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Models of electrical excitation and recovery in the heart have become increasingly detailed, but have yet to be used routinely in the clinical setting to guide personalized intervention in patients. One of the main challenges is calibrating models from the limited measurements that can be made in a patient during a standard clinical procedure. In this work, we propose a novel framework for the probabilistic calibration of electrophysiology parameters on the left atrium of the heart using local measurements of cardiac excitability. Parameter fields are represented as Gaussian processes on manifolds and are linked to measurements via surrogate functions that map from local parameter values to measurements. The posterior distribution of parameter fields is then obtained. We show that our method can recover parameter fields used to generate localised synthetic measurements of effective refractory period. Our methodology is applicable to other measurement types collected with clinical protocols, and more generally for calibration where model parameters vary over a manifold., 14 pages, 6 figures, preprint

We outline the mathematical model of the ultrasonic response of cancellous bone and its time harmonic formulation. In contrast to the Biot model, the fluid is not inviscid. Our fluid is viscous, bu...

This investigation is devoted to exhibit the thermal damage of skin tissue exposed to a moving heat source. Modelling of the problem is performed by adopting dual phase lag theory of bio heat trans...

The stability of a stabilized with polydimethylsiloxane (PDMS) magnetic fluid to alcohols of a saturated homologous series was investigated. We used alcohols with a linear molecular structure and t...

The present paper investigates the degradation of compressible polymers based on the proposed model on strain-induced degradation of incompressible polymers. In a non-equilibrium thermodynamic framework, constitutive equations and evolution laws are derived using the principle of maximum energy dissipation rate and specifying how energy can be stored and dissipated. As a computational model, the governing equations are applied to the pressurized polymeric vessel subjected to the Ogden–Hill compressible hyperelastic material model. To analyze the axisymmetric plane-strain degradable vessel, programming in ANSYS Parametric Design Language (APDL) and the Standard Galerkin Finite Element Method (SGFEM) are applied. The results show that the degradable compressible Ogden–Hill model can also predict the degradation of incompressible polymers subjected to the neo-Hookean model. Results also reveal that the highest dissipation rate and material softening occur at the inner radius of the inflated degradable vessel. Creep-like and stress-relaxation-like responses of the polymeric vessel with time-position-dependent material properties are examined. ANSYS coding indicates good accuracy and efficiency in studying the compressible vessel subjected to inhomogeneous degradation.

Neutron response functions of a silicon sensor, which is applied to a new real-time personal albedo neutron dosemeter, have been simulated for low energy neutrons from 0.01 eV to 10 keV using the Monte Carlo technique. The angular neutron response functions were obtained by multiplying simulated neutron energy spectra crossing the neutron sensor and the cross-section of the 6Li(n,t)4He reaction. The neutron response functions have been closed to the dose conversion coefficient of personal doses, Hp(10) recommended by the International Commission on Radiological Protection by selecting neutrons incident from angles of 105° to 180° with respect to an axis perpendicular to an acrylic phantom surface. From these simulation results, the neutron energy response function has been improved by shielding the sensor with cadmium box without a face toward the phantom. The neutron sensor provides a good conformance to the Hp(10) conversion coefficients within 15% for low energy neutrons.

Divergence-free smoothing with wall treatment (DFSwt) method is proposed for processing with four-dimensional (4D) flow magnetic resonance imaging (MRI) data of blood flows to enhance the quality of flow field with physical constraints. The new method satisfies the no-slip wall boundary condition and applies wall function of velocity profile for better estimating the velocity gradient in the near-wall region, and consequently improved wall shear stress (WSS) calculation against the issue of coarse resolution of 4D flow MRI. In the first testing case, blood flow field obtained from 4D flow MRI is well smoothed by DFSwt method. A great consistency is observed between the post-processed 4D flow MRI data and the computational fluid dynamics (CFD) data in the interested velocity field. WSS has an apparent improvement due to the proposed near-wall treatment with special wall function comparing to the result from original 4D flow MRI data or the DFS-processed data with no wall function. The other five cases also show the same performance that smoothed velocity field and improved WSS estimation are achieved on 4D flow MRI data optimized by DFSwt. The improvements will benefit the study of hemodynamics regarding the determination of location or the potential possibility of lesions.

Surface-enhanced Raman spectroscopy (SERS), as induced by noble metal nanoparticles, is used for medical applications. In this study, gold nanoparticle parameters such as size, shape, separation, substrate etc. are varied systematically using electron beam lithographic fabrication methods. The resultant Raman spectra intensities are correlated with the nanoparticle surface plasmon energies as determined by electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) at nanometer-scale resolution. It is found that the largest enhancement is achieved when the illuminating laser energy closely matches, or is slightly higher than, the surface plasmon energies. In general, nanoparticle size is a strong determinant factor, and higher intensities are generated by sharply defined features. This approach allows a procedure to identify the optimum combination of nanoparticle parameters and laser energy to generate the largest Raman signals, thus enabling detection, for instance, of smaller, early-stage cancer tumors.

