1. Articles from Martin Leahy

    1-25 of 25
    1. Comparing an FFT filter for multiple reference optical coherence tomography (MR-OCT) with an Chebychev and an elliptic filter

      Comparing an FFT filter for multiple reference optical coherence tomography (MR-OCT) with an Chebychev and an elliptic filter

      Portable and low-cost optical coherence tomography (OCT) is increasingly used to improve the accuracy of point-of-care applications. The increasing research efforts to use photonics integrated circuits (PIC) is without doubts the future for highest packaging densities in miniature optical systems. MR-OCT is another technology that is using the advantages of well known CD/DVD-ROM technology to build miniaturized and low-cost OCT systems and may be more readily available before PICs reach their full potential. For MR-OCT it is essential to separate the the multiple signals originating from the multiple reflections of the partial mirror in the reference arm of Michelson ...

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    2. Enhanced in vivo visualization of the microcirculation by topical application of fructose solution confirmed with correlation mapping optical coherence tomography

      Enhanced in vivo visualization of the microcirculation by topical application of fructose solution confirmed with correlation mapping optical coherence tomography

      Changes within the microcirculation can provide an early indication of the onset of a plethora of ailments. Various techniques have thus been developed that enable the study of microcirculatory irregularities. Correlation mapping optical coherence tomography (cmOCT) is a recently proposed technique, which enables mapping of vasculature networks at the capillary level in a noninvasive and noncontact manner. This technique is an extension of conventional optical coherence tomography (OCT) and is therefore likewise limited in the penetration depth of ballistic photons in biological media. Optical clearing has previously been demonstrated to enhance the penetration depth and the imaging capabilities of OCT ...

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    3. Quantitative assessment of rat corneal thickness and morphology during stem cell therapy by high-speed optical coherence tomography

      Quantitative assessment of rat corneal thickness and morphology during stem cell therapy by high-speed optical coherence tomography

      Optical Coherence Tomography (OCT) is a non-invasive 3 dimensional optical imaging modality that enables high resolution cross sectional imaging in biological tissues and materials. Its high axial and lateral resolution combined with high sensitivity, imaging depth and wide field of view makes it suitable for wide variety of high resolution medical imaging applications at clinically relevant speed. With the advent of swept source lasers, the imaging speed of OCT has increased considerably in recent years. OCT has been used in ophthalmology to study dynamic changes occurring in the cornea and iris, thereby providing physiological and pathological changes that occur within ...

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    4. Optimization of modified scanning protocol based correlation mapping optical coherence tomography at 200 kHz VCSEL source for in vivo microcirculation imaging applications

      Optimization of modified scanning protocol based correlation mapping optical coherence tomography at 200 kHz VCSEL source for in vivo microcirculation imaging applications

      Optical Coherence Tomography (OCT) is a non-invasive 3 dimensional optical imaging modality that enables high resolution cross sectional imaging in biological tissues and materials. Unlike other 3 D medical imaging modalities, OCT provides high axial and lateral resolution combined with high sensitivity, imaging depth and wide field of view which makes it suitable for wide variety of medical imaging applications1. Apart from analysing the morphological characteristics of the biological organs with micron scale axial and lateral resolution, OCT also provides functional information from the biological sample. Among the various functional extensions of OCT, angiographic OCT that enables visualization of lumens ...

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    5. The impact of relative intensity noise on the signal in multiple reference optical coherence tomography

      The impact of relative intensity noise on the signal in multiple reference optical coherence tomography

      Multiple reference optical coherence tomography (MR-OCT) applies a unique low-cost solution to enhance the scanning depth of standard time domain OCT by inserting an partial mirror into the reference arm of the interferometric system. This novel approach achieves multiple reflections for different layers and depths of an sample with minimal effort of engineering and provides an excellent platform for low-cost OCT systems based on well understood production methods for micro-mechanical systems such as CD/DVD pick-up systems. The direct integration of a superluminescent light-emitting diode (SLED) is a preferable solution to reduce the form- factor of an MR-OCT system. Such ...

