Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Y40: Physiological and Medical Physics |
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Sponsoring Units: DBP Chair: Krastan Blagoev, National Science Foundation Room: 412 |
Friday, March 20, 2009 8:00AM - 8:12AM |
Y40.00001: Biophysical investigation of the apoptotic force Yusuke Toyama, Xomalin Peralta, Adrienne Wells, Daniel Kiehart, Glenn Edwards Understanding tissue dynamics during development requires knowledge of how cells produce and respond to forces. We have experimentally shown that apoptosis (programmed cell death, which remodels tissue by eliminating cells) also contributes a significant tissue force that promotes cell sheet fusion during dorsal closure in Drosophila development [Science, 321, 1683 (2008)]. By genetically suppressing (enhancing) apoptosis, we slow (increase) the rate of dorsal closure. These changes correlate with the forces produced by the amnioserosa tissue and the rate of seam formation (zipping) for two advancing sheets of lateral epidermis. This apoptotic force is used to drive cell sheet movements during development, a role not classically attributed to apoptosis. [Preview Abstract] |
Friday, March 20, 2009 8:12AM - 8:24AM |
Y40.00002: Reorganization of neuronal circuits in growing visual cortex Wolfgang Keil, Siegrid Loewel, Fred Wolf, Matthias Kaschube The dynamics of reorganization of large cortical circuits is rooted in plasticity of individual synapses, but rules governing the collective behavior of large networks of neurons are only poorly understood. The postnatal brain growth partly evoked by extensive formation of new synaptic connections may expose cortical areas to a 'natural perturbation' sufficiently strong to observe signatures of large scale reorganization. Quantifying large sets of imaging data from juvenile cat visual cortex, we observe a novel mode of reorganization of domains that prefer inputs from one eye or the other. Our theoretical analysis shows that this mode can be explained quantitatively by the so called Zigzag instability, a dynamical reorganization, well-known in the field of pattern formation in physics, by which 2D isotropic Turing patterns respond to an increase in their typical spatial scale with a zigzag-like bending of domains. We point out that this instability has in fact been predicted, albeit implicitly, by most models of visual cortical development that have been proposed so far. We conclude that cortical networks can undergo large scale reorganizations during normal postnatal development. [Preview Abstract] |
Friday, March 20, 2009 8:24AM - 8:36AM |
Y40.00003: Epithelial oscillations enhance signal detection in a peripheral sensory system Alexander Neiman, Tatiana Engel, David Russell, Brian Helbig, Lutz Schimansky-Geier Rhythmic spontaneous activity was observed in various peripheral sensory systems. Many sensory receptors have a specific structure where detector cells in a sensory epithelium excite primary afferent neurons. We explore how stochastic oscillations of epithelial cells affect the ability of peripheral receptors to detect weak stimuli. We use a simple analytically tractable model to contrast signal detection in two situations: (i) when epithelial oscillations are coherent, and (ii) when the coherence of epithelial oscillations is destroyed. We show that coherent epithelial oscillations decrease the variability of neuronal firing and thus to enhance discriminability of weak signals. Model predictions are supported by the analysis of experimental data from the electroreceptors of paddlefish. [Preview Abstract] |
Friday, March 20, 2009 8:36AM - 8:48AM |
Y40.00004: Sound Localization in Lizards: Functioning of a Pressure-Gradient Receiver J. Leo van Hemmen Because of their small interaural distance, lizards as well as some other animals have developed a special hearing mechanism, the ``pressure-gradient receiver''. The lizard peripheral auditory system differs from the mammalian one by a coupling of the two eardrums through the internal mouth cavity. We present a three-dimensional analytical model of the pressure-gradient receiver. The central aspect of the coupling of the membranes through the mouth cavity is realized by means of the boundary conditions. Moreover, the lizard's middle ear, a simple lever construction called \textit{columella}, is asymmetrically attached to the tympanic membrane. This has motivated us to solve the problem of how the middle ear influences the spatial-amplitude profile and the frequency distribution of the tympanic membrane vibration. Finally, we show results from numerical simulations of the eigenfunctions and eigenfrequencies in a lizard's internal mouth cavity bounded by the eardrums. To this end, we have constructed the complex geometry from a cast imprint of the cavity with the help of three-dimensional scans. Our results led to an interesting speculation regarding the neurobiological use of the pressure-gradient system. [Preview Abstract] |
