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arXiv2012

Assessment of Radio-Frequency Radiation Exposure Level from Selected Mobile Base Stations (MBS) in Lokoja, Kogi State, Nigeria

The acquisition and use of mobile phone is tremendously increasing especially in developing countries, but not without a concern. The greater concern among the public is principally over the proximity of mobile base stations (MBS) to residential areas rather than the use of handsets. In this paper, we present an assessment of Radio-Frequency (RF) radiation exposure level measurements and analysis of radiation power density (in W/sq m) from mobile base stations relative to radial distance (in metre). The minimum average power density from individual base station in the town was about 47uW/sq m while the average maximum was about 1.5mW/sq m. Our result showed that average power density of a base station decreased with increase in distance (away from base station) and that radiation intensity varies from one base station to another even at the same distance away. Our result (obtained signature of power density variation from data) was also compared the with an 'expected' signature. It was found that radiation from external sources (indicative) interfered with the reference base station and accounted for the deviation observed in this study. Finally, our result showed that the RF exposure hazard index in the town of Lokoja was below the permitted RF exposure limit to the general public recommended by ICRNIP. Useful recommendations were also made to the Policy and Regulatory Agencies responsible to Telephony in Nigeria.

physics.med-ph↗

arXiv2013

Relative acceleration approach for conduction failure of cardiac excitation propagation on anisotropic curved surfaces

In cardiac electrophysiology, it is important to predict the necessary conditions for conduction failure, the failure of the cardiac excitation propagation even in the presence of normal excitable tissue, in high-dimensional anisotropic space because these conditions may provide feasible mechanisms for abnormal excitation propagations such as atrial re-entry and, subsequently, atrial fibrillation even without taking into account the time-dependent refractory region. Some conditions of conduction failure have been studied for anisotropy or simple curved surfaces, but the general conditions on anisotropic curved surfaces (anisotropic and curved surface) remain unknown. To predict and analyze conduction failure on anisotropic curved surfaces, a new analytic approach is proposed, called the relative acceleration approach borrowed from spacetime physics. Motivated by a discrete model of cardiac excitation propagation, this approach is based on the hypothesis that a large relative acceleration can translate to a dramatic increase in the curvature of the wavefront and, subsequently, to conduction failure. For simple anisotropic surfaces, the relative acceleration approach is validated by computational simulations or the previously known results from the kinematics approach. As a practical application, this approach is proposed to provide theoretical explanations of the mechanism of cardiac excitation propagation around the pulmonary vein with anatomically observed anisotropy.

physics.med-ph↗

arXiv2012

Demonstrating the Usefulness of CAELinux for Computer Aided Engineering using an Example of the Three Dimensional Reconstruction of a Pig Liver

CAELinux is a Linux distribution which is bundled with free software packages related to Computer Aided Engineering (CAE). The free software packages include software that can build a three dimensional solid model, programs that can mesh a geometry, software for carrying out Finite Element Analysis (FEA), programs that can carry out image processing etc. Present work has two goals: 1) To give a brief description of CAELinux 2) To demonstrate that CAELinux could be useful for Computer Aided Engineering, using an example of the three dimensional reconstruction of a pig liver from a stack of CT-scan images. One can note that instead of using CAELinux, using commercial software for reconstructing the liver would cost a lot of money. One can also note that CAELinux is a free and open source operating system and all software packages that are included in the operating system are also free. Hence one can conclude that CAELinux could be a very useful tool in application areas like surgical simulation which require three dimensional reconstructions of biological organs. Also, one can see that CAELinux could be a very useful tool for Computer Aided Engineering, in general.

cs.MS↗

arXiv2012

In Vivo Quantification of Clot Formation in Extracorporeal Circuits

Clot formation is a common complication in extracorporeal circuits. In this paper we describe a novel method for clot formation analysis using image processing. We assembled a closed extracorporeal circuit and circulated blood at varying speeds. Blood filters were placed in downstream of the flow, and clotting agents were added to the circuit. Digital images of the filter were subsequently taken, and image analysis was applied to calculate the density of the clot. Our results show a significant correlation between the cumulative size of the clots, the density measure of the clot based on image analysis, and flow duration in the system.

cs.CV↗

arXiv2013

To what extent does not wearing shoes affect the local dynamic stability of the gait? Effect size and intra-session repeatability

