Time-integrated Images Research Articles

Couch height–based patient setup for abdominal radiation therapy

There are 2 methods commonly used for patient positioning in the anterior-posterior (A-P) direction: one is the skin mark patient setup method (SMPS) and the other is the couch height–based patient setup method (CHPS). This study compared the setup accuracy of these 2 methods for abdominal radiation therapy. The enrollment for this study comprised 23 patients with pancreatic cancer. For treatments (539 sessions), patients were set up by using isocenter skin marks and thereafter treatment couch was shifted so that the distance between the isocenter and the upper side of the treatment couch was equal to that indicated on the computed tomographic (CT) image. Setup deviation in the A-P direction for CHPS was measured by matching the spine of the digitally reconstructed radiograph (DRR) of a lateral beam at simulation with that of the corresponding time-integrated electronic portal image. For SMPS with no correction (SMPS/NC), setup deviation was calculated based on the couch-level difference between SMPS and CHPS. SMPS/NC was corrected using 2 off-line correction protocols: no action level (SMPS/NAL) and extended NAL (SMPS/eNAL) protocols. Margins to compensate for deviations were calculated using the Stroom formula. A-P deviation > 5mm was observed in 17% of SMPS/NC, 4% of SMPS/NAL, and 4% of SMPS/eNAL sessions but only in one CHPS session. For SMPS/NC, 7 patients (30%) showed deviations at an increasing rate of > 0.1mm/fraction, but for CHPS, no such trend was observed. The standard deviations (SDs) of systematic error (Σ) were 2.6, 1.4, 0.6, and 0.8mm and the root mean squares of random error (σ) were 2.1, 2.6, 2.7, and 0.9mm for SMPS/NC, SMPS/NAL, SMPS/eNAL, and CHPS, respectively. Margins to compensate for the deviations were wide for SMPS/NC (6.7mm), smaller for SMPS/NAL (4.6mm) and SMPS/eNAL (3.1mm), and smallest for CHPS (2.2mm). Achieving better setup with smaller margins, CHPS appears to be a reproducible method for abdominal patient setup.

A time-domain deconvolution technique for meteor photometry applied to double-station CCD image data

Aims. We describe a new algorithm for extracting photometric information from meteor images. Methods. The time history of a moving point source of variable brightness is explicitly deconvolved from the spatial distribution of the meteor signal on the image. The method can be applied to time-integrated meteor images if kinematic information is independently available or, alternatively, assumed. Formal uncertainty estimation and reporting is included. Results. We test the algorithm on synthetic meteor images and meteors recorded during a recent double-station meteor observing campaign in Greece. In the first case, we find that both the synthetic signal and the a priori time variation of the flux are faithfully reproduced. In the second, the fluxes obtained from the two stations agree to ∼20%.

Soft x-ray studies of plasma-focus pinch structures in PF-1000U experiments

This work reports on recent experiments performed at the modernized PF-1000U plasma-focus facility. In contrast to earlier studies the main attention was focussed on measurements of the soft x-ray emission. Detailed time-integrated x-ray measurements, carried out using filtered pinhole cameras with sensitive x-ray films, are presented and analysed. The fine structure of the collapsing current sheath and dense pinch column is investigated. Observations of ‘plasma filaments’ are discussed and compared with those from the old POSEIDON facility. New results are time-integrated x-ray images of PF-1000U discharges with additional gas puffing, which in many cases show distinct plasma filaments and/or ‘hot spots’ formed inside the dense pinch column. The formation of such ‘hot-spots’ is explained by necking and breaking of the plasma filaments. Results of time-resolved x-ray measurements, performed outside the experimental chamber by means of scintillation probes, and inside with PIN-diodes placed behind pinholes and absorption filters, are also presented Time-resolved measurements, carried out using an old XUV framing-camera and a new soft x-ray four-frame camera (SXRFFC), are also presented and discussed. Correlations of the time-integrated x-ray images (of plasma filaments and hot spots) with time-resolved x-ray signals are discussed. The hypothesis that plasma-current filaments appear in almost all PF-type discharges is supported by pictures of radial erosion tracks on the anode front-plate after many discharges.

Ultrafast camera’s early history

For the record, scientists at Los Alamos National Laboratory developed systems that use a streak tube and image compression to record ultrafast two-dimensional movies of transient events some 30 years ago11. C. T. Mottershead, IEEE Trans. Nucl. Sci. 29, 900 (1982). https://doi.org/10.1109/TNS.1982.4335986,22. M. Wilke, N. S. P. King, N. Gray, D. Johnson, D. Esquibel, P. Nedrow, S. Ishiwata, Proc. SPIE 0566, 185 (1986). https://doi.org/10.1117/12.949787 (Physics Today, February 2015, page 12). A cylindrical lens focuses the light from a 2D scene into a 1D line, which is actually a tomographic projection integral containing unfiltered information from the entire image. Four such time-dependent projections of a rapidly evolving scene, one every 45 degrees, were fed into coherent fiber-optic ribbons and sent some 25 m to the photocathode of a streak tube. The fiber-optic ribbons, filtered by both wavelength and mode, achieved subnanosecond time resolution. A digital video system recorded the resulting spacetime streak-tube image, with each scan line containing a time sample of the four projections.In the data analysis, a modified version of G. Minerbo’s maximum entropy tomography algorithm33. G. Minerbo, Comput. Graphics Image Process. 10, 48 (1979). https://doi.org/10.1016/0146-664X(79)90034-0,44. C. T. Mottershead, in Maximum Entropy and Bayesian Methods: Santa Fe, New Mexico, U.S.A., 1985, K. M. Hanson, R. N. Silver, eds., Kluwer Academic (1996), p. 425. 978-94-010-6284-8 was used to reconstruct a frame of the output movie from each scan line of the streak-tube image. A later variant of the algorithm produced a 3D spacetime tomographic reconstruction using a time-integrated 2D image of the same scene, exposed for the duration of the streak-tube sweep, as a tomographic projection along the time axis. The reconstructed movie solution is then constrained to add up to the time exposure.More recently, workers at the Dual Axis Radiographic Hydrodynamic Test Facility at Los Alamos successfully used several streak-tomography systems as near-real-time beam diagnostics in the commissioning of the facility’s high-current pulsed electron accelerator.55. H. Bender, C. Carlson, D. Frayer, D. Johnson, K. Jones, A. Meidinger, C. Ekdahl, Rev. Sci. Instrum. 78, 013301 (2007); https://doi.org/10.1063/1.2409770 D. K. Frayer, D. Johnson, C. Ekdahl, in Proceedings of 2010 Beam Instrumentation Workshop, TUPSM012, available at http://accelconf.web.cern.ch/accelconf/BIW2010/papers/tupsm012.pdf.REFERENCESSection:ChooseTop of pageREFERENCES <<1. C. T. Mottershead, IEEE Trans. Nucl. Sci. 29, 900 (1982). https://doi.org/10.1109/TNS.1982.4335986, Google ScholarCrossref2. M. Wilke, N. S. P. King, N. Gray, D. Johnson, D. Esquibel, P. Nedrow, S. Ishiwata, Proc. SPIE 0566, 185 (1986). https://doi.org/10.1117/12.949787, Google ScholarCrossref3. G. Minerbo, Comput. Graphics Image Process. 10, 48 (1979). https://doi.org/10.1016/0146-664X(79)90034-0, Google ScholarCrossref4. C. T. Mottershead, in Maximum Entropy and Bayesian Methods: Santa Fe, New Mexico, U.S.A., 1985, K. M. Hanson, R. N. Silver, eds., Kluwer Academic (1996), p. 425. 978-94-010-6284-8, Google ScholarCrossref5. H. Bender, C. Carlson, D. Frayer, D. Johnson, K. Jones, A. Meidinger, C. Ekdahl, Rev. Sci. Instrum. 78, 013301 (2007); https://doi.org/10.1063/1.2409770 , Google ScholarCrossrefD. K. Frayer, D. Johnson, C. Ekdahl, in Proceedings of 2010 Beam Instrumentation Workshop, TUPSM012, available at http://accelconf.web.cern.ch/accelconf/BIW2010/papers/tupsm012.pdf. , Google Scholar© 2015 American Institute of Physics.

Droplet-based microfluidic platform for measurement of rapid erythrocyte water transport.

