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At least 145 records · Page 8Linked to original sources
arXiv2014

Dependence of the thermoluminescent high-temperature ratio (HTR) of LiF:Mg,Ti detectors on proton energy and dose

The high-temperature ratio (HTR) is a parameter quantifying changes of the shape of the high-temperature part of the LiF:Mg,Ti glow-curve after exposure to densely ionizing radiation. It was introduced in order to estimate the effective LET of an unknown radiation field and to correct the decreased relative TL efficiency for high Linear Energy Transfer (LET) radiation. In the present work the dependence of HTR on proton energy (14.5 to 58 MeV) and dose (0.5 to 30 Gy) was investigated. All measured HTR values were at the level of 1.2 or higher, therefore significantly different from the respective value for gamma rays (HTR is equal to 1), but HTR was found to be insensitive to changes of proton energy above 20 MeV. As a result the relationship between HTR and relative TL efficiency is not unequivocal. The HTR was found to be dependent on absorbed dose even for the lowest studied doses.

physics.ins-det↗
arXiv2014

Analysis of Femoral Components of Cemented Total Hip- Arthroplasty

In cemented Total Hip Arthroplasty (THA), material chosen for femoral stem and cross section of stem itself, proved to be critical parameters for, stress distribution in the femoral components, interfacial stresses and micro movements. Titanium alloy (Ti6Al4V), when used as a material for femoral stem, recorded large displacement as compared to Chromium alloy (CoCrMo) stems. This large displacement in case of Ti6Al4V caused the stem to bend inside the cement mantle, thus destroying it. Thus, CoCrMo proved to be a better in cemented THA. Failure in THA may occur at cement-stem or cement-bone interface, thus interfacial stresses and micro movements were analysed in the present study. Comparison between trapezium and circular cross section showed that, femoral stem with trapezium cross section underwent lesser amount of sliding and debonding, at both interfaces, as compared to circular cross section. Moreover, trapezium cross section also generated lower peak stresses in femoral stem and cortical femur. The present study also took into account, effect of diameter of femur head. A 36mm diameter femur head generated lower peak stress in acetabulum liner and arrested dislocation. Metallic femur head was coupled with a liner made of cross linked polyethylene (XLPE). This material experiences almost negligible wear when compared to typical metallic and polyethylene liners, and unlike metallic liner, it is non-carcinogenic.

physics.med-ph↗
arXiv2014

Reconstructing human organ cross-sectional imaging along any axis

Cross-sectional imaging of human organ serves as a critical tool to provide diagnostic results of many diseases. Based on a unique body coordinate system, we present a method that we use to reconstruct any cross-sectional imaging of organ regardless of its original section going along which scanning or cutting axis. In clinical medicine, this method enables a patient to undergo only one scanning, and then the doctor can observe the structure of lesion sections along any axis, and it can help find changes of lesions at the same section from different scanning results and thus quantify diagnosis by cross-sectional imaging. Significant progress has thus been made towards quantitative diagnosis cross-sectional imaging.

physics.med-ph↗
arXiv2014

Dimensional Analysis and the Time Required to Urinate

According to the recently discovered 'Law of Urination', mammals, ranging in size from mice to elephants, take, on the average, 21s to urinate. We attempt to gain insights into the physical processes responsible for this uniformity using simple dimensional analysis. We assume that the biological apparatus for urination in mammals simply scales with linear size, and consider the scenarios where the driving force is gravity or elasticity, and where the response is dominated by inertia or viscosity. We ask how the time required for urination depends on the length scale, and find that for the time to be independent of body size, the dominant driving force must be elasticity, and the dominant response viscosity. Our note demonstrates that dimensional analysis can indeed readily give insights into complex physical and biological processes.

physics.med-ph↗
arXiv2014

Estimation of conductivity changes in a region of interest with electrical impedance tomography

