Delay Maps Research Articles

Tropospheric Correction of Sentinel-1 Synthetic Aperture Radar Interferograms Using a High-Resolution Weather Model Validated by GNSS Measurements

Synthetic Aperture Radar Interferometry (InSAR) is a space geodetic technique used for mapping deformations of the Earth’s surface. It has been developed and used increasingly during the last thirty years to measure displacements produced by earthquakes, volcanic activity and other crustal deformations. A limiting factor to this technique is the effect of the troposphere, as spatial and temporal variations in temperature, pressure, and relative humidity introduce significant phase delays in the microwave imagery, thus “masking” surface displacements due to tectonic or other geophysical processes. The use of Numerical Weather Prediction (NWP) models as a tropospheric correction method in InSAR can tackle several of the problems faced with other correction techniques (such as timing, spatial coverage and data availability issues). High-resolution tropospheric modelling is particularly useful in the case of single interferograms, where the removal of the atmospheric phase screen (and especially the highly variable turbulent component) can reveal large-amplitude deformation signals (as in the case of an earthquake). In the western Gulf of Corinth, prominent topography makes the removal of both the stratified and turbulent atmospheric phase screens a challenging task. Here, we investigate the extent to which a high-resolution WRF 1-km re-analysis can produce detailed tropospheric delay maps of the required accuracy by coupling its output (in terms of Zenith Total Delay or ZTD) with the vertical delay component in GNSS measurements. The model is operated with varying physical parameterization in order to identify the best configuration, and validated with GNSS zenithal tropospheric delays, providing a benchmark of real atmospheric conditions. We correct sixteen Sentinel-1A interferograms with differential delay maps at the line-of-sight (LOS) produced by WRF re-analysis. In most cases, corrections lead to a decrease in the phase gradient, with average root-mean-square (RMS) and standard deviation (SD) reductions in the wrapped phase of 6.0% and 19.3%, respectively. Results suggest a high potential of the model to reproduce both the long-wavelength stratified atmospheric signal and the short-wave turbulent atmospheric component which are evident in the interferograms.

TLDR: time lag/delay reconstructor

ABSTRACT We present the time lag/delay reconstructor (TLDR), an algorithm for reconstructing velocity delay maps in the maximum a posteriori framework for reverberation mapping. Reverberation mapping is a tomographical method for studying the kinematics and geometry of the broad-line region of active galactic nuclei at high spatial resolution. Leveraging modern image reconstruction techniques, including total variation and compressed sensing, TLDR applies multiple regularization schemes to reconstruct velocity delay maps using the alternating direction method of multipliers. Along with the detailed description of the TLDR algorithm we present test reconstructions from TLDR applied to synthetic reverberation mapping spectra as well as a preliminary reconstruction of the Hβ feature of Arp 151 from the 2008 Lick Active Galactic Nuclei Monitoring Project.

Use of GNSS Tropospheric Delay Measurements for the Parameterization and Validation of WRF High-Resolution Re-Analysis over the Western Gulf of Corinth, Greece: The PaTrop Experiment

