212 research outputs found
Minimally Invasive Optical Biopsy for Oximetry
The study of localised oxygen saturation in blood vessels can shed light on the etiology and progression of
many diseases with which hypoxia is associated. For example, hypoxia in the tendon has been linked to early
stages of rheumatoid arthritis, an auto-immune inflammatory disease. Vascular oximetry of deep tissue presents
significant challenges as vessels are not optically accessible. In this paper, we present a novel multispectral
imaging technique for vascular oximetry, and recent developments made towards its adaptation for minimally
invasive imaging. We present proof-of-concept of the system and illumination scheme as well as the analysis
technique. We present results of a validation study performed in vivo on mice with acutely inflamed tendons.
Adaptation of the technique for minimally invasive microendoscopy is also presented, along with preliminary
results of minimally invasive ex vivo vascular oximetry
Multispectral oximetry of murine tendon microvasculature with inflammation
We report a novel multispectral imaging technique for localised measurement of vascular oxygen saturation (SO2) in vivo. Annular back-illumination is generated using a Schwarzchild-design reflective objective. Analysis of multispectral data is performed using a calibration-free oximetry algorithm. This technique is applied to oximetry in mice to measure SO2 in microvasculature supplying inflamed tendon tissue in the hind leg. Average SO2 for controls was 94.8 ± 7.0 % (N = 6), and 84.0 ± 13.5 % for mice with inflamed tendon tissue (N = 6). We believe this to be the first localised measurement of hypoxia in tendon microvasculature due to inflammation. Quantification of localised SO2 is important for the study of inflammatory diseases such as rheumatoid arthritis, where hypoxia is thought to play a role in pathogenesis
Human retinal oximetry using hyperspectral imaging
The aim of the work reported in this thesis was to investigate the possibility of
measuring human retinal oxygen saturation using hyperspectral imaging. A direct
non-invasive quantitative mapping of retinal oxygen saturation is enabled by
hyperspectral imaging whereby the absorption spectra of oxygenated and deoxygenated
haemoglobin are recorded and analysed. Implementation of spectral
retinal imaging thus requires ophthalmic instrumentation capable of efficiently
recording the requisite spectral data cube. For this purpose, a spectral retinal imager
was developed for the first time by integrating a liquid crystal tuneable filter into the
illumination system of a conventional fundus camera to enable the recording of
narrow-band spectral images in time sequence from 400nm to 700nm. Postprocessing
algorithms were developed to enable accurate exploitation of spectral
retinal images and overcome the confounding problems associated with this technique
due to the erratic eye motion and illumination variation.
Several algorithms were developed to provide semi-quantitative and quantitative
oxygen saturation measurements. Accurate quantitative measurements necessitated an
optical model of light propagation into the retina that takes into account the
absorption and scattering of light by red blood cells. To validate the oxygen saturation
measurements and algorithms, a model eye was constructed and measurements were
compared with gold-standard measurements obtained by a Co-Oximeter. The
accuracy of the oxygen saturation measurements was (3.31%± 2.19) for oxygenated
blood samples. Clinical trials from healthy and diseased subjects were analysed and
oxygen saturation measurements were compared to establish a merit of certain retinal
diseases. Oxygen saturation measurements were in agreement with clinician
expectations in both veins (48%±9) and arteries (96%±5). We also present in this
thesis the development of novel clinical instrument based on IRIS to perform retinal
oximetry.Al-baath University, Syri
Combined high contrast and wide field-of-view in the Scanning Laser Ophthalmoscope through dual detection of light paths
We demonstrate a multimode detection system in a scanning laser ophthalmoscope (SLO) that
enables simultaneous operation in confocal, indirect, and direct modes to permit an agile trade between image
contrast and optical sensitivity across the retinal field of view to optimize the overall imaging performance,
enabling increased contrast in very wide-field operation. We demonstrate the method on a wide-field SLO
employing a hybrid pinhole at its image plane, to yield a twofold increase in vasculature contrast in the central
retina compared to its conventional direct mode while retaining high-quality imaging across a wide field of the
retina, of up to 200 deg and 20 μm on-axis resolution
A multispectral microscope for in vivo oximetry of rat dorsal spinal cord vasculature
Quantification of blood oxygen saturation (SO2) in vivo is essential for understanding the pathogenesis of diseases in which hypoxia is thought to play a role, including inflammatory disorders such as multiple sclerosis (MS) and rheumatoid arthritis (RA). We describe a low-cost multispectral microscope and oximetry technique for calibration-free absolute oximetry of surgically exposed blood vessels in vivo. We imaged the vasculature of the dorsal spinal cord in healthy rats, and varied inspired oxygen (FiO2) in order to evaluate the sensitivity of the imaging system to changes in SO2. The venous SO2 was calculated as 67.8  ±  10.4% (average  ±  standard deviation), increasing to 83.1  ±  11.6% under hyperoxic conditions (100% FiO2) and returning to 67.4  ±  10.9% for a second normoxic period; the venous SO2 was 50.9  ±  15.5% and 29.2  ±  24.6% during subsequent hypoxic states (18% and 15% FiO2 respectively). We discuss the design and performance of our multispectral imaging system, and the future scope for extending this oximetry technique to quantification of hypoxia in inflamed tissue