Local dynamic stability (LDS) quantifies how a system responds to small perturbations. Several experimental and clinical findings have highlighted the association between gait LDS and fall risk. Walking without shoes is known to slightly modify gait parameters. Barefoot walking (BW) may cause unusual sensory feedback to individuals accustomed to shod walking (SW), and this may impact on LDS. The objective of this study was therefore to compare the LDS of SW and BW in healthy individuals and to analyze the intrasession repeatability. Forty participants traversed a 70 m indoor corridor wearing normal shoes in one trial and walking barefoot in a second trial. Trunk accelerations were recorded with a 3D-accelerometer attached to the lower back. The LDS was computed using the finite-time maximal Lyapunov exponent method. Absolute agreement between the forward and backward paths was estimated with the intraclass correlation coefficient (ICC). BW did not significantly modify the LDS as compared to SW (average standardized effect size: +0.12). The intrasession repeatability was high in SW (ICC: 0.73-0.79) and slightly higher in BW (ICC: 0.82-0.88). Therefore, it seems that BW can be used to evaluate LDS without introducing bias as compared to SW, and with a sufficient reliability.

q-bio.QM↗

arXiv2013

Inverse Z-spectrum analysis for MT- and spillover-corrected and T1-compensated steady-state pulsed CEST-MRI - application to pH-weighted MRI of acute stroke

Endogenous chemical exchange saturation transfer (CEST) effects are always diluted by competing effects such as direct water proton saturation (spillover) and macromolecular magnetization transfer (MT). This leads to T2-and MT-shine-through effects in the actual biochemical contrast of CEST. Therefore, a simple evaluation algorithm which corrects the CEST signal was searched for. By employing a recent eigenspace theory valid for spinlock and continuous wave (cw) CEST we predict that the inverse Z-spectrum is beneficial to Z-spectrum itself. Based on this we propose a new spillover- and MT-corrected magnetization transfer ratio (MTRRex) yielding Rex, the exchange dependent relaxation rate in the rotating frame. For verification, the amine proton exchange of creatine in solutions with different agar concentration was studied experimentally at clinical field strength of 3T. In contrast to the compared standard evaluation for pulsed CEST experiments, MTRasym, our approach shows no T2 or MT shine through effect. We demonstrate that spillover can be corrected properly and also quantitative evaluation of pH and creatine concentration is possible which proves MTRRex as quantitative CEST-MRI method. A spillover correction is of special interest for clinical static field strengths and protons resonating near the water peak. This is the case for -OH-CEST effects like gagCEST or glucoCEST, but also amine exchange of creatine or glutamate which require high B1. Although, only showed for amine exchange, we propose our normalization to work generally for DIACEST, PARACEST in slow- and fast exchange regime not just as a correction, but also for quantitative CEST-MRI. Applied to acute stroke induced in rat brain, the corrected CEST signal shows significantly higher contrast between stroke area and normal tissue as well as less B1 dependency compared to conventional approaches.

physics.med-ph↗

arXiv2013

Nanoscale resolution immersion scanning thermal microscopy

Nanoscale thermal properties are becoming of extreme importance for modern electronic circuits that dissipate increasing power on the length scale of few tens of nanometers, and for chemical and physical properties sensors and biosensors using nanoscale sized features. While Scanning Thermal Microscopy (SThM) is known for its ability to probe thermal properties and heat generation with nanoscale resolution, until today it was perceived impossible to use it in the liquid environment due to dominating direct heat exchange between microfabricated thermal probe and surrounding liquid that would deteriorate spatial resolution. Nonetheless, our theoretical analysis of SThM in liquids showed that for certain design of SThM probe with resistive heater located near the probe tip, their thermal signal is only moderately affected, by less than half on immersion in a dodecane environment. More significantly, its spatial resolution, surprisingly, would remain practically unaffected, and the thermal contact between the tip apex and the studied sample would be beneficially improved. Our experimental trials of such immersion SThM, or iSThM, were fully successful and here we report for the first time nanoscale SThM measurements of thermal conductivity of Ultra Large Scale Integration polymerceramic metal interconnects with the spatial thermal resolution down to 50 nm. Further studies of heat transport in nanoscale graphite flakes in iSThM suggested, in particular, that highly anisotropic thermal conductivity in graphene layers may play significant role in the nanoscale thermal transport in liquid environment. New iSThM opens a wide range of applications from noncontact measurements of thermal transport in semiconductor devices to exploring graphene energy storage, catalytic reactions and heat generation in biological systems.

