Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Spectral filter array cameras as a diagnostic skin imaging tool

Skin is the human’s largest organ and has many vital functions including protection from pathogens, temperature regulation, touch sensation, vitamin D synthesis and protecting the water inside the body. It does not only protect the body from the environment but also carries information about the health of individuals. Diagnosis and monitoring of skin and vital functions measured in non-contact is a broad field of research. Measuring vital signs, monitoring oxygenation and skin diagnosis can benefit from spatially resolved images of the tissue. Standard three channel colour imaging provides the ease of use and acquisition speed for a clinical setup but lacks the spectral resolution to identify specific narrow bands of interest containing the essential information. Spectral imaging has been used to quantify diagnostically relevant physical properties of living tissue but suffers from slow acquisition speed and time delays between the acquisition of different bands. Recent sensor development has led to so-called spectral filter array (SFA) cameras, which combine the acquisition speed and ease of use of standard RGB imaging with the spectral resolution of spectral cameras. To utilise all the benefits of this new imaging modality, additional processing steps are required. This thesis explores SFA imaging in the context of skin diagnosis, and the imaging is enhanced with physical skin simulation models. Skin models based on Monte Carlo simulation allow change and control over optical properties and resulting spectral reflectance from skin can be recorded. The simulated spectral reflectance with known optical properties is used in three different ways within this research. First, they are tested, by studying the impact of the optical properties on a resulting colour patch. This provides a better understanding of the relationship between colour shade and different combinations of optical properties. Secondly, the simulations are used to enhance the interpretability of spectral measurements regarding important physical skin properties with diagnostic value. This approach is applied to two different spectral filter array cameras and an RGB imager in conjunction with multiple LEDs. Thirdly, skin simulations are performed to generate an exhaustive spectral reflectance database, for training and enhancement of spectral reconstructions of skin reflectance. This specialised database covers a wide range of physically, but not physiologically possible optical properties. Different spectral imagers in the visual and near-infrared spectrum are applied to measuring oxygenation spatially resolved in living tissue. Additionally, a processing framework is proposed for spectral filter array cameras. This framework combines several SFA camera-specific processing steps and shows transferability to other cameras. It is tested by comparing oxygenation estimations from both a visual range (VIS) and a near-infrared (NIRS) spectral filter array camera with the de facto clinical standard in an upper arm occlusion test. Finally, this work proposes a framework for selecting and testing SFA cameras for skin diagnosis tasks without the need of (extensive) clinical studies. This framework could aid in the development of SFA cameras for specific tasks and explores currently commercially available models for skin oxygenation measurements. In the future, it can be expected that spectral filter array cameras will become cheaper and more common. This work establishes a solid foundation for applying this new versatile form of spectral imaging in the context of skin diagnosis. Both general practitioners, dermatologists and, anesthesiologists can benefit from an easy to use, spatially resolved, real-time oxygenation measurement tool

A Spectral Filter Array Camera for Clinical Monitoring and Diagnosis: Proof of Concept for Skin Oxygenation Imaging

The emerging technology of spectral filter array (SFA) cameras has great potential for clinical applications, due to its unique capability for real time spectral imaging, at a reasonable cost. This makes such cameras particularly suitable for quantification of dynamic processes such as skin oxygenation. Skin oxygenation measurements are useful for burn wound healing assessment and as an indicator of patient complications in the operating room. Due to their unique design, in which all pixels of the image sensor are equipped with different optical filters, SFA cameras require specific image processing steps to obtain meaningful high quality spectral image data. These steps include spatial rearrangement, SFA interpolations and spectral correction. In this paper the feasibility of a commercially available SFA camera for clinical applications is tested. A suitable general image processing pipeline is proposed. As a ’proof of concept’ a complete system for spatial dynamic skin oxygenation measurements is developed and evaluated. In a study including 58 volunteers, oxygenation changes during upper arm occlusion were measured with the proposed SFA system and compared with a validated clinical device for localized oxygenation measurements. The comparison of the clinical standard measurements and SFA results show a good correlation for the relative oxygenation changes. This proposed processing pipeline for SFA cameras shows to be effective for relative oxygenation change imaging. It can be implemented in real time and developed further for absolute spatial oxygenation measurements

A Spectral Filter Array Camera for Clinical Monitoring and Diagnosis: Proof of Concept for Skin Oxygenation Imaging

The emerging technology of spectral filter array (SFA) cameras has great potential forclinical applications, due to its unique capability for real time spectral imaging, at a reasonable cost.This makes such cameras particularly suitable for quantification of dynamic processes such as skinoxygenation. Skin oxygenation measurements are useful for burn wound healing assessment and asan indicator of patient complications in the operating room. Due to their unique design, in which allpixels of the image sensor are equipped with different optical filters, SFA cameras require specificimage processing steps to obtain meaningful high quality spectral image data. These steps includespatial rearrangement, SFA interpolations and spectral correction. In this paper the feasibility ofa commercially available SFA camera for clinical applications is tested. A suitable general imageprocessing pipeline is proposed. As a ’proof of concept’ a complete system for spatial dynamicskin oxygenation measurements is developed and evaluated. In a study including 58 volunteers,oxygenation changes during upper arm occlusion were measured with the proposed SFA system andcompared with a validated clinical device for localized oxygenation measurements. The comparisonof the clinical standard measurements and SFA results show a good correlation for the relativeoxygenation changes. This proposed processing pipeline for SFA cameras shows to be effective forrelative oxygenation change imaging. It can be implemented in real time and developed further forabsolute spatial oxygenation measurements

