1
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Struyvenberg M, Kahn A, Fleischer D, Swager AF, Bouma B, Ganguly EK, Konda V, Lightdale CJ, Pleskow D, Sethi A, Smith M, Trindade AJ, Wallace MB, Wang K, Wolfsen HC, Tearney GJ, Curvers WL, Leggett CL, Bergman JJ. Expert assessment on volumetric laser endomicroscopy full scans in Barrett's esophagus patients with or without high grade dysplasia or early cancer. Endoscopy 2021; 53:218-225. [PMID: 32515006 DOI: 10.1055/a-1194-0397] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
BACKGROUND Volumetric laser endomicroscopy (VLE) allows for near-microscopic imaging of the superficial esophageal wall and may improve detection of early neoplasia in Barrett's esophagus (BE). Interpretation of a 6-cm long, circumferential VLE "full scan" may however be challenging for endoscopists. We aimed to evaluate the accuracy of VLE experts in correctly diagnosing VLE full scans of early neoplasia and non-dysplastic BE (NDBE). METHODS 29 VLE full scan videos (15 neoplastic and 14 NDBE) were randomly evaluated by 12 VLE experts using a web-based module. Experts were blinded to the endoscopic BE images and histology. The 15 neoplastic cases contained a subtle endoscopically visible lesion, which on endoscopic resection showed high grade dysplasia or cancer. NDBE cases had no visible lesions and an absence of dysplasia in all biopsies. VLE videos were first scored as "neoplastic" or "NDBE." If neoplastic, assessors located the area most suspicious for neoplasia. Primary outcome was the performance of VLE experts in differentiating between non-dysplastic and neoplastic full scan videos, calculated by accuracy, sensitivity, and specificity. Secondary outcomes included correct location of neoplasia, interobserver agreement, and level of confidence. RESULTS VLE experts correctly labelled 73 % (95 % confidence interval [CI] 67 % - 79 %) of neoplastic VLE videos. In 54 % (range 27 % - 66 %) both neoplastic diagnosis and lesion location were correct. NDBE videos were consistent with endoscopic biopsies in 52 % (95 %CI 46 % - 57 %). Interobserver agreement was fair (kappa 0.28). High level of confidence was associated with a higher rate of correct neoplastic diagnosis (81 %) and lesion location (73 %). CONCLUSIONS Identification of subtle neoplastic lesions in VLE full scans by experts was disappointing. Future studies should focus on improving methodologies for reviewing full scans, development of refined VLE criteria for neoplasia, and computer-aided diagnosis of VLE scans.
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Affiliation(s)
- Maarten Struyvenberg
- Department of Gastroenterology and Hepatology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
| | - Allon Kahn
- Division of Gastroenterology and Hepatology, Mayo Clinic, Scottsdale, Arizona, USA
| | - David Fleischer
- Division of Gastroenterology and Hepatology, Mayo Clinic, Scottsdale, Arizona, USA
| | - Anne-Fre Swager
- Department of Gastroenterology and Hepatology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
| | - Brett Bouma
- Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Eric K Ganguly
- Department of Gastroenterology and Hepatology, University of Vermont Medical Center, Burlington, Vermont, USA
| | - Vani Konda
- Department of Gastroenterology and Hepatology, Baylor Scott & White Quality Alliance in Dallas, Texas, USA
| | - Charles J Lightdale
- Division of Gastroenterology and Hepatology, New York-Presbyterian Hospital, New York, New York, USA
| | - Douglas Pleskow
- Department of Gastroenterology and Hepatology, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
| | - Amrita Sethi
- Department of Gastroenterology and Hepatology, Columbia University Medical Center, New York, New York, USA
| | - Michael Smith
- Division of Gastroenterology and Hepatology, The Mount Sinai Hospital, New York, New York, USA
| | - Arvind J Trindade
- Division of Gastroenterology and Hepatology, Long Island Jewish Medical Center, New Hyde Park, New York, USA
| | - Michael B Wallace
- Division of Gastroenterology and Hepatology, Mayo Clinic, Jacksonville, Florida, USA
| | - Kenneth Wang
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota, USA
| | - Herbert C Wolfsen
- Division of Gastroenterology and Hepatology, Mayo Clinic, Jacksonville, Florida, USA
| | - G J Tearney
- Department of Pathology, Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Wouter L Curvers
- Department of Gastroenterology and Hepatology, Catharina Hospital, Eindhoven, The Netherlands
| | - Cadman L Leggett
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota, USA
| | - Jacques J Bergman
- Department of Gastroenterology and Hepatology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
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2
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Struyvenberg MR, de Groof AJ, Kahn A, Weusten BLAM, Fleischer DE, Ganguly EK, Konda VJA, Lightdale CJ, Pleskow DK, Sethi A, Smith MS, Trindade AJ, Wallace MB, Wolfsen HC, Tearney GJ, Meijer SL, Leggett CL, Bergman JJGHM, Curvers WL. Multicenter study on the diagnostic performance of multiframe volumetric laser endomicroscopy targets for Barrett's esophagus neoplasia with histopathology correlation. Dis Esophagus 2020; 33:5860590. [PMID: 32607539 PMCID: PMC7720006 DOI: 10.1093/dote/doaa062] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 05/27/2020] [Accepted: 06/01/2020] [Indexed: 12/11/2022]
Abstract
Volumetric laser endomicroscopy (VLE) has been shown to improve detection of early neoplasia in Barrett's esophagus (BE). However, diagnostic performance using histopathology-correlated VLE regions of interest (ROIs) has not been adequately studied. We evaluated the diagnostic accuracy of VLE assessors for identification of early BE neoplasia in histopathology-correlated VLE ROIs. In total, 191 ROIs (120 nondysplastic and 71 neoplastic) from 50 BE patients were evaluated in a random order using a web-based module. All ROIs contained histopathology correlations enabled by VLE laser marking. Assessors were blinded to endoscopic BE images and histology. ROIs were first scored as nondysplastic or neoplastic. Level of confidence was assigned to the predicted diagnosis. Outcome measures were: (i) diagnostic performance of VLE assessors for identification of BE neoplasia in all VLE ROIs, defined as accuracy, sensitivity, and specificity; (ii) diagnostic performance of VLE assessors for only high level of confidence predictions; and (iii) interobserver agreement. Accuracy, sensitivity, and specificity for BE neoplasia identification were 79% (confidence interval [CI], 75-83), 75% (CI, 71-79), and 81% (CI, 76-86), respectively. When neoplasia was identified with a high level of confidence, accuracy, sensitivity, and specificity were 88%, 83%, and 90%, respectively. The overall strength of interobserver agreement was fair (k = 0.29). VLE assessors can identify BE neoplasia with reasonable diagnostic accuracy in histopathology-correlated VLE ROIs, and accuracy is enhanced when BE neoplasia is identified with high level of confidence. Future work should focus on renewed VLE image reviewing criteria and real-time automatic assessment of VLE scans.