The impact of the human nasal airway complexity on the pharyngeal airway fluid mechanics is investigated at inspiration. It is the aim to find a suitable degree of geometrical reduction that allows for an efficient segmentation of the human airways from cone-beam computed tomography images. The flow physics is simulated by a lattice Boltzmann method on high-performance computers. For two patients, the flow field through the complete upper airway is compared to results obtained from three surface variants with continuously decreasing complexity. The most complex reduced airway model includes the middle and inferior turbinates, while the moderate model only features the inferior turbinates. In the simplest model, a pipe-like artificial structure is attached to the airway. For each model, the averaged pressure is computed at different cross sections. Furthermore, the flow fields are investigated by means of averaged velocity magnitudes, in-plane velocity vectors, and streamlines. By analyzing the averaged pressure loss from the nostrils to each cross section, it is found that only the most complex reduced models are capable of approximating the pressure distribution from the original geometries. In the moderate models, the geometry reductions lead to overpredictions of the pressure loss in the pharynx. Attaching a pipe-like structure leads to a higher deceleration of the incoming flow and underpredicted pressure losses and velocities, especially in the upper part of the pharynx. Dean-like vortices are observed in the moderate and pipe-like models, since their shape comes close to a $$90^\circ$$ -bend elbow pipe.

Electron and photon beams demonstrate extraordinary characteristics useful for the treatment of cancer. These characteristics are essential to analyze before the calibration of the linear accelerator with dual energies. This study focused on the dosimetric characteristics of the different energies of electron beam for different field sizes. The basic objective of this work was to calculate the dosimetric parameters and characteristics of the electron beam, especially depth dose characteristics along the central axis. In this work, 6 MeV, 9 MeV, 12 MeV, 15 MeV and 18 MeV of electron beam and 6 MV and 15 MV of photon beam with different field sizes were used. The characteristics of the depth dose of electron and photon beams in water were analyzed to optimize the radiation quality for radiation treatment planning. The different beam characteristics are due to different interactions that occur between electron beams giving them a definite range, whereas photon beams are attenuated leading to dose deposition and a much larger range with no definite end. Depth dose characteristics of electron and photon beams are not similar since the interaction of these beams with matter depends on their quality. Attenuation and penetration factors change with changing dosimetric parameters. A complete analysis of the dosimetric characteristics of electron and photon beams helps to choose the more accurate beam for the treatment of cancer. This work helps to increase accuracy in the treatment of cancer with radiotherapy. Copyright(c) The Authors

The AC losses of high-temperature superconducting (HTS) coils have a large impact on the efficiency of superconducting power devices, so the research on AC losses of HTS coils has become a current hot topic. This paper mainly studied the effects of coil turns, inter-turn spacing, and coil radius of the same superconducting coil structure on its magnetization loss in the external alternating magnetic field environment. Using the finite element simulation software, the two-dimensional axisymmetric model of single-pancake coil with double-tape winding is built. Under the condition of external alternating magnetic field with the same frequency and amplitude, the three structural parameters of superconducting coil are changed, respectively, to calculate the magnetization loss under different conditions. The simulation results are also analyzed theoretically to clarify the main reasons for the change of magnetization loss of the superconducting coil caused by the three variables. The results show that the magnetization loss of the multi-turn superconducting coil is mainly focused on the hysteresis loss. Within a certain range, the more turns of superconducting coil, the smaller the magnetization loss, while the size of inter-turn spacing, and coil radius are positively correlated with the magnetization loss of HTS coils. The simulation results are consistent with the theoretical analysis, which provides ideas and references for the subsequent study of the magnetization loss of HTS coils.

We report the observation of photoluminescence emission from airborne gold, silver, and copper nanoparticles. A continuous wave 532 nm laser was employed for excitation. Photoluminescence from gold nanoparticles carried in a nitrogen gas flow was both spectrally resolved and directly imaged in situ using an intensified charge-coupled device camera. The simultaneously detected Raman signal from the nitrogen molecules enables quantitative estimation of the photoluminescence quantum yield of the gold nanoparticles. Photoluminescence from metal nanoparticles carried in a gas flow provides a potential tool for operando imaging of plasmonic metal nanoparticles in aerosol reactions., Graphical Abstract

Numerical calculations were used to investigate influence of sabot structures of kinetic energy projectiles into the armour penetration depth. Areas of sabot structure for possible optimization and the influence of various sabot materials on the projectile combat efficiency were indicated. The analysis was performed using the finite element method in the Solidworks Simulation environment. It allowed examination of dynamic loads the sabot is subjected to at the time of the shot. Impact of various sabot materials and projectile geometry modifications on the strength of penetrator - sabot connection was investigated. Distributions of dynamical loads for penetrator-sabot connections were simulated and visualised. Calculations on terminal ballistics were performed for some options of the structure. It allowed identification of development trends for this type of ammunition.

