Gradient-based quantitative image reconstruction in ultrasound-modulated optical tomography: first harmonic measurement type in a linearised diffusion formulation

Ultrasound-modulated optical tomography is an emerging biomedical imaging modality which uses the spatially localised acoustically-driven modulation of coherent light as a probe of the structure and optical properties of biological tissues. In this work we begin by providing an overview of forward modelling methods, before deriving a linearised diffusion-style model which calculates the first-harmonic modulated flux measured on the boundary of a given domain. We derive and examine the correlation measurement density functions of the model which describe the sensitivity of the modality to perturbations in the optical parameters of interest. Finally, we employ said functions in the development of an adjoint-assisted gradient based image reconstruction method, which ameliorates the computational burden and memory requirements of a traditional Newton-based optimisation approach. We validate our work by performing reconstructions of optical absorption and scattering in two- and three-dimensions using simulated measurements with 1% proportional Gaussian noise, and demonstrate the successful recovery of the parameters to within +/-5% of their true values when the resolution of the ultrasound raster probing the domain is sufficient to delineate perturbing inclusions.Comment: 12 pages, 6 figure

Underwater Celestial Navigation Using the Polarization of Light Fields

Global-scale underwater navigation presents challenges that modern technology has not solved. Current technologies drift and accumulate errors over time (inertial measurement), are accurate but short-distance (acoustic), or do not sufficiently penetrate the air-water interface (radio and GPS). To address these issues, I have developed a new mode of underwater navigation based on the passive observation of patterns in the polarization of in-water light. These patterns can be used to infer the sun__s relative position, which enables the use of celestial navigation in the underwater environment. I have developed an underwater polarization video camera based on a bio-inspired polarization image sensor and the image processing and inference algorithms for estimating the sun__s position. My system estimates heading with RMS error of 6.02_ and global position with RMS error of 442 km. Averaging experimental results from a single site yielded a 0.38_ heading error and a 61 km error in global position. The instrument can detect changes in polarization due to a 0.31_ movement of the sun, which corresponds to 35.2 km of ground movement, with 99% confidence. This technique could be used by underwater vehicles for long-distance navigation and suggests additional ways that marine animals with polarization-sensitive vision could perform both local and long-distance navigation

Fourier domain diffuse correlation spectroscopy with heterodyne holographic detection

We present a new approach to diffuse correlation spectroscopy which overcomes the limited light throughput of single-mode photon counting techniques. Our system employs heterodyne holographic detection to allow parallel measurement of the power spectrum of a fluctuating electric field across thousands of modes, at the shot noise limit, using a conventional sCMOS camera. This yields an order of magnitude reduction in detector cost compared to conventional techniques, whilst also providing robustness to the effects of ambient light and an improved signal-to-noise ratio during in vitro experiments. We demonstrate a GPU-accelerated holographic demodulation system capable of processing the incoming data (79.4 M pixels per second) in real-time, and a novel Fourier domain model of diffuse correlation spectroscopy which permits the direct recovery of flow parameters from the measured data. Our detection and modelling strategy are rigorously validated by modulating the Brownian component of an optical tissue phantom, demonstrating absolute measurements of the Brownian diffusion coefficient in excellent agreement with conventional methods. We further demonstrate the feasibility of our system through in vivo measurement of pulsatile flow rates measured in the human forearm

A Cholecystokinin B Receptor-Specific Aptamer Does Not Activate Receptor Signaling

Targeted nanoparticles which deliver effective doses of chemotherapeutic drugs directly to pancreatic tumors could improve treatment efficacy without the toxicities associated with systemic drug administration. One protein on tumor cells that can be targeted by nanoparticles is a G-protein coupled cell surface receptor, the cholecystokinin B receptor (CCKBR). Previously, we had shown that attaching the CCKBR ligand gastrin to the surface of nanoparticles can enhance their up-take by tumors. The drawback of using gastrin is that it can also activate the receptor, causing tumor cell growth. This study shows that a DNA aptamer that binds to the CCKBR and enhances nanoparticle up-take by tumors does not activate this receptor. PANC-1 cells, a cultured human pancreatic cancer cell line, were treated for 24 h with CCKBR aptamer 1153. Cell lysates were run on Bis-Tris gels, transferred to membranes, blocked in 5% BSA and incubated overnight with primary antibodies, including antibodies directly against phosphorylated-Akt (Ser473), total Akt, and beta-actin, a protein loading control. Although the CCKBR aptamer 1153 is internalized by pancreatic cancer cells in a receptor-mediated fashion, it does not stimulate cell proliferation. Because of this, we anticipate that it will not activate CCKBR signaling. If aptamer 1153 does not activate downstream receptor signaling, our future work will test whether the aptamer could be used to specifically direct drug-containing nanoparticles to tumors, making chemotherapy treatments for pancreatic cancer patients more effective with fewer off-target effects and toxicity

Efficient inversion strategies for estimating optical properties with Monte Carlo radiative transport models