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Affiliation(s)
- M R Struyvenberg
- Department of Gastroenterology and Hepatology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
| | - A J de Groof
- Department of Gastroenterology and Hepatology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
| | - A Kahn
- Division of Gastroenterology and Hepatology, Mayo Clinic, Scottsdale, AZ, USA
| | - B L A M Weusten
- Department of Gastroenterology and Hepatology, St. Antonius Hospital, Nieuwegein, The Netherlands
| | - D E Fleischer
- Division of Gastroenterology and Hepatology, Mayo Clinic, Scottsdale, AZ, USA
| | - E K Ganguly
- Department of Gastroenterology and Hepatology, University of Vermont Medical Center, Burlington, VT, USA
| | - V J A Konda
- Department of Gastroenterology and Hepatology, Baylor University Medical Center, Dallas, TX, USA
| | - C J Lightdale
- Division of Gastroenterology and Hepatology, New York-Presbyterian Hospital, New York, NY, USA
| | - D K Pleskow
- Department of Gastroenterology and Hepatology, Beth Israel Deaconess Medical Center, Boston, MA, USA
| | - A Sethi
- Department of Gastroenterology and Hepatology, Columbia University Medical Center, New York, NY, USA
| | - M S Smith
- Division of Gastroenterology and Hepatology, Mount Sinai West and Mount Sinai St. Luke’s Hospitals, New York, NY, USA
| | - A J Trindade
- Division of Gastroenterology and Hepatology, Zucker School of Medicine at Hofstra/Northwell, Long Island Jewish Medical Center, New York, NY, USA
| | - M B Wallace
- Division of Gastroenterology and Hepatology, Mayo Clinic, Jacksonville, NY, USA
| | - H C Wolfsen
- Division of Gastroenterology and Hepatology, Mayo Clinic, Jacksonville, NY, USA
| | - G J Tearney
- Department of Pathology, Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA
| | - S L Meijer
- Department of Pathology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
| | - C L Leggett
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN, USA
| | - J J G H M Bergman
- Department of Gastroenterology and Hepatology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands,Address correspondence to: Professor Dr J.J.G.H.M. Bergman, Department of Gastroenterology and Hepatology, Amsterdam UMC, location AMC, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
| | - W L Curvers
- Department of Gastroenterology and Hepatology, Catharina Hospital, Eindhoven, The Netherlands
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3
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Levink IJM, Wolfsen HC, Siersema PD, Wallace MB, Tearney GJ. Measuring Barrett's Epithelial Thickness with Volumetric Laser Endomicroscopy as a Biomarker to Guide Treatment. Dig Dis Sci 2019; 64:1579-1587. [PMID: 30632054 PMCID: PMC6522645 DOI: 10.1007/s10620-018-5453-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Accepted: 12/31/2018] [Indexed: 01/10/2023]
Abstract
BACKGROUND Radiofrequency ablation (RFA) treatment outcomes vary for unknown reasons. One hypothesis is that variations in Barrett's epithelial thickness (BET) are associated with reduced RFA efficacy for thicker BET and strictures for thinner BET. Volumetric laser endomicroscopy (VLE) is an imaging modality that acquires high-resolution, depth-resolved images of BE. However, the attenuation of light by tissue and the lack of layering in Barrett's tissue challenge BET measurements and the study of relationships between thickness and RFA outcomes. We aimed to quantify BET and compared the reliability of standard and contrast-enhanced VLE images. METHODS Baseline VLE scans from BE patients without prior ablative therapy and a Prague (M) length of > 1 cm were obtained from the US VLE Registry. An algorithm was applied to the VLE images to flatten the mucosal surface and enhance the contrast of different esophageal wall layers. Subsequently, BET was measured by two independent VLE readers using both contrast- and non-contrast-enhanced datasets. In order to validate these adjusted images, intra- and interobserver agreements were calculated. RESULTS VLE scans from fifty-seven patients were included in this study. BET was measured at eight equidistant locations on the selected cross-sectional images at 0.5 cm intervals from the GEJ to the proximal-most extent of BE. The intra-observer coefficients of the two readers for the contrast-enhanced images were 0.818 (95% CI 0.798-0.836) and 0.890 (95% CI 0.878-0.900). The interobserver agreement for the contrast-enhanced images (0.880; 95% CI 0.867-0.891) was significantly better than for the original images (0.778; 95% CI 0.754-0.799). CONCLUSION We developed an algorithm that improves VLE visualization of the mucosal layers of the esophageal wall and enables rapid and reliable measurement of BET. Interobserver variability measurements were significantly reduced when using contrast enhancement. Studies are underway to correlate BET with treatment response.
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Affiliation(s)
- I. J. M. Levink
- 0000 0004 0443 9942grid.417467.7Division of Gastroenterology and Hepatology, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224 USA ,0000 0004 0444 9382grid.10417.33Division of Gastroenterology and Hepatology, Radboud University Medical Center, Geert Grooteplein Noord 10, 6525 GA Nijmegen, The Netherlands ,000000040459992Xgrid.5645.2Department of Gastroenterology and Hepatology, Erasmus University Medical Center, Doctor Molewaterplein 40, 3015 GD Rotterdam, The Netherlands
| | - H. C. Wolfsen
- 0000 0004 0443 9942grid.417467.7Division of Gastroenterology and Hepatology, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224 USA
| | - P. D. Siersema
- 0000 0004 0444 9382grid.10417.33Division of Gastroenterology and Hepatology, Radboud University Medical Center, Geert Grooteplein Noord 10, 6525 GA Nijmegen, The Netherlands
| | - M. B. Wallace
- 0000 0004 0443 9942grid.417467.7Division of Gastroenterology and Hepatology, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224 USA
| | - G. J. Tearney
- 0000 0004 0386 9924grid.32224.35Department of Pathology & Wellman Center for Photomedicine, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114 USA
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4
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Nishimiya K, Sharma G, Singh K, Osman H, Gardecki JA, Tearney GJ. P2772A novel approach for uric acid crystal detection in human coronary arteries with polarization-sensitive micro-OCT. Eur Heart J 2018. [DOI: 10.1093/eurheartj/ehy565.p2772] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- K Nishimiya
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - G Sharma
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - K Singh
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - H Osman
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - J A Gardecki
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - G J Tearney
- Massachusetts General Hospital, Wellman Center for Photomedicine, Department of Pathology, Boston, United States of America
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5
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Nishimiya K, Yin B, Piao Z, Osman H, Ryu J, Leung HM, Sharma G, Gardecki JA, Tearney GJ. P2271Super high-resolution OCT for endothelial cell visualization in the coronary arteries. Eur Heart J 2018. [DOI: 10.1093/eurheartj/ehy565.p2271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- K Nishimiya
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - B Yin
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - Z Piao
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - H Osman
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - J Ryu
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - H M Leung
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - G Sharma
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - J A Gardecki
- Massachusetts General Hospital, Wellman Center for Photomedicine, Boston, United States of America
| | - G J Tearney
- Massachusetts General Hospital, Wellman Center for Photomedicine, Department of Pathology, Boston, United States of America
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6
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Kang DK, Suter MJ, Boudoux C, Yachimski PS, Puricelli WP, Nishioka NS, Mino-Kenudson M, Lauwers GY, Bouma BE, Tearney GJ. Co-registered spectrally encoded confocal microscopy and optical frequency domain imaging system. J Microsc 2010; 239:87-91. [PMID: 20629914 DOI: 10.1111/j.1365-2818.2010.03367.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Spectrally encoded confocal microscopy and optical frequency domain imaging are two non-contact optical imaging technologies that provide images of tissue cellular and architectural morphology, which are both used for histopathological diagnosis. Although spectrally encoded confocal microscopy has better transverse resolution than optical frequency domain imaging, optical frequency domain imaging can penetrate deeper into tissues, which potentially enables the visualization of different morphologic features. We have developed a co-registered spectrally encoded confocal microscopy and optical frequency domain imaging system and have obtained preliminary images from human oesophageal biopsy samples to compare the capabilities of these imaging techniques for diagnosing oesophageal pathology.
