Ms Temporal Resolution Research Articles

Three‐dimensional cine imaging using variable‐density spiral trajectories and SSFP with application to coronary artery angiography

A single breath-hold 3D cardiac phase resolved steady-state free precession (SSFP) sequence was developed, allowing 3D visualization of the moving coronary arteries. A 3D stack of spirals was acquired continuously throughout the cardiac cycle, and a sliding window reconstruction was used to achieve high temporal resolution. A coil specific field of view reconstruction technique was combined with Parallel Imaging with Localized Sensitivities (PILS) to allow acquisition of a reduced field of view. A view ordering incorporating fat suppression was employed to allow use of sliding window reconstruction. The technique was evaluated on healthy volunteers (n=8), yielding images with 102 ms temporal resolution and 1.35 mm in-plane resolution, and reasonable visualization of the left and right coronary arteries was achieved.

Synchronous neural interactions assessed by magnetoencephalography: a functional biomarker for brain disorders**Contribution by the authors: Designed research (APG); acquired data (AAA, IGK, FJPL, ACL, SML, JJS); analyzed data (APG, EK, ACL, JKL); wrote the paper (APG, EK, ACL, SML); contributed subjects (AAA, ZA, AFC, AG, LSH, IGK, FJPL, SML, JRM, SEM, JVP, PJP, GJP, SJR, BMS, SRS, MS, JJS, JJW);

We report on a test to assess the dynamic brain function at high temporal resolution using magnetoencephalography (MEG). The essence of the test is the measurement of the dynamic synchronous neural interactions, an essential aspect of the brain function. MEG signals were recorded from 248 axial gradiometers while 142 human subjects fixated a spot of light for 45–60 s. After fitting an autoregressive integrative moving average (ARIMA) model and taking the stationary residuals, all pairwise, zero-lag, partial cross-correlations (PCCij0) and their z-transforms (zij0) between i and j sensors were calculated, providing estimates of the strength and sign (positive, negative) of direct synchronous coupling at 1 ms temporal resolution. We found that subsets of zij0 successfully classified individual subjects to their respective groups (multiple sclerosis, Alzheimer's disease, schizophrenia, Sjögren's syndrome, chronic alcoholism, facial pain, healthy controls) and gave excellent external cross-validation results.

Altitude resolved sprite spectra with 3 ms temporal resolution

Altitude resolved sprite spectra have been obtained with an imaging slit spectrograph with 3 ms temporal and ∼3 nm spectral resolution. Spectral coverage is from 640 to 820 nm. The slit was vertical to provide altitude resolution. The observed spectra are exclusively composed of emissions from the N2 first positive (1PG) bands. There are no obvious N2+ Meinel emissions, probably due to a combination of quenching and rapid motion of the streamer heads in which ionization is assumed to take place. The spectral analysis shows that the vibrational population in the upper state of the 1PG bands, N2 B 3Πg state, varies with altitude and is similar to that of laboratory afterglow at high pressure. This result suggests that secondary interactions among excited states created by electron impact may also play a role in exciting the B 3Πg state.

Estimating firing rates from calcium signals in locust projection neurons in vivo

Combining intracellular electrophysiology and multi-photon calcium imaging in vivo, we studied the relationship between calcium signals (sampled at 500–750 Hz) and spike output in principal neurons in the locust antennal lobe. Our goal was to determine whether the firing rate of individual neurons can be estimated in vivo with calcium imaging and, if so, to measure directly the accuracy and resolution of our estimates. Using the calcium indicator Oregon Green BAPTA-1, we describe a simple method to reconstruct firing rates from dendritic calcium signals with 80–90% accuracy and 50 ms temporal resolution.

