PANSS insight item and HAMD total score at admission and at discharge. They developed significantly more side effects. No differences were found concerning response and remission between the two patient subgroups. Conclusion:, Despite receiving significantly more antidepressants the suicidal patients suffered from significantly more depressive symptoms up to discharge, yet without differing regarding response and remission. [source]

Cardiovascular disease prevalence and risk factors of persons with mental retardation

DEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 1 2006
Christopher C. Draheim
Abstract This paper reviews the recent literature on cardiovascular disease (CVD) prevalence, CVD-related mortality, physiological CVD risk factors, and behavioral CVD risk factors in adults with mental retardation (MR). The literature on the potential influences of modifiable behavioral CVD risk factors and the physiological CVD risk factors are also reviewed. Adults with mild to moderate MR residing in community settings appear to have an elevated disease prevalence, elevated CVD-related mortality, more adverse physiological CVD risk factors, and elevated behavioral risk compared to others with and without MR. Preliminary evidence supports the benefits of participating in the recommended physical activity levels and consuming the recommended diets to reduce the risk for CVD. The lack of large-scale longitudinal or experimental research indicates a gap in the research. The development of research-based, appropriate, primary prevention programs and intervention strategies aimed at lowering the risk for CVD is highly recommended. Programs should focus on educating individuals with MR along with direct care providers and family members on the importance of appropriate dietary concepts, physical activity habits, and regular health screenings by physicians. Programs should be individualized to regional and cultural issues. MRDD Research Reviews 2006;12:3,12. © 2006 Wiley-Liss, Inc. [source]

Graphic and movie illustrations of human prenatal development and their application to embryological education based on the human embryo specimens in the Kyoto collection

DEVELOPMENTAL DYNAMICS, Issue 2 2006
Shigehito Yamada
Abstract Morphogenesis in the developing embryo takes place in three dimensions, and in addition, the dimension of time is another important factor in development. Therefore, the presentation of sequential morphological changes occurring in the embryo (4D visualization) is essential for understanding the complex morphogenetic events and the underlying mechanisms. Until recently, 3D visualization of embryonic structures was possible only by reconstruction from serial histological sections, which was tedious and time-consuming. During the past two decades, 3D imaging techniques have made significant advances thanks to the progress in imaging and computer technologies, computer graphics, and other related techniques. Such novel tools have enabled precise visualization of the 3D topology of embryonic structures and to demonstrate spatiotemporal 4D sequences of organogenesis. Here, we describe a project in which staged human embryos are imaged by the magnetic resonance (MR) microscope, and 3D images of embryos and their organs at each developmental stage were reconstructed based on the MR data, with the aid of computer graphics techniques. On the basis of the 3D models of staged human embryos, we constructed a data set of 3D images of human embryos and made movies to illustrate the sequential process of human morphogenesis. Furthermore, a computer-based self-learning program of human embryology is being developed for educational purposes, using the photographs, histological sections, MR images, and 3D models of staged human embryos. Developmental Dynamics 235:468,477, 2006. © 2005 Wiley-Liss, Inc. [source]

Aetiology in severe and mild mental retardation: a population-based study of Norwegian children

DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 2 2000
Petter Strømme MD PhD
The aetiology of mental retardation (MR) was studied in a population-based series of Norwegian children derived from 30 037 children born between 1980 and 1985. The study included 178 children, 79 with severe MR (SMR) (IQ<50) and 99 with mild MR (MMR) (IQ 50 to 70). Aetiology was divided into two main groups: biopathological and unspecified. The biopathological group comprised 96% of SMR and 68% of MMR, and was subdivided into prenatal (70% and 51%), perinatal (4% and 5%), and postnatal damage (5% and 1%), and a group of undetermined timing of the damaging event (18% and 11%). Single-gene disorders accounted for 15 of the 63 children with genetic disorders, including X-linked recessive in six. During the course of the study, at least 27 (15%) children had their aetiological diagnosis revised. Gestational age <32 weeks, birthweight <1500g, and Apgar scores 0 to 2 at 1 and 5 minutes implied a significantly increased risk of MR, but contributed to only 4% of the children in the study. Decreased birthweight (1500 to 2499 g) and Apgar scores 3 to 6 at 1 and 5 minutes showed increased probability of MR. Despite extensive investigations, 4% of SMR and 32% of MMR were not identified with any biological markers and were considered as unspecified MR, several most probably representing the lower end of the normal IQ distribution in the population. [source]

