Upper Limit for Angular Compounding Speckle Reduction

Previous studies of angular compounding for speckle reduction in optical coherence tomography may not have fully accounted for optical aberrations, which produce unintended spatial averaging and concomitant loss of spatial resolution. We accounted for such aberrations by aligning our system and measuring distortions in the images, and found that speckle reduction by angular compounding was limited. Our theoretical analysis using Monte Carlo simulations indicates that \"pure\" angular compounding over 13{degrees} (our full numerical aperture) can improve the signal-to-noise ratio by no more than a factor of 1.5, significantly lower than values reported in literature. Analysis suggests that illuminating only part of the lens to further reduce speckle also involves a trade-off with resolution roughly equivalent to spatial averaging. We conclude that angular compounding provides substantially less benefit than previously expected.