Friday, March 20, 2009 8:48AM - 9:00AM |
Y40.00005: Direct Neural Imaging using Ultra-Low Field Magnetic Resonance Karlene Maskaly, Michelle Espy, Mark Flynn, John Gomez, Robert Kraus, Andrei Matlashov, John Mosher, Shaun Newman, Tuba Owens, Mark Peters, J. Sandin, Larry Schultz, Algis Urbaitis, Petr Volegov, Vadim Zotev An enduring challenge in neuroscience is the accurate in vivo mapping of neural activity with high spatial and temporal resolution. A method being developed by our group tries to meet this challenge by using Ultra-Low Field (ULF) MRI. Other groups have attempted direct neural imaging (DNI) using high field MRI. However, the use of ULF presents two advantages. First, the susceptibility artifact at high fields, which masks the DNI signal, is negligible at low fields. Second, the reduced Larmor frequency at ULF may overlap with the frequency spectrum of the neural magnetic field, resonantly enhancing the MRI signal. In this presentation, I will first show our custom-built ULF MRI setups that have successfully produced ULF anatomical images. I will then highlight the numerous studies we have done to investigate the feasibility of DNI with these systems, including both experimental and theoretical studies. [Preview Abstract] |
Friday, March 20, 2009 9:00AM - 9:12AM |
Y40.00006: Synaptic vesicle dynamics in Hippocampal Slices Krastan Blagoev, Denis Bragin, Wolfgang Mueller Synaptic vesicle pool dynamics in hippocampal slices have been observed using FM-dye as an activity-dependent contrast agent with two-photon microscopy. Separate vesicle pools for spontaneous and stimulated vesicle release and their dynamics, and vesicle exchange dynamics between the pools was inferred from the signal with and without stimulation. To interpret the experimental results we developed a multi-compartmental kinetic model of the FM-dye dynamics during loading and unloading of vesicles. Using this mathematical model we estimated the exchange rates between the synaptic vesicle pools and the resulting vesicle release dynamics. We will discuss important differences between the vesicle pool dynamics in ex-vivo brain slices and in disassociated neuronal cultures. [Preview Abstract] |
Friday, March 20, 2009 9:12AM - 9:24AM |
Y40.00007: The surface properties of a lung mucus model system Markus Weygand, Beautia Dew, Stephen Garoff, Mathias L\"{o}sche, Todd Przybycien, Robert Tilton Adding surfactants to aerosol drug therapies may improve drug delivery by inducing surface tension gradient driven flows along the lung airway surfaces. Understanding the surface structure and properties of the mucus that lines the lung airways is crucial to the proper design of such formulations. In our studies, we use mucin solutions made from porcine gastric mucus as a model system. Surface tension measurements revealed a time and humidity dependence, which led us to investigate the structure of the air/solution interface using X-ray and neutron reflectivity. These studies reveal a compact adsorption layer at the air/liquid interface whose density distribution decays with a long tail extension into the bulk liquid. This structure showed only a minor dependence on the humidity above the mucus surface. To examine possible interaction between lipids present in the lung with the mucus, we deposited DPPC and DMPC onto the mucin solution surface and observed that the lipid layer remained on the solution surface for times long compared to the lifetime of mucus in the lung. The analysis of the reflectivity data impart a microscopic picture of the mucin solution surface and its alteration by lipid deposition. [Preview Abstract] |
Friday, March 20, 2009 9:24AM - 9:36AM |