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Affiliation(s)
- D K Kang
- Wellman Center for Photomedicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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7
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Ha JY, Shishkov M, Colice M, Oh WY, Yoo H, Liu L, Tearney GJ, Bouma BE. Compensation of motion artifacts in catheter-based optical frequency domain imaging. Opt Express 2010; 18:11418-27. [PMID: 20589002 PMCID: PMC3003228 DOI: 10.1364/oe.18.011418] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
A novel heterodyne Doppler interferometer method for compensating motion artifacts caused by cardiac motion in intracoronary optical frequency domain imaging (OFDI) is demonstrated. To track the relative motion of a catheter with regard to the vessel, a motion tracking system is incorporated with a standard OFDI system by using wavelength division multiplexing (WDM) techniques. Without affecting the imaging beam, dual WDM monochromatic beams are utilized for tracking the relative radial and longitudinal velocities of a catheter-based fiber probe. Our results demonstrate that tracking instantaneous velocity can be used to compensate for distortion in the images due to motion artifacts, thus leading to accurate reconstruction and volumetric measurements with catheter-based imaging.
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8
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Motaghian Nezam SMR, Joo C, Tearney GJ, de Boer JF. Application of maximum likelihood estimator in nano-scale optical path length measurement using spectral-domain optical coherence phase microscopy. Opt Express 2008; 16:17186-17195. [PMID: 18957999 PMCID: PMC2754191 DOI: 10.1364/oe.16.17186] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Spectral-domain optical coherence phase microscopy (SD-OCPM) measures minute phase changes in transparent biological specimens using a common path interferometer and a spectrometer based optical coherence tomography system. The Fourier transform of the acquired interference spectrum in spectral-domain optical coherence tomography (SD-OCT) is complex and the phase is affected by contributions from inherent random noise. To reduce this phase noise, knowledge of the probability density function (PDF) of data becomes essential. In the present work, the intensity and phase PDFs of the complex interference signal are theoretically derived and the optical path length (OPL) PDF is experimentally validated. The full knowledge of the PDFs is exploited for optimal estimation (Maximum Likelihood estimation) of the intensity, phase, and signal-to-noise ratio (SNR) in SD-OCPM. Maximum likelihood (ML) estimates of the intensity, SNR, and OPL images are presented for two different scan modes using Bovine Pulmonary Artery Endothelial (BPAE) cells. To investigate the phase accuracy of SD-OCPM, we experimentally calculate and compare the cumulative distribution functions (CDFs) of the OPL standard deviation and the square root of the Cramér-Rao lower bound (1/ square root 2SNR ) over 100 BPAE images for two different scan modes. The correction to the OPL measurement by applying ML estimation to SD-OCPM for BPAE cells is demonstrated.
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Affiliation(s)
- S M R Motaghian Nezam
- Harvard Medical School and the Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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9
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Abstract
The capability to image tissue motion such as blood flow through an endoscope could have many applications in medicine. Spectrally encoded endoscopy (SEE) is a recently introduced technique that utilizes a single optical fiber and miniature diffractive optics to obtain endoscopic images through small diameter probes. Using spectral-domain interferometry, SEE is furthermore capable of three-dimensional volume imaging at video rates. Here we show that by measuring relative spectral phases, this technology can additionally measure Doppler shifts. Doppler SEE is demonstrated in flowing Intralipid phantoms and vibrating middle ear ossicles.
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Affiliation(s)
- Dvir Yelin
- Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel.
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10
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Oh WY, Vakoc BJ, Yun SH, Tearney GJ, Bouma BE. Single-detector polarization-sensitive optical frequency domain imaging using high-speed intra A-line polarization modulation. Opt Lett 2008; 33:1330-2. [PMID: 18552948 PMCID: PMC2697108 DOI: 10.1364/ol.33.001330] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We demonstrate a novel high-speed polarization-sensitive optical frequency domain imaging system employing high-speed polarization modulation. Rapid and continuous polarization modulation of light prior to illumination of the sample is accomplished by shifting the frequency of one polarization eigenstate by an amount equal to one quarter of the digitization sampling frequency. This approach enables polarization-sensitive imaging with a single detection channel and overcomes artifacts that may arise from temporal variations of the birefringence in fiber-optic imaging probes and spatial variation of birefringence in the sample.
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Affiliation(s)
- W Y Oh
- Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA 02114, USA.
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11
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Abstract
Endoscopic imaging below tissue surfaces and through turbid media may provide improved diagnostic capabilities and visibility in surgical settings. Spectrally encoded endoscopy (SEE) is a recently developed method that utilizes a single optical fiber, miniature optics and a diffractive grating for high-speed imaging through small diameter, flexible endoscopic probes. SEE has also been shown to provide three-dimensional topological imaging capabilities. In this paper, we have configured SEE to additionally image beneath tissue surfaces, by increasing the system's sensitivity and acquiring the complex spectral density for each spectrally resolved point on the sample. In order to demonstrate the capability of SEE to obtain subsurface information, we have utilized the system to image a resolution target through intralipid solution, and conduct volumetric imaging of a mouse embryo and excised human middle-ear ossicles. Our results demonstrate that real-time subsurface imaging is possible with this miniature endoscopy technique.
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Affiliation(s)
- D Yelin
- Department of Biomedical Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel.
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12
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Oh WY, Yun SH, Vakoc BJ, Shishkov M, Desjardins AE, Park BH, de Boer JF, Tearney GJ, Bouma BE. High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing. Opt Express 2008; 16:1096-103. [PMID: 18542183 PMCID: PMC2752304 DOI: 10.1364/oe.16.001096] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm.
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Affiliation(s)
- W Y Oh
- Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR 704, Boston, Massachusetts 02114, USA.
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13
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Motaghian Nezam SMR, Vakoc BJ, Desjardins AE, Tearney GJ, Bouma BE. Increased ranging depth in optical frequency domain imaging by frequency encoding. Opt Lett 2007; 32:2768-70. [PMID: 17909567 PMCID: PMC2703590 DOI: 10.1364/ol.32.002768] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
A technique for increasing the ranging depth in optical frequency domain imaging utilizing frequency encoding is presented. Ranging depth is enhanced by using two interferometer reference arms with different path lengths and independent modulation frequencies (25 and 50 MHz). With this configuration, the sensitivity decreases by 6 dB over a depth range of 7 mm, approximately a threefold improvement over the conventional optical frequency domain imaging technique. We demonstrate that the reference arm frequency separation, tuning speed, center wavelength, and instantaneous coherence length determine the signal-to-cross-talk ratio.
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14
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Desjardins AE, Vakoc BJ, Bilenca A, Tearney GJ, Bouma BE. Estimation of the scattering coefficients of turbid media using angle-resolved optical frequency-domain imaging. Opt Lett 2007; 32:1560-2. [PMID: 17546188 PMCID: PMC2713055 DOI: 10.1364/ol.32.001560] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Noninvasive measurements of the scattering coefficients of optically turbid media using angle-resolved optical frequency-domain imaging (OFDI) are demonstrated. It is shown that, by incoherently averaging OFDI reflectance signals acquired at different backscattering angles, speckle noise is reduced, allowing scattering coefficients to be extracted from a single A-line with much higher accuracy than with measurements from conventional OFDI and optical coherence tomography systems. Modeling speckle as a random phasor sum, the relationship between the measurement accuracy and the number of compounded angles is derived. The sensitivity analysis is validated with measurements from a tissue phantom.
