Maximum likelihood estimation for rician distributed data in analytical q-ball imaging

Analytical q-ball imaging is widely used for reconstruction of orientation distribution function (ODF) using diffusion weighted MRI data. Estimating the spherical harmonic coefficients is a critical step in this method. Least squares (LS) is widely used for this purpose assuming the noise to be additive Gaussian. However, Rician noise is considered as a more appropriate model to describe noise in MR signal. Therefore, the current estimation techniques are valid only for high SNRs with Gaussian distribution approximating the Rician distribution. The aim of this study is to present an estimation approach considering the actual distribution of the data to provide reliable results particularly for the case of low SNR values. Maximum likelihood (ML) is investigated as a more effective estimation method. However, no closed form estimator is presented as the estimator becomes nonlinear for the noise assumption of the Rician distribution. Consequently, the results of LS estimator is used as an initial guess and the more refined answer is achieved using iterative numerical methods. According to the results, the ODFs reconstructed from low SNR data are in close agreement with ODFs reconstructed from high SNRs when Rician distribution is considered. Also, the error between the estimated and actual fiber orientations was compared using ML and LS estimator. In low SNRs, ML estimator achieves less error compared to the LS estimator.

Visualisation of chemical processes during corrosion of zinc using magnetic resonance imaging

Compositional and structural changes within an electrolyte solution above an electrochemically active metal surface have been visualised using magnetic resonance imaging (MRI) for the first time. In these proof-of-concept experiments, zinc metal was galvanically corroded in a saturated lithium chloride solution. Magnetic resonance relaxation maps were taken during the corrosion process and spatial variations in both T₁ and T₂ relaxation times were observed to change with time. These changes were attributed to changes in the speciation of zinc ions in the electrolyte.

Maximum-likelihood based estimation for Q-ball imaging using diffusion-weighted MRI data

Q-ball imaging has been presented to reconstruct diffusion orientation distribution function using diffusion weighted MRI. In this thesiis, we present a novel and robust approach to satisfy the smoothness constraint required in Q-ball imaging. Moreover, we developed an improved estimator based on the actual distribution of the MR data.

Analysis of dynamic strains in tibia during human locomotion based on flexible multibody approach integrated with magnetic resonance imaging technique

Bone is known to adapt to the prevalent strain environment while the variation in strains, e.g., due to mechanical loading, modulates bone remodeling, and modeling. Dynamic strains rather than static strains provide the primary stimulus of bone functional adaptation. The finite element method can be generally used for estimating bone strains, but it may be limited to the static analysis of bone strains since the dynamic analysis requires expensive computation. Direct in vivo strain measurement, in turn, is an invasive procedure, limited to certain superficial bone sites, and requires surgical implementation of strain gauges and thus involves risks (e.g., infection). Therefore, to overcome difficulties associated with the finite element method and the in vivo strain measurements, the flexible multibody simulation approach has been recently introduced as a feasible method to estimate dynamic bone strains during physical activity. The purpose of the present study is to further strengthen the idea of using the flexible multibody approach for the analysis of dynamic bone strains. Besides discussing the background theory, magnetic resonance imaging is integrated into the flexible multibody approach framework so that the actual bone geometry could be better accounted for and the accuracy of prediction improved.

Two-photon endomicroscopy for 3D imaging of cancer cells labelled with gold nanorods

Biofunctional nanorods are developed to specifically target cancer cells. The cervical cancer cells, HeLa cells, are labeled by these biofunctional gold nanorods. Those cancer cells can be detected by a multi-photon-excited photoluminescence endomicroscope, which proves that the cancers can be in vivo diagnosed by using biofunctional gold nanorods with nonlinear endomicroscopy.

Two-photon imaging and photothermal therapy of cancer cells using biofunctional gold nanorods

Transferrin-conjugated gold nanorods were used for targeting, two-photon imaging and photothermal therapy of cancer cells. The presence of nanorods significantly reduced the laser power effective for therapy.

Fabrication and biofunctionalization of selenium-polypyrrole core-shell nanoparticles for targeting and imaging of cancer cells

Selenium-polypyrrole core-shell nanoparticles are fabricated by an in-situ polymerization process and functionalized with transferrin for targeting and imaging of human cervical cancer cells. The shell thickness and chemical composition of the as-synthesized particles can be manipulated by controlling the precursor concentration. The presence of the polymer layer can greatly increase the thermal stability of the selenium nanoparticles. The presence of transferrin molecules on the surface of the core-shell nanoparticles can significantly enhance their cellular uptake. The tranferrin-conjugated core-shell nanoparticles can be potentially used for the targeting and imaging of cancer cells.

