Final publication is available at http://journals.lww.com/otology-neurotology/Pages/default.aspx / 京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19574号 / 医博第4081号 / 新制||医||1013(附属図書館) / 32610 / 京都大学大学院医学研究科医学専攻 / (主査)教授 渡邉 大, 教授 伊佐 正, 教授 一山 智 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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No current imaging technology can directly and without significant distortion visualize the defining microscopic features of the human brain. Ex vivo histological techniques yield exquisite planar images, but the cutting, mounting and staining they require induce slice-specific distortions, introducing cross-slice differences that prohibit true 3D analysis. Clearing techniques have proven difficult to apply to large blocks of human tissue and cause dramatic distortions as well. Thus, we have only a poor understanding of human brain structures that occur at a scale of 1–100 μm, in which neurons are organized into functional cohorts. To date, mesoscopic features which are critical components of this spatial context, have only been quantified in studies of 2D histologic images acquired in a small number of subjects and/or over a small region of the brain, typically in the coronal orientation, implying that features that are oblique or orthogonal to the coronal plane are difficult to properly analyze. A serial sectioning optical coherence tomography (OCT) imaging infrastructure will be developed and utilized to obtain images of cyto- and myelo-architectural features and microvasculature network of post-mortem human brain tissue. Our imaging infrastructure integrates vibratome with imaging head along with pre and post processing algorithms to construct volumetric OCT images of cubic centimeters of brain tissue blocks. Imaging is performed on tissue block-face prior to sectioning, which preserves the 3D information. Serial sections cut from the block can be subsequently treated with multiplexed histological staining of multiple molecular markers that will facilitate cellular classification or imaged with high-resolution transmission birefringence microscope. The successful completion of this imaging infrastructure enables the automated reconstruction of undistorted volume of human tissue brain blocks and permits studying the pathological alternations arising from diseases. Specifically, the mesoscopic and microscopic pathological alternations, as well as the optical properties and cortical morphological alternations of the dorsolateral prefrontal cortical region of two difference neurodegeneration diseases, Chronic Traumatic Encephalopathy (CTE) and Alzheimer’s Disease (AD), were evaluated using this imaging infrastructure.

Yes / Combining information from optical coherence tomography (OCT) imaging and visual field testing is useful in the clinical assessment and monitoring of patients with glaucoma. Measurements of retinal nerve fibre layer thickness or neuroretinal rim width taken around the optic nerve head may be related to the visual field using a structure–function map. In this review, the structure–function mapping methods in clinical use are discussed. Typical clinical maps provide a population average, ‘one size fits all’ representation, but in recent years methods for customising structure–function maps to individual eyes have been developed and these are reviewed here. In the macula, visual field stimuli stimulate photoreceptors for which associated retinal ganglion cells are peripherally displaced. Recently developed methods that relate OCT measurements to visual field test locations in the macula are therefore also reviewed. The use of structure–function maps to relate OCT measurements to localised visual field sensitivity in new applications is also explored. These new applications include the selection of visual field test locations and stimulus intensities based on OCT data, and the formal post‐test combination of results across modalities. Such applications promise to exploit the structure–function relationship in glaucoma to improve disease diagnosis and monitoring of progression. Limitations in the validation and use of current structure–function mapping techniques are discussed. / >Heidelberg Engineering >Australian Research Council. Grant Number: LP130100055 >College of Optometrists. Grant Number: College of Optometrists Research Fellowship

Optical Coherence Tomography (OCT) is a coherence-gated, micrometer-resolution imaging technique that focuses a broadband near-infrared laser beam to penetrate into optical scattering media, e.g. biological tissues. The OCT resolution is split into two parts, with the axial resolution defined by half the coherence length, and the depth-dependent lateral resolution determined by the beam geometry, which is well described by a Gaussian beam model. The depth dependence of lateral resolution directly results in the defocusing effect outside the confocal region and restricts current OCT probes to small numerical aperture (NA) at the expense of lateral resolution near the focus. Another limitation on OCT development is the presence of a mixture of speckles due to multiple scatterers within the coherence length, and other random noise. Motivated by the above two challenges, a multiple scattering model based on Rytov approximation and Gaussian beam optics is proposed for the OCT setup. Some previous papers have adopted the first Born approximation with the assumption of small perturbation of the incident field in inhomogeneous media. The Rytov method of the same order with smooth phase perturbation assumption benefits from a wider spatial range of validity. A deconvolution method for solving the inverse problem associated with the first Rytov approximation is developed, significantly reducing the defocusing effect through depth and therefore extending the feasible range of NA.

