In vivo oximetry of human bulbar conjunctival and episcleral microvasculature using snapshot multispectral imaging

A retinal-fundus camera fitted with a custom Image-Replicating Imaging Spectrometer was used to image the bulbar conjunctival and episcleral microvasculature in ten healthy human subjects at normoxia (21% Fraction of Inspired Oxygen [FiO2]) and acute mild hypoxia (15% FiO2) conditions. Eyelid closure was used to control oxygen diffusion between ambient air and the sclera surface. Four subjects were imaged for 30 seconds immediately following eyelid opening. Vessel diameter and Optical Density Ratio (ODR: a direct proxy for oxygen saturation) of vessels was computed automatically. Oximetry capability was validated using a simple phantom that mimicked the scleral vasculature. Acute mild hypoxia resulted in a decrease in blood oxygen saturation (SO2) (i.e. an increase in ODR) when compared with normoxia in both bulbar conjunctival (p < 0.001) and episcleral vessels (p = 0.03). Average episcleral diameter increased from 78.9 ± 8.7 μm (mean ± standard deviation) at normoxia to 97.6 ± 14.3 μm at hypoxia (p = 0.02). Diameters of bulbar conjunctival vessels showed no significant change from 80.1 ± 7.6 μm at normoxia to 80.6 ± 7.0 μm at hypoxia (p = 0.89). When exposed to ambient air, hypoxic bulbar conjunctival vessels rapidly reoxygenated due to oxygen diffusion from ambient air. Reoxygenation occured in an exponential manner, and SO2 reached normoxia baseline levels. The average ½ time to full reoxygenation was 3.4 ± 1.4 s. As a consequence of oxygen diffusion, bulbar conjunctival vessels will be highly oxygenated (i.e. close to 100% SO2) when exposed to ambient air. Episcleral vessels were not observed to undergo any significant oxygen diffusion, instead behaving similarly to pulse oximetry measurements. This is the first study to the image oxygen dynamics of bulbar conjunctival and episcleral microvasculature, and consequently, the first study to directly observe the rapid reoxygenation of hypoxic bulbar conjunctival vessels when exposed to ambient air. Oximetry of bulbar conjunctival vessels could potentially provide insight into conditions where oxygen dynamics of the microvasculature are not fully understood, such as diabetes, sickle-cell diseases, and dry-eye syndrome. Oximetry in the bulbar conjunctival and episcleral microvasculature could be complimentary or alternative to retinal oximetry

Infrared face recognition: a comprehensive review of methodologies and databases

Automatic face recognition is an area with immense practical potential which includes a wide range of commercial and law enforcement applications. Hence it is unsurprising that it continues to be one of the most active research areas of computer vision. Even after over three decades of intense research, the state-of-the-art in face recognition continues to improve, benefitting from advances in a range of different research fields such as image processing, pattern recognition, computer graphics, and physiology. Systems based on visible spectrum images, the most researched face recognition modality, have reached a significant level of maturity with some practical success. However, they continue to face challenges in the presence of illumination, pose and expression changes, as well as facial disguises, all of which can significantly decrease recognition accuracy. Amongst various approaches which have been proposed in an attempt to overcome these limitations, the use of infrared (IR) imaging has emerged as a particularly promising research direction. This paper presents a comprehensive and timely review of the literature on this subject. Our key contributions are: (i) a summary of the inherent properties of infrared imaging which makes this modality promising in the context of face recognition, (ii) a systematic review of the most influential approaches, with a focus on emerging common trends as well as key differences between alternative methodologies, (iii) a description of the main databases of infrared facial images available to the researcher, and lastly (iv) a discussion of the most promising avenues for future research.Comment: Pattern Recognition, 2014. arXiv admin note: substantial text overlap with arXiv:1306.160

