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Leiloglou M, Kedrzycki MS, Chalau V, Chiarini N, Thiruchelvam PTR, Hadjiminas DJ, Hogben KR, Rashid F, Ramakrishnan R, Darzi AW, Leff DR, Elson DS. Indocyanine green fluorescence image processing techniques for breast cancer macroscopic demarcation. Sci Rep 2022; 12:8607. [PMID: 35597783 PMCID: PMC9124184 DOI: 10.1038/s41598-022-12504-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 05/05/2022] [Indexed: 12/13/2022] Open
Abstract
Re-operation due to disease being inadvertently close to the resection margin is a major challenge in breast conserving surgery (BCS). Indocyanine green (ICG) fluorescence imaging could be used to visualize the tumor boundaries and help surgeons resect disease more efficiently. In this work, ICG fluorescence and color images were acquired with a custom-built camera system from 40 patients treated with BCS. Images were acquired from the tumor in-situ, surgical cavity post-excision, freshly excised tumor and histopathology tumour grossing. Fluorescence image intensity and texture were used as individual or combined predictors in both logistic regression (LR) and support vector machine models to predict the tumor extent. ICG fluorescence spectra in formalin-fixed histopathology grossing tumor were acquired and analyzed. Our results showed that ICG remains in the tissue after formalin fixation. Therefore, tissue imaging could be validated in freshly excised and in formalin-fixed grossing tumor. The trained LR model with combined fluorescence intensity (pixel values) and texture (slope of power spectral density curve) identified the tumor's extent in the grossing images with pixel-level resolution and sensitivity, specificity of 0.75 ± 0.3, 0.89 ± 0.2.This model was applied on tumor in-situ and surgical cavity (post-excision) images to predict tumor presence.
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Affiliation(s)
- Maria Leiloglou
- Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK. .,Department of Surgery and Cancer, Imperial College London, London, UK.
| | - Martha S Kedrzycki
- Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK.,Department of Surgery and Cancer, Imperial College London, London, UK.,Department of Breast Surgery, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK
| | - Vadzim Chalau
- Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK.,Department of Surgery and Cancer, Imperial College London, London, UK
| | - Nicolas Chiarini
- Department of Surgery and Cancer, Imperial College London, London, UK
| | - Paul T R Thiruchelvam
- Department of Surgery and Cancer, Imperial College London, London, UK.,Department of Breast Surgery, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK
| | - Dimitri J Hadjiminas
- Department of Breast Surgery, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK
| | - Katy R Hogben
- Department of Breast Surgery, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK
| | - Faiza Rashid
- Department of Histopathology, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK
| | - Rathi Ramakrishnan
- Department of Histopathology, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK
| | - Ara W Darzi
- Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK.,Department of Surgery and Cancer, Imperial College London, London, UK
| | - Daniel R Leff
- Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK.,Department of Surgery and Cancer, Imperial College London, London, UK.,Department of Breast Surgery, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK
| | - Daniel S Elson
- Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK.,Department of Surgery and Cancer, Imperial College London, London, UK
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2
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Rank EA, Agneter A, Schmoll T, Leitgeb RA, Drexler W. Miniaturizing optical coherence tomography. TRANSLATIONAL BIOPHOTONICS 2022. [DOI: 10.1002/tbio.202100007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- Elisabet A. Rank
- Center for Medical Physics and Biomedical Engineering Medical University of Vienna Vienna Austria
| | - Anja Agneter
- Center for Medical Physics and Biomedical Engineering Medical University of Vienna Vienna Austria
| | - Tilman Schmoll
- Center for Medical Physics and Biomedical Engineering Medical University of Vienna Vienna Austria
- Carl Zeiss Meditec, Inc. Dublin California USA
| | - Rainer A. Leitgeb
- Center for Medical Physics and Biomedical Engineering Medical University of Vienna Vienna Austria
| | - Wolfgang Drexler
- Center for Medical Physics and Biomedical Engineering Medical University of Vienna Vienna Austria
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3
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Leitgeb R, Placzek F, Rank E, Krainz L, Haindl R, Li Q, Liu M, Andreana M, Unterhuber A, Schmoll T, Drexler W. Enhanced medical diagnosis for dOCTors: a perspective of optical coherence tomography. JOURNAL OF BIOMEDICAL OPTICS 2021; 26:JBO-210150-PER. [PMID: 34672145 PMCID: PMC8528212 DOI: 10.1117/1.jbo.26.10.100601] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 09/23/2021] [Indexed: 05/17/2023]
Abstract