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Affiliation(s)
- A E Desjardins
- Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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15
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Desjardins AE, Vakoc BJ, Oh WY, Motaghiannezam SM, Tearney GJ, Bouma BE. Angle-resolved optical coherence tomography with sequential angular selectivity for speckle reduction. Opt Express 2007; 15:6200-9. [PMID: 19546925 PMCID: PMC2704484 DOI: 10.1364/oe.15.006200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
We present a novel method for rapidly acquiring optical coherence tomography (OCT) images at multiple backscattering angles. By angularly compounding these images, high levels of speckle reduction were achieved. Signal-to-noise ratio (SNR) improvements of 3.4 dB were obtained from a homogeneous tissue phantom, which was in good agreement with the predictions of a statistical model of speckle that incorporated the optical parameters of the imaging system. In addition, the fast acquisition rate of the system (10 kHz A-line repetition rate) allowed angular compounding to be performed in vivo without significant motion artifacts. Speckle-reduced OCT images of human dermis show greatly improved delineation of tissue microstructure.
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Affiliation(s)
- A E Desjardins
- Harvard Medical School and Wellman Center of Photomedicine, Massachusetts General Hospital 50 Blossom Street, BAR-708, Boston, Massachusetts 02114, USA.
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16
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Abstract
Imaging large tissue areas with microscopic resolution in vivo may offer an alternative to random excisional biopsy. We present an approach for performing confocal imaging of large tissue surface areas using spectrally encoded confocal microscopy (SECM). We demonstrate a single-optical-fiber SECM apparatus, designed for imaging luminal organs, that is capable of imaging with a transverse resolution of 2.1 microm over a subsurface area of 16 cm2 in less than 1 min. Due to the unique probe configuration and scanning geometry, the speed and resolution of this new imaging technology are sufficient for comprehensively imaging large tissues areas at a microscopic scale in times that are appropriate for clinical use.
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Affiliation(s)
- D Yelin
- Wellman Center for Photomedicine, Massachusetts General Hospital, MA 02114, USA
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17
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Bilenca A, Lasser T, Ozcan A, Leitgeb RA, Bouma BE, Tearney GJ. Image formation in fluorescence coherence-gated imaging through scattering media. Opt Express 2007; 15:2810-2821. [PMID: 19532519 DOI: 10.1364/oe.15.002810] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Recently, we have experimentally demonstrated a new form of cross-sectional, coherence-gated fluorescence imaging referred to as SD-FCT ('spectral-domain fluorescence coherence tomography'). Imaging in SD-FCT is accomplished by spectrally detecting self-interference of the spontaneous emission of fluorophores, thereby providing depth-resolved information on the axial positions of fluorescent probes. Here, we present a theoretical investigation of the factors affecting the detected SD-FCT signal through scattering media. An imaging equation for SD-FCT is derived that includes the effects of defocusing, numerical-aperture, and the optical properties of the medium. A comparison between the optical sectioning capabilities of SD-FCT and confocal microscopy is also presented. Our results suggest that coherence gating in fluorescence imaging may provide an improved approach for depth-resolved imaging of fluorescently labeled samples; high axial resolution (a few microns) can be achieved with low numerical apertures (NA<0.09) while maintaining a large depth of field (a few hundreds of microns) in a relatively low scattering medium (6 mean free paths), whereas moderate NA's can be used to enhance depth selectivity in more highly scattering biological samples.
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18
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Yelin D, Rizvi I, White WM, Motz JT, Hasan T, Bouma BE, Tearney GJ. Three-dimensional miniature endoscopy. Nature 2006; 443:765. [PMID: 17051200 DOI: 10.1038/443765a] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Accepted: 09/14/2006] [Indexed: 02/03/2023]
Affiliation(s)
- D Yelin
- Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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19
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Desjardins AE, Vakoc BJ, Tearney GJ, Bouma BE. Speckle Reduction in OCT using Massively-Parallel Detection and Frequency-Domain Ranging. Opt Express 2006; 14:4736-45. [PMID: 19516630 PMCID: PMC2704480 DOI: 10.1364/oe.14.004736] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Speckle noise significantly limits the information content provided by coherent optical imaging methods such as optical coherence tomography and its recent derivative, optical frequency-domain imaging (OFDI). In this paper, we demonstrate a novel OFDI system that simultaneously acquires hundreds of angularly resolved images, which can be compounded to reduce speckle noise. The system comprises an InGaAs line-scan camera and an interferometer, configured so that the elements of the detector array simultaneously capture light spanning a backscattering angular range of 32 degrees. On successive read-outs of the array, the wavelength of the laser source was stepped through a range of 130 nm centered at 1295 nm to concurrently generate 400 angle-resolved OFDI images. A theory of angle-resolved OFDI and the design equations of the system are presented. Incoherent averaging of the angle-resolved data is shown to yield substantial speckle reduction (as high as an 8 dB SNR improvement) in images of a tissue phantom and esophageal tissue ex vivo.
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20
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Bilenca A, Yun SH, Tearney GJ, Bouma BE. Numerical study of wavelength-swept semiconductor ring lasers: the role of refractive-index nonlinearities in semiconductor optical amplifiers and implications for biomedical imaging applications. Opt Lett 2006; 31:760-2. [PMID: 16544615 PMCID: PMC2713050 DOI: 10.1364/ol.31.000760] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Recent results have demonstrated unprecedented wavelength-tuning speed and repetition rate performance of semiconductor ring lasers incorporating scanning filters. However, several unique operational characteristics of these lasers have not been adequately explained, and the lack of an accurate model has hindered optimization. We numerically investigated the characteristics of these sources, using a semiconductor optical amplifier (SOA) traveling-wave Langevin model, and found good agreement with experimental measurements. In particular, we explored the role of the SOA refractive-index nonlinearities in determining the intracavity frequency-shift-broadening and the emitted power dependence on scan speed and direction. Our model predicts both continuous-wave and pulse operation and shows a universal relationship between the output power of lasers that have different cavity lengths and the filter peak frequency shift per round trip, therefore revealing the advantage of short cavities for high-speed biomedical imaging.
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Affiliation(s)
- A Bilenca
- Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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21
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Vakoc BJ, Yun SH, Tearney GJ, Bouma BE. Elimination of depth degeneracy in optical frequency-domain imaging through polarization-based optical demodulation. Opt Lett 2006; 31:362-4. [PMID: 16480209 PMCID: PMC2713047 DOI: 10.1364/ol.31.000362] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
A novel optical frequency-domain imaging system is demonstrated that employs a passive optical demodulation circuit and a chirped digital acquisition clock derived from a voltage-controlled oscillator. The demodulation circuit allows the separation of signals from positive and negative depths to better than 50 dB, thereby eliminating depth degeneracy and doubling the imaging depth range. Our system design is compatible with dual-balanced and polarization-diverse detection, important techniques in the practical biomedical application of optical frequency-domain imaging.
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Affiliation(s)
- B J Vakoc
- Harvard Medical School and the Wellman Center for Photomedicine, Massachusetts General Hospital, Boston 02114, USA.