The effects of swift heavy ion irradiation on implanted glassy carbon, the modification and migration of indium after vacuum annealing have been investigated. Radiation damage was introduced to the glassy carbon substrates after room temperature implantation by 360 keV indium ions to a fluence of 2.0 × 1016 ions/cm 2. The implanted samples were subsequently irradiated at room temperature by swift heavy ions (167 MeV Xe 26+ ions). Isochronal annealing of both sets of samples from 200 to 600 °C for 1 h was performed in vacuum. The SHI irradiation, induced some restructuring in the damaged glassy carbon substrates. Vacuum annealing of the SHI irradiated samples gave rise to recovery and the diffusion of implanted In which was different from that of the as-implanted sample. Higher retention was observed at each temperature for SHI irradiated samples compared to as-implanted samples. The diffusion coefficients of the SHI irradiated samples were lower than for un-irradiated sample.

The features of the fluid compression in a vapor bubble during its collapse in cold (273 K) and cool (293 K) acetone are studied. The liquid pressure $$p_{0}$$ is varied in the range 0.12–5 bar. The full hydrodynamic model is used in vapor and liquid. The non-stationary heat conductivity of both fluids and non-equilibrium mass transfer across the bubble surface are taken into account. Realistic wide-range equations of state are applied. It is shown that as the liquid pressure $$p_{0}$$ is diminished, the depth of the bubble collapse decreases in cold acetone, but grows in cool acetone. The maximum of the collapse rate decreases monotonically in cool acetone. In cold acetone it is reduced only in an interval bounded by a certain value of $$p_{0}$$ , and then it increases. As a result, with decreasing $$p_{0}$$ of cool acetone, the vapor in the bubble is compressed first by radially convergent shock waves, then by isentropic waves, and after that its nearly uniform compression takes place, whereas only the first scenario is realized in cold acetone.

With the blossom of information industry, electromagnetic wave technology shows increasingly potential in many fields. Nevertheless, the trouble caused by electromagnetic waves has also drawn extensive attention. For instance, electromagnetic pollution can threaten information safety in vital fields and the normal function of delicate electronic devices. Consequently, electromagnetic pollution and interference become an urgent issue that needs to be addressed. Carbon nanotubes (CNTs) have become a potential candidate to deal with these problems due to many advantages, such as high dielectric loss, remarkable thermodynamic stability, and low density. With the appearance of climbing demands, however, the carbon nanotubes combining various composites have shown greater prospects than the single CNTs in microwave absorbing materials. In this short review, recent advances in CNTs-based microwave absorbing materials were comprehensively discussed. Typically, we introduced the electromagnetic wave absorption mechanism of CNTs-based microwave absorbing materials and generalized the development of CNTs-based microwave absorbers, including CNTs-based magnetic metal composites, CNTs-based ferrite composites, and CNTs-based polymer composites. Ultimately, the growing trend and bottleneck of CNTs-based composites for microwave absorption were analyzed to provide some available ideas to more scientific workers.

Dealing with the different artifacts in medical images is necessary to perform several tasks, in particular segmentation and registration. We introduce in this paper a novel method for bias field correction in Magnetic Resonance Images (MRI). Using the segmentation results obtained by a modified Expectation Maximization clustering, the bias field is fitted as an hyper-surface in a 4D hyper-space. Then, it is corrected based on the fact that voxels belonging to the same tissue should have the same intensity in the whole image. So, after a quick and coarse unsupervised voxel labeling by clustering by parts is performed, the bias field is computed at the voxels that have been reliably labeled as belonging to one of the tissues of interest. For the less reliably labeled voxels the bias field is interpolated using an hyper-surface, estimated by a 4D lagrangian interpolation. In order to evaluate the efficiency of the proposed method, we compare the MRI segmen- tation results with and without bias field correction, and we use also the coefficient of variations within the MRI volume.Segmentation results, and the coefficient of variations results were significantly enhanced after bias field correction by the proposed method. Furthermore, the proposed method is considered fast compared to other methods, that are often time consuming du to their iterative nature.

Breast cancer represents one of the main reasons of death among women. As an alternative to the gold standard techniques for breast cancer diagnosis, microwave imaging has been proposed from research community and many microwave systems have been designed mainly to work at low microwave frequencies. Based both on the results of recent dielectric characterization campaigns on human breast ex-vivo tissues up to 50 GHz and on the promising feasibility studies of mm-wave imaging systems, in this article, we propose and test inverse scattering techniques as effective tool to process mm-wave data to image breast cancer. Differently from radar techniques so far adopted in conjunction with mm-wave imaging system, inverse scattering techniques turn out to be more versatile and robust with respect to the reduction of the amount of data and eventually also able to characterize the anomaly in terms of electromagnetic properties. In particular, in the above, two image reconstruction techniques, the Linear Sampling Method and the Born Approximation, are proposed and compared against both simulated and experimental data.

The optical properties of Gafchromic EBT films are investigated under various solar power intensities. The films are exposed to solar radiation with different powers (0, 0.3, 0.5, 0.8, 1 SUN) for 30 min in each case. The absorbance, transmittance and reflectance of the films are thoroughly investigated. Other important parameters such as: absorption coefficient, extinction coefficient, energy bandgaps and refractive index are determined. These parameters show strong dependence on the solar power intensity, suggesting that EBT films can be considered as suitable candidates for many sensing and dosimetry applications.

The existence of uniform minimal trajectory and global attractors for weak solutions of the nonautonomous modified Kelvin–Voigt model is proved.