In the last thirty years, Synthetic Aperture Radar interferometry (InSAR) and the Global Navigation Satellite System (GNSS) have become fundamental space geodetic techniques for mapping surface deformations due to tectonic movements. One major limiting factor to those techniques is the effect of the troposphere, as surface velocities are of the order of a few mm yr−1, and high accuracy (to mm level) is required. The troposphere introduces a path delay in the microwave signal, which, in the case of GNSS Precise Point Positioning (PPP), can nowadays be partly removed with the use of specialized mapping functions. Moreover, tropospheric stratification and short wavelength spatial turbulences produce an additive noise to the low amplitude ground deformations calculated by the (multitemporal) InSAR methodology. InSAR atmospheric phase delay corrections are much more challenging, as opposed to GNSS PPP, due to the single pass geometry and the gridded nature of the acquired data. Thus, the precise knowledge of the tropospheric parameters along the propagation medium is extremely useful for the estimation and correction of the atmospheric phase delay. In this context, the PaTrop experiment aims to maximize the potential of using a high-resolution Limited-Area Model for the calculation and removal of the tropospheric noise from InSAR data, by following a synergistic approach and integrating all the latest advances in the fields of remote sensing meteorology (GNSS and InSAR) and Numerical Weather Forecasting (WRF). In the first phase of the experiment, presented in the current paper, we investigate the extent to which a high-resolution 1 km WRF weather re-analysis can produce detailed tropospheric delay maps of the required accuracy, by coupling its output (in terms of Zenith Total Delay or ZTD) with the vertical delay component in GNSS measurements. The model is initially operated with varying parameterization, with GNSS measurements providing a benchmark of real atmospheric conditions. Subsequently, the final WRF daily re-analysis run covers an extended period of one year, based on the optimum model parameterization scheme demonstrated by the parametric analysis. The two datasets (predicted and observed) are compared and statistically evaluated, in order to investigate the extent to which meteorological parameters that affect ZTD can be simulated accurately by the model under different weather conditions. Results demonstrate a strong correlation between predicted and observed ZTDs at the 19 GNSS stations throughout the year (R ranges from 0.91 to 0.93), with an average mean bias (MB) of –19.2 mm, indicating that the model tends to slightly underestimate the tropospheric ZTD as compared to the GNSS derived values. With respect to the seasonal component, model performance is better during the autumn period (October–December), followed by spring (April–June). Setting the acceptable bias range at ±23 mm (equal to the amplitude of one Sentinel-1 C-band phase cycle when projected to the zenithal distance), it is demonstrated that the model produces satisfactory results, with a percentage of ZTD values within the bias margin ranging from 57% in summer to 63% in autumn.

Three-focal-spot terahertz diffractive optical element-iterative design and neural network approach.

The redistribution of an incoming radiation into several beams is necessary in telecommunication to demultiplex data signals. In the terahertz spectral range, it can be realized by easy-to-manufacture diffractive optical elements (DOEs) allowing to focus the radiation into multiple focal spots in a single plane. In this article, we present diffractive optical elements focusing THz radiation into three focal spots. Different focal spot distributions (symmetric and asymmetric) are designed using an iterative algorithm. The phase distribution forming asymmetric focal spots can be realized by iterative design, which is a novel approach, to our knowledge. Then, the structures are manufactured using a sintering-based 3D-printing method from polyamide 12 (PA 12) and measured in an experimental setup for 150 GHz frequency. A novel approach based on neural networks (NNs) is proposed to optimize the phase delay maps of the structures to further improve their performance - the higher efficiency and the lower unwanted background noise.

Abstract P133: Geospatial Mapping of Prehospital Delay in Acute Ischemic Stroke and Association With Social Vulnerability

Introduction: Prehospital delay, defined as the delay between symptom discovery and hospital arrival, remains a major barrier to timely acute stroke treatments. Delay is worse in socially vulnerable populations. A geospatial map of prehospital delay may identify high-risk areas and highlight the role of community social vulnerability in delay. We hypothesized that a community’s social vulnerability would be associated with delay. Methods: We analyzed national Get With The Guidelines ischemic stroke data between 2015 and 2017. We calculated the median arrival time (symptom discovery-to-door times) for each Zip Code Tabulation Area (ZCTA), and created geospatial map using ArcGIS. The primary exposure variable was the Center for Disease Control’s Social Vulnerability Index (SVI), and its 4 subcomponents. The SVI is a composite metric of community vulnerability using U.S. Census data (0, least vulnerable to 1, most vulnerable). To account for clustering within ZCTAs, we performed a multilevel linear regression of community-level SVI and patient-level prehospital delay. Results: During the study period, 149,774 patients had an ischemic stroke in 16,949 ZCTAs. Across patients, the median time of arrival was 140 mins, IQR was 60-459 mins, and range was 1-1439 mins. Arrival by 2h occurred in 46% of patients. Multilevel regression showed a strong positive association between the SVI and prehospital delay, evident in the maps (Figure). For every 10% increase in the SVI, the arrival time increased by 38 minutes [CI, 30 - 47] (p<0.001). Considering the 4 SVI subcomponents, delay was most strongly associated with socioeconomic status, household composition, and housing/transportation, but not minority status/language. Conclusion: Using geospatial mapping of prehospital delay across the United States, we show that community SVI is strongly associated with delayed ischemic stroke arrival. These maps help identify communities to target for stroke preparedness campaigns.