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22
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Oh WY, Bouma BE, Iftimia N, Yun SH, Yelin R, Tearney GJ. Ultrahigh-resolution full-field optical coherence microscopy using InGaAs camera. Opt Express 2006; 14:726-35. [PMID: 19503391 DOI: 10.1364/opex.14.000726] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Full-field optical coherence microscopy (FFOCM) is an interferometric technique for obtaining wide-field microscopic images deep within scattering biological samples. FFOCM has primarily been implemented in the 0.8 mum wavelength range with silicon-based cameras, which may limit penetration when imaging human tissue. In this paper, we demonstrate FFOCM at the wavelength range of 0.9 - 1.4 mum, where optical penetration into tissue is presumably greater owing to decreased scattering. Our FFOCM system, comprising a broadband spatially incoherent light source, a Linnik interferometer, and an InGaAs area scan camera, provided a detection sensitivity of 86 dB for a 2 sec imaging time and an axial resolution of 1.9 mum in water. Images of phantoms, tissue samples, and Xenopus Laevis embryos were obtained using InGaAs and silicon camera FFOCM systems, demonstrating enhanced imaging penetration at longer wavelengths.
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23
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Cense B, Chen TC, Nassif N, Pierce MC, Yun SH, Park BH, Bouma BE, Tearney GJ, de Boer JF. Ultra-high speed and ultra-high resolution spectral-domain optical coherence tomography and optical Doppler tomography in ophthalmology. Bull Soc Belge Ophtalmol 2006:123-32. [PMID: 17265794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We present ultra-high resolution optical coherence tomography (OCT) structural intensity and optical Doppler tomography (ODT) flow velocity images of the human retina in vivo. The ultra-high speed OCT system is based on Spectral Domain or Fourier Domain technology, which provides a sensitivity advantage over conventional OCT of more than 2 orders of magnitude. This sensitivity improvement allows video rate OCT and ODT cross sectional imaging of retinal structures. Images will be presented with axial resolutions of 6 and 3.5 microns. We observed small features in the inner and outer plexiform layers, which are believed to be small blood vessels. Flow velocity images will be presented showing pulsatile flow in retinal arteries and veins.
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Affiliation(s)
- B Cense
- Harvard Medical School, Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA 02114, USA
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24
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Abstract
We demonstrate an ultrahigh-speed wavelength-swept semiconductor laser using a polygon-based wavelength scanning filter. With a polygon rotational speed of 900 revolutions per second, a continuous wavelength tuning rate of 9200 nm/ms and a tuning repetition rate of 115 kHz were achieved. The wavelength tuning range of the laser was 80 nm centered at 1325 nm, and the average polarized output power was 23 mW.
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Affiliation(s)
- W Y Oh
- Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston 02114, USA.
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25
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Abstract
We present a novel heterodyne approach for performing fast, three-dimensional spectrally encoded imaging. Volumetric data of a volunteer's finger and of coin surfaces were acquired at a rate of 5 volume sets per second with a depth resolution of 145 microm.
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Affiliation(s)
- D Yelin
- Harvard Medical School, Wellman Center for Photomedicine, Massachusetts General Hospital, 55 Fruit Street, BAR 703, Boston, Massachusetts 02114, USA.
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26
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Oh WY, Yun SH, Tearney GJ, Bouma BE. Wide Tuning Range Wavelength-Swept Laser With Two Semiconductor Optical Amplifiers. IEEE Photonics Technol Lett 2005; 17:678-680. [PMID: 20651947 PMCID: PMC2907922 DOI: 10.1109/lpt.2004.841003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
We demonstrate a wide tuning range high-speed wavelength-swept semiconductor laser based on a polygon scanning filter that is common to two laser cavities. Linear wavelength tuning was achieved over 145 nm around 1310 nm at a tuning repetition rate of 20 kHz. The wavelength tuning filter is expandable to accommodate multiple semiconductor optical amplifiers for further widening of the laser wavelength tuning range.
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27
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Abstract
Endoscopes employing a single optical fiber may have advantages over conventional fiber-bundle or CCD array imaging techniques, including the potential for greater flexibility and miniaturization. Although single-mode fibers can provide superior resolution compared with multimode fibers, they are prone to increased speckle noise and suffer from limited optical throughput and reduced depth of field. We demonstrate the use of a double-clad fiber for single-mode illumination and multimode detection to achieve high-resolution, reduced-speckle imaging with high optical throughput and a large depth of field.
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Affiliation(s)
- D Yelin
- Harvard Medical School, Wellman Center for Photomedicine, Pathology Department, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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28
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Yun SH, Boudoux C, Pierce MC, de Boer JF, Tearney GJ, Bouma BE. Extended-Cavity Semiconductor Wavelength-Swept Laser for Biomedical Imaging. IEEE Photonics Technol Lett 2004; 16:293-295. [PMID: 20640193 PMCID: PMC2905174 DOI: 10.1109/lpt.2003.820096] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
We demonstrate a compact high-power rapidly swept wavelength tunable laser source based on a semiconductor optical amplifier and an extended-cavity grating filter. The laser produces excellent output characteristics for biomedical imaging, exhibiting >4-mW average output power, <0.06-nm instantaneous linewidth, and >80-dB noise extinction with its center wavelength swept over 100 nm at 1310 nm at variable repetition rates up to 500 Hz.
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Affiliation(s)
- S. H. Yun
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | - C. Boudoux
- Harvard-MIT Division of Health Sciences and Technology and Department of Nuclear Engineering, Wellman Laboratories of Photomedicine, Massachusetts Institute of Technology, Boston, MA 02114 USA
| | - M. C. Pierce
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | - J. F. de Boer
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | - G. J. Tearney
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | - B. E. Bouma
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, Boston, MA 02114 USA
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29
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Abstract
A method for three-dimensional surface measurements with phase-sensitive spectrally encoded imaging is demonstrated. Both transverse and depth information is transmitted through a single-mode optical fiber, allowing this scheme to be incorporated into a miniature probe. This approach is demonstrated by measurement of the profile of a lens surface and by three-dimensional imaging of the face of a small doll.
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Affiliation(s)
- D Yelin
- Harvard Medical School, Wellman Laboratories of Photomedicine, Massachusetts General Hospital, 55 Fruit Street, BAR 703, Boston, Massachusetts 02114, USA.
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30
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Abstract
We demonstrate high-speed, high-sensitivity, high-resolution optical imaging based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. We derive and show experimentally that frequency-domain ranging provides a superior signal-to-noise ratio compared with conventional time-domain ranging as used in optical coherence tomography. A high sensitivity of -110 dB was obtained with a 6 mW source at an axial resolution of 13.5 microm and an A-line rate of 15.7 kHz, representing more than an order-of-magnitude improvement compared with previous OCT and interferometric imaging methods.
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Affiliation(s)
- S. H. Yun
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR-7, Boston, Massachusetts 02114
| | - G. J. Tearney
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR-7, Boston, Massachusetts 02114
| | - J. F. de Boer
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR-7, Boston, Massachusetts 02114
| | - N. Iftimia
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR-7, Boston, Massachusetts 02114
| | - B. E. Bouma
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR-7, Boston, Massachusetts 02114
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31
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Yun SH, Boudoux C, Tearney GJ, Bouma BE. High-speed wavelength-swept semiconductor laser with a polygon-scanner-based wavelength filter. Opt Lett 2003; 28:1981-3. [PMID: 14587796 DOI: 10.1364/ol.28.001981] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Ultrahigh-speed tuning of an extended-cavity semiconductor laser is demonstrated. The laser resonator comprises a unidirectional fiber-optic ring, a semiconductor optical amplifier as the gain medium, and a novel scanning filter based on a polygonal scanner. Variable tuning rates up to 1150 nm/ms (15.7-kHz repetition frequency) are demonstrated over a 70-nm wavelength span centered at 1.32 microm. This tuning rate is more than an order of magnitude faster than previously demonstrated and is facilitated in part by self-frequency shifting in the semiconductor optical amplifier. The instantaneous linewidth of the source is <0.1 nm for 9-mW cw output power and a low spontaneous-emission background of -80 dB.
