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Transcript of An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography...
![Page 1: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/1.jpg)
An Alternative Method of Extending Imaging Window of
Fourier Domain – Optical Coherence Tomography by Using a Complex
Conjugate Removal Technique
Amine Bouchti
University California Davis
Research Advisor: John S. Werner
Research Supervisor: Robert J
Zawadzki
![Page 2: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/2.jpg)
Optical Coherence Tomography (OCT)
– An interferometric technique that offers, in vivo, cross-sectional views of biological microstructure tissue such as the human retina.
– The depth structure of the sample is reconstructed from backscattered light by Fourier domain OCT (FD-OCT).
– The images are generated by scanning the incident light beam at different axial depths and transverse positions.
![Page 3: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/3.jpg)
What is Fourier Domain ?
• Fourier domain is the analysis of functions or signal with respect to frequency.
• It relates to the Fourier transform by decomposing a function into a finite number of frequencies.
• Fourier transform functions are complex ( they have Amplitude and phase.) In standard FD-OCT only the magnitude of Fourier transform is displayed.
Position(z)
![Page 4: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/4.jpg)
Main Applications of OCT• The axial resolution of OCT in retinal tissue is about 1-
15 µm, which is 10 to 100 times better than ultrasound or MRI.
• It enables visualization of the internal architectural morphology of the retina noninvasively; in real time and provides a 3 dimensional view of the retina.
• OCT can detect and diagnose early stages of disease before physical symptoms and irreversible vision loss can occur.
![Page 5: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/5.jpg)
OCT apparatus
• Schematic of the OCT System
SLD: Superluminescent diode source.
PC:polarization controllers.
NDF: Neural density filter.
FI: Faraday isolator.
M: Mirror.
DG: Diffraction grating.
CCD: CCD cameras.
![Page 6: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/6.jpg)
FD-OCT Signal Processing
Amplitude Vs. pixelsAmplitude Vs. Pixels
•Di[km] .S[ Km].(RR+Rs+2√(RRRs) cos(2∆xkm +I))
Subtract DC
Di[km] .S[ Km] 2√(RRRs) cos(2∆xkm +I)
![Page 7: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/7.jpg)
•Fourier transform: Di[Xn] = Di[km]e-
(j2(kmXn))
Di[xn] S[xn] 2√(RRRS)((xn+∆x)+(xn-∆x))
Amplitude Vs. Pixels
Di[km] .S[ Km] 2√(RRRs) cos(2∆xkm +I)
Fourier Transform
Amplitude Vs.Position
![Page 8: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/8.jpg)
• In Standard FD-OCT only half of the imaging window can be used.
• Due to a reflection at + ∆X that cannot be distinguished from a reflection at -∆X. This is called Complex Conjugate Artifact.
Limitations
![Page 9: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/9.jpg)
Goal
How can this artifact be removed?
![Page 10: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/10.jpg)
Setting up andaligning thespectrometer
Simultaneousdetecting from both
cameras
Connecting thefibers and calculatingthe coupler splitting
ratios
Minimizedispersion
Lab viewDrive
the system Process
data
3X3fiber coupler
2spectrometers
Creat a complexinterferometric signal
Solution
![Page 11: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/11.jpg)
The Complex FD-OCT Schematic
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
1
2
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3x3 algorithms
•Signal 1 ( I1) -DC: Di[km] .S[ Km] 2√(RRRs) cos(2∆xkm +I)
•Signal 2 (I2) -DC: Di[km] .S[ Km] 2√(RRRs) cos(2∆xkm +I)
•Complex equation: real part + j imaginary part
If we assume that I1= the real part
the imaginary part can be obtained by the following equation:
I1cos(∆) - I2
Iim=
Sin(∆)
Graph of , I2/ I1 Graph of ∆Graph of CCD1Vs. CCD2
![Page 13: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/13.jpg)
Results
• The removal of the complex conjugate artifact
![Page 14: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/14.jpg)
Did it Work?
Single CCD ImageHalf screenSingle CCD Image
Full screen
Single CCD ImageFull screen
Two CCD ImageFull screen
![Page 15: An Alternative Method of Extending Imaging Window of Fourier Domain – Optical Coherence Tomography by Using a Complex Conjugate Removal Technique Amine.](https://reader033.fdocuments.in/reader033/viewer/2022042814/55165344550346b2068b59c3/html5/thumbnails/15.jpg)
Acknowledgments
•Center for Adaptive Optics, a National
Science Foundation Science and technology
Center(STC), AST-987683.
•UC Davis medical Center.
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References
• University of California Davis Medical center, http://vsri.ucdavis.edu/.• Marinko V.Sarunie, Michael A. Choma, Changhuei Yang, Joseph A. Izatt,
“Instantaneous complex conjugate resolved spectra domain and swept-source OCT using 3x3 fiber coupler,”Opt.Express 13,957- 967 (2005)
• Michael A. Choma, Changhuei Yang, Joseph A. Izatt, “Instantaneous quadrature low-coherence interferometry with 3x3 fiber-optic couplers,” Opt.Lett.28 , 2162-2164 (2003)
• N.A. Nassif, B. Cense, B.H. Park, M.C. Pierce, S.H. Yun, B.E. Bouma,G.J.Tearney, “In vivo high-resolution video-rate spectral-domain optical coherence tomography of the human retina and optic nerve,” Opt.Express 12,367- 376 (2004)