1. Articles from Peter H. Tomlins

    1-17 of 17
    1. Heart rate sensitive optical coherence angiography

      Heart rate sensitive optical coherence angiography

      Optical coherence angiography (OCA) enables visualisation of three-dimensional micro-vasculature from optical coherence tomography data volumes. Typically, various statistical methods are used to discriminate static tissue from blood flow within vessels. In this paper, we introduce a new method that relies upon the beating heart frequency to isolate blood vessels from the surrounding tissue. Vascular blood flow is assumed to be more strongly modulated by the heart-beat compared to surrounding tissue and therefore short-time Fourier transform of sequential measurements can discriminate the two. Furthermore, it is demonstrated that adjacent B-Scans within an OCT data volume can provide the required sampling frequency ...

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    2. Heart-rate sensitive optical coherence angiography for measuring vascular changes due to posttraumatic brain injury in mice

      Heart-rate sensitive optical coherence angiography for measuring vascular changes due to posttraumatic brain injury in mice

      Traumatic brain injury (TBI) results in direct vascular disruption, triggering edema, and reduction in cerebral blood flow. Therefore, understanding the pathophysiology of brain microcirculation following TBI is important for the development of effective therapies. Optical coherence angiography (OCA) is a promising tool for evaluating TBI in rodent models. We develop an approach to OCA that uses the heart-rate frequency to discriminate between static tissue and vasculature. This method operates on intensity data and is therefore not phase sensitive. Furthermore, it does not require spatial overlap of voxels and thus can be applied to pre-existing datasets for which oversampling may not ...

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    3. Dynamic measurement of the optical properties of bovine enamel demineralization models using four-dimensional optical coherence tomography

      Dynamic measurement of the optical properties of bovine enamel demineralization models using four-dimensional optical coherence tomography

      Dental enamel mineral loss is multifactorial and is consequently explored using a variety of in vitro models. Important factors include the presence of acidic pH and its specific ionic composition, which can both influence lesion characteristics. Optical coherence tomography (OCT) has been demonstrated as a promising tool for studying dental enamel demineralization. However, OCT-based characterization and comparison of demineralization model dynamics are challenging without a consistent experimental environment. Therefore, an automated four-dimensional OCT system was integrated with a multispecimen flow cell to measure and compare the optical properties of subsurface enamel demineralization in different models. This configuration was entirely automated ...

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    4. Methods to assess sensitivity of optical coherence tomography systems

      Methods to assess sensitivity of optical coherence tomography systems

      Measuring the sensitivity of an optical coherence tomography (OCT) system determines the minimum sample reflectivity it can detect and provides a figure of merit for system optimization and comparison. The published literature lacks a detailed description of OCT sensitivity measurement procedures. Here we describe a commonly-used measurement method and introduce two new phantom-based methods, which also offer a means to directly visualize low reflectivity conditions relevant to biological tissue. We provide quantitative results for the three methods from different OCT system configurations and discuss the methods’ advantages and disadvantages.

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    5. Variations in optical coherence tomography resolution and uniformity: a multi-system performance comparison

      Variations in optical coherence tomography resolution and uniformity: a multi-system performance comparison

      Point spread function (PSF) phantoms based on unstructured distributions of sub-resolution particles in a transparent matrix have been demonstrated as a useful tool for evaluating resolution and its spatial variation across image volumes in optical coherence tomography (OCT) systems. Measurements based on PSF phantoms have the potential to become a standard test method for consistent, objective and quantitative inter-comparison of OCT system performance. Towards this end, we have evaluated three PSF phantoms and investigated their ability to compare the performance of four OCT systems. The phantoms are based on 260-nm-diameter gold nanoshells, 400-nm-diameter iron oxide particles and 1.5-micron-diameter silica ...

