Дисертації з теми "Optical tomography"
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1
Xu, Weiming. "Offset Optical Coherence Tomography." Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1626870603439104.
2
Huang, David. "Optical coherence tomography." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12675.
3
Muscat, Sarah. "Optical coherence tomography." Thesis, Connect to e-thesis, 2003. http://theses.gla.ac.uk/630/.
Анотація:
Thesis (Ph.D.) - University of Glasgow, 2003.Ph.D. thesis submitted to the Department of Cardiovascular and Medical Sciences, Faculty of Medicine, University of Glasgow, 2003. Includes bibliographical references. Print version also available.
4
Nam, Haewon. "Ultrasound-modulated optical tomography." Texas A&M University, 2002. http://hdl.handle.net/1969/448.
5
Akcay, Avni Ceyhun. "System design and optimization of optical coherence tomography." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3586.
Анотація:
Optical coherence imaging, including tomography (OCT) and microscopy (OCM), has been a growing research field in biomedical optical imaging in the last decade. In this imaging modality, a broadband light source, thus of short temporal coherence length, is used to perform imaging via interferometry. A challenge in optical coherence imaging, as in any imaging system towards biomedical diagnosis, is the quantification of image quality and optimization of the system components, both a primary focus of this research. We concentrated our efforts on the optimization of the imaging system from two main standpoints: axial point spread function (PSF) and practical steps towards compact low-cost solutions. Up to recently, the criteria for the quality of a system was based on speed of imaging, sensitivity, and particularly axial resolution estimated solely from the full-width at half-maximum (FWHM) of the axial PSF with the common practice of assuming a Gaussian source power spectrum. As part of our work to quantify axial resolution we first brought forth two more metrics unlike FWHM, which accounted for side lobes in the axial PSF caused by irregularities in the shape of the source power spectrum, such as spectral dips. Subsequently, we presented a method where the axial PSF was significantly optimized by suppressing the side lobes occurring because of the irregular shape of the source power spectrum. The optimization was performed through optically shaping the source power spectrum via a programmable spectral shaper, which consequentially led to suppression of spurious structures in the images of a layered specimen. The superiority of the demonstrated approach was in performing reshaping before imaging, thus eliminating the need for post-data acquisition digital signal processing. Importantly, towards the optimization and objective image quality assessment in optical coherence imaging, the impact of source spectral shaping was further analyzed in a task-based assessment method based on statistical decision theory. Two classification tasks, a signal-detection task and a resolution task, were investigated. Results showed that reshaping the source power spectrum was a benefit essentially to the resolution task, as opposed to both the detection and resolution tasks, and the importance of the specimen local variations in index of refraction on the resolution task was demonstrated. Finally, towards the optimization of OCT and OCM for use in clinical settings, we analyzed the detection electronics stage, which is a crucial component of the system that is designed to capture extremely weak interferometric signals in biomedical and biological imaging applications. We designed and tested detection electronics to achieve a compact and low-cost solution for portable imaging units and demonstrated that the design provided an equivalent performance to the commercial lock-in amplifier considering the system sensitivity obtained with both detection schemes.Ph.D.
Optics and Photonics
Optics
6
Beitel, David. "Development of optical sources for optical coherence tomography." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112557.
Анотація:
The development of two different classes of optical sources for TD-OCT and FD-OCT are presented in this thesis. The design of several low-cost, high-performance BBSs, based on the ASE of two SOAs and EDF, are presented. Two different configuration types that were designed in this thesis are found to be effective BBSs. These sources are implemented in a TD-OCT system and therefore imaging performance is discussed as well. Secondly, two different WSSs based on mode-locked SFRLs with applications in SS-OCT are presented.From our experimental results with BBSs, we conclude that: (1) S/C-band output produced by the ASE emitted from two cascaded SOAs can be effectively extended with L-band output produced from the ASE of EDF; (2) An even broader output is achievable by: coupling the C-band and L-band outputs from a C-band SOA and EDF respectively and then amplifying the coupled output through an S-band SOA; (3) OCT imaging systems employing a light source with an S+C+L band output, with a center wavelength of approximately 1520 nm, can achieve high penetration depths in biological tissue.
From our experimental results with SFRLs, we conclude that: (1) Our two SFRL configurations generate picosecond pulses with reasonably narrow linewidths: 0.2--0.5 nm, and a sweeping range of about 50 nm; (2) These SFRLs can function as laser swept sources by setting the driving frequency of the RF generator to a periodic ramping function.
7
Behrooz, Ali. "Multiplexed fluorescence diffuse optical tomography." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50401.
Анотація:
Fluorescence tomography (FT) is an emerging non-invasive in vivo molecular imaging modality that aims at quantification and three-dimensional (3D) localization of fluorescent tagged inclusions, such as cancer lesions and drug molecules, buried deep in human and animal subjects. Depth-resolved 3D reconstruction of fluorescent inclusions distributed over the volume of optically turbid biological tissue using the diffuse fluorescent photons detected on the skin poses a highly ill-conditioned problem, as depth information must be extracted from boundary data. Due to this ill-posed nature of FT reconstructions, noise and errors in the data can severely impair the accuracy of the 3D reconstructions. Consequently, improvements in the signal-to-noise ratio (SNR) of the data significantly enhance the quality of the FT reconstructions. Furthermore, enhancing the SNR of the FT data can greatly contribute to the speed of FT scans. The pivotal factor in the SNR of the FT data is the power of the radiation illuminating the subject and exciting the administered fluorescent agents. In existing single-point illumination FT systems, the illumination power level is limited by the skin maximum radiation exposure levels. In this research, a multiplexed architecture governed by the Hadamard transform was conceptualized, developed, and experimentally implemented for orders-of-magnitude enhancement of the SNR and the robustness of FT reconstructions. The multiplexed FT system allows for Hadamard-coded multi-point illumination of the subject while maintaining the maximal information content of the FT data. The significant improvements offered by the multiplexed FT system were validated by numerical and experimental studies carried out using a custom-built multiplexed FT system developed exclusively in this work. The studies indicate that Hadamard multiplexing offers significantly enhanced robustness in reconstructing deep fluorescent inclusions from low-SNR FT data.
8
Watson, Thomas. "Advances in optical projection tomography." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/58486.
Анотація:
Optical projection tomography (OPT) is a 3D imaging technique that can be applied to non- or weakly scattering samples and is often described as the optical equivalent of x-ray computed tomography (CT). Analogous to x-ray CT, OPT acquires wide-field images of a sample from many angles and uses this projection data to reconstruct the 3D distribution, applicable to both absorption and fluorescence contrast. This thesis describes how to implement OPT on a standard wide-field microscope, derives rigorous models for image formation and reconstruction in OPT, and discusses how performance can be improved in terms of spatial resolution and acquisition time through the use of focal scanning, particularly for samples < 1 mm in diameter. After a brief overview of 3D optical imaging techniques, a mathematical framework is developed for the standard experimental approaches to OPT based on telecentric imaging, which allows a rigorous comparison with x-ray CT. It is shown that reconstruction of the optical projections using filtered back projection introduces anisotropy to the spatial resolution in the reconstructed images. The OPTiM adapter plate is then described. This open hardware component, together with openly shared software, allows an existing microscope to be adapted for OPT at low cost, thereby increasing the accessibility of OPT for a wide range of researchers. To improve the performance of OPT in terms of spatial resolution and acquisition time, an alternative data acquisition model for OPT is developed that is based on telecentric remote focal scanning. Detailed analysis quantifies the expected improvement in the spatial resolution of the 3D image reconstructions and the reduction in the acquisition time. The derived mathematical framework is also used to identify factors for further optimisation. The focal-scanning concept is extended to “region-of-interest OPT”, where it is shown that the dynamic control of focal plane position can lead to improved signal to background ratios as well as reducing the impact of streak artefacts. The final section of the thesis addresses the equivalence between a non-telecentric optical system and cone-beam CT, which removes the telecentricity requirement of the traditional approach to OPT. Derivation of the associated optical transform leads to a modified form of reconstruction based on the FDK algorithm. It is shown that axial and lateral tracking enables this new OPT approach to acquire 3D images of a sub-volume within a larger body. The optical setup and associated optical transforms for both telecentric and non-telecentric systems are described.