SIGNIFICANCE After three decades, more than 75,000 publications, tens of companies being involved in its commercialization, and a global market perspective of about USD 1.5 billion in 2023, optical coherence tomography (OCT) has become one of the fastest successfully translated imaging techniques with substantial clinical and economic impacts and acceptance. AIM Our perspective focuses on disruptive forward-looking innovations and key technologies to further boost OCT performance and therefore enable significantly enhanced medical diagnosis. APPROACH A comprehensive review of state-of-the-art accomplishments in OCT has been performed. RESULTS The most disruptive future OCT innovations include imaging resolution and speed (single-beam raster scanning versus parallelization) improvement, new implementations for dual modality or even multimodality systems, and using endogenous or exogenous contrast in these hybrid OCT systems targeting molecular and metabolic imaging. Aside from OCT angiography, no other functional or contrast enhancing OCT extension has accomplished comparable clinical and commercial impacts. Some more recently developed extensions, e.g., optical coherence elastography, dynamic contrast OCT, optoretinography, and artificial intelligence enhanced OCT are also considered with high potential for the future. In addition, OCT miniaturization for portable, compact, handheld, and/or cost-effective capsule-based OCT applications, home-OCT, and self-OCT systems based on micro-optic assemblies or photonic integrated circuits will revolutionize new applications and availability in the near future. Finally, clinical translation of OCT including medical device regulatory challenges will continue to be absolutely essential. CONCLUSIONS With its exquisite non-invasive, micrometer resolution depth sectioning capability, OCT has especially revolutionized ophthalmic diagnosis and hence is the fastest adopted imaging technology in the history of ophthalmology. Nonetheless, OCT has not been completely exploited and has substantial growth potential-in academics as well as in industry. This applies not only to the ophthalmic application field, but also especially to the original motivation of OCT to enable optical biopsy, i.e., the in situ imaging of tissue microstructure with a resolution approaching that of histology but without the need for tissue excision.
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Affiliation(s)
- Rainer Leitgeb
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
- Medical University of Vienna, Christian Doppler Laboratory OPTRAMED, Vienna, Austria
| | - Fabian Placzek
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Elisabet Rank
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Lisa Krainz
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Richard Haindl
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Qian Li
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Mengyang Liu
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Marco Andreana
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Angelika Unterhuber
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Tilman Schmoll
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
- Carl Zeiss Meditec, Inc., Dublin, California, United States
| | - Wolfgang Drexler
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
- Address all correspondence to Wolfgang Drexler,
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4
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Song G, Jelly ET, Chu KK, Kendall WY, Wax A. A review of low-cost and portable optical coherence tomography. PROGRESS IN BIOMEDICAL ENGINEERING (BRISTOL, ENGLAND) 2021; 3:032002. [PMID: 37645660 PMCID: PMC10465117 DOI: 10.1088/2516-1091/abfeb7] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
Optical coherence tomography (OCT) is a powerful optical imaging technique capable of visualizing the internal structure of biological tissues at near cellular resolution. For years, OCT has been regarded as the standard of care in ophthalmology, acting as an invaluable tool for the assessment of retinal pathology. However, the costly nature of most current commercial OCT systems has limited its general accessibility, especially in low-resource environments. It is therefore timely to review the development of low-cost OCT systems as a route for applying this technology to population-scale disease screening. Low-cost, portable and easy to use OCT systems will be essential to facilitate widespread use at point of care settings while ensuring that they offer the necessary imaging performances needed for clinical detection of retinal pathology. The development of low-cost OCT also offers the potential to enable application in fields outside ophthalmology by lowering the barrier to entry. In this paper, we review the current development and applications of low-cost, portable and handheld OCT in both translational and research settings. Design and cost-reduction techniques are described for general low-cost OCT systems, including considerations regarding spectrometer-based detection, scanning optics, system control, signal processing, and the role of 3D printing technology. Lastly, a review of clinical applications enabled by low-cost OCT is presented, along with a detailed discussion of current limitations and outlook.
