An effective scene recognition strategy for biomimetic robotic navigation

Master'sMASTER OF ENGINEERIN

Computational Mid-Level Vision: From Border Ownership to Categorical Object Recognition

Since it was proposed in 1890 by Christian von Ehrenfels, Gestalt psychology has remained a key school of thought that explains how one perceives the world ("the whole'') from the sum of its individual components ("the parts'') or processes. These processes are aptly summarized in the well known "Rules of Gestalt''. In spite of its influence in other fields, the empirical nature of Gestalt rules impedes their widespread adoption in Computer Science. This thesis serves to bridge this apparent divide by making Mid-level Vision, or Computer Vision based on Gestalt rules, not only computationally feasible but also practical for real applications. We address the general problem of figure-ground organization, where the goal is to separate the foreground (or object) from the background. To do this, we first formulate a fast approach that pairs Structured Random Forests (SRFs) with Gestalt-like features, for both boundary detection and border ownership assignment. We then show how border ownership information is useful for shape-based recognition of object categories. This is done by embedding ownership information into the image torque, a grouping operator that detects closure patterns in the image edge, so that we modulate the operator in an efficient manner for detecting class-specific contours in clutter and occlusion. Next, we show how symmetry, an important shape-based regularity in Gestalt psychology, can be detected in clutter and be used for guiding segmentation of symmetric foreground regions. Besides shape and symmetry, functionality is another important mid-level cue that supports categorical object recognition. Based on Gibson's principle of affordance, we introduce a fast technique based on a SRF trained with geometric features that provides pixel-accurate affordances of tool parts. Finally, we describe as future work how language can be exploited to "activate'' such mid-level processes so that a joint semantic space can be obtained for linking visual concepts to language to solve even more challenging problems in Computer Vision, effectively reducing the so-called "semantic gap'' between these two related domains

Optical coherence tomography angiography of the macula and optic nerve head: microvascular density and test-retest repeatability in normal subjects

Abstract Background Despite the potential usefulness of optical coherence tomography angiography in retinal and optic disc conditions, the reliability of the imaging modality remains unclear. This study set out to measure the microvascular density of macula and optic disc by mean of optical coherence tomography angiography and report the repeatability of the vessel density measurements. Methods Cross sectional observational cohort study. Subjects with normal eyes were recruited. Two sets of optical coherence tomography angiography images of macula and optic nerve head were acquired during one visit. Novel in-house developed software was used to count the pixels in each images and to compute the microvessel density of the macula and optic disc. Data were analysed to determine the measurement repeatability. Results A total of 176 eyes from 88 consecutive normal subjects were recruited. For macular images, the mean vessel density at superficial retina, deep retina, outer retina and choriocapillaries segment was OD 0.113 and OS 0.111, OD 0.239 and OS 0.230, OD 0.179 and OS 0.164, OD 0.237 and OS 0.215 respectively. For optic disc images, mean vessel density at vitreoretinal interface, radial peripapillary capillary, superficial nerve head and disc segment at the level of choroid were OD 0.084 and OS 0.085, OD 0.140 and OS 0.138, OD 0.216 and OS 0.209, OD 0.227 and OS 0.236 respectively. The measurement repeatability tests showed that the coefficient of variation of macular scans, for right and left eyes, ranged from 6.4 to 31.1% and 5.3 to 59.4%. Likewise, the coefficient of variation of optic disc scans, for right and left eyes, ranged from 14.3 to 77.4% and 13.5 to 75.3%. Conclusions Optical coherence tomography angiography is a useful modality to visualise the microvasculature plexus of macula and optic nerve head. The vessel density measurement of macular scan by mean of optical coherence tomography angiography demonstrated good repeatability. The optic disc scan, on the other hand, showed a higher coefficient of variation indicating a lower measurement repeatability than macular scan. Interpretation of optical coherence tomography angiography should take into account test-retest repeatability of the imaging system. Trial registration National Healthcare Group Domain Specific Review Board (NHG DSRB) Singapore. DSRB Reference: 2015/00301

ROS-generating alginate-coated gold nanorods as biocompatible nanosonosensitisers for effective sonodynamic therapy of cancer

Sonodynamic therapy (SDT) emerges as a promising non-invasive alternative for eradicating malignant tumours. However, its therapeutic efficacy remains limited due to the lack of sonosensitisers with high potency and biosafety. Previously, gold nanorods (AuNRs) have been extensively studied for their applications in photodynamic or photothermal cancer therapy, but their sonosensitising properties are largely unexplored. Here, we reported the applicability of alginate-coated AuNRs (AuNRsALG) with improved biocompatibility profiles as promising nanosonosensitisers for SDT for the first time. AuNRsALG were found stable under ultrasound irradiation (1.0 W/cm2, 5 min) and maintained structural integrity for 3 cycles of irradiation. The exposure of the AuNRsALG to ultrasound irradiation (1.0 W/cm2, 5 min) was shown to enhance the cavitation effect significantly and generate a 3 to 8-fold higher amount of singlet oxygen (1O2) than other reported commercial titanium dioxide nanosonosensitisers. AuNRsALG exerted dose-dependent sonotoxicity on human MDA-MB-231 breast cancer cells in vitro, with ∼ 81% cancer cell killing efficacy at a sub-nanomolar level (IC50 was 0.68 nM) predominantly through apoptosis. The protein expression analysis showed significant DNA damage and downregulation of anti-apoptotic Bcl-2, suggesting AuNRsALG induced cell death through the mitochondrial pathway. The addition of mannitol, a reactive oxygen species (ROS) scavenger, inhibited cancer-killing effect of AuNRsALG-mediated SDT, further verifying that the sonotoxicity of AuNRsALG is driven by the production of ROS. Overall, these results highlight the potential application of AuNRsALG as an effective nanosonosensitising agent in clinical settings