Abstract
Speckle is an intrinsic noise of interferometric signals which reduces contrast and degrades the quality of optical coherence tomography (OCT) images. Here, we present a frequency compounding speckle reduction technique using the dual window (DW) method. Using the DW method, speckle noise is reduced without the need to acquire multiple frames. A ~25% improvement in the contrast-to-noise ratio (CNR) was achieved using the DW speckle reduction method with only minimal loss (~17%) in axial resolution. We also demonstrate that real-time speckle reduction can be achieved at a B-scan rate of ~21 frames per second using a graphic processing unit (GPU). The DW speckle reduction technique can work on any existing OCT instrument without further system modification or extra components. This makes it applicable both in real-time imaging systems and during post-processing.
Highlights
Optical coherence tomography (OCT) has been proven to be a successful tool for imaging through highly scattering media, such as biological tissues, with high resolution
Frequency compounding is achieved by processing each A-scan with multiple narrow spectral windows each with independent speckle realizations which are combined, Significantly, there is minimal loss of axial resolution by using the Dual Window (DW) approach where each low-resolution windowed image is multiplied by the full-bandwidth image
The contrast-to-noise ratio (CNR) were calculated to be 4.27 dB and 6.24 dB before and after DW speckle reduction (DW-SR), respectively. This means that a ~25% (1.97 dB) increase in CNR was achieved by using the DW-SR method
Summary
Optical coherence tomography (OCT) has been proven to be a successful tool for imaging through highly scattering media, such as biological tissues, with high resolution. Frequency compounding techniques are powerful tools for speckle suppression, but result in images with reduced axial resolution since the total spectral bandwidth is divided into narrow bands to create uncorrelated speckle patterns. Narrow spectral windows (Δλ1) evenly spaced in k-space were used to create multiple images with uncorrelated speckle patterns These images were averaged to suppress speckle noise. The DW method was used to process the same interferometric data with 30 nm windows, and we found out that the FWHM of the mirror peak was degraded to 4.4 μm. The axial resolution imaging through the highly scattering sample was characterized by measuring the FWHM of the mirror peak. A FWHM of 7.5 μm was measured using the full bandwidth of the system As expected, for both the DW and STFT methods, a wider spectral window generally provides better axial resolution. Good axial resolution (< 30 μm) is retained by the DW method even using spectral windows as narrow as 5 nm
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