9
Bateni, Vahid. "Isogeometric Approach to Optical Tomography." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103863.
Анотація:
Optical Tomography is an imaging modality that enhances early diagnosis of disease through use of harmless Near-Infrared rays instead of conventional x-rays. The subsequent images are used to reconstruct the object. However Optical Tomography has not been effectively utilized due to the complicated photon scattering phenomenon and ill-posed nature of the corresponding image reconstruction scheme.
The major method for reconstruction of the object is based on an iterative loop that constantly minimizes the difference between the predicted model of photon scattering with acquired images. Currently the most effective method of predicting the photon scattering pattern is the solution of the Radiative Transfer Equation (RTE) using the Finite Elements Method (FEM). However, the conventional FEM uses classical C0 interpolation functions, which have shortcomings in terms of continuity of the solution over the domain as well as proper representation of geometry. Hence higher discretization is necessary to maintain accuracy of gradient-based results which may significantly increase the computational cost in each iteration.
This research implements the recently developed Isogeometric Approach (IGA) and particularly IGA-based FEM to address the aforementioned issues. The IGA-based FEM has the potential to enhance adaptivity and reduce the computational cost of discretization schemes. The research in this study applies the IGA method to solve the RTE with the diffusion approximation and studies its behavior in comparison to conventional FEM.
The results show comparison of the IGA-based solution with analytical and conventional FEM solutions in terms of accuracy and efficiency. While both methods show high levels of accuracy in reference to the analytical solution, the IGA results clearly excel in accuracy. Furthermore, FE solutions tend to have shorter runtimes in low accuracy results. However, in higher accuracy solutions, where it matters the most, the IGA proves to be considerably faster.Doctor of Philosophy
CT scans can save lives by allowing medical practitioners observe inside the patient's body without use of invasive surgery. However, they use high energy, potentially harmful x-rays to penetrate the organs. Due to limits of the mathematical algorithm used to reconstruct the 3D figure of the organs from the 2D x-ray images, many such images are required. Thus, a high level of x-ray exposure is necessary, which in periodic use can be harmful. Optical Tomography is a promising alternative which replaces x-rays with harmless Near-infrared (NIR) visible light. However, NIR photons have lower energy and tend to scatter before leaving the organs. Therefore, an additional algorithm is required to predict the distribution of light photons inside the body and their resulting 2D images. This is called the forward problem of Optical Tomography. Only then, like conventional CT scans, can another algorithm, called the inverse solution, reconstruct the 3D image by diminishing the difference between the predicted and registered images. Currently Optical Tomography cannot replace x-ray CT scans for most cases, due to shortcomings in the forward and inverse algorithms to handle real life usages. One obstacle stems from the fact that the forward problem must be solved numerous times for the inverse solution to reach the correct visualization. However, the current numerical method, Finite Element Method (FEM), has limitations in generating accurate solutions fast enough using economically viable computers. This limitation is mostly caused by the FEM's use of a simpler mathematical construct that requires more computations and is limited in accurately modelling the geometry and shape. This research implements the recently developed Isogeometric Analysis (IGA) and particularly IGA-based FEM to address this issue. The IGA-based FEM uses the same mathematical construct that is used to visualize the geometry for complicated applications such as some animations and computer games. They are also less complicated to apply due to much lower need for partitioning the domain. This study applies the IGA method to solve the forward problem of diffuse Optical Tomography and compare the accuracy and speed of IGA solution to the conventional FEM solution. The comparison reveals that while both methods can reach high accuracy, the IGA solutions are relatively more accurate. Also, while low accuracy FEM solutions have shorter runtimes, in solutions with required higher accuracy levels, the IGA proves to be considerably faster.
10
Armstrong, Julian. "Anatomical optical coherence tomography in the human upper airway." University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0022.
Анотація:
[Truncated abstract] This thesis describes the development, clinical validation and initial application of a technique for taking measurements of the shape and dimensions of the human upper airway, called anatomical optical coherence tomography (aOCT). The technique uses a transparent catheter containing a rotating optical probe which is introduced transnasally and positioned in the airway and oesophagus. Optical coherence tomography is used to take calibrated cross-sectional images of the airway lumen as the probe rotates. The probe can also be advanced or withdrawn within the catheter during scanning to build up three-dimensional information. The catheter remains stationary so that the subject is not aware of the probe motion. The initial application of the system is research into obstructive sleep apnoea (OSA), a serious condition characterized by repetitive collapse of the upper airway during sleep and an independent risk factor for deaths by heart disease, strokes or car accidents. Measurement of upper airway size and shape is important for the investigation of the pathophysiology of OSA, and for the development and assesment of new treatments. . . We have used aOCT to capture three-dimensional data sets of the airway shape from upper oesophagus to the nasal cavity, undertaken measurements of compliance and other airway characteristics, and recorded dynamic airway shape during confirmed sleep apnoea events in a hospital sleep laboratory. We have shown that aOCT generates quantitative, real-time measurements of upper airway size and shape, allowing study over lengthy periods during both sleep and wakefulness. These features should make it useful for study of upper airway behavior to investigate OSA pathophysiology, and aid clinical management and treatment development.
11
Zuluaga, Andrés Felipe. "Contrast agents for tumor detection with optical coherence tomography /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
12
Trifanov, Irina. "Fibre optical sources and systems for optical coherence tomography." Thesis, University of Kent, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.593914.
Анотація:
Optical Coherence Tomography (OCT) is a powerful imaging technology in biomedical research and medicine. It enables in situ. 3D visualization of tissue structure and pathology, without the need. to excise the tissue and resolution approaching that of histology. OCT has had the most clinical impact in ophthalmology, where it provides structural and quantit ative informat ion that cannot be obtained by any other modality. The objective of the work presented in this thesis was the development of new imaging methods and optical devices to progress the OCT technology in t erms of its versatility, as well as to improve on parameters such as resolution, wavelength availability, integration effort and reliability. One of the most desired features in high resolution imaging is the display of simultaneously generated confocal images. The implementation of a confocal channel at the core of an OCT with quasi-simultaneous display of both images is demonstrated by synchronous optical switching of the power in the reference arm of the interferometer with the scanner determining the line in the final raster. The 1.0-1.1 11m region of the optical spectrum emerged as an attractive option compared to the standard 700-900 nm region, due to increased penetration beyond the retina, into the choroid, and reduced scat tering. Therefore, in this thesis, two novel optical sources based on fiber optic technology at 1 micrometer have been researched, assembled and tested: (a) a broadband ASE source based on combination of Yb-doped and Nd-doped silica fibers . The source emits at a cent ral wavelength of 1060 nm with a full-width-halfmaximum exceeding 70 nrn and 20 m\V output power; and (b) a swept fiber laser source emitting at 1065 nm central wavelength, with :::::l 50 nm tuning range and 40 m Woutput average power. A simple solution to linearize the sweeping in wavenumber (optical frequency), as required for image rendering, is demonstrated. The two prototype sources have been packaged and their performances validated in fully func tional OCT systems.
