Ultrasonography.  2023 Apr;42(2):249-258. 10.14366/usg.22171.

High-contrast spectroscopic photoacoustic characterization of thermal tissue ablation in the visible spectrum

• Song H
• Song TK
• Kang J

• KMID: 2540927
• DOI: http://doi.org/10.14366/usg.22171

Abstract

Purpose
High-contrast tissue characterization of thermal ablation has been desired to evaluate therapeutic outcomes accurately. This paper presents a photoacoustic (PA) characterization of thermal tissue ablation in the visible spectrum, in which higher light absorbance can produce spectral contrast starker than in the near-infrared range.
Methods
Ex vivo experiments were performed to measure visible PA spectra (480-700 nm) from fresh porcine liver tissues that received a thermal dose in a range of cumulative equivalent minutes at 43°C (CEM₄₃). The local hemoglobin lobe area between 510-600 nm and wholespectral area under the curve were evaluated to represent the transition of hemoglobin into methemoglobin (MetHb) in the target tissue.
Results
The thermal process below an estimated therapeutic CEM₄₃ threshold (80-340 minutes) presented a progressive elevation of the PA spectrum and an eventual loss of local hemoglobin peaks in the visible spectrum, closer to the MetHb spectrum. Interestingly, an excessive CEM43 produced a substantial drop in the PA spectrum. In the spectral analysis, the visible spectrum yielded 13.9-34.1 times higher PA sensitivity and 1.42 times higher contrast change than at a near-infrared wavelength.
Conclusion
This novel method of PA tissue characterization in the visible spectrum could be a potential modality to evaluate various thermal therapeutic modalities at high-contrast resolution.

Keyword

Spectroscopic; Photoacoustic; Thermal ablation; Tissue characterization; Visible spectrum