Non-invasive Photoacoustic Temperature Measurement and Processing with Correlation Coefficient (R2) Linearity of 0.99

Photoacoustic (PA) combines the high contrast of optical imaging with the deep penetration of ultrasound imaging, making it an ideal non-invasive method for deep tissue imaging and temperature measurement. However, traditional attribute to that the nonlinearity of PA signal intensity with respect to temperature changes is primarily caused by the variation of the Grüneisen coefficient (Γ) contrarily, recent studies suggest that Γ remains linear in ultrapure water over typical experimental temperature ranges used in PA experiments, conflicting with previous conclusions. In this study we focus on ultrapure water with a linearly varying Γ in the temperature range of -6°C to 30°C. The dependence of optical absorption on temperature was found to be contingent upon the operational waveband, thereby informing the selection of the experimental wavelength. Results revealed that the variation of PA signal intensity is primarily governed by optical absorption properties, which are significantly influenced by wavelength. At a wavelength with highly linear absorption characteristics (960 nm), the PA signal exhibited a linear correlation with temperature, achieving a correlation coefficient (R²) of 