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    6. Depth-dependent displacement sensitivity analysis and the influence of Doppler angle for quantitative assessment of mechanical properties using phase-sensitive spectral domain optical coherence tomography

      Depth-dependent displacement sensitivity analysis and the influence of Doppler angle for quantitative assessment of mechanical properties using phase-sensitive spectral domain optical coherence tomography

      Optical coherence elastography (OCE) asesses the mechanical properties of samples by applying a mechanical stimulation and detecting the resulting sample displacement using optical coherence tomography (OCT). OCE methods which utilise the phase of the OCT signal offer the potential to detect displacements on the sub-nanometre scale. However, the displacement sensitivity achieveable is directly related to the signal-to-noise ratio and phase stability of the underlying OCT system. Furthermore, the estimation of Doppler angle is imperative in accurately measuring the sample displacement. This work evaluates the contributions of each of these parameters for quantitative assessment of mechanical properties using phase-sensitive spectral domain ...

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    7. Assessment of curing behavior of light-activated dental composites using intensity correlation based multiple reference optical coherence tomography

      Assessment of curing behavior of light-activated dental composites using intensity correlation based multiple reference optical coherence tomography

      Background and Objectives Monitoring the curing kinetics of light-activated resin is a key area of research. These resins are used in restorative applications and particularly in dental applications. They can undergo volumetric shrinkage due to poor control of the depth dependent curing process, modulated by the intensity and duration of the curing light source. This often results in the formation of marginal gaps, causing pain and damage to the restoration site. In this study, we demonstrate the capabilities of a correlation method applied using a multiple references optical coherence tomography (MR-OCT) architecture to monitor the curing of the resin. Study ...

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    8. 3D nondestructive testing system with an affordable multiple reference optical-delay-based optical coherence tomography

      3D nondestructive testing system with an affordable multiple reference optical-delay-based optical coherence tomography

      Optical coherence tomography (OCT) is emerging as a powerful noncontact imaging technique, allowing high-quality cross-sectional imaging of scattering specimens nondestructively. However, the complexity and cost of current embodiments of an OCT system limit its use in various nondestructive testing (NDT) applications at resource-limited settings. In this paper, we demonstrate the feasibility of a novel low-cost OCT system for a range of nondestructive testing (NDT) applications. The proposed imaging system is based on an enhanced time-domain OCT system with a low cost and small form factor reference arm optical delay, called multiple reference OCT (MR-OCT), which uses a miniature voice coil ...

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    9. Characterization of light distribution and optimization of detector position for multiple reference optical coherence tomography

      Characterization of light distribution and optimization of detector position for multiple reference optical coherence tomography

      A time-domain optical coherence tomography system with respect to multiple reflections in the reference arm is simulated with Zemax and the optimal detector position is discussed based on the wavefront error. Multiple reference optical coherence tomography (MR-OCT) is a novel optical imaging platform using a single miniature actuator and partial mirror to recirculate light multiple times within the interferometric system. The recirculation corresponds to multiple path delays extending effectively the axial scan-range. The simulation of MR-OCT with lenses of 5 mm diameter shows that it is suitable to build a compact system using low-cost components. Subsequently MR-OCT enables an affordable ...

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    10. Signal simulation and signal processing for multiple reference optical coherence tomography

      Signal simulation and signal processing for multiple reference optical coherence tomography

      The generation of a synthetic MR-OCT signal is presented and compared to a real acquired signal. Multiple reference optical coherence tomography (MR-OCT) is a novel time-domain interferometric system. The MR-OCT principle is adding a partial mirror to extend the axial scan range, which effectively extends the scan depth for imaging. The actuation of the scan mirror required for time-domain OCT, was demonstrated to operate with a low cost miniature voice coil, such as a speaker extracted from a smartphone or CD/DVD pick-up system. Building a compact and cost-effective optical imaging system will enable affordable medical diagnosis at low-resource setting ...