Navigator Notes

Navigator Notes

A two-level traffic smoothing method for efficient cloud–IoT communications

The Internet of Things (IoT) is an integration of smart sensing devices with connection ability for ease of communication. Introducing decision-making systems (DMSs) in the IoT for request processing improves the ease of access and service reliability for mobile end users. This paper proposes a two-level DMS for user service traffic smoothing (TS) in IoT communications. The two-level decision-making (2LDM) method employs traffic-aware queuing and minimum time scheduling processes for controlling the request message flows. The decision-making algorithm is modeled on time-dependent processing for minimizing the time delay in the queuing and request scheduling. The DMS considers the attributes associated with the cloud and devices to classify the request messages to prevent resource mapping failures. The disagreement between the request processing and cloud response is resolved optimally for improving the end user communication reliability in terms of the delay and resource mapping failures. Simulations evaluate the proposed DMS performance for the following metrics: sum rate, access delay, failure probability, response latency, and queue utilization. The results indicate that the proposed TS-2LDM outperforms the existing traffic controlling methods by improving the sum rate and queue utilization with controlled delay, failure, and response time.

Space Telescope and Optical Reverberation Mapping Project. IX. Velocity–Delay Maps for Broad Emission Lines in NGC 5548

Abstract In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM campaign by recovering velocity–delay maps for the prominent broad emission lines (Lyα, C iv, He ii, and Hβ) in the spectrum of NGC 5548. These are the most detailed velocity–delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He ii response inside 5–10 lt-day has a broad single-peaked velocity profile. The Lyα, C iv, and Hβ responses extend from inside 2 to outside 20 lt-day, with double peaks at ±2500 km s−1 in the 10–20 lt-day delay range. An incomplete ellipse in the velocity–delay plane is evident in Hβ. We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay τ = ( R / c ) ( 1 − sin i ) ≈ 5 days gives the inclination i ≈ 45°. The inferred black hole mass is M BH ≈ 7 × 107 M ⊙. In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the “BLR Holiday” identified in previous work. Moreover, a helical “Barber-Pole” pattern, with stripes moving from red to blue across the C iv and Lyα line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.

Regional Ionospheric Delay Mapping for Low‐Latitude Environments

AbstractThe ionosphere in low‐latitude regions has strong dynamics reflected by unique phenomena such as the equatorial ionization anomaly and equatorial plasma bubbles. Since the ionosphere can significantly affect space‐to‐Earth technologies, notably communication systems and Global Navigation Satellite Systems (GNSS), the variations in ionospheric total electron content are of great interest to the space weather community and operators of these technologies. Motived by these issues, this paper proposes a new methodology to generate ionospheric delay maps using data from a network of GNSS monitoring stations. The methodology developed is suitable for low latitudes and has low level of complexity. It is based on the thin shell model of the ionosphere and uses groupings of measurements in time and space, triangulation, linear interpolation, and smoothing. The resulting maps show detailed coverage of large‐scale phenomena, like structures of equatorial plasma bubbles, in a way that other geophysical instruments are not able to provide. In a qualitative validation using a network of stations in Brazil, it was demonstrated that the maps were able to clearly identify plasma bubble structures also captured by other instruments, like scintillation monitors and all‐sky imager. The quantitative assessment showed errors less than 4 m in 99.9% of the times in days with high variability of the ionosphere and less than 1 m in a day with very low ionization. The quality of the generated maps with this new methodology using this density of data opens a wide range of possibilities for scientific and operational applications in low‐latitude ionosphere environment.