Cell membrane water permeability is an important determinant of epithelial fluid secretion, tissue swelling, angiogenesis, tumor spread and other biological processes. Cellular water channels, aquaporins, are important drug targets. Water permeability is generally measured from the kinetics of cell volume change in response to an osmotic gradient. Here, we developed a microfluidic platform in which cells expressing a cytoplasmic, volume-sensing fluorescent dye are rapidly subjected to an osmotic gradient by solution mixing inside a ~0.1 nL droplet surrounded by oil. The solution mixing time was <10 ms. Osmotic water permeability was deduced from a single, time-integrated fluorescence image of an observation area in which the time after mixing was determined through spatial position. Water permeability was accurately measured in aquaporin-expressing erythrocytes with half-times for osmotic equilibration down to <50 ms. Compared with conventional water permeability measurements using costly stopped-flow instrumentation, the microfluidic platform here utilizes sub-microliter blood sample volume, does not suffer from mixing artifacts, and replaces challenging kinetic measurements by single image capture using a standard laboratory fluorescence microscope.

Temporal evolution of atmosphere pressure plasma jets driven by microsecond pulses with positive and negative polarities

Current-voltage characteristics, discharge images, and optical spectra of atmospheric pressure plasma jets (APPJs) are studied using a microsecond pulse length generator producing repetitive output pulses with different polarities. The experimental results show that the APPJs excited by the pulses with positive polarity have longer plume, faster propagation speed, higher power, and more excited species, such as , O, He, , than that with the negatively excited APPJs. The images taken using an intensified charge-coupled device show that the APPJs excited by pulses with positive polarity are characterized by a bullet-like structure, while the APPJs excited by pulses with negative polarity are continuous. The propagation speed of the APPJs driven by a microsecond pulse length generator is about tens of km/s, which is similar to the APPJs driven by a kHz frequency sinusoidal voltage source. The analysis shows that the space charge accumulation effect plays an important role during the discharge. The transient enhanced electric field induced by the accumulated ions between the needle-like electrode and the nozzle in the APPJs excited by pulses with negative polarity enhances electron field emission from the cathode, which is illustrated by the bright line on the time-integrated images. This makes the shape of the APPJ excited using pulses with negative polarity different from the bullet-like shape of the APPJs excited by pulses with positive polarity.

Study of the termination phase of plasma production and the formation of magnetic flux breakthroughs during wire array implosion

The phenomenon of magnetic flux breakthrough into a wire array during its implosion was studied experimentally at the Angara-5-1 facility. It is shown that breakthroughs develop in the final stage of plasma production from the wire material and occur near the initial wire position. The spatial distributions of the azimuthal magnetic field within tungsten, molybdenum, copper, and aluminum wire arrays were studied using magnetic probes. The distributions of the azimuthal magnetic field B φ(z, t) along the array height in different stages of implosion were measured, and the characteristic dimensions of regions with a nonuniform magnetic field that appear during magnetic flux breakthroughs at the outer boundary of the wire array plasma were determined. The dimensions of these regions are compared with those of the regions with depressed plasma radiation observed in frame and time-integrated X-ray images. The dynamics of the distribution B φ(z, t) in regions with a nonuniform magnetic field during breakthroughs of the azimuthal magnetic flux is compared with that of the spatial distribution of pinch radiation in the frame X-ray images in different stages of implosion. The experimental data on the characteristics of spatially nonuniform breakthroughs of the magnetic flux into the wire array are analyzed using the plasma rainstorm model proposed by V.V. Aleksandrov et al. (JETP 97, 745 (2003)). The plasma density in the region of magnetic flux breakthrough is estimated.

A concept to collect neutron and x-ray images on the same line of sight at NIF.

Neutron and x-ray images are collected at the National Ignition Facility (NIF) to measure the size and shape of inertial confinement fusion implosions. The x-ray images provide a measure of the size and shape of the hot region of the deuterium-tritium fuel while the neutron images provide a measure of the size and shape of the burning plasma. Although these two types of images are collected simultaneously, they are not collected along the same line of sight (LOS). One 14 MeV neutron image is collected on the NIF equator, and two x-ray images are collected along the polar axis and nearly perpendicular to the neutron imaging line of sight on the equator. Both measurements use pinhole apertures to form the images, but existing x-ray imaging provides time-resolved measurements while the neutron images are time-integrated. Detailed comparisons of the x-ray and neutron images can provide information on the fuel assembly, but these studies have been limited because the implosions are not azimuthally symmetric and the images are collected along different LOS. We have developed a conceptual design of a time-integrated x-ray imaging system that could be added to the existing neutron imaging LOS. This new system would allow these detailed studies, providing important information on the fuel assembly of future implosions. Here we present this conceptual design and the expected performance characteristics.