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    11. Developing cross-correlation as a method for microvessel imaging using clinical intravascular optical coherence tomography systems

      Developing cross-correlation as a method for microvessel imaging using clinical intravascular optical coherence tomography systems

      Current clinical intravascular optical coherence tomography (IV-OCT) imaging systems have limited in-vivo flow imaging capability because of non-uniform catheter rotation and inadequate A-line scan density. Thus any flow-localisation method that seeks to identify sites of variation within the OCT image data-sets, whether that is in amplitude or phase, produces non-representative correlation (or variance) maps. In this study, both mean and the variation within a set of cross-correlation maps, for static OCT imaging was used to differentiate flow from nonflow regions. Variation was quantified by use of standard deviation. The advantage of this approach is its ability to image flow, even ...

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    12. MR-OCT: Affordable Tomographic Imaging Applications

      MR-OCT: Affordable Tomographic Imaging Applications

      The application of optical coherence tomography (OCT) in the field of biomedical imaging has increased rapidly in recent years and may continue on this trajectory with growth potential in clinical diagnostics. 1 Integration of OCT for affordable point-of-care (POC) diagnostic applications and personal-care monitoring should lead to miniature, inexpensive, portable, robust optical instrumentation that is accurate and simple to use. However, the current embodiments of OCT systems are highly expensive, utilize large-form-factor optical design, and require accurate alignment of complex optics, making them impractical for the POC environment. In recent years, there has been an increasing interest in the development ...

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    13. Dermascope guided multiple reference optical coherence tomography

      Dermascope guided multiple reference optical coherence tomography

      In this paper, we report the feasibility of integrating a novel low cost optical coherence tomography (OCT) system with a dermascope for point-of-care applications. The proposed OCT system is based on an enhanced time-domain optical coherence tomographic system, called multiple reference OCT (MR-OCT), which uses a single miniature voice coil actuator and a partial mirror for extending the axial scan range. The system can simultaneously register both the superficial dermascope image and the depth-resolved OCT sub-surface information by an interactive beam steering method. A practitioner is able to obtain the depth resolved information of the point of interest by simply ...

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    14. High resolution coherence domain depth-resolved nailfold capillaroscopy based on correlation mapping optical coherence tomography

      High resolution coherence domain depth-resolved nailfold capillaroscopy based on correlation mapping optical coherence tomography

      In this paper we demonstrate a novel application of correlation mapping optical coherence tomography (cm-OCT) for volumetric nailfold capillaroscopy (NFC). NFC is a widely used non-invasive diagnostic method to analyze capillary morphology and microvascular abnormalities of nailfold area for a range of disease conditions. However, the conventional NFC is incapable of providing volumetric imaging, when volumetric quantitative microangiopathic parameters such as plexus morphology, capillary density, and morphologic anomalies of the end row loops most critical. cm-OCT is a recently developed well established coherence domain magnitude based angiographic modality, which takes advantage of the time-varying speckle effect, which is normally dominant ...

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    15. High-sensitive full-range optical vibrometry based on Fourier-domain optical coherence tomography

      High-sensitive full-range optical vibrometry based on Fourier-domain optical coherence tomography

      Optical vibrometery based on low coherence Fourier-domain optical coherence tomography (FD-OCT) technique are well capable for providing depth resolved vibration information in comparison with conventional laser based vibrometery. Recently, there has been growing interest in developing coherence-domain vibrometry for various clinical and pre-clinical applications. However, a major drawback of the conventional vibrometer based on Fourier-domain low coherence interferometry is the complex-conjugate ambiguity. This is because in FD-OCT, the detected real valued spectral interferogram is Fourier transformed to localize the scatter within the sample. The Fourier transform of a real valued function is Hermitian, so the reconstructed image is symmetric with ...

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    16. Variation in cross-correlation as a discriminator for microvessel imaging using clinical intravascular optical coherence tomography systems

      Variation in cross-correlation as a discriminator for microvessel imaging using clinical intravascular optical coherence tomography systems

      Cross-correlation of Intravascular Optical Coherence Tomography (IV-OCT) images is affected by image distortion due to the non-uniform rotational velocity of the imaging catheter. It results in non-representative cross-correlation maps such that for a static scan, the coefficients fluctuate from high to low correlation values. The variation in cross-correlation at flow locations is muted, in comparison to stationary regions. In the present study, the variation of correlation values and its standard deviation (SD) is used to suppress the distortion related noise effects and to extract flow maps from static scan images. The standard deviation of the cross-correlation variation can distinguish flow ...