This paper proposes a novel approach to reconstruct changes in a target conductivity from electrical impedance tomography measurements. As in the conventional difference imaging, the reconstruction of the conductivity change is based on electrical potential measurements from the exterior boundary of the target before and after the change. In this paper, however, images of the conductivity before and after the change are reconstructed simultaneously based on the two data sets. The key feature of the approach is that the conductivity after the change is parameterized as a linear combination of the initial state and the change. This allows for modeling independently the spatial characteristics of the background conductivity and the change of the conductivity - by separate regularization functionals. The approach also allows in a straightforward way the restriction of the conductivity change to a localized region of interest inside the domain. While conventional difference imaging reconstruction is based on a global linearization of the observation model, the proposed approach amounts to solving a non-linear inverse problem. The feasibility of the proposed reconstruction method is tested experimentally and with a simulation which demonstrates a potential new medical application of electrical impedance tomography: imaging of vocal folds in voice loading studies.

physics.comp-ph↗
arXiv2014

CT Reconstruction from Simultaneous Projections: A Step towards Capturing CT in One Go

This paper focuses on minimizing the time requirement for CT capture through innovative simultaneous x-ray capture method. The state-of-the-art CT imaging methodology captures a sequence of projections during which the internal organ movements may lead to poor reconstruction due to motion artefacts. Traditional CT scanners' minimize such effect by taking more projections than necessary. In this work we focus on an innovative CT capture method that captures projections simultaneously, promising super fast scans along with possible radiation dose reductions. While the simultaneous CT capture model has already been proposed in our earlier work 'Multi-axial CT Reconstruction from Few View Projections' (in SPIE Optical Engineering and Applications, pp. 85000A-85000A. International Society for Optics and Photonics, 2012) and 'A New Imaging Method for Real-time 3D X-ray Reconstruction' (in SPIE Medical Imaging, pp. 86685G-86685G. International Society for Optics and Photonics, 2013), in this work we enhance the model through better initialization along with prior smoothing before successive iterations of the iterative algorithms. We also elaborate the model considering different X-ray source/detector configurations. Results show that it is possible reconstruct a cross-section slice by considering only four angular projections. With eight projections, the reconstruction is further improved. The main promising matter about this method is that, all these projections (i.e. four or eight) can in principle be captured simultaneously, implying CT capture in one go just like a chest X-ray.

physics.med-ph↗
arXiv2014

Couple Control Model Implementation on Antagonistic Mono- and Bi-Articular Actuators

Recently, robot assisted therapy devices are increasingly used for spinal cord injury (SCI) rehabilitation in assisting handicapped patients to regain their impaired movements. Assistive robotic systems may not be able to cure or fully compensate impairments, but it should be able to assist certain impaired functions and ease movements. In this study, a couple control model for lower-limb orthosis of a body weight support gait training system is proposed. The developed leg orthosis implements the use of pneumatic artificial muscle as an actuation system. The pneumatic muscle was arranged antagonistically to form two pair of mono-articular muscles (i.e., hip and knee joints), and a pair of bi-articular actuators (i.e., rectus femoris and hamstring). The results of the proposed couple control model showed that, it was able to simultaneously control the antagonistic mono- and bi-articular actuators and sufficiently performed walking motion of the leg orthosis.

physics.med-ph↗
arXiv2014

Liquid Metal as Connecting or Functional Recovery Channel for the Transected Sciatic Nerve

In this article, the liquid metal GaInSn alloy (67% Ga, 20.5% In, and 12.5% Sn by volume) is proposed for the first time to repair the peripheral neurotmesis as connecting or functional recovery channel. Such material owns a group of unique merits in many aspects, such as favorable fluidity, super compliance, high electrical conductivity, which are rather beneficial for conducting the excited signal of nerve during the regeneration process in vivo. It was found that the measured electroneurographic signal from the transected bullfrog sciatic nerve reconnected by the liquid metal after the electrical stimulation was close to that from the intact sciatic nerve. The control experiments through replacement of GaInSn with the conventionally used Riger Solution revealed that Riger Solution could not be competitive with the liquid metal in the performance as functional recovery channel. In addition, through evaluation of the basic electrical property, the material GaInSn works more suitable for the conduction of the weak electroneurographic signal as its impedance was several orders lower than that of the well-known Riger Solution. Further, the visibility under the plain radiograph of such material revealed the high convenience in performing secondary surgery. This new generation nerve connecting material is expected to be important for the functional recovery during regeneration of the injured peripheral nerve and the optimization of neurosurgery in the near future.

