Abnormal Brain Connectivity in the Primary Visual Pathway in Human Albinism

In albinism, the ipsilateral projection of retinal axons is significantly reduced, and most fibres project contralaterally. The retina and optic chiasm have been proposed as sites for misrouting. The number of lateral geniculate nucleus (LGN) relay neurons has been linked to LGN volume, suggesting a correlation between LGN size and the number of tracts traveling through the optic radiation (OR) to the primary visual cortex (V1). Using diffusion data and both deterministic and probabilistic tractography, we studied differences in OR between albinism and controls. Statistical analyses measured white matter integrity in areas corresponding to the OR, as well as LGN to V1 connectivity. Results revealed reduced white matter integrity and connectivity in the OR region in albinism compared to controls, suggesting altered structural development. Previous reports of smaller LGN and the altered thalamo-cortical connectivity reported here demonstrate the effect of misrouting on structural organization of the visual pathway in albinism

The Advanced Applications For Optical Coherence Tomography In Skin Imaging

Optical coherence tomography (OCT), based on the principle of interferometry, is a fast and non-invasive imaging modality, which has been approved by FDA for dermatologic applications. OCT has high spatial resolution up to micrometer scale compared to traditional ultrasound imaging. In addition, OCT can provide real-time cross-sectional images with 1 to 2 mm penetration depth, which makes it an ideal imaging technique to assess the skin micro-morphology and pathology without any tissue removal. Many studies have investigated the possibilities of using OCT to evaluate dermatologic conditions, such as skin cancer, dermatitis, psoriasis, and skin damages. Hence, OCT has tremendous potential to provide skin histological and pathological information and assist differential diagnosis of various skin diseases. In this study, we used a swept-source OCT with 1305 nm central wavelength to explore its advanced applications in dermatology. This dissertation consists of four major research projects. First, we explored the feasibility of OCT imaging for assisting real-time visualization in skin biopsy. We showed that OCT could be used to guide and track a needle insertion in mouse skin in real-time. The structure of skin and the movement of needle can be clearly seen on the OCT images without any time delay during the procedures. Next, we tested the concept of performing the punch biopsy using OCT hand-held probe attached to a piercing tip in a phantom. We proved that using the OCT is a reliable technique to delineate the margin of lesion in phantom. And it is possible to perform the punch biopsy with the OCT probe. Second, we tested the performance of contrast-enhanced OCT in melanoma detection in an in vitro study. Melanoma is the most lethal type of skin cancer. Early detection could significantly improve the long-term survival rate of patients. In this initial study, a contrast agent (Gal3-USGNPs) is developed by conjugating melanoma biomarker (Gal3) to ultra-small gold nanoparticles (USGNPs). We showed that the contrast agent can differentiate B16 melanoma cells from normal skin keratinocytes in vitro. To avoid systemic administration of USGNPs, the third project continues to explore the enhanced topical delivery of USGNPs. In this study, we used OCT to monitor the topical delivery of nanoparticles on pig skin over time. And the diffusion and penetration of USGNPs in skin can be improved by applying chemical and physical enhancers such as DMSO and sonophoresis. Finally, in addition to image the cross-sectional structure of skin, we also aim to extract quantitative information from OCT images. The skin optical properties such as attenuation coefficient can be measured from OCT images. We measured and compared the skin attenuation coefficient in the skin of forehead and lateral hip, the skin of three different age groups, and the skin of three different Fitzpatrick types. The statistical analysis showed that epidermis has much higher attenuation coefficient than dermis. And the skin type V & VI have a relatively lower attenuation coefficient than the other skin types. These studies could aid the detection of skin cancer using imaging techniques and provide some new insights into the future applications of OCT in dermatology