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    6. Feature Of The Week 1/8/12: Ultrafast Processing and Rendering of OCT Data using a GPU

      Feature Of The Week 1/8/12: Ultrafast Processing and Rendering of OCT Data using a GPU
      Processing of the large volumetric data is the bottleneck of the current FD-OCT systems. Solving this issue enables real time visualisation. Various groups have applied utilising the full power of GPU for OCT data processing allows to realise the full potential of OCT. GPU based data processing to OCT. Here we present a GPU-CPU based processing methodology as well evaluates the performance of various GPUs.In standard processing, interference data are copied to GPU and entire computation is carried out on GPU. Processed data are stored in GPU memory, which allows rendering and visualising the data.To benchmark the processing ...
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    7. Estimating the resolution of a commercial optical coherence tomography system with limited spatial sampling

      Estimating the resolution of a commercial optical coherence tomography system with limited spatial sampling
      Optical coherence tomography (OCT) is becoming increasingly widespread as an experimental tool for clinical investigation, facilitated by the development of commercial instruments. In situ performance evaluation of such 'black box' systems presents a challenge, where the instrument hardware and software can limit access to important configuration parameters and raw data. Two key performance metrics for imaging systems are the point-spread function (PSF) and the associated modulation transfer function (MTF). However, previously described experimental measurement techniques assume user-variable spatial sampling and may not be appropriate for the characterization of deployed commercial instruments. Characterization methods developed for other modalities do not address ...
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    8. Femtosecond laser micro-inscription of optical coherence tomography resolution test artifacts

      Femtosecond laser micro-inscription of optical coherence tomography resolution test artifacts
      Optical coherence tomography (OCT) systems are becoming more commonly used in biomedical imaging and, to enable continued uptake, a reliable method of characterizing their performance and validating their operation is required. This paper outlines the use of femtosecond laser subsurface micro-inscription techniques to fabricate an OCT test artifact for validating the resolution performance of a commercial OCT system. The key advantage of this approach is that by utilizing the nonlinear absorption a three dimensional grid of highly localized point and line defects can be written in clear fused silica substrates.
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    9. Processing and rendering of Fourier domain optical coherence tomography images at a line rate over 524 kHz using a graphics processing unit

      Processing and rendering of Fourier domain optical coherence tomography images at a line rate over 524 kHz using a graphics processing unit
      In Fourier domain optical coherence tomography (FD-OCT), a large amount of interference data needs to be resampled from the wavelength domain to the wavenumber domain prior to Fourier transformation. We present an approach to optimize this data processing, using a graphics processing unit (GPU) and parallel processing algorithms. We demonstrate an increased processing and rendering rate over that previously reported by using GPU paged memory to render data in the GPU rather than copying back to the CPU. This avoids unnecessary and slow data transfer, enabling a processing and display rate of well over 524,000 A-scan/s for a ...
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    10. Spatially deconvolved optical coherence tomography

      Spatially deconvolved optical coherence tomography
      In this paper we present spatially mapped point-spread function (PSF) measurements of an optical coherence tomography (OCT) instrument and subsequent spatial deconvolution. The OCT B-scan image plane was divided into 2400 subimages, for which PSFs were determined from OCT measurements of a specially designed phantom. Each PSF was deconvolved from its corresponding subimage of the phantom using the Lucy-Richardson algorithm. Following deconvolution, all of the subimages were reassembled to form a final deconvolved image, from which the resolution improvement was quantitatively assessed. The lateral resolution was found to improve by 3.1 μm compared to an axial resolution enhancement of ...
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    11. Contrast phantoms for optical coherence tomography

      Contrast phantoms for optical coherence tomography
      In this work we present contrast measurement phantoms for optical coherence tomography. In this initial study, contrast has been evaluated from OCT images of a USAF-1951 bar target, buried beneath scattering layers of different density. Preliminary results indicate that scattering does not degrade imaging contrast significantly, however further work is required to verify these findings. This work has important implications from a quality control perspective as well for OCT inter-comparisons at, for example, different wavebands.
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    12. Point-spread function phantoms for optical coherence tomography

      Point-spread function phantoms for optical coherence tomography
      Recently scientists at the Uk's National Physical Laboratory completed an initial study into the development of robust point-spread function (PSF) phantoms, that are potentially suitable as OCT calibration standards. The findings have been published in a publicly available NPL report, available freely from the NPL website or upon request to Pete Tomlins (pete.tomlins@npl.co.uk).
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    13. Optical coherence refractometry

