Detection of thermal acoustic radiation from laser-heated deep tissue

Abstract

A multichannel acoustic antenna with a linear piezoelectric transducer array was developed to detect thermal acoustic radiation from a deep-lying sample zone heated by laser. A cw Nd:YAG laser (wavelength, 1064 nm; power, 1 W) was used as the thermal source. An optical fiber was inserted into the sample (beef liver) to deliver laser radiation into the deep zone and to heat the area around the fiber tip through absorption. The experiments demonstrated the capability of a new device for real-time monitoring of internal temperature at depths up to 3.5 cm with a spatial resolution of about 5 mm and a sensitivity of about 0.5 K. It is shown that experimental data can be used to visualize heat diffusion effects in deep-lying zones and the spatial position of the fiber tip, and to quantitatively estimate thermal diffusivity and acoustic and optical absorption coefficients. In addition to its laser applications, the described technique could be a promising tool for monitoring temperature distribution at the deposition of an alternative external energy (microwave, focused ultrasound, etc.) in deep-lying tissues.