Ovarian cancer is the deadliest gynecologic cancer for women. Diagnosis at the local stage leads to 91% 5-year survival rates, but only 15% of cases are detected early. Existing screening methods have proven ineffective in large clinical trials. Screening is complicated by the heterogeneity of the disease with multiple types of ovarian cancer originating both on the ovary and in the fallopian tube. Early stage cancer is too subtle for non-invasive imaging techniques such as ultrasound or magnetic resonance imaging. This study evaluates the feasibility and design of dual modality, multispectral fluorescence imaging (MFI) and optical coherence tomography (OCT) endoscopes for improved ovarian cancer screening. The study is broken up into three sections. In the first study MFI is validated in an ex vivo imaging study of human ovarian and fallopian tube tissue samples. Tissue autofluorescence excited by ultraviolet and blue wavelengths is shown to be a promising discriminator between normal and cancerous tissue. The second study combines OCT and MFI into a sub millimeter diameter endoscope designed to screen for ovarian cancer by screening inside the fallopian tube and at the ovary. The small size is required for screening the full length of the fallopian tube. MFI is implemented as a wide-field navigational imaging technique with high sensitivity complemented by high resolution structural depth imaging of OCT over a limited field of view. The final study presents a novel lens design for a scanning fiber endoscope with forward-viewing navigation and side-viewing OCT. A piezo tube is used to scan an optical fiber providing both the navigation channel’s illumination and OCT imaging. The design spatially separates the forward-viewing illumination from the OCT. As the piezo fiber circularly scans at its maximum deviation the OCT beam focus is rotationally scanned out the side of the endoscope tip by a rotationally symmetric double reflection in the cover plate.

Optical Coherence Tomography (OCT) is an imaging technique that uses near infra-red light to non-invasively form cross-sectional images of specimens, in a similar way to ultrasound and RADAR. A number of research groups have used OCT to study natural and artificial carious lesions and to some extent erosive lesions. For this, a variety of in vitro models have been used. However, the exact mechanism by which these demineralised enamel lesions affect the OCT measurements is not fully understood. This remains a barrier to its adoption as both an analytical laboratory tool and a widespread technique in clinical dentistry. Therefore, the aim of this thesis was to develop an understanding of how different demineralised enamel lesions manifest in OCT measurements. This is necessary for the technique to become useful as an in vivo clinical measurement and imaging system. Consequently, this study was carried out in a controlled laboratory environment for which a novel specimen holder was designed. This mitigated against specimen movement and maintained specimen hydration, which can be a source of uncertainty in the measurements. A custom-built OCT microscope was used for this work, which enabled automation of experiments and continuous time-lapse OCT imaging over time periods of hours to several days. This enabled bovine enamel demineralisation dynamics to be captured during in vitro caries and erosion formation. The stability of the system also enabled direct comparison between the OCT measurements of the optical properties of different demineralisation models. To achieve these measurements, the OCT system was carefully characterised and compared to established profilometry measurements. Interestingly, this revealed that the experimental protocol used to obtain lesions for profilometry was not to be representative of the lesions formed and measured by OCT. This is an important point when interpreting OCT data in light of other techniques. A novel method of analysis was developed that uses longitudinal OCT image correlation to quantify early stage surface softening during erosion. By using OCT volumetric data, this technique was able to measure sub-resolution changes at the specimen surface. Early results also indicate sensitivity to remineralisation. This thesis shows that OCT is sensitive to different demineralisation models produced and measured under controlled conditions. New method of handling the data can observe changes not previously seen in OCT. However, further work is still required to understand the underlying physical changes that lead to this sensitivity in OCT.