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Affiliation(s)
- Ge Song
- Author to whom any correspondence should be addressed.
| | | | - Kengyeh K Chu
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, United States of America
| | - Wesley Y Kendall
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, United States of America
| | - Adam Wax
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, United States of America
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5
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Rank EA, Sentosa R, Harper DJ, Salas M, Gaugutz A, Seyringer D, Nevlacsil S, Maese-Novo A, Eggeling M, Muellner P, Hainberger R, Sagmeister M, Kraft J, Leitgeb RA, Drexler W. Toward optical coherence tomography on a chip: in vivo three-dimensional human retinal imaging using photonic integrated circuit-based arrayed waveguide gratings. LIGHT, SCIENCE & APPLICATIONS 2021; 10:6. [PMID: 33402664 PMCID: PMC7785745 DOI: 10.1038/s41377-020-00450-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 11/14/2020] [Accepted: 12/03/2020] [Indexed: 05/19/2023]
Abstract
In this work, we present a significant step toward in vivo ophthalmic optical coherence tomography and angiography on a photonic integrated chip. The diffraction gratings used in spectral-domain optical coherence tomography can be replaced by photonic integrated circuits comprising an arrayed waveguide grating. Two arrayed waveguide grating designs with 256 channels were tested, which enabled the first chip-based optical coherence tomography and angiography in vivo three-dimensional human retinal measurements. Design 1 supports a bandwidth of 22 nm, with which a sensitivity of up to 91 dB (830 µW) and an axial resolution of 10.7 µm was measured. Design 2 supports a bandwidth of 48 nm, with which a sensitivity of 90 dB (480 µW) and an axial resolution of 6.5 µm was measured. The silicon nitride-based integrated optical waveguides were fabricated with a fully CMOS-compatible process, which allows their monolithic co-integration on top of an optoelectronic silicon chip. As a benchmark for chip-based optical coherence tomography, tomograms generated by a commercially available clinical spectral-domain optical coherence tomography system were compared to those acquired with on-chip gratings. The similarities in the tomograms demonstrate the significant clinical potential for further integration of optical coherence tomography on a chip system.
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Affiliation(s)
- Elisabet A Rank
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4 L, 1090, Vienna, Austria.
| | - Ryan Sentosa
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4 L, 1090, Vienna, Austria
| | - Danielle J Harper
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4 L, 1090, Vienna, Austria
| | - Matthias Salas
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4 L, 1090, Vienna, Austria
| | - Anna Gaugutz
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4 L, 1090, Vienna, Austria
| | - Dana Seyringer
- Research Centre for Microtechnology, Vorarlberg University of Applied Sciences, Hochschulstrasse 1, 6850, Dornbirn, Austria
| | - Stefan Nevlacsil
- AIT Austrian Institute of Technology GmbH, Gieffinggasse 4, 1210, Vienna, Austria
| | - Alejandro Maese-Novo
- AIT Austrian Institute of Technology GmbH, Gieffinggasse 4, 1210, Vienna, Austria
| | - Moritz Eggeling
- AIT Austrian Institute of Technology GmbH, Gieffinggasse 4, 1210, Vienna, Austria
| | - Paul Muellner
- AIT Austrian Institute of Technology GmbH, Gieffinggasse 4, 1210, Vienna, Austria
| | - Rainer Hainberger
- AIT Austrian Institute of Technology GmbH, Gieffinggasse 4, 1210, Vienna, Austria
| | | | - Jochen Kraft
- ams AG, Tobelbader Strasse 30, 8141, Premstaetten, Austria
| | - Rainer A Leitgeb
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4 L, 1090, Vienna, Austria
| | - Wolfgang Drexler
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4 L, 1090, Vienna, Austria
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6
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Chopra R, Wagner SK, Keane PA. Optical coherence tomography in the 2020s-outside the eye clinic. Eye (Lond) 2020; 35:236-243. [PMID: 33168975 DOI: 10.1038/s41433-020-01263-6] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 10/20/2020] [Accepted: 10/27/2020] [Indexed: 11/09/2022] Open
Abstract
Optical coherence tomography (OCT) is a paragon of success in the translation of biophotonics science to clinical practice. OCT systems have become ubiquitous in eye clinics but access beyond this is limited by their cost, size and the skill required to operate the devices. Remarkable progress has been made in the development of OCT technology to improve the speed of acquisition, the quality of images and into functional extensions of OCT such as OCT angiography. However, more needs to be done to radically improve the access to OCT by addressing its limitations and enable penetration outside of typical clinical settings and into underserved populations. Beyond high-income countries, there are 6.5 billion people with similar eye-care needs, which cannot be met by the current generation of bulky, expensive and complex OCT systems. In addition, advancing the portability of this technology to address opportunities in point-of-care diagnostics, telemedicine and remote monitoring may aid development of personalised medicine. In this review, we discuss the major milestones in OCT hardware development to reach those beyond the eye clinic.