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Affiliation(s)
- S H Yun
- Harvard Medical School and Wellman Laboratories for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR 718, Boston, Massachusetts 02114, USA.
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32
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Iftimia N, Bouma BE, Tearney GJ. Speckle reduction in optical coherence tomography by "path length encoded" angular compounding. J Biomed Opt 2003; 8:260-3. [PMID: 12683852 DOI: 10.1117/1.1559060] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2002] [Revised: 10/07/2002] [Accepted: 10/07/2002] [Indexed: 05/19/2023]
Abstract
Speckle, the dominant factor reducing image quality in optical coherence tomography (OCT), limits the ability to identify cellular structures that are essential for diagnosis of a variety of diseases. We describe a new high-speed method for implementing angular compounding by path length encoding (ACPE) for reducing speckle in OCT images. By averaging images obtained at different incident angles, with each image encoded by path length, ACPE maintains high-speed image acquisition and requires minimal modifications to OCT probe optics. ACPE images obtained from tissue phantoms and human skin in vivo demonstrate a qualitative improvement over traditional OCT and an increased SNR that correlates well with theory.
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Affiliation(s)
- N Iftimia
- Harvard Medical School, Massachusetts General Hospital, 50 Blossom Street, BAR 703, Boston, Massachusetts 02114, USA
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33
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Bouma BE, Tearney GJ, Yabushita H, Shishkov M, Kauffman CR, DeJoseph Gauthier D, MacNeill BD, Houser SL, Aretz HT, Halpern EF, Jang IK. Evaluation of intracoronary stenting by intravascular optical coherence tomography. Heart 2003; 89:317-20. [PMID: 12591841 PMCID: PMC1767586 DOI: 10.1136/heart.89.3.317] [Citation(s) in RCA: 203] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
BACKGROUND Conventional contrast cineangiography and intravascular ultrasound (IVUS) provide a limited definition of vessel microstructure and are unable to evaluate dissection, tissue prolapse, and stent apposition on a size scale less than 100 micro m. OBJECTIVE To evaluate the use of intravascular optical coherence tomography (OCT) to assess the coronary arteries in patients undergoing coronary stenting. METHODS OCT was employed in patients having percutaneous coronary interventions. Images were obtained before initial balloon dilatation and following stent deployment, and were evaluated for vessel dissection, tissue prolapse, stent apposition, and stent asymmetry. IVUS images were obtained before OCT, using an automatic pull back device. RESULTS 42 stents were imaged in 39 patients without complications. Dissection, prolapse, and incomplete stent apposition were observed more often with OCT than with IVUS. Vessel dissection was identified in eight stents by OCT and two by IVUS. Tissue prolapse was identified in 29 stents by OCT and 12 by IVUS; the extent of the prolapse (mean (SD)) was 242 (156) microm by OCT and 400 (100) microm by IVUS. Incomplete stent apposition was observed in seven stents by OCT and three by IVUS. Irregular strut separation was identified in 18 stents by both OCT and IVUS. CONCLUSIONS Intracoronary OCT for monitoring stent deployment is feasible and provides superior contrast and resolution of arterial pathology than IVUS.
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Affiliation(s)
- B E Bouma
- Wellman Laboratories of Photomedicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
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34
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White WM, Tearney GJ, Fabian RL, Gaz RD. Non-invasive imaging of freshly excised parathyroid glands using confocal reflectance microscopy. Br J Surg 2002. [DOI: 10.1046/j.1365-2168.2000.01601-29.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Abstract
Background
Successful surgical management of primary hyperparathyroidism requires an understanding of the underlying pathological diagnosis. Various methods have been employed to distinguish normal from hyperfunctional diseased glands. Confocal reflectance microscopy (CRM) is a novel optical method of imaging tissue non-invasively without the need for fixation, sectioning and staining as in standard histopathology. Gray-scale images are displayed in real time on a monitor, and represent horizontal (en face) optical sections through the tissue. Using CRM, the goal of this study was to delineate histological features characteristic of the parathyroid gland, and to determine if confocal imaging could distinguish normal from adenomatous parathyroid tissue.
Methods
In this pilot observational cohort study, a total of 18 parathyroid glands was imaged using CRM immediately after excision in eight patients undergoing surgery for primary hyperparathyroidism. Confocal images were compared with corresponding permanent, haematoxylin and eosin-stained sections obtained from the same gland. For each patient, the percentage area occupied by fat cells was calculated in ten independent images (593 μm × 509 μm) of both normal and diseased glands.
Results
Characteristic histological features of the parathyroid gland were readily discernible by CRM and correlated well with permanent, haematoxylin and eosin-stained sections. The fat content of both normal and diseased glands could be determined easily. The percentage area occupied by fat cells was distinctly different in normal (mean(s.d.) 21·8(5·3) per cent) and diseased (0·9(2·4) per cent) parathyroid glands.
Conclusion
CRM rapidly revealed histological features of the parathyroid gland without histological processing. This new, simple, rapid and non-invasive technique has the potential for use as an adjunct to frozen-section analysis in intraoperative consultation during parathyroidectomy. This may provide a technique for in situ histological diagnosis of endocrine or other tissues without an excisional biopsy. Work is currently under way to develop an intraoperative probe for in vivo use.
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Affiliation(s)
- W M White
- Massachusetts General Hospital, Boston, Massachusetts, USA
| | - G J Tearney
- Massachusetts General Hospital, Boston, Massachusetts, USA
| | - R L Fabian
- Massachusetts General Hospital, Boston, Massachusetts, USA
| | - R D Gaz
- Massachusetts General Hospital, Boston, Massachusetts, USA
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35
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36
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Abstract
A method for performing miniature endoscopy with a high number of resolvable points is presented. This approach, spectrally encoded endoscopy (SEE), uses a broad-bandwidth light source and a diffraction grating to simultaneously detected the reflectivity at multiple points along a transverse line within the sample. As opposed to images from miniature optical fiber bundle endoscopes, the number of resolvable points in SEE images is dependent on the spectral width and the groove density of the diffraction grating. We acquired images of a human finger in vivo, using a 550-mu;m -diameter SEE system to demonstrate the feasibility of this technique.
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Abstract
BACKGROUND AND AIMS Optical coherence tomography (OCT) is an imaging technique that produces high-resolution cross-sectional images in vivo. The aim of this study was to establish the sensitivity and specificity of OCT for diagnosing specialized intestinal metaplasia (SIM). METHODS OCT was used to image the stomach and esophagus of 121 patients. A total of 288 biopsy-correlated OCT images were acquired. OCT criteria for SIM were formulated by analyzing 75 images of SIM. The SIM image criteria were retrospectively tested by applying them to images of gastric, squamous, SIM, and cardiac epithelium. The criteria were then tested prospectively to determine the sensitivity and specificity of OCT for diagnosing SIM. RESULTS OCT images of SIM are characterized by (1) absence of the layered structure of normal squamous epithelium and the vertical "pit and crypt" morphology of gastric mucosa, (2) disorganized architecture with inhomogeneous tissue contrast and an irregular mucosal surface, and (3) presence of submucosal glands. These criteria were 100% sensitive and 93% specific for SIM when applied retrospectively and 97% sensitive and 92% specific when tested prospectively. CONCLUSIONS OCT is highly sensitive and specific for SIM and may aid in the diagnosis and surveillance of this preneoplastic lesion.