Changes in the in-situ measured diffuse reflection spectra and the integrated absorption coefficient of a barium-sulfate powder modified by silicon-dioxide nanoparticles are analyzed comparatively after separate and simultaneous events of irradiation with 30-keV electrons and solar-spectrum quanta. Two kinetic regions on the curves of degradation of the optical properties are found. Simultaneous irradiation is additive with respect to separate irradiation in the first region. In the second region, the changes caused by simultaneous irradiation are smaller than the sum of changes caused by separate irradiation.

© 2021 The Authors. Many biomedical applications require accurate non-rigid image registration that can cope with complex deformations. However, popular diffeomorphic Demons registration algorithms suffer from difficulties for complex and serious distortions since they only use image greyscale and gradient information. To address these difficulties, a new diffeomorphic Demons registration algorithm is proposed using hierarchical neighbourhood spectral features namely HNSF Log-Demons in this paper. In view of three important properties of hierarchical neighbourhood spectral features based on line graph such as rotation invariance, invariance of linear changes of brightness, and robustness to noise, the hierarchical neighbourhood spectral features of a reference image and a moving image is first extracted and these novel spectral features are incorporated into the energy function of the diffeomorphic registration framework to improve the capability of capturing complex distortions. Secondly, the Nystr ö o ̈ m approximation based on random singular value decomposition is employed to effectively enhance the computational efficiency of HNSF Log-Demons. Finally, the hybrid multi-resolution strategy based on wavelet decomposition in the registration process is utilised to further improve the registration accuracy and efficiency. Experimental results show that the proposed HNSF Log-Demons not only effectively ensures the generation of smooth and reversible deformation field, but also achieves better performance than state-of-the-art algorithms. National Natural Science Foundation of China. Grant Numbers: 61762058, 61861024, 61871259; Natural Science Foundation of Gansu Province of China. Grant Number: 20JR5RA404; Natural Science Basic Research Program of Shaanxi. Grant Number: 2021JC-47.

A system for transcutaneous inductive power transfer to implanted medical devices was studied. A class E power amplifier with dynamic capacitive tuning was used in the transmitting part of the system to maintain constant power output to an implanted medical device. The influence of the operation mode of the implanted device on the output power range of the transcutaneous inductive power transfer system and its operational stability under conditions of coil misalignment was studied. In all modes local maxima were observed near the upper boundary of the output power range. The maximum values were almost identical for all operation modes of the implanted medical device.

A significant research problem of recent interest is the localization of targets like vessels, surgical needles, and tumors in photoacoustic (PA) images. To achieve accurate localization, a high photoacoustic signal-to-noise ratio (SNR) is required. However, this is not guaranteed for deep targets, as optical scattering causes an exponential decay in optical fluence with respect to tissue depth. To address this, we develop a novel deep learning method designed to explicitly exhibit robustness to noise present in photoacoustic radio-frequency (RF) data. More precisely, we describe and evaluate a deep neural network architecture consisting of a shared encoder and two parallel decoders. One decoder extracts the target coordinates from the input RF data while the other boosts the SNR and estimates clean RF data. The joint optimization of the shared encoder and dual decoders lends significant noise robustness to the features extracted by the encoder, which in turn enables the network to contain detailed information about deep targets that may be obscured by noise. Additional custom layers and newly proposed regularizers in the training loss function (designed based on observed RF data signal and noise behavior) serve to increase the SNR in the cleaned RF output and improve model performance. To account for depth-dependent strong optical scattering, our network was trained with simulated photoacoustic datasets of targets embedded at different depths inside tissue media of different scattering levels. The network trained on this novel dataset accurately locates targets in experimental PA data that is clinically relevant with respect to the localization of vessels, needles, or brachytherapy seeds. We verify the merits of the proposed architecture by outperforming the state of the art on both simulated and experimental datasets., Accepted by IEEE Transactions on Medical Imaging

Single-phase Ni-Cu ferrite nanoparticles have been prepared by sol–gel method and exposed using an Am-Be source for time periods of one and two months. The effects of irradiation on structure and magnetic properties of prepared nanoparticles are investigated by X-ray diffraction, positron annihilation spectroscopy and vibrating sample magnetometer. The X-ray measurements showed that unirradiated and irradiated samples have cubic spinel structure and variation of structural parameters with irradiation is nonuniform. The positron annihilation measurements showed that the main effect of irradiation on samples is variation in momentum distribution of core electrons in metallic cations. The magnetic measurements represent that irradiation cause an increase in saturation magnetization and a decrease in coercivity. The increase in saturation magnetization is attributed to cation redistribution because of atomic displacement. The decrease in coercivity is attributed to the variation of magnetocrystalline anisotropy constant due to the effect of irradiation on the core electrons of cations.