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Affiliation(s)
- Reena Chopra
- NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
| | - Siegfried K Wagner
- NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
| | - Pearse A Keane
- NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.
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7
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Pham QD, Hayasaki Y. Low-coherence digital holography with a multireflection reference mirror. OPTICS LETTERS 2020; 45:4393-4396. [PMID: 32796966 DOI: 10.1364/ol.397475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 07/13/2020] [Indexed: 06/11/2023]
Abstract
A method for expanding the measurement range of low-coherence digital holography up to several times longer than the coherence length is proposed. The method was implemented with a multireflection reference mirror composed of partially and highly reflective mirrors, in conjunction with the Fourier transform method with spatial filtering for single-shot complex amplitude imaging, making it useful for observing a moving and deforming object. One of the features of the reference arm is that the measurement range is simply controlled by adjusting the position and angle of the highly reflective mirror. The measurement of objects with a general curved shape and a large step height was demonstrated.
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8
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Fitzgerald BW. The physiology of impenetrable skin: Colossus of the X-Men. ADVANCES IN PHYSIOLOGY EDUCATION 2018; 42:529-540. [PMID: 30192188 DOI: 10.1152/advan.00107.2018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The X-Men are an ensemble of superheroes whose powers are associated with the X-Gene, a mutant genetic factor. The powers exhibited by each character differ and are dependent on how the X-Gene has modified their individual genomes. For instance, Wolverine possesses regenerative healing, Storm can control local weather systems, and Colossus can create an impenetrable "organic steel" layer around his body. Thanks to the establishment of the superhero genre in modern cinema, audiences are familiar with Colossus from films such as X-Men: Days of Future Past and Deadpool. While attaining this power might be attractive to many people, there are innumerate scientific obstacles to be overcome to replicate this "organic steel" layer. Due to its unique combination of high strength and flexibility, a graphene-based layer might be a more realistic material for Colossus' impenetrable skin and would also address a number of physiological issues associated with an "organic steel" layer. The actualization of this layer would depend on complex processes associated with protein folding, protein self-assembly, and changing the structure of his skin. In the classroom, Colossus can foster a multidisciplinary learning environment where concepts in physiology can overlap with topics in physics, engineering, and materials science. Just like other superheroes, Colossus can also be used to promote scientific content in outreach for the general public.
