Abstract
Tissue dispersion could be used as a marker of early disease changes to further improve the diagnostic potential of optical coherence tomography (OCT). However, most methods to measure dispersion, described in the literature, rely on the presence of distinct and strong reflectors and are, therefore, rarely applicable in vivo. A novel technique has been developed which estimates the dispersion-induced resolution degradation from the image speckle and, as such, is applicable in situ. This method was verified experimentally ex vivo and was applied to the classification of a set of normal and cancerous colon OCT images resulting in 96% correct classification.
Highlights
Wavelength-dependent index of refraction variations are common in many materials giving rise to the phenomenon of dispersion
Dual optical fiber stretchers have been employed for dispersion compensation allowing some degree of tunability. These devices require large and complex hardware and are not very practical [5,6]. Another approach is numerical dispersion compensation based on the use of the Fractional Fourier transform (FrFT) which has served as a visual tool to highlight the physics behind dispersion compensation [7]
To demonstrate the applicability of the novel speckle-based method to human tissues, the technique was applied to Optical Coherence tomography (OCT) images of normal and cancerous colon obtained from patients who were scheduled for surgical excision of their tumors
Summary
Wavelength-dependent index of refraction variations are common in many materials giving rise to the phenomenon of dispersion. For example, is to insert a fused-silica prism pair, with faces contacted and index matched, in the reference arm, to form a variable-thickness window This method is usually only practical for compensating dispersion of up to second order [1,2,3]. Three main methods are described in the literature for estimating the dispersion from OCT images: (i) measuring the degradation of the PSF [13,14], (ii) measuring the shift (walk-off) between images taken at different center wavelengths [15], and (iii) calculating the second derivative of the phase of the spectrum [16,17] These methods require that a strong, distinct, reflector is present in the image which is rarely the case in tissue. The proposed method was verified ex vivo and its applicability to cancer diagnosis was evaluated on a small set of gastrointestinal (GI) normal and adenocarcinoma OCT images
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