Retrospective cine 3He ventilation imaging under spontaneous breathing conditions: a non‐invasive protocol for small‐animal lung function imaging

A non-invasive and free-breathing hyperpolarized (HP) (3)He imaging protocol for small animals was implemented and validated on rats for lung function imaging. Animals were allowed to breathe a mixture of air and (3)He from a mask and a gas reservoir fitted to their heads. Radial imaging sequences were used, and MRI signal intensity changes were monitored for retrospective cine image reconstruction. The ventilation cycle of the animals was imaged with a 100 ms temporal resolution. The sliding window imaging technique was applied to reconstruct 5 ms time-shifted image series covering the complete breathing cycle. Image series were processed to extract quantitative ventilation parameters such as the gas arrival time. The reproducibility and the non-invasiveness of this ventilation imaging protocol were evaluated by multiple acquisitions on the same animals.

Fast automated analysis of high-resolution reflectometer density profiles on DIII-D

High temporal (⩾10 µs) and spatial (⩾4 mm) resolution electron density profiles can now be automatically obtained on a between-shot basis from profile reflectometry data on the DIII-D tokamak. Fast, automated analysis is made possible by a new between-shot analysis package, details of which are presented. Analysis of X-mode data covering ∼0–3 × 1019 m−3 with 1 ms duration data bursts every 5 ms for 5–6 s, for a total of ∼1000 profiles, takes 4–5 min, allowing the profiles to be viewed and used between shots. Additional details are provided of how the system density coverage at the above temporal and spatial resolution was recently expanded to (0–6.4) × 1019 m−3 using a novel simultaneous, dual-polarization (O- and X- mode) measurement technique. Automatic (but not between-shot) analysis for the complete O- and X-mode data set (1.5 GB for each discharge, about 100 000 profiles at 25 µs temporal resolution) is available after the experiment. The improved capabilities of the system are illustrated using new results from a variety of areas such as edge localized mode dynamics, L–H transition and pedestal physics, impurity deposition and ITB studies, and direct comparisons with Thomson data are presented.

On Heat Transfer Mechanism of Nucleate Boiling with MEMS Sensors (1st Report, Temperature Measurement beneath Boiling Bubble)

Local temperature variation beneath boiling bubble was measured with a MEMS (Micro Electro-Mechanical Systems) integrated sensor to investigate a boiling heat transfer mechanism. The sensor consisting two trigger heaters and six thin film thermocouples across the heaters within 880 region on a silicon or glass substrate can measure temperature distribution of heating surface with less than 0.1 ms temporal resolution. As a result, measured temperature variations can be brought into correspondence with the bubble behavior taken by a synchronized high-speed video. The temperature variations also show a formation of micro layer, extension of a local dryout region and rewetting with bubble departure. Based on the measurement, a state transition chart of the heating wall beneath the bubble in temporal and spatial domain can be drawn. This study presents a new approach method to the heat transfer mechanism of mucleate boiling.

Molecular motors one at a time: FIONA to the rescue

Processive molecular motors act as intracellular transporters of a broad range of cargoesvarying from organelles to messenger RNAs. Due to the nanometre range movements andcomplex dynamics of these motors, highly specialized tools are required to study them, inparticular at the single-molecule level. Such tools are what physicists are providing forunderstanding these biological systems. Fluorescence based real-time localizationtechniques, with 1 nm spatial resolution and down to 1 ms temporal resolution (FIONA:fluorescence imaging with one-nanometre accuracy), and their applications to a group ofmolecular motors (myosin V, myosin VI, kinesin, and dynein) are the topics of this paper.In addition to the well established in vitro studies, the recent applications of thesetechniques to the much more challenging, but also more informative, in vivo realm will bediscussed.

