Frequency Domain Photoacoustic Signal Analysis for Temperature Sensing

Abstract

Monitoring temperature in biological tissue is vital for different therapy applications like photo-thermal therapy, high-intensity focused ultrasound therapy, etc. Photoacoustic imaging has been used for volumetric temperature imaging in the time domain. In this thesis, we analyzed the photoacoustic (PA) signals in the frequency domain as a function of temperature and explored the possibility of measuring the absolute temperature of the medium being investigated. Photoacoustic magnitude ratios and phase differences were used to measure the absolute temperature of the sample. Further, the magnitude ratio and phase difference corresponded well with the analytical solution and numerical simulations. Multiple measurements were performed to compare the differences between the estimated and ground truth temperatures (measured using a thermal camera). The results indicate that the estimated temperatures were accurate, with mean error ranging between 0.6°C - 1°C (clinically acceptable) with phantoms and ex-vivo samples.