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Affiliation(s)
- J M Poneros
- Gastrointestinal Unit, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
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38
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White WM, Tearney GJ, Pilch BZ, Fabian RL, Anderson RR, Gaz RD. A novel, noninvasive imaging technique for intraoperative assessment of parathyroid glands: confocal reflectance microscopy. Surgery 2000; 128:1088-1100; discussion 1100-1. [PMID: 11114647 DOI: 10.1067/msy.2000.111190] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND Successful surgical management of primary hyperparathyroidism requires the ability to identify and distinguish normal from abnormal parathyroid tissue. Microscopic pathologic confirmation often helps with the diagnoses and decisions regarding the extent of parathyroid resection. Confocal reflectance microscopy (CRM) is an optical method of noninvasively imaging tissue without fixation, sectioning, and staining as in standard histopathology. The goal of this study was to determine if CRM imaging could be used to distinguish normal from diseased parathyroid tissue intraoperatively. METHODS In this study, 44 parathyroid glands from 21 patients undergoing operations for primary hyperparathyroidism were imaged immediately after excision. CRM images were compared with conventional hematoxylin-and-eosin stained sections obtained from the same gland. The percentage area occupied by fat cells was calculated in images of both normal and diseased glands. RESULTS Characteristic microscopic features of parathyroid glands were distinguishable by CRM and correlated well with histopathology. The stromal fat content of normal and diseased glands could easily be determined. The percentage area occupied by fat cells differed significantly (P <.00001) in normal glands (average, 23.0% +/- 10.9%) and adenomatous glands (average, 0.4% +/- 0.7%). CONCLUSIONS CRM imaging rapidly revealed microscopic features that reliably differentiated normal and diseased parathyroid glands. The success of this preliminary ex vivo study promotes interest in further development of an in situ probe for in vivo clinical diagnostic use.
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Affiliation(s)
- W M White
- Wellman Laboratories of Photomedicine, Massachusetts General Hospital, Boston, MA, USA
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39
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Abstract
Optical coherence tomography (OCT) is a high-resolution, cross-sectional optical imaging technique that allows in situ imaging of tissue by measuring back-reflected light. OCT provides images in real time with a resolution approaching that of conventional histopathology, but without the need for tissue removal. OCT imaging can be performed endoscopically to visualize gastrointestinal tissue using a fiberoptic catheter passed through the instrument channel of a conventional endoscope. The resolution of OCT allows visualization of the different layers of gastrointestinal epithelium and the differentiation of Barrett's epithelium from normal gastric and squamous mucosa. OCT has also been used to image esophageal adenocarcinoma and colonic polyps. Recent developments include Doppler OCT, spectroscopic OCT, and ultrahigh-resolution OCT, which can visualize nuclei within single cells. Although still in its infancy as a clinical tool, OCT currently provides high-resolution images over the same imaging depth as conventional mucosal biopsy, and may prove to be a useful and minimally invasive technique for evaluating gastrointestinal tissue, particularly for early neoplastic changes.
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Affiliation(s)
- S Brand
- Gastrointestinal Unit, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
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Tearney GJ, Jang IK, Kang DH, Aretz HT, Houser SL, Brady TJ, Schlendorf K, Shishkov M, Bouma BE. Porcine coronary imaging in vivo by optical coherence tomography. Acta Cardiol 2000; 55:233-7. [PMID: 11041121 DOI: 10.2143/ac.55.4.2005745] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
OBJECTIVE A high-resolution coronary artery imaging modality has the potential to address important diagnostic and management problems in cardiology. Optical coherence tomography (OCT) is a promising new optical imaging technique with a resolution of approximately 10 microm. The purpose of this study was to use a new OCT catheter to demonstrate the feasibility of performing OCT imaging of normal coronary arteries, intimal dissections, and deployed stents in vivo. METHODS AND RESULTS Normal coronary arteries, intimal dissections, and stents were imaged in five swine with OCT and compared with intravascular ultrasound (IVUS). In the normal coronary arteries, visualization of all of the layers of the vessel wall was achieved with a saline flush, including the intima which was not identified by IVUS. Following dissection, detailed layered structures including intimal flaps, intimal defects, and disruption of the medial wall were visualized by OCT. IVUS failed to show clear evidence of intimal and medial disruption. Finally, the microanatomic relationships between stents and the vessel walls were clearly identified only by OCT. CONCLUSIONS In this preliminary experiment, we have demonstrated that in vivo OCT imaging of normal coronary arteries, intimal dissections, and deployed stents is feasible, and allows identification of clinically relevant coronary artery morphology with high-resolution and contrast.
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Affiliation(s)
- G J Tearney
- Wellman Laboratories of Photomedicine, Massachusetts General Hospital and Harvard Medical School, Boston 02114, USA
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41
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Abstract
BACKGROUND Optical coherence tomography is a new, high spatial-resolution, cross-sectional imaging technique. We investigated the ability of optical coherence tomography to provide detailed images of subsurface structures in the upper gastrointestinal (GI) tract. METHODS Optical coherence tomography was performed during routine upper GI endoscopy on 32 patients including 20 patients with Barrett's esophagus. An endoscopic mucosal biopsy was obtained immediately after imaging and was used for histopathologic correlation. RESULTS Optical coherence tomography provided clear delineation of layers of the normal human esophagus extending from the epithelium to the longitudinal muscularis propria. Gastric mucosa was differentiated from esophageal mucosa, Barrett's esophagus was differentiated from normal esophageal mucosa, and esophageal adenocarcinoma was distinguished from normal esophagus and Barrett's esophagus. CONCLUSIONS Optical coherence tomography allows visualization of the subsurface architectural morphology of the upper GI tract. The diagnostic information provided by this new imaging modality suggests that it may be a useful adjunct to endoscopy.
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Affiliation(s)
- B E Bouma
- Wellman Laboratories of Photomedicine and Department of Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts, USA
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42
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Abstract
BACKGROUND Optical coherence tomography (OCT) is a new method of catheter based micron scale imaging. OCT is analogous to ultrasound, measuring the intensity of backreflected infrared light rather than sound waves. OBJECTIVE To demonstrate the ability of OCT to perform high resolution imaging of arterial tissue in vivo. METHODS OCT imaging of the abdominal aorta of New Zealand white rabbits was performed using a 2.9 F OCT imaging catheter. Using an ultrashort pulse laser as a light source for imaging, an axial resolution of 10 micrometer was achieved. RESULTS Imaging was performed at 4 frames/second and data were saved in either super VHS or digital format. Saline injections were required during imaging because of the signal attenuation caused by blood. Microstructure was sharply defined within the arterial wall and correlated with histology. Some motion artefacts were noted at 4 frames/second. CONCLUSIONS In vivo imaging of the rabbit aorta was demonstrated at a source resolution of 10 micrometer, but required the displacement of blood with saline. The high resolution of OCT allows imaging to be performed near the resolution of histopathology, offering the potential to have an impact both on the identification of high risk plaques and the guidance of interventional procedures.
