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Title: Correction of Motion Artifacts in Whole Heart Optical Mapping Data Using Ratiometry and Image Processing Techniques
Author: Rodriguez Ramirez, Marcela Patricia
Advisor: Nygren, Anders
Keywords: Engineering--Biomedical;Engineering--Electronics and Electrical
Issue Date: 22-Dec-2015
Abstract: Cardiac optical mapping is a powerful tool to understand the electrophysiological mechanisms responsible for normal and abnormal cardiac rhythm. However, motion artifacts contained in the optical action potentials (APs) represent a major drawback of the technique. The calculation of electrophysiological parameters of interest such as action potential duration (APD) is challenged by the presence of motion artifacts. The use of chemical motion blockers is currently a preferable method to control motion artifacts, however these may affect the cardiac electrophysiology and consensus regarding their effects has not been reached. This thesis presents several key developments in techniques for motion artifact correction. Weighted ratiometry was implemented aiming to reduce motion artifacts in dual wavelength recordings. This thesis reports differences in shape and amplitude between motion artifacts contained in corresponding APs at both wavelengths. A new mathematical representation for motion artifacts is also presented to model such differences. Gross motion artifacts due to misalignment of the preparation with the imaging sensor across time are the result of the mechanical contraction of the heart. Landmark-based image registration is introduced to correct for such artifacts. It was concluded that the use of scale invariant feature transform (SIFT) is preferable for the datasets presented among the techniques evaluated for motion estimation. Several landmark-based non-rigid registration methods are studied in this thesis and their performance compared; coherence point drift (CPD) algorithms performed better for this application. Image registration resulted in good correction of gross motion artifacts, however artifacts with other origins must be handled separately. The combination of weighted ratiometry and landmark-based non-rigid registration is also evaluated as a composite method to further reduce artifacts that the techniques were not able to correct individually. The technique produced good correction and APDs calculated from the corrected datasets present low error values compared to a gold standard. APD modulation with 4-Aminopyridine served as a tool to corroborate that the combination of weighted ratiometry and image registration is able to reduce motion artifacts in APs to the point where APD can be calculated and the modulation of APD quantified.
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