In order to fully understand the interaction between the Abdominal Aortic Aneurysms (AAAs) and the arterial bifurcations interface it is important to attain more detailed information on blood hemodynamics stresses by using an accurate and real model of the vascular system of the human. In this study, a computer simulation, which integrates dinically acquired of 73-year-old male patient with saccular AAA MR angiograms image is considered. The numerical predictions for 2D of two models (with and without saccular AAA) – axisymmetric, rigid wall Newtonian and non-Newtonian Carreau blood model are presented. The finite volume method performed by ANSYS-Fluent Package was used to model this problem. The blood hemodynamics is considered as steady state condition in two values of Reynolds numbers of laminar flow condition. Blood hemodynamics is calculated for an improved set of dimensionless values pointer parameters include the pressure dimensionless, dimensionless Wall Shear Stress (WSS) and flow velocity. The results show that at the turbulent flow, velocity is with highest fluctuation profile and generate some vortices near the inner wall of AAA. The highest WSS levels are obtained downstream of AAA and at bifurcation apex. The presence of AAA in flow path will increase blood velocity of the distal by 35% for laminar and about 42% for turbulent. Finally, the velocity profile was compared with previous literature and give good agreement at the same computational condition.

The goal of the work is to develop computational and experimental approaches to determine the wear resistance of friction units with internal contact of cylinders with slip. The scientific novelty consists in taking into account the slip for calculating the friction path and the wear of the cylinders with internal contact and the proposed method for identifying the parameters of the wear law based on the test results. Practical value is the proposed methods to account load, slip and lubrication conditions on the resource for the design of friction units. The dependences for determining the friction path for internal rolling of cylinders have been considered. The design of an experimental setup for studying friction and wear of cylinders with slip has been proposed. Experimental studies have been carried out: paths of friction; wear of surfaces both with a key and without a key; the effect of lubricants on wear has been studied. The form of the wear model is proposed to determine the effectiveness of methods for increasing wear resistance. The method for determining the parameters of the wear law has been implemented based on the test results. The results show the efficiency of copper powder as an additive to a lubricant. It has been established that the wear of cylinders with a key is greater than the wear of cylinders without a key due to different friction paths. A practical example of determining the wear of a car hub shaft using the wear patterns is presented.

The time-of-flight (TOF) information makes Orlov’s condition not necessary for positron emission tomography (PET) imaging. One-view imaging has never been attempted before. This article investigates whether one-view imaging is possible. We claim that it is possible to obtain an image with measurements from only one-view, provided the TOF time resolution is good enough and the photon counts are high enough. In fact, the image value at a point can be reconstructed by measurements along one line of response (LOR) that passes through the point of interest. The region of interest (ROI) can be reconstructed with ray-by-ray deblurring methods, which make TOF PET a local tomography system. One-view imaging is a severely ill-posed problem if the TOF resolution is not good enough. One indicator of an ill-posed problem is the ringing artifacts in the reconstruction. We show that ringing artifacts can be eliminated by using the nonnegativity constraint for the dot-like objects with a zero background.

Stopping powers (SP) for electrons with energies greater than 10 keV are well described through the Bethe approximation. However, for energies below, such an approach is inadequate. SP in LiF, CaF2 and Al2O3 as the luminescent materials commonly used for dosimetry study and liquid-water are scarce at energies below 10 keV. This work investigated SP and CSDA-range of electrons in in these compounds from the energy gap up to 433 keV using the full Penn algorithm. In particular, the influence of the exciton states was evaluated. The experimental optical data were selected after a rigorous evaluation process. The results indicate that the exciton states affect the SP mainly at energies below 100 eV by up to 48%, 39%, 32% and 15% for liquid-water, LiF, CaF2 and Al2O3, respectively. Furthermore, we observed a certain relationship between the minimum excitation-energy (exciton state) and the energy at which the SP is maximum.

This paper examines the wall jet flow and heat transfer of the Glauert problem with the effect of the hybrid nanoparticles. Also, the influence of the magnetic field and the variable surface temperature are taken into consideration. Here, we consider copper (Cu) and alumina (Al2O3) as the hybrid nanoparticles while water is the base fluid. The governing equations are reduced to the similarity equations using similarity transformations. Then, the numerical solutions are obtained by using the bvp4c function in MATLAB software. The findings reveal that hybrid nanofluid provides a higher heat transfer rate compared to regular nanofluid. Besides, the heat transfer rate and the skin friction coefficient increase in the presence of nanoparticles. Moreover, the rise of the temperature index parameter contributes to the enhancement of the heat transfer rate, but it does not affect the skin friction coefficient. The stronger magnetic strength led to the reduction of the heat transfer rate and the skin friction coefficient.

A new particle tracking velocimetry (PTV) algorithm, which has no interpolation process requirement, has been constructed. An affine transformation and a hybrid fitness function were used to obtain final vector fields. A match probability method (MPM)-based PTV algorithm was used to save calculation convergences. The constructed algorithm was tested with synthetic images using the numerical data of Taylor-Green vortex flow and experimental images for the flow of a rectangular body with Re = 5300. Results obtained by the constructed PTV algorithm were compared with those obtained by the conventional cross-correlation particle image velocimetry (PIV) and the MPM. Comparison results revealed that the constructed interpolation-free PTV (IFPTV) algorithm demonstrated better performance than the aforementioned PIV and PTV algorithms. Furthermore, the constructed PTV algorithm does not need an error removal and interpolation process, enabling easy processing in PTV calculations while providing high-resolution grid vectors.