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Affiliation(s)
- J G Fujimoto
- Department of Electrical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Bouma BE, Tearney GJ. Power-efficient nonreciprocal interferometer and linear-scanning fiber-optic catheter for optical coherence tomography. Opt Lett 1999; 24:531-3. [PMID: 18071562 DOI: 10.1364/ol.24.000531] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
A nonreciprocal fiber-optic interferometer is demonstrated in an optical coherence tomography (OCT) system. The increased power efficiency of this system provides a 4.1-dB advantage over standard Michelson implementations. In addition, a new linear-scanning fiber-optic catheter is demonstrated that avoids the rotary optical junction that is required in circumferential scanning systems. These advancements have permitted the clinical implementation of OCT imaging in the human gastrointestinal tract.
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Abstract
An endoscope-compatible, submicrometer-resolution scanning confocal microscopy imaging system is presented. This approach, spectrally encoded confocal microscopy (SECM), uses a quasi-monochromatic light source and a transmission diffraction grating to detect the reflectivity simultaneously at multiple points along a transverse line within the sample. Since this method does not require fast spatial scanning within the probe, the equipment can be miniaturized and incorporated into a catheter or endoscope. Confocal images of an electron microscope grid were acquired with SECM to demonstrate the feasibility of this technique.
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Affiliation(s)
- G J Tearney
- Wellman Laboratories of Photomedicine, Massachusetts General Hospital, 50 Blossom Street, BAR 703, Boston, Massachusetts 02114, USA
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Boppart SA, Bouma BE, Pitris C, Tearney GJ, Southern JF, Brezinski ME, Fujimoto JG. Intraoperative assessment of microsurgery with three-dimensional optical coherence tomography. Radiology 1998; 208:81-6. [PMID: 9646796 DOI: 10.1148/radiology.208.1.9646796] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To evaluate three-dimensional optical coherence tomography (OCT) for use in the assessment of the microsurgical anastomoses of vessels and nerves. MATERIALS AND METHODS OCT is an optical analogue of ultrasonography and is capable of imaging nontransparent biologic tissue by detecting backscattered infrared light. Cross-sectional in vitro images of rabbit and human vessels and nerves were obtained in as little as 125 msec at 10-micron resolution by using a solid-state laser as a light source. A surgical microscope was integrated with OCT to perform simultaneous imaging with en face visualization. Cross-sectional images were assembled to produce three-dimensional reconstructions of microsurgical specimens. RESULTS Three-dimensional OCT reconstructions depicted the structure within an arterial anastomosis and helped identify sites of luminal obstruction. The longitudinal spatial orientation of individual nerve fascicles was tracked in three dimensions to identify changes in position. In vitro human arteries and nerves embedded in highly scattering tissue and not visible at microscopy were located and imaged with OCT at eight frames per second. CONCLUSION The three-dimensional, micrometer-scale, diagnostic imaging capabilities of OCT permit rapid feedback for assessment of microsurgical procedures. OCT technology can be readily integrated with surgical microscopes and has potential for intraoperative monitoring to improve patient outcome.
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Affiliation(s)
- S A Boppart
- Dept of Electrical Engineering and Computer Science, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge 02139, USA
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46
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Abstract
Optical coherence tomography (OCT) is a new technique for performing high-resolution, cross-sectional tomographic imaging in human tissue. OCT is analogous to ultrasound B mode imaging except that it uses light rather than acoustical waves. As a result, OCT has over 10 times the resolution of currently available clinical high-resolution cross-sectional imaging technologies. In this work, we investigate the capability of OCT to differentiate the architectural morphology of pancreatobiliary tissues. Normal pancreatobiliary tissues, including the gallbladder, common bile duct, pancreatic duct, and pancreas were taken postmortem and imaged using OCT. Images were compared to corresponding histology to confirm tissue identity. Microstructure was delineated in different tissues, including tissue layers, glands, submucosal microvasculature, and pancreatic islets of Langerhans. The ability of OCT to provide high-resolution imaging of pancreatobiliary architectural morphology suggests the feasibility of using OCT as a powerful diagnostic endoscopic imaging technology to image early stages of pancreatobiliary disease.
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Affiliation(s)
- G J Tearney
- Harvard Medical School and Cardiac Unit, Massachusetts General Hospital, Boston 02114, USA
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Pitris C, Brezinski ME, Bouma BE, Tearney GJ, Southern JF, Fujimoto JG. High resolution imaging of the upper respiratory tract with optical coherence tomography: a feasibility study. Am J Respir Crit Care Med 1998; 157:1640-4. [PMID: 9603149 DOI: 10.1164/ajrccm.157.5.9707075] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
A need exists in respiratory medicine for a technology capable of identifying airway pathology on a micron scale. This study has demonstrated the feasibility of optical coherence tomography (OCT) for ultrahigh resolution imaging of the upper respiratory tract by in vitro studies of human tissue. OCT is a relatively new technique that can be used to noninvasively collect tomographic images of tissue microstructure with micron-scale resolution. OCT is analogous to ultrasound, measuring the intensity of infrared light rather than acoustical waves. Samples throughout the upper respiratory tract, from the epiglottis to the secondary bronchi, were imaged. The resulting images were compared with histopathology and verified the ability of OCT to delineate relevant structures such as the epithelium, mucosa, cartilage and its sublayers, and glands at a resolution higher than any clinical imaging technology. The ability of OCT to generate image resolution in the range close to that of histopathology in real time, as well as easy integration with small, relatively inexpensive endoscopes, low cost, and lack of a need for a transducing medium, supports the hypothesis that this optical technology could become a powerful modality in the diagnosis and management of a wide range of clinical respiratory pathology.
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Affiliation(s)
- C Pitris
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, USA
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Fujimoto JG, Bouma B, Tearney GJ, Boppart SA, Pitris C, Southern JF, Brezinski ME. New technology for high-speed and high-resolution optical coherence tomography. Ann N Y Acad Sci 1998; 838:95-107. [PMID: 9511798 DOI: 10.1111/j.1749-6632.1998.tb08190.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Optical coherence tomography (OCT) is an optical imaging technique that is capable of performing micron-scale, cross-sectional imaging of internal microstructure in biological systems. OCT is analogous to ultrasound B mode imaging except that it uses light rather than sound and performs imaging by measuring the back-scattered intensity of light from structures in tissue. We describe recent advances in OCT technology including the application of short pulse solid state lasers based on Ti: Al2O3 and Cr: Mg2SiO4 to enable high-resolution, high-speed imaging as well as the development of OCT catheter/endoscope delivery to permit imaging of internal organ systems. OCT enables the nonexcisional, in situ, real-time imaging of tissue microstructure and is thus a powerful and promising technique for optical biopsy.
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Affiliation(s)
- J G Fujimoto
- Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge 02139, USA
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49
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Abstract
A need exists in medicine for a technology capable of 'optical biopsy,' imaging at or near the resolution of histopathology without the need for excisional biopsy. Optical coherence tomography (OCT) is a recently developed imaging technology that uses infrared light to generate cross-sectional images on a micron scale. In this work, the feasibility of OCT for optical biopsy was confirmed with in vitro tissue from the skeletal and male reproductive systems. This work supports the hypothesis that OCT is an attractive technology for in vivo optical biopsy.
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Affiliation(s)
- M E Brezinski
- Cardiac Unit, Massachusetts General Hospital, Boston 02114, USA.
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50
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Tearney GJ, Brezinski ME, Southern F, Bouma BE, Boppart SA, Fujimoto JG, Karrer S, Abels C, Szeimies RM, Baumler W, Dellian M, Hohenleutner U, Goetz AE, Landthaler M, Teichman JM, Rogenes VJ, McIver BJ, Harris JM. New Laser Literature. Lasers Med Sci 1998. [DOI: 10.1007/bf00592964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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