In vivo microvascular oximetry using multispectral imaging

This thesis describes the application of multispectral imaging to several novel oximetry applications. Chapter 1 motivates optical microvascular oximetry, outlines oxygen transport in the body, describes the theory of oximetry, and describes the challenges associated with in vivo oximetry, in particular imaging through tissue. Chapter 2 reviews various imaging techniques for quantitative in vivo oximetry of the microvasculature, including multispectral and hyperspectral imaging, photoacoustic imaging, optical coherence tomography, and laser speckle techniques. Chapter 3 describes a two-wavelength oximetry study of two microvascular beds in the anterior segment of the eye: the bulbar conjunctival and episcleral microvasculature. This study reveals previously unseen oxygen diffusion from ambient air into the bulbar conjunctival microvasculature, altering the oxygen saturation of the bulbar conjunctiva. The response of the bulbar conjunctival and episcleral microvascular beds to acute mild hypoxia is quantified and the rate at which oxygen diffuses into bulbar conjunctival vessels is measured. Chapter 4 describes the development and application of a highly novel non-invasive retinal angiography technique: Oximetric Ratio Contrast Angiography (ORCA). ORCA requires only multispectral imaging and a small perturbation of blood oxygen saturation to produce angiographic sequences. A pilot study of ORCA in human subjects was conducted. This study demonstrates that ORCA can produce angiographic sequences with features such as sequential vessel filling and laminar flow. The application and challenges of ORCA are discussed, with emphasis on comparison with other angiography techniques, such as fluorescein angiography. Chapter 5 describes the development of a multispectral microscope for oximetry in the spinal cord dorsal vein of rats. Measurements of blood oxygen saturation are made in the dorsal vein of both healthy rats, and in rats with the Experimental autoimmune encephalomyelitis (EAE) disease model of multiple sclerosis. The venous blood oxygen saturation of EAE disease model rats was found to be significantly lower than that of healthy controls, indicating increased oxygen uptake from blood in the EAE disease model of multiple sclerosis. Chapter 6 describes the development of video-rate red eye oximetry; a technique which could enable stand-off oximetry of the blood-supply of the eye with high temporal resolution. The various challenges associated with video-rate red eye oximetry are investigated and their influence quantified. The eventual aim of this research is to track circulating deoxygenation perturbations as they arrive in both eyes, which could provide a screening method for carotid artery stenosis, which is major risk-factor for stroke. However, due to time constraints, it was not possible to thoroughly investigate if video-rate red eye can detect such perturbations. Directions and recommendations for future research are outlined

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

Snapshot multispectral oximetry using image replication and birefringent spectrometry