physics.ins-det↗

arXiv2013

A numerical method for imaging of biological microstructures by VHF waves

Imaging techniques give a fundamental support to medical diagnostics during the pathology discovery as well as for the characterization of biological structures. The imaging methods involve electromagnetic waves in a frequency range that spans from some Hz to GHz and over. Most of these methods involve scanning of wide human body areas even if only small areas need to be analyzed. In this paper, a numerical method to evaluate the shape of micro-structures for application in the medical field, with a very low invasiveness for the human body, is proposed. A flexible thin-wire antenna radiates the VHF waves and then, by measuring the spatial magnetic field distribution it is possible to reconstruct the micro-structures image by estimating the location of the antenna against a sensors panel. The typical inverse problem described above is solved numerically, and first simulation results are presented in order to show the validity and the robustness of the proposed approach.

physics.comp-ph↗

arXiv2013

Radiation Exposure Theory Comparison of data on Mutation Frequencies of Mice

We propose Radiation Exposure Theory (RET), a mathematical framework to estimate biological damage caused by irradiation. This is an extension of LDM model which was proposed in the paper [Y. Manabe et al.: J. Phys. Soc. Jpn. 81, 104004(2012)]. The theory is based on physical protocol, 'a stimulus and its response'. It takes account of considerable response including mutation, cell death caused by outer stimulus, as well as biological functions such as proliferation, apoptosis and repair. By taking account of biological issues, namely a variety of preventable effects, which is characteristic feature of living object. RET can explain various data which simple LNT does not reproduce. As one of the characteristic features of RET, we propose a scaling law, namely all the data point with different dose rate irradiation are predicted to lie on the universal line if the variables, the biological damage function as a function of time development after artificial irradiation starts are converted to renormalized ones. The above scaling law can be compared with experimental data. We adopt the accumulated experiments performed by so-called mega mouse projects. It is found that their data points are converted into a universal scaling function and are in reasonably agreement with the prediction of RET.

physics.bio-ph↗

arXiv2013

Construction of a Gas Electron Multiplier (GEM) Detector for Medical Imaging

A prototype Gas Electron Multiplier (GEM) detector is under construction for medical imaging purposes. A single thick GEM of size 10x10 cm^2 is assembled inside a square shaped air-tight box which is made of Perspex glass. In order to ionize gas inside the drift field two types of voltage supplier circuits were fabricated, and array of 2x4 pads of each size 4x8 mm^2 were utilized for collecting avalanche charges. Preliminary testing results show that the circuit which produces high voltage and low current is better than that of low voltage and high current supplier circuit in terms of x-ray signal counting rates.

physics.ins-det↗

arXiv2013

Novel detector systems for the Positron Emission Tomography

In this contribution we describe a novel solution for the construction of Positron Emission Tomograph. We present the device allowing for determination of the impact position as well as time and deph of interaction of the annihilation gamma quanta. The device is comprised of scintillation chamber consisting of organic scintillators surrounding the body of the patient. We discuss two possible solutions: (i) the tomograph built out of scintillator strips, and (ii) the tomograph built out of the scintillator plates. The application of the fast scintillators will enable to take advantage of the difference between time of the registration of the annihilation quanta. The invented method will permit to use a thick layers of detector material with the possibility of measuring the depth of the gamma quantum interaction (DOI) and the determination of their time of flight (TOF), and will allow for increasing the size of the diagnostic chamber without a significant increase of costs. The method is a subject of two patent applications which are based on the techniques used in the particle physics experiments.

physics.med-ph↗

arXiv2013

TOF-PET detector concept based on organic scintillators

In this contribution we present a new concept of the large acceptance detector systems based on organic scintillators which may allow for simultaneous diagnostic of large fraction of the human body. Novelty of the concept lies in employing large blocks of polymer scintillators instead of crystals as detectors of annihilation quanta, and in using predominantly the timing of signals instead of their amplitudes.

physics.ins-det↗

arXiv2013

STRIP-PET: a novel detector concept for the TOF-PET scanner

We briefly present a design of a new PET scanner based on strips of polymer scintillators arranged in a barrel constituting a large acceptance detector. The solution proposed is based on the superior timing properties of the polymer scintillators. The position and time of the reaction of the gamma quanta in the detector material will be determined based on the time of arrival of light signals to the edges of the scintillator strips.