Optical coherence tomography (OCT) - guided ophthalmic therapy

In this work, we demonstrate OCT-based guidance of two ophthalmic therapies, subretinal injection and selective retina therapy (SRT). Firstly, the “SMART,” a hand-held robotic surgical device actively guided by a common-path OCT (CP-OCT) distal sensor, improves in two aspects for being applied to subretinal injection: (i) A high-performance fiber probe based on high index epoxy lensed-fiber to enhance the CP-OCT retinal image quality; (ii) Automated retinal layer identification and tracking : retinal layer boundaries are tracked using convolutional neural network (CNN)-based segmentation for accurate subretinal injection guidance. It is shown that high index epoxy lensed-fiber probe improves the SNR and retinal image quality of the CP-OCT system. We propose and implement real-time retinal boundary tracking of A-scan OCT images using CNNs for accurate localization of a surgical tool tip. Unwanted axial motions of the surgical tools are compensated by a piezo-electric linear motor based on the retinal boundary tracking. A CNN-based CP-OCT distal sensor successfully tracks retinal boundaries, especially the PR/CH boundary for subretinal injection, and automatically guides the needle’s axial position in real-time. The micro-scale depth targeting accuracy of our system shows its promising possibility for clinical application. We also propose and demonstrate SRT monitoring based on speckle variance OCT (svOCT) for dosimetry control. M-scans of a phantom, ex vivo bovine iris, and ex vivo bovine retina are obtained by a swept-source OCT system during laser pulses irradiation. SvOCT images are calculated as interframe intensity variance of the sequence, and they show abrupt speckle variance change induced by laser pulse irradiation. The axially averaged svOCT signals show a sharp peak corresponding to each laser pulse, and the peak values are proportional to irradiated laser pulse energy. For the ex vivo retinal study, microscopic images of treated spots are obtained before and after removing the upper neural retinal layer to assess the damage in both RPE and neural layers. Spatial and temporal temperature distributions in the retina are numerically calculated in a 2D retinal model using COMSOL Multiphysics. We find that the svOCT peak values have a reliable correlation with the degree of retinal lesion formation. The temperature at the neural retina and RPE is estimated from the svOCT peak values using numerically calculated temperature, which is consistent with the observed lesion creation

Development of High-speed Photoacoustic Imaging technology and Its Applications in Biomedical Research

Photoacoustic (PA) tomography (PAT) is a novel imaging modality that combines the fine lateral resolution from optical imaging and the deep penetration from ultrasonic imaging, and provides rich optical-absorption–based images. PAT has been widely used in extracting structural and functional information from both ex vivo tissue samples to in vivo animals and humans with different length scales by imaging various endogenous and exogenous contrasts at the ultraviolet to infrared spectrum. For example, hemoglobin in red blood cells is of particular interest in PAT since it is one of the dominant absorbers in tissue at the visible wavelength.The main focus of this dissertation is to develop high-speed PA microscopy (PAM) technologies. Novel optical scanning, ultrasonic detection, and laser source techniques are introduced in this dissertation to advance the performance of PAM systems. These upgrades open up new avenues for PAM to be applicable to address important biomedical challenges and enable fundamental physiological studies.First, we investigated the feasibility of applying high-speed PAM to the detection and imaging of circulating tumor cells (CTCs) in melanoma models, which can provide valuable information about a tumor’s metastasis potentials. We probed the melanoma CTCs at the near-infrared wavelength of 1064 nm, where the melanosomes absorb more strongly than hemoglobin. Our high-speed PA flow cytography system successfully imaged melanoma CTCs in travelling trunk vessels. We also developed a concurrent laser therapy device, hardware-triggered by the CTC signal, to photothermally lyse the CTC on the spot in an effort to inhibit metastasis.Next, we addressed the detection sensitivity issue in the previous study. We employed the stimulated Raman scattering (SRS) effect to construct a high-repetition-rate Raman laser at 658 nm, where the contrast between a melanoma CTC and the blood background is near the highest. Our upgraded PA flow cytography successfully captured sequential images of CTCs in mouse melanoma xenograft model, with a significantly improved contrast-to-noise ratio compared to our previous results. This technology is readily translatable to the clinics to extract the information of a tumor’s metastasis risks.We extended the Raman laser technology to the field of brain functional studies. We developed a MEMS (micro-electromechanical systems) scanner for fast optical scanning, and incorporated it to a dual-wavelength functional PAM (fPAM) for high-speed imaging of cerebral hemodynamics in mouse. This fPAM system successfully imaged transient changes in blood oxygenation at cerebral micro-vessels in response to brief somatic stimulations. This fPAM technology is a powerful tool for neurological studies.Finally, we explored some approaches of reducing the size the PAM imaging head in an effort to translate our work to the field of wearable biometric monitors. To miniaturize the ultrasonic detection device, we fabricated a thin-film optically transparent piezoelectric detector for detecting PA waves. This technology could enable longitudinal studies on free-moving animals through a wearable version of PAM