Soft X-Ray Emission Analysis Of A Pulsed Capillary Discharge Operated In Nitrogen

We present results from a pulsed capillary ns discharge source, operated in Nitrogen and N/He mixtures, in an alumina capillary 2.1mm long with outer diameter of 6.3mm and inner diameter of 1.6mm. The electrical energy stored is 0.5J with peak current of 6kA. Fast charging from an IGBT based pulsed power circuit allows operation at 35-600 Hz with voltages in the range of 18-24kV. Characteristic time-integrated N/He spectra were recorded and analyzed for values of 20-200 Å, with clear evidence of He-like Nitrogen emission at 28.8Å, which represents a possible source for water window soft x-ray microscopy. Filtered diode measurements reveal the influence of axial electron beams, generated by hollow cathode dynamics, on the x-ray emission in the range of 300-450 eV. We discuss optimal voltage applied and pressure conditions for soft x-ray generation. Time-integrated MCP images of a filtered slit-wire system delivered clear evidence of full wall detachment with ~500μm in radial size for the entire emission range and ~200μm for the emission in the 300-450 eV range.

Anisotropy of energy losses in high-current Z-pinches produced by the implosion of cylindrical tungsten wire arrays

Results are presented from measurements of the anisotropy of energy losses in high-current Z-pinches produced by the implosion of wire arrays at the ANGARA-5-1 facility at load currents of up to 4MA. The energy losses were measured in the radial direction and along the pinch axis from the anode side. The main diagnostics were time-integrated thermocouple calorimeters, nanosecond X-ray diodes (XRDs) with different filters, and a foil radiation calorimeter with a time resolution of 2 μs. The azimuthal anisotropy of energy losses was measured for different wire array configurations and different shapes of the high-voltage electrode. The presence of strong initial azimuthal inhomogeneity of the wire mass distribution (sectioned arrays), as well as the use of conical electrodes instead of plane ones, does not increase the azimuthal inhomogeneity of the total energy losses. For cylindrical wire arrays, energy losses in the radial direction are compared with those along the pinch axis. According to XRD and calorimetric measurements, the radiation yield per unit solid angle along the pinch axis is two to three times lower than that in the radial direction. In the axial direction, the energy flux density of the expanding plasma is two to three times lower than the radiation intensity. The measured radiation yield across the pinch is 2.5–5 kJ/sr, while that along the pinch axis is 1–2 kJ/sr. The results obtained by means of XRDs agree to within measurement errors with those obtained using the radiation calorimeter. It is found that the energy per unit solid angle carried by the expanding plasma in the radial direction does not exceed 10% of the soft X-ray yield. Analysis of the structure of time-integrated pinhole images and signals from the radial and axial XRDs shows that radiation emitted in the radial direction from the hot central region of the pinch is partially screened by the less dense surrounding plasma halo, whereas radiation emitted in the axial direction is a superposition of the emissions from the hot dense central region of the pinch and the colder less dense peripheral plasma.

Periodic-driven vibration of discharge filaments induced by surface charges in a dielectric-barrier discharge

The periodic-driven vibration of filament pairs in a dielectric-barrier discharge (DBD) pattern is investigated with successive discharges by a high-speed camera. Images correlated with successive half-driven cycles present three representative types of vibrations of the filament pairs, i.e. vibration along a line, vibration with orientational changes and vibration with a ‘stop’. Based on the time-reversal discharge order of the paired filaments, which is demonstrated by images correlated with successive discharge current pulse phases, the involved physics of the vibration is explained by analysis and simulation of the electric field influence induced by surface charges of the filament pairs. Finally, this vibration is proved to be in good agreement with the phenomenon observed from time-integrated images. Moreover, from these results, three general conclusions for filamentary structures in streamer DBDs are obtained and a ‘preferential discharge’ mechanism is proposed, which is further development of the ‘memory effect’ of surface charges.

