Alan H. Greenaway

Heriot-Watt University, Edinburgh, Scotland, United Kingdom

Are you Alan H. Greenaway?

Claim your profile

Publications (90)109.8 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper compares experimentally temporal and subband implementations of the Minimum Variance (MV) adaptive beamformer for medical ultrasound imaging. The performance of the two approaches is tested by comparing wire phantom measurements, obtained by the research ultrasound scanner SARUS. A 7 MHz BK8804 linear transducer was used to scan a wire phantom in which wires are separated by 10 mm. Performance is then evaluated by the lateral Full-Width-Half-Maximum (FWHM), the Peak Sidelobe Level (PSL), and the computational load. Beamformed single emission responses are also compared with those from conventional Delay-and-Sum (DAS) beamformer. FWHM measured at the depth of 46.6 mm, is 0.02 mm (0.09λ) for both adaptive methods while the corresponding values for Hanning and Boxcar weights are 0.64 and 0.44 mm respectively. Between the MV beamformers a -2 dB difference in PSL is noticed in favor of the subband approach (-31 and -33 dB), whereas values from conventional are not lower than -29 dB. This slight improvement in the case of the subband implementation comes at the expense of increased computational cost; 3.7 TFLOPs per image are required in contrast to 130 GFLOPs of the temporal one, when only 0.5 GFLOPs are needed in DAS beamforming.
    No preview · Conference Paper · Sep 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper compares the performance between temporal and subband Minimum Variance (MV) beamformers for medical ultrasound imaging. Both adaptive methods provide an optimized set of apodization weights but are implemented in the time and frequency domains respectively. Their performance is evaluated with simulated synthetic aperture data obtained from Field II and is quantified by the Full-Width-Half-Maximum (FWHM), the Peak-Side-Lobe level (PSL) and the contrast level. From a point phantom, a full sequence of 128 emissions with one transducer element transmitting and all 128 elements receiving each time, provides a FWHM of 0.03 mm (0.14λ) for both implementations at a depth of 40 mm. This value is more than 20 times lower than the one achieved by conventional beamforming. The corresponding values of PSL are -58 dB and -63 dB for time and frequency domain MV beamformers, while a value no lower than -50 dB can be obtained from either Boxcar or Hanning weights. Interestingly, a single emission with central element #64 as the transmitting aperture provides results comparable to the full sequence. The values of FWHM are 0.04 mm and 0.03 mm and those of PSL are -42 dB and -46 dB for temporal and subband approaches. From a cyst phantom and for 128 emissions, the contrast level is calculated at -54 dB and -63 dB respectively at the same depth, with the initial shape of the cyst being preserved in contrast to conventional beamforming. The difference between the two adaptive beamformers is less significant in the case of a single emission, with the contrast level being estimated at -42 dB for the time domain and -43 dB for the frequency domain implementation. For the estimation of a single MV weight of a low resolution image formed by a single emission, 0.44 * 109 calculations per second are required for the temporal approach. The same numbers for the subband approach are 0.62 * 109 for the point and 1.33 * 109 for the cyst phantom. The comparison demonstrates similar resolution but slightly lower side-lobes and higher contrast for the subband approach at the expense of increased computation time.
    No preview · Article · Feb 2014 · Proceedings of SPIE - The International Society for Optical Engineering
  • Javid Khan · Chi Can · Alan Greenaway · Ian Underwood
    [Show abstract] [Hide abstract]
    ABSTRACT: We have built a HOE-based display capable of reconstructing arbitrary images, in mid-air at fixed focal depths, that can interact with the viewer in real-time. The display system comprises the HOE, a laser projection subsystem, a Kinect motion sensor and an embedded controller. The HOE functions as a fast converging lens and is A4 page sized (20×30cm). We have written a number of simple apps for the display that allow the user to draw in mid-air or to touch icons and buttons that trigger other actions. The reconstructed holographic images are high-resolution, relatively bright and visible under ambient indoor lighting conditions.
    No preview · Conference Paper · Mar 2013
  • Source
    Yan Feng · Paul A Dalgarno · David Lee · Yi Yang · Robert R Thomson · Alan H Greenaway
    [Show abstract] [Hide abstract]
    ABSTRACT: It is shown that grisms, a grating and prism combination, are a simple way to achieve chromatic control in 3D multi-plane imaging. A pair of grisms, whose separation can be varied, provide a collimated beam with a tuneable chromatic shear from a collimated polychromatic input. This simple control permits the correction of chromatic smearing in 3D imaging using off-axis Fresnel zone plates and improved control of the axial profile of a focussed spot in multi-photon experiments. (C) 2012 Optical Society of America
    Full-text · Article · Aug 2012 · Optics Express
  • Anne Marie Johnson · Richard J Eastwood · Alan H Greenaway
    [Show abstract] [Hide abstract]
