University College London

On the inverse problem in optical coherence tomography

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We examine the inverse problem of retrieving sample refractive index information in the context of optical coherence tomography. Using two separate approaches, we discuss the limitations of the inverse problem which lead to it being ill-posed, primarily as a consequence of the limited viewing angles available in the reflection geometry. This is first considered from the theoretical point of view of diffraction tomography under a weak scattering approximation. We then investigate the full non-linear inverse problem using a variational approach. This presents another illustration of the non-uniqueness of the solution, and shows that even the non-linear (strongly scattering) scenario suffers a similar fate as the linear problem, with the observable spatial Fourier components of the sample occupying a limited support. Through examples we demonstrate how the solutions to the inverse problem compare when using the variational and diffraction-tomography approaches.

Adaptive optics scanning laser ophthalmoscopy and optical coherence tomography (AO-SLO-OCT) system for in vivo mouse retina imaging

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Optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) are imaging technologies invented in the 1980s that have revolutionized the field of in vivo retinal diagnostics and are now commonly used in ophthalmology clinics as well as in vision science research. Adaptive optics (AO) technology enables high-fidelity correction of ocular aberrations, resulting in improved resolution and sensitivity for both SLO and OCT systems. The potential of gathering multi-modal cellular-resolution information in a single instrument is of great interest to the ophthalmic imaging community. Although similar instruments have been developed for imaging the human retina, developing such a system for mice will benefit basic science research and should help with further dissemination of AO technology. Here, we present our work integrating OCT into an existing mouse retinal AO-SLO system, resulting in a multi-modal AO-enhanced imaging system of the living mouse eye. The new system allows e...

Pilot study of optical coherence tomography angiography-derived microvascular metrics in hands and feet of healthy and diabetic people

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Optical coherence tomography angiography (OCTA) is a non-invasive, high-resolution imaging modality with growing application in dermatology and microvascular assessment. Accepted reference values for OCTA-derived microvascular parameters in skin do not yet exist but need to be established to drive OCTA into the clinic. In this pilot study, we assess a range of OCTA microvascular metrics at rest and after post-occlusive reactive hyperaemia (PORH) in the hands and feet of 52 healthy people and 11 people with well-controlled type 2 diabetes mellitus (T2DM). We calculate each metric, measure test–retest repeatability, and evaluate correlation with demographic risk factors. Our study delivers extremity-specific, age-dependent reference values and coefficients of repeatability of nine microvascular metrics at baseline and at the maximum of PORH. Significant differences are not seen for age-dependent microvascular metrics in hand, but they are present for several metrics in the foot. Signi...

Pilot study of optical coherence tomography angiography-derived microvascular metrics in hands and feet of healthy and diabetic peopl

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Optical coherence tomography angiography (OCTA) is a non-invasive, high-resolution imaging modality with growing application in dermatology and microvascular assessment. Accepted reference values for OCTA-derived microvascular parameters in skin do not yet exist but need to be established to drive OCTA into the clinic. In this pilot study, we assess a range of OCTA microvascular metrics at rest and after post-occlusive reactive hyperaemia (PORH) in the hands and feet of 52 healthy people and 11 people with well-controlled type 2 diabetes mellitus (T2DM). We calculate each metric, measure test–retest repeatability, and evaluate correlation with demographic risk factors. Our study delivers extremity-specific, age-dependent reference values and coefficients of repeatability of nine microvascular metrics at baseline and at the maximum of PORH. Significant differences are not seen for age-dependent microvascular metrics in hand, but they are present for several metrics in the foot. Signi...

Senior Research Fellow in Optical Coherence Tomography – Institute of Ophthalmology University College London

Full Job Description Ref Number: B02-04320 Professional Expertise: Research and Research Support Department: School of Life & Medical Sciences (B02) Location: London Working Pattern: Full time Salary: See advert text Contract Type: Fixed-term Working Type: On site (> 80% of working time) Available For Secondment: No Closing Date: 22-Jan-2023 About us The post of Senior Research Fellow is for biophotonics research with a focus on optical coherence tomography (OCT). The research fellow will join Prof. Sarunic’s group, which is primarily based at UCL Institute of Ophthalmology and cross-appointed with the UCL Department of Medical Physics and Biomedical Engineering, for the development of novel ocular imaging technologies. The post of Senior Research Fellow offers an exciting opportunity for someone to play a key role in developing new OCT-based diagnostics in a highly successful and dynamic research Institute, as well as benefiting from the clinical collabora...

Senior Research Fellow in Optical Coherence Tomography, University College London

Location: London Salary: £47,414 inclusive of London Allowance Hours: Full Time Contract Type: Fixed-Term/Contract Placed On: 5th January 2023 Closes: 22nd January 2023 Job Ref: B02-04320 About us The post of Senior Research Fellow is for biophotonics research with a focus on optical coherence tomography (OCT). The research fellow will join Prof. Sarunic’s group, which is primarily based at UCL Institute of Ophthalmology and cross-appointed with the UCL Department of Medical Physics and Biomedical Engineering, for the development of novel ocular imaging technologies. The post of Senior Research Fellow offers an exciting opportunity for someone to play a key role in developing new OCT-based diagnostics in a highly successful and dynamic research Institute, as well as benefiting from the clinical collaborations and translational opportunities at the NIHR Moorfields Biomedical Research Centre. About the role The Senior Research Fellow role will combine practical re...

Extracting Morphological and Sub-Resolution Features from Optical Coherence Tomography Images, a Review with Applications in Cancer Diagnosis

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Extracting Morphological and Sub-Resolution Features from Optical Coherence Tomography Images, a Review with Applications in Cancer Diagnosis Before they become invasive, early cancer cells exhibit specific and characteristic changes that are routinely used by a histopathologist for diagnosis. Currently, these early abnormalities are only detectable ex vivo by histopathology or, non-invasively and in vivo, by optical modalities that have not been clinically implemented due to their complexity and their limited penetration in tissues. Optical coherence tomography (OCT) is a noninvasive medical imaging technology with increasing clinical applications in areas such as ophthalmology, cardiology, gastroenterology, etc. In addition to imaging the tissue micro-structure, OCT can also provide additional information, describing the constituents and state of the cellular components of the tissue. Estimates of the nuclear size, sub-cellular morphological variations, dispersion and index of refraction can be extracted from the OCT images and can serve as diagnostically useful biomarkers. Moreover, the development of fully automated...

Spectral Bandwidth Recovery of Optical Coherence Tomography Images using Deep Learning

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Optical coherence tomography (OCT) captures cross-sectional data and is used for the screening, monitoring, and treatment planning of retinal diseases. Technological developments to increase the speed of acquisition often results in systems with a narrower spectral bandwidth, and hence a lower axial resolution. Traditionally, image-processing-based techniques have been utilized to reconstruct subsampled OCT data and more recently, deep-learning-based methods have been explored. In this study, we simulate reduced axial scan (A-scan) resolution by Gaussian windowing in the spectral domain and investigate the use of a learning-based approach for image feature reconstruction. In anticipation of the reduced resolution that accompanies wide-field OCT systems, we build upon super-resolution techniques to explore methods to better aid clinicians in their decision-making to improve patient outcomes, by reconstructing lost features using a pixel-to-pixel approach with an altered super-resol...

PhD studentship Opening in Optical Coherence Elastography ad University College London

    Primary Supervisor: Professor Peter Munro Secondary Supervisor: Dr Sami Sahmed, Professor Simon Arridge Project Summary A four-year fully funded PhD studentship, co-funded by the Royal Society, is available in UCL’s Computational Optics Group within the Department of Medical Physics. The successful candidate will be part of the UCL CDT in Intelligent, Integrated Imaging in Healthcare (i4health) and will benefit from the activities and events organised by the centre. The project will involve close interaction with researchers from UCL Hospital. The successful applicant can start at the beginning of the 2023/2024 academic year, or earlier. Background Oesophageal cancer is one of four cancers of “unmet need” (Cancer Research UK) mainly due to its poor survival rates and late diagnosis. Significant deficiencies exist at all stages of surveillance, staging, and treatment. We aim to overcome this problem using optical Coherence Elastogra...

A Deep Learning Framework for the Detection and Quantification of Reticular Pseudodrusen and Drusen on Optical Coherence Tomography

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Purpose: The purpose of this study was to develop and validate a deep learning (DL) framework for the detection and quantification of reticular pseudodrusen (RPD) and drusen on optical coherence tomography (OCT) scans. Methods: A DL framework was developed consisting of a classification model and an out-of-distribution (OOD) detection model for the identification of ungradable scans; a classification model to identify scans with drusen or RPD; and an image segmentation model to independently segment lesions as RPD or drusen. Data were obtained from 1284 participants in the UK Biobank (UKBB) with a self-reported diagnosis of age-related macular degeneration (AMD) and 250 UKBB controls. Drusen and RPD were manually delineated by five retina specialists. The main outcome measures were sensitivity, specificity, area under the receiver operating characteristic (ROC) curve (AUC), kappa, accuracy, intraclass correlation coefficient (ICC), and free-response receiver operating characteristic...

The Role of the Inner Nuclear Layer for Perception of Persisting Tiling Inside a Monocular Scotoma

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We report two patients, one with and one without long-term persistent tiling inside an arcuate macular scotoma. In both cases, the scotoma was caused by a cilioretinal artery occlusion. Both patients were almost identical regarding the location and extent of the scotoma. In both cases, there was a comparable degree of atrophy on optical coherence tomography for the retinal nerve fibre, ganglion cell, and inner plexiform layers. The main difference was the preservation of the inner nuclear layer in the patient with persistent tiling. In this patient, optical coherence angiography demonstrates preserved perfusion of the superior vascular plexus, which was not the case in the patient with the negative scotoma who also had atrophy of the inner nuclear layer. Recreational use of cannabinoid enhanced the intensity of perceived tiling in the relative scotoma of the first patient. A review of the literature suggests that the persistent tiling described in our case is different to teichopsia...

Progress in Probe-Based Sensing Techniques for In Vivo Diagnosis

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Advancements in robotic surgery help to improve the endoluminal diagnosis and treatment with minimally invasive or non-invasive intervention in a precise and safe manner. Miniaturized probe-based sensors can be used to obtain information about endoluminal anatomy, and they can be integrated with medical robots to augment the convenience of robotic operations. The tremendous benefit of having this physiological information during the intervention has led to the development of a variety of in vivo sensing technologies over the past decades. In this paper, we review the probe-based sensing techniques for the in vivo physical and biochemical sensing in China in recent years, especially on in vivo force sensing, temperature sensing, optical coherence tomography/photoacoustic/ultrasound imaging, chemical sensing, and biomarker sensing. ( Read Full Article )

Senior Research Fellow Opening at Institute of Ophthalmology, University College London

      Location: London Salary: From £46,979 UCL Grade 8, per annum, inclusive of London Allowance Hours: Full Time Contract Type: Fixed-Term/Contract Placed On: 22nd September 2022 Closes: 18th October 2022 Job Ref: 1886911 Interview Date: TBC Full time, Fixed Term: The post is funded for 12 months (in the first instance).   Applications are invited for the post of Senior Research Fellow to join the research group of Professor Marinko Sarunic at the UCL Institute of Ophthalmology. The project involves developing adaptive optics optical coherence tomography (AOOCT) imaging systems. The duties include designing and building a user-friendly optical system that will correct for the eye’s optical imperfections and acquire high resolution structural and functional retinal images.   The post is funded for 12 months (in the first instance).   The successful candidate should have a first degree in physics, engineering or a related field, and a PhD in...

Optical Coherence Tomography Angiography (OCTA) to Assess Cardiac Output and Cerebral Perfusion at the Time of Children’s Cardiac Surgery

Around 3500 children including 1,000 babies a year in the UK require heart surgery. Open-heart repairs involve the heart being stopped, while blood is pumped around the body using a cardiopulmonary bypass machine. Following complex operations, the patient may temporarily develop poor heart function, leading to reduced organ blood supply. Low heart output leads to post-operative complications or even death. The current methods to assess cardiac output and to see if vital organs, especially the brain, are receiving enough blood flow, are indirect and can be inaccurate. If we find a better way to detect and then avert or ameliorate periods of poor cardiac output and / or reduced brain perfusion, then this would be helpful for clinicians and could lead to better outcomes for children. We believe that optical coherence tomography angiography (OCTA), a non-invasive way to image the blood vessels in the retina at the back of the eye, could help us to assess cardiac output and brain perfusi...

Comparing Retinal Structure in Patients with Achromatopsia and Blue Cone Monochromacy Using OCT

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Purpose: To compare foveal hypoplasia and the appearance of the ellipsoid zone (EZ) at the fovea in patients with genetically confirmed achromatopsia (ACHM) and blue cone monochromacy (BCM). Design: Retrospective, multi-center observational study. Subjects: Molecularly confirmed patients with ACHM (n = 89) and BCM (n = 33). Methods: We analyzed high-resolution spectral domain optical coherence tomography (SD-OCT) images of the macula from aforementioned patients with BCM. Three observers independently graded SD-OCT images for foveal hypoplasia (i.e. retention of one or more inner retinal layers at the fovea) and four observers judged the integrity of the EZ at the fovea, based on an established grading scheme. These measures were compared with previously published data from the ACHM patients. Main outcome measures: Presence of foveal hypoplasia and EZ grade. Results: Foveal hypoplasia was significantly more prevalent in ACHM than in BCM (p<0.001). In addition, we observed a signi...

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