Y40.00008: Structural Measurements from Images of Noble Gas Diffusion Robert V. Cadman, Stephen J. Kadlecek, KiaRash Emami, John MacDuffie Woodburn, Vahid Vahdat, Masaru Ishii, Rahim R. Rizi Magnetic resonance imaging of externally polarized noble gases such as $^3$He has been used for pulmonary imaging for more than a decade. Because gas diffusion is impeded by the alveoli, the diffusion coefficient of gas in the lung, measured on a time scale of milliseconds, is reduced compared to that of the same gas mixture in the absence of restrictions. When the alveolar walls decay, as in emphysema, diffusivity in the lung increases. In this paper, the relationship between diffusion measurements and the size of the restricting structures will be discussed. The simple case of diffusion in an impermeable cylinder, a structure similar to the upper respiratory airways in mammals, has been studied. A procedure will be presented by which airways of order 2 mm in diameter may be accurately measured; demonstration experiments with plastic tubes will also be presented. The additional developments needed before this technique becomes practical will be briefly discussed. [Preview Abstract] |
Friday, March 20, 2009 9:36AM - 9:48AM |
Y40.00009: Clusters of decelerations of heart rate appear to be a Hopf bifurcation, and provide early warning of illness in premature infants Abigail Flower, Randall Moorman, Douglas Lake, John Delos The pacemaking system of the heart is complex; a healthy heart constantly integrates and responds to extracardiac signals, resulting in highly complex heart rate patterns with a great deal of variability. In the laboratory and in some pathological or age-related states, however, dynamics can show reduced complexity that is more readily described and modeled. Reduced heart rate complexity has both clinical and dynamical significance -- it may provide warning of impending illness or clues about the dynamics of the heart's pacemaking system. Here we describe uniquely simple and interesting heart rate dynamics observed in premature human infants - reversible transitions to large-amplitude periodic oscillations. We propose a mathematical interpretation based on Hopf bifurcation theory. (Supported by NIGMS, by the National Heart, Lung, and Blood Institute, and by NSF, with computing support provided by William and Mary.) [Preview Abstract] |
Friday, March 20, 2009 9:48AM - 10:00AM |
Y40.00010: New Outlet Conditions for Three-Dimensional Computational Fluid Dynamic Simulations of Blood Flow in Arteries David Johnson, Ulhas Naik, Antony Beris In three-dimensional (3D) simulation of a component of the arterial network, we have the problem of properly specifying outlet conditions due to coupling with the rest of the arterial network. In this work we propose to use an approximate solution, based on a one-dimensional (in space) but time periodic approximation of the flow, in order to obtain these outlet conditions. These are used in fully 3D and time periodic computational fluid dynamic (CFD) simulations of a coronary arterial junction, using the commercial software Fluent. A consistent implementation requires an iterative procedure that has been developed based on a lubrication approximation. The application of these boundary conditions has been applied to both a normal/healthy coronary artery junction and a diseased case, where an occlusion has developed causing impairment of flow. Results will be shown that demonstrate significant changes to the solution. [Preview Abstract] |
Friday, March 20, 2009 10:00AM - 10:12AM |
Y40.00011: Millimeter Wave Spectroscopy for Breast Cancer Diagnostics and Detection Konstantin Korolev, Shu Chen, Mohammed Afsar, Stephen Naber Broad-band millimeter wave transmittance measurements of normal and tumorous (cancerous) human breast tissue samples have been acquired \textit{in--vitro} by employing a free-space, quasi-optical spectrometer. Freshly excised breast tissues were prepared and preserved in 10{\%} neutral-buffered formalin solution before testing. Significant differences in the transmittance profiles have been found between the normal and tumorous tissues. It has been found that despite the inhomogeneity and variable structure and composition of each single tissue, the tumorous specimens consistently manifest much higher absorption level of millimeter wave radiation than the normal ones. It has been shown that free space, quasi-optical spectrometer is capable of contributing valuable insights into the dielectric properties of normal and tumorous human breast tissues and aiding in further developments of millimeter wave spectroscopy and mammography for the breast cancer diagnostics and detection. [Preview Abstract] |