    ABSTRACT: We extend the redundant spacings calibration method for finding piston coefficients affecting the elements of a dilute aperture array so that tilt phase coefficients can also be calculated and corrected without the need for assumptions about the object. The tilt coefficient retrieval method is successfully demonstrated in simulation, and the specifics of correction by image sharpness are discussed, showing that in dilute aperture systems this method does not necessarily produce a unique image. (C) 2012 Optical Society of America
    No preview · Article · May 2012 · Journal of the Optical Society of America A
  • Lei Yang · Zhen Qiu · Alan H Greenaway · Weiping Lu
    [Show abstract] [Hide abstract]
    ABSTRACT: Image denoising and signal enhancement are two common steps to improve particle contrast for detection in low-signal-to-noise ratio (SNR) fluorescence live-cell images. However, denoising may oversmooth features of interest, particularly weak features, leading to false negative detection. Here, we propose a robust framework for particle detection in which image denoising in the grayscale image is not needed, so avoiding image oversmoothing. A key to our approach is the new development of a particle enhancement filter based on the recently proposed particle probability image to obtain significantly enhanced particle features and greatly suppressed background in low-SNR and low-contrast environments. The new detection method is formed by combining foreground and background markers with watershed transform operating in both particle probability and grayscale spaces; dynamical switchings between the two spaces can optimally make use the information in images for accurate determination of particle position, size, and intensity. We further develop the interacting multiple mode filter for particle motion modeling and data association by incorporating the extra information obtained from our particle detector to enhance the efficiency of multiple particle tracking. We find that our methods lead to significant improvements in particle detection and tracking efficiency in fluorescence live-cell applications.
    No preview · Article · Apr 2012 · IEEE transactions on bio-medical engineering
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper discusses a range of phase-diversity and tracking applications that have been demonstrated experimentally, and will present an analysis of experimental errors associated with the system used. Simultaneous imaging in multiple imaging modes is demonstrated and the use of wavefront-sensing techniques to achieve nanometric depth resolution is reviewed.
    Full-text · Article · Dec 2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe a method for tracking the position of small features in three dimensions from images recorded on a standard microscope with an inexpensive attachment between the microscope and the camera. The depth-measurement accuracy of this method is tested experimentally on a wide-field, inverted microscope and is shown to give approximately 8 nm depth resolution, over a specimen depth of approximately 6 µm, when using a 12-bit charge-coupled device (CCD) camera and very bright but unresolved particles. To assess low-flux limitations a theoretical model is used to derive an analytical expression for the minimum variance bound. The approximations used in the analytical treatment are tested using numerical simulations. It is concluded that approximately 14 nm depth resolution is achievable with flux levels available when tracking fluorescent sources in three dimensions in live-cell biology and that the method is suitable for three-dimensional photo-activated localization microscopy resolution. Sub-nanometre resolution could be achieved with photon-counting techniques at high flux levels.
    Full-text · Article · May 2011 · Journal of The Royal Society Interface
  • Source
    Lei Yang · Richard Parton · Graeme Ball · Zhen Qiu · Alan H Greenaway · Ilan Davis · Weiping Lu
    [Show abstract] [Hide abstract]
    ABSTRACT: Fluorescence imaging of dynamical processes in live cells often results in a low signal-to-noise ratio. We present a novel feature-preserving non-local means approach to denoise such images to improve feature recovery and particle detection. The commonly used non-local means filter is not optimal for noisy biological images containing small features of interest because image noise prevents accurate determination of the correct coefficients for averaging, leading to over-smoothing and other artifacts. Our adaptive method addresses this problem by constructing a particle feature probability image, which is based on Haar-like feature extraction. The particle probability image is then used to improve the estimation of the correct coefficients for averaging. We show that this filter achieves higher peak signal-to-noise ratio in denoised images and has a greater capability in identifying weak particles when applied to synthetic data. We have applied this approach to live-cell images resulting in enhanced detection of end-binding-protein 1 foci on dynamically extending microtubules in photo-sensitive Drosophila tissues. We show that our feature-preserving non-local means filter can reduce the threshold of imaging conditions required to obtain meaningful data.
    Full-text · Article · Dec 2010 · Journal of Structural Biology
  • Javid Khan · Ian Underwood · Alan Greenaway · Mikko Halonen
    [Show abstract] [Hide abstract]