Radiation Anisotropy at the Implosion of Multiwire Arrays

We present the results of studying the dynamics of soft X-ray radiation (SXR) emission in the axial and radial directions in the current implosion of multiwire tungsten arrays with discharge currents of up to 3.5 MA at the Angara-5-1 facility. The size of the region emitting soft X-rays was determined by the measurements of the radiation anisotropy. It was found that the size of the emitting region is ~ 4-5 mm in the SXR range for cylindrical multiwire arrays at peak X-ray power, which corresponds to approximately two to threefold radial compression of the plasma. The time-integrated pinhole camera images show the presence of a significant amount of emitting plasma around the pinch core-trailing mass. We measured the time-integrated radial resolved pinch spectra. It is shown that the presence of trailing mass decreases the spectral power of radiation and changes the characteristics of the spectrum. The size of the emitting region received from the radial resolved spectra is identical to those obtained from the radiation anisotropy and time-integrated pinhole camera images.

Experimental observations of turbulent mixing due to Kelvin–Helmholtz instability on the OMEGA Laser Facility

Shear-flow, Kelvin–Helmholtz (KH) turbulent mixing experiments were performed on the OMEGA Laser Facility [Boehly et al., Opt. Commun. 133, 495 (1997)] in which laser-driven shock waves propagated through a low-density plastic foam placed on top of a higher-density plastic foil. The plastic foil was comprised a thin iodine-doped plastic tracer layer bonded on each side to an undoped density-matched polyamide-imide plastic. Behind the shock front, lower-density foam plasma flowed over the higher-density plastic plasma, such that the interface between the foam and plastic was KH unstable. The initial perturbations consisted of pre-imposed, sinusoidal 2D perturbations, and broadband 3D perturbations due to surface roughness at the interface between the plastic and foam. KH instability growth was measured using side-on radiography with a point-projection 5-keV vanadium backlighter. Time-integrated images were captured on D-8 x-ray film. Spatial density profiles of iodine-doped plastic mixed with foam were inferred using x-ray radiographs. The mixing layer ensuing from the KH instability with layer width up to ∼100 μm was observed at a location ∼1 mm behind the shock front. The measured mixing layer width was in good agreement with predictions based on a simple self-similar model of KH instability growth using an estimate of the shear velocity obtained from numerical simulations of the experiments.

Simultaneous high-resolution two-dimensional spatial and one-dimensional picosecond streaked x-ray pinhole imaging

A Kentech x-ray streak camera was run at the LLNL compact multipulse terawatt (COMET) laser to record simultaneous space- and time-resolved measurements of picosecond laser-produced plasmas. Four different x-ray energy channels were monitored using broadband filters to record the time history of Cu targets heated at irradiances of 10(16)-10(19) W∕cm(2). Through the Cu filter channel, a time-resolution below 3 ps was obtained. Additionally, an array of 10 μm diameter pinholes was placed in front of the camera to produce multiple time-resolved x-ray images on the photocathode and time-integrated images on the phosphor with 10 and 15 times magnification, respectively, with spatial resolution of < 13 μm.

The signal from an emitting source moving in a Schwarzschild spacetime under the influence of a radiation field

The motion of matter immersed in a radiation field is affected by a radiation drag, as a result of scattering or absorption and re-emission. The resulting friction-like drag, also known as the Poynting–Robertson effect, has been recently studied in the general relativistic background of the Schwarzschild and Kerr metric, under the assumption that all photons in the radiation field possess the same angular momentum. We calculate here the signal produced by an emitting point-like specific source moving in a Schwarzschild spacetime under the influence of such a radiation field. We derive the flux, redshift factor and solid angle of the hot spot as a function of (coordinate) time, as well as the time-integrated image of the hot spot as seen by an observer at infinity. The results are then compared with those for a spot moving on a circular geodesic in a Schwarzschild metric.

Experimental study of time characteristic of optical radiation in femtosecond laser interaction with solid targets

In this paper, the time-integrated image pattern of spatial distribution and time-resolved image of optical radiation are measured in the normal direction from the rear side of targets by employing optical streak camera on the 100 TW femtosecond laser facility. The image pattern of spatial distribution presents a strip-shape: the region of optical radiation has a radiation angle and optical intensity distribution, and contains various components; the time-resolved image of optical radiation presents the time-resolved pattern of the optical radiation, witch further proves that the transition radiation is intense, which has short duration (ps) and correspouns to duration of TR of 85.5 ps. and other optical radiations are weak, which have very long duration (ns). The time-resolved characteristic of optical radiation can provide new evidence for discrimination and judgement of TR.

