Image-based motion correction for optical mapping of cardiac electrical activity.

Optical mapping, with membrane-bound, voltage-sensitive dyes, is widely used for in vitro recording of cardiac electrical activity. The spatial registration of such maps is lost when the heart moves with respect to a fixed photodetector array and contraction can generate substantial artifact if background fluorescence is not uniformly distributed. While motion artifact is commonly suppressed with electromechanical uncoupling agents, there are circumstances where these are undesirable. This study outlines a novel image-based approach for retrospective motion artifact correction. Isolated Langendorff-supported rat hearts (n = 8), stained with di-4-ANEPPS, were illuminated at 516 ± 14 nm and fluorescent emission (>565 ± 10 nm) was acquired with a charge multiplying CCD camera. Background fluorescence was segmented in successive frames and stabilized using a non-rigid image registration algorithm. The resultant image deformation was used to estimate material point movement on the heart surface, so that total fluorescence could be mapped frame-by-frame to appropriate reference pixels. Finally, residual motion artifact was identified and removed. The effectiveness of this correction method was evaluated over 18 experimental datasets. Signal-to-noise ratio was increased more than fourfold, and activation time and action potential duration (APD) could be estimated at 24% more pixels than in the raw data. The variability of all APD measures was substantially reduced (i.e. APD50 estimated as 83.8 ± 45.8 ms before correction was 52.1 ± 4.7 ms afterward). This approach provides a robust means of recovering optical action potentials in the presence of substantial motion artifact.

Characteristics of motion artifacts in cardiac optical mapping studies.

Motion artifacts are one of the issues in cardiac optical mapping studies. This paper is focused on the description of the motion artifacts caused by planar movement. The theory of its origin and possibilities of its suppression is described. The suppression of the motion artifacts is based on image registration techniques. There are introduced the characteristics about influence of the weighted area averages on presence of these artifacts. In this study conventional pharmacological or mechanical ways of motion artifacts suppression were not involved.