physics.med-ph↗
arXiv2014

Sinogram constrained TV-minimization for metal artifact reduction in CT

A new method for reducing metal artifacts in X-ray computed tomography (CT) images is presented. It bases on the solution of a convex optimization problem with inequality constraints on the sinogram, and total variation regularization for the reconstructed image. The Chambolle-Pock algorithm is used to numerically solve the discretized version of the optimization problem. As proof of concept we present and discuss numerical results for synthetic data.

math.NA↗
arXiv2014

Computed-torque method for the control of a 2 DOF orthosis actuated through pneumatic artificial muscles: a specific case for the rehabilitation of the lower limb

In this paper we give a new control model based on the so called computed-torque method for the control of a 2 degrees of freedom orthosis for the rehabilitation of the lower limb, the AIRGAIT exoskeleton's leg orthosis. The actuation of the AIRGAIT is made through self-made pneumatic muscles. For this reason this work starts with the static and dynamic characterization of our pneumatic muscles. The followed approach is based on the analytical description of the system. For this, we describe the pneumatic muscles behaviour with an easy-invertible polynomial fit function in order to model its non-linear trend. We give a geometrical model of the mechanical system to compute the length between the attachments of the pneumatic muscles to the structure for every angles assumed by the two joints. We evaluate through Newton-Euler equation the couples at the joints for each values of the angles. At last we show some validation tests in order to characterize the functioning of the proposed control model on the actuation of the orthosis.

physics.med-ph↗
arXiv2014

Attenuation Correction of L-shell X-ray Fluorescence Computed Tomography Imaging

X-ray Fluorescence Computed Tomography(XFCT) is a prevalent experimental technique which is utilized to investigate the spatial distribution of elements in sample. The sensitivity of L-shell XFCT of some elements is lower than that of K-shell XFCT. However, the image reconstruction for this technique has much more problems than that of transmission tomography, one of which is self-absorption. In the present work, a novel strategy was developed to deal with such problems. But few researches are concerned on attenuation correction of L-shell XFCT that are essential to get accurate reconstructed image. We make use of the known quantities and the unknown elemental concentration of interest to express the unknown attenuation maps. And then the attenuation maps are added in the contribution value of the pixel in MLEM reconstruction method. Results indicate that the relative error is less than 14.1%, which is proved this method can correct L-shell XFCT very well.

physics.ins-det↗
arXiv2014

PET image reconstruction with system matrix containing point spread function derived from single photon incidence response

In positron emission tomography (PET) imaging, statistical iterative reconstruction (IR) techniques appear particularly promising since they can provide accurate system model. The system model matrix which describes the relationship between image space and projection space is important to the image quality. It contains some factors such as geometrical component and blurring component. The blurring component is usually described by point spread function (PSF). A PSF matrix derived from the single photon incidence response function is studied. And then an IR method based on the system matrix containing the PSF is developed. More specifically, the gamma photon incidence on a crystal array is simulated by Monte Carlo (MC) simulation, and then the single photon incidence response functions are calculated. Subsequently, the single photon incidence response functions is used to compute the coincidence blurring factor according to the physical process of PET coincidence detection. Through weighting the ordinary system matrix response by the coincidence blurring factors, the IR system matrix containing PSF is finally established. Using this system matrix, the image is reconstructed by ordered subset expectation maximization (OSEM) algorithm. The experimental results show that the proposed system matrix can obviously improve the image radial resolution, contrast and noise property. Furthermore, the simulated single gamma-ray incidence response function only depends on the crystal configuration, so the method could be extended to any PET scanners with the same detector crystal configuration.

physics.med-ph↗
arXiv2014

Shear loading of costal cartilage

A series of tests were performed on a single post-mortem human subject at various length scales. First, tabletop tests were performed. Next, the ribs and intercostal muscles were tested with the view to characterize the load transfer between the ribs. Finally, the costal cartilage was tested under shear loading, as it plays an important in the transfer of the load between the ribs and the sternum. This paper reports the results of dynamic shear loading tests performed on three samples of costal cartilage harvested from a single post-mortem human subject, as well as the quantification of the effective Young's modulus estimated from the amount of cartilage calcification.