Hyperspectral Computed Tomographic Imaging Spectroscopy of Vascular Oxygen Gradients in the Rabbit Retina In Vivo
Diagnosis of retinal vascular diseases depends on ophthalmoscopic findings that most often occur after severe visual loss (as in vein occlusions) or chronic changes that are irreversible (as in diabetic retinopathy). Despite recent advances, diagnostic imaging currently reveals very little about the vascular function and local oxygen delivery. One potentially useful measure of vascular function is measurement of hemoglobin oxygen content. In this paper, we demonstrate a novel method of accurately, rapidly and easily measuring oxygen saturation within retinal vessels using in vivo imaging spectroscopy. This method uses a commercially available fundus camera coupled to two-dimensional diffracting optics that scatter the incident light onto a focal plane array in a calibrated pattern. Computed tomographic algorithms are used to reconstruct the diffracted spectral patterns into wavelength components of the original image. In this paper the spectral components of oxy- and deoxyhemoglobin are analyzed from the vessels within the image. Up to 76 spectral measurements can be made in only a few milliseconds and used to quantify the oxygen saturation within the retinal vessels over a 10–15 degree field. The method described here can acquire 10-fold more spectral data in much less time than conventional oximetry systems (while utilizing the commonly accepted fundus camera platform). Application of this method to animal models of retinal vascular disease and clinical subjects will provide useful and novel information about retinal vascular disease and physiology
A combined method to quantify the retinal metabolic rate of oxygen using photoacoustic ophthalmoscopy and optical coherence tomography
Quantitatively determining physiological parameters at a microscopic level in the retina furthers the understanding of the molecular pathways of blinding diseases, such as diabetic retinopathy and glaucoma. An essential parameter, which has yet to be quantified noninvasively, is the retinal oxygen metabolic rate (rMRO(2)). Quantifying rMRO(2) is challenging because two parameters, the blood flow rate and hemoglobin oxygen saturation (sO(2)), must be measured together. We combined photoacoustic ophthalmoscopy (PAOM) with spectral domain-optical coherence tomography (SD-OCT) to tackle this challenge, in which PAOM measured the sO(2) and SD-OCT mapped the blood flow rate. We tested the integrated system on normal wild-type rats, in which the measured rMRO(2) was 297.86 +/- 70.23 nl/minute. This quantitative method may shed new light on both fundamental research and clinical care in ophthalmology in the future
Holistic Monte-Carlo optical modelling of biological imaging
The invention and advancement of biological microscopy depends critically on an ability to accurately simulate imaging of complex biological structures embedded within complex scattering media. Unfortunately no technique exists for rigorous simulation of the complete imaging process, including the source, instrument, sample and detector. Monte-Carlo modelling is the gold standard for the modelling of light propagation in tissue, but is somewhat laborious to implement and does not incorporate the rejection of scattered light by the microscope. On the other hand microscopes may be rigorously and rapidly modelled using commercial ray-tracing software, but excluding the interaction with the biological sample. We report a hybrid Monte-Carlo optical ray-tracing technique for modelling of complete imaging systems of arbitrary complexity. We make the software available to enable user-friendly and rigorous virtual prototyping of biological microscopy of arbitrary complexity involving light scattering, fluorescence, polarised light propagation, diffraction and coherence. Examples are presented for the modelling and optimisation of representative imaging of neural cells using light-sheet and micro-endoscopic fluorescence microscopy and imaging of retinal vasculature using confocal and non-confocal scanning-laser ophthalmoscopes
Snapshot spectral imaging using image replication and birefringent interferometry : principles and applications
This thesis explores the image-replicating imaging spectrometer (IRIS). This relatively
recent invention is a two-dimensional, snapshot spectral-imaging technology, capable
of recording the spectral and spatial data from a scene instantaneously. Whereas
conventional spectral-imaging technologies require multiple detector frames to record
the entire data set, IRIS is able to record the data set in a single frame, a capability
which is useful for highly dynamic scenes.
The IRIS concept and the design of IRIS systems are explained in detail, and constraints
on the performance of IRIS are determined. Practical issue in the use of IRIS
systems are identi ed and solutions are identi ed and appraised. Some applications of
IRIS are also shown, demonstrating its viability as a spectral imaging technology.
Novel aspects of this work include the re nement of the IRIS design, demonstration
of a registration algorithm for IRIS, designs for achromatic Wollaston prisms, a comparison
of the IRIS technology with conventional spectral imaging technologies, and the
application of IRIS to practical problems.Engineering and Physical Sciences Research Council (EPSRC)Selex Galile
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