This thesis describes the improvements to the image replicating imaging spectrometer (IRIS) and the development of novel applications in the field of oximetry. IRIS is a snapshot multispectral device with a high transmission output and no need of inversion for data recovering, hence, with high signal-to-noise ratio (SNR). IRIS shows great versatility due to the possibility of choosing multiple contiguous or non-contiguous wavelengths inside its free spectral range. IRIS uses a set of waveplates and Wollaston prisms to demultiplex the spectral information of an object and replicate the image of such object in different wavelengths. The birefringent nature of IRIS means that different wavelengths are separated by the Wollaston prisms with different angles, introducing multiple images of the same object. In addition, the spectral transmission function shows multiple spectral sidelobes that contaminate each IRIS band with light belonging to other wavelengths. These issues can lower the performance of IRIS as a multispectral imaging device. In this thesis, these problems were assessed with the introduction of a filter plate array placed in the image plane of the optical system. This filter array is a set of narrow-band filters (Full Width Half Maximum (FWHM) =10 ± 2 nm ) that removes undesired wavelengths from each IRIS band. Since the spectral transmission of IRIS is replicated along the free spectral range, the filters can be designed to match any of the present spectral lobes in IRIS. The design and fabrication of a filter array enhance the performance of IRIS as a multispectral imaging device: it allows wavelength selection and improves spectral and spatial image quality. The design and manufacture of the corresponding filter holder and camera adapter were critical in terms of offering an easy filter-camera implementation. The filter plate allowed the removal of other dispersed wavelengths by the Wollaston prisms, improving image registration between the set of spectral images created by IRIS, and so, improving the quality of the registered spectral 3-D cube. The implemented improvements on IRIS allow high quality, calibration-free oximetry using eight different wavelengths optimised for oximetry. Two main experiments were performed: 1) Using an inverted microscopy interfaced with IRIS and a linear spectral unmixing technique, we measured the deoxygenation of single horse red blood cells (RBC) in vitro in real time. The oximetry was performed with a subcellular spatial resolution of 0.5 μ m , a temporal resolution of 30 Hz, and an accuracy (standard error of the mean) of ± 1.1% in oxygen saturation. 2) Eight-wavelength calibration-free retinal oximetry performed in nine healthy subjects demonstrated an increase in the stability of the oxygen saturation measurements along retinal vessels when compared with more traditional analysis methods such as two wavelengths oximetry. The stability was measured as the standard deviation along the retinal vessels of the nine subjects and was found to be ∼ 3% in oxygen saturation for eight-wavelengths oximetry and ∼ 5% in oxygen saturation for two-wavelengths oximetry. A modified physical model was used to improve the characterization of light propagation through the eye, retina, and blood vessels by applying a set of feasible physiological assumptions. This model was optimised by an algorithm which solves for the different variables involved in the retinal vessels transmissions in order to accurately calculate the oxygen saturation. The oximetry algorithm was applied in retinal vessels, in collaboration in vivo on rat spinal cord to assess hypoxia in inflammatory diseases such as multiple sclerosis and rheumatoid arthritis and on mice legs to assess hypoxia on autoimmune diseases. A third experiment using a microscope interfaced with IRIS was performed. The experiment aimed to replicate laminar flow conditions observed in retinal vessels and to calculate oxygen diffusion between adjacent streams of blood with different oxygen saturation. For this purpose a PDMS multichannel flow cell with cross sections of 40x100 μm was designed and fabricated allowing us to replicate conditions found in retinal blood vessels. Laminar flow was replicated but the experiment failed in calculating oxygen diffusion due to flaws in the experiment. The experiment with the results and recommendations on how to improve it can be found in Apendix B for future researcher

Retinal perfusion changes in radiation retinopathy-post brachytherapy for choroidal melanoma