13
Silva, K. K. M. Buddhika Dilusha. "Optical coherence tomography : technology enhancements and novel applications." University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0087.
Анотація:
In the last fifteen years, a great deal of effort has been put forth, worldwide, for investigating and enhancing various aspects of optical coherence tomography (OCT). This thesis begins with a description of the technique of OCT, and an analysis of its underlying theory. The design and construction of an OCT system is described, with particular emphasis on a novel delay scanning method, and novel signal processing. Application of OCT to non-destructive characterisation of seeds, examination of skin lesions, measurement of fluid flow, and refractive index determination, are then demonstrated. Two technological enhancements to OCT are presented in this thesis. The first, an extended-range Fourier domain optical delay line (FDODL), extends the scan range of the traditional FDODL by a factor of almost 9, by scanning the galvanometer mirror around the region of zero tilt-angle. Polarisation optics are used to prevent light coupling back into the interferometer after only a single pass through the FDODL. A non-coplanar version of the FDODL is also presented, which overcomes the losses associated with the polarisation-based design, but trades off scan range to do so. Both versions of FDODL demonstrated excellent linearity and scan uniformity. The second technology presented here, bifocal optical coherence refractometry (BOCR), affords OCT the ability to measure refractive indices within turbid media. It achieves this by generating two confocal gates within the sample. From knowledge of the system parameters, and measurements of the confocal gate separation, the refractive index within the medium is evaluated to within ±0.01. Refractive index mapping is then demonstrated in a number of turbid samples. Three other applications of OCT are also demonstrated in this thesis. The first is the use of OCT to measure full thickness in lupin seeds. Although OCT could not penetrate the entire thickness of the hull, it is demonstrated that the variation in thickness of the two layers observed with OCT, explained 81% of the variation in thickness of the entire hull measured under a SEM. OCT was then applied, for what is believed to be the first time, in a large scale seed screening program. The second application is a preliminary investigation of the suitability of OCT to aid in the diagnosis of skin lesions. Although our system did not possess sufficient positioning accuracy to enable a direct one-to-one comparison between OCT and histology, a number of correspondences between OCT and histology images were demonstrated. The final application of OCT demonstrated here is a novel phase-locked-loop based demodulation scheme, to perform Doppler OCT. This demodulation scheme demonstrated a dynamic range of 98dB, a velocity range of ±20mm/s, and velocity resolution of 0.5mm/s. Using this system, laminar flow was demonstrated in milk flowing through a capillary tube.
14
Recaldini, Valentino. "Optical diffraction tomography: a resolution study." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21258/.
Анотація:
In the past years, optical diffraction tomography (ODT) has been used both in cell imaging and to investigate the three-dimensional refractive index (RI) of large-scale (millimetre-sized) samples. In this technique, the projections at different illumination angles are acquired through digital holography (DH) and used to estimate the complex wave fields, which can be refocused with the aid of numerical diffraction algorithms. However, real extended specimens may not completely lie on a single plane. In this case, the (refocused) projections retain a certain amount of defocus which will affect the tomographic reconstruction.
For this reason, this thesis aims to study the spatial resolution of an ODT system when a point-like object is allowed to go in and out of focus and is reconstructed without numerical refocusing. Two-dimensional rotation and computational Fourier optics will be used to track and model defocus and lenses during the simulation of the projections. Spatial resolution will be assessed both qualitatively and quantitatively by numerically computing the full width at half maximum (FWHM) in relation to the maximum defocus to which a simulated point was subjected during acquisition.
Lastly, deconvolution is used to remove unwanted blur.
15
Malmström, Mikael. "Multi-angle Oblique Optical Coherence Tomography." Thesis, KTH, Laserfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-72978.
Анотація:
Optical Coherence Tomography (OCT) is a non-invasive high-resolutionmethod for measuring the reectance of scattering media in 1/2/3D, e.g.skin. The method has been used in a number of dierent medical elds andfor measurement of tissue optical properties.The software developed in this thesis is able to display features hidden ina shadowed volume by adding multiple OCT measurements taken at obliqueangles, a technique here called Multiple-Angle Oblique Optical CoherenceTomography (MAO-OCT).Three dierent objects with were measured at 5 to 9 angles. The measurementswere automatically and manually aligned in the software. They werealso tested with 6 dierent high pass intensity lters (HPIF) and reduced insize using 4 dierent methods to speed up calculations.The software's automatic alignment was tested with one tilted computergenerated test at 9 angles and with 5 dierent shadow strengths.With MAO-OCT it is possible to remove some eects of shadows in OCT,though it comes with a cost of reduced sharpness. The errors depend muchon the dierences in index of refraction in the sample.The software managed to automatically align 90% of the articial measurements,and 60% of the OCT measurements. The shadow strength andthe resize method had no noticeable eect on the automatic alignment of themeasurements.
16
Li, Ang. "Diffuse optical tomography with multiple priors /." Thesis, Connect to Dissertations & Theses @ Tufts University, 2005.
Анотація:
Thesis (Ph.D.)--Tufts University, 2005.Advisers: David A. Boas; Yaacov Shapira. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 113-126). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
17
Alex, Aneesh. "Multispectral three-dimensional optical coherence tomography." Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/54164/.
Анотація:
A spectral-domain OCT system operating at 1300 nm wavelength region, capable of acquiring 47,000 A-lines/s, was designed and developed. Its axial and transverse resolutions were ∼ 6 µm and ∼15 µm respectively. OCT images of human skin were obtained in vivo using three OCT systems, in order to find the optimal wavelength region for dermal imaging. 800 nm OCT system provided better image contrast over other two wavelength regions. Meanwhile, 1300 nm wavelength region was needed to obtain information from deeper dermal layers. To determine the effect of melanin pigmentation on OCT, images were taken from subjects with different ethnic origins. Interestingly, melanin pigmentation was found to have little effect on penetration depth in OCT. In vitro tumour samples, comprising samples with different degrees of dysplasia, were imaged at 800 nm, 1060 nm and 1300 nm wavelength regions to find the capability of OCT to diagnose microstructural changes occurring during tumour progression. 800 nm OCT system was capable to detect the malignant changes with higher contrast than other wavelength regions. However, higher wavelength regions were required to penetrate deeper in densely scattering tumour samples at advanced stages. OCT system operating at 1060 nm was combined with a photoacoustic imaging (PAT) system to obtain complementary information from biological tissues. This multimodal OCT/PAT system demonstrated its potential to deliver microstructural information based on optical scattering and vascular information based on optical absorption in living mice and human skin. The results indicate OCT as a promising imaging modality that can have profound applications in several areas of clinical diagnostic imaging.
18
Lee, Michael. "Optical diffusion tomography data acquisition system." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36540.
19
Hee, Michael Richard. "Optical coherence tomography of the eye." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10263.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 221-230).
by Michael Richard Hee.
Ph.D.
20
Müller, Paul. "Optical Diffraction Tomography for Single Cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-202261.