Trapping and imaging of embryonic organisms using dielectrophoresis

Development of dielectrophoretic (DEP) arrays for real-time imaging of embryonic organisms is described. Microelectrode arrays were used for trapping both embryonated eggs and larval stages of Antarctic nematode Panagrolaimus davidi. Ellipsoid single-shell model was also applied to study the interactions between DEP fields and developing multicellular organisms. This work provides proof-of-concept application of chip-based technologies for the analysis of individual embryos trapped under DEP force.

Understanding fish-habitat associations using video observations and sonar imaging

This thesis was motivated by the increasing role of species distribution models in managing marine fishes and their habitats. These models provided new information about fish-habitat associations. However, models are potentially influenced by fish behaviour towards underwater video systems.

Trapping and imaging of micron-sized embryos using dielectrophoresis

Development of dielectrophoretic (DEP) arrays for real-time imaging of embryonic organisms is described. Microelectrode arrays were used for trapping both embryonated eggs and larval stages of Antarctic nematode Panagrolaimus davidi. Ellipsoid single-shell model was also applied to study the interactions between DEP fields and developing multicellular organisms. This work provides proof-of-concept application of chip-based technologies for the analysis of individual embryos trapped under DEP force.

Predatory vision : 3D imaging and the transformation of screen-space

Despite Wheatstone’s academic interests in the device, the stereoscope languished somewhat as an optical toy. Yet the advent of 3D screen-spaces for home and mass entertainment suggests today’s consumers and practitioners of screen culture hold the view that screen culture will be ‘improved’ through 3D imaging technologies. Like cinema and photography, stereoscopic 3D imaging has the potential to transform visual culture. But what is transformed, as optics and electronic imaging techniques deliver Alice in Wonderland in 3D? This paper links the advent of 3D cinema and TV to the notion that vision is itself a ‘technology of the visual’. As such, our innate binocular stereoacuity is ripe for exploitation by developers of 3D imaging technologies. I argue that contemporary 3D imaging marks an epistemological visual-perceptual shift: toward screenspaces becoming spaces for potential action. Such a shift entails seeing as doing rather than seeing as thinking. 3D imaging exploits binocular vision’s spatial acuity (stereopsis), but is effective only for objects within near distal space. The 3D effect tapers off dramatically for objects only some metres away, because the two retinal images lack significant lateral disparity (difference) to trigger stereopsis: the imagery flattens out and becomes ‘monoscopic’. Information available from conventional 2D media entails a peculiarly unspecified spatiality. Perceptually, the contents of a conventional cinematic screen are like those of a painting: they are situated neither near nor far, and constitute a shared and ambiguous visual space. Our own eyes are like those of a cat: frontally placed for predatory action. The visuality of 3D screen-spaces assumes a perceptuality of the near-by and close at hand, since this is the structure of the visible information to which stereopsis is adapted to respond. Noting the binocular acuity of predatory animals, as well as some etymological links, this paper examines the implications of perceptually ‘capturing’ the sensation of visually solid objects in one’s immediate space. Stereopsis is about decisive action within an immediate environment: but it also presupposes the single viewpoint of an active observer toward which the 3D imagery is targeted.

Enactive research : transversal possibilities for expanding the imaging of science

This paper explores the notion of the expanded image as a transdisciplinary interaction between people and environments. In support of this proposition, images and imaging will be discussed through a series of transformative steps: from the diagram to the biogram and from the biogram to biotopology. Two research projects, exemplary of a transdisciplinary approach, inform the move to biotopology (the continuous surface of interactions tied to imaging practices): first, theories of enaction in cognitive science foreground co-selective processes and the precariousness of self- organizing systems and supply new ways of imaging body-environment relationships (Stewart et al 2010; Thompson 2007; and Varela et al 1993); and second, the procedural architecture of artist- turned-architects Arakawa and Gins foregrounds the reconfigurability of the co-selective process that becomes an enactive practice. These approaches suggest that if the image were expanded to include the intersection of the human organism’s behaviors, artifacts (such as images) and built- environments, then the ‘person’ whose myriad surfaces flicker towards future action, might become the best description of an expanded form of imaging, always in process and flickering towards future action. The many and non-locatable surfaces of person would defy disciplinary boundaries and interfere with habitual patterns of imaging. Ultimately, the aim of expanding imaging practices is to expand an embodied capacity to configure and reconfigure conceptual and material realms.

Graphene oxide nanoparticles as a nonbleaching optical probe for two-photon luminescence imaging and cell therapy

Lasting glow: Under femtosecond laser irradiation, graphene oxide nanoparticles (GONs) give strong two-photon luminescence (TPL; see picture). The presence of GONs also induces microbubbling, which causes cell death at an order of magnitude lower laser power than when cells are not labeled. The results show that GONs can be used for TPL-based imaging and photothermal cancer therapy.