Use Of Induced Pluripotent Stem Cell Models To Elucidate Retinal Disease Pathogenesis And To Develop Gene-Based Therapies

Choroideremia (CHM) is a rare monogenic, X-linked recessive inherited retinal degenerative disease caused by mutations in the Rab Escort Protein-1 (REP1) encoding CHM gene. CHM is characterized by childhood-onset night blindness (nyctalopia), progressive peripheral vision loss due to the degeneration of neural retina, RPE and choroid in a peripheral-to-central fashion. Most of CHM mutations are loss-of-function mutations leading to the complete lacking of REP1 protein. However, the primary retinal cell type leading to CHM and molecular mechanism remains unknown in addition to the fact of lacking proper disease models. In this study, we explored the utility of induced pluripotent stem cell-derived models of retinal pigment epithelium (iPSC-RPE) to study disease pathogenesis and a potential gene-based intervention in four different genetically distinct forms of CHM. A number of abnormal cell biologic, biochemical, and physiologic functions were identified in the CHM patient cells. Transduction efficiency testing using 11 recombinant adeno-associated virus (AAV) serotype 1-9, 7m8 and 8b showed a differential cell tropism on iPSC and iPSC-derived RPE. We identified AAV7m8 to be optimal for both delivering transgenes to iPSC-RPEs as well as to appropriate target cells (RPE cells and rod photoreceptors) in the primate retina. To establish the proof of concept of AAV7m8 mediated CHM gene therapy, we developed a AAV7m8.hCHM viral vector, which delivers the human CHM cDNA under control of CMV-enhanced chicken β-actin promoter (CβA). Delivery of AAV7m8.CMV.CβA.hCHM to CHM iPSC-RPEs restored protein prenylation, trafficking and phagocytosis defects. The results confirm that AAV-mediated delivery of the REP1-encoding gene can rescue defects in CHM iPSC-RPE regardless of the type of disease-causing mutation. The results also extend our understanding of mechanisms involved in the pathophysiology of choroideremia

A Multispectral Bidirectional Reflectance Distribution Function Study of Human Skin for Improved Dismount Detection

In 2008, the Sensors Exploitation Research Group at the Air Force Institute of Technology began using spectral properties of skin for the detection and classification of humans. Since then a multispectral skin detection system was developed to exploit the optical properties of human skin at wavelengths in the visible and near infrared region of the electromagnetic spectrum. A rules-based detector, analyzing an image spectrally, currently bases its skin pixel selection criteria on a diffuse skin reflectance model. However, when observing skin in direct view of the sun, a glint of light off skin is common and indicates specularity. The areas of skin with a high degree of specular reflectance, results in misdetections. We show that skin is characterized by diffuse and specular reflectance, with both components dependent on the scene configuration. While we cannot always rely on the person to directly face the camera or have constant illumination conditions, it is important to have flexibility with the rules-based detector as the scene changes. Our research better characterizes skin reflectance as a function of source and detector angular locations to improve on the rules-based detector