Анотація:
Analyzing the structure of a single cell based on its refractive index (RI) distribution is a common and valued approach, because it does not require any artificial markers. The RI is an inherent structural marker that can be quantified in three dimensions with optical diffraction tomography (ODT), an inverse scattering technique. This work reviews the theory of ODT and its implementation with an emphasis on single-cell analysis, identifying the Rytov approximation as the most efficient descriptor for light propagation. The accuracy of the reconstruction method is verified with in silico data and imaging artifacts associated with the inverse scattering approach are addressed. Furthermore, an experimental ODT setup is presented that consists of a bright-field microscope, a phase-imaging camera, and an optical trap combined with a microfluidic chip. A novel image analysis pipeline is proposed that addresses image corrections and frame alignment of the recorded data prior to the RI reconstruction. In addition, for a rotational axis that is tilted with respect to the image plane, an improved reconstruction algorithm is introduced and applied to single, suspended cells in vitro, achieving sub-cellular resolution.
21
Valdez, Ashley. "Snapshot Spectral Domain Optical Coherence Tomography." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/613413.
Анотація:
Optical coherence tomography systems are used to image the retina in 3D to allow ophthalmologists diagnose ocular disease. These systems yield large data sets that are often labor-intensive to analyze and require significant expertise in order to draw conclusions, especially when used over time to monitor disease progression. Spectral Domain Optical Coherence Tomography (SD-OCT) instantly acquires depth profiles at a single location with a broadband source. These systems require mechanical scanning to generate two- or three-dimensional images. Instead of mechanically scanning, a beamlet array was used to permit multiple depth measurements on the retina with a single snapshot using a 3x 3 beamlet array. This multi-channel system was designed, assembled, and tested using a 1 x 2 beamlet lens array instead of a 3 x 3 beamlet array as a proof of concept prototype. The source was a superluminescent diode centered at 840nm with a 45nm bandwidth. Theoretical axial resolution was 6.92um and depth of focus was 3.45mm. Glass samples of varying thickness ranging from 0.18mm to 1.14mm were measured with the system to validate that correct depth profiles can be acquired for each channel. The results demonstrated the prototype system performed as expected, and is ready to be modified for in vivo applicability.
22
Cong, Alexander Xiao. "Reconstruction Methods for Optical Molecular Tomography." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19253.
Анотація:
Molecular imaging plays an important role for development of systems biomedicine, which non-invasively extracts pictorial information on physiological and pathological activities at the cellular and molecular levels. Optical molecular tomography is an emerging area of molecular imaging. It locates and quantifies a 3D molecular probe distribution in vivo from data measured on the external surface of a small animal around the visible and infrared range. This approach can facilitate or enable preclinical applications such as cancer studies, involving angiogenesis, tumor growth, cell motility, metastasis, and interaction with a micro-environment. The reconstruction of diffuse light sources is the central task of optical molecular tomography, and generally ill-posed and rather complex. The key element of optical molecular tomography includes the geometrical model, tissue properties, photon characteristics, transport model, and reconstruction algorithm. This dissertation focuses mainly on the development optical molecular tomography methods based on bioluminescence/fluorescence probes to solve some well-known challenges in this field. Our main results are as follows. We developed a new algorithm for estimation of optical parameters based on the phase-approximation model. Our iterative algorithm takes advantage of both the global search ability of the differential evolution algorithm and the ef"ciency of the conjugate gradient method. We published the first paper on multispectral bioluminescence tomography (BLT). The multispectral BLT approach improves the accuracy and stability of the BLT reconstruction even if data are highly noisy. We established a well-posed inverse source model for optical molecular tomography. Based on this model, we proposed a differential evolution-based reconstruction algorithm to determine the source locations and strengths accurately and reliably. Furthermore, to enhance the spatial resolution of fluorescence molecular tomography, we proposed fluorescence micro-tomography to image cells in a tissue scaffold based on Monte Carlo simulation on a massive parallel processing architecture. Each of these methods shows better performance in numerical simulation, phantom experiments, and mouse studies than the conventional methods.
Ph. D.
23
Wang, Zhao. "Intravascular Optical Coherence Tomography Image Analysis." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1364673682.
24
Meemon, Panomsak. "Development of optical coherence tomography for tissue diagnostics." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4558.
Анотація:
Endoscopic OCT utilizes a special miniature probe in the sample arm to access tubular organs inside the human body, such as the cardiovascular system, the lung, the gastrointestinal tract, the urinary tract, and the breast duct. We present an optical design of a dynamic focus endoscopic probe that is capable of about 4 to 6 micrometers] lateral resolution over a large working distance (i.e. up to 5 mm from the distal end of the probe). The dynamic focus capability allows integration of the endoscopic probe to GD-OCM imaging to achieve high resolution endoscopic tomograms. We envision the future of this developing technology as a solution to high resolution, minimally invasive, depth-resolved imaging of not only structure but also the microvasculature of in vivo biological tissues that will be useful for many clinical applications, such as dermatology, ophthalmology, endoscopy, and cardiology. The technology is also useful for animal study applications, such as the monitoring of an embryo's heart for the development of animal models and monitoring of changes in blood circulation in response to external stimulus in small animal brains.; However, the improvement in imaging speed of FD-OCT comes at the expense of a reduction in sensitivity to slow flow information and hence a reduction in detectable velocity range; 2) A structural ambiguity so-called 'mirror image' in FD-OCT prohibits the use of maximum sensitivity and imaging depth range; 3) The requirement of high lateral resolution to resolve capillary vessels requires the use of an imaging optics with high numerical aperture (NA) that leads to a reduction in depth of focus (DOF) and hence the imaging depth range (i.e. less than 100 microns) unless dynamic focusing is performed. Nevertheless, intrinsic to the mechanism of FD-OCT, dynamic focusing is not possible. In this dissertation, the implementation of PR-DOCT in a high speed swept-source based FD-OCT is investigated and optimized. An acquisition scheme as well as a processing algorithm that effectively extends the detectable velocity dynamic range of the PR-DOCT is presented. The proposed technique increased the overall detectable velocity dynamic range of PR-DOCT by about five times of that achieved by the conventional method. Furthermore, a novel technique of mirror image removal called 'Dual-Detection FD-OCT' (DD-FD-OCT) is presented. One of the advantages of DD-FD-OCT to Doppler imaging is that the full-range signal is achieved without manipulation of the phase relation between consecutive axial lines. Hence the full-range DD-FD-OCT is fully applicable to phase-resolved Doppler detection without a reduction in detectable velocity dynamic range as normally encountered in other full-range techniques. In addition, PR- DOCT can utilize the maximum SNR ratio provided by the full-range capability.; Microvasculature can be found in almost every part of the human body, including the internal organs. Importantly, abnormal changes in microvasculature are usually related to pathological development of the tissue cells. Monitoring of changes in blood flow properties in microvasculature, therefore, provides useful diagnostic information about pathological conditions in biological tissues as exemplified in glaucoma, diabetes, age related macular degeneration, port wine stains, burn-depth, and potentially skin cancer. However, the capillary network is typically only one cell in wall thickness with 5 to 10 microns in diameter and located in the dermis region of skin. Therefore, a non-invasive flow imaging technique that is capable of depth sectioning at high resolution and high speed is demanded. Optical coherence tomography (OCT), particularly after its advancement in frequency domain OCT (FD-OCT), is a promising tool for non-invasive high speed, high resolution, and high sensitivity depth-resolved imaging of biological tissues. Over the last ten years, numerous efforts have been paid to develop OCT-based flow imaging techniques. An important effort is the development of phase-resolved Doppler OCT (PR-DOCT). Phase-resolved Doppler imaging using FD-OCT is particularly of interest because of the direct access to the phase information of the depth profile signal. Furthermore, the high speed capability of FD-OCT is promising for real time flow monitoring as well as 3D flow segmentation applications. However, several challenges need to be addressed; 1) Flow in biological samples exhibits a wide dynamic range of flow velocity caused by, for example, the variation in the flow angles, flow diameters, and functionalities.; This capability is particularly useful for imaging of blood flow that locates deep below the sample surface, such as blood flow at deep posterior human eye and blood vessels network in the dermis region of human skin. Beside high speed and functional imaging capability, another key parameter that will open path for optical diagnostics using OCT technology is high resolution imaging (i.e. in a regime of a few microns or sub-micron). Even though the lateral resolution of OCT can be independently improved by opening the NA of the imaging optics, the high lateral resolution is maintained only over a short range as limited by the depth of focus that varies inversely and quadratically with NA. Recently developed by our group, 'Gabor-Domain Optical Coherence Microscopy' (GD-OCM) is a novel imaging technique capable for invariant resolution of about 2-3 micrometers] over a 2 mm cubic field-of-view. This dissertation details the imaging protocol as well as the automatic data fusion method of GD-OCM developed to render an in-focus high-resolution image throughout the imaging depth of the sample in real time. For the application of absolute flow measurement as an example, the precise information about flow angle is required. GD-OCM provides more precise interpretation of the tissue structures over a large field-of-view, which is necessary for accurate mapping of the flow structure and hence is promising for diagnostic applications particularly when combined with Doppler imaging. Potentially, the ability to perform high resolution OCT imaging inside the human body is useful for many diagnostic applications, such as providing an accurate map for biopsy, guiding surgical and other treatments, monitoring the functional state and/or the post-operative recovery process of internal organs, plaque detection in arteries, and early detection of cancers in the gastrointestinal tract.ID: 029050978; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 145-154).