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Affiliation(s)
- Barry W Fitzgerald
- Intensified Reaction and Separation Systems, Department of Process and Energy, Delft University of Technology , Delft , The Netherlands
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Dsouza R, Won J, Monroy GL, Spillman DR, Boppart SA. Economical and compact briefcase spectral-domain optical coherence tomography system for primary care and point-of-care applications. JOURNAL OF BIOMEDICAL OPTICS 2018; 23:1-11. [PMID: 30251484 PMCID: PMC6170142 DOI: 10.1117/1.jbo.23.9.096003] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 08/29/2018] [Indexed: 05/28/2023]
Abstract
Development of low-cost and portable optical coherence tomography (OCT) systems is of global interest in the OCT research community. Such systems enable utility broadly throughout a clinical facility, or in remote areas that often lack clinical infrastructure. We report the development and validation of a low-cost, portable briefcase spectral-domain optical coherence tomography (SD-OCT) system for point-of-care diagnostics in primary care centers and/or in remote settings. The self-contained briefcase OCT contains all associated optical hardware, including light source, spectrometer, hand-held probe, and a laptop. Additionally, this system utilizes unique real-time mosaicking of surface video images that are synchronized with rapid A-scan acquisition to eliminate the need for lateral scanning hardware, and enable the construction of cross-sectional B-mode images over extended lateral distances. The entire briefcase system weighs 9 kg and costs ∼USD$8000 using off-the-shelf components. System performance was validated by acquiring images of in vivo human skin on the fingertip, palm, and nail fold. The efficiency, portability, and low-cost enable accessibility and utility in primary care centers and low-resource settings.
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Affiliation(s)
- Roshan Dsouza
- University of Illinois at Urbana-Champaign, Beckman Institute for Advanced Science and Technology, Urbana, Illinois, United States
| | - Jungeun Won
- University of Illinois at Urbana-Champaign, Beckman Institute for Advanced Science and Technology, Urbana, Illinois, United States
- University of Illinois at Urbana-Champaign, Department of Bioengineering, Urbana, Illinois, United States
| | - Guillermo L. Monroy
- University of Illinois at Urbana-Champaign, Beckman Institute for Advanced Science and Technology, Urbana, Illinois, United States
- University of Illinois at Urbana-Champaign, Department of Bioengineering, Urbana, Illinois, United States
| | - Darold R. Spillman
- University of Illinois at Urbana-Champaign, Beckman Institute for Advanced Science and Technology, Urbana, Illinois, United States
| | - Stephen A. Boppart
- University of Illinois at Urbana-Champaign, Beckman Institute for Advanced Science and Technology, Urbana, Illinois, United States
- University of Illinois at Urbana-Champaign, Department of Bioengineering, Urbana, Illinois, United States
- University of Illinois at Urbana-Champaign, Department of Electrical and Computer Engineering, Urbana, Illinois, United States
- University of Illinois at Urbana-Champaign, Carle-Illinois College of Medicine, Urbana, Illinois, United States
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10
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O'Gorman S, Neuhaus K, Alexandrov S, Hogan J, Wilson C, McNamara P, Leahy M. Characterization of an amplified piezoelectric actuator for multiple-reference optical coherence tomography. APPLIED OPTICS 2018; 57:E142-E146. [PMID: 30117912 DOI: 10.1364/ao.57.00e142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Accepted: 05/29/2018] [Indexed: 06/08/2023]
Abstract
The characterization of an amplified piezoelectric actuator (APA) as a new axial scanning method for multiple-reference optical coherence tomography (MR-OCT) is described. MR-OCT is a compact optical imaging device based on a recirculating reference-arm-scanning optical delay using a partial mirror that can enhance the imaging depth range by more than 10 times the reference mirror's scanning amplitude. The scanning amplitude of the used APA was varied between 30 μm and 250 μm, depending on the scanning frequency of between 0.8 kHz and 1.2 kHz. A silver-coated miniature mirror was attached to the APA via ultraviolet-cured optical adhesive, and the light source was a super-luminescent diode with 1310 nm center wavelength and 56 nm bandwidth. The sensitivity was measured with and without the partial mirror in the reference delay line as a function of scan speed, frequency, and range, therefore providing results for MR-OCT and TD-OCT modes. It was found that the APA provides more than twice the mechanical scanning range compared to other opto-mechanic actuators, but results indicate degradation of signal-to-noise ratio and sensitivity at larger imaging depths. In conjunction with MR-OCT, the scan range of maximum 200 μm can be enhanced up to 1-1.5 mm by using a reduced amount of orders of reflections, which could be of interest to increase sensitivity in the future.
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