Using time-integrated Kα images to study refluxing and the extent of pre-plasmas in intense laser-plasma experiment

We report the results of an experimental and numerical modeling study of the formation of time-integrated Kα images by electrons excited during an intense laser-plasma interaction. We report the use of the spatial structure of time-integrated Kα images to quantitatively characterize the pre-plasma profile near the critical surface and to verify the near elimination of back-surface refluxing from targets when a thick layer of a low-Z material is attached to the back. The time integrated Kα images are found to be sensitive to the relative separation between the critical surface and the bulk target, permitting a single parameter exponential pre-plasma scale length to be determined by fitting to experimental results. The refluxed electrons affect different parts of the Kα images in a manner that varies depending on the location of the refluxing. We use these properties to characterize refluxing also by fitting to experimental results. Experiments were performed using the Titan laser at the Lawrence Livermore National Laboratory and the simulations used a customized version of the hybrid-PIC code, LSP. We find good quantitative match between experiment and simulation.

Filamentary Structure of Current Sheath in Miniature Plasma Focus

Current sheath dynamics is an important parameter for good focusing or pinching in a dense plasma focus device. In this paper, we present pinching evidence and details of the filamentary structure of the current sheath in a miniature plasma focus device using a time-resolved laser shadowgraphic technique and time-integrated optical imaging.

Modeling of K-shell Al and Mg radiation from compact single, double planar and cylindrical alloyed Al wire array plasmas produced on the 1 MA Zebra generator at UNR

Radiative emission from alloyed Al single, double and compact cylindrical wire arrays have been studied using the 1 MA Zebra UNR generator. Single planar wire arrays using ten wires and double planar wire arrays and compact cylindrical wire arrays (CCWA) that both had sixteen wires were utilized. The wire composition is Al-5056 (95% of Al and 5% of Mg). We have observed that implosion of these alloyed Al wire loads generated optically thick Al plasmas that can be diagnosed using K-shell Mg lines. In particular, among the considered loads, the K-shell lines of Al from implosions of the double planar wire arrays have the highest optical depth for He-like Al resonance transitions, which occurred near the stagnation phase. X-ray time-gated and time-integrated spectra and pinhole images as well as photoconductive detectors signals were analyzed to provide information on the plasma parameters; electron temperatures and densities, implosion dynamics features and power and yields of the X-ray radiation. Previously developed non-LTE models were applied to model axially-resolved time-integrated, as well as time-gated spatially-integrated, K-shell spectra from Al and Mg. The derived time-dependent electron temperature, density and axial opacity were studied and compared. In addition, the wire ablation dynamics model (WADM) was used to calculate the kinetic energy of the plasma, which with the aid of a Local Thermal Equilibrium (LTE) magneto-hydrodynamics (MHD) simulation, allowed to estimate the precursor and stagnated z-pinch plasma electron temperatures from implosions of wire array loads.

How well do time-integrated Kα images represent hot electron spatial distributions?

A computational study is described, which addresses how well spatially resolved time-integrated Kα images recorded in intense laser-plasma experiments correlate with the distribution of “hot” (&amp;gt;1 MeV) electrons as they propagate through the target. The hot electron angular distribution leaving the laser-plasma region is critically important for many applications such as Fast Ignition or laser based x-ray sources; and Kα images are commonly used as a diagnostic. It is found that Kα images can easily mislead due to refluxing and other effects. Using the particle-in-cell code LSP, it is shown that a Kα image is not solely determined by the initial population of forward directed hot electrons, but rather also depends upon “delayed” hot electrons, and in fact continues to evolve long after the end of the laser interaction. Of particular note, there is a population of hot electrons created during the laser-plasma interaction that acquire a velocity direction opposite that of the laser and subsequently reflux off the front surface of the target, deflect when they encounter magnetic fields in the laser-plasma region, and then traverse the target in a wide spatial distribution. These delayed fast electrons create significant features in the Kα time-integrated images. Electrons refluxing from the sides and the back of the target are also found to play a significant role in forming the final Kα image. The relative contribution of these processes is found to vary depending on depth within target. These effects make efforts to find simple correlations between Kα images and, for example, Fast Ignition relevant parameters prone to error. Suggestions for future target design are provided.