Radial Phase Research Articles

A 3D MR-acquisition scheme for non-rigid bulk motion correction in simultaneous PET-MR.

Positron emission tomography (PET) is commonly used to detect tumours and assess the progress of cancer treatment by measuring standardized uptake values (SUV). Physiological motion during data acquisition can negatively impair obtained SUV. Simultaneous PET-MR combines metabolic PET information with high-resolution anatomical MR images and has the potential to minimize motion artefacts. A 3D MR-acquisition scheme is proposed which allows for the automatic detection and correction of non-rigid bulk motion shifts, i.e. changes of the patient’s position leading to non-rigid changes of the patient’s anatomy, in PET and MR images (both T1-weighted gradient echo and T2-weighted turbo spin echo images) without an increase in scan time. Six respiratory gated T1- and T2-weighted 3D data sets with an isotropic resolution of 1.5mm were obtained using a radial phase encoding (RPE) acquisition. Volunteers are asked to move the abdomen during data acquisition resulting in overall 19 movements at arbitrary time points. RPE allows for a retrospective reconstruction of dynamic 3D MR images with different temporal resolutions from the same data. Non-rigid bulk motion is detected and corrected from these dynamic images. A simultaneous PET acquisition is simulated to assess the effect of motion correction on image quality and SUV for lesions with different diameters. Every bulk motion shift was accurately detected and corrected. Non-rigid motion fields describing the different motion states were obtained with an accuracy of 1.71 ± 0.29mm. The PET simulation showed SUV errors of up to 67% due to bulk motion which could be reduced to 10% with the proposed motion compensated approach. The presented MR acquisition scheme yields both high resolution 3D anatomical data and highly accurate non-rigid motion information without an increase in scan time. This method strongly improves both MR and PET image quality and ensures an accurate assessment of tracer uptake.

A 3D MR-acquisition scheme for nonrigid bulk motion correction in simultaneous PET-MR.

Positron emission tomography (PET) is a highly sensitive medical imaging technique commonly used to detect and assess tumor lesions. Magnetic resonance imaging (MRI) provides high resolution anatomical images with different contrasts and a range of additional information important for cancer diagnosis. Recently, simultaneous PET-MR systems have been released with the promise to provide complementary information from both modalities in a single examination. Due to long scan times, subject nonrigid bulk motion, i.e., changes of the patient's position on the scanner table leading to nonrigid changes of the patient's anatomy, during data acquisition can negatively impair image quality and tracer uptake quantification. A 3D MR-acquisition scheme is proposed to detect and correct for nonrigid bulk motion in simultaneously acquired PET-MR data. A respiratory navigated three dimensional (3D) MR-acquisition with Radial Phase Encoding (RPE) is used to obtain T1- and T2-weighted data with an isotropic resolution of 1.5 mm. Healthy volunteers are asked to move the abdomen two to three times during data acquisition resulting in overall 19 movements at arbitrary time points. The acquisition scheme is used to retrospectively reconstruct dynamic 3D MR images with different temporal resolutions. Nonrigid bulk motion is detected and corrected in this image data. A simultaneous PET acquisition is simulated and the effect of motion correction is assessed on image quality and standardized uptake values (SUV) for lesions with different diameters. Six respiratory gated 3D data sets with T1- and T2-weighted contrast have been obtained in healthy volunteers. All bulk motion shifts have successfully been detected and motion fields describing the transformation between the different motion states could be obtained with an accuracy of 1.71 ± 0.29 mm. The PET simulation showed errors of up to 67% in measured SUV due to bulk motion which could be reduced to less than 10% with the proposed motion compensation approach. A MR acquisition scheme which yields both high resolution 3D anatomical data and highly accurate nonrigid motion information without an increase in scan time is presented. The proposed method leads to a strong improvement in both MR and PET image quality and ensures an accurate assessment of tracer uptake.

