129 research outputs found
Laser doppler vibrometry for cardiovascular monitoring and photoacoustic imaging
Nowadays, techniques for health monitoring mainly require physical contact with patients, which is not
always ideal. Non-contact health monitoring has become an important research topic in the last decades.
The non-contact detection of a patient's health condition represents a beneficial tool in different
biomedical fields. Examples can be found in intensive care, home health care, the nursing of the elderly,
the monitoring of physical efforts, and in human-machine interactions. Cardiovascular diseases (CV)
are one of the most spread causes of death in developed countries. Their monitoring techniques involve
physical contact with patients. A non-contact technique for cardiovascular monitoring could overcome
problems related to the contact with the patient such as skin lesions. It could also expand the availability
of monitoring to those cases where contact is not possible or should be avoided to reduce the exposure
of medical personnel to biochemical hazard conditions.Several research groups have investigated
different techniques for non-contact monitoring of health; among them, the laser Doppler Vibrometry
(LDVy) has one of the highest accuracies and signal to noise ratios for cardiorespiratory signals
detection. Moreover, the simplicity of data processing, the long-distance measurement range, and the
high bandwidth make the laser Doppler vibrometer (LDV) suitable for daily measurements.
LDVy is an interferometric technique employed for the measurements of displacement or velocity
signals in various fields. In particular, it is deployed in the biomedical field for the extraction of several
cardiovascular parameters, such as the PR-time. Generally, the extraction of these parameters requires
ideal measuring conditions (measuring spot and laser direction), which are not realistic for daily
monitoring in non-laboratory conditions, and especially in tracking applications.
The first scientific hypothesis of this work is that the PR-time detected with LDV has an acceptable
uncertainty for a realistic variety of measurement spot positions and angles of the incident laser beam.
Therefore, I investigated the uncertainty contribution to the detection of the PR-time from LDV signals
resulting from the laser beam direction and from the measurement point position; these investigations
were carried out with a multipoint laser Doppler vibrometer. The uncertainties were evaluated according
to the Guide to the Expression of Uncertainty in Measurement. Successively, the ranges of PR-time
values where it is possible to state with 95% certainty that a diagnosis is correct are identified. Normal
values of PR-time are included in the range 120 ms -200 ms. For single value measurements with precise
alignment the reliable range for the detection of the healthy condition is 146.4 ms -173.6 ms. The
detection of CV diseases is reliable for measured values lower than 93.6 ms and greater than 226.4 ms.
For mean value measurements with precise alignment the reliable range for the detection of the healthy
condition is 126.6 ms -193.4 ms. The detection of CV diseases is reliable for measured values lower
than 113.4 ms and greater than 206.6 ms. Therefore, for measured values included in the mentioned
ranges, the detection of the PR-time and relative diagnosis with the LDVy in non-laboratory conditions
is reliable. The method for the estimation of the uncertainty contribution proposed in this work can be
applied to other cardiovascular parameters extracted with the LDVy.
Recently, the LDVy was employed for the detection of tumors in tissue-mimic phantoms as a noncontact alternative to the ultrasound sensors employed in photoacoustic imaging (PAI). A non-contact
method has considerable advantages for photoacustic imaging, too.
Several works present the possibility to perform PAI measurements with LDVy. However, a successful
detection of the signals generated by a tumor depends on the metrological characteristics of the LDV,
on the properties of the tumor and of the tissue. The conditions under which a tumor is detectable with
the laser Doppler vibrometer has not been investigated yet.
The second scientific hypothesis of this work is that, under certain conditions, photoacoustic imaging
measurements with LDVy are feasible. Therefore, I identified those conditions to determine the
detection limits of LDVy for PAI measurements. These limits were deduced by considering the
metrological characteristics of a commercial LDV, the dimensions and the position of the tumor in the
tissue. I derived a model for the generation and propagation of PA signals and its detection with an LDV.
The model was validated by performing experiments on silicone tissue-micking phantoms. The
validated model with breast-tissue parameters reveals the limits of tumor detection with LDVy-based
PAI. The results show that commercial LDVs can detect tumors with a minimal radius of ≈350 μm
reliably if they are located at a maximal depth in tissue of ≈2 cm.
