28 research outputs found
Machine learning algorithm development of SPO2 sensor for improved robustness in wearables
Wearable devices application in the digital measurement of health has gained attention by
researchers. These devices allow for data acquisition during real-life activities, resulting
in higher data availability. They often include photoplethysmography (PPG) sensors, the
sensor behind pulse oximetry. Pulse oximetry is a non-invasive method for continuous
oxygen saturation (SpO2) measurements, a standard monitor for anesthesia procedures,
an essential tool for managing patients undergoing pulmonary rehabilitation and an
effective method for assessing sleep-disordered breathing. However, the current market
focuses on heart rate measurements and lacks the robustness of clinical applications
for SpO2 assessment. In addition, the most common obstacle in PPG measurements
is the signal quality, especially in the form of motion artifacts. Thus, this work aims
at increasing the clinical robustness in this devices by evaluating its quality and then
extracting relevant metrics.
Firstly, a data acquisition protocol was developed, focused on acquiring data during
daily activities. This resulted in a dataset with different signal qualities, which was manually
annotated to be used as the base for the Machine Learning models. A second protocol
was also developed especially designed for the extraction of the SpO2 measurement.
Several Machine Learning models were developed to evaluate the signal in three distinct
qualities (corrupted, suboptimal, optimal) in real time. A Random Forest classifier
achieved accuracies of 79% and 80% for the binary models capable of differentiating between
usable and unusable signals, and accuracies of 74% and 80% when distinguishing
between optimal and suboptimal signals, for the two utilized channels. The multi-class
models achieved accuracies of 66% and 65% for the two utilized channels.
Three clinically relevant metrics were also extracted from the PPG signal: heart rate,
respiratory rate and SpO2. The heart rate and respiratory rate algorithms resulted in performances
similar to the ones found in the literature and in other devices currently on the
market. However, while promising, more data is needed to reach statistical significance
for the SpO2 measurement.A monitorização do estado de saúde de pacientes em ambulatório utilizando dispositivos
wearables tem vindo a ser cada vez mais investigada. Estes dispositivos permitem uma
aquisição de dados durante o dia a dia, resultando num maior conjunto de dados. Frequentemente,
estes dispositivos incluem fotopletismógrafos (PPG), o sensor por detrás da
oximetria de pulso. A oximetria de pulso é um método não invasivo para a medição da
saturação de oxigénio no sangue (SpO2) de forma contÃnua. É um equipamento padrão
para procedimentos com anestesia, uma ferramenta essencial para monitorizar pacientes
em reabilitação pulmonar e um método eficaz para avaliar respiração desordenada do
sono. Ainda assim, o mercado atual foca-se principalmente em medições da frequência
cardÃaca e carece robustez para aplicações clÃnicas da medição de SpO2. Para além disso,
o obstáculo mais comum em medições com PPG é a qualidade do sinal. Consequentemente,
este trabalho procura melhorar a robustez clÃnica destes dispositivos analisando a
qualidade do sinal e, posteriormente, extrair métricas relevantes.
Primeiramente, foi desenvolvido um protocolo para aquisição de dados de atividades
do dia a dia. Assim, foram adquiridos dados com diferentes qualidades, que foram avaliados
manualmente de forma a servir de base para os vários modelos de Machine Learning.
Também foi desenvolvido um segundo protocolo para a extração do valor de SpO2.
Diferentes modelos de Machine Learning foram desenvolvidos para avaliar em tempo
real a qualidade do sinal em três qualidades (corrompido, subótimo, ótimo) . Um classificador
baseado em Random Forest atingiu exatidões de 79% e 80% em classificadores
binários capazes de distinguir entre sinais úteis e inúteis, e exatidões de 74% e 80% a diferenciar
entre um sinal subótimo e ótimo, para os dois canais usados. Os classificadores
multi-classe atingiram exatidões de 66% e 65% para os dois canais usados.
Três medidas clinicamente relevantes foram também extraÃdas do sinal de PPG: frequências
cardÃaca e respiratória, cujos algoritmos atingiram resultados semelhantes aos encontrados
na literatura e em aparelhos no mercado, e SpO2 que, ainda que promissores, mais
dados seriam necessários para os resultados serem estatisticamente significativo
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Investigation of fontanelle photoplethysmographs and oxygen saturations in intensive care neonates and infants utilising miniature photometric sensors
In children and newborn babies on intensive care, information regarding blood oxygen saturation (SpO2) is determined non-invasively by a device called a pulse oximeter. Sensors are usually placed on a hand or foot where their operation relies on the presence of pulsatile arterial blood. Light shines at two or more wavelengths (usually red and infrared) into the tissue where the pulsatile blood modulates, absorbs and scatters the different wavelengths of light in varying amounts and is detected by a photo-detector as a photoplethysmograph (PPG). The spectral information received is then processed electronically and digitally to determine the amount of haemoglobin present.
In the sickest of children blood supply can become compromised to these sensor locations and the pulsatile component of the blood may diminish and pulse oximeter readings may become unreliable, especially at times when accurate blood oxygen information would be vital. Currently the alternative is to take blood from an arterial line and run a relatively lengthy analysis (pulse oximeters are near-instantaneous in their operation) that may be unnecessary if the pulse oximeter could be relied upon at these critical moments. In the smallest of babies invasive sampling of blood becomes even more of an issue as any blood loss could lead to hypovolaemia and introduce extra sites of infection plus it causes a lot of stress to the neonate.
Since central blood flow may be preferentially preserved, the anterior fontanelle was investigated as an alternative monitoring site. Custom reflectance fontanelle and reference PPG sensors have been designed and built to investigate the fontanelle in those children at risk of peripheral supply compromise. Dedicated instrumentation and software has also been successfully developed for the control of the sensor electronics and the data-logging of PPG signals for retrospective analysis.
Sixteen neonates were recruited for fontanelle monitoring; all were ASA 1 – 3 (ASA ranges from 1 to 5 where 1 is the least sick and 5 is the most critically ill). As part of the approved protocol the delivered oxygen to the patients was artificially altered to look for corresponding changes in PPG signal amplitudes. Amplitude results reveal strong correlations (R > 0.5) between the reference sensor (placed on the foot) and the fontanelle sensor. This suggests that the fontanelle sensor is sensitive to changes in amplitude when oxygen in the blood alters. Correlation of the health of the child, using the ASA score, and the difference in amplitudes of PPGs between the sensors reveals that the fontanelle sensor does detect increasing fontanelle PPG amplitudes when compared to the PPGs from the reference sensor the sicker the child is, confirming that pulsatile flow is being preferentially preserved at the fontanelle in those children who are the most at risk from peripheral supply compromise. SpO2 estimation at the fontanelle reveals a mean difference of 2.2 % to the SpO2 as read by the commercial device and a 1.7 % difference to the blood gas results. These results confirm that the anterior fontanelle may be used as an alternative location for SpO2 measurement in those who are at most risk of peripheral supply compromise
On-Chip Integrated Functional Near Infra-Red Spectroscopy (fNIRS) Photoreceiver for Portable Brain Imaging
RÉSUMÉ
L'imagerie cérébrale fonctionnelle utilisant la Spectroscopie Fonctionnelle Proche-Infrarouge (SFPI)
propose un outil portatif et non invasif de surveillance de l'oxygénation du sang. SFPI est une technique de
haute résolution temporelle non invasive, sûr, peu intrusive en temps réel et pour l'imagerie cérébrale Ã
long terme. Il permet de détecter des signaux hémodynamiques à la fois rapides et neuronaux ou lents. Outre les avantages importants des systèmes SFPI, ils souffrent encore de quelques inconvénients,
notamment d’une faible résolution spatiale, d’un bruit de niveau modérément élevé et d’une grande
sensibilité au mouvement. Afin de surmonter les limites des systèmes actuellement disponibles de SFPI non-portables, dans cette thèse, nous en avons introduit une nouvelle de faible puissance, miniaturisée sur une puce photodétecteur frontal destinée à des systèmes de SFPI portables. Elle contient du silicium
photodiode à avalanche (SiAPD), un amplificateur de transimpédance (TIA), et « Quench-Reset », circuits
mis en oeuvre en utilisant les technologies CMOS standards pour fonctionner dans les deux modes :
linéaire et Geiger. Ainsi, elle peut être appliquée pour les deux fNIRS : en onde continue (CW- SFPI) et
pour des applications de comptage de photon unique. Plusieurs SiAPDs ont été mises en oeuvre dans de nouvelles structures et formes (rectangulaires, octogonales, double APDs, imbriquées, netted, quadratiques et hexadecagonal) en utilisant différentes techniques de prévention de la dégradation de bord
prématurée. Les principales caractéristiques des SiAPDs sont validées et l'impact de chaque paramètre ainsi que les simulateurs de l'appareil (TCAD, COMSOL, etc) ont été étudiés sur la base de la simulation et de mesure des résultats. Proposées SiAPDs techniques d'exposition avec un gain de grande avalanche,
tension faible ventilation et une grande efficacité de détection des photons dans plus de faibles taux de comptage sombres. Trois nouveaux produits à haut gain, bande passante (GBW) et à faible bruit TIA sont introduits basés sur le concept de gain distribué, d’amplificateur logarithmique et sur le rejet automatique
du bruit pour être appliqué en mode de fonctionnement linéaire. Le TIA proposé offre une faible consommation, un gain de haute transimpédance, une bande passante ajustable et un très faible bruit
d'entrée et de sortie. Le nouveau circuit mixte trempe-reset (MQC) et un MQC contrôlable (CMQC)
frontaux offrent une faible puissance, une haute vitesse de comptage de photons avec un commandable de
temps de hold-off et temps de réinitialiser. La première intégration sur puce de SiAPDs avec TIA et Photon circuit de comptage a été démontrée et montre une amélioration de l'efficacité de la
photodétection, spécialement en ce qui concerne la sensibilité, la consommation d'énergie et le rapport signal sur bruit.----------ABSTRACT
Optical brain imaging using functional near infra-red spectroscopy (fNIRS) offers a direct and
noninvasive tool for monitoring of blood oxygenation. fNIRS is a noninvasive, safe, minimally
intrusive, and high temporal-resolution technique for real-time and long-term brain imaging. It allows detecting both fast-neuronal and slow-hemodynamic signals. Besides the significant
advantages of fNIRS systems, they still suffer from few drawbacks including low spatial-
resolution, moderately high-level noise and high-sensitivity to movement. In order to overcome
the limitations of currently available non-portable fNIRS systems, we have introduced a new
low-power, miniaturized on-chip photodetector front-end intended for portable fNIRS systems. It
includes silicon avalanche photodiode (SiAPD), Transimpedance amplifier (TIA), and Quench-
Reset circuitry implemented using standard CMOS technologies to operate in both linear and
Geiger modes. So it can be applied for both continuous-wave fNIRS (CW-fNIRS) and also
single-photon counting applications. Several SiAPDs have been implemented in novel structures
and shapes (Rectangular, Octagonal, Dual, Nested, Netted, Quadratic and Hexadecagonal) using
different premature edge breakdown prevention techniques. The main characteristics of the
SiAPDs are validated and the impact of each parameter and the device simulators (TCAD,
COMSOL, etc.) have been studied based on the simulation and measurement results. Proposed
techniques exhibit SiAPDs with high avalanche-gain (up to 119), low breakdown-voltage (around
12V) and high photon-detection efficiency (up to 72% in NIR region) in additional to a low dark-
count rate (down to 30Hz at 1V excess bias voltage). Three new high gain-bandwidth product
(GBW) and low-noise TIAs are introduced and implemented based on distributed-gain concept,
logarithmic-amplification and automatic noise-rejection and have been applied in linear-mode of operation. The implemented TIAs offer a power-consumption around 0.4 mW, transimpedance gain of 169 dBΩ, and input-output current/voltage noises in fA/pV range accompanied with ability to tune the gain, bandwidth and power-consumption in a wide range. The implemented
mixed quench-reset circuit (MQC) and controllable MQC (CMQC) front-ends offer a quenchtime of 10ns, a maximum power-consumption of 0.4 mW, with a controllable hold-off and resettimes. The on-chip integration of SiAPDs with TIA and photon-counting circuitries has been demonstrated showing improvement of the photodetection-efficiency, specially regarding to the
sensitivity, power-consumption and signal-to-noise ratio (SNR) characteristics
Investigation of fontanelle photoplethysmographs and oxygen saturations in intensive care neonates and infants utilising miniature photometric sensors
In children and newborn babies on intensive care, information regarding blood oxygen saturation (SpO2) is determined non-invasively by a device called a pulse oximeter. Sensors are usually placed on a hand or foot where their operation relies on the presence of pulsatile arterial blood. Light shines at two or more wavelengths (usually red and infrared) into the tissue where the pulsatile blood modulates, absorbs and scatters the different wavelengths of light in varying amounts and is detected by a photo-detector as a photoplethysmograph (PPG). The spectral information received is then processed electronically and digitally to determine the amount of haemoglobin present. In the sickest of children blood supply can become compromised to these sensor locations and the pulsatile component of the blood may diminish and pulse oximeter readings may become unreliable, especially at times when accurate blood oxygen information would be vital. Currently the alternative is to take blood from an arterial line and run a relatively lengthy analysis (pulse oximeters are near-instantaneous in their operation) that may be unnecessary if the pulse oximeter could be relied upon at these critical moments. In the smallest of babies invasive sampling of blood becomes even more of an issue as any blood loss could lead to hypovolaemia and introduce extra sites of infection plus it causes a lot of stress to the neonate. Since central blood flow may be preferentially preserved, the anterior fontanelle was investigated as an alternative monitoring site. Custom reflectance fontanelle and reference PPG sensors have been designed and built to investigate the fontanelle in those children at risk of peripheral supply compromise. Dedicated instrumentation and software has also been successfully developed for the control of the sensor electronics and the data-logging of PPG signals for retrospective analysis. Sixteen neonates were recruited for fontanelle monitoring; all were ASA 1 – 3 (ASA ranges from 1 to 5 where 1 is the least sick and 5 is the most critically ill). As part of the approved protocol the delivered oxygen to the patients was artificially altered to look for corresponding changes in PPG signal amplitudes. Amplitude results reveal strong correlations (R > 0.5) between the reference sensor (placed on the foot) and the fontanelle sensor. This suggests that the fontanelle sensor is sensitive to changes in amplitude when oxygen in the blood alters. Correlation of the health of the child, using the ASA score, and the difference in amplitudes of PPGs between the sensors reveals that the fontanelle sensor does detect increasing fontanelle PPG amplitudes when compared to the PPGs from the reference sensor the sicker the child is, confirming that pulsatile flow is being preferentially preserved at the fontanelle in those children who are the most at risk from peripheral supply compromise. SpO2 estimation at the fontanelle reveals a mean difference of 2.2 % to the SpO2 as read by the commercial device and a 1.7 % difference to the blood gas results. These results confirm that the anterior fontanelle may be used as an alternative location for SpO2 measurement in those who are at most risk of peripheral supply compromise.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 06)
For abstract, see N75-20149
Pulse Oximetry using a Buried Quad Junction Photodetector
International audienceTraditional pulse oximeters rely on the use of red and infrared LEDs and a photodiode for measuring transmittance between tissues and estimate the functional oxygen saturation. Currently, studies are being made for the development of multiwavelength pulse oximeters in order to increase accuracy and to estimate the presence of other compounds such as carboxyhemoglobin or methemoglobin. The purpose of this work is the characterization and implementation of a pulse oximeter with a Buried Quad Junction photodetector (BQJ), which can reduce both: the number of photodetectors and the area needed for multiwavelength pulse oximetry. With this type of photodetector, it is also possible to continuously estimate oxygen saturation without the need of pulsating LED
NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 42)
A subject index is provided for over 4900 patents and patent applications for the period May 1969 through December 1992. Additional indexes list personal authors, corporate authors, contract numbers, NASA case numbers, U.S. patent class numbers, U.S. patent numbers, and NASA accession numbers
NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 46)
A subject index is provided for over 5600 patents and patent applications for the period May 1969 through December 1994. Additional indexes list personal authors, corporate authors, contract numbers, NASA case numbers, U.S. patent class numbers, U.S. patent numbers, and NASA accession numbers
NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 23)
Entries for 4000 patent and patent applications citations for the period May 1969 through June 1983 are listed. Subject, invention, source, number, and accession number indexes are included