PLATO (PLAnetary Transits and Oscillation of stars) is the ESA M-size mission aimed to the discovery of exo-planets hosted by bright, nearby stars. The launch of PLATO spaceship is scheduled for 2026. It will orbit Sun-Earth L2 for 4 years, looking towards deep space and covering a wide (2132 deg 2 total) area of space. To do so, PLATO will use 26 fully dioptric designed cameras, each composed of a telescope optical unit (TOU) and a focal plane array (FPA). For manufacturing purposes, the FPA will be assembled at ambient temperature, although the best image plane (BIP) of the TOU will be determined during test at cryo-vacuum conditions (-80°C). This poses a metrology challenge at TOU manufacturing and testing and at FPA integration facilities. To this extent, the procedures for the precise characterization and localization of the BIP during TOU tests are presented. In order to circumvent the thermal effects of contraction of the fixture, which in part operate at ambient and in part are cooled at -80°C (operation temperature), the final measurement will be derived by the repeated assessment of the coordinates of a set of fiducials at ambient and operation temperature. Compliance with a strict error budget is achieved by using a combination of sensors (confocal, focusvariation), mounted on very precise and repeatable hexapods. Hartmann masks are also used to co-register the position and orientation of mounting of the FPA between facilities.
PLATO is an exoplanet hunting mission of the European Space Agency. It is a medium-class mission, with a launch foreseen in 2026. Its prime objective is to uncover Earth-sized planets residing in their habitable zone. The payload consists of 26 cameras with a very wide field of view. These cameras consist of a Telescope Optical Unit (TOU), aligned at ambient and characterized at the operational temperature, and a Focal Plane Array bearing the detectors and delivered after coupling with the Front End Electronics. In this contribution, we report on the methods used at TOU level to characterize Focal Plane using a Hartmann Mask, i.e. we illustrate the analysis pipeline after data collection in the cryo-vacuum chamber at Leonardo (LDO), the implementation of new algorithms, and an extended uncertainties study for the Hartmann analysis.
KEYWORDS: Sensors, Modulation transfer functions, Point spread functions, Stars, Telescopes, Detection and tracking algorithms, Cameras, Imaging systems, Exoplanets, Data modeling
The ESA M-size mission PLATO (PLAnetary Transits and Oscillation of stars) is scheduled for launch in 2026. During its 4-year mission orbiting Sun-Earth L2 is aimed at the discovery of exo-planets in nearby star systems. Its 26 cameras will be looking toward deep space, covering a wide area of the sky. Each camera is based on a fully dioptric design. Each camera is composed of a telescope optical unit (TOU) and a focal plane array (FPA). Here the procedure for the characterization of the best imaging plane (BIP) for each TOU is described. Camera manufacturing activity faces the challenge, by design, of locating the BIP for each TOU with high precision (±30 μm). Strict tolerances for accommodating the FPA are in fact in place in terms of inter-distances with respect to the mechanical mounts and tilts. Localization of the BIP will be carried out by mathematical optimization of the enclosed energy performances that will be evaluated at a pre-defined set of 45 field positions. Given the relatively big field-of-view of each camera (1037 deg2 for 24 normal-type and 610 deg2 for the 2 fast-type), this poses a challenge for a single service detector. Instead, an approach based on stitching single views of a smaller active area detector will be carried out. To circumvent performance limitations of detectors, for example, image degradation due to finite-size pixel sampling, dithering will be performed by leveraging a very precise mechanical positioner (hexapods) on which the detector is mounted.
KEYWORDS: Near infrared spectroscopy, Continuous wave operation, Measurement devices, Medical devices, In vivo imaging, Tissues, Tissue optics, Spectroscopes, Reliability, Oxygen
During the first peak of the COVID-19 pandemic, we have set up a clinical campaign in ten hospitals worldwide to assess the endothelial health of COVID-19 patients using commercial continuous-wave near-infrared spectroscopy (CW-NIRS) devices (PortaMon, Artinis, NL). In spite of the wide range of clinical applications, the reliability of common CW-NIRS systems for absolute oxygenation measurements was often questioned, opening issues of standardization. In addition, a multi-center trial itself opens issues about how to compare measurements performed by different operators, in different conditions and longitudinally over more than a year. Here, we present how we address these challenges by characterizing and comparing the performance of the devices, with phantom and in vivo experiments.
