The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures; https://iopscience.iop.org/article/10.1088/1538-3873/acb29

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Simulation, estimation spectrale et imagerie des agents de contraste ultrasonores

Dans cette thèse, nous apportons notre contribution aux techniques permettant de rendre l'utilisation des agents de contraste ultrasonore plus performante. Dans un premier temps, nous avons développé un simulateur d'imagerie échographique de contraste (SECI) qui permet de simuler la formation d'images ultrasonores avec agent de contraste. Il prend en compte, la sonde, le milieu de propagation des ultrasons et le comportement individuel, non linéaire, de chaque bulle. Des simulations de bulles isolées, en fonction du MI, de la fréquence incidente et du rayon au repos ont été réalisées. Dans un second temps, nous avons validé SECI avec des acquisitions in vitro. Puis une étude expérimentale de l'agent de contraste a été menée, en fonction du MI. Finalement nous avons proposé des paramètres dédiés à la visualisation des agents de contraste basés sur l'estimation spectrale, la modélisation AR et la projection atomique. Ces paramètres ont été testés sur des acquisitions in vitro et in vivoIn this work, we contribute to make ultrasound contrast agent simpler and more effective to use. First we developed a Simulator of Echo Contrast Imaging (SECI). SECI can simulate ultrasound imaging with contrast agent. It takes into account the probe, the propagating medium, the individual, non linear, response of each bubble. Simulations of bubbles alone, have also been performed, at different MI, transmit frequency, and radius. Then, we validate SECI by comparison with in-vitro experiments. An experimental study of the influence of the MI over the contrast agent behavior has been done. Finally, visualization techniques, based on spectral estimation, auto-regressive modelization, and atomical projection have been tested on in-vitro and in-vivo acquisitionLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Quantification of the cerebrospinal fluid from a new whole body MRI sequence

International audienceOur work aims to develop a biomechanical model of hydrocephalus both intended to perform clinical research and to assist the neurosurgeon in diagnosis decisions. Recently, we have defined a new MR imaging sequence based on SPACE (Sampling Perfection with Application optimized Contrast using different flip-angle Evolution). On these images, the cerebrospinal fluid (CSF) appears as a homogeneous hypersignal. Therefore such images are suitable for segmentation and for volume assessment of the CSF. In this paper we present a fully automatic 3D segmentation of such SPACE MRI sequences. We choose a topological approach considering that CSF can be modeled as a simply connected object (i.e. a filled sphere). First an initial object which must be strictly included in the CSF and homotopic to a filled sphere, is determined by using a moment-preserving thresholding. Then a priority function based on an Euclidean distance map is computed in order to control the thickening process that adds "simple points" to the initial thresholded object. A point is called simple if its addition or its suppression does not result in change of topology neither for the object, nor for the background. The method is validated by measuring fluid volume of brain phantoms and by comparing our volume assessments on clinical data to those derived from a segmentation controlled by expert physicians. Then we show that a distinction between pathological cases and healthy adult people can be achieved by a linear discriminant analysis on volumes of the ventricular and intracranial subarachnoid spaces

Volume Assessment of the Cerebrospinal Fluid Spaces for Computer Aided Diagnosis

The present work aims to provide support in the diagnosis of hydrocephalus, which requires an assessment to the volumes of the cerebrospinal fluid (CSF) within its total, ventricular and subarachnoid spaces. In this paper we describe a fully automatic method to estimate the CSF volumes from a new 3D whole body MR imaging sequence. The method was developed using image properties as well as anatomical and geometrical features, completed with a topological assumption on the CSF shape. Experiments on phantoms and clinical data were performed and evaluated by comparing our assessments of volumes with those derived from a segmentation controlled by expert physicians. Then we show that a robust distinction between pathological cases and healthy adult people can be achieved by a linear discriminant analysis on volumes of the ventricular and intracranial subarachnoid spaces. We also find that healthy adults maintain a proportional relationship between these volumes

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies