Scattering angle resolved optical coherence tomography for early retinal detection of Alzheimer’s disease in a murine model

Alzheimer’s disease (AD), a debilitating neurodegenerative disease, is becoming more prevalent with an aging population. Early detection of AD is critical to extending healthy lives, but current techniques for AD detection are invasive and cost-prohibitive. The retina is embryonically derived from the forebrain and, with recent mounting evidence that it may reveal markers of brain injury, is considered a “window to the brain.” Early neurodegenerative changes in the brain are likely to be observed in the retina—synaptic failure and shifts in mitochondrial dynamics. Optical imaging techniques could hold the key to non-invasive early detection of AD in the retina since these disruptions may be observed with light. In particular, optical coherence tomography (OCT) retinal imaging offers 3D images of retinal neurons, but the resolution of clinical OCT systems is not fine enough to observe disruptions in the sub-cellular space. Scattering angle resolved (SAR-) OCT, a new method introduced in this work, aims to access sub-resolution scattering properties which could expose fundamental changes in the neurons associated with AD. In this dissertation, a custom SAR-OCT system and new image processing protocols are designed and constructed for murine retinal imaging. Then, three in-vivo studies are conducted using the imaging system to demonstrate its potential use in disease detection. In the first study, which establishes fundamental measures provided by SAR OCT, the imaging system discerns native scattering differences between retinal layers and regions in healthy mice. In the second study, significant scattering angle shifts are observed in ischemic retinas. Finally, a cross-sectional study compares a transgenic murine model of AD (3xTg-AD) with age-matched wild type controls. By examining the distribution of scattering angles detected by the SAR-OCT system, significant differences are observed in the earliest ages of the diseased mice compared the control mice. In the final chapter, limitations of these studies as well as the imaging and image processing protocols are examined, and recommendations are made for future studies to leverage SAR-OCT for early detection of AD or other neurodegenerative diseasesBiomedical Engineerin

Modern optical astronomy: technology and impact of interferometry

The present `state of the art' and the path to future progress in high spatial resolution imaging interferometry is reviewed. The review begins with a treatment of the fundamentals of stellar optical interferometry, the origin, properties, optical effects of turbulence in the Earth's atmosphere, the passive methods that are applied on a single telescope to overcome atmospheric image degradation such as speckle interferometry, and various other techniques. These topics include differential speckle interferometry, speckle spectroscopy and polarimetry, phase diversity, wavefront shearing interferometry, phase-closure methods, dark speckle imaging, as well as the limitations imposed by the detectors on the performance of speckle imaging. A brief account is given of the technological innovation of adaptive-optics (AO) to compensate such atmospheric effects on the image in real time. A major advancement involves the transition from single-aperture to the dilute-aperture interferometry using multiple telescopes. Therefore, the review deals with recent developments involving ground-based, and space-based optical arrays. Emphasis is placed on the problems specific to delay-lines, beam recombination, polarization, dispersion, fringe-tracking, bootstrapping, coherencing and cophasing, and recovery of the visibility functions. The role of AO in enhancing visibilities is also discussed. The applications of interferometry, such as imaging, astrometry, and nulling are described. The mathematical intricacies of the various `post-detection' image-processing techniques are examined critically. The review concludes with a discussion of the astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics, 2002, to appear in April issu

Topics in Adaptive Optics

Advances in adaptive optics technology and applications move forward at a rapid pace. The basic idea of wavefront compensation in real-time has been around since the mid 1970s. The first widely used application of adaptive optics was for compensating atmospheric turbulence effects in astronomical imaging and laser beam propagation. While some topics have been researched and reported for years, even decades, new applications and advances in the supporting technologies occur almost daily. This book brings together 11 original chapters related to adaptive optics, written by an international group of invited authors. Topics include atmospheric turbulence characterization, astronomy with large telescopes, image post-processing, high power laser distortion compensation, adaptive optics and the human eye, wavefront sensors, and deformable mirrors

A New Versatile Electronic Speckle Pattern Interferometer For Vibration Measurements

Electronic speckle pattern interferometry (ESPI) has been widely used for vibration amplitude and phase measurements. Conventional ESPI systems are bulk and expensive and need careful alignment of all the optical components which is a time consuming task. To overcome these problems alternative compact ESPI systems were developed using fibre-optical components or holographic optical elements (HOEs). The fibre-optic based ESPI systems suffer from random phase fluctuations induced by environmental temperature changes. Hence HOEs can be used as more powerful alternative optical elements to design ESPI systems. The time average ESPI method is widely used for vibration studies. The time average method combined with phase stepping can be used for automatic vibration measurements. Using this technique higher vibration amplitudes cannot be measured because fringe patterns follow Bessel function intensity distribution. To overcome this problem an alternative technique can be used by modulating the phase of the reference beam in an unbalanced interferometer. This thesis reports a novel ESPI system for vibration measurements by combining use of holographic optical elements (HOEs) and optical path length modulation (reference beam phase modulation). The optical path length modulation is implemented using laser diode wavelength (frequency) modulation. Different HOE based ESPI systems are reported in this thesis using either a single HOE or dual HOE. This thesis examines performance of different HOE based ESPI systems that are sensitive to out-of-plane displacement components using laser diodes operating either in the near infrared or visible electromagnetic spectrum. Vibration modes of a circular metal plate clamped at the edges of a loud speaker and a circular metal plate driven by a piezoelectric actuator (PZT) were studied using a single RHOE based ESPI system and a hybrid (transmission HOE with a partially reflecting mirror) HOE based ESPI system respectively using a near infrared laser diode (763nm). Optical path length modulation technique was implemented using a laser diode operating in visible electromagnetic spectrum (658nm). Vibration mode patterns of a circular metal plate driven by a PZT actuator were obtained using both single RHOE and dual HOE based ESPI systems. Using optical path length modulation technique in a dual HOE based ESPI system detailed phase and amplitude maps of a circular metal plate driven by a PZT actuator are obtained. The dual HOE based ESPI system was also used for measuring roations of a circular metal plate mounted on a mirror mount. In conclusion we have developed a compact HOE based ESPI system to conduct vibration measurements. A few potential future developments are also suggested at the end of the thesis

Optical In-Process Measurement Systems

Information is key, which means that measurements are key. For this reason, this book provides unique insight into state-of-the-art research works regarding optical measurement systems. Optical systems are fast and precise, and the ongoing challenge is to enable optical principles for in-process measurements. Presented within this book is a selection of promising optical measurement approaches for real-world applications

Realising the head-shadow benefit to cochlear implant users

Cochlear implant (CI) users struggle to understand speech in noise. They suffer from elevated hearing thresholds and, with practically no binaural unmasking, they rely heavily on better-ear listening and lip reading. Traditional measures of spatial release from masking (SRM) quantify the speech reception threshold (SRT) improvement due to the azimuthal separation of speech and interferers when directly facing the speech source. The Jelfs et al. (2011) model of SRM predicts substantial benefits of orienting the head away from the target speech. Audio-only and audio-visual (AV) SRTs in normally hearing (NH) listeners and CI users confirmed model predictions of speech-facing SRM and head-orientation benefit (HOB). The lip-reading benefit (LRB) was not disrupted by a modest 30° orientation. When attending to speech with a gradually diminishing speech-to-noise-ratio (SNR), CI users were found to make little spontaneous use of their available HOB. Following a simple instruction to explore their HOB, CI users immediately reached as much as 5 dB lower SNRs. AV speech presentation significantly inhibited head movements (it nearly eradicated CI users’ spontaneous head turns), but had a limited impact on the SNRs reached post-instruction, compared to audio-only presentation. NH listeners age-matched to our CI participants made more spontaneous head turns in the free-head experiment but were poorer than CI users at exploiting their HOB post-instruction, despite their exhibiting larger objective HOB. NH listeners’ and CI users’ LRB measured 3 and 5 dB, respectively. Our findings both dispel the erroneous beliefs held by CI professionals that facing the speech constitutes an optimal listening strategy (whether for lip-reading or to optimise the use of microphone directionality) and pave the way to obvious translational applications

Nondestructive Testing in Composite Materials

In this era of technological progress and given the need for welfare and safety, everything that is manufactured and maintained must comply with such needs. We would all like to live in a safe house that will not collapse on us. We would all like to walk on a safe road and never see a chasm open in front of us. We would all like to cross a bridge and reach the other side safely. We all would like to feel safe and secure when taking a plane, ship, train, or using any equipment. All this may be possible with the adoption of adequate manufacturing processes, with non-destructive inspection of final parts and monitoring during the in-service life of components. Above all, maintenance should be imperative. This requires effective non-destructive testing techniques and procedures. This Special Issue is a collection of some of the latest research in these areas, aiming to highlight new ideas and ways to deal with challenging issues worldwide. Different types of materials and structures are considered, different non-destructive testing techniques are employed with new approaches for data treatment proposed as well as numerical simulations. This can serve as food for thought for the community involved in the inspection of materials and structures as well as condition monitoring

Multifrequency Aperture-Synthesizing Microwave Radiometer System (MFASMR). Volume 1

Background material and a systems analysis of a multifrequency aperture - synthesizing microwave radiometer system is presented. It was found that the system does not exhibit high performance because much of the available thermal power is not used in the construction of the image and because the image that can be formed has a resolution of only ten lines. An analysis of image reconstruction is given. The system is compared with conventional aperture synthesis systems