Significance: Indirect imaging problems in biomedical optics generally require repeated evaluation of forward models of radiative transport, for which Monte Carlo is accurate yet computationally costly. We develop an approach to reduce this bottleneck, which has significant implications for quantitative tomographic imaging in a variety of medical and industrial applications.Aim: Our aim is to enable computationally efficient image reconstruction in (hybrid) diffuse optical modalities using stochastic forward models.Approach: Using Monte Carlo, we compute a fully stochastic gradient of an objective function for a given imaging problem. Leveraging techniques from the machine learning community, we then adaptively control the accuracy of this gradient throughout the iterative inversion scheme to substantially reduce computational resources at each step.Results: For example problems of quantitative photoacoustic tomography and ultrasound-modulated optical tomography, we demonstrate that solutions are attainable using a total computational expense that is comparable to (or less than) that which is required for a single high-accuracy forward run of the same Monte Carlo model.Conclusions: This approach demonstrates significant computational savings when approaching the full nonlinear inverse problem of optical property estimation using stochastic methods

Reconstruction-classification method for quantitative photoacoustic tomography

We propose a combined reconstruction-classification method for simultaneously recovering absorption and scattering in turbid media from images of absorbed optical energy. This method exploits knowledge that optical parameters are determined by a limited number of classes to iteratively improve their estimate. Numerical experiments show that the proposed approach allows for accurate recovery of absorption and scattering in two and three dimensions, and delivers superior image quality with respect to traditional reconstruction-only approaches

The treatment of disabling intermittent claudication in patients with superficial femoral artery occlusive disease—Decision analysis

ObjectiveTo determine the preferred approach to superficial femoral artery (SFA) revascularization of Trans-Atlantic Inter-Societal Consensus (TASC) B and C lesions in claudicants requiring intervention based on a review of published data.DesignDecision analysis, Markov state transition model.SubjectsHypothetical cohorts of claudicants with TASC B or TASC C superficial femoral artery lesions considered candidates for either angioplasty with selective stenting (PTA/S) or greater saphenous vein bypass (GSVB).Main outcome measureQuality adjusted life years (QALYs).ResultsFor a 65-year-old man with disabling claudication, percutaneous transluminal angioplasty and selective stenting (PTA/S) was preferred over GSVB for a TASC B SFA lesion. In an otherwise identical patient with a TASC C lesion, bypass was the preferred therapy. Treating PTA/S failures with subsequent bypass increased the utility of PTA/S but bypass remained the preferred initial therapy for TASC C lesions. Sensitivity analysis showed that PTA/S surpasses bypass efficacy for TASC C lesions if PTA/S primary patency is >32% at 5 years, patient age is >80 years, or GSVB operative mortality is > 6%.ConclusionPTA/S is the preferred initial therapy over GSVB for TASC B SFA lesions in patients with disabling intermittent claudication who require intervention. Given contemporary published outcomes for TASC C lesions, GSVB is the preferred therapy in operative candidates. In elderly patients or patients at high risk for bypass, PTA/S should be considered over GSVB. Improved technology that results in a 5-year primary patency of 32% would also justify PTA/S for TASC C SFA lesions

An Exploration of System Factors Influencing Older Adults’ Initial Engagement with Physical Activity Interventions

Background: Previous work has highlighted the need for researchers to look beyond the behavioural, cognitive, and motivational components of physical activity interventions for older adults, and to investigate the ‘system-related’ factors that may influence physical activity behaviour, which pertain to their social, physical, and operational contexts. Objective: This qualitative study aimed to explore the system factors influencing older adults’ initial engagement with physical activity interventions. Methods: Semi-structured one-to-one telephone interviews were conducted with 12 individuals aged 55 and over to gather their views on the subject. The study employed a qualitative descriptive approach, and a thematic analysis was carried out. Results: Participants identified various system factors they felt could influence older adults’ engagement with physical activity interventions, particularly relating to social support and relationships (e.g. being able to bring a friend to the first session), and the physical, social, and information environments (e.g. venues being reachable by bus or car). Conclusion: This study highlights system factors as a potentially important yet largely unexplored concept in the field of physical activity promotion. The findings provide practical information for public health practitioners to use when attempting to design physical activity interventions that older adults will willingly engage with, and the rationale for future research seeking to expand understanding of the influence of system factors on older adults’ initial engagement with physical activity interventions, as well as their subsequent physical activity behaviours beyond this

BeeMapper Quick Guide

BeeMapper is an interactive web tool that displays land cover and predicted wild bee abundance throughout the Maine wild blueberry production landscape. Information from BeeMapper can be used to: 1. Determine placement of honey bee hives during blueberry pollination. 2. Establish a pollinator conservation plan for particular crop fields. 3. Understand wild bee communities in different types of land. The Users Guide provides instructions on using the tool, interpreting its data, and suggests wild bee conservation and management actions. View the Bee Mapper Website