Motherless rats show deficits in maternal behavior towards fostered pups

DEVELOPMENTAL PSYCHOBIOLOGY, Issue 2 2010
Daniela J. Palombo
Abstract Complete maternal deprivation in rats, through artificial rearing (AR), produces deficits in subsequent maternal behavior of the offspring. These deficits are partially reversed when isolated pups are provided with additional tactile stimulation designed to simulate maternal licking (e.g., Gonzalez et al. [2001] Developmental Psychobiology, 38, 11,32). These findings highlight the importance of the early maternal environment in subsequent development. However, given the possibility that prenatal environments may differ between AR and maternally reared (MR) offspring, the deficits in the behavior of AR mothers may be driven by the characteristics of their pups derived from the effects of an altered prenatal environment. Hence differences in the neonatal pups of AR mothers may produce the alterations in the AR maternal behavior. To rule out this possibility, we employed a fostering paradigm where AR and MR mothers received cross-fostered mother-reared pups. AR mothers showed the same level of deficits in maternal behavior towards MR foster pups as they do with their own pups and these deficits were partially reversed with additional tactile stimulation. Hence, maternal behavior deficits reported in mothers who had been reared in isolation are due primarily to the direct effects of the earlier experience on mechanisms regulating their maternal behavior and not to the effects on their offspring. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 52:142,148, 2010 [source]

Artificial rearing alters the response of rats to natural and drug-mediated rewards

DEVELOPMENTAL PSYCHOBIOLOGY, Issue 4 2006
Anna M. Lomanowska
Abstract Artificial rearing (AR) of infant rats permits precise control over key features of the early environment without maternal influence. The present study examined the behavioral response of AR rats towards natural and drug-mediated rewards, as well as their exploratory and affective behaviors. Adolescent AR rats showed increased preference for sucrose consumption relative to chow and demonstrated greater activity in the open field and in the elevated plus-maze compared to maternally reared (MR) rats. With respect to measures of emotionality, AR rats showed enhanced avoidance of the open arms of the plus-maze, indicating increased anxiety, but they did not differ from MR rats in exploring the center of the open field. Adult AR rats displayed a stronger conditioned response to morphine in a place preference test. These findings support the potential of the AR model to contribute to understanding the role of early experience in the development of behavioral motivation. © 2006 Wiley Periodicals, Inc. Dev Psyshobiol 48: 301,314, 2006. [source]

Maternal and littermate deprivation disrupts maternal behavior and social-learning of food preference in adulthood: Tactile stimulation, nest odor, and social rearing prevent these effects

DEVELOPMENTAL PSYCHOBIOLOGY, Issue 3 2006
Angel I. Melo
Abstract Maternal and littermate (social) separation, through artificial rearing (AR), disrupts the development of subsequent maternal behavior and social learning in rats. The addition of maternal-licking-like stimulation during AR, partially reverses some of these effects. However, little is know about the role of social stimuli from littermates and nest odors during the preweaning period, in the development of the adult maternal behavior and social learning. The purpose of this study was to examine the effects of peer- and peer-and-odor rearing on the development of maternal behavior and social learning in rats. Female pups were reared with mothers (mother reared,MR) or without mothers (AR) from postnatal day (PND) 3. AR rats received three different treatments: (1) AR-CONTROL group received minimal tactile stimulation, (2) AR-ODOR females received exposure to maternal nest material inside the AR-isolation-cup environment, (3) AR-SOCIAL group was reared in the cup with maternal nest material and a conspecific of the same-age and same-sex and received additional tactile stimulation. MR females were reared by their mothers in the nest and with conspecifics. In adulthood, rats were tested for maternal behavior towards their own pups and in a social learning task. Results confirm our previous report that AR impairs performance of maternal behavior and the development of a social food preference. Furthermore, social cues from a littermate, in combination with tactile stimulation and the nest odor, reversed the negative effects of complete isolation (AR-CONTROL) on some of the above behaviors. Exposure to the odor alone also had effects on some of these olfactory-mediated behaviors. These studies indicate that social stimulation from littermates during the preweaning period, in combination with odor from the nest and tactile stimulation, contributes to the development of affiliative behaviors. © 2006 Wiley Periodicals, Inc. Dev Psyshobiol 48: 209,219, 2006. [source]