Extinction of Cocaine Self-Administration Reveals Functionally and Temporally Distinct Dopaminergic Signals in the Nucleus Accumbens

While Pavlovian and operant conditioning influence drug-seeking behavior, the role of rapid dopamine signaling in modulating these processes is unknown. During self-administration of cocaine, two dopaminergic signals, measured with 100 ms resolution, occurred immediately before and after the lever press (termed pre- and post-response dopamine transients). Extinction of self-administration revealed that these two signals were functionally distinct. Pre-response transients, which could reflect the motivation to obtain the drug, did not decline during extinction. Remarkably, post-response dopamine transients attenuated as extinction progressed, suggesting that they encode the learned association between environmental cues and cocaine. A third type of dopamine transient, not time locked to overt stimuli, decreased in frequency during extinction and correlated with calculated cocaine concentrations. These results show that dopamine release transients involved in different aspects of cocaine self-administration are highly plastic--differentially governed by motivation, learned associations linked with environmental stimuli, and the pharmacological actions of cocaine.

Non-invasive evaluation of coronary artery bypass grafts using 16-row multi-slice computed tomography with 188 ms temporal resolution

Background Cardiac multi-slice computed tomography (MSCT) scanners permit visualization of the coronary arteries and coronary artery bypass grafts. The latest MSCT generation with true 16-detector slices (Sensation 16 Speed 4 D®, Siemens, Forchheim, Germany) provides improved temporal and spatial resolution, as well as significantly reduced scan time. To assess, whether this technical improvement has also an impact on image quality and accuracy of MSCT diagnosis in patients with previous coronary artery bypass graft (CABG) surgery the following study was conducted. Methods and material Thirteen consecutive patients (pts) (10 male, 3 female, mean age 62 ± 6.4 [55–73] years, heart rate 68 ± 11 [52–88] bpm) and a total number of 43 coronary bypass grafts (11 arterial, 32 venous grafts) were examined by MSCT (gantry rotation time 375 ms). In addition to the analysis of coronary bypass grafts, 13 coronary segments (sgts) were evaluated in each patient ( n = 169 sgts). MSCT results were compared with coronary angiography. Results Forty-one of 43 bypass grafts (95%) were analyzable by MSCT. In conventional angiography 16 of 43 (37%) grafts were occluded. Sixteen of them were correctly diagnosed by MSCT (sensitivity 100%). One graft showed a 50% anastomosis stenosis which was also detected. Twenty-five of 27 grafts without severe lesion showed no significant stenosis in MSCT (specificity 93%, positive predictive value (PPV) 89%, negative predictive value (NPV) 100%). Ninety of 108 (83%) high-grade stenosis (> 70%) of the native coronary vessels were correctly detected (sensitivity 83%, PPV 78%). From the 61 sgts without high grade stenosis 36 were correctly classified (specificity 59%, NPV 67%). If sgts number 8, 9 and 10, which are normally not target for revascularization, are excluded sensitivity rises to 89%, specificity to 71%, PPV to 87% and NPV to 75%. The correct clinical diagnosis (absence or presence of a high grade stenosis of at least one bypass graft) was achieved in all patients. Conclusions True 16-slice MSCT with faster gantry rotation time allows detection of lesions in coronary artery bypass grafts with high sensitivity and specificity. The evaluation of native vessels in pts with known CAD remains a diagnostic challenge. However, the correct clinical diagnosis was achieved in all pts. MSCT is a non-invasive tool to assess coronary artery bypass grafts.

Restricted diffusion of DNA segments within the isolated Escherichia coli nucleoid

To study the dynamics and organization of the DNA within isolated Escherichia coli nucleoids, we track the movement of a specific DNA region. Labeling of such a region is achieved using the Lac-O/Lac-I system. The Lac repressor-GFP fusion protein binds to the DNA section where tandem repeats of the Lac operator are inserted, which allows us to monitor the motion of the DNA. The movement of such a GFP spot is followed at 48 ms temporal resolution during 12 s. The spots are found to diffuse within a confined space, so that the nucleoid appears to behave like a viscoelastic network. The distribution of the “particle” position in time can be fitted to a Gaussian function indicating that the motion of the particle is Brownian. An average self-diffusion constant D s = 0.12 μm 2 s −1 is derived via the time auto-correlation functions of the displacement and is compatible with the collective diffusion coefficient measured previously by dynamic light scattering. Restriction of a DNA sequence to a small region of the nucleoid is tentatively related to the existence of so-called supercoiling domains.