A collocation framework to retrieve tropospheric delays from a combination of GNSS and InSAR

High spatio-temporal variability of atmospheric water vapor affects microwave signals of Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR). A better knowledge of the distribution of water vapor improves both GNSS- and InSAR-derived data products. In this work, we present a collocation framework to combine and retrieve zenith and (relative) slant tropospheric delays. GNSS and InSAR meteorological products are combined aiming at a better retrieval of the atmospheric water vapor. We investigate the combination approach with synthetic and real data acquired in the Alpine region of Switzerland. Based on a closed-loop validation with simulated delays, a few mm accuracy is achieved for the GNSS-InSAR combination in terms of retrieved ZTDs. Furthermore, when real delays are collocated, the combination results are more congruent with InSAR computed products. This research is a contribution to improve the spatio-temporal mapping of tropospheric delays by combining GNSS-derived and InSAR-derived delays.

On the Definition of the Strategy to Obtain Absolute InSAR Zenith Total Delay Maps for Meteorological Applications

Atmospheric Phase Screens (APSs) derived from Interferometric Synthetic Aperture Radar (InSAR) observations contain the difference between the tropospheric water vapor induced delay of two acquisition epochs, i.e. the slave and the master (or reference) epochs. Using estimates of the atmospheric state coming from independent sources, for example numerical models and/or Global Navigation Satellite System (GNSS) observations, the APSs can be transformed into absolute maps of Tropospheric Delay (Zenith Total Delay or ZTD), related to the columnar atmospheric water vapor content. In this work, a systematic comparison between various APS and ZTD products aims to determine a convenient strategy to go from APSs to InSAR-derived absolute ZTD maps, highlighting the uncertainties and approximations introduced in the entire processing. The main problem to solve is the evaluation of a sufficiently accurate high resolution master delay map. Different sources of data and two different approaches to derive the master are validated and compared to define the most suitable strategy for meteorological applications. Maps of ZTD obtained by an iterative interpolation of a global atmospheric circulation model values result more suited than those derived from the assimilation of GNSS observations into a NWP model. A time average approach to estimate the master map is more robust than the single epoch approach with respect to the choice of the master epoch. Still the choice of a proper master epoch in the InSAR processing chain as well as that of the maps to be averaged result crucial in the estimate of the master.

Reexamining Low-Latitude Ionospheric Error Bounds: An SBAS Approach for Brazil

The ionosphere in low-latitude regions is a major challenge for a satellite-based augmentation system (SBAS). The intense dynamics of this layer of the atmosphere in this part of the globe is one of the main reasons why Brazil discarded years ago the idea of deploying its own SBAS. In this article, we re-examine the ionospheric error bounds for a high-density ground station network in Brazil by updating previous work that assessed specific parameters for low latitudes, especially the ones related to the generation of the ionospheric error bounds expressed by the grid ionospheric vertical error (GIVE). Ionospheric delay maps and their respective GIVE values were generated by varying the functional model used in the interpolation of the grid points and the decorrelation parameter of the measurements for quiet and active days of the ionosphere. The resulting GIVE maps show values significantly higher than the bounds found in mid-latitudes and represent one of the main contributions of this article. An availability assessment for APV-I shows that the planar fit model with a spatial decorrelation standard deviation of 1 m provides the best availability for quiet days, while a quadratic fit with a decorrelation parameter of 2 m results in better availability for active days. Even though it would be possible to provide some service in quiet days within the area with a higher density of reference stations, the resulting availability is not ideal for a real SBAS when the ionosphere is more active.

