Baseline Wandering Removal in Optical Mapping Measurements With PID Control in Phase Space

Optical imaging methods on ex-vivo hearts have had large impact in furthering our understanding of cardiac electrophysiology. One common problem in this method is a baseline wandering of the fluorescence signals over time, caused by dye photo-bleaching, small variation of the excitation light source, or other similar artifacts. Due to its relative magnitude, the removal of baseline wandering can be a nontrivial task and has major implications for analyzing important physiological dynamics such as traveling waves and alternans. Here we present a computational technique for the removal of such baseline wandering based on Proportional-Integral-Derivative (PID) closed loop feedback. The PID method applied a continuous control stimulus to the input Vm based on an error value which is defined by Euclidean distance from a pre-computed setpoint in phase space. We quantify and validate the PID control method by adding a linear combination of arbitrary sinusoidal drift, of frequency less than the signal pacing frequency, to the system signal Vm. The PID control loop effectively removed the baseline wandering with minimal degradation to the input Vm, and thus provides a viable tool for baseline wandering removal when implemented in an appropriate phase space. The computational simplicity of the method also lends itself to implementation in embedded systems, such as Arduinos and Raspberry-Pis.