6
Speckle in Optical Coherence Tomography
Andrea Curatolo, Brendan F. Kennedy
Optical+Biomedical Engineering Laboratory (OBEL), School of Electrical, Electronic and Com-
puter Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, Western
Australia, Australia
David D. Sampson
Optical+Biomedical Engineering Laboratory (OBEL), School of Electrical, Electronic and Com-
puter Engineering, and Centre for Microscopy, Characterisation and Analysis, The University of
Western Australia, 35 Stirling Highway, Crawley, Western Australia, Australia
Timothy R. Hillman
Optical+Biomedical Engineering Laboratory (OBEL), School of Electrical, Electronic and Com-
puter Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, Western
Australia 6009, Australia
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
6.2 OCT Speckle Characteristics in the Single Scattering Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
6.3 OCT Speckle Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
6.4 OCT Image Formation Using Singly Backscattered Light: Linear System Framework . . . . . 226
6.5 OCT Image Formation: Multiple Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
6.6 Retrieving Information from Speckle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
6.7 Mitigation of OCT Speckle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
6.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Optical coherence tomography (OCT) is a biomedical imaging modality that produces high-resolu-
tion cross-sectional images of tissues, using infrared light and low-coherence interferometry. For a
thorough discussion of OCT, please refer to Chapter 5. As OCT is a coherent modality, its images
are corrupted by speckle, giving them a grainy or mottled appearance.
In this chapter, we discuss OCT speckle in detail. In Section 6.1, we start with a brief overview
of speckle and its main characteristics, as discussed in the copious literature on the phenomenon.
In Section 6.2, we introduce a simple model of OCT image formation in the single-backscattering
regime. This permits us to define speckle and to understand its most important properties as a
fundamental characteristic of coherent imaging.
In Section 6.3, classification of different types of speckle are provided based on situations for
which the model of Section 6.2 is not applicable, leading to different statistics of speckle when
treated as a s tochastic phenomenon. Both first- and second-order statistics are described in order to
quantify the extent to which speckle is a corrupting influence on the image. In the former case, the
magnitude of the speckle fluctuations is assessed us ing the contrast ratio. In the latter case, speckle
size is assessed by virtue of the speckle correlation coefficient. To calculate the speckle correlation
211

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