A model code for the radiative theta pinch

A model for the theta pinch is presented with three modelled phases of radial inward shock phase, reflected shock phase, and a final pinch phase. The governing equations for the phases are derived incorporating thermodynamics and radiation and radiation-coupled dynamics in the pinch phase. A code is written incorporating correction for the effects of transit delay of small disturbing speeds and the effects of plasma self-absorption on the radiation. Two model parameters are incorporated into the model, the coupling coefficient f between the primary loop current and the induced plasma current and the mass swept up factor fm. These values are taken from experiments carried out in the Chulalongkorn theta pinch.

To construct a stable and tunable optical trap in the focal region of a high numerical aperture lens

Based on the diffraction theory, the focusing properties of a radially polarized quadratic Bessel–Gaussian beam (QBG) with on-axis radial phase variance wavefront are investigated theoretically in the focal region of a high numerical aperture (NA) objective lens. The phase wavefront C and pupil beam parameter μ of QBG are the functions of the radial coordinate. The detailed numerical calculation of the focusing property of a QBG beam is presented. The numerical calculation shows that the beam parameter μ and phase parameter C have greater effect on the total electric field intensity distribution. It is observed that under the condition of different μ, evolution principle of focal pattern differs very remarkably on increasing C. Also, some different focal shapes may appear, including rhombic shape, quadrangular shape, two-spherical crust focus shape, two-peak shape, one dark hollow focus, two dark hollow focuses pattern, and triangle dark hollow focus, which find wide optical applications such as optical trapping and nanopatterning.

Numerical experiments on neutron yield and soft x-ray study of a ∼100 kJ plasma focus using the current profile fitting technique

Numerical experiments using the Lee model were performed to study the neutron yield and soft x-ray emission from the IR-MPF-100 plasma focus using the current fitting technique. The mass sweeping factor and the current factor for the axial and radial phase were used to represent the imperfections encountered in experiments. All gross properties including the yields were realistically simulated once the computed and measured current profiles were well fitted. The computed neutron yield Yn was in agreement with the experimentally measured Yn at 20 kV (E0 ∼ 30 kJ) charging voltage. The optimum computed neutron yield of Yn = 1.238 × 109 neutrons per shot was obtained at optimum physics parameters of the plasma focus operated with deuterium gas. It was also observed that no soft x-rays were emitted from the IR-MPF-100 plasma focus operated with argon gas due to the absence of helium-like and hydrogen-like ions at a low plasma temperature (∼0.094 keV) and axial speed (8.12 cm µs−1). However, the soft x-ray yield can be achieved by increasing the charging voltage, using a higher ratio of outer anode radius to inner anode radius c or shorter anode length z0, or using neon as the operating gas.

The local standard of rest from data on young objects with account for the Galactic spiral density wave

To estimate the peculiar velocity of the Sun with respect to the Local Standard of Rest (LSR), we used young objects in the Solar neighborhood with distance measurement errors within 10%-15%. These objects were the nearest Hipparcos stars of spectral classes O-B2.5, masers with trigonometric parallaxes measured by means of VLBI, and two samples of the youngest and middle-aged Cepheids. The most significant component of motion of all these stars is induced by the spiral density wave. As a result of using all these samples and taking into account the differential Galactic rotation, as well as the influence of the spiral density wave, we obtained the following components of the vector of the peculiar velocity of the Sun with respect to the LSR: (Uo,Vo,Wo)_{LSR}=(6.0,10.6,6.5)+\-(0.5,0.8,0.3) km/s. We have found that components of the Solar velocity are quite insensitive to errors of the distance Ro in a broad range of its values, from Ro=7.5 kpc to Ro=8.5 kpc, that affect the Galactic rotation curve parameters. In the same time, the Solar velocity components(Uo)_{LSR} and (Vo)_{LSR}$ are very sensitive to the Solar radial phase in the spiral density wave.

Correcting vortex splitting in higher order vortex beams.

