Polarization-based Optical System for Myocardial Tissue Characterization

The study by Global Burden of Diseases (GBD) reports that cardiovascular diseases are the leading cause of mortality globally, with rheumatic heart disease (RHD) and myxomatous valve disease (MVD) responsible for significant disability and fatalities damaging heart valves, leading to regurgitation or stenosis, and fibrosis [1]. Extensive literature highlights that changes in heart tissue constituents significantly alter their optical properties, serving as crucial biomarkers for diagnosis [2], [3]. However, current diagnostic tools do not characterize myocardial tissues as healthy or fibrotic. This clinical need is met by developing an optical system integrated with an optical fiber-based probe to perform real-time and precise characterization of healthy and fibrotic myocardial tissues, facilitating quicker and more accurate diagnosis. Fig. 1 illustrates the schematic of the developed optical system, which includes transmission and reception polarization modules connected by a probe. In the transmission module, the laser diode's light is collimated and focused through a linear polarizer onto the transmission fiber. The reflected light from heart tissue passes through the probe into the reception polarization system, where it is focused onto the photodetector. The developed system utilizes Mueller matrix polarimetry to analyze the polarization properties of the tissue sample and different Mueller matrix components, which provide valuable insights into tissue heterogeneity. Heart tissue samples were collected from three distinct groups of human subjects: Healthy (samples from cadaver bodies), patients with RHD, and MVD (samples excised during endomyocardial biopsy). The study adhered to the protocols outlined by the institutional ethics committees at Indian Institute of Science (IHEC No: 04/20.02.2024) and at Sri Jayadeva Institute of Cardiovascular Sciences and Research (Ref: SJIR/EC/2024-25/07). The experiments were performed on the left and right ventricle tissues excised from N=5 healthy, N=5 RHD, and N=5 MVD subjects. The measured optical parameters were anisotropy degrees (t1,t2), normalized anisotropy (A), and depolarization coefficient (b). Fig. 2 compares the optical parameters obtained for Healthy versus RHD, Healthy versus MVD, and RHD versus MVD groups, respectively. All four optical parameters (t1, t2, A, b) were statistically significant in delineating myocardial tissues of healthy from RHD subjects. The healthy and MVD groups can be distinguished based on normalized anisotropy. Additionally, anisotropy degree (t2) and depolarization coefficient were statistically significant in delineating fibrotic tissues excised from RHD and MVD subjects, with p-values of 0.0432 and 0.0232, respectively. These findings are attributed to heart tissue constituents that significantly alter their optical properties and heterogeneity, such as the accretion of collagen in extracellular matrix of fibrotic tissues [3], [4]. Future research will extend these findings by analyzing a larger tissue sample cohort for validation. Adopting such an optical polarimetry-based system provides additional insights to the cardiothoracic surgeon to make an informed assessment. It is envisaged that the proposed technology has the potential to transform cardiac care and improve patient outcomes, thus reducing the global burden of heart diseases.