The HEMOCOVID-19 clinical trial, carried out in 10 hospitals from 5 countries, aims to non-invasively assess, through continuous-wave near-infrared spectroscopy (CW-NIRS), the microvascular and endothelial health in COVID-19 patients admitted to intensive care. We achieve this by performing a vascular occlusion test on the forearm muscle while continuously measuring local tissue oxygen saturation and hemoglobin concentration. We found significant alterations in systemic microcirculation of COVID-19 patients with respect to healthy subjects (i.e. slower deoxygenation during the ischemia and reoxygenation after releasing the cuff, and lower hyperemic response). In addition, we found that, within the group of COVID-19 patients, the systemic microcirculation alterations correlate with severity of pulmonary disease.
Time-domain diffuse correlation spectroscopy (TD-DCS) is a non-invasive optical technique, which measures tissue blood flow with path-length resolution. Ideally, this technique requires a pulsed laser with an adequate illumination power, a long coherence length, and a narrow instrument response function (IRF), while available laser modules cannot satisfy all these conditions. We systematically characterized three pulsed laser sources and compared their performances using phantom and in vivo measurements. We found that each laser has the potential to be used in TD-DCS applications. Also, the effects caused by the IRF are more significant than the effect of the limited coherence length.
KEYWORDS: In vivo imaging, Single photon detectors, Superconductors, Nanowires, Spectroscopy, Signal to noise ratio, Sensors, Picosecond phenomena, Liquids, Tissues
Diffuse correlations spectroscopy (DCS) is a non-invasive optical technique that, studying the speckle intensity fluctuations of light diffused through a biological tissue, measures its microvascular blood flow. Typically, a long coherence length continuous wave source is used, which limits the possibility to resolve the photon path lengths. Recently, time-domain (TD) DCS was proposed, where a pulsed yet coherent light source is used to resolve the speckle fluctuations at different time-of-flights. Due to the constraint of single-speckle detection and time-resolved acquisition, the technique has a limited throughput which limits depth sensitivity. Here, we demonstrate TD DCS with a superconducting nanowire single-photon detector (SNSPD). The SNSPD has a high quantum efficiency and temporal resolution, while maintaining a very low background and no after-pulsing.We report results on phantom and in vivo experiments, which show the potentiality of the proposed detection system for highly accurate TD DCS experiments.
KEYWORDS: Hemodynamics, Near infrared spectroscopy, Tissues, In vivo imaging, Blood circulation, Tissue optics, Spectroscopes, Skin, Dubnium, Time metrology
A multi-distance Diffuse Correlation Spectroscopy system combined with a compact state-of-the-art Time Domain Near-Infrared Spectroscopy device is presented. The device was used to validate the protocol of VASCOVID project on healthy subject.
We propose a standardized approach for performance assessment and quality-control of the novel VASCOVID system based on optical phantoms. This approach is tailored to meet the requirements of the Medical Device Regulation, and is extendable to other biophotonics devices.
HEMOCOVID-19 project spans four countries and eight hospitals to evaluate the microvascular and endothelial health of severe COVID-19 patients using near-infrared spectroscopy (NIRS) of the forearm muscle. In order to implement the project, we have developed protocols and
tested ten commercial continuous-wave NIRS devices of the same model (PortaMon, Artinis, NL). They were characterized and compared for intra- and inter-device, inter- and intra-operator and temporal variability in solid phantoms and in vivo.
We present the HEMOCOVID-19 study spanning four countries and eight hospitals where near-infrared spectroscopy is utilized to evaluate microvascular and endothelial health of severe COVID-19 patients at the intensive care.
The VASCOVID project aims to develop an hybrid diffuse optical device with a vascular occlusion protocol for evaluating endothelial and microvascular health in severe COVID-19 patients admitted to the ICU.
As coronavirus disease 2019 (COVID-19) has spread across the world, the surge in patients requiring ICU admission has been overwhelming.The rapid diagnosis and isolation, clinical management, and infection prevention are the main challenges associated with this pandemic. When the disease becomes critical, adequate management of acute respiratory failure and supporting the hemodynamics is key in order to minimize the negative impact on survival. However, many questions on prognosis and efficient clinical management remain unanswered. HEMOCOVID-19 uses near-infrared diffuse optical technologies to non-invasively evaluate endothelial and microvascular dysfunction to aid both the development of targeted therapies and also to personalize rescue therapies. HEMOCOVID-19 has eleven partners in four countries and is open for new members. I will present the project and the preliminary results. I will then briefly explain the vision for the longer-term.