In the optical three-dimensional measurements of complex objects, the process of phase unwrapping affects the measurement accuracy and measurement speed. To avoid phase unwrapping, S-transform and ...

The greatest advantage of scattering theory-based ultrasound tomography (UT) is its ability to investigate small structures. DBIM is the Distorted Born Iterative Method. The nearest neighbour inter...

PURPOSE To demonstrate a novel 3D radial echo planar imaging (3D REPI) sequence for flexible, rapid, and motion-robust sampling in fMRI. METHODS The 3D REPI method expands on the recently described golden angle rotated EPI trajectory using radial batched internal navigator echoes (TURBINE) approach by exploiting the unused perpendicular direction in the EPI readout to form fast analogues of rotated stack of stars or spirals trajectories that cover all 3 dimensions of k-space. An iterative conjugate gradient algorithm with SENSE reconstruction and time-segmented non-uniform fast Fourier transform (FFT) was used for parallel imaging acceleration and to account for the effects of B0 inhomogeneity. The golden angle rotation allowed for sliding window reconstruction schemes to be applied in brain BOLD fMRI experiments. RESULTS Combined whole brain visual and motor fMRI experiments were successfully carried out on a clinical 3T scanner at 2 mm isotropic and 1 × 1 × 2 mm3 resolutions using the 3D REPI design. Improved sampling characteristics and image quality were observed for twisted trajectories at the expense of prolonged readout times and off-resonance effects. The ability to correct for rigid motion correction was also demonstrated. CONCLUSIONS 3D REPI presents a flexible approach for segmented volumetric fMRI with motion correction and high in-plane spatial resolutions. Improved BOLD fMRI brain activation maps were obtained using a sliding window reconstruction.

By establishing a mathematical model for the uneven structure of a spherical pressure vessel, based on the moment theory, a formula for calculating the stress at the joint between the neck and the ...

We designed a beta radiation detector to measure beta particles from Nickel-63. Since the beta radiation has energy below 66.7 keV, a PIN diode was used. Film dosimetry and a liquid scintillation counter were used to measure the absorbed dose rate and radioactivity of the source. These results were compared with the detector count. The measured count rate increased proportionally to the radioactivity of the source, while the absorbed dose rate was not correlated to the activity. The beta radiation detector can be used to measure surface emission rates of Ni-63 quickly without destruction of the source.

A distributed multichannel synthetic aperture radar system refers to a multichannel synthetic aperture radar system with channels distributed and installed at different locations on the platform. I...

Stroke is one of the foremost common disorders among the elderly. Early detection of stroke from Magnetic Resonance Imaging (MRI) is typically based on the representation method of these images. Representing MRI slices in two dimensional structures (matrices) implies ignoring the dependencies between these slices. Additionally, to combine all features exist in these slices requires more computations and time. However, this results in inexact diagnosis. In this paper, we propose a new tensor-based approach for stroke detection from MRI. The proposed methodology has two phases. In first phase, each patient’s MRI are represented as a tensor. Tensor representations are powerful because they capture the dependencies in high-dimensional data, MRI of patient, which gives more reliable and accurate results. Also, tensor factorization is used as a method for feature extraction and reduction, which improves the performance and accuracy of classifiers. In second phase, these extracted features are used to train support vector machine (SVM) and XGBoost classifiers to classify MRI images into normal and abnormal. The proposed method is assessed with MRI dataset, and the conducted experiments illustrate the efficiency of this approach. It achieves classification accuracy of 98%.

PURPOSE The aim of this work is the reconciliation of high spatial and temporal resolution for MRI. For this purpose, a novel sampling strategy for 3D encoding is proposed, which provides flexible k-space segmentation along with uniform sampling density and benign filtering effects related to signal decay. METHODS For time-critical MRI applications such as functional MRI (fMRI), 3D k-space is usually sampled by stacking together 2D trajectories such as echo planar imaging (EPI) or spiral readouts, where each shot covers one k-space plane. For very high temporal and medium to low spatial resolution, tilted hexagonal sampling (T-Hex) was recently proposed, which allows the acquisition of a larger k-space volume per excitation than can be covered with a planar readout. Here, T-Hex is described in a modified version where it instead acquires a smaller k-space volume per shot for use with medium temporal and high spatial resolution. RESULTS Mono-planar T-Hex sampling provides flexibility in the choice of speed, signal-to-noise ratio (SNR), and contrast for rapid MRI acquisitions. For use with a conventional gradient system, it offers the greatest benefit in a regime of high in-plane resolution

The dynamical behaviors of three oscillators (the classical linear oscillator, the Van der Pol oscillator and the Grudzinsky-Zebrowsky oscillator) subjected to periodic pulse excitation, assumed to come from blood pressure, are studied theoretically and experimentally using microcontrollers. The pulsatile electrical signal is generated by a microcontroller. For some selected frequencies, it is found that the models exhibit responses having the same shape as those of the pulsatile blood pressure. This suggests the possibility of using such a conversion and excitation mechanism to replicate the functioning of artificial pacemakers.