We demonstrate a general method for the first order compensation of singularity splitting in a vortex beam at a single plane. By superimposing multiple forked holograms on the SLM used to generate the vortex beam, we are able to compensate vortex splitting and generate beams with desired phase singularities of order ℓ = 0, 1, 2, and 3 in one plane. We then extend this method by application of a radial phase, in order to simultaneously compensate the observed vortex splitting at two planes (near and far field) for an ℓ = 2 beam.

Effect of temporal resolution on 4D flow MRI in the portal circulation

PurposeTo demonstrate the use of temporal averaging with radial 4D flow magnetic resonance imaging (MRI) to reduce scan time for quantification and visualization of flow in the portal circulation. This study compared phase‐contrast MR angiography, 3D flow visualization, and flow quantification of portal venous hemodynamics of time‐averaged vs. time‐resolved reconstructions.Materials and MethodsTime‐resolved 3D radial (“4D”) phase contrast data were acquired from 44 subjects (15 volunteers, 29 cirrhosis patients) at 3T. Images were reconstructed as a fully sampled time‐resolved reconstruction and multiple time‐averaged reconstructions using a variable number of acquired projections to simulate different scan times. Images from each reconstruction were evaluated to compare the quality of anatomical and hemodynamic visualization.ResultsTime‐averaged reconstructions outperformed time‐resolved reconstructions for flow quantification (3.9 ± 3.1% error vs. 5.2 ± 4.4% error), average streamline length (47 ± 7 mm vs. 34 ± 15 mm), and visualization quality (average grading = 3.7 ± 0.5 vs. 2.2 ± 0.9). In addition, excellent visualization quality was achieved using fewer acquired projections.ConclusionReductions in scan time can be achieved through time‐averaging while still providing excellent visualization and quantification in the portal circulation. Scan time reduction of up to 70%–80% was possible for high‐quality assessment, translating into a reduction in scan time from 10–12 minutes to ∼3–4 minutes. J. Magn. Reson. Imaging 2014;39:819–826. © 2013 Wiley Periodicals, Inc.

Reelin and CXCL12 regulate distinct migratory behaviors during the development of the dopaminergic system

The proper functioning of the dopaminergic system requires the coordinated formation of projections extending from dopaminergic neurons in the substantia nigra (SN), ventral tegmental area (VTA) and retrorubral field to a wide array of forebrain targets including the striatum, nucleus accumbens and prefrontal cortex. The mechanisms controlling the assembly of these distinct dopaminergic cell clusters are not well understood. Here, we have investigated in detail the migratory behavior of dopaminergic neurons giving rise to either the SN or the medial VTA using genetic inducible fate mapping, ultramicroscopy, time-lapse imaging, slice culture and analysis of mouse mutants. We demonstrate that neurons destined for the SN migrate first radially and then tangentially, whereas neurons destined for the medial VTA undergo primarily radial migration. We show that tangentially migrating dopaminergic neurons express the components of the reelin signaling pathway, whereas dopaminergic neurons in their initial, radial migration phase express CXC chemokine receptor 4 (CXCR4), the receptor for the chemokine CXC motif ligand 12 (CXCL12). Perturbation of reelin signaling interferes with the speed and orientation of tangentially, but not radially, migrating dopaminergic neurons and results in severe defects in the formation of the SN. By contrast, CXCR4/CXCL12 signaling modulates the initial migration of dopaminergic neurons. With this study, we provide the first molecular and functional characterization of the distinct migratory pathways taken by dopaminergic neurons destined for SN and VTA, and uncover mechanisms that regulate different migratory behaviors of dopaminergic neurons.

