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Performance optimisation of a holographic Fourier domain diffuse correlation spectroscopy instrument (2022)
Journal Article
James, E., Powell, S., & Munro, P. (2022). Performance optimisation of a holographic Fourier domain diffuse correlation spectroscopy instrument. Biomedical Optics Express, 13(7), 3836-3853. https://doi.org/10.1364/boe.454346

We have previously demonstrated a novel interferometric multispeckle Fourier domain diffuse correlation spectroscopy system that makes use of holographic camera-based detection, and which is capable of making in vivo pulsatile flow measurements. In t... Read More about Performance optimisation of a holographic Fourier domain diffuse correlation spectroscopy instrument.

Time domain optical imaging device based on a commercial time-to-digital converter (2021)
Journal Article
Pérez-Tirador, P., Papadimitriou, K. I., Powell, S., & Hebden, J. C. (2021). Time domain optical imaging device based on a commercial time-to-digital converter. Review of Scientific Instruments, 92(10), Article 103704. https://doi.org/10.1063/5.0054516

Time-domain diffuse optical imaging is a noninvasive technique that uses pulsed near-infrared light as the interrogation source to produce quantitative images displaying the variation in blood volume and oxygenation in the human brain. Measuring the... Read More about Time domain optical imaging device based on a commercial time-to-digital converter.

Simulation of statistically accurate time-integrated dynamic speckle patterns in biomedical optics (2021)
Journal Article
James, E., Powell, S., & Munro, P. (2021). Simulation of statistically accurate time-integrated dynamic speckle patterns in biomedical optics. Optics Letters, 46(17), 4390-4393. https://doi.org/10.1364/OL.435812

The simulation of statistically accurate time-integrated dynamic speckle patterns using a physics-based model that accounts for spatially varying sample properties is yet to be presented in biomedical optics. In this Letter, we propose a solution to... Read More about Simulation of statistically accurate time-integrated dynamic speckle patterns in biomedical optics.

Evaluating a new generation of wearable high-density diffuse optical tomography technology via retinotopic mapping of the adult visual cortex (2021)
Journal Article
Vidal-Rosas, E. E., Zhao, H., Nixon-Hill, R. W., Smith, G., Dunne, L., Powell, S., …Everdell, N. L. (2021). Evaluating a new generation of wearable high-density diffuse optical tomography technology via retinotopic mapping of the adult visual cortex. Neurophotonics, 8(02), https://doi.org/10.1117/1.nph.8.2.025002

Significance: High-density diffuse optical tomography (HD-DOT) has been shown to approach the resolution and localization accuracy of blood oxygen level dependent-functional magnetic resonance imaging in the adult brain by exploiting densely spaced,... Read More about Evaluating a new generation of wearable high-density diffuse optical tomography technology via retinotopic mapping of the adult visual cortex.

Fourier domain diffuse correlation spectroscopy with heterodyne holographic detection (2020)
Journal Article
James, E., & Powell, S. (2020). Fourier domain diffuse correlation spectroscopy with heterodyne holographic detection. Biomedical Optics Express, 11(11), 6755-6779. https://doi.org/10.1364/boe.400525

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 spect... Read More about Fourier domain diffuse correlation spectroscopy with heterodyne holographic detection.

Functional imaging of the developing brain with wearable high-density diffuse optical tomography: a new benchmark for infant neuroimaging outside the scanner environment (2020)
Journal Article
Frijia, E. M., Billing, A., Lloyd-Fox, S., Rosas, E. V., Collins-Jones, L., Crespo-Llado, M. M., …Cooper, R. J. (2021). Functional imaging of the developing brain with wearable high-density diffuse optical tomography: a new benchmark for infant neuroimaging outside the scanner environment. NeuroImage, 225, Article 117490. https://doi.org/10.1016/j.neuroimage.2020.117490

Studies of cortical function in the awake infant are extremely challenging to undertake with traditional neuroimaging approaches. Partly in response to this challenge, functional near-infrared spectroscopy (fNIRS) has become increasingly common in de... Read More about Functional imaging of the developing brain with wearable high-density diffuse optical tomography: a new benchmark for infant neuroimaging outside the scanner environment.

Efficient inversion strategies for estimating optical properties with Monte Carlo radiative transport models (2020)
Journal Article
Macdonald, C. M., Arridge, S., & Powell, S. (2020). Efficient inversion strategies for estimating optical properties with Monte Carlo radiative transport models. Journal of Biomedical Optics, 25(08), https://doi.org/10.1117/1.jbo.25.8.085002

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 bottlene... Read More about Efficient inversion strategies for estimating optical properties with Monte Carlo radiative transport models.

A wide field-of-view, modular, high-density diffuse optical tomography system for minimally constrained three-dimensional functional neuroimaging (2020)
Journal Article
Zhao, H., Brigadoi, S., Chitnis, D., Vita, E. D., Castellaro, M., Powell, S., …Cooper, R. J. (2020). A wide field-of-view, modular, high-density diffuse optical tomography system for minimally constrained three-dimensional functional neuroimaging. Biomedical Optics Express, 11(8), 4110-4129. https://doi.org/10.1364/BOE.394914

The ability to produce high-quality images of human brain function in any environment and during unconstrained movement of the subject has long been a goal of neuroimaging research. Diffuse optical tomography, which uses the intensity of back-scatter... Read More about A wide field-of-view, modular, high-density diffuse optical tomography system for minimally constrained three-dimensional functional neuroimaging.