The basic parameters of an irradiation and their registration system for constructional materials irradiated on the helium ions linear accelerator are resulted. Experimental techniques and some researches results of the microscopic, electrophysical, frictional and ultrasonic characteristics of atomic power stations (APS) and fusion reactors (FR) constructional materials irradiated on a linear accelerator of the helium ions with energies 0.12 and 4 MeV are presented.

DNA strands are powerful tools as ligand molecules that bind nanoparticles to each other via programmable self-assembly for colloidal crystallization. We found that hydrated DNA-functionalized nanoparticle (DNA-NP) superlattices with a properly controlled volume fraction and spatial arrangement of nanoparticles successfully maintained their crystallinity even after dehydration, which involves drastic contraction. A detailed study of the structural changes was performed for the self-assembled DNA-NP sample using small-angle X-ray scattering (SAXS) after dehydration. Then, an optimal volume fraction of nanoparticles in the superlattice, ϕ, which minimized the level of distortion of the dehydrated superlattice, was found for each bcc and fcc structure. By acquiring clear SAXS diffraction patterns showing crystal symmetries for dehydrated DNA-NP superlattices, their lattice distortion was evaluated using our analysis technique, which is based on Hosemann’s paracrystalline theory and involves SAXS and scanning electron microscopy data. Geometrical calculations substantiated the ease of movement of a nanoparticle under the influence of repulsions from adjacent particles that mainly affect the dehydration stability. These results suggest that it is possible to design the crystal structure of solid nanoparticle superlattices via DNA-guided nanoparticle assembly under a near-equilibrium state in solution as the first step, followed by dehydration under nonequilibrium conditions as the second step.

Purpose MR-guided radiotherapy has different requirements for the images than diagnostic radiology, thus requiring development of novel imaging sequences. MRI simulation is an excellent tool for optimizing these new sequences; however, currently available software does not provide all the necessary features. In this paper, we present a digital framework for testing MRI sequences that incorporates anatomical structure, respiratory motion, and realistic presentation of MR physics. Methods The extended Cardiac-Torso (XCAT) software was used to create T1 , T2 , and proton density maps that formed the anatomical structure of the phantom. Respiratory motion model was based on the XCAT deformation vector fields, modified to create a motion model driven by a respiration signal. MRI simulation was carried out with JEMRIS, an open source Bloch simulator. We developed an extension for JEMRIS, which calculates the motion of each spin independently, allowing for deformable motion. Results The performance of the framework was demonstrated through simulating the acquisition of a two-dimensional (2D) cine and demonstrating expected motion ghosts from T2 weighted spin echo acquisitions with different respiratory patterns. All simulations were consistent with behavior previously described in literature. Simulations with deformable motion were not more time consuming than with rigid motion. Conclusions We present a deformable four-dimensional (4D) digital phantom framework for MR sequence development. The framework incorporates anatomical structure, realistic breathing patterns, deformable motion, and Bloch simulation to achieve accurate simulation of MRI. This method is particularly relevant for testing novel imaging sequences for the purpose of MR-guided radiotherapy in lungs and abdomen.

We proposed the air-core cyclotron using high-temperature superconducting (HTS) technology, named Skeleton Cyclotron, as high intensity compact, variable-energy and multi-particle cyclotron for RI production. Skeleton Cyclotron consists of HTS split circular main coils generating the isochronous field and HTS non-circular sector coils generating the azimuthally varying field (AVF). Now, we are currently developing the small-scale cryocooler-cooled HTS coil system of Skeleton Cyclotron, which accelerates the proton up to energy of 5 MeV at an extraction radius of 20 cm. Skeleton cyclotron is multi-coil system consists of HTS split circular main NI (no-insulation) coils and HTS non-circular sector NI coils. Therefore, the electromagnetic, thermal, and mechanical behaviors are expected to be very complicated. In this study, the structure analysis based on finite element method using COMSOL Multiphysics is performed for a non-circular sector coil. The coils in Ultra-Baby Cyclotron are reinforced with YOROI-coil structure. Therefore, the effect of YOROI-coil structure was numerically investigated during cool-down process and excitation process. YOROI-coil structure is effective for non-circular sector coil against the electromagnetic force.

We have been studying no-insulation (NI) high temperature superconducting (HTS) coils that do not use turn-to-turn electrical insulation. The no-insulation winding technique can provide high stability of the HTS coils against the quenching, but it cannot prevent mechanical deterioration of the HTS coil due to electromagnetic force and multiple cooling. To solve these problems, we propose the installation of metal protection ring on the outermost turn of NI HTS coil to improve thermal, mechanical, and electrical stability. In this study, the current bypass characteristics in the transverse direction within an NI test coil wound with 37 turns of REBCO wire with/without copper protection ring were experimentally investigated for various amounts of heating by a heater and various heater positions. Eight repeated cooling experiments with liquid nitrogen proved that the proposed copper protection ring was effective against shape deformation of the NI test coil and deterioration of contact resistance between turns due to thermal stress.