Introduction: Radiation retinopathy (RR) is a chronic progressive vasculopathy developing secondary to the impact of ionizing radiation to the retina. RR develops post radiation therapy using radioactive plaque to treat intraocular tumors. It is not possible to predict which patients will develop RR. Changes in retinal blood oxygen saturation and blood flow could predict the future onset of RR, thereby facilitating the use of treatment such as intra-vitreal anti-vascular endothelial growth factor (VEGF). Methods: Chapter 3 and 4: Total retinal blood flow (TRBF) and retinal blood oxygen saturation (SO2) was non-invasively measured in eleven healthy human volunteers using a novel and exact provocation technique (RespirAct) that allows the precise control of the end-tidal partial pressure of oxygen (PETO2). Between-visits repeatability and within-visit variability of TRBF and SO2 measurements were assessed. Inner retinal oxygen delivery and consumption was calculated using Fick’s principle during stages of normoxia, hypoxia and hyperoxia. Chapter 5 and 6: Seventeen patients diagnosed with unilateral choroidal melanoma (CM) and eight patients who had developed unilateral ischemic RR were recruited from Ocular Oncology Clinic in the Princess Margaret Hospital, Toronto, Canada i.e. the only center all over Canada to treat CM patients with radiation therapy. The subjects underwent measurement of TRBF using a prototype methodology based upon Doppler Spectral Domain Optical Coherence Tomography (SD-OCT) and retinal vessel SO2 using a prototype Hyperspectral Retinal Camera (HRC), following pupil dilation with 1% tropicamide. In CM patients, the retinal hemodynamic parameters were studied in both eyes, before, 3months and 6months post 125Iodine plaque brachytherapy treatment. For RR patients, the measurements were taken once in both eyes after confirming the ischemic changes by wide-field fluorescein angiography. Results: Chapter 3 and 4: When the arterial PETO2 (end-tidal partial pressure of oxygen) was increased from baseline (PETO2=100mmHg) to 200 and 300mmHg, the TRBF significantly reduced (p=0.020) from 44.60 μL/min (+8.9) to 40.28 μL/min (+8.9) and 36.23 μL/min (+4.6), respectively. Retinal arteriolar SO2 (SaO2) did not show any significant change during PETO2 of 200 and 300mmHg, compared to baseline. However, retinal venular SO2 (SvO2) significantly increased (p<0.000) from 57.2% (+3.9) to 61.3% (+3.6) and 62.0% (+3.4) during PETO2 of 200 and 300mmHg, respectively, compared to baseline. Lowering the arterial PETO2, from baseline to 80, 60 and 50mmHg, TRBF significantly increased (p=0.040) from 43.17 μL/min (+12.7) to 45.19 μL/min (+5.5), 49.71 μL/min (+13.4) and 52.89 μL/min (+10.9) with simultaneous reduction in the SaO2 and SvO2 from 99.3 % (+ 5.8) and 56.3% (+ 4.2) to 95.6% (+ 5.1) and 52.5 (+ 4.1), 89.6% (+ 2.8) and 49.5% (+ 2.9), 83.3% (+ 3.9) and 45.0 % (+ 6.1), respectively (p<0.000). The group mean coefficient of repeatability (COR) for the retinal blood SaO2, SvO2 and TRBF were 18.4% (relative to a mean effect of 104.4%), 15.2% (relative to a mean effect of 60.3%), and 21.8 μL/min (relative to a mean effect of 44.72 μL/min). The overall coefficient of variability (COV) for SaO2, SvO2 and TRBF measurements were 4.7% and 6.9%, and, 15.1% respectively. The inner retinal oxygen extraction was calculated as 3.64 mLO2/min/100g tissue in humans. Chapter 5: The average TRBF in the eye with RR was significantly lower compared to the fellow eye (33.48 + 12.73 µL/min vs 50.37 + 15.26 µL/min; p = 0.013). The SaO2 and SvO2 was higher in the retinopathy eye compared to the fellow eye (101.11 + 4.26%, vs 94.45 + 5.79%; p=0.008) and (62.96 + 11.05% vs 51.24 + 6.88%, p=0.051), respectively. Chapter 6: Out of 17 CM patients recruited, 2 patient data was excluded due to poor image quality, and 3 others were lost to follow-up. During the six month follow up period, one person developed RR. The SaO2 measurement was found to be significantly increased (p=0.026) from 94.4 % (+7.9) to 98.9% (+8.8) and 100.6 % (+6.4), respectively during 3 and 6 month follow up post 125Iodine plaque brachytherapy compared to before treatment. Conclusions: Chapter 3: Our study demonstrated significant changes in retinal blood SO2 and TRBF during systemic changes in arterial PETO2. The variability in TRBF measurements may reflect the impact of subjective assessment in venous area estimation as well as Doppler signal strength differences between visits. One needs to note that, a common clinical test such as visual acuity measurement also has a reported variability of up to ±0.15 logMAR (or + 8 logMAR letters), relative to a mean effect of 0.017 logMAR (+ 4.2 letters), yet it is still being utilized as a useful clinical tool. The Doppler SD-OCT and HRC offer a quantifiable and repeatable technique of assessing retinal hemodynamics. Minimizing subjectivity in terms of blood flow analysis as well as correcting imperfections in the optics design of the HRC could possibly improve the repeatability of TRBF and retinal blood SO2, respectively. Chapter 4: Oxygen extracted from the inner retinal vessels remains unchanged during safe levels of systemic hypoxia and hyperoxia. Chapter 5: The effect of ionizing radiation has an impact on the TRBF and retinal blood SO2, clinically presenting similar to a rapidly developing diabetic retinopathy. The results show an altered retinal vascular physiology in patients with radiation related retinopathy. Chapter 6: 125Iodine brachytherapy significantly increases the retinal arteriolar blood SO2, suggesting improved retinal tissue perfusion in the treated eye. It is interesting to note that one patient developed RR in this six month period. About a 20% increase in retinal arteriolar and venular blood oxygen saturation was observed in this patient, 6 month post brachytherapy compared to pre-treatment value. In order to predict who will develop RR following brachytherapy, it is important to follow up rest of the eleven subjects to measure SO2 and TRBF during 12 and 18 month period or until they develop retinopathy. This will be a future work of interest, to recruit even large number of CM patients in a longitudinal approach. Only then a pattern or model for predicting RR in terms of SO2 or TRBF measurements could be established. The study examines the early effects of brachytherapy on retinal hemodynamics

