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Biomedical Imaging 2

Biomedical Imaging 2. Class 4 – Optical Coherence Tomography (OCT) 02/19/08. Optical biopsy – definition . The in situ imaging of tissue microstructure with a resolution approaching that of histology, but without the need for tissue excision and processing

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Biomedical Imaging 2

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  1. Biomedical Imaging 2 Class 4 – Optical Coherence Tomography (OCT) 02/19/08

  2. Optical biopsy – definition • The in situ imaging of tissue microstructure with a resolution approaching that of histology, but without the need for tissue excision and processing • A ballistic optical imaging modality • Analogous to ultrasonography

  3. Optical coherence tomography • Three-dimensional imaging technique with ultrahigh spatial resolution, even in highly scattering media • Based on measurements of the reflected light from tissue discontinuities • e.g., the epidermis-dermis junction • i.e., principal contrast mechanism is the tissue scattering coefficient μs • To a lesser extent, polarization is a contrast mechanism • Based on interferometry • involves interference between the reflected light and the reference beam.

  4. Components of NIR Propagation in Tissue • Light propagation (Monte Carlo simulation) Absorption “Snake” component Incident light Ballistic component Diffuse reflectance Diffuse transmittance Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  5. Concept of Interferometry

  6. E = ER + ES Concept of Interferometry

  7. The OCTsetup Fiber-optic beamsplitter Broadband source Tissue Scanning reference mirror Detector Computer Amplifier Bandpass filter Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  8. Reference mirror Tissue How To Achieve a Depth Profile

  9. Source spectrum and envelope Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  10. Significance of Short Coherence Length/Time

  11. Resolution (log) 1 mm Ultrasound 100 mm 10 mm Confocalmicroscopy 1 mm Penetration depth (log) 1 mm 1 cm 10 cm OCT vs. standard imaging Standardclinical Highfrequency OCT Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  12. Construction of image Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  13. Choosing the light source • Four primary considerations • wavelength, • bandwidth, • power (in a single-transverse-mode), • stability; • portability, ease-of-use, etc. Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  14. Choose light source – wavelength Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  15. Choose light source – wavelength Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  16. Lateral resolution (2/2) Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  17. Light propagation in sample • The sample • need to describe light-tissue interaction taking temporal and spatial coherence properties into account; • can transport theory be used? • Light-tissue interaction may be modelled by using, for example, the extended Huygens-Fresnel principle • correlation between tissue, state of tissue (lesions) and optical properties? Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  18. Schematic of fitting algorithm D. Levitz et al., Opt. Express 12, 249-259 (2004) Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  19. Analytical OCT model • Mean square heterodyne signal current – general expression • μs scattering coefficient • w spot size (H,absence, & S, presence of scattering) • beffective backscattering cross section • P optical power (R: reference; S: sample) • a conversion from optical power to current •  heterodyne efficiency factor Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  20. Ophthalmology diagnosing retinal diseases. Dermatology skin diseases, early detection of skin cancers. Cardio-vascular diseases vulnerable plaque detection. Endoscopy (fiber-optic devices) gastrology, … Functional imaging Doppler OCT, spectroscopic OCT, optical properties, PS-OCT. OCT in non-invasive diagnostics • Guided surgery • delicate procedures • brain surgery, • knee surgery, • … Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  21. Commercial systems • Ophthalmology • Humphrey (division of Zeiss), US; • www.humphrey.com, • Ophthalmic Technologies Inc., Can. • … • Cardio-vascular diseases • Lightlab Imaging, US; • www.lightlabimaging.com. • Dermatology • Isis Optronics, D; • www.isis-optronics.de, • OCT Innovation, Den, • … Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  22. Applications:Ophthalmology Humphrey® Optical Coherence Tomography scanner at Herlev Hospital. Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  23. Applications:Ophthalmology Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  24. Applications: Ophthalmology Department of Ophthalmology, The New York Eye & Ear Infirmary, New York, NY 10003, USA Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  25. Normal Eye 250 microns Humphrey Nominal width of scan: 2.8 mm Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  26. UHR-OCT versus commercial OCT W. Drexler et al., “Ultrahigh-resolution ophthalmic optical coherence tomography”, Nature Medicine 7, 502-507 (2001) Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  27. Applications:Ophthalmology • Assessment of treatment (choroid) Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  28. Clinically adapted systems Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  29. Applications: Dermatology • Dermatology • Medical Laser Center Lübeck GmbH, Lübeck, Germany. sub-epidermal blister (in vivo) at the forearm (3 by 1.5 mm2) sub-dermal blister (in vivo) at the forearm (2 by 1.5 mm2) Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  30. Applications: Dermatology Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  31. Applications: Dermatology Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  32. Basics of disease From Essential Pathology, Emanual Rubin & John L. Farber, second edition, J. B. Lippincott Company, 1995, p. 252 Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  33. Applications: Cardiology • Imaging inside veins OCT Ultrasound Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  34. OCT vs. histology D. Levitz, L. Thrane, M. H. Frosz, P. E. Andersen, C. B. Andersen, J. Valanciunaite, J. Swartling, S. Andersson-Engels, and P. R. Hansen, Opt. Express 12, 249-259 (2004). Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  35. Extract scattering coefficient Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  36. Extract geff Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  37. In-vitro clinical study – samples • Analysis of the scattering properties at 1300 nm of the human arterial intima • 4 normal, 4 lipid-rich, 3 fibrous, and 3 fibrocalcific aortic segments, • imaged with OCT in Phosphate Buffered Saline, • routine histological processing • intima identified in histology first, then in the corresponding OCT image. • Reference • D. Levitz, L. Thrane, M. H. Frosz, P. E. Andersen, C. B. Andersen, J. Valanciunaite, J. Swartling, S. Andersson-Engels, and P. R. Hansen, Optics Express 12, 249-259 (2004). Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  38. Image interpretation • OCT images are divided into transverse blocks (~200-300 µm): • normal: 41 • lipid-rich: 40 • fibrous: 34 • fibrocalcific: 36 Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  39. Application: results Normal arterial blocks 15 – 39 mm-1: 95% Lipid-rich and fibrocalcific arterial blocks < 15 mm-1: 60% Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  40. Application: results (2) Normal arterial blocks 0.95 - 1: 87.8% Atherosclerotic arterial blocks < 0.95: > 50% Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

  41. OCT: suggested reading • OCT • D. Huang et al., Science 254, 1178 (1991) • A. Fercher, J. Biomed. Optics 1, 157 (1996) • J. M. Schmitt, “Optical coherence tomography (OCT): A review”, IEEE J. Select. Topics Quantum Electron. 5, 1205-1215 (1999) • J. G. Fujimoto et al., “Optical coherence tomography: An emerging technology for biomedical imaging and optical biopsy”, Neoplasia 2, 9-25 (2000) • W. Drexler et al., “Ultrahigh-resolution ophthalmic optical coherence tomography”, Nature Medicine 7, 502-507 (2001) • W. Drexler, “Ultrahigh-resolution optical coherence tomography”, J. Biomed. Opt. 9, 47-74 (2004) Courtesy of Prof. P.E. Andersen, Risø, Technical University of Denmark

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