OCT A-scan Processing Pipeline in MATLAB

This repository presents a MATLAB implementation of a spectral-domain OCT A-scan processing pipeline using synthetic data.
The goal is to demonstrate the core signal-processing steps required to reconstruct depth-resolved OCT signals and to visualize the effect of each key step.

The pipeline is implemented as a live MATLAB script (.mlx). In particular, dispersion phase mismatch and compensation are explained in detail in the script, including the mathematical background and intuition.

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Overview of the Pipeline

The processing chain demonstrated in this project includes:

• Synthetic OCT interferogram generation for multiple reflectors
• k-linearization (resampling to uniform wavenumber spacing)
• DC (background) removal
• Apodization using a Hann window
• Dispersion phase mismatch simulation and compensation
• FFT-based depth reconstruction
• Conversion from frequency domain to physical depth (mm)

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Key Demonstrations and Results

1. Effect of k-linearization

FFT-based depth reconstruction requires uniform sampling in wavenumber (k).
This figure compares the A-scan magnitude obtained with and without k-linearization.

Without k-linearization, reflector peaks are broadened and distorted.
After resampling to a uniform k-grid, peaks become sharper and correctly localized.

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2. Effect of DC Removal

The OCT interferogram contains a strong DC (background) component that appears as a dominant low-depth peak in the FFT.

Subtracting the mean suppresses the DC peak and improves visibility of the true depth-resolved signal.

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3. Effect of Hann Window (Apodization)

Finite-length interferograms introduce sidelobes in the depth profile.
Applying a Hann window reduces sidelobes at the cost of slight axial resolution loss.

This tradeoff is clearly visible in the depth-domain FFT magnitude.

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4. Final A-scan with Physical Depth Axis

After k-linearization, DC removal, windowing, and dispersion compensation, the FFT result is converted to a physical depth axis.

The reconstructed A-scan correctly recovers the reflector depths used in the synthetic model.

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Notes

• Synthetic data is used to allow full control over reflector positions and dispersion effects.
• Dispersion compensation is described in detail inside the live script, including the mathematical model (quadratic and cubic phase terms) and how the compensating phase is applied.
• The depth axis assumes uniform k-spacing and vacuum propagation; refractive index effects can be incorporated if needed.

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Files

• oct_ascan_processing.mlx
  Live MATLAB script containing the full pipeline, detailed dispersion explanation, and visualizations.

• Figures/
  Key result figures used in this README.

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Requirements

• MATLAB (tested with recent versions)
• Signal Processing Toolbox (for hilbert and window functions)

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🧑‍💻 Author

Arman Rajaei