Correlation of measured neon soft X-ray pulses of the INTI plasma focus with the reflected shock phase at 12KV

The six-phase Lee Model Code is used to fit the computed current waveform to the measured waveform of the INTI Plasma Focus (PF;2.2 kJ at 12 kV), a T2 PF device, operated as a source of Neon soft X-ray (SXR) with optimum yield around 2.5 - 3 Torr of neon. The characteristic He-like and H-like neon line SXR pulse is measured using a pair of SXR detectors with selected filters that, by subtraction, have a photon energy window of 900 to 1550 eV covering the region of the characteristic neon SXR lines. The aim of this paper is to investigate the correlation between the time histories of the measured Neon soft X-ray pulse and the reflected shock phase of the computed current waveform which has been fitted to the measured current waveform. Results shows that the characteristic neon SXR measured at 3.17 J with a pulse duration of 249 ns starts typically after the radial inward shock phase and increases in magnitude few ns before the pinch phase. It tails unto the first anomalous resistance, and decays at the second anomalous resistance.

An Effective Criterion to Prevent Injection Test Numerical Simulation from Spurious Oscillations

Injection/fall-off tests are one of the most promising alternatives to the conventional production/build-up sequence because they eliminate surface emissions and can significantly reduce testing costs. This kind of test is characterized by the presence of two mobile phases, the fluid originally in place (hydrocarbon) and the injected fluid (Diesel, brine or nitrogen). The conventional analytical approach used to describe the transient pressure behavior is no longer suitable due to the variations in fluid saturations during the test. Although applicable in theory, the analytical approach often implies excessive simplifications of the real system behavior, such as piston-like displacement. Thus only numerical simulations can thoroughly describe the phenomena occurring during the injection process. However, the pressure and pressure derivative response calculated numerically often shows non-physical oscillations during the radial flow phase, when the pressure derivative is expected to be horizontal. It was found that these spurious oscillations arise in convection-dominated problems and are associated with sharp saturation fronts. In this paper, an effective methodology, based on an adaptive time-step calculation, is presented so as to avoid pressure oscillations. The proposed time-step selection is both computationally efficient and suitable to capture the physics of the system.

An alternative method for phase-unwrapping of interferometric data

In this paper we present a novel algorithm for phase unwrapping where only a subset of data from the wrapped phase map is used to reconstruct the unwrapped phase map as a linear combination of radial basis functions (RBF’s). For noisy phase maps this algorithm gives better results than three reference algorithms based on radial basis functions, Zernike polynomials and path dependent phase unwrapping strategies.

Apical control of xylem formation in the pine stem. I. Auxin effects and distribution of assimilates

The effect of IAA upon cambial activity, xylem differentiation and translocation of assimilates from the lateral shoot was investigated in spring and late summer in decapitated and ring-barked young trees of <em>Pinus silvestris</em> in the forest stand. Decapitation interrupted cambial xylem production in the uppermost part of the main stem of decapitated trees in spring and late summer, regardless of whether lateral branches below were growing, dormant or disbudded, and the contact through phloem with the roots was maintained or severed. Auxin supplied to the decapitated stems caused an increasing stimulation of cambial xylem production in spring. It also stimulated cambial activity in August but was ineffective in September. Apical control of cambial xylem production was strongly dependent upon the continuity of phloem and/or cambial tissues of the decapitated main-stem-section with lower parts of the plant. Decapitation of the stem strongly reduced the daily rate of cell wall deposition in the cambial xylem derivatives which on the day the experiment started constituted the zones of radial enlargement and maturation. This reduction limited progressively secondary wall deposition in consecutive maturing tracheids even though the cells differentiated longer. Irrespective of the season, auxin prevented the effect of decapitation in cells which were already differentiating when the experiment started as well as extension of the maturation phase. The effect of auxin was somewhat reduced when the lateral branches were additionally decapitated in early summer. In early summer auxin caused a significant increase of the daily rate of cell wall deposition in cells of the cambial zone or the newly produced ones, thus resulting in formation of progressively thicker secondary walls. Late in summer assimilates were transported mostly to the lower part of the stem. Decapitation changed the intact tree pattern of assimilate distribution, increasing the transport in spring and reducing it later in the summer. Prevention of the contact with roots via phloem and cambium in spring (by ring-barking the stem at tree base) decreased decapitation-induced downward transport of assimilates. Application of auxin to the decapitated uppermost segment of the main stem resulted in a significant increase of assimilate translocation into the stem. At least two mechanisms of auxin involvement in regulation of the rate of secondary wall deposition in pine stem tracheids can be considered: (a) induction (or activation) of the cell wall metabolic potential which seems to occur during meristematic or early radial enlargement phases of tracheid differentiation, and (b) regulation of substrate availability during the phase of tracheid maturation.