Improved performance of ERA5 in global tropospheric delay retrieval

Reanalysis products have played an important role in space geodetic tropospheric delay retrieval and modeling in the past two decades. As the release of the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA5), with improved temporal-spatial resolutions compared to its predecessor, ECMWF Re-Analysis Interim (ERAI), the performance of ERA5 in tropospheric delay retrieval was comprehensively investigated in this study. Hourly tropospheric delays in zenith and 5° elevation directions at 312 International GNSS Service (IGS) stations covering the year of 2018 from ERA5 and ERAI were ray-traced. Taking IGS Zenith Total Delay (ZTD) as reference, the reanalysis-derived ZTDs were evaluated in annual, seasonal and diurnal scales, and superior performances of ERA5 ZTD to ERAI ZTD in all scales were revealed, with bias, Root Mean Square (RMS) and standard deviation of 1.6, 11.0 and 10.1 mm for ERA5, and of 3.1, 13.8 and 12.6 mm for ERAI, respectively. Due to the absence of reliable Slant Path Delay (SPD) references, the SPDs as well as the mapping factors derived from ERA5 and ERAI were directly compared and converted to equivalent station height errors at these stations. Obvious differences were also found for SPDs and mapping factors, especially for the wet component, with slant wet delay and wet mapping factor difference RMSs of 51.9 mm and 146.1 × 10−3, respectively, corresponding to equivalent station height RMSs of about 10.4 mm. Tropospheric delays and models (e.g., mapping functions) derived from ERA5, with improved performance and temporal resolution (e.g., to support potential tropospheric parameter diurnal variation study), therefore can be expected for space geodetic applications.

Observational signatures of close binaries of supermassive black holes in active galactic nuclei

Inspired by the General Relativity for many decades, experimental physicists and astronomers have a solid dream to detect gravitational waves (GWs) from mergers of black holes, which came true until the excellent performance of the Laser Interferometer Gravitational-Wave Observatory (LIGO) at hundreds Hz. Nano-Hz GWs are expected to be radiated by close-binaries of supermassive black holes (CB-SMBHs; defined as those with separations less than ∼0.1 pc) formed during galaxy mergers and detected through the Pulsar Timing Array (PTA) technique. As of the writing, there remains no nano-Hz GWs detection. Searching for CB-SMBHs is also observationally elusive though there exist a number of possible candidates. In this review, we focus on observational signatures of CB-SMBHs from theoretic expectations, simulations and observations. These signatures appear in energy distributions of multiwavelength continuum, long term variations of continuum, jet morphology, reverberation delay maps and spectroastrometry of broad emission lines, AGN type transitions between type-1 and type-2 (changing-look), and gaseous dynamics of circumbinary disks, etc. Unlike hundred-Hz GWs from stellar mass black hole binaries, the waveform chirping of nano-Hz GWs is too slow to detect in a reasonable human timescale. We have to resort to electromagnetic observations to measure orbital parameters of CB-SMBHs to test nano-Hz GW properties. Reverberation mapping is a powerful tool for probing kinematics and geometry of ionized gas in the gravitational well of SMBHs (single or binary) and therefore provides a potential way to determine orbital parameters of CB-SMBHs. In particular, a combination of reverberation mapping with spectroastrometry (realized at the Very Large Telescope Interferometer) will further reinforce this capability. The Atacama Large Millimeter/submillimeter Array (ALMA) and the forthcoming Square Kilometre Array (SKA) are suggested to reveal dynamics of circumbinary disks through molecular emission lines.

A delayed modified Ricker map and its cicada-type oscillations

Without trying to develop a model for a biological system, we introduce a delay map that shows a large spike followed by 16 iterations of much smaller values. Upon variation of one of the parameters, we can get a 13 cycles stable oscillation. The analyses of the bifurcation diagrams for the delayed extended Ricker's map yield a straightforward approach to find parameter values for any periodicity. In particular, we determine the values for the 13 and 17 periodic oscillations. We also notice that the bifurcation diagrams show no chaotic regions, and their structures show self-similarity properties. In general, the bifurcation diagrams have self-similarity structures, where n-periodic oscillations change into (n-1)-periodic oscillations.