    ABSTRACT: A simple low resolution volumetric display is presented, based on holographic volume-segments. The display system comprises a proprietary holographic screen, laser projector, associated optics plus a control unit. The holographic screen resembles a sheet of frosted glass about A4 in size (20x30cm). The holographic screen is rear-illuminated by the laser projector, which is in turn driven by the controller, to produce simple 3D images that appear outside the plane of the screen. A series of spatially multiplexed and interleaved interference patterns are pre-encoded across the surface of the holographic screen. Each illumination pattern is capable of reconstructing a single holographic volume-segment. Up to nine holograms are multiplexed on the holographic screen in a variety of configurations including a series of numeric and segmented digits. The demonstrator has good results under laboratory conditions with moving colour 3D images in front of or behind the holographic screen.
    No preview · Article · Apr 2010 · Proceedings of SPIE - The International Society for Optical Engineering
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A conventional microscope produces a sharp image from just a single object-plane. This is often a limitation, notably in cell biology. We present a microscope attachment which records sharp images from several object-planes simultaneously. The key concept is to introduce a distorted diffraction grating into the optical system, establishing an order-dependent focussing power in order to generate several images, each arising from a different object-plane. We exploit this multiplane imaging not just for bio-imaging but also for nano-particle tracking, achieving approximately 10 nm z position resolution by parameterising the images with an image sharpness metric.
    Full-text · Article · Jan 2010 · Optics Express
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A feature-preserving non-local means (FP-NLM) filter has been developed recently for denoising images containing small and weak particlelike objects. It explores the commonly used non-local means filter to employ two similarity measurements taken in the original greyscale image and a feature image which measures the particle probability in the original image. In this paper, we report a new approach to image mapping for constructing the feature image by incorporating both spatial and temporal (2D+t) characteristics of objects. We present a 2D+t FP-NLM filter based on the improved particle probability image. Experiments show that the new filter can achieve better balance between particle enhancement and background smoothing for images under severe noise contamination and has a greater capability in detecting particles of interest in such environments. © 2010. The
    Full-text · Conference Paper · Jan 2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the application of wavefront sensing to three-component, three-dimensional micro particle tracking velocimetry (μPTV). The technique is based upon examining the defocus of the wavefront scattered by a tracer particle and from such information establishing the 3-D tracer location. The imaging system incorporates a cylindrical lens acting as an anamorphic element that creates different magnifications in the two orthogonal axes. A single anamorphic image is obtained from each tracer, which contains sufficient information to reconstruct the wavefront defocus and uniquely identify the tracer’s axial position. A mathematical model of the optical system is developed and shows that the lateral and depth performance of the sensor can be largely independently varied across a wide range. Hence, 3-D image resolution can be achieved from a single viewpoint, using simple and inexpensive optics and applied to a wide variety of microfluidic or biological systems. Our initial results show that an uncertainty in depth of 0.18 μm was achieved over a 20-μm range. The technique was employed to measure the 3-D velocity field of micron-sized fluorescent tracers in a flow within a micro channel, and an uncertainty of 2.8 μm was obtained in the axial direction over a range of 500 μm. The experimental results were in agreement with the expected fluid flow when compared to the corresponding CFD model. Thus, wavefront sensing proved to be an effective approach to obtain quantitative measurements of three-component three-dimensional flows in microfluidic devices.
    Full-text · Article · Oct 2009 · Experiments in Fluids
  • Source
    Richard J Eastwood · Anne Marie Johnson · Alan H Greenaway
    [Show abstract] [Hide abstract]
    ABSTRACT: The principle of redundant spacings calibration has previously been described for the purpose of calibrating piston phase aberration affecting elements of a dilute aperture array using a system of linear equations in terms of the aperture phases as well as object phase information. Here we develop matrices for the correction of piston phase aberration by use of image sharpness and also by phase retrieval. These are both presented in wavefront sensor formulation in order to draw analogy between the approaches. We then discuss solution ambiguity affecting both methods and describe array design criteria to prevent such ambiguity. The problem of increased image aliasing under image sharpness correction is also highlighted.
    Preview · Article · Feb 2009 · Journal of the Optical Society of America A
  • Source
    F. H. P. Spaan · A. H. Greenaway
    [Show abstract] [Hide abstract]
    ABSTRACT: Pupil replication and hypertelescope systems for imaging telluric exoplanets in scattered light are treated. Analytic expressions for the spread functions in one and two dimensions and in the presence of various forms of error are given. Error effects considered include aperture misalignment, tilts, piston, pointing errors, and unequal beam amplitude. The performance of the two approaches is contrasted, and the analytic results are compared with simulation results.