Accelerating the acquisition of the 3D Dual Cardiac Phase technique using RPE trajectories

Background A 3D Dual Cardiac Phase (3D-DCP) scan was proposed to obtain systolic and diastolic images with equivalent quality and scan time compared to the 3D single cardiac phase acquisition (Uribe et al, Radiology 2008). In this work, we propose to accelerate the acquisition and reconstruction of the 3D-DCP approach by sharing information from the outer k-space of both cardiac phases using Radial Phase Encoding (RPE) trajectories (Boubertak, et al., MRM 2009) and gridding-CLEAR reconstruction

Developing a plasma focus research training system for the fusion energy age

The 3 kJ UNU/ICTP Plasma Focus Facility is the most significant device associated with the AAAPT (Asian African Association for Plasma Training). In original and modified/upgraded form it has trained generations of plasma focus (PF) researchers internationally, producing many PhD theses and peer-reviewed papers. The Lee Model code was developed for the design of this PF. This code has evolved to cover all PF machines for design, interpretation and optimization, for derivation of radiation scaling laws; and to provide insights into yield scaling limitations, radiative collapse, speed-enhanced and current-stepped PF variants. As example of fresh perspectives derivable from this code, this paper presents new results on energy transfers of the axial and radial phases of generalized PF devices. As the world moves inexorably towards the Fusion Energy Age it becomes ever more important to train plasma fusion researchers. A recent workshop in Nepal shows that demand for such training continues. Even commercial project development consultants are showing interest. We propose that the AAAPT-proven research package be upgraded, by modernizing the small PF for extreme modes of operation, switchable from the typical strong-focus mode to a slow-mode which barely pinches, thus producing a larger, more uniform plasma stream with superior deposition properties. Such a small device would be cost-effective and easily duplicated, and have the versatility of a range of experiments from intense multi-radiation generation and target damage studies to superior advanced-materials deposition. The complementary code is used to reference experiments up to the largest existing machine. This is ideal for studying machine limitations and scaling laws and to suggest new experiments. Such a modernized versatile PF machine complemented by the universally versatile code would extend the utility of the PF experience; so that AAAPT continues to provide leadership in pulsed plasma research training in preparation for the Fusion Energy Age.

Robust watermarking against geometric attacks using partial calculation of radial moments and interval phase modulation

This paper presents a new image watermarking scheme which is blind and robust against geometric attacks. The proposed algorithm is based on the features of radial moments. In this algorithm the radial moments were first computed and then the watermark was embedded into the differential phase of various blocks of the original image using a special type of PSK modulation called interval phase modulation (IPM). In order to embed the watermark into the phase of moments, a particular method, namely the partial calculation of moments was utilized for computation. The implementation results show the improvement in the robustness and quality of the watermarked images in comparison with other methods.

Effect of temporal resolution on 4D flow MRI in the portal circulation

To demonstrate the use of temporal averaging with radial 4D flow magnetic resonance imaging (MRI) to reduce scan time for quantification and visualization of flow in the portal circulation. This study compared phase-contrast MR angiography, 3D flow visualization, and flow quantification of portal venous hemodynamics of time-averaged vs. time-resolved reconstructions. Time-resolved 3D radial ("4D") phase contrast data were acquired from 44 subjects (15 volunteers, 29 cirrhosis patients) at 3T. Images were reconstructed as a fully sampled time-resolved reconstruction and multiple time-averaged reconstructions using a variable number of acquired projections to simulate different scan times. Images from each reconstruction were evaluated to compare the quality of anatomical and hemodynamic visualization. Time-averaged reconstructions outperformed time-resolved reconstructions for flow quantification (3.9 ± 3.1% error vs. 5.2 ± 4.4% error), average streamline length (47 ± 7 mm vs. 34 ± 15 mm), and visualization quality (average grading = 3.7 ± 0.5 vs. 2.2 ± 0.9). In addition, excellent visualization quality was achieved using fewer acquired projections. Reductions in scan time can be achieved through time-averaging while still providing excellent visualization and quantification in the portal circulation. Scan time reduction of up to 70%-80% was possible for high-quality assessment, translating into a reduction in scan time from 10-12 minutes to ∼3-4 minutes.