Spectral Detection of Human Skin in VIS-SWIR Hyperspectral Imagery without Radiometric Calibration

Many spectral detection algorithms require precise ground truth measurements that are hand-selected in the image to apply radiometric calibration, converting image pixels into estimated reflectance vectors. That process is impractical for mobile, real-time hyperspectral target detection systems, which cannot empirically derive a pixel-to-reflectance relationship from objects in the image. Implementing automatic target recognition on high-speed snapshot hyperspectral cameras requires the ability to spectrally detect targets without performing radiometric calibration. This thesis demonstrates human skin detection on hyperspectral data collected at a high frame rate without using calibration panels, even as the illumination in the scene changes. Compared to an established skin detection method that requires calibration panels, the illumination-invariant methods in this thesis achieve nearly as good detection performance in sunny scenes and superior detection performance in cloudy scenes

Multimodal Assessment of Structure and Function in Inherited Retinal Degenerations

Inherited retinal degenerations (IRDs) affect approximately 1:4,000 people worldwide and are currently the leading cause of vision loss of people between the ages of 15-45. The mechanisms of degeneration in many IRDs remain unclear. It is vital to establish relationships between retinal structural and functional measures in order to better understand the relationship between the genetic mutations and the phenotypes they cause in these diseases. For example, retinitis pigmentosa (RP), the most prevalent IRD, and choroideremia (CHM), an X-linked degeneration that affects choroidal, RPE and photoreceptor cells, both progress over time due to rod, then cone, photoreceptor loss. Greater understanding of disease progression may clarify the underlying mechanisms of retinal degenerations. Furthermore, the development of novel outcome measures could accelerate clinical trials of treatments designed to treat these relentless, sight-threatening diseases. The experiments and research described in this document use multimodal state-of-the-art, novel, high-resolution techniques in addition to standard technologies used in the clinical setting to study the relationship between structure and function of the retina including rod and cone photoreceptors, retinal pigment epithelium, choriocapillaris and other retinal layers affected in the eyes of patients with retinal degeneration

Design and Verification of an Optical System to Interrogate Dermally-implanted Microparticle Sensors

Diabetes mellitus affects 25.8 million Americans (8.3%) and over 300 million people worldwide. Clinical trials indicate that proper management of blood glucose levels is critical in preventing or delaying complications associated with diabetes. Thus, there is a common need to monitor and manage blood glucose properly for people with diabetes. However, the patients’ compliance for recommended monitoring frequency is low due to the pain and inconvenience of current standard finger-pricking tests. To promote patient adherence to the recommended self-monitoring frequency, non-invasive/ minimally invasive glucose testing approaches are needed. Luminescent microparticle sensor is an attractive solution. For these sensors to be deployed in vivo, a matched optical system is needed to interrogate dermally-implanted sensors. This research project investigated the light propagation in skin and the interaction with implants using Monte Carlo modeling. The results of the modeling were used to design an optical system with high interrogation and collection efficiency (40~300 times improvement). The optical system was then constructed and evaluated experimentally. A stable skin phantom mimicking the optical properties of human skin was developed as a permanent evaluation medium to minimize the use of animals. The optical properties of the skin phantom matched the maximum published values of human skin in scattering and absorption over the spectral range of 540~700nm in order to avoid overestimation of the capability of the system. The significant photon loss observed at the connection between the designed system and a commercial spectrometer was overcome using two optimized designs: a two-detector system and a customized low-resolution spectrometer system. Both optimization approaches effectively address the photon loss problem and each showed good SNR (>100) while maintaining a sufficient system resolution for use with fluorescent materials. Both systems are suitable for luminescence measurement, because broad bands of the luminescent spectrum are of interest. In the future, either system can be easily modified into a more compact system (e.g. handheld), and it can be directly coupled to an analog-to-digital converter and integrated circuits offering potential for a single compact and portable device for field use with luminescent diagnostic systems as well as implanted sensors