Feature Selection on Hyperspectral Data for Dismount Skin Analysis

Many security applications require the ability to accurately identify dismounts based on their distinctive identification properties. A dismount can be identified by many personal characteristics to include clothing, height, and gait. In particular, a dismount\u27s skin can be used as an identifying feature because of the vast variability of skin pigmentation amongst individuals. Hyperspectral data, which is comprised of hundreds of spectral channels sampled from a nearly contiguous electromagnetic spectrum, is used to detect skin spectral variability amongst dismounts. However, hyperspectral data is often highly correlated and computationally expensive to process. Feature selection methods can be employed to reduce the data to a manageable size. This thesis presents the results of applying the fast correlation based filter (FCFB) [51] to a data set that contains hyperspectral data from the forearms of 62 subjects. The reduced data is used to train an artificial neural network (ANN) to discriminate a dismount of interest (DOI) amongst a group of 4 non-DOI\u27s. The trained model is then tested to find the same DOI amongst a group of 62 new non-DOI\u27s. The FCBF selected four features (1014, 1024, 1033, and 1348nm) to discriminate amongst the dismounts. Using these four features, the ANN on average misclassified dismounts amongst four separate DOI validation tests. More specifically, the amount of possible DOI suspects was reduced from 62 to 4 dismounts. The FCBF outperformed three other feature selection methods with 4 times less misclassified instances

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

Design Analysis of a Sapce Based Chromotomographic Hyperspectral Imaging Experiment

This research develops the design of several components and/or systems for an experimental space-based chromotomographic hyperspectral imager that is being built by the Air Force Institute of Technology. The design work includes three separate topics. The first topic was the development of a structure utilizing finite element analysis and eigenanalysis for the ground-based version of the chromotomographic experiment (CTEx). The ground-based experiment was performed as a risk mitigation measure for the space-based experiment. The second topic includes a design review of a contractor\u27s proposed off-axis Mersenne telescope for the space-based chromotomographic hyperspectral imager. The work included the creation of preliminary verification requirements from the contract and sub- sequent analysis of the telescope design based on those requirements. The third topic addressed was a trade study of on-orbit focus, alignment, and calibration schemes for the space-based version of CTEx. The selected imaging focusing method entails imaging Earth-based sodium lights at night while stepping through several focus settings. The optimal focus setting shows the clearest sodium spectral features. The critical alignment concerns were identified as the alignment of the prism and of the collimated light onto the prism. The space-based CTEx utilizes three separate calibration methods involving vicarious Earth-based targets, and on-board laser diodes and spectral filters. The results of the research varied by topic. For the first topic, a structural assembly was successfully fabricated that allowed the goals of the ground-based CTEx to be met, validating the design approach. The design review for the second topic was successful with the contractor\u27s telescope design currently undergoing fabrication with delivery in May 2010. For the third topic, applicable methods and procedures were developed for the space-based CTEx