Depending on the position of the detection point, the maximal depth can diminish and depending on the
absorption characteristics of the tumor, the detection range increases.Heutzutage erfordern Techniken zur Gesundheitsüberwachung hauptsächlich den physischen Kontakt
mit dem Patienten, was nicht immer ideal ist. Die berührungslose Gesundheitsüberwachung hat sich in
den letzten Jahrzehnten zu einem wichtigen Forschungsthema entwickelt. Die berührungslose
Erkennung des Gesundheitszustands eines Patienten stellt ein nützliches Instrument in verschiedenen
biomedizinischen Bereichen dar. Beispiele finden sich in der Intensivpflege, der häuslichen
Krankenpflege, der Altenpflege, der Überwachung körperlicher Anstrengungen und in der MenschMaschine-Interaktion. Herz-Kreislauf-Erkrankungen sind eine der am weitesten verbreiteten
Todesursachen in den Industrieländern. Ihre Überwachungstechniken erfordern einen physischen
Kontakt mit den Patienten. Eine berührungslose Technik für die Überwachung von Herz-KreislaufErkrankungen könnte Probleme im Zusammenhang mit dem Kontakt mit dem Patienten, wie z. B.
Hautverletzungen, überwinden. Verschiedene Messgeräte wurden für die berührungslose Überwachung
der Gesundheit untersucht; unter ihnen hat das Laser-Doppler-Vibrometrer (LDV) eine der höchsten
Genauigkeiten und Signal-Rausch-Verhältnisse für die Erkennung kardiorespiratorischer Signale.
Darüber hinaus ist das Laser-Doppler-Vibrometer (LDV) aufgrund der einfachen Datenverarbeitung,
des großen Messbereichs und der hohen Bandbreite für tägliche Messungen geeignet. LDV ist ein
interferometrisches Verfahren, das zur Messung von Weg- oder Geschwindigkeitssignalen in
verschiedenen Bereichen eingesetzt wird. Insbesondere wird es im biomedizinischen Bereich für die
Extraktion verschiedener kardiovaskulärer Parameter, wie z. B. der PR-Zeit, eingesetzt. Im Allgemeinen
erfordert die Extraktion dieser Parameter ideale Messbedingungen (Messfleck und Laserrichtung), die
für die tägliche Überwachung unter Nicht-Laborbedingungen und insbesondere für TrackingAnwendungen nicht realistisch sind.
Die erste wissenschaftliche Hypothese dieser Arbeit ist, dass die mit dem LDV ermittelte PR-Zeit eine
akzeptable Unsicherheit für eine realistische Vielzahl von Messpunktpositionen und Winkeln des
einfallenden Laserstrahls aufweist. Daher wurde der Unsicherheitsbeitrag zur Ermittlung der PR-Zeit
aus LDV-Signalen untersucht, der sich aus der Laserstrahlrichtung und der Messpunktposition ergibt;
diese Untersuchungen wurden mit einem Mehrpunkt-Laser-Doppler-Vibrometer durchgeführt. Die
Unsicherheiten wurden gemäß der Technische Regel ISO/IEC Guide 98-3:2008-09 Messunsicherheit –
Teil 3: Leitfaden zur Angabe der Unsicherheit beim Messen bewertet. Nacheinander werden die
Bereiche der PR-Zeit-Werte ermittelt, in denen mit 95%iger Sicherheit eine korrekte Diagnose gestellt
werden kann. Die in dieser Arbeit vorgeschlagene Methode zur Schätzung des Unsicherheitsbeitrags
kann auch auf andere kardiovaskuläre Parameter angewendet werden, die mit dem LDV extrahiert
werden.
Kürzlich wurde das LDV zur Erkennung von Tumoren in gewebeähnlichen Phantomen als
berührungslose Alternative zu den Ultraschallsensoren eingesetzt, die bei der photoakustischen
Bildgebung (PAI) verwendet werden. Eine berührungslose Methode hat auch für die photoakustische
Bildgebung erhebliche Vorteile. In mehreren Arbeiten wird die Möglichkeit vorgestellt, PAIMessungen mit LDV durchzuführen. Die erfolgreiche Erkennung der von einem Tumor erzeugten
Signale hängt jedoch von den messtechnischen Eigenschaften des LDV sowie von den Eigenschaften
des Tumors und des Gewebes ab. Die Bedingungen, unter denen ein Tumor mit dem LDV detektierbar
ist, wurden bisher nicht untersucht.