Experimental and analytical study on pounding reduction of base-isolated highway bridges using MR dampers

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2009
Anxin Guo
Abstract Pounding between adjacent superstructures has been a major cause of highway bridge damage in the past several earthquakes. This paper presents an experimental and analytical study on pounding reduction of highway bridges subjected to earthquake ground motions by using magnetorheological (MR) dampers. An analytical model, which incorporates structural pounding and MR dampers, is developed. A series of shaking table tests on a 1:20 scaled base-isolated bridge model are performed to investigate the effects of pounding between adjacent superstructures on the dynamics of the structures. Based on the test results, the parameters of the linear and the nonlinear viscoelastic impact models are identified. Performance of the semiactive system for reducing structural pounding is also investigated experimentally, in which the MR dampers are used in conjunction with the proposed control strategy, to verify the effectiveness of the MR dampers. Structural responses are also simulated by using the established analytical model and compared with the shaking table test results. The results show that pounding between adjacent superstructures of the highway bridge significantly increases the structural acceleration responses. For the base-isolated bridge model considered here, the semiactive control system with MR dampers effectively precludes pounding. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Experimental performance evaluation of an equipment isolation using MR dampers

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2009
Yu-Cheng Fan
Abstract Critical non-structural equipments, including life-saving equipment in hospitals, circuit breakers, computers, high technology instrumentations, etc., are vulnerable to strong earthquakes, and the failure of these equipments may result in a heavy economic loss. In this connection, innovative control systems and strategies are needed for their seismic protections. This paper presents the performance evaluation of passive and semi-active control in the equipment isolation system for earthquake protection. Through shaking table tests of a 3-story steel frame with equipment on the first floor, a magnetorheological (MR)-damper together with a sliding friction pendulum isolation system is placed between the equipment and floor to reduce the vibration of the equipment. Various control algorithms are used for this semi-active control studies, including the decentralized sliding mode control (DSMC) and LQR control. The passive-on and passive-off control of MR damper is used as a reference for the discussion on the control effectiveness. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Experimental verification of a wireless sensing and control system for structural control using MR dampers

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2007
Chin-Hsiung Loh
Abstract The performance aspects of a wireless ,active' sensor, including the reliability of the wireless communication channel for real-time data delivery and its application to feedback structural control, are explored in this study. First, the control of magnetorheological (MR) dampers using wireless sensors is examined. Second, the application of the MR-damper to actively control a half-scale three-storey steel building excited at its base by shaking table is studied using a wireless control system assembled from wireless active sensors. With an MR damper installed on each floor (three dampers total), structural responses during seismic excitation are measured by the system's wireless active sensors and wirelessly communicated to each other; upon receipt of response data, the wireless sensor interfaced to each MR damper calculates a desired control action using an LQG controller implemented in the wireless sensor's computational core. In this system, the wireless active sensor is responsible for the reception of response data, determination of optimal control forces, and the issuing of command signals to the MR damper. Various control solutions are formulated in this study and embedded in the wireless control system including centralized and decentralized control algorithms. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Experimental study of the semi-active control of building structures using the shaking table

