30 research outputs found
Retinal and choroidal oximetry using snapshot multispectral imaging
The principal aim of the research was to validate and develop a non-invasive multispectral imaging technique of measuring oxygen saturation in retinal and choroidal vasculature. The Image replicating imaging spectrometer (IRIS) snapshot multispectral fundus camera used for retinal imaging, and image analysis protocols used to perform oximetry are described.
In vitro and in vivo validation of oximetry techniques was performed. For in vitro validation an artificial eye containing blood at varying oxygenation was used. For in vivo validation the pig was used as an animal model. The calculated oxygen saturation was compared to blood gas analysis (gold standard) results and was found to be in close agreement.
Retinal oximetry was performed on healthy human subjects. The average oxygen saturation value (± SD) for retinal arterioles and venules were 96.08% ± 1.9% and 68.04% ± 2.1%, respectively.
The application of retinal oximetry technique was explored by conducting human hypoxia trials, in which the effect of acute mild hypoxia on retinal oxygenation and autoregulation was assessed on healthy human subjects. Hypoxic exposure resulted in a decline in both retinal arterial and venous saturation, as well as a significant increase in retinal vessel calibre, suggesting an autoregulatory response.
This thesis also explored the possibility of exploiting fundus reflections to measure the choroidal oxygenation non-invasively. Fundus reflection intensity at two wavelengths, 780 nm and 800 nm (oxygen sensitive and isosbestic) were used to calculate intensity ratio (R), which is directly proportional to the blood oxygenation. A pilot study on 10 healthy humans was conducted. Fundus reflection was recorded at room air (normoxia) and 15% inspired oxygen (mild hypoxia). A significant reduction (P < 0.001) in intensity ratio was observed during hypoxia
Deconvolution and Restoration of Optical Endomicroscopy Images
Optical endomicroscopy (OEM) is an emerging technology platform with
preclinical and clinical imaging applications. Pulmonary OEM via fibre bundles
has the potential to provide in vivo, in situ molecular signatures of disease
such as infection and inflammation. However, enhancing the quality of data
acquired by this technique for better visualization and subsequent analysis
remains a challenging problem. Cross coupling between fiber cores and sparse
sampling by imaging fiber bundles are the main reasons for image degradation,
and poor detection performance (i.e., inflammation, bacteria, etc.). In this
work, we address the problem of deconvolution and restoration of OEM data. We
propose a hierarchical Bayesian model to solve this problem and compare three
estimation algorithms to exploit the resulting joint posterior distribution.
The first method is based on Markov chain Monte Carlo (MCMC) methods, however,
it exhibits a relatively long computational time. The second and third
algorithms deal with this issue and are based on a variational Bayes (VB)
approach and an alternating direction method of multipliers (ADMM) algorithm
respectively. Results on both synthetic and real datasets illustrate the
effectiveness of the proposed methods for restoration of OEM images
Controlled core-to-core photo-polymerisation – fabrication of an optical fibre-based pH sensor
The fabrication of fluorescence-based pH sensors, embedded into etched pits of an optical fibre via highly controllable and spatially selective photo-polymerisation is described and the sensors validated.</p
Fibre-based ratiometric fluorescence imaging for contrast enhancement of spectrally similar signals in the lung
Remote sensing of blood oxygenation using red-eye pupil reflection
To access publisher's full text version of this article click on the hyperlink belowObjective: To develop a technique for remote sensing of systemic blood oxygenation using red-eye pupil reflection.
Approach: The ratio of the intensities of light from the bright pupil reflections at oxygen sensitive and isosbestic wavelengths is shown to be sensitive to the oxygenation of blood in the eye. A conventional retinal camera, fitted with an image-replicating imaging spectrometer, was used at standoff range to record snapshot spectral images of the face and eyes at eight different wavelengths. In our pilot study we measured optical-density ratios (ODRs) of pupil reflections at wavelengths of 780 nm and 800 nm, simultaneous with pulse oximetry, for ten healthy human subjects under conditions of normoxia and mild hypoxia (15% oxygen). The low absorption at these infrared wavelengths localises the sensing to the choroid. We propose that this can be used for as a proxy for systemic oximetry.
Main results: A significant reduction (P < 0.001) in ODR of the pupil images was observed during hypoxia and returned to baseline on resumption of normoxia. We demonstrate that measurement of the choroidal ODR can be used to detect changes in blood oxygenation that correlate positively with pulse oximetry and with a noise-equivalent oximetry precision of 0.5%.
Significance: We describe a new method to remotely and non-invasively sense the oxygen saturation of choroidal blood. The methodology provides a proxy for remote sensing of cerebral and systemic blood oxygenation. We demonstrate the technique at short range but it has potential for systemic oximetry at large standoff ranges
Molecular detection of Gram-positive bacteria in the human lung through an optical fiber–based endoscope
High fidelity fibre-based physiological sensing deep in tissue
Physiological sensing deep in tissue, remains a clinical challenge. Here a
flexible miniaturised sensing optrode providing a platform to perform minimally
invasive in vivo in situ measurements is reported. Silica microspheres
covalently coupled with a high density of ratiometrically configured
fluorophores were deposited into etched pits on the distal end of a 150 micron
diameter multicore optical fibre. With this platform, multiplexed photonic
measurements of pH and oxygen concentration with high precision in the distal
alveolar space of the lung is reported. We demonstrated the phenomenon that
high-density deposition of carboxyfluorescein covalently coupled to silica
microspheres shows an inverse shift in fluorescence in response to varying pH.
This platform delivered fast and accurate measurements, near instantaneous
response time, no photobleaching, immunity to power fluctuations and a flexible
architecture for addition of multiple sensors
Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo
Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level