Behavior of the fast neutrals generated during a disruption in the T-11M tokamak

Results are presented from experimental studies of the generation of high-energy neutrals during a major disruption in the T-11M tokamak. Fast-neutral fluxes from the plasma, magnetic perturbations, and the neutral-hydrogen and impurity radiation from the plasma core are measured simultaneously in the course of disruption. A high (∼1 μs) temporal resolution of the recording system (the characteristic disruption time being about 100 μs) makes it possible to thoroughly investigate the time behavior of the processes that occur during a disruption.

Diagnostic accuracy of noninvasive coronary imaging using 16-detector slice spiral computed tomography with 188 ms temporal resolution

The aim of our study was to evaluate the diagnostic accuracy of 16-multi-detector spiral computed tomography (MDCT) with 188 ms temporal resolution. Because of rapid technical innovations, MDCT coronary imaging has significantly improved in the last five years. Recent results indicate a high diagnostic accuracy, especially in patients with clinical suspicion of coronary artery disease (CAD). A total of 72 consecutive patients (30 women, 42 men, age 64 +/- 10 years) scheduled for invasive coronary angiography (ICA) because of suspected CAD were additionally studied by MDCT (Sensation 16 Speed 4D, Siemens, Forchheim, Germany). Thirty-seven of 72 patients (51%) received an additional beta-blockade before MDCT because of heart rates >65 beats/min. The MDCT scans were analyzed regarding the presence of coronary artery lesions. Results were compared with ICA. All 72 scans showed diagnostic image quality (heart rate: 64.1 +/- 9.2 beats/min, calcium mass: 86 +/- 156 mg). Thirteen coronary segments were evaluated in each patient. Sixty-two of 936 (6.6%) segments showed a nondiagnostic image quality. All segments were included in the analysis. A total of 117 relevant lesions (diameter stenosis >50%) were detected using ICA, and 96 of 117 (82%) were detected by MDCT. Sensitivity, specificity, and positive and negative predictive values for the whole study group were as follows: 82%, 98%, 87%, and 97%, respectively. The correct clinical diagnosis of presence or absence of significant CAD was obtained in 65 of 72 (90%) patients. All stenoses were detected by MDCT in 52 of 72 (72%) patients. Our results indicate a high diagnostic accuracy of 16-slice MDCT with improved temporal resolution.

Performance Evaluation of a 64-Slice CT System with z-Flying Focal Spot

The meanwhile established generation of 16-slice CT systems enables routine sub-millimeter imaging at short breath-hold times. Clinical progress in the development of multidetector row CT (MDCT) technology beyond 16 slices can more likely be expected from further improvement in spatial and temporal resolution rather than from a mere increase in the speed of volume coverage. We present an evaluation of a recently introduced 64-slice CT system (SOMATOM Sensation 64, Siemens AG, Forchheim, Germany), which uses a periodic motion of the focal spot in longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices. This technique acquires 64 overlapping 0.6 mm slices per rotation. The sampling scheme corresponds to that of a 64 x 0.3 mm detector, with the goal of improved longitudinal resolution and reduced spiral artifacts. After an introduction to the detector design, we discuss the basics of z-flying focal spot technology (z-Sharp). We present phantom and specimen scans for performance evaluation. The measured full width at half maximum (FWHM) of the thinnest spiral slice is 0.65 mm. All spiral slice widths are almost independent of the pitch, with deviations of less than 0.1 mm from the nominal value. Using a high-resolution bar pattern phantom (CATPHAN, Phantom Laboratories, Salem, NY), the longitudinal resolution can be demonstrated to be up to 15 lp/cm at the isocenter independent of the pitch, corresponding to a bar diameter of 0.33 mm. Longitudinal resolution is only slightly degraded for off-center locations. At a distance of 100 mm from the isocenter, 14 lp/cm can be resolved in the z-direction, corresponding to a bar diameter of 0.36 mm. Spiral "windmill" artifacts presenting as hyper- and hypodense structures around osseous edges are effectively reduced by the z-flying focal spot technique. Cardiac scanning benefits from the short gantry rotation time of 0.33 s, providing up to 83 ms temporal resolution with 2-segment ECG-gated reconstruction.