A spectral filter array camera for clinical monitoring and diagnosis: Proof of concept for skin oxygenation imaging

The emerging technology of spectral filter array (SFA) cameras has great potential for clinical applications, due to its unique capability for real time spectral imaging, at a reasonable cost. This makes such cameras particularly suitable for quantification of dynamic processes such as skin oxygenation. Skin oxygenation measurements are useful for burn wound healing assessment and as an indicator of patient complications in the operating room. Due to their unique design, in which all pixels of the image sensor are equipped with different optical filters, SFA cameras require specific image processing steps to obtain meaningful high quality spectral image data. These steps include spatial rearrangement, SFA interpolations and spectral correction. In this paper the feasibility of a commercially available SFA camera for clinical applications is tested. A suitable general image processing pipeline is proposed. As a’proof of concept’ a complete system for spatial dynamic skin oxygenation measurements is developed and evaluated. In a study including 58 volunteers, oxygenation changes during upper arm occlusion were measured with the proposed SFA system and compared with a validated clinical device for localized oxygenation measurements. The comparison of the clinical standard measurements and SFA results show a good correlation for the relative oxygenation changes. This proposed processing pipeline for SFA cameras shows to be effective for relative oxygenation change imaging. It can be implemented in real time and developed further for absolute spatial oxygenation measurements

The vascular occlusion test using multispectral imaging: a validation study

Multispectral imaging (MSI) is a new, non-invasive method to continuously measure oxygenation and microcirculatory perfusion, but has limitedly been validated in healthy volunteers. The present study aimed to validate the potential of multispectral imaging in the detection of microcirculatory perfusion disturbances during a vascular occlusion test (VOT). Two consecutive VOT’s were performed on healthy volunteers and tissue oxygenation was measured with MSI and near-infrared spectroscopy (NIRS). Correlations between the rate of desaturation, recovery and the hyperemic area under the curve (AUC) measured by MSI and NIRS were calculated. Fifty-eight volunteers were included. The MSI oxygenation curves showed identifiable components of the VOT, including a desaturation and recovery slope and hyperemic area under the curve, similar to those measured with NIRS. The correlation between the rate of desaturation measured by MSI and NIRS was moderate: r = 0.42 (p = 0.001) for the first and r = 0.41 (p = 0.002) for the second test. Our results suggest that non-contact multispectral imaging is able to measure changes in regional oxygenation and deoxygenation during a vascular occlusion test in healthy volunteers. When compared to measurements with NIRS, correlation of results was moderate to weak, most likely reflecting differences in physiology of the regions of interest and measurement technique

Towards real-time non contact spatial resolved oxygenation monitoring using a multi spectral filter array camera in various light conditions

Non contact spatial resolved oxygenation measurements remain an open challenge in the biomedical field and non contact patient monitoring. Although point measurements are the clinical standard till this day, regional differences in the oxygenation will improve the quality and safety of care. Recent developments in spectral imaging resulted in spectral filter array cameras (SFA). These provide the means to acquire spatial spectral videos in real-time and allow a spatial approach to spectroscopy. In this study, the performance of a 25 channel near infrared SFA camera was studied to obtain spatial oxygenation maps of hands during an occlusion of the left upper arm in 7 healthy volunteers. For comparison a clinical oxygenation monitoring system, INVOS, was used as a reference. In case of the NIRS SFA camera, oxygenation curves were derived from 2-3 wavelength bands with a custom made fast analysis software using a basic algorithm. Dynamic oxygenation changes were determined with the NIR SFA camera and INVOS system at different regional locations of the occluded versus non-occluded hands and showed to be in good agreement. To increase the signal to noise ratio, algorithm and image acquisition were optimised. The measurement were robust to different illumination conditions with NIR light sources. This study shows that imaging of relative oxygenation changes over larger body areas is potentially possible in real time

An Evaluation Framework for Spectral Filter Array Cameras to Optimize Skin Diagnosis

Comparing and selecting an adequate spectral filter array (SFA) camera is application-specific and usually requires extensive prior measurements. An evaluation framework for SFA cameras is proposed and three cameras are tested in the context of skin analysis. The proposed framework does not require application-specific measurements and spectral sensitivities together with the number of bands are the main focus. An optical model of skin is used to generate a specialized training set to improve spectral reconstruction. The quantitative comparison of the cameras is based on reconstruction of measured skin spectra, colorimetric accuracy, and oxygenation level estimation differences. Specific spectral sensitivity shapes influence the results directly and a 9-channel camera performed best regarding the spectral reconstruction metrics. Sensitivities at key wavelengths influence the performance of oxygenation level estimation the strongest. The proposed framework allows to compare spectral filter array cameras and can guide their application-specific development

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta