Abstract

In this study, the capability of a photoacoustic (PA) method in detecting high-intensity focused ultrasound (HIFU) thermal lesions was investigated in chicken breast tissue in vitro and the optical properties of the HIFU-treated and native tissues were determined. Created with a 1-MHz HIFU transducer, the detectability of the induced thermal lesions was assessed photoacoustically at 720 and 845 nm and their optical properties were characterized in the wavelength range 500-900 nm. The results show that the averaged ratio of the peak-to-peak PA signal amplitude of HIFU-treated tissue to that of native tissue is more than 3 fold. The optical spectroscopy investigation revealed that the absorption and reduced scattering coefficients are higher for HIFU-treated tissues than native tissues. This work demonstrates the capability of the PA method in detecting HIFU-induced thermal lesions due, in part, to the increase in their optical absorption coefficient, reduced scattering coefficient, and deposited laser energy fluence.

Highlights

  • High-intensity focused ultrasound (HIFU) is a bloodless surgical modality that is capable of inducing thermal and mechanical effects in deep-seated regions of interest (ROI) selectively and non-invasively.[1]

  • Our spectroscopic investigation has shown that high-intensity focused ultrasound (HIFU)-treated tissues have a greater optical absorption and reduced scattering coefficients than native tissues in the wavelength range of 500-900 nm

  • Based on our spectroscopic investigation, we conclude that the observed PA contrast between HIFU-induced thermal lesions and untreated tissue is due, in part, to the increase in the optical absorption coefficient, the reduced scattering coefficient and, the deposited laser energy fluence in HIFU-treated tissues

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Summary

Introduction

High-intensity focused ultrasound (HIFU) is a bloodless surgical modality that is capable of inducing thermal and mechanical effects in deep-seated regions of interest (ROI) selectively and non-invasively.[1]. Using a high-power focused transducer, HIFU beams can be achieved and focalized within the transducer’s focal zone in order to deposit acoustic energy in the ROI with minimal or no harm to intervening tissue layers. The spatially-confined, coagulated tissue volumes are termed thermal lesions,[3] since the predominant mechanism of HIFU is thermal, cavitation and boiling bubbles are involved in the formation and shaping of the induced thermal lesions,[2] at higher temperatures. HIFU therapy demonstrated a great potential for oncological applications including treatments of tumours in the prostate,[10–12] breast fibroadenoma,[13] uterine fibroids,[14], kidney,[12], liver,[12], bladder,[18] bone,[19, 20] and brain.[21, 22]. HIFU has been explored for various therapeutic applications including, but not limited to, hemostasis,[4, 5] neurology and pain management,[6] cosmetic surgery,[7] and ophthalmology.[8, 9] HIFU therapy demonstrated a great potential for oncological applications including treatments of tumours in the prostate,[10–12] breast fibroadenoma,[13] uterine fibroids,[14], kidney,[12], liver,[12], bladder,[18] bone,[19, 20] and brain.[21, 22] Oncologic and other applications of HIFU are expected to expand with the development of optimized imaging techniques that can provide realtime HIFU treatment monitoring, evaluation, and control

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