First measurement of time-resolved neutron yield on JT-60U using a microfission chamber

Microfission chambers, which are pencil sized ionization chamber containing fissile material inside, will be installed in the vacuum vessel as neutron monitors for International Thermonuclear Experimental Reactor (ITER). We have performed first measurements of the detector installed between the vacuum vessel and toroidal coils on JT-60U. The technical validity as a neutron monitor, such as magnetic field effect and electromagnetic noises from the plasma and heating devices, has been investigated. The detector had an excellent linearity with a U235 fission chamber as a neutron monitor on JT-60U with the standard deviation of 3% except for some noise signals. The electromagnetic noises were caused by neutral beam injection (NBI) breakdowns, probably due to long wiring between the detector and the preamplifier. In case of plasma disruption, improper signals have not been observed. The magnetic field effect also has not been observed up to 2 T. In JT-60U, we confirmed availability of the micro fission chamber as a neutron monitor over three decades of neutron source strength up to 1.3×1016 neutrons/s with 1 ms temporal resolution. The biggest weakness in the detector was its noise sensitivity to NBI breakdowns. Therefore, by suppressing the electromagnetic noise, microfission chambers can be available as neutron monitors for ITER.

Two-dimensional phase contrast interferometer for fluctuations study on LHD

C O 2 laser based phase contrast interferometer was used previously on LHD to study plasma density microfluctuations. New two-dimensional 6×8 elements array of CdHgTe photoconductors was employed for detection. In addition to commonly measured intensity, frequency spectrum, and two-point correlation two-dimensional detector array allows determining the direction of propagation of waves in plasma. From the angular distribution it is possible to obtain localized along the viewing line properties of fluctuations using strong magnetic shear in LHD. As a result, the radial profiles of density microfluctuations can be obtained with 1 μs temporal resolution determined by detector bandwidth. The described scheme was tested using ultrasonic wave in air. New imaging diagnostics has been installed on LHD and first experimental results are reported.

Multichannel and multicolour infrared thermography in Tore Supra

An imaging spectrometer using a sapphire prism as dispersing element has been conceived at Tore Supra for the spectral range of 1–4 μm. It measures simultaneously at various wavelengths the temperature on distributed high heat-flux elements under plasma impact with 36 optical fibers, four of which are ZrF4 fibers. It employs an InSb focal plane array detector (256*320 pixels) behind a silicon filter and a ZnS window yielding a dynamic range of 200–1500 °C with 20 ms temporal resolution. The fiber transmission and the spatial variation of gain and background of the camera are calibrated using a light source with integrating sphere. With a blackbody source one determines the nonlinearity of the average gain and controls its stability during operation. The spectral dispersion of about 24 nm/pixel is determined with interference filters and controlled with a spectral lamp. The measurements at various wavelengths allow to determine the temperature distribution in the field of view.

Numerical modeling of microbubble backscatter to optimize ultrasound particle image velocimetry imaging: initial studies