Diffuse correlation spectroscopy (DCS) is an optical technique which, by studying the speckle intensity fluctuations of coherent light diffused in a turbid medium, retrieves information regarding the scatterers motion. In the case of biological tissues, the particles of interest are the red blood cells, from which is possible to measure non-invasively microvascular blood flow (BF). However, being based on a continuous-wave light source, depth discrimination is achievable only by using multiple source-detector separations. On the other hand, time-domain (TD) DCS is a novel approach which exploits a pulsed yet coherent light source to discriminate the intensity fluctuations at different photon time-of-flights. This additional information is beneficial for in vivo applications, due to the physical relationship between photon time-of-flight and mean depth penetration. TD-DCS is typically performed in the spectral range between 700 and 800 nm. Here, we explore TD-DCS in a new spectral range compared to the typical one, moving to the spectral region beyond the water absorption peak (i.e., >970 nm). We performed liquid phantom and in vivo experiments on the human muscle at a wavelength of 1000 nm. Also, the possible advantages in terms of depth sensitivity and signal-to-noise ratio are discussed.
Diffuse correlation spectroscopy (DCS) is an emerging diffuse optical technique that quantifies microvascular blood flow. In spite of the wide range of clinical/research applications, DCS instrumentation is not yet standardized. In this study, we have analyzed the effect of experimental parameters as the measurement duration time and the number of detectors, at different photon count-rates, on the precision of a DCS experiment. This provides a recipe for finding device and experimental settings that optimize the precision while balancing cost and temporal resolution.
Time-domain diffuse optics exploits near infrared light pulses diffused in turbid samples to retrieve their optical properties e.g., absorption and reduced scattering coefficients. Typically, interference effect are discarded, but speckle effects are exploited in other techniques e.g., diffuse correlation spectroscopy (DCS) to retrieve information regarding the tissue dynamics. Here, using a highly coherent Ti:Sapphire mode-locked laser and a single-mode detection fiber, we report the direct observation of temporal fluctuations in the measured distribution of time-of-flights (DTOF) curve. We study the dependence of these fluctuations on the sample dynamical properties (moving from fluid to rigid tissue-mimicking phantoms) and on the area of the detection fiber, which is directly linked to the number of collected coherence areas. Our observation agree with a time-resolved speckle pattern, and may enable the simultaneous monitoring of the tissue optical and dynamical properties.
Time-domain diffuse correlation spectroscopy (TD-DCS) is an emerging noninvasive optical technique with the potential to resolve blood flow (BF) and optical coefficients (reduced scattering and absorption) in depth. Here, we study the effects of finite temporal resolution and gate width in a realistic TD-DCS experiment. We provide a model for retrieving the BF from gated intensity autocorrelations based on the instrument response function, which allows for the use of broad time gates. This, in turn, enables a higher signal-to-noise ratio that is critical for in vivo applications. In numerical simulations, the use of the proposed model reduces the error in the estimated late gate BF from 34% to 3%. Simulations are also performed for a wide set of optical properties and source–detector separations. In a homogeneous phantom experiment, the discrepancy between later gates BF index and ungated BF index is reduced from 37% to 2%. This work not only provides a tool for data analysis but also physical insights, which can be useful for studying and optimizing the system performance.
Time-domain diffuse correlation spectroscopy (TD-DCS) is an emerging optical technique with the potential to resolve the blood flow (BF) in depth. The first in vivo measurements have been shown recently on humans, however improvements in terms of signal-to-noise ratio (SNR) and depth sensitivity would be beneficial for biological applications. In this contribution, we explore the possibility of in vivo TD-DCS measurements above 1000 nm, and discuss its possible advantages compared to standard wavelengths (i.e. 700-800 nm). In our experimental setup, we exploited a tunable pulsed laser source extended more to the infrared and an InGaAs photomultiplier. Here, we report the results of a cuff occlusion on the forearm of a healthy adult subject at a wavelength of 1000 nm. Compared to the same experiment at standard wavelength (785 nm), the electric-field auto-correlation functions show a slower decay rate during all the experiment (both during and after the occlusion) as expected, suggesting a higher SNR. Even longer wavelengths, for diminishing water absorption, can be obtained through optimization of the laser source and the use of more efficient detectors.
