![]() 10 In other studies, adjacent A-lines or frames have been registered by maximizing crosscorrelation between the speckle in adjacent search regions. 8, 9 Reflections from the sheath or optical components of the catheters can also be used for correcting rotational fluctuations caused by NURD. Structural landmarks, or fiducial markers, have been used to register successive frames using extrinsic objects. Several techniques have been proposed to correct NURD in catheter-based OCT systems. Understanding and correcting motion artifacts may improve image quality and subsequent interpretation. ![]() Moreover, due to the difficulty in fabricating perfectly balanced micromotors, NURD can still degrade image quality. Catheters using micromotors to directly rotate the optical assembly are expected to have less severe NURD artifacts compared to proximally driven torque cable catheters 8 however, the miniaturization of these catheters to access the narrowest organ sites is limited by the relatively large size of the motor. Cardiac and respiratory motion artifacts can be reduced to some degree by decreasing the image acquisition time, but even then there remains a need to compensate for NURD artifacts. 4 Cardiac and breathing motion artifacts are more prominent when the heartbeat and respiratory periods are much shorter than the total data acquisition time. Successful application of catheter-based OCT for in vivo pulmonary imaging requires overcoming several challenges including motion artifacts associated with the cardiac cycle, breathing, and nonuniform rotation distortion (NURD), that make identification of structures such as blood vessels difficult. Our group has previously reported a combined endoscopic OCT–AFI instrument using a double-clad fiber (DCF) catheter that is capable of detecting pulmonary nodules and vascular networks. 2, 6, 7 Therefore, combined OCT–AFI systems can produce complementary information that may enable increased detection and characterization of structural and functional features associated with different lung diseases. 1 – 5 Specifically in the lung, OCT can visualize distal airway tissue structures at high resolution and when combined with autofluorescence imaging (AFI), can probe specific molecular components of airway tissue such as collagen and elastin. Catheter-based systems for in vivo clinical imaging have been developed for cardiology, gastroenterology, and pulmonology. In order to access these highly constrained and hard-to-reach areas, OCT systems are often catheter based. 1 OCT applications are currently being developed for many organs, including the small distal airways of the lung. Optical coherence tomography (OCT) is a three-dimensional (3-D) imaging modality providing high-resolution and high-speed volumetric images with depth of penetration in tissue on the order of a millimeter, which has become more common in clinical and biomedical applications due to the ability to resolve diagnostically relevant features.
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