Friday, March 20, 2009 10:12AM - 10:24AM |
Y40.00012: Diffusion dependence of proton NMR relaxation rates in the presence of ferritin Michael Boss, P. Chris Hammel Ferritin is the predominant iron-storage protein in living organisms. It may serve as an indicator of neurodegenerative diseases such as Alzheimer's. Measuring brain ferritin concentration non-invasively via MRI could enable better diagnoses and treatments of such diseases. Quantitative MRI determination of the ferritin concentration requires an understanding of the NMR relaxation mechanisms of hydrogen protons in the presence of ferritin. In aqueous solutions, ferritin enhances the transverse relaxation rate (R$_{2})$ of the protons. This is thought to occur due to a diffusive mechanism, where protons diffusing near ferritin pass through a region of elevated magnetic field, and a chemical exchange mechanism, where protons bind to the protein for a period of time, experiencing an even higher magnetic field. These two mechanisms exhibit different dependencies on the self-diffusion coefficient of the protons. By adding glycerol to aqueous solutions, we control the self-diffusion of protons. We measure the R$_{2}$ of protons in ferritin-containing binary mixtures of water and glycerol using CPMG sequences, and compare the experimental results to theoretical predictions of diffusion dependence in order to distinguish the relative importance of the mechanisms. [Preview Abstract] |
Friday, March 20, 2009 10:24AM - 10:36AM |
Y40.00013: Application of Histogram Analysis in Radiation Therapy (HART) in Intensity Modulation Radiation Therapy (IMRT) Treatments Anil Pyakuryal A carcinoma is a malignant cancer that emerges from epithelial cells in structures through out the body.It invades the critical organs, could metastasize or spread to lymph nodes.IMRT is an advanced mode of radiation therapy treatment for cancer. It delivers more conformal doses to malignant tumors sparing the critical organs by modulating the intensity of radiation beam.An automated software, \textbf{\textit{HART}} (S. Jang et al.,2008,Med Phys 35,p.2812) was used for efficient analysis of dose volume histograms (DVH) for multiple targets and critical organs in four IMRT treatment plans for each patient. IMRT data for ten head and neck cancer patients were exported as AAPM/RTOG format files from a commercial treatment planning system at Northwestern Memorial Hospital (NMH).HART extracted DVH statistics were used to evaluate plan indices and to analyze dose tolerance of critical structures at prescription dose (PD) for each patient. Mean plan indices (n=10) were found to be in good agreement with published results for Linac based plans. The least irradiated volume at tolerance dose (TD50) was observed for brainstem and the highest volume for larynx in SIB treatment techniques. Thus HART, an open source platform, has extensive clinical implications in IMRT treatments. [Preview Abstract] |
Friday, March 20, 2009 10:36AM - 10:48AM |
Y40.00014: Role of Physique on Probability of Injury to the Low Back Saami J. Shaibani In a related study of the response of the upper and lower cervical spine[1], there was some correlation between a change in physique and the potential for injury to the neck during automotive events. A similar undertaking in this research on the lumbar spine and sacral spine revealed a much more marked effect, namely an increase in injury potential to the low back when weight is increased. Although there were some exceptions to this, the overall trend was distinct. This is perhaps to be expected when one considers that most additional weight at the same height tends to be located in the center or lower torso. However, it is first time in any comparable analysis of injury causation that there has been a more noticeable pattern for the low back than the neck. The latter was more pronounced with environment geometry, as seen when the height of the seat back was varied. Such changeability again reinforces previous findings that injury outcomes for individual patients cannot always be predicted by what happens in general. 1. http://meetings.aps.org/link/BAPS.2007.MAR.K1.2 (Role of physique on probability of injury to the neck). [Preview Abstract] |
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