FBG Demodulation With Enhanced Performance Based on Optical Fiber Relative Delay Measurement

Fiber Bragg grating (FBG) demodulation based on microwave photonics (MWP) would have a high resolution but the measurement range is usually limited. Here, we propose an FBG demodulation system based on wavelength to optical fiber relative delay (OFRD) mapping, where the signal reflected by the FBG is first modulated by an RF signal and then sent to a dispersion compensation fiber (DCF). The OFRD can be acquired by measuring the slope change of the phase response of the DCF. Thanks to the sub-picosecond resolution OFRD measurement of the phase-derived ranging, the FBG demodulation resolution would be very high. The integer ambiguity, which is the primary limitation for large measurement range, is removed by sweeping the frequency of the RF signal in a certain range. In addition, the relative slope change of the phase response can be obtained using a larger frequency sweep interval compared to the traditional phase-derived ranging method, leading to a significant reduction of the measurement time. An experiment is performed, which applies the system to measure the temperature. A measurement range of more than 300 °C (corresponding to a wavelength shift of 3 nm) and measurement precision of ± 0.2 °C (corresponding to a wavelength shift of 2 pm) are achieved with a measurement speed of 20 ms.

The Effect of Scan Length on the Assessment of BOLD Delay in Ischemic Stroke.

Objectives: To evaluate the impact of resting-state functional MRI scan length on the diagnostic accuracy, image quality and lesion volume estimation of BOLD delay maps used for brain perfusion assessment in acute ischemic stroke.Methods: Sixty-three acute ischemic stroke patients received a 340 s resting-state functional MRI within 24 h of stroke symptom onset. BOLD delay maps were calculated from the full scan and four shortened versions (68 s, 136 s, 204 s, 272 s). The BOLD delay lesions on these maps were compared in terms of spatial overlap and volumetric agreement with the lesions derived from the full scans and with time-to-maximum (Tmax) lesions derived from DSC-MRI in a subset of patients (n = 10). In addition, the interpretability and quality of these maps were compared across different scan lengths using mixed models.Results: Shortened BOLD delay scans showed a small volumetric bias (ranging from 0.05 to 5.3 mL; between a 0.13% volumetric underestimation and a 7.7% overestimation relative to the mean of the volumes, depending on scan length) compared to the full scan. Decreased scan length was associated with decreased spatial overlap with both the BOLD delay lesions derived from the full scans and with Tmax lesions. Only the two shortest scan lengths (68 and 136 s) were associated with substantially decreased interpretability, decreased structure clarity, and increased noisiness of BOLD delay maps.Conclusions: BOLD delay maps derived from resting-state fMRI scans lasting 272 and 204 s provide sufficient diagnostic quality and adequate assessment of perfusion lesion volumes. Such shortened scans may be helpful in situations where quick clinical decisions need to be made.

General Survey of Large-scale Land Subsidence by GACOS-Corrected InSAR Stacking: Case Study in North China Plain

Abstract. Satellite-based InSAR (Interferometric Synthetic Aperture Radar) provides an effective way to measure large-scale land surface motions. Currently, the atmospheric phase delay is one of the most critical issues in InSAR deformation monitoring. Generic Atmospheric Correction Online Service (GACOS) is a free, globally available and easy-to-implement tool to generate high-resolution zenith total delay maps, which could be used for InSAR atmospheric delay correction. The mean velocity could then be estimated by stacking multiple GACOS-corrected interferograms. We applied the proposed GACOS-corrected InSAR stacking method in the North China Plain and analysed its performance. Within the 549 interferograms, more than 85 % gained positive correction performances. The correlation between the phase-dZTD indicator and the performance reached 0.89, demonstrating a significant relationship. Deformation maps revealed by InSAR stacking with and without GACOS corrections showed that GACOS could mainly remove the topography-related and long wavelength signals.

SPARC: Brain‐stomach Synchrony Observed with Functional Magnetic Resonance Imaging and Electrogastrogram in Rats