Ph.D.
Doctorate
Optics and Photonics
25
Faber, Dirk Johannes. "Functional optical coherence tomography spatially resolved measurements of optical properties /." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2005. http://dare.uva.nl/document/88794.
26
Toadere, Florin. "Dispersion in optical configurations and sources for Optical Coherence Tomography." Thesis, University of Kent, 2017. https://kar.kent.ac.uk/64278/.
Анотація:
Optical coherence tomography is a biomedical imaging technique employed to visualize tissue structure, ocular vasculature and blood flow. An OCT system is a non-invasive biomedical imaging system that provides bi-dimensional and three-dimensional images of biological tissue with micrometer scale resolution and millimeter scale depth range. In clinical application, OCT is employed in vivo imaging of the human eye. Swept source optical coherence tomography (SS-OCT) is the latest and fastest method of scanning. However, there are several disadvantages of the SS-OCT such as: the decrease of the roll-off sensitivity as the depth of scanning increases and the presence of mirror terms in the OCT images. The main objective of the work presented throughout this thesis was to evaluate the effects of dispersion on the performance of OCT. This study extends the research from the optical configurations at the core of OCT systems to the optical sources, where we show that dispersion can be usefully employed to obtain sweeping. We prove that an akinetic swept source (AKSS) can be devised for the important band of OCT, 800 nm, where there is still no MHz swept source available. In a Michelson interferometer a Fourier domain optical delay line was used for dispersion compensation that subsequently was employed to control the dispersion in an OCT system. A first goal of this thesis was to increase dispersion in order to evaluate the possibility of removing mirror terms from the OCT images. Therefore, three methods of dispersion measurement were evaluated. The first method measures the full width half maximum of the autocorrelation function. The second method uses a super continuous laser and an acoustic-optic tunable filter to measure the path dispersion in the position of the autocorrelation peak. A third method consists in a fitting method applied to channeled spectra collected from the interferometer when using a mirror. A second goal of this thesis was to prove the usefulness of employing dispersion in building a SS. In the process of akinetic swept source optimization, several types of dispersive fibres were tested and the most optimum conditions for driving a semiconductor optical amplifier were established. A dual mode locking scheme was used to tune the akinetic swept source at MHz rates. The axial range of the swept source was evaluated by scanning through the channeled spectrum of a Michelson interferometer.
27
Siddiqui, Meena. "Optical domain subsampling for data-efficient optical coherence tomography (OCT)." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82390.
Анотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 97-100).
Recent advances in optical coherence tomography (OCT) have led to higher-speed sources that support imaging over longer depth ranges. Limitations in the bandwidth of state-of-the-art acquisition electronics, however, prevent adoption of these advances into clinical applications. This thesis introduces optical-domain subsampling as a method for increasing the imaging range while reducing the acquisition bandwidth. Optically subsampled lasers utilize a discrete set of wavelengths to alias fringe signals along an extended depth range into a bandwidth limited window. By detecting the complex fringe signals and under the assumption of a depth-constrained signal, optical domain subsampling enables recovery of the depth-resolved scattering signal without overlapping artifacts. Key principles behind subsampled imaging will be discussed, as well as the design criteria for an experimental subsampled laser. A description of the laser, interferometer, data acquisition system, and signal processing steps is given, and the results of point spread functions compressed into a baseband window are presented. Images that were taken with the subsampled OCT system and a wide-field microscope show that this imaging scheme is viable in vivo and can advantageously image samples that span a long depth range.
by Meena Siddiqui.
S.M.
28
Tearney, Guillermo J. "Optical biopsy of in vivo tissue using optical coherence tomography." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10139.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 213-220).
by Guillermo James Tearney.
Ph.D.
29
Fleming, Christine P. "Characterization of Cardiac Tissue Using Optical Coherence Tomography." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1270718628.
30
Adie, Steven G. "Enhancement of contrast in optical coherence tomography : new modes, methods and technology." University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0127.
Анотація:
This thesis is concerned with exploiting the native optical coherence tomography (OCT) contrast mechanism in new ways and with a new contrast mechanism, in both cases to enhance the information content of the tomographic image. Through experiments in microsphere solutions, we show that static speckle contains information about local particle density when the effective number of scatterers in the OCT resolution volume is less than about five. This potentially provides contrast enhancement in OCT images based on local scatterer density, and we discuss the experimental conditions suited to utilising this in biological tissue. We also describe the corrupting effects of multiple scattering, a ubiquitous phenomenon in OCT, on the information content of the static speckle. Consequently, we detail the development of polarisation-based metrics for characterising multiple scattering in OCT images of solid biological tissues. We exploit a detection scheme used for polarisation-sensitive contrast for a new purpose. We present experiments demonstrating the behaviour of these metrics in liquid phantoms, and in biological tissues, ranging from homogeneous non-birefringent to highly heterogeneous and birefringent samples. We discuss the conditions under which these metrics could be used to characterise the relative contribution of single and multiple scattering and, thus, aid in the study of penetration depth limits in OCT. We present a study of a new contrast mechanism - dynamic elastography which seeks to determine the dynamic mechanical properties of tissues. We present a framework for describing the OCT signal in samples undergoing vibrations, and perform experiments at vibration frequencies in the order of tens to hundreds of Hertz, to confirm the theory, and demonstrate the modes of measurement possible with this technique. These modes of measurement, including acoustic amplitude-sweep and frequency-sweep, could provide new information about the local mechanical properties of a sample. We describe a technological advancement enabling, in principle, measurements of local tissue refractive index contrast much deeper within a sample, than is possible with conventional OCT imaging. The design is based on measurement of the optical path length through tissue filling a fixed-width channel situated at the tip of a needle. The needle design and calibration is presented, as well as measurements of scattering phantoms and various biological tissues. This design potentially enables the use of refractive index-based contrast enhancement in the guidance of breast biopsy procedures.
31
Guggenheim, James A. "Multi-modal diffuse optical tomography and bioluminescence tomography system for preclinical imaging." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5278/.
Анотація:
The development, characterisation and testing of a novel all-optical, multi-modal preclinical biomedical imaging system is presented. The system aims to provide a new way of accurately visualising the spatial distribution and activity of molecular structures and processes in small animals by combining 3D bioluminescence tomography (BLT; reconstruction-based 3D imaging of internal bioluminescent reporter distributions), diffuse optical tomography (DOT; reconstruction-based imaging of optical parameter distributions) and optical surface capture techniques. The key principle of the imaging system is to use surface capture results to enhance the accuracy of DOT image reconstruction, and to use the results of both surface capture and DOT to enhance the accuracy of BLT. Presented experiments show that the developed system can reconstruct luminescent source distributions and optical parameters accurately and that small animal imaging is feasible with the system.
32
Tuten, William Scott. "Anterior Segment Optical Coherence Tomography-Based Phakometry Measurements in Children." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243629782.
33
Armstrong, Julian. "Anatomical optical coherence tomography in the human upper airway /." Connect to this title, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0022.
34
Bachmann, Adrian H. "Phase-locked Fourier domain optical coherence tomography /." Lausanne : EPFL, 2007. http://library.epfl.ch/theses/?nr=3847.
Анотація:
Thèse Ecole polytechnique fédérale de Lausanne EPFL, no 3847 (2007), Faculté des sciences et techniques de l'ingénieur STI, Programme doctoral Photonique, Institut d'imagerie et optique appliquée IOA (Laboratoire d'optique biomédicale LOB). Dir.: Theo Lasser, Rainer Leitgeb.
35
Jiao, Shuliang. "Polarization-sensitive Mueller-matrix optical coherence tomography." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/398.
Анотація:
Measuring the Mueller matrix with optical coherence tomography (OCT) makes it possible to acquire the complete polarization properties of scattering media with three-dimensional spatial resolution. We first proved that the measured degree-of-polarization (DOP) of the backscattered light by OCT remains unity-a conclusion that validated the use of Jones calculus in OCT. A multi-channel Mueller-matrix OCT system was then built to measure the Jones-matrix, which can be transformed into a Mueller matrix, images of scattering biological tissues accurately with single depth scan. We showed that when diattenuation is negligible, the round-trip Jones matrix represents a linear retarder, which is the foundation of conventional PS-OCT, and can be calculated with a single incident polarization state although the one-way Jones matrix generally represents an elliptical retarder; otherwise, two incident polarization states are needed. We discovered the transpose symmetry in the roundtrip Jones matrix, which is critical for eliminating the arbitrary phase difference between the two measured Jones vectors corresponding to the two incident polarization states to yield the correct Jones matrix. We investigated the various contrast mechanisms provided by Mueller-matrix OCT. Our OCT system for the first time offers simultaneously comprehensive polarization contrast mechanisms including the amplitude of birefringence, the orientation of birefringence, and the diattenuation in addition to the polarization-independent intensity contrast, all of which can be extracted from the measured Jones or the equivalent Mueller matrix. The experimental results obtained from rat skin samples, show that Mueller OCT provides complementary structural and functional information on biological samples and reveal that polarization contrast is more sensitive to thermal degeneration of biological tissues than amplitude-based contrast. Finally, an optical-fiber-based multi-channel Mueller-matrix OCT was built and a new rigorous algorithm was developed to retrieve the calibrated polarization properties of a sample. For the first time to our knowledge, fiber-based polarization-sensitive OCT was dynamically calibrated to eliminate the polarization distortion caused by the single-mode optical fiber in the sample arm, thereby overcoming a key technical impediment to the application of optical fibers in this technology.
36
Li, Jun. "Ultrasound-modulated optical tomography for biomedical applications." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1274.
Анотація:
I experimentally studied ultrasound-modulated optical tomography, which holds the promise for biomedical diagnosis. I measured the degree of polarization of laser speckles generated by scattered light transmitted through turbid media, investigated three signal-detection schemes for extracting the intensity of the ultrasound-modulated light, carried out experiments to image thick biological-tissue samples, and studied two techniques providing resolution in the cross-sections containing the ultrasonic axis.
The study of degree of polarization presented results important for the understanding of polarization phenomena in turbid media. I explored an optical-filtering based signal detection scheme, improved the parallel-lock-in speckle detection scheme and proposed a speckle-contrast detection scheme. With the speckle-contrast detection scheme, I successfully obtained images of biological-tissue samples up to 50 mm thick. Further I studied frequency-swept ultrasound-modulated optical tomography for sub-millimeter resolution imaging, and developed ultrasound-modulated optical computed tomography that was based on a back-projection image reconstruction method and obtained clear images of biological-tissue samples.
37
Kirillin, M. (Mikhail). "Optical coherence tomography of strongly scattering media." Doctoral thesis, University of Oulu, 2008. http://urn.fi/urn:isbn:9789514287572.
Анотація:
Abstract
Optical coherence tomography (OCT) is a modern rapidly developing technique for non-invasive imaging of the internal structure of optically non-uniform objects based on the principles of low-coherent interferometry. However, multiple scattering of light in the objects under study brings distortions to the images obtained by OCT. The analysis of formation of the OCT signals is required for understanding the role of multiple scattering in this formation and providing recommendations for optimal configuration of a measuring setup. In the present thesis formation of the OCT signals and images is analyzed implementing Monte Carlo simulations of light propagation in scattering media. Blood, intralipid solution, human skin and paper samples are chosen as the objects under study due to the interest in the diagnostics of these objects in biomedicine and paper industry.
Multilayer models of skin phantoms, skin and paper were developed in the frames of the present study for simulation of OCT signals and two-dimensional OCT images of these objects. The contribution of different scattering orders as well as different fractions of photons (least and multiply scattered, diffusive and non-diffusive) to these images was found allowing to evaluate the maximal depth of non-distorted imaging in each particular case.
The simulated OCT images were compared to the experimental ones demonstrating qualitative similarity. This fact allowed the author to analyze qualitatively the influence of parameters of the OCT setup on the images which have also been acquired in this work. The formation of the OCT images of paper samples with various refractive index matching liquids was also studied.
38
Meer, Freek Jeroen van der. "Vascular applications of quantitative optical coherence tomography." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2005. http://dare.uva.nl/document/89109.
39
Fergusson, James. "Full field swept source optical coherence tomography." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/49959/.
Анотація:
Optical Coherence Tomography (OCT) is a non-invasive volumetric imaging technique that offers micron scale resolution over several millimetres of depth penetration in tissue. The aim of the project was to develop Full Field Swept Source OCT (FFSSOCT), charting the specifications of the system throughout and drawing comparisons with available Fourier domain OCT (FDOCT) systems. A super luminescent diode (SLD) light source was tuned to different optical frequencies using an acousto-optical tunable filter. The successive optical frequencies were distributed across the sample in parallel and the sequential interference spectra were recorded with a high speed digital camera. Using a 5mW optical source at 850nm, 70dB sensitivity was ultimately achieved in a single five second acquisition, improving the original performance by 5dB and increasing acquisition and processing time significantly. Ex vivo retinal images of rat and tree shrew were recorded with multiple layers visible. All software was custom written in Labview, improving the user interface and processing time over the existing Matlab code. To enhance the performance of the system, the camera was subsequently upgraded from 15 to 45% quantum efficiency and from 250k to 1.3M pixels. The light source was also upgraded to 20mW. The software was improved with spectral processing and dispersion compensation. 85dB sensitivity was ultimately achieved. Further ex vivo retinal images were taken, showing comparative image quality to those of the same retinal samples recorded with FDOCT. Further attempts to increase the system performance were limited by internal reflections and interfering surfaces within the FFSSOCT design leading to saturation of the digital camera. In vivo imaging was attempted using software based phase jitter compensation. Improvement could be seen with simple reflecting structures.
40
Kwee, Ivo Widjaja. "Towards a Bayesian framework for optical tomography." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325658.
41
Byers, Robert. "Clinical applications of angiographic optical coherence tomography." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21904/.
Анотація:
Angiographic optical coherence tomography (OCTA) has rapidly found utility within many facets of medical research. Here OCTA algorithms are enabled on a commercial OCT system and verified through correlation with intra-vital light microscopy (IVM). While the vast majority of vessels were accurately measured, smaller vessels (< 30μm) have a tendency to appear dilated in comparison to IVM. The technique was also expanded upon to facilitate the imaging of subcutaneous murine fibrosarcoma tumours, negating the requirement for an intra-vital window. It was found that vessel measurement sensitivity was sufficiently high such that the morphologies of vessels within tumours expressing unique vascular endothelial growth factor (VEGF) isoforms could be differentiated, potentially providing a new angle of approach in the study of anti-angiogenic treatments. OCTA was then applied to human studies of atopic dermatitis, where it was found that metrics corresponding to vessel depth and morphology could be correlated with the sub-clinical severity of the condition. Knowledge of this could be utilised to observe the therapeutic response to treatment, past the point of clinical remission. A range of image-processing techniques were also developed, including automatic segmentation of the epidermal layer within skin being utilised to quantify the degree of epidermal thinning in response to applied skin strain, calculation of the skin capillary loop density and the response of skin vessels to temperature and pressure.
42
Panagiotou, C. "Information theoretic regularization in diffuse optical tomography." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1310436/.
Анотація:
Diffuse optical tomography (DOT) retrieves the spatially distributed optical characteristics of a medium from external measurements. Recovering these parameters of interest involves solving a non-linear and severely ill-posed inverse problem. In this thesis we propose methods towards the regularization of DOT via the introduction of spatially unregistered, a priori information from alternative high resolution anatomical modalities, using the information theory concepts of joint entropy (JE) and mutual information (MI). Such functionals evaluate the similarity between the reconstructed optical image and the prior image, while bypassing the multi-modality barrier manifested as the incommensurate relation between the gray value representations of corresponding anatomical features in the modalities involved. By introducing structural a priori information in the image reconstruction process, we aim to improve the spatial resolution and quantitative accuracy of the solution. A further condition for the accurate incorporation of a priori information is the establishment of correct alignment between the prior image and the probed anatomy in a common coordinate system. However, limited information regarding the probed anatomy is known prior to the reconstruction process. In this work we explore the potentiality of spatially registering the prior image simultaneously with the solution of the reconstruction process. We provide a thorough explanation of the theory from an imaging perspective, accompanied by preliminary results obtained by numerical simulations as well as experimental data. In addition we compare the performance of MI and JE. Finally, we propose a method for fast joint entropy evaluation and optimization, which we later employ for the information theoretic regularization of DOT. The main areas involved in this thesis are: inverse problems, image reconstruction & regularization, diffuse optical tomography and medical image registration.
43
Tung, Kai-Pin. "Coronary segmentation in intravascular optical coherence tomography." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24126.
Анотація:
Cardiovascular disease (CVD) is a fatal disease of the heart or blood vessels. The greatest number of deaths from CVD is coronary heart disease (CHD). It is characterised by thickening of the arterial vessel wall due to atheromatous plaque which may result in narrowing or even occlusion of arterial lumen. Currently, intravascular optical coherence tomography (IVOCT) has been increasingly used in the clinic for the diagnosis of CHD because it permits high-resolution direct tomographic visualisation of cross-sectional images. With IVOCT techniques, stenosis and restenosis caused by plaques and neointima can be detected and analysed. The first main contribution of the thesis is a technique for the automatic segmentation of the lumen border when the guide-wire artifacts are noticeable. The proposed segmentation technique is capable of eliminating guide-wire artifacts and generating accurate lumen borders from IVOCT sequences. Compared to commercially available systems, the proposed method is robust and accurate. The second main contribution of this thesis is an approach for the stent strut detection that can detect stent struts when their intensity responses are weak. This technique is based on stent strut shadow detection. The innovative aspect of our technique is that, for every detected strut shadow, a-priori probability map is applied to estimate the stent strut position. With the detected stent struts, a stent area can be estimated to analyse the neointima hyperplasia (NIH) thickness in IVOCT sequences. The thesis also proposes an approach for the neointima segmentation without any information of the stent but instead with the lumen border. The approach is a combination of a multi-atlas based segmentation approach and a patch-based segmentation approach. With the approach, the neointima label can be obtained by fusing labels from atlases. Compared to other label fusion approaches, a significant increase in segmentation accuracy can be observed.
44
Darrell, Alexander Louis. "Image reconstruction for emission optical projection tomography." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566048.
Анотація:
Emission Optical Projection Tomography (eO PT) is a relatively new imag- ing modality that bridges a gap between micro Magnetic Resonance Imag- ing and Confocal Laser Scanning Microscopy. eO PT can be used to image the anatomy and gene expression of intact biological specimens at high resolution and thus provides an alternative to time consuming methods such as serial sectioning. Tomographic image reconstruction for eOPT is currently performed using the Filtered Back Projection algorithm which, while being fast, does not account for the physics of image formation and thus can result in reconstructions of reduced resolution and questionable quantitative consistency. This thesis describes work that was done on eOPT in three areas, including image formation, tomographic reconstruction, and memory savings, the latter of which were required to bring implementation of 3D iterative reconstruction algorithms within reach for the relatively high-resolution eO PT imaging modality. In the area of image formation, measurements were taken to reveal the effects of optical blurring, diffraction and charge-coupled device (CCD) camera noise. Accurate models of each of these phenomena were developed and compared against the measurements. The subject of image reconstruction was first addressed with a modi- fication to the FBP algorithm designed to correct for the quantitative inaccuracies suspected of being introduced by the FBP algorithm when reconstructing specimens consisting of very fine detail. This was done by incorporating the quantitative aspects of the model of image formation into the FBP algorithm. The full model of image formation was incorpo- rated into the iterative Maximum Likelihood Expectation Maximisation (MLEM) algorithm. The third strand of this thesis focuses on various memory saving meth- ods developed to enable the implementation and testing of a variation of MLEM known as the Ordered Subsets Expectation Maximisation (OSEM). , Without such memory saving methods, the implementation of an iterative 3D reconstruction algorithm such as MLEM or OSEM using a full model of image formation would have remained beyond the capacity of modern computers for the foreseeable future, requiring several Terabytes of RAM. Comparisons were made between the quality of and the time required to produce FBP and OSEM reconstructions of the same data sets given the availability of limited computing resources. The feasibility of adopting OSEM reconstructions as an alternative to FBP reconstructions was dis- cussed, based on the use of currently available cutting edge computing hardware.
45
Arthur, Donna Louise. "Doppler optical coherence tomography for microcirculation studies." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/doppler-optical-coherence-tomography-for-microcirculation-studies(a18d59c3-6cfb-4266-98b1-188040bc120f).html.
Анотація:
This thesis forms part of an ongoing long-term project to investigate the suitability of Doppler optical coherence tomography (OCT) as a measurement tool to investigate skin thickness and blood flow in patients with systemic sclerosis. There is a discussion of the characterisation of an electro-optic phase modulator for use in a Doppler OCT imaging system which is being built for the purpose of clinical studies. In addition to this the development of software for the same system is described. The work includes a comparison of two methods of obtaining Doppler information that were tested with the system; a phase resolved method and a correlation mapping method. Initial structural and Doppler images obtained using the system are presented. In addition to this the development of semi-automated software to measure skin thickness from both OCT and high frequency ultrasound images is discussed. The results of a study, for which this software was developed, into skin thickness measurements using both techniques in both patients with systemic sclerosis and healthy controls are presented. Both OCT and high frequency ultrasound were able to measure a statistically significant difference in epidermal thickness at multiple locations on the body. Finally, the modification of a freely available Monte Carlo simulation for light propagation in multi-layered tissue (MCML) to enable the simulation of structural and Doppler OCT images is covered. The simulation was able to extract the magnitude of the simulated flow accurately to within an order of magnitude, and after a simple filter was applied to eliminate fluctuations in the data the structure of the Doppler image closely matched what was modelled.
46
Nurgiyatna, Nurgiyatna. "Tomography imaging based on plastic optical fibre." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/tomography-imaging-based-on-plastic-optical-fibre(481b898a-b1dc-49ae-aa3f-3555a982bb75).html.
Анотація:
Plastic optical fibres (POF) can be made sensitive to various parameters. Therefore, a successful implementation of tomographic imaging based on POF sensors will open the way to develop imagers for various parameters utilising this inexpensive sensor material. The work reported in this thesis is aiming to implement real time tomographic imaging based on the POF sensor. As the system uses light (photons) guided along the sensor to capture the information and deliver a signal at the periphery of the sensor, this technique is referred to as Photonic Guided Path Tomography (PGPT). As an initial stage of the work, we perform systematic testing of the sensitivity of POF transmission to bending. The results confirm that grooving can enhance this sensitivity of the POF sensor. They also provide an empirical proof of the anticipated changes in transmission loss by positive and negative bending for grooved POF (opening and closing of grooves respectively). We show that small positive bending increases the power loss, while for negative bending the power loss experiences a minimum, corresponding to the best achievable waveguiding recovery because of the closing of grooves. Beyond certain deformation, the sensitivity of the POF sensor is dominated by losses in the un-grooved regions. A bending test for the mechanical integrity of grooved POFs shows that repetitive bending to a small radius results in a quick deterioration depending on the depth of the groove. However for bending radii more than 20mm and groove depths up to 0.3mm, the lifetime of the POF sensor is still acceptable for many targeted sensor application.While it is clear that the grooved POF is more sensitive to small bending compared to the un-grooved POF, the latter offers uncompromised mechanical integrity and is more desirable when the highest possible sensitivity is not a priority. Therefore, in the final stage of the work, both grooved and un-grooved POF are considered as candidates for developing the tomographic imaging modality. Further detail is considered in view of the targeted deliverable, a real PGPT system for footstep imaging, based on POF sensors. This has been successfully achieved by designing, integrating and testing two different PGPT systems: one based on grooved POF with sensor head size of 0.9m x 0.9m incorporating a multiplexed photodetector and another based on un-grooved POF with sensor head size of 2m x 1m, incorporating independent POF sensors. Both are capable of performing the real time imaging task as well as storing the numerical data for alternative processing. The image reconstruction is by applying a median-filtered Landweber method to solve the inverse tomography problem. The frame rate achieved is 2Hz and 1Hz with spatial resolution estimated as 10cm and 3cm for the first and second system respectively
47
Chang, Whan Wook. "Functional optical coherence tomography for clinical otolaryngology." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12730.
Анотація:
Thesis (Ph.D.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Cross-sectional imaging of rapidly vibrating tissues or biomaterials under rapid periodic motion is useful for medical diagnosis and tissue engineering. Optical coheret:tce tomography (OCT) is a powerful technique, but its relatively low frame rates limited its use in such applications. Here, we present a novel method that enables capturing 4-dimensional (4D) images of samples in motion at oscillation frequencies of up to 10kHz and potentially far beyond. Employing continuous axial-line acquisition, motion-triggered beam scanning, and subsequent space-time registration, phase-aligned snapshots of tissue oscillation over the entire vibratory cycle can be obtained. This technique is applied to structural and functional imaging of major systems of speech and hearing: aerodynamically driven vibrations of the vocal fold in an ex vivo calf larynx and acoustically driven vibrations of the middle ear in an ex vivo chinchilla and human cadaveric temporal bones. Oscillations of the surface and interior structure of both organs can be viewed and analyzed with high three-dimensional resolution of 10-15 µm, and temporal resolution of 20 µs· For functional middle ear imaging, we employed phase sensitive OCT to achieve sub-nanometer scale vibration sensitivity to differentiate simulated pathologies. The results suggest that the dynamic 4D OCT technique has the potential to become a powerful tool in clinical and research applications for assessing health and mechanical properties of vocal folds and middle ear in the field of otolaryngology.
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Sakadzic, Sava. "Ultrasound-modulated optical tomography in soft biological tissues." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5875.
Анотація:
Optical imaging of soft biological tissues is highly desirable since it is nonionizing
and provides sensitive contrast information which enables detection of physiological
functions and abnormalities, including potentially early cancer detection. However,
due to the diffusion of light, it is dificult to achieve simultaneously both good spatial
resolution and good imaging depth with the pure optical imaging modalities.
This work focuses on the ultrasound-modulated optical tomography - a hybrid
technique which combines advantages of ultrasonic resolution and optical contrast.
In this technique, focused ultrasound and optical radiation of high temporal co-herence are simultaneously applied to soft biological tissue, and the intensity of the
ultrasound-modulated light is measured. This provides information about the optical
properties of the tissue, spatially localized at the interaction region of the ultrasonic
and electromagnetic waves.
In experimental part of this work we present a novel implementation of high-resolution ultrasound-modulated optical tomography that, based on optical contrast,
can image several millimeters deep into soft biological tissues. A long-cavity confocal
Fabry-Perot interferometer was used to detect the ultrasound-modulated coherent
light that traversed the scattering biological tissue. Using 15-MHz ultrasound, we
imaged with high contrast light absorbing structures placed 3 mm below the surface
of chicken breast tissue. The resolution along the axial and the lateral directions with respect to the ultrasound propagation direction was better than 70 and 120ùm, respectively. This technology is complementary to other imaging technologies,
such as confocal microscopy and optical-coherence tomography, and has potential for
broad biomedical applications.
In the theoretical part we present various methods to model interaction be-tween the ultrasonic and electromagnetic waves in optically scattering media. We first extend the existing theoretical model based on the diffusing-wave spectroscopy
approach to account for anisotropic optical scattering, Brownian motion, pulsed ul-trasound, and strong correlations between the ultrasound-induced optical phase in-crements. Based on the Bethe-Salpeter equation, we further develop a more general
correlation transfer equation, and subsequently a correlation diffusion equation, for
ultrasound-modulated multiply scattered light. We expect these equations to be
applicable to a wide spectrum of conditions in the ultrasound-modulated optical tomography of soft biological tissues.
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Peric, Borislava. "Optical coherence tomography applied to investigations of optical properties of paintings." Thesis, Nottingham Trent University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510265.
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Mok, Kwok-hei, and 莫國熙. "The characterization of retinal nerve fiber layer thickness in normal,high-tension and normal-tension glaucoma using optical coherencetomography." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B31381005.