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 15 2003
Qing Sun
Abstract A magnetorheological (MR) damper has been manufactured and tested and a non-linear model is discussed. The parameters for the model are identified from an identification set of experimental data; these parameters are then used to reconstruct the force vs. displacement and the force vs. velocity hysteresis cycles of the MR damper for the hysteretic model. Then experiments are conducted on a three-storey frame model using impact excitation, which identifies dynamic parameters of the model equipped with and without the MR damper. Natural frequencies, damping ratios and mode shapes, as well as structural properties, such as the mass, stiffness and damping matrices, are obtained. A semi-active control method such as a variable structure controller is studied. Based on the ,reaching law' method, a feedback controller is presented. In order to evaluate the efficiency of the control system and the effect of earthquake ground motions, both numerical analysis and shaking table tests of the model, with and without the MR damper, have been carried out under three different ground motions: El Centro 1940, Taft 1952, and Ninghe 1976 (Tangshan Earthquake in Chinese). It is found from both the numerical analysis and the shaking table tests that the maximum accelerations and relative displacements for all floors are significantly reduced with the MR damper. A reasonable agreement between the results obtained from the numerical analysis and those from the shaking table tests is also observed. On the other hand, tests conducted at different earthquake excitations and various excitation levels demonstrate the ability of the MR damper to surpass the performance of a comparable passive system in a variety of situations. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Usefulness and Limitation of Dobutamine Stress Echocardiography to Predict Acute Response to Cardiac Resynchronization Therapy

ECHOCARDIOGRAPHY, Issue 1 2010
F.R.C.P.C., Mario Sénéchal M.D.
Background: It has been hypothesized that a long-term response to cardiac resynchronization therapy (CRT) could correlate with myocardial viability in patients with left ventricular (LV) dysfunction. Contractile reserve and viability in the region of the pacing lead have not been investigated in regard to acute response after CRT. Methods: Fifty-one consecutive patients with advanced heart failure, LV ejection fraction , 35%, QRS duration > 120 ms, and intraventricular asynchronism , 50 ms were prospectively included. The week before CRT implantation, the presence of viability was evaluated using dobutamine stress echocardiography. Acute responders were defined as a ,15% increase in LV stroke volume. Results: The average of viable segments was 5.8 ± 1.9 in responders and 3.9 ± 3 in nonresponders (P = 0.03). Viability in the region of the pacing lead had an excellent sensitivity (96%), but a low specificity (56%) to predict acute response to CRT. Mitral regurgitation (MR) was reduced in 21 patients (84%) with acute response. The presence of MR was a poor predictor of response (sensibility 93% and specificity 17%). However, combining the presence of MR and viability in the region of the pacing lead yields a sensibility (89%) and a specificity (70%) to predict acute response to CRT. Conclusion: Myocardial viability is an important factor influencing acute hemodynamic response to CRT. In acute responders, significant MR reduction is frequent. The combined presence of MR and viability in the region of the pacing lead predicts acute response to CRT with the best accuracy. (Echocardiography 2010;27:50-57) [source]

Mitral Regurgitation Associated with Mitral Annular Dilation in Patients with Lone Atrial Fibrillation: An Echocardiographic Study

ECHOCARDIOGRAPHY, Issue 8 2009
Takashi Kihara M.D.
Background: Whether and how lone atrial fibrillation (AF) is associated with functional mitral regurgitation (MR) remain unclear. Method: We studied 12 lone AF patients without left ventricular (LV) dysfunction and/or dilatation, who underwent mitral valve annuloplasty for functional mitral regurgitation (MR). Ten lone AF patients without MR served as controls. Results: Lone AF Patients with MR had a greater mitral valve annular area and left atrial area than those without MR. There were no differences in LV volumes or LV ejection fraction. Conclusions: Therefore, we concluded that left atrial dilation and corresponding mitral annular dilation may cause MR in lone AF patients without LV dysfunction and/or dilatation. [source]