PurposeThe gut communicates with the brain, allowing the gastrointestinal state to influence cognition and emotion and vice versa. In the resting state, gastric electrical activity has been shown to be synchronized with the blood‐oxygen‐level‐dependent (BOLD) signal in the so‐called gastric network in humans [1]. However, the finding has been rarely replicated. Here, we explored the gut‐brain synchrony in rats. Whole‐brain functional magnetic resonance imaging (fMRI) was acquired simultaneously with electrogastrogram (EGG) recording. Cross‐correlation between EGG and BOLD signals was used to map resting state networks influenced by gastric activity.MethodBrain fMRI was performed on three SD rats together with multi‐channel EGG recording. Each rat was trained to consume diet gel enriched with Gadolinium contrast media. Before the experiment, the rat was fed with 5g diet gel. After the feeding, the animal was anesthetized with continuous dexmedetomidine and isoflurane. The multi‐channel EGG signal was recorded using an electrophysiological recording system (Tucker Davis Technologies Inc.) together with fMRI scans using a 7‐tesla small‐animal MRI system (BioSpec 70/30, Bruker). The principal component analysis was applied to EGG signals. The correlation between the voxel‐wise fMRI signal and the component‐wise EGG signal was calculated, yielding multiple gut‐associated brain networks. The voxel‐wise fMRI signal was also modeled as a linear combination of EGG component time series with varying time shifts.ResultsFMRI was acquired simultaneously with the EGG recording ( Fig. 1A). EGG was denoised and cross‐correlated with the BOLD activity in every voxel to map an EGG‐correlated network (or the gastric network) ( Fig. 1C). The BOLD signal was averaged across voxels in the gastric network. The resulting network‐wide signal was found to be phase‐locked to EGG with a time delay ( Fig. 1B). Accounting for the delay variable across voxels, we mapped an even broader network phase‐locked with EGG ( Fig. 2A). Different EGG‐coupled regions were found to lag behind EGG by different times, ranging from 4 to 12 seconds ( Fig. 2B & C). From the EGG‐coupled BOLD response, the visual and auditory cortex had a relatively longer delay, whereas the somatosensory and anterior cingulate cortex had a shorter delay. The cingulate cortex showed a complex response pattern, likely implying multiple functional roles with respect to the gut.ConclusionIn rats, brain activity is intrinsically synchronized with gastric activity at a specific resting state network. In this network, different brain regions are time‐locked to gastric activity with varying time delays. Speculatively, the pattern of time delay may reflect how gastric information propagates through a cascade of brain regions for sequential processing.Support or Funding InformationThis study was funded by National Institutes of Health’s SPARC ‐ Stimulating Peripheral Activity to Relieve Conditions ‐ program (OT2OD023847).Simultaneous EGG and brain fMRI recording. (A) shows the layout of the 32‐channel electrode array for EGG recording. (B) are examples of EGG and fMRI time series. (C) shows an example of the EGG correlation map. The correlation between EGG and fMRI time series is color‐coded.Figure 1The EGG network considering the phase delays between EGG and fMRI signal. (A) is a summary of the EGG network. The color represents the F statistic of the multiple linear regression. (B) selects six voxels in the EGG network. The curve shows the relation between the F statistic and EGG‐fMRI delays for the selected voxels, which are marked with blue box in (A). (C) is the phase delay map that delineates the phase differences between EGG and fMRI time series.Figure 2

33 “Striking Back Against Stroke”

Abstract Background 2 million brain cells die every minute increasing the risk of permanent brain damage, disability or death. Despite the fact that IV Thrombolysis and Thrombectomy are now the standard of care, optimal rates of door to needle times and door to decision times have not been managed to be achieved throughout Ireland. There is a gap between what we know and what we do. Treatment within a shorter time frame improves patient outcomes. Aim: To reduce door to decision time for Thrombectomy to <30minutes in conjunction with the National Thrombectomy Quality Improvement Programme. Methods A Stroke Committee was set up consisting of a wider group of Stakeholders involved in FAST positive calls. A pre-audit of baseline times was conducted. Each step was mapped out in a process map and areas of delays were identified to reduce the overall KPI times. Delays and areas for change: Results Door to CT times reduced from 37minutes to 22 minutes (↓ 15minutes) Door to CTA time reduced from 35 minutes to 28 minutes (↓ 7minutes) Door to Thrombolysis reduced from 65 minutes to 30 minutes (↓ 35 minutes) CTA to time of contact Beaumont (↓ 5minutes) Door to decision re: Thrombectomy or not reduced from 166 minutes to 24.5 minutes (↓ 141.5 minutes) Conclusion This is an ongoing process which continues to ultimately improve patient outcomes. “Time is Brain”