Die zweite wissenschaftliche Hypothese dieser Arbeit ist, dass unter bestimmten Bedingungen
photoakustische Bildgebungsmessungen mit dem LDV möglich sind. Daher wurden diese Bedingungen
ermittelt, um die Nachweisgrenzen von LDV für PAI-Messungen zu bestimmen. Diese Grenzen wurden
unter Berücksichtigung der messtechnischen Eigenschaften eines handelsüblichen LDV, der
Abmessungen und der Position des Tumors im Gewebe abgeleitet. In dieser Arbeit wurde ein Modell
für die Erzeugung und Ausbreitung von PA-Signalen und deren Nachweis mit einem LDV abgeleitet.
Das Modell wurde durch Experimente an Silikongewebe-Phantomen validiert. Das validierte Modell
mit Parametern des Brustgewebes zeigt die Grenzen der Tumorerkennung mit LDV-basierter PAI auf.
Die Ergebnisse zeigen, dass kommerzielle LDV Tumore mit einem minimalen Radius von ≈350 μm
zuverlässig erkennen können
Equal Protection and the Male Gaze: An Approach to \u3cem\u3eNew Hampshire v. Lilley\u3c/em\u3e
This Article uses New Hampshire v. Lilley, a case recently decided by the New Hampshire Supreme Court, as a starting point for an equal protection analysis of indecent exposure laws that distinguish between women and men. After discussing contemporary equal protection jurisprudence and historicizing these laws, this Article uses the film theorist Laura Mulvey\u27s concept of the male gaze to demonstrate how overbroad generalizations about sex and sexuality serve as the foundation for this legal distinction. This Article concludes by emphasizing that municipalities and states may continue to enact and enforce indecent exposure laws that reflect community standards, so long as they apply equally to women and men
A Matter for Interpretation: An Inquiry into Confederate Symbolism and the Florida State Flag
Are the red bars found on Florida’s state flag a remnant of early twentieth-century nostalgia for the Confederacy? Who first proposed this design and why? What did this change mean to the citizens who witnessed it? This Article is an attempt to answer these questions by approaching them through the lenses of original intent and original meaning. In doing so, the Authors advance new strategies for decision-makers interested in uncovering the motives of those who first erected or affixed allegedly Confederate monuments and symbols
Model validation and prediction of photoacoustic tumor detection with LDV
Photoacoustic (PA) imaging enables the detection of tumors with ultrasound sensors. A laser Doppler vibrometer (LDV) measures sound waves without contact and may enable non-contact PA imaging (PAI). A successful acquisition with LDV of the PA-signals generated by a tumor irradiated by a pulsed laser depends on several factors: the metrological characteristics of the LDV, the characteristics of the laser pulse as well as the properties of the tumor and of the tissue. In this work, we prove with experiments on tissue-mimicking phantoms the validity of a simulation model based on prior work. We use the validated model to simulate the photoacoustic tumor detection with LDV. Subsequently, we estimate the photoacoustic tumor detection capabilities of a self-designed LDV with the validated model. We derive the limits for the minimal detectable size of tumors for a given depth in tissue. The smallest inclusion detected with our LDV-system on a tissue-mimicking phantom was a sphere with a radius of 200 μm at a depth of 14 mm. With our experimentally validated model, we have predicted the possibility to detect an inclusion in breast tissue with a radius up to approximately 300 μm at a depth of 22 mm
The influence of Al: Nb ratio on the microstructure and mechanical response of quaternary Ni-Cr-Al-Nb alloys
The influence of Al:Nb ratio on the microstructure and properties of Ni–Cr–Al–Nb alloys has been investigated following long-term exposure at elevated temperatures. The γ′ volume fraction, size and lattice misfit were seen to increase with a larger Al:Nb ratio, although these changes resulted in reduced hardness. The change in the critical resolved shear stress (CRSS) associated with strong dislocation coupling was determined to be the dominant strengthening mechanism and increased with decreasing Al:Nb ratio. A distribution of tertiary γ′ was observed to be necessary in maximising the mechanical properties of these alloys.This work was supported by the EPSRC/Rolls-Royce Strategic Partnership (EP/H022309/1 and EP/H500375/1).This is the final published version, which can also be found on the Elsevier website at: http://www.sciencedirect.com/science/article/pii/S0921509314007369
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