Worsening of Left Ventricular End-Systolic Volume and Mitral Regurgitation without Increase in Left Ventricular Dyssynchrony on Acute Interruption of Cardiac Resynchronization Therapy

ECHOCARDIOGRAPHY, Issue 7 2009
Suman S. Kuppahally M.D.
Background: Responders to cardiac resynchronization therapy (CRT) have greater left ventricular (LV) dyssynchrony than nonresponders prior to CRT. Aim: We conducted this study to see whether the long term responders have more worsening of LV dyssynchrony and LV function on acute interruption of CRT. Materials and Methods: We identified 22 responders and 13 nonresponders who received CRT as per standard criteria for 23.73 ± 7.9 months (median 24.5 months). We assessed the acute change in LV function, mitral regurgitation (MR) and compared LV dyssynchrony in CRT on and off modes. Results: On turning off CRT, there was no significant worsening of LV dyssynchrony in both responders and nonresponders. The dyssynchrony measurements by SPWMD, TDI and 3D echocardiography did not correlate significantly. LVESV increased (p = 0.02) and MR (p = 0.01) worsened in CRT-off mode in responders only without significant change in LVEF or LV dimensions. Discussion and Conclusion: In long-term responders to CRT, there is alteration in the function of remodeled LV with acute interruption of CRT, without significant worsening of LV dyssynchrony. The role of different echocardiographic parameters in the assessment of LV dyssynchrony remains controversial. Even after long-term CRT reversely remodels the LV, the therapy needs to be continued uninterrupted for sustained benefits. [source]

Can a Novel Echocardiographic Score Better Predict Outcome after Percutaneous Balloon Mitral Valvuloplasty?

ECHOCARDIOGRAPHY, Issue 2 2009
Osama Rifaie M.D.
Objective: The assessment of patients with mitral stenosis before percutaneous balloon mitral valvuloplasty (PBMV) is crucial to predict outcome after the procedure. We tried to explore the prognostic power of a novel echocardiographic score to predict immediate postprocedural outcome in comparison to the standard score. Methods: We enrolled 50 consecutive patients with moderate to severe mitral stenosis admitted to undergo PBMV. For all patients, we assessed both the standard Massachusetts General Hospital (MGH) score and a novel score based on calcification (especially commissural) and subvalvular involvement. Patients underwent PBMV with the double balloon technique. Thereafter, patients were classified into two groups: group 1 (poor outcome) defined as no procedural success and/or increase of MR by more than 1 grade and group 2 (optimal outcome) defined as procedural success with increase of MR by 1 grade or less. Results: The total MGH score did not differ significantly between the two groups. However, among the individual parameters of the score, both calcification and subvalvular affection were significantly higher in group 1 versus group 2 (2.8 ± 0.4 versus 1.7 ± 0.8, and 2.4 ± 0.5 versus 1.6 ± 0.4, respectively, P < 0.01 for both). The total novel score and its two individual parameters (calcification and subvalvular involvement) were all significantly higher in group 1 versus group 2 (6 ± 1.5 versus 2.9 ± 1.9, 4.9 ± 1.2 versus 2.4 ± 1.5, 1.5 ± 1.6 versus 0.5 ± 0.9, respectively, P < 0.01 for all). Multivariate analysis demonstrated the novel score to be the only independent predictor of poor outcome. Conclusion: The novel score is more reliable and correlates with outcome better than the standard score. [source]

Local Dysfunction and Asymmetrical Deformation of Mitral Annular Geometry in Ischemic Mitral Regurgitation: A Novel Computerized 3D Echocardiographic Analysis