With current needs to better understand the interaction between atrial tissue microstructure and atrial fibrillation dynamics, micrometer scale imaging with optical coherence tomography has significant potential to provide further insight on arrhythmia mechanisms and improve treatment guidance. However, optical coherence tomography imaging of cardiac tissue in humans is largely unexplored, and the ability of optical coherence tomography to identify the structural substrate of atrial fibrillation has not yet been investigated. Therefore, the objective of this thesis was to develop an optical coherence tomography imaging atlas of the human heart, study the utility of optical coherence tomography in providing useful features of human left atrial tissues, and develop a framework for optical coherence tomography-informed cardiac modeling that could be used to probe dynamics between electrophysiology and tissue structure. Human left atrial tissues were comprehensively imaged by optical coherence tomography for the first time, providing an imaging atlas that can guide identification of left atrial tissue features from optical coherence tomography imaging. Optical coherence tomography image features corresponding to myofiber and collagen fiber orientation, adipose tissue, endocardial thickness and composition, and venous media were established. Varying collagen fiber distributions in the myocardial sleeves were identified within the pulmonary veins. A scheme for mapping optical coherence tomography data of dissected left atrial tissues to a three-dimensional, anatomical model of the human left atrium was also developed, enabling the mapping of distributions of imaged adipose tissue and fiber orientation to the whole left atrial geometry. These results inform future applications of structural substrate mapping in the human left atrium using optical coherence tomography-integrated catheters, as well as potential directions of ex vivo optical coherence tomography atrial imaging studies. Additionally, we developed a workflow for creating optical mapping models of atrial tissue as informed by optical coherence tomography. Tissue geometry, fiber orientation, ablation lesion geometry, and heterogeneous tissue types were extracted from optical coherence tomography images and incorporated into tissue-specific meshes. Electrophysiological propagation was simulated and combined with photon scattering simulations to evaluate the influence of tissue-specific structure on electrical and optical mapping signals. Through tissue-specific modeling of myofiber orientation, ablation lesions, and heterogeneous tissue types, the influence of myofiber orientation on transmural activation, the relationship between fluorescent signals and lesion geometry, and the blurring of optical mapping signals in the presence of heterogeneous tissue types were investigated. By providing a comprehensive optical coherence tomography image database of the human left atrium and a workflow for developing optical coherence tomography-informed cardiac tissue models, this work establishes the foundation for utilizing optical coherence tomography to improve the structural substrate characterization of atrial fibrillation. Future developments include analysis of optical coherence tomography imaged tissue structure with respect to clinical presentation, development of automated processing to better leverage the large amount of imaging data, enhancements and validation of the modeling scheme, and in vivo evaluation of the left atrial structural substrate through optical coherence tomography-integrated catheters

Papilledema is a particular type of optic disc swelling caused by elevated intracranial pressure. By observing the visible features from fundus images or direct funduscopic examination, a typical method of assessing papilledema (i.e., the six-stage Fris\'en grading system) is qualitative and frequently suffers from low reproducibility. Compared to fundus images, spectral-domain optical coherence tomography (SD-OCT) is a relatively new imaging technique and enables the cross-sectional information of the retina to be acquired. Using SD-OCT images, quantitative measurements like evaluating the retinal volume or depth are intuitively more robust than the traditional qualitative approach to evaluate papilledema. Also, multiple studies suggest that the deformation of the peripapillary retinal pigment epithelium and/or Bruch's membrane (pRPE/BM) may reflect the intracranial pressure change. In other words, modeling/quantifying the pRPE/BM shape can potentially be another indicator of papilledema. However, when the optic disc is severely swollen, the retinal structure is dramatically deformed and often causes the commercial SD-OCT devices to fail to segment the retinal layers. Without appropriate layer segmentation, all the retinal measurements are not reliable. To solve the current issue of inconsistently assessing papilledema severity, a comprehensive machine-learning framework is proposed in this doctoral work to achieve the goal by accomplishing following four aims. First, robust approaches are developed to automatically segment the retinal layers in 2D and 3D SD-OCT images, even though the optic discs can be severely swollen. Second, the semi- and fully automated methodologies are designed to segment the pRPE/BM opening under the swollen inner retina in these SD-OCT images. Third, the pRPE/BM shape models are constructed using both 2D and 3D SD-OCT images, and then the 2D/3D pRPE/BM shape measures are computed. Finally, based on the previously segmented retinal layers, eight OCT 2D/3D global/local measurements of retinal structure are reliably computed. Considering both the 2D/3D pRPE/BM shape measures and these eight OCT features as an input set, a machine-learning framework using the random forest technique is proposed to compute a papilledema severity score (PSS) on a continuous scale. The newly proposed PSS is expected to be an alternative to the traditional qualitative method to provide a more objective measurement of assessing papilledema severity.

Acquiring the motions of the inner ear sensory tissues provides insight to how the cochlea works. For this purpose, Spectral Domain Optical Coherence Tomography (SDOCT) is an ideal tool as it has a penetration depth of several millimeters. SDOCT can not only image inside the cochlear partition, but also measure the sample structures’ simultaneous displacements. We customized a commercial Spectral Domain Optical Coherence Tomography system for such functions and detailed the software and hardware steps so this powerful system could be more accessible to auditory researchers. The cochlea is surrounded by bones and tissues, and damage to it would make it passive. For this reason, cochlear vibrometry measuring locations have been limited to either the basal or apical regions. That is why I fabricated a two-dimensional scanning SDOCT-based probe, to access more cochlear locations through a small hand-drilled hole. What is exciting about the probe is that an electrode can be attached to its side to acquire spatially and temporally coincident voltage and displacement data. This would help us better understand the cochlear mechano-electrical feedback process. Lastly, I investigated how the SDPM-reported displacement could be influenced by its neighboring signals and demonstrated this signal competition phenomenon experimentally and theoretically.