    Preview · Article · Dec 2008 · The Astrophysical Journal
  • Source
    A. H. Greenaway · F. H. P. Spaan · and V. Mourai
    [Show abstract] [Hide abstract]
    ABSTRACT: Pupil replication is a new optical technique that decreases the diameter of the image of a star on the optical axis. With pupil replication, one can improve the suppression of starlight in high dynamic range exoplanet imaging and image planets closer to their host star. Pupil replication is an auxiliary technique intended to improve the imaging spectroscopic performance of coronographic or pupil apodization techniques. Here we introduce pupil replication and use numerical simulations to show that it may be combined with pupil apodization to improve exoplanet detection and spectroscopy.
    Preview · Article · Dec 2008 · The Astrophysical Journal
  • Source
    R R Thomson · A S Bockelt · E Ramsay · S Beecher · A H Greenaway · A K Kar · D T Reid
    [Show abstract] [Hide abstract]
    ABSTRACT: We use a two-dimensional deformable mirror to shape the spatial profile of an ultrafast laser beam that is then used to inscribe structures in a soda-lime silica glass slide. By doing so we demonstrate that it is possible to control the asymmetry of the cross section of ultrafast laser inscribed optical waveguides via the curvature of the deformable mirror. When tested using 1.55 mum light, the optimum waveguide exhibited coupling losses of approximately 0.2 dB/facet to Corning SMF-28 single mode fiber and propagation losses of approximately 1.5 dB.cm(-1). This technique promises the possibility of combining rapid processing speeds with the ability to vary the waveguide cross section along its length.
    Full-text · Article · Sep 2008 · Optics Express
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: EAGLE is a multi-object 3D spectroscopy instrument currently under design for the 42-metre European Extremely Large Telescope (E-ELT). Precise requirements are still being developed, but it is clear that EAGLE will require (~100 x 100 actuator) adaptive optics correction of ~20 - 60 spectroscopic subfields distributed across a ~5 arcminute diameter field of view. It is very likely that LGS will be required to provide wavefront sensing with the necessary sky coverage. Two alternative adaptive optics implementations are being considered, one of which is Multi-Object Adaptive Optics (MOAO). In this scheme, wavefront tomography is performed using a set of LGS and NGS in either a completely open-loop manner, or in a configuration that is only closed-loop with respect to only one DM, probably the adaptive M4 of the E-ELT. The fine wavefront correction required for each subfield is then applied in a completely open-loop fashion by independent DMs within each separate optical relay. The novelty of this scheme is such that on-sky demonstration is required prior to final construction of an E-ELT instrument. The CANARY project will implement a single channel of an MOAO system on the 4.2m William Herschel Telescope. This will be a comprehensive demonstration, which will be phased to include pure NGS, low-order NGS-LGS and high-order woofer-tweeter NGS-LGS configurations. The LGSs used for these demonstrations will be Rayleigh systems, where the variable range-gate height and extension can be used to simulate many of the LGS effects on the E-ELT. We describe the requirements for the various phases of MOAO demonstration, the corresponding CANARY configurations and capabilities and the current conceptual designs of the various subsystems.
    Full-text · Article · Jul 2008 · Proceedings of SPIE - The International Society for Optical Engineering
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose an annular-aperture-based defocusing technique for three-dimensional (3D) particle metrology from a single camera view. This simple configuration has high optical efficiency and the ability to deal with overlapped defocused images. Initial results show that an uncertainty in depth of 23 microm can be achieved over a range of 10 mm for macroscopic systems. This method can also be applied in microscopy for the measurement of fluorescently doped microparticles, thus providing a promising solution for 3D flow metrology at both macroscales and microscales.
    Full-text · Article · Jun 2008 · Optics Letters
  • David M. Faichnie · Alan H. Greenaway · Ian Bain
    [Show abstract] [Hide abstract]
    ABSTRACT: Thin film metrology is an important quality control mechanism used in many industrial processes. Conventional techniques of Ellipsometry and Spectral Reflectance are limited in applicability to in situ measurements during film manufacture. This paper considers the measurement of wavefront shape reflected from interfaces within a laminate for determination of layer thickness and profile. For thick layers a wavefront sensor can provide the requisite wavefront shape data, for thin layers the interference between reflected wavefronts is used to retrieve wavefront shape.
    No preview · Article · Jan 2008

Publication Stats

1k Citations
109.80 Total Impact Points

Institutions

  • 2004-2014
    • Heriot-Watt University
      • • School of Engineering and Physical Sciences
      • • Department of Physics
      Edinburgh, Scotland, United Kingdom
  • 2000
    • Hokkaido University
      • Division of Media and Network Technologies
      Sapporo-shi, Hokkaido, Japan