| Intravascular optical coherence tomography(IV-OCT), a newly developed interventional imaging modality, is used for diagnosing vascular diseases, especially coronary artery diseases. Motion artifacts, which are caused by periodic cardiac motion and pulsatile blood within the vascular lumen during continuous pullback(non-gated) image acquisition, lead to the misalignment of luminal cross sections between consecutive frames in a cross-sectional view and a saw-tooth-shaped vessel wall in a longitudinal view. They hinder visualization of longitudinal cuts, quantitative measurement of vascular morphology, and three-dimensional(3-D) vessel reconstruction.Methods for image-based retrospective gating and direct compensation of motion artifacts for non-gated IV-OCT image sequences are studied in this dissertation based on the comprehensive analysis of mechanism and presentation of motion artifacts. Regarding to the image-based gating, we select one frame per cardiac cycle to form a subsequence by tracking the cyclic change of the image intensity or the lumen contour along the overall sequence. As to the direct compensation, a rigid motion model of the vessel wall in each IV-OCT slice is first constructed. Then, the motion components due to cardiac motion are separated from those caused by the vascular geometry with spectral analysis. Finally, the cardiac motion components are compensated to suppress rigid motion artifacts. No frames are discarded and the integrity of the image sequence is ensured. Neither special ECG-gating image acquisition devices nor ECG signals are needed.Our methods have validated with clinically acquired image data. The results show that the artifacts caused by cardiac motion are reduced effectively and the visualization of the IV-OCT longitudinal view is improved. More accurate image data is provided for quantitative measurement of the vascular morphology, fusion of IV-OCT images with other vascular images, and three-dimensional reconstruction of vessels. |
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