Dual wavelength spread-spectrum time-resolved diffuse optical instrument for the measurement of human brain functional responses (2020)
Journal Article
Papadimitriou, K. I., Vidal Rosas, E. E., Zhang, E., Cooper, R. J., Hebden, J. C., Arridge, S. R., & Powell, S. (2020). Dual wavelength spread-spectrum time-resolved diffuse optical instrument for the measurement of human brain functional responses. Biomedical Optics Express, 11(7), 3477-3490. https://doi.org/10.1364/boe.393586

Near-infrared spectroscopy has proven to be a valuable method to monitor tissue oxygenation and haemodynamics non-invasively and in real-time. Quantification of such parameters requires measurements of the time-of-flight of light through tissue, typi... Read More about Dual wavelength spread-spectrum time-resolved diffuse optical instrument for the measurement of human brain functional responses.

Quantitative PA tomography of high resolution 3-D images: Experimental validation in a tissue phantom (2020)
Journal Article
Laufer, J., Prohaska, S., Powell, S., Buchmann, J., & Kaplan, B. (2020). Quantitative PA tomography of high resolution 3-D images: Experimental validation in a tissue phantom. Photoacoustics, 17, https://doi.org/10.1016/j.pacs.2019.100157

© 2019 The Author(s) Quantitative photoacoustic tomography aims to recover the spatial distribution of absolute chromophore concentrations and their ratios from deep tissue, high-resolution images. In this study, a model-based inversion scheme based... Read More about Quantitative PA tomography of high resolution 3-D images: Experimental validation in a tissue phantom.

A pseudospectral method for solution of the radiative transport equation (2019)
Journal Article
Powell, S., Cox, B. T., & Arridge, S. R. (2019). A pseudospectral method for solution of the radiative transport equation. Journal of Computational Physics, 384, 376-382. https://doi.org/10.1016/j.jcp.2019.01.024

The radiative transport equation accurately describes light transport in participating media, though analytic solutions are known only for simple geometries. We present a pseudospectral technique to efficiently compute numerical solutions to large-sc... Read More about A pseudospectral method for solution of the radiative transport equation.

A spread spectrum approach to time-domain near-infrared diffuse optical imaging using inexpensive optical transceiver modules (2018)
Journal Article
Papadimitriou, K. I., Dempsey, L. A., Hebden, J. C., Arridge, S. R., & Powell, S. (2018). A spread spectrum approach to time-domain near-infrared diffuse optical imaging using inexpensive optical transceiver modules. Biomedical Optics Express, 9(6), 2648 - 2663. https://doi.org/10.1364/boe.9.002648

We introduce a compact time-domain system for near-infrared spectroscopy using a spread spectrum technique. The proof-of-concept single channel instrument utilises a low-cost commercially available optical transceiver module as a light source, contro... Read More about A spread spectrum approach to time-domain near-infrared diffuse optical imaging using inexpensive optical transceiver modules.

Quantitative photoacoustic tomography using forward and adjoint Monte Carlo models of radiance (2016)
Journal Article
Hochuli, R., Powell, S., Arridge, S., & Cox, B. (2016). Quantitative photoacoustic tomography using forward and adjoint Monte Carlo models of radiance. Journal of Biomedical Optics, 21(12), https://doi.org/10.1117/1.jbo.21.12.126004

Forward and adjoint Monte Carlo (MC) models of radiance are proposed for use in model-based quantitative photoacoustic tomography. A two-dimensional (2-D) radiance MC model using a harmonic angular basis is introduced and validated against analytic s... Read More about Quantitative photoacoustic tomography using forward and adjoint Monte Carlo models of radiance.

Reconstruction-classification method for quantitative photoacoustic tomography (2015)
Journal Article
Malone, E., Powell, S., Cox, B. T., & Arridge, S. (2015). Reconstruction-classification method for quantitative photoacoustic tomography. Journal of Biomedical Optics, 20(12), https://doi.org/10.1117/1.jbo.20.12.126004

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 limi... Read More about Reconstruction-classification method for quantitative photoacoustic tomography.

Gradient-Based Quantitative Image Reconstruction in Ultrasound-Modulated Optical Tomography: First Harmonic Measurement Type in a Linearised Diffusion Formulation (2015)
Journal Article
Powell, S., Arridge, S. R., & Leung, T. S. (2016). Gradient-Based Quantitative Image Reconstruction in Ultrasound-Modulated Optical Tomography: First Harmonic Measurement Type in a Linearised Diffusion Formulation. IEEE Transactions on Medical Imaging, 35(2), 456-467. https://doi.org/10.1109/tmi.2015.2478742

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 w... Read More about Gradient-Based Quantitative Image Reconstruction in Ultrasound-Modulated Optical Tomography: First Harmonic Measurement Type in a Linearised Diffusion Formulation.