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A PRESENTATION ON OCT

(OPTICAL COHERENCE TOMOGRAPHY)

PREPARED BY PUNEET SINGH THAKUR IET DAVV (INDORE) DIGITAL INSTRUMENTATION ROLL NO.- DI15719

"There is a crack in everything. That's how the light goes in"

"There is a crack in everything. That's how the light goes in" 2

What is OCT ?

OCT basically refers to Optical coherence tomography. It is a non contact, non destructive technique for 3D imaging of engineering and bio medical samples.

OCT is a new type of optical imaging technology perform high resolution cross section tomography imaging of the internal microstructure in a material and biological system by measuring backscattered or beck reflected light.

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Basic Principle

• For biomedical engineering OCT use low-coherence interferometry to produce a two or three dimensional image of optical scattering from internal tissue microstructures.

• OCT is basically based on the interference phenomenon of light.• For the basic setup of OCT we use “Michaelson Interferometer”.

Sample is to be analyse is placed on one of the arm of the interferometer.

• But the source we use for the OCT is SLED, that is a Broad band source preferred for depth scanning.

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Component

MirrorCCD or CMOS cameraSuperluminescent Emitting Diode (SLED) (800-1300nm, 5mW)• The unique property of Superluminescent diodes (SLD) is the

combination of laser-diode-like output power and brightness with broad LED-like optical spectrum. Such combination is allowed by high optical gain in semiconductor laser materials and its wide optical spectrum

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Superluminescent Emitting Diode (SLED)

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Grating• Any periodic perturbation is generally refers as grating. Here when we

consider Fourier domain OCT we will deal with Diffraction grating.• Diffraction grating is an optical component with a periodic structure,

which reflect the light into several beams travelling in different direction.

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Beam Splitter

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Michaelson interferometer

Condition for MaximaPath difference ∆x=nλ

Condition for minimaPath difference ∆x=(2n+1)λ/2

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Basic Set Up for OCT

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Type Of OCT

1. Time Domain OCT2. Frequency domain OCT3. Swept Source OCT

"There is a crack in everything. That's how the light goes in"

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Time Domain OCT

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Frequency Domain OCT

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Swept source OCT

RF Generator Frequency changed from 87 to 95 MHz with the step of 0.1 MHz

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OCT of a fingertip pattern

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Important Parameter

• Depth resolution-:The larger the bandwidth of the source in TD-OCT and SB-OCT and the wider the tuning bandwidth in SS-OCT, the better the depth resolution is.

• Penetration depth-:Due to scattering and absorption in the examined object, the number of photons in the backscattered wave conserving stable phase relations to the photons in the incident wave reduces with depth.

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• Wavelength range-:Biomedical optics requires imaging within the therapeutic window, situated between 600 and 1000 nm, where the main constituents of the tissue exhibit low absorption.• Power to the object -:In scanning regime, safety standards allow: 0.7 mW at the cornea for imaging the retina of the human eye at 830 nm and up to 2 mW at 1060 nm ;15 mW in imaging the anterior chamber at 1300 nm and larger power when imaging internal structures and skin.

"There is a crack in everything. That's how the light goes in"

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Limitations

• Penetration: 2-3mm Ideal: 4mm• Acquisition rate: <10frames/second• Lack of large-scale clinical trials

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Advantages

• Non contact• Non destructive• Non invasive• Broad dynamic range• No preparation of the sample or subject• No ionizing radiation• High resolution (1 to 15 μm)• It can be implemented compact fiber optic components and integrated

with wide range of medical instrument.

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APPLICATION

Meteorological ApplicationDefect detection of LCDInspection of touch screen panel

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Biomedical applicationDetection of malignancy in human cellsEye imagingSkin imaging

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References• https://www.researchgate.net/publication/37438932_Optical_Coherence_Tomography-

Principles_and_Applications• Smart optical coherence tomography for ultra-deep imaging through highly scattering

media Amaury Badon, Dayan Li, Geoffroy Lerosey, Albert C. Boccara, Mathias Fink, and Alexandre Aubry Institut Langevin, ESPCI ParisTech, PSL Research University,CNRS UMR 7587, 1 rue Jussieu, 75005 Paris, France (Dated: October 19, 2015)

• http://www.sciencedirect.com/science/article/pii/S0939388909001524• J.G. Fujimoto “Optical Coherence Tomography: Technology and Application” IEEE 2002• Simultaneous topography and tomography of latent fingerprints using full-field swept-

source optical coherence tomography by Satish Kumar Dubey1, Dalip Singh Mehta1, Arun Anand2 and Chandra Shakher1, JOURNAL OF OPTICS A: PURE AND APPLIED OPTICS , 10 (2008) 015307 (8pp)

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