physics.med-ph↗
arXiv2014

Mid-IR fiber optic light source around 6 micron through parametric wavelength translation

We report numerically designed highly nonlinear all glass chalcogenide microstructured optical fiber for efficient generation of light around 6 micron through degenerate four wave mixing by considering continuous wave CO laser of 5 to 10 Watts power emitting at 5.6 micron as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, narrow and broad band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20 decibel is achievable for the narrow band source at 6.46 micron with a maximum power conversion efficiency of 33 percent while amplification of 22 decibel is achievable for a B-band source over the wavelength range of 5 to 6.3 micron with a conversion efficiency of 40 percent.

physics.optics↗
arXiv2014

Towards Laser Driven Hadron Cancer Radiotherapy: A Review of Progress

It has been known for about sixty years that proton and heavy ion therapy is a very powerful radiation procedure for treating tumours. It has an innate ability to irradiate tumours with greater doses and spatial selectivity compared with electron and photon therapy and hence is a tissue sparing procedure. For more than twenty years powerful lasers have generated high energy beams of protons and heavy ions and hence it has been frequently speculated that lasers could be used as an alternative to RF accelerators to produce the particle beams necessary for cancer therapy. The present paper reviews the progress made towards laser driven hadron cancer therapy and what has still to be accomplished to realise its inherent enormous potential.

physics.plasm-ph↗
arXiv2014

Mathematical modeling of mechanical vibration assisted conductivity imaging

This paper aims at mathematically modeling a new multi-physics conductivity imaging system incorporating mechanical vibrations simultaneously applied to an imaging object together with current injections. We perturb the internal conductivity distribution by applying time-harmonic mechanical vibrations on the boundary. This enhances the effects of any conductivity discontinuity on the induced internal current density distribution. Unlike other conductivity contrast enhancing frameworks, it does not require a prior knowledge of a reference data. In this paper, we provide a mathematical framework for this novel imaging modality. As an application of the vibration-assisted impedance imaging framework, we propose a new breast image reconstruction method in electrical impedance tomography (EIT). As its another application, we investigate a conductivity anomaly detection problem and provide an efficient location search algorithm. We show both analytically and numerically that the applied mechanical vibration increases the data sensitivity to the conductivity contrast and enhances the quality of reconstructed images and anomaly detection results. For numerous applications in impedance imaging, the proposed multi-physics method opens a new difference imaging area called the vibration-difference imaging, which can augment the time-difference and also frequency-difference imaging methods for sensitivity improvements.

physics.med-ph↗
arXiv2014

Direct determination of radiation dose in human blood

Our purpose is to measure the internal radiation dose (ID) using human blood sample. In the literature, there is no process that allows the direct measurement of ID received by a person. This study has shown that it is possible to determine ID in human blood exposed to internal or external ionizing radiation treatment both directly and retrospectively. OSL technique was used to measure the total dose from the blood sample. OSL counts from the waste blood of the patient injected with a radiopharmaceutical for diagnostic or treatment purposes and from a blood sample having a laboratory-injected radiation dose were both used for measurements. The decay and dose-response curves (DRC) were plotted for different doses. The doses received by different blood aliquots have been determined by interpolating the natural luminescence counts to DRC. In addition, OSL counts from a healthy blood sample exposed to an external radiation source were measured. The blood aliquots were given different 0-200Gy beta doses and their decay and dose-response curves were plotted. The internal dose received by the blood aliquots injected with radioisotope was determined by interpolating the natural luminescence counts to DRC. The internal dose values were found as 0.46Gy and 0.51Gy for different dose range. The blood aliquots were exposed to different external laboratory doses. The internal dose values corresponding to 10Gy laboratory dose from the aliquots exposed to external radiation were found as 10.94Gy for Disc3 and ~10.79Gy for Disc1.This study shows that the dose received by a person can be measured directly, simply and retrospectively by using only a very small amount of blood sample. The results will have important ramifications for the medicine and healthcare fields in particular.

physics.med-ph↗