In the framework of the HL-LHC project, the present LHC low-β superconducting quadrupoles will be substituted with higher performance Nb3Sn magnets (MQXF) with 11.4 T coil peak field. MQXF coils are impregnated with epoxy resin to reduce risk of stress concentration on the brittle conductor. The magnet quench protection is provided by CLIQ and quench heaters to ensure a redundant system. Quench heaters are impregnated with the coils in order to have suitable thermal contact with them, and to prevent the hot spot temperature from exceeding 350K during normal operation in case of a quench. Quench heaters are insulated from the coil by S-2 Glass and polyimide. The test of the first MQXF prototype (4 m long) MQXFAP1 was stopped by a coil-to-ground short circuit triggered by a heater-to-coil short. This issue triggered a root analysis of the causes of this short. Here we prove that the use of a non-conforming cloth in coil impregnation, further weakened by non-conforming high voltage test, has triggered the shorts. Moreover, we present an analysis of the heater-to-coil insulation strength, showing the role of blistering phenomena and how they are triggered by a combination of magnet powering and heater firing.

Photoacoustic imaging (PAI) is a noninvasive biomedical imaging technology capable of multiscale imaging of biological samples from organs down to cells. Multiscale PAI requires different ultrasound transducers that are flat or focused because the current widely-used piezoelectric transducers are rigid and lack the flexibility to tune their spatial ultrasound responses. Inspired by the rapidly-developing flexible photonics, we exploited the inherent flexibility and low-loss features of optical fibers to develop a flexible fiber-laser ultrasound sensor (FUS) for multiscale PAI. By simply bending the fiber laser from straight to curved geometry, the spatial ultrasound response of the FUS can be tuned for both wide-view optical-resolution photoacoustic microscopy at optical diffraction-limited depth (~1 mm) and photoacoustic computed tomography at optical dissipation-limited depth of several centimeters. A radio-frequency demodulation was employed to get the readout of the beat frequency variation of two orthogonal polarization modes in the FUS output, which ensures low-noise and stable ultrasound detection. Compared to traditional piezoelectrical transducers with fixed ultrasound responses once manufactured, the flexible FUS provides the freedom to design multiscale PAI modalities including wearable microscope, intravascular endoscopy, and portable tomography system, which is attractive to fundamental biological/medical studies and clinical applications.

The aim of this work is to analyze existing detectors for the relative dosimetry of small radiation fields in external beam radiation therapy and the requirements for them, consider the problems in carrying out dosimetry of small radiation fields, determine the physical conditions under which an external photon beam can be designated as a small field. In modern radiation therapy, there is an increase in the use of small static fields, which is facilitated by the general availability of standard and optional multileaf collimators and new generation treatment machines of various designs. There is growing interest in the use of such radiation techniques as stereotactic radiosurgery, stereotactic body radiotherapy, intensity modulated radiotherapy, which are widely used small fields. This has increased the uncertainties in clinical dosimetry, especially for small fields. Accurate dosimetry of small fields is important when commissioning linear accelerators and is a difficult task, especially for very small fields used in stereotactic radiotherapy. In the course of the work, a study of topical problems in the dosimetry of small radiation fields in external beam radiation therapy has been carried out. The physical conditions under which the external photon beam can be designated as a small field are considered. A review and analysis of existing detectors for the relative dosimetry of small radiation fields, as well as an analysis of the requirements for the character. The analysis revealed that liquid ionization chambers, silicon diodes, diamond detectors, organic scintillators, radiochromic films, thermoluminescent dosimeters and optically stimulated luminescence detectors are considered suitable for relative dosimetry of small photon fields and are recommended for use in clinics where radiotherapy is performed.

This letter proposes a general formula to determine the amount of compound required to produce water–oil-based phantoms that can emulate the electrical properties of a specific body tissue at microwave frequencies. The existing process to produce such a phantom usually involves mixing together a number of different materials, where the proportion of each compound needs to be known a priori to reproduce the dielectric properties of a specific tissue. In this letter, we first investigate the dielectric variation of the mixture by changing the proportion of each compound over a wide frequency band. By utilizing Lichtenecker's logarithmic mixture formula, the gradient descent iterative optimization method is applied to train the relations obtained, and a formula that determines the amount of each compound required to produce a phantom given a specific tissue type is derived. The formula is verified by constructing representative tissues of the human head, with the durability and fidelity of the produced phantom also analyzed.

We have designed the first superconducting bulk coil for radio frequency (RF) applications. We investigated the effect of the line gap and line width of the coil by simulating the quality factor of the coil for each gap and width. We investigated several supporting dielectric materials and identified one that negligibly affects the quality factor and thus maintains the coil configuration. To investigate the potential for obtaining a high quality factor for the superconducting bulk coil, we measured a frequency response and quality factor of a test sample of superconducting bulk coil with an unoptimized line gap and line width. Despite the non-optimized structure, the quality factor of the coil was three times that of a copper coil. Since there have been no reports on the conductivity of superconducting bulk in the MHz range, we determined an effective conductivity on basis of the measured quality factor. When the superconducting bulk coil was redesigned on the basis of the assumed effective conductivity, the simulated quality factor of an optimized superconducting bulk coil was 19 times that of a copper coil.