We propose a time domain speckle contrast optical spectroscopy (SCOS) system that makes use of a gated detector and pulsed light source to measure the blood flow variations at very short, quasi-null (<3mm) source-detector separation. We present the results of a human arm cuff occlusion and a comparison with standard SCOS, highlighting that we can probe deeper into tissue, reduce probe footprint, make efficient use of the signal and decrease cost.3
The BabyLux device is a hybrid diffuse optical neuromonitor that has been developed and built to be employed in neonatal intensive care unit for the noninvasive, cot-side monitoring of microvascular cerebral blood flow and blood oxygenation. It integrates time-resolved near-infrared and diffuse correlation spectroscopies in a user-friendly device as a prototype for a future medical grade device. We present a thorough characterization of the device performance using test measurements in laboratory settings. Tests on solid phantoms report an accuracy of optical property estimation of about 10%, which is expected when using the photon diffusion equation as the model. The measurement of the optical and dynamic properties is stable during several hours of measurements within 3% of the average value. In addition, these measurements are repeatable between different days of measurement, showing a maximal variation of 5% in the optical properties and 8% for the particle diffusion coefficient on a liquid phantom. The variability over test/retest evaluation is <3 % . The integration of the two modalities is robust and without any cross talk between the two. We also perform in vivo measurements on the adult forearm during arterial cuff occlusion to show that the device can measure a wide range of tissue hemodynamic parameters. We suggest that this platform can form the basis of the next-generation neonatal neuromonitors to be developed for extensive, multicenter clinical testing.
We present the first broadband (600-1100 nm) diffuse optical characterization of thyroglobulin and tyrosine, which are thyroid-specific tissue constituents. In-vivo measurements at the thyroid region enabled their quantification for functional and diagnostic applications.
Improved cerebral monitoring systems are needed to prevent preterm infants from long-term cognitive and motor restrictions. Combining advanced near-infrared diffuse spectroscopy measurement technologies, time-resolved spectroscopy (TRS) and diffuse correlation spectroscopy (DCS) will introduce novel indicators of cerebral oxygen metabolism and blood flow for neonatology. For non-invasive sensing a fiber-optical probe is used to send and receive light from the infant head. In this study we introduce a new fiber-based hybrid probe that is designed for volume production. The probe supports TRS and DCS measurements in a cross geometry, thus both technologies gain information on the same region inside the tissue. The probe is highly miniaturized to perform cerebral measurements on heads of extreme preterm infants down to head diameters of 6cm. Considerations concerning probe production focus on a reproducible accuracy in shape and precise optical alignment. In this way deviations in measurement data within a series of probes should be minimized. In addition to that, requirements for clinical use like robustness and hygiene are considered. An additional soft-touching sleeve made of FDA compatible silicone allows for a flexible attachment with respect to the individual anatomy of each patient. We present the technical concept of the hybrid probe and corresponding manufacturing methods. A prototype of the probe is shown and tested on tissue phantoms as well as in vivo to verify its operational reliability.
We report a broadband time-resolved characterization of selected bony prominence locations of the human body. A clinical study was performed at six different bony prominence locations of 53 subjects. A portable broadband time-resolved system equipped with pulse drift and distortion compensation strategy was used for absorption and scattering measurements. Key tissue constituents were quantified as a pilot step towards non-invasive optical assessment of bone pathologies.
We report on the design, performance assessment, and first in vivo measurement of a Time-Resolved Diffuse Optical system for broadband (600-1350 nm) nm measurement of absorption and scattering spectra of biological tissues for non-invasive clinical diagnostics. Two strategies to reduce drift and enhance responsivity are adopted. The system was enrolled in a first in vivo test phase on healthy volunteers, carrying out non-invasive, in vivo quantification of key tissue constituents (oxy- and deoxy-hemoglobin, water, lipids, collagen) and tissue micro-structure (scatterer size and density).
The in vitro and in vivo detection of visible photons from radioisotopes using optical techniques is a fast-growing field in molecular imaging. Tc 99m -pertechnetate is used as an alternative to I 123 in imaging of the thyroid and is generally imaged with gamma cameras or single photon emission tomography instruments. The uptake in the thyroid tissue is mediated by the sodium-iodide symporter (NIS), a glycoprotein that actively mediates iodide transport into the thyroid follicular cells and several extrathyroidal tissues. The luminescence of the gamma emitter Tc 99m -pertechnetate in order to visualize its biodistribution in healthy small living animals by using a commercial optical imaging system is investigated. Here we show that in Nu/Nu mice, the uptake of Tc 99m -pertechnetate in the thyroid gland and in salivary glands is very detectable by using radionuclide luminescence imaging. We also found light emission from the stomach in accordance with the literature. The localization of the light signals in the anatomical regions where the radiopharmaceutical is expected, confirmed by resections, shows that it is possible to image NIS-expressing tissues.
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