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    17. Nano-sensitive optical coherence tomography (nsOCT) for depth resolved characterization of 3D submicron structure

      Nano-sensitive optical coherence tomography (nsOCT) for depth resolved characterization of 3D submicron structure

      Nowadays optical coherence tomography (OCT) is a rapidly developing technique with various applications, including biomedical imaging and diagnosis. One of the main shortcomings of current OCT techniques is low resolution and sensitivity to structural changes (typically about 10 microns). The best ultra-high resolution OCT techniques demonstrate sensitivity to structural changes and depth resolution of about 1 micron. Since many applications of interest (such as cancer) depend on structural changes at the nanoscale, OCT would definitely benefit from improved structural resolution and sensitivity. A new spectral encoding of spatial frequency (SESF) approach for quantitative characterization of the structure with nanoscale sensitivity ...

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    18. Photothermal optical coherence tomography for depth-resolved imaging of mesenchymal stem cells via single wall carbon nanotube

      Photothermal optical coherence tomography for depth-resolved imaging of mesenchymal stem cells via single wall carbon nanotube

      The progress in stem cell research over the past decade holds promise and potential to address many unmet clinical therapeutic needs. Tracking stem cell with modern imaging modalities are critically needed for optimizing stem cell therapy, which offers insight into various underlying biological processes such as cell migration, engraftment, homing, differentiation, and functions etc. In this study we report the feasibility of photothermal optical coherence tomography (PT-OCT) to image human mesenchymal stem cells (hMSCs) labeled with single-walled carbon nanotubes (SWNTs) for in vitro cell tracking in three dimensional scaffolds. PT-OCT is a functional extension of conventional OCT with extended capability ...

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    19. Dermascope assisted interactive patient interface for multiple reference optical coherence tomography

      Dermascope assisted interactive patient interface for multiple reference optical coherence tomography

      There has been a growing interest in the development of a low cost depth-resolved non-invasive dermis imaging tool for both clinical and fundamental investigations of skin diseases. Multiple reference optical coherence tomography (MR-OCT) is a recently developed miniature time-domain low coherence interferometeric imaging platform, which promises to fit into robust, cost-effective designs that are virtually solid state, typical of handheld devices. In this paper we demonstrate the feasibility of MR-OCT for dermis imaging applications by incorporating it in a dermascope, which provides simultaneous imaging of dermis and an interactive tool for beam steering and registration of the OCT imaging beam ...

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    20. Voice coil based robust and miniature optical delay for multiple reference optical coherence tomography

      Voice coil based robust and miniature optical delay for multiple reference optical coherence tomography

      Multiple reference optical coherence tomography (MR-OCT) is a recently developed time-domain interferometeric imaging platform, which promises to fit into robust, cost-effective designs that are virtually solid state. An optical delay is created by the reference mirror which is mounted on a piezo-electric transducer (PZT) and the key element of MR-OCT technology is the presence of a partial mirror in front of the reference mirror. However, the limited axial displacement range at higher scanning-frequencies are a limitation of a PZT-based optical delay. Moreover, PZT-based actuators require a relatively high operational voltage and are expensive. In this paper we present a voice ...

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    21. Feature Of The Week: High-speed full-range spectral domain correlation mapping optical coherence tomography for in vivo microcirculation imaging applications

      Feature Of The Week: High-speed full-range spectral domain correlation mapping optical coherence tomography for in vivo microcirculation imaging applications

      Microcirculation imaging is a key parameter for studying the pathophysiological processes of various disease conditions, in both clinical and fundamental research. Recently, the functional extension of the OCT technique to image depth-resolved microcirculation has become a very promising area of research. There is a growing interest in the field of development of various types of OCT-based angiographic techniques, which aims to visualize the lumens and architecture of blood vessels in many clinical and fundamental areas of research, including cardiology, dermatology, neurology, ophthalmology, small animal imaging studies, and so forth. OCT-based angiography techniques utilize the red blood cell scattering dynamics as ...

