Characterization of the Optical and Thermal Properties of Cardiac Tissue as a Function of Temperature

Abstract

In this work, we devised the first characterization of the optical and thermal properties of ex vivo cardiac tissue as a function of different selected temperatures, ranging from room temperature to hyperthermic and ablative temperatures. The broadband (i.e., from 650 nm to 1100 nm) estimation of the optical properties, i.e., absorption coefficient (μa) and reduced scattering coefficient (μ's), was performed by means of timedomain diffuse optics. Besides, the measurement of the thermal properties was based on the transient hot-wire technique, employing a dual-needle probe to estimate the tissue thermal conductivity (k), thermal diffusivity (α), and volumetric heat capacity (Cv). Increasing the tissue temperature led to variations in the spectral characteristics of μa (e.g., the redshift of the 780 nm peak, the rise of a new peak at 840 nm, and the formation of a valley at 900 nm). Moreover, an increase in the values of μ's was assessed as tissue temperature raised (e.g., for 800 nm, at 25 °C μ's= 9.8 cm -1 , while at 77 °C μ's= 29.1 cm -1 ). Concerning the thermal properties characterization, k was almost constant in the selected temperature interval. Conversely, α and Cv were subjected to an increase and a decrease with temperature, respectively; thus, they registered values of 0.190 mm 2 /s and 3.03 MJ/(m 3 •K) at the maximum investigated temperature (79 °C), accordingly. Clinical Relevance-The experimentally obtained optical and thermal properties of cardiac tissue are useful to improve the accuracy of simulation-based tools for thermal therapy planning. Furthermore, the measured properties can serve as a reference for the realization of tissue-mimicking phantoms for medical training and testing of medical instruments. I. INTRODUCTIONAccurate information on the physical properties of biological tissues is fundamental for improving diagnostic and therapeutic procedures and medical treatments. Hence, many efforts have been devoted, in the field of bioengineering, to the evaluation of optical, thermal, mechanical, and dielectric properties of biological media [1], [2]. In this regard, the investigation of the optical and thermal behavior of tissues is pivotal for the realization of tissue-mimicking materials [3], [4], employed for fine-tuning and the pre-clinical testing of medical devices, as well as for medical training, and the implementation of numerical models for therapy preplanning. These models are indeed useful to foresee the outcome of interventional procedures and select the best treatment strategy [5]- [7]. However, their accuracy and prediction capabilities