We have developed a promising non-invasive ultrasound-based method for performing particle image velocimetry (PIV) in vivo. This method, termed echo PIV, provides multi-component blood velocity data with good (∼2 ms) temporal resolution. The method takes advantage of the non-linear ultrasound backscatter characteristics of small gas-filled microbubbles (ultrasound contrast) that are seeded into the blood stream. In this study, we use a numerical model to explore potential areas to focus future work in echo PIV. Ultrasound backscatter from encapsulated microbubbles was modeled using a modified Rayleigh–Plesset equation (Church model, 1995), taking into account the protein/lipid shell layer as a thick, mass-conserving incompressible fluid surrounded by incompressible blood-like fluid. The equation of motion was solved numerically to characterize the fundamental and second harmonic components of the backscattered pressure. Results show a significant advantage in using the second harmonic component for echo PIV, especially for small bubble sizes less than 3 μm in diameter at 2.2 MHz frequency. The effect of the shell thickness ranging from 10 to 500 nm on the vibration amplitude of the bubble was examined and it is shown that the presence of the shell requires mechanical index (MI)>0.2 of incident pressure amplitude to improve bubble detectability. Analysis of the effect of pulse length shows a tradeoff between axial resolution (short pulse length) and bubble detectability (longer pulse length) will most likely be required. The effect of varying MI between 0.1 and 0.6 was also studied at a center frequency of 2.2 MHz and the results indicate that the resonance of the second harmonic is maximized for bubbles with diameter of approximately 2.75 μm. Bubble non-linearities at MI>0.2 induced a resonant frequency shift away from the integer multiple of the incident frequency in the second harmonic backscatter. For a given bubble size, there is a combination of optimal incident frequency and mechanical index range that maximizes the ratio of the second harmonic compared to the fundamental. This resonant frequency decreases with increasing bubble radius. Further, a narrow bandwidth pulse is shown to increase signal strength. Both of these effects may cause conflict with factors governing spatial resolution. Optimization of the incident frequency, microbubble size and mechanical index to enhance bubble detectability will depend on the particular clinical application. These theoretical predictions provide further understanding of the physics behind our echo PIV technique, and should be useful for guiding the design of echo PIV systems.

Heat transfer mapping in 3–5 μm planar light emitting structures

We report on the heat distribution inside a p+-InAsSb(Zn)/n-InAsSbP/n-InAs planar structure, emitting at 4.3 μm at 300 K. The experimental setup consists of both an infrared scanning microscope and a fiber tip as remote heat sensors (spatial resolution of some μm) operating in a time-resolved (10 μs temporal resolution) manner in the 3–5 μm spectral range. By comparing light and heat maps, we show that current crowding generates local hot regions (somewhat like heat traps) and remarkable temperature gradients (up to 3000 °C/cm) inside the emitting structure.

Development of in-vessel neutron monitor using micro-fission chambers for ITER

A neutron monitor using micro-fission chambers to be installed inside the vacuum vessel has been designed for the International Thermonuclear Experimental Reactor (ITER). The monitoring system needs to be insensitive to the changes of the plasma position and the profile, and the locations behind upper and lower outboard blankets were selected as appropriate based on the neutron transport calculations with the Monte Carlo code for neutron and photon transport (MCNP). Employing both pulse counting and Campbelling modes in the electronics, the ITER requirement of 107 dynamic range with 1 ms temporal resolution will be accomplished. The system meets the 10% accuracy required for the fusion power monitor. A set of a U235 micro-fission chamber with 12 mg UO2 and a fissile-material-free “blank” detector to eliminate noise issues arising from γ rays, etc. were fabricated based on the design. The vacuum leak rate of the chamber with the mineral insulated (MI) cable, resistances between the central conductor and outer sheath, and mechanical strength up to 50 G acceleration were tested to meet the design criteria. The output signals for γ rays were measured with the Co60 γ-ray irradiation facility at Japan Atomic Energy Research Institute (JAERI)-Takasaki and the influence was estimated to be less than 0.1% of the signals for neutrons. Excellent linearities between count rates, square of Campbelling voltage, and neutron fluxes were confirmed in the temperature range from 20 °C (room) to 250 °C with the Fusion Neutronics Source (FNS) facility of JAERI. The influence of the surrounding material was studied with the shielding blanket mock-up, and it was verified that the chamber provides an effective response although the sensitivity was enhanced by slow-downed neutrons. As a result, it was concluded that the present micro-fission chamber is applicable to ITER power monitoring.