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    22. High-speed full-range spectral-domain correlation mapping optical coherence tomography

      High-speed full-range spectral-domain correlation mapping optical coherence tomography

      We present a full range spectral-domain correlation mapping optical coherence tomography (cm-OCT) method to obtain complex conjugate free, full-range correlation mapping angiography. The mirror image elimination is based on linear phase modulation of B-frames by introducing a slight off-set of the probe beam with respect to the lateral scanning fast mirror’s pivot axis. An algorithm that exploits Hilbert transform to obtain complex-conjugate free image in conjunction with the cm-OCT algorithm is used to obtain full-range imaging of microcirculation within tissue beds in vivo. The proposed system is based on a high speed spectrometer at 92kHz with a modified scanning ...

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    23. In vivo microcirculation imaging of the sub surface fingertip using correlation mapping optical coherence tomography (cmOCT)

      In vivo microcirculation imaging of the sub surface fingertip using correlation mapping optical coherence tomography (cmOCT)

      We describe a novel application of correlation mapping optical coherence tomography (cmOCT) for sub-surface fingerprint biometric identification. Fingerprint biometrics including automated fingerprint identification systems, are commonly used to recognise the fingerprint, since they constitute simple, effective and valuable physical evidence. Spoofing of biometric fingerprint devices can be easily done because of the limited information obtained from the surface topography. In order to overcome this limitation a potentially more secure source of information is required for biometric identification applications. In this study, we retrieve the microcirculation map of the subsurface fingertip by use of the cmOCT technique. To increase probing depth ...

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    24. In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (cmOCT)

      In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (cmOCT)
      Correlation mapping optical coherence tomography (cmOCT) is a recently proposed technique that extends the capabilities of OCT to enable mapping of vasculature networks. The technique is achieved as a processing step on OCT intensity images that does not require any modification to existing OCT hardware. In this paper we apply the cmOCT processing technique to in vivo human imaging of the volar forearm. We illustrate that cmOCT can produce maps of the microcirculation that clearly follow the accepted anatomical structure. We demonstrate that the technique can extract parameters such as capillary density and vessel diameter. These parameters are key clinical ...
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    25. In-vivo dynamic characterization of microneedle skin penetration using optical coherence tomography

      In-vivo dynamic characterization of microneedle skin penetration using optical coherence tomography
      The use of microneedles as a method of circumventing the barrier properties of the stratum corneum is receiving much attention. Although skin disruption technologies and subsequent transdermal diffusion rates are being extensively studied, no accurate data on depth and closure kinetics of microneedle-induced skin pores are available, primarily due to the cumbersome techniques currently required for skin analysis. We report on the first use of optical coherence tomography technology to image microneedle penetration in real time and in vivo. We show that optical coherence tomography (OCT) can be used to painlessly measure stratum corneum and epidermis thickness, as well as ...
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    1-25 of 25
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    1. (25 articles) Martin J. Leahy
    2. (24 articles) National University of Ireland, Galway
    3. (21 articles) Hrebesh M. Subhash
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    5. (4 articles) Compact Imaging, Inc
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    In-vivo dynamic characterization of microneedle skin penetration using optical coherence tomography In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (cmOCT) In vivo microcirculation imaging of the sub surface fingertip using correlation mapping optical coherence tomography (cmOCT) High-speed full-range spectral-domain correlation mapping optical coherence tomography Feature Of The Week: High-speed full-range spectral domain correlation mapping optical coherence tomography for in vivo microcirculation imaging applications Dermascope assisted interactive patient interface for multiple reference optical coherence tomography Nano-sensitive optical coherence tomography (nsOCT) for depth resolved characterization of 3D submicron structure Variation in cross-correlation as a discriminator for microvessel imaging using clinical intravascular optical coherence tomography systems Dermascope guided multiple reference optical coherence tomography 3D nondestructive testing system with an affordable multiple reference optical-delay-based optical coherence tomography Review: Optical Scanning Probe for Optical Coherence Tomography Gastrointestinal Endoscopy Editorial Board top 10 topics: advances in GI endoscopy in 2017