ECHOCARDIOGRAPHY, Issue 4 2008
Masao Daimon M.D.
Objective: Most studies of the pathogenesis of functional mitral regurgitation (MR) have focused on alterations in ventricular function and geometry. We used a novel 3D echocardiographic method to assess abnormalities in mitral annular (MA) geometry and motion in patients with ischemic MR (IMR) and compared these data to those obtained from normal subjects and from patients with MR caused by dilated cardiomyopathy (DMR). Methods: Real time 3D echo was performed in 12 normal subjects, 25 with IMR, and 14 with DMR. Eight points along the saddle-shaped MA were identified using our software at systole and diastole. From these eight points, four annular diameters at each cardiac phase were determined. Annular motion was assessed by measuring local displacement (LD) of a given point between systole and diastole. Results: Annular motion was different between groups: IMR had smaller LD in posterior MA segments than did normals (2.6 ± 1.1 vs 4.8 ± 1.9 mm, P < 0.01), while DMR had globally reduced LD. In IMR systolic MA dilatation was striking in the anterior,posterior (diameter; IMR vs controls, 28.3 ± 3.5 vs 22.5 ± 2.2 mm, P< 0.05) and anterolateral,posteromedial (31.7 ± 3.5 vs 25.1 ± 2.2 mm, P < 0.05) directions; in IMR, systolic MA diameters in these two directions correlated with MR severity(P = 0.02). MA dilatation occurred globally in DMR. Conclusion: This novel 3D echo method demonstrated that MA motion and dilatation were asymmetric in IMR and symmetric in DMR. These differences in MA geometry and motion may aid in the development of distinct new therapies for IMR and DMR. [source]

REVIEW: Aortic Atheromas: Current Concepts and Controversies,A Review of the Literature

ECHOCARDIOGRAPHY, Issue 2 2008
Thenappan Thenappan M.D.
The frequent use of transesophageal echocardiogram (TEE) has led to the increased recognition of aortic atheromas. Retrospective and prospective follow-up studies have reported an association between aortic atheromas and stroke in the high-risk patient population, with complex plaques being more likely to embolize than simple plaques. However, TEE-based studies in the low-risk cohorts have failed to show a similar association. There is growing body of evidence suggesting that aortic atheroma is a marker of generalized atherosclerosis. Although magnetic resonance (MR) imaging and computed tomography (CT) scan are emerging as a powerful noninvasive tool for characterization of aortic atheromas, TEE is the imaging modality of choice. Currently, treatment of aortic atheromas is not well defined, and mixed outcomes have been reported for anticoagulation therapy with warfarin. Statins appear promising based on their plaque stabilization properties. However, there are no randomized control trials to establish the role of both anticoagulation and statins in patients with aortic atheromas, and are warranted in the future. [source]

Reference Values Describing the Normal Mitral Valve and the Position of the Papillary Muscles

ECHOCARDIOGRAPHY, Issue 7 2007
Petrus Nordblom M.Sc.
In patients with functional mitral regurgitation (MR), the principal mechanisms are insufficient coaptation due to dilatation of the mitral annulus (MA), global ventricular dysfunction with tethering of leaflets, or restricted leaflet motion with incorrect apposition due to regional ventricular dysfunction and displacement of the papillary muscles (PMs). These different entities often coexist and for this reason, knowledge of the normal reference values describing the shape and size of the MA and the position of the PMs is essential. In the present study, we describe the MA dimensions and the position of the PMs in a group of normal individuals (n = 38, 60% women, age [mean ± SD] 51 ± 9 years and BSA 1.83 ± 0.16 m2) investigated with transthoracic echocardiography. The anteroposterior dimension (AP) of the ellipse-shaped MA was measured in a parasternal long axis, while the distance from the posteromedial (PoM) to the anterolateral (AL) commissure was measured in a parasternal short axis (CC). The annular area was calculated assuming elliptic geometry. The MA shape was described by the ratios AP/CC and AP/length of the anterior leaflet. The PMs' position was described by the following distances: (a) from the MA to the tip of the PoM and AL, PMs measured in a modified two-chamber view where both PMs could be identified, (b) the interpapillary distance, and (c) the tethering distance from the tip of the PM to the contralateral MA. These data on the normal mitral valve morphology should provide useful information when assessing the underlying mechanism of functional MR. [source]