physics.ins-det↗

arXiv2013

Diffusion imaging with stimulated echoes: signal models and experiment design

Purpose: Stimulated echo acquisition mode (STEAM) diffusion MRI can be advantageous over pulsed-gradient spin-echo (PGSE) for diffusion times that are long compared to $\ttwo$. It is important therefore for biomedical diffusion imaging applications at 7T and above where $\ttwo$ is short. However, imaging gradients in the STEAM sequence contribute much greater diffusion weighting than in PGSE, but are often ignored during post-processing. We demonstrate here that this can severely bias parameter estimates. Method: We present models for the STEAM signal for free and restricted diffusion that account for crusher and slice-select (butterfly) gradients to avoid such bias. The butterfly gradients also disrupt experiment design, typically by skewing gradient-vectors towards the slice direction. We propose a simple compensation to the diffusion gradient vector specified to the scanner that counterbalances the butterfly gradients to preserve the intended experiment design. Results: High-field data fixed from a monkey brain experiments demonstrate the need for both the compensation during acquisition and correct modelling during post-processing for both diffusion tensor imaging and ActiveAx axon-diameter index mapping. Simulations support the results and indicate a similar need in in-vivo human applications. Conclusion: Correct modelling and compensation are important for practical applications of STEAM diffusion MRI.

physics.med-ph↗

arXiv2013

Measurement and Analysis of Radio-frequency Radiation Exposure Level from Different Mobile Base Transceiver Stations in Ajaokuta and Environs, Nigeria

We present the result of a preliminary assessment of radio-frequency radiation exposure from selected mobile base stations in Ajaokuta environs. The Power density of RF radiation within a radial distance of 125m was measured. Although values fluctuated due to the influence of other factors, including wave interference from other electromagnetic sources around reference base stations, we show from analysis that radiation exposure level is below the standard limit (4.5W/sqm for 900MHz and 9W/sqm for 18000MHz) set by the International Commission on Non-ionizing Radiation Protection (ICNIRP) and other regulatory agencies.

physics.med-ph↗

arXiv2013

Three-Dimensional Reconstruction of Erythrocyte in the Capillary

The dynamic analysis of erythrocyte deformability is used as an important means for early diagnosis of blood diseases and blood rheology. Yet no effective method is available in terms of three-dimensional reconstruction of erythrocytes in a capillary. In this study, ultrathin serial sections of skeletal muscle tissue are obtained from the ultramicrotome, the tomographic images of an erythrocyte in a capillary are captured by the transmission electron microscope, and then a method to position and restore is devised to demonstrate the physiological relationship between two adjacent tomographic images of an erythrocyte. Both the modeling and the physical verification reveal that this method is effective, which means that it can be used to make three-dimensional reconstruction of an erythrocyte in a capillary. An example of reconstructed deformation of erythrocyte based on the serial ultrathin sections is shown at the end of this paper.

physics.med-ph↗

arXiv2014

Averaging VMAT treatment plans for multi-criteria navigation

The main approach to smooth Pareto surface navigation for radiation therapy multi-criteria treatment planning involves taking real-time averages of pre-computed treatment plans. In fluence-based treatment planning, fluence maps themselves can be averaged, which leads to the dose distributions being averaged due to the linear relationship between fluence and dose. This works for fluence-based photon plans and proton spot scanning plans. In this technical note, we show that two or more sliding window volumetric modulated arc therapy (VMAT) plans can be combined by averaging leaf positions in a certain way, and we demonstrate that the resulting dose distribution for the averaged plan is approximately the average of the dose distributions of the original plans. This leads to the ability to do Pareto surface navigation, i.e. interactive multi-criteria exploration of VMAT plan dosimetric tradeoffs.

physics.med-ph↗

arXiv2014

Probing the viscoelastic properties of polyacrylamide polymer gels in a wide frequency range

Polymer gels have been shown to behave as viscoelastic materials but only a small amount of data is usually provided in the glassy transition. In this paper, the dynamic moduli G' and G" of polyacrylamide hydrogels are investigated using both an AFM in contact force modulation mode and a classical rheometer. The validity is shown by perfect matching of the two techniques. Measurements are carried out on gels of increasing polymer concentration in a wide frequency range. A model based on fractional derivatives is proposed, covering the whole frequency range. G_0^N, the plateau modulus, as well as nf, the slope of the G" modulus, are obtained at low frequencies. The model also predicts the slope a of both moduli in the transition regime, as well as a new transition time T. The whole frequency spectrum is recovered, and the model parameters contain interesting information about the physics of such gels.

physics.med-ph↗