Enhancing triaxial cyclic compression testing of hot mix asphalt by introducing cyclic confining pressure

Permanent deformation in terms of rutting is a major deterioration mode of bituminous bound pavements. The triaxial cyclic compression test (TCCT) is a scientifically accepted and standardised test method to assess the resistance to permanent deformation. Presently, the standard TCCT according to EN 12697-25 is carried out with cyclic axial loading and constant confining pressure. In road pavements, dynamic traffic loading due to passing tyres leads to cyclic confining pressures. Thus, to bring the TCCT closer to reality, within the study presented in this paper, (a) the radial reaction and its phase lag to axial loading in standard TCCTs is measured and (b) an enhanced TCCT with cyclic confining pressure which takes into account the viscoelastic material response in terms of radial phase lag to axial loading is introduced. In a subsequent test programme, TCCTs with various confining pressure amplitudes are run on different materials and results from standard and enhanced TCCTs are analysed and compared in terms of resistance to permanent deformation. It is shown that the resistance to permanent deformation increases significantly when the viscoelastic material response is taken into account in the TCCTs with cyclic confining pressure.

Applications of Feed-Forward Neural Network to Study Irregular-Shape Particle Effects on Hydrodynamics Behavior in a Liquid–Solid Circulating Fluidized Bed Riser

Abstract Feed-forward neural network (FFNN) modeling techniques are applied to study the flow behavior of different-size irregular-shape particles in a pilot scale liquid–solid circulating fluidized bed (LSCFB) riser. The adequacy of the developed model is examined by comparing the model predictions with experimental data obtained from the LSCFB using lava rocks (dmean 500 and 920 µm) and water as solids and liquid phases, respectively. Axial and radial solid holdup profiles are measured in the riser at four axial locations (H 1, 2, 3 and 3.8 m above the distributor) above the liquid distributor for different operating liquids. In the model training, the effects of various auxiliary and primary liquid velocities, superficial liquid velocities and superficial solid velocities on radial phase distribution at different axial positions are considered. For model validation along with other experimental parameters, dimensionless normalized superficial liquid velocities and net superficial liquid velocities are also introduced. The correlation coefficient values of the predicted output and the experimental data are found to be 0.95 and 0.94 for LR-500 and LR-920 particles, respectively which reflects the competency of the developed FFNN model.

Concentration tuned bandgap and corresponding nonlinear refractive index dispersion in Ga-Ge-Se nanocolloids

Solution-processing of chalcogenide glass materials has attracted attention for the fabrication of photonic devices. We have carried out linear and nonlinear optical studies on Ga9Ge27Se64 nanocolloidal solutions with varying concentrations and witnessed the opportunity for engineering the optical properties of the material by simply changing the concentration of solute in the solvent. An enhancement of bandgap, deterioration, and blue shift in the band tail states with decrease in concentration were observed from the absorption spectra. Open and closed aperture Z-scan studies reveal tunability of nonlinear absorption coefficient (β) and nonlinear refractive index (n2). As the bandgap approaches the one photon absorption edge, the material shows very large negative nonlinear refraction and also “two step photon absorption” due to the presence of intermediate tail states. The radial phase shift (Δφ0) induced after travelling through the nanocolloidal solution with respect to bandgap is plotted and we predict that the variation of Δφ0 is governed by a quadratic polynomial of Eg.