      Peter H. Tomlins, Peter Woolliams, Christian Hart, Andrew Beaumont, Matthew Tedaldi We introduce a novel approach to refractometry using a low coherence interferometer at multiple angles of incidence. We show that for plane parallel samples it is possible to measure their phase refractive index rather than the group index that is usually measured by interferometric methods. This ... [Opt. Lett. 33, 2272-2274 (2008)]
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    14. Measurement of the three-dimensional point-spread function in an optical coherence tomography imaging system

      Peter H. Tomlins, Peter Woolliams, Matthew Tedaldi et al. Two significant figures of merit for optical coherence tomography (OCT) systems are the axial and transverse resolutions. Transverse resolution has been defined using the Rayleigh Criterion or from Gaussian beam optics. The axial resolution is generally defined in terms of the coherence length of a ... [Proc. SPIE Int. Soc. Opt. Eng. 6847, 68472Q (2008)] published Mon Feb 18, 2008.
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    15. Dynamic cure measurement of dental polymer composites using optical coherence tomography

      Peter H. Tomlins, Will M. Palin, and Adrian C. Shortall Dental amalgam is being increasingly replaced by Light-activated resin-based dental composites. However, these materials are limited by inefficient setting reactions as a function of depth, constraining the maximum extent of cure and reducing biocompatibility. In this paper we demonstrate a novel me ... [Proc. SPIE Int. Soc. Opt. Eng. 6843, 68430D (2008)] published Mon Feb 11, 2008.
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      Mentions: Pete H. Tomlins
    16. Complex flow characterisation of a porous tissue scaffold measured by Doppler optical coherence tomography

      Peter H. Tomlins, Yiwei Wang, Bufa Zhang et al. The flow of culture medium through a mechanically stimulated cell-seeded tissue scaffold is a factor influencing not only the transport of essential nutrients and waste product removal but also impacting on the degradation kinetics of the scaffold. Being able to map spatial and temporal changes in f ... [Proc. SPIE Int. Soc. Opt. Eng. 6858, 685804 (2008)] published Wed Feb 6, 2008.
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    17. Digital phase stabilization to improve detection sensitivity for optical coherence tomography

      Optical coherence tomography has become an important tool for medical imaging and increasingly for quantitative metrological applications. As a consequence detection sensitivity is highly valued. In this paper, we introduce a novel post-processing technique for digitally stabilizing and spectrally averaging optical coherence tomography datasets in order to enhance detection sensitivity. We demonstrate sensitivity gains of 18 dB when the algorithm is applied to data from a high-speed Fourier domain system.
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    1-17 of 17
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  2. Topics in the News

    1. (17 articles) Pete H. Tomlins
    2. (10 articles) UK National Physical Laboratory
    3. (10 articles) Peter D. Woolliams
    4. (4 articles) University of London
    5. (3 articles) Janarthanan Rasakanthan
    6. (3 articles) Kate Sugden
    7. (2 articles) FDA
    8. (2 articles) Matthew Tedaldi
    9. (2 articles) Anant Agrawal
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    Point-spread function phantoms for optical coherence tomography Spatially deconvolved optical coherence tomography Processing and rendering of Fourier domain optical coherence tomography images at a line rate over 524 kHz using a graphics processing unit Femtosecond laser micro-inscription of optical coherence tomography resolution test artifacts Estimating the resolution of a commercial optical coherence tomography system with limited spatial sampling Feature Of The Week 1/8/12: Ultrafast Processing and Rendering of OCT Data using a GPU Direct inverse linearization of piezoelectric actuator’s initial loading curve and its applications in full-field optical coherence tomography (FF-OCT) Peripapillary Retinal and Choroidal Perfusion in Nonarteritic Ischemic Optic Neuropathy Using Optical Coherence Tomography Angiography Reliability of foveal avascular zone measurements in eyes with retinal vein occlusion using optical coherence tomography angiography SD-OCT parameters and visual field defect in chiasmal compression and the diagnostic value of neural network model Visualization of deep choroidal vasculatures and measurement of choroidal vascular density: a swept-source optical coherence tomography angiography approach Model-to-Data Approach for Deep Learning in Optical Coherence Tomography Intraretinal Fluid Segmentation