1. Optical Coherence Tomography1
Optical Coherence
Tomography

2. 2
INTRODUCTION
Medical imaging modality with 1-10um resolution and 1-2mm penetration depths
High-resolution, sub- surface, non-invasive or minimally invasive internal body imaging technique for structural and quantitative imaging
OCT is analogous to ultrasound imaging

3. PRINCIPLE AND INSTRUMENTATION3
PRINCIPLE AND INSTRUMENTATION
Based on principle of low coherence interferometry
Imaging is performed by measuring the echo time delay and intensity of back-reflected or backscattered light
Measurements are performed using a Michelson interferometer with a low coherence length light source

4. OCT SYSTEMS USING MICHELSON’S4
OCT SYSTEMS USING MICHELSON’S
INTERFEROMETER

5. TYPES OF OCT SYSTEMS Time Domain (TD) OCT Systems5
TYPES OF OCT SYSTEMS
Time Domain (TD) OCT Systems
Spectral Domain (SD) OCT systems
Swept Source (SS) OCT Systems

6. TIME DOMAIN (TD) OCT SYSTEMS6

7. SPECTRAL DOMAIN (OCT) SYSTEMS7
SPECTRAL DOMAIN (OCT) SYSTEMS

8. ADVANTAGES OF SD-OCT OVER TD-OCT8
ADVANTAGES OF SD-OCT OVER TD-OCT
Permits faster acquisition of the entire depth profile(A-scans)
Video-rate imaging is possible
High-speed acquisition without any moving parts minimizes any distortion in the OCT images due to motion in the sample
Entire depth profile (A scan)is measured from a single spectrum with no mechanical scanning of the reference path

9. SWEPT SOURCE (SS) OCT SYSTEMS9
SWEPT SOURCE (SS) OCT SYSTEMS

10. BASELINE SIGNAL PROCESSING CHAIN IN OCT SYSTEMS
1010
BASELINE SIGNAL PROCESSING CHAIN IN OCT SYSTEMS

11. BACKGROUND SUBTRACTION
1111
BACKGROUND SUBTRACTION
The background is subtracted from the acquired data
To eliminate the reference power term, the reference spectrum from only the reference arm is detected and subtracted from the interference spectrum
Variations due to fixed pattern noise in the line scan camera and variations in power spectral densities of source can be suppressed.

12. 1212
RE-SAMPLING
In SD-OCT systems, spectrometers measure optical intensity as a function of wavelength
In order to apply the Fast Fourier Transform (FFT) reconstructing the axial scan as a function of depth, the spectrum should be evenly sampled in k-space
Therefore, the spectrometer output must be transformed from the wavelength to the frequency space

13. 1313
IMAGE FORMATION (FFT)
The basic operation to get the depth resolved A-scan from the interference fringes
The structural image is obtained by taking the magnitude
of the complex FFT output
Each FFT creates a particular A-scan
By moving the galvanometer in x direction ,the successive A-scan line is created
By moving the galvanometer in both x-y direction, a full 3D volume can be generated

14. MAGNITUDE COMPUTATION
1414
MAGNITUDE COMPUTATION
FFT output is a complex number
The structural information is contained in the magnitude of the FFT output
The function provide 15.5 bits of accuracy

15. LOG COMPRESSION 16 bit value provides 96 dB dynamic range
1515
LOG COMPRESSION
16 bit value provides 96 dB dynamic range
Human visualization range is about 40-60dB
16 bit data is compressed using a non-linear function to reduce the dynamic range for visualization
Log function is a common non-linearity used in OCT
Two approximations of log compression to map the 16-bit input to 8-bit data for display
Linear approximation
Quadratic approximation

16. 1616
ADVANTAGES OF OCT
Depth resolution is independent of the sample beam aperture
High depth and traversal resolution
Contact-free and non-invasive operation
Coherence gate can substantially improve the probing depth in scattering media

17. APPLICATIONS OF OCT Ophthalmology Dentistry Dermatology
1717
APPLICATIONS OF OCT
Ophthalmology
Dentistry
Dermatology
Gastroenterology
Intra-Operating Surgery
Cancer Diagnosis
Non-medical OCT Applications

18. 1818

19. 1919
CONCLUSION
OCT is a new imaging modality somewhat comparable to ultrasound in that it provides structural information without ionizing radiation.
The depth of penetration is low compared to ultrasound.
Polarization sensitive and spectroscopic imaging mode allow additional information regarding the biological tissues to be imaged.
OCT has been used both in vivo and ex vivo.
It has also been used non-invasively as well as in minimally invasive in vivo imaging.

20. 2020
REFERENCE
1. D. C. Adler, T. H. Ko, P. R. Herz, and J. G. Fujimoto, Optical Coherence Tomography Contrast
Enhancement Using Spectroscopic Analysis with Spectral Auto- Correlation, Optics Express, pp..
2. Algorithms for Optical Coherence Tomography on TMS320C64x+ TI DSP (SPRABB7)
3. M. Brezinsky, Optical Coherence Tomography, Elsevier, 2006.
Optical Coherence Tomography Using a Single Line Scan Camera, Optics Express, pp