Photon Diffusion Attenuation Length in Tyrode and Blood-Perfused Myocardial Tissue

Abstract

Photon attenuation length (δ) in biological tissues determines interrogation depth, spatial resolution, and amplitude of fluorescence signal in various types of optical imaging, including imaging of cardiac excitation using voltage-sensitive dyes. We assessed δ in human and pig myocardium at excitation/emission wavelengths of commonly used and recently developed near-infrared voltage-sensitive dyes. We also compare δ in Tyrode vs blood-perfused tissues and simulate respective voltage-sensitive fluorescent signals in the context of potential clinical applications (in vivo optical mapping of heart electrical activity). Experiments were conducted in isolated slabs of ventricular myocardium. Light decay inside the tissue was measured via a 600μm diameter optrode at 520, 650, and 715nm. The δ was determined by fitting data to a theoretical formula for light attenuation [Mitrea et al. 2009].View Large Image | View Hi-Res Image | Download PowerPoint SlideFor wavelengths tested, (see table) the δ in porcine and human myocardium are similar, which makes porcine myocardium a good model for development of clinical imaging applications. Blood perfusion reduces δ, particularly at 520nm. However, our simulations show that, the resulting reduction of optical action potential is <16% (for NIR dyes). which would not be a major impediment for in vivo imaging of cardiac excitation.