Adaptive optics optical coherence tomography (AO-OCT) has allowed for the reliable 3-D imaging of individual retinal cells. The current AO-OCT systems are limited to tabletop implementation due to their size and complexity. This work describes the design and implementation of the first dual modality handheld AO-OCT (HAOOCT) and scanning laser ophthalmoscope (SLO) probe to extend AO-OCT imaging to previously excluded patients. Simultaneous SLO imaging allows for tracking of imaging features for HAOOCT localization. Pilot experiments on stabilized and recumbent adults using HAOOCT, weighing only 665 grams, revealed the 3-D photoreceptor structure for the first time using a handheld AO-OCT/SLO device.
The incorporation of adaptive optics (AO) technology into ophthalmic imaging systems has enhanced the understanding of retinal structure and function and the progression of various retinal diseases in adults by allowing for the dynamic correction of ocular and/or system aberrations. However, the in vivo visualization of important human retinal microanatomy, including cone photoreceptors, has been largely limited to fully cooperative subjects who are able to fixate and/or sit upright for extended imaging sessions in large tabletop AO systems. Previously, we developed the first handheld AO scanning laser ophthalmoscope capable of 2-D imaging of cone photoreceptors in supine adults and infants. In this work, we present the design and fabrication of the first handheld AO optical coherence tomography (HAOOCT) probe capable of collecting high-resolution volumetric images of the human retina. We designed custom optomechanics to build a spectral domain OCT system with a compact form factor of 22 cm × 18 cm × 5.2 cm and a total weight of 630 grams. The OCT imaging channel has a theoretical lateral resolution of 2.26 μm over a 1.0° × 1.0° field of view and an axial resolution of 4.01 μm. Stabilized imaging of healthy human adult volunteers revealed the 3-D photoreceptor structure and retinal pigment epithelium cells. HAOOCT was then deployed in handheld operation to image photoreceptors in upright and recumbent adults, indicating its potential to extend AO-OCT to previously excluded patient populations.
Quantitative features of individual ganglion cells (GCs) are potential paradigm changing biomarkers for improved diagnosis and treatment monitoring of GC loss in neurodegenerative diseases like glaucoma and Alzheimer’s disease. The recent incorporation of adaptive optics (AO) with extremely fast and high-resolution optical coherence tomography (OCT) allows visualization of GC layer (GCL) somas in volumetric scans of the living human eye. The current standard approach for quantification – manual marking of AO-OCT volumes – is subjective, time consuming, and not practical for large scale studies. Thus, there is a need to develop an automatic technique for rapid, high throughput, and objective quantification of GC morphological properties. In this work, we present the first fully automatic method for counting and measuring GCL soma diameter in AO-OCT volumes. Aside from novelty in application, our proposed deep learningbased algorithm is novel with respect to network architecture. Also, previous deep learning OCT segmentation algorithms used pixel-level annotation masks for supervised learning. Instead in this work, we use weakly supervised training, which requires significantly less human input in curating the training set for the deep learning algorithm, as our training data is only associated with coarse-grained labels. Our automatic method achieved a high level of accuracy in counting GCL somas, which was on par with human performance yet orders of magnitude faster. Moreover, our automatic method’s measure of soma diameters was in line with previous histological and in vivo semi-automatic measurement studies. These results suggest that our algorithm may eventually replace the costly and time-consuming manual marking process in future studies.
KEYWORDS: Functional magnetic resonance imaging, Brain, Cognitive neuroscience, Canonical correlation analysis, Simulation of CCA and DLA aggregates, Functional imaging, Machine learning, Matrices, Statistical analysis, Medical research, Neuroimaging
Resting state functional connectivity (rsFC) studies using fMRI provides a great deal of knowledge on the spatiotemporal organization of the brain. The relationships between and within a number of resting state functional networks, namely the default mode network (DMN), salience network (SN) and executive control network (ECN) have been intensely studied in basic and clinical cognitive neuroscience [1]. However, the presumption of spatial and temporal stationarity has mostly restricted the assessment of rsFC [1]. In this study, sliding window correlation analysis and k-means clustering were exploited to examine the temporal dynamics of rsFC of these three networks in 24 abstinent methamphetamine dependents. Afterwards, using canonical correlation analysis (CCA) the possible relationship between the level of self-reported craving and the temporal dynamics was examined. Results indicate that the rsFC transits between 6 discrete "FC states" in the meth dependents. CCA results show that higher levels of craving are associated with higher probability of transiting from state 4 to 6 (positive FC of DMN-ECN getting weak and negative FC of DMN-SN appearing) and staying in state 4 (positive FC of DMN-ECN), lower probability of staying in state 2 (negative FC of DMN-ECN), transiting from state 4 to 2 (change of positive FC of DMN-ECN to negative FC), and transiting from state 3 to 5 (appearance of negative FC of DMN-SN and positive FC of DMN-ECN with the presence of negative FC of SN-ECN). Quantitative measures of temporal dynamics in large-scale brain networks could bring new added values to increase potentials for applications of rsfMRI in addiction medicine.
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