Open-source low-cost cardiac optical mapping system

PLOS ONE RESEARCH ARTICLE Open-source low-cost cardiac optical mapping system Dmitry Rybashlykov1, Jaclyn Brennan2, Zexu Lin2, Igor R. Efimov2*, Roman Syunyaev ID1,3* 1 Human Physiology Lab, Moscow Institute of Physics and Technology, Moscow, Russia, 2 Department of Biomedical Engineering, The George Washington University, Washington DC, United States of America, 3 Sechenov University, Moscow, Russia a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Rybashlykov D, Brennan J, Lin Z, Efimov IR, Syunyaev R (2022) Open-source low-cost cardiac optical mapping system. PLoS ONE 17(3): e0259174. https://doi.org/10.1371/journal. pone.0259174 Editor: Alexander V. Panfilov, Universiteit Gent, BELGIUM Received: October 12, 2021 Accepted: February 23, 2022 Published: March 31, 2022 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0259174 Copyright: © 2022 Rybashlykov et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All optical mapping recordings files is available from the zenodo database DOI:10.5281/zenodo.5557829 Funding: The research was supported by Russian Foundation for Basic Research (https://www.rfbr. * (IRE); (RS) Abstract Fluorescent imaging with voltage- or calcium-sensitive dyes, known as optical mapping, is one of the indispensable modern techniques to study cardiac or neural electrophysiology, unsurpassed by temporal and spatial resolution. High-speed CMOS cameras capable of optical registration of action potential propagation are in general very costly. We present a complete solution priced below US$1,000 (including camera and lens) at the moment of publication with an open-source image acquisition and processing software. We demonstrate that the iDS UI-3130CP rev.2 camera we used in this study is capable of 200x200 977 frames per second (FPS) action potential recordings from rodent hearts, with the signal-tonoise-ratio of a conditioned signal of 16 ± 10. A comparison with a specialized MiCAM Ultimate-L camera has shown that signal-to-noise ratio (SNR) while lower is sufficient for accurate measurements of AP waveform, conduction velocity (± 0.04 m/s) and action potential duration (± 7ms) in mouse and rat hearts. We used 4-aminopyridine to prolong the action potential duration in mouse heart, thus demonstrating that the proposed system is adequate for pharmacological studies. Introduction An optical technique of measurements of cellular transmembrane voltage via potentiometric dyes was introduced in the 1970s, known today as optical mapping [1–4]. Potentiometric dye molecules bind to cell membranes and undergo either molecular motion or an electronic redistribution upon excitation and emission [5]. The changes of the external electrical field affect transition energy, corresponding emission spectrum can be detected and recorded. Further advances in the field include calcium-sensitive dyes (changing emission spectrum upon binding with calcium ions) [6], metabolic imaging (via intrinsic NADH and/or FAD fluorescence) [7], simultaneous mapping of voltage and calcium [8,9], simultaneous imaging from the several sides of the heart (panoramic mapping) [10,11], and transmural imaging via long wavelength dyes [12]. One notable advantage of optical mapping in comparison to traditional multielectrode arrays is high spatial and temporal resolution that makes it possible to accurately track the PLOS ONE | https://doi.org/10.1371/journal.pone.0259174 March 31, 2022 1 / 15 PLOS ONE ru/rffi/eng) grant 19-29-04111 (to RS) and Leducq Foundation (https://www.fondationleducq.org/) project RHYTHM (to IE). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: NO authors have competing interests. Open-source low-cost cardiac optical mapping system rapidly propagating excitation wavefronts in ventricular and atrial arrhythmias [13]. However high spatio-temporal resolution requires highly specialized cameras: 100x100 pixels, 1,000 frames per second (FPS) and digital image acquisition hardware. It typically has a high price of US$50,000–100,000. This price is prohibitively high for education and some research applications, for example, several cameras are required for multiparametric and panoramic optical mapping. Recently, high speed USB 3.0 machine vision-specialized industrial CMOS cameras entered the mass market eliminating the need for specialized data-acquisition systems and, thus, reducing the price of a fast imaging system. Previously, Lee et al. [14] have demonstrated that it is possible to optically map pig and rabbit hearts with relatively inexpensive ($600– 1200) CMOS cameras, as it was possible with inexpensive CCD cameras [15]. In particular, Lee et al. have shown that action potential (AP) recordings up to 1,000 Hz and SNR of up to ~50 (defined as (AP Amplitude)/(SD during diastolic intervals)) are possible in large animal hearts with USB3.0 iDS (Imaging Development Systems, GmbH) cameras. Unfortunately, this method was not applied to rodent models, which are much more popular models compared to pigs and rabbits, and not made available to the wider research community. In our open-source research and development presented here we used iDS UI3130CP-M-GL (~$700US including lens) and iDS Software Suite programming interface that makes it possible to customize image acquisition (Fig 1). Here, we demonstrate capabilities of action potential recordings in the two most popular laboratory animal models in cardiovascular research: rat and mouse hearts. Small rodent hearts are more challenging for optical recordings as compared to large animal hearts due to much lower optical signal intensity. We compared this inexpensive solution to the state-of-the-art MiCAM ULTIMA-L system, which has superior SNR (Fig 2), but at a much higher price approaching $100,000. New inexpensive optical mapping system provides sufficient quality data to track activation and repolarization sequences and action potential duration (APD). Materials and methods iDS UI-3130CP camera and software In this study we used a UI-3130CP camera from Imaging Development Systems, which is capable of 10-bit recordings at resolutions up to 800 by 600 pixels. The “uEye cockpit” image acquisition software provided by iDS has neither an option to save recordings in lossless format, nor an option to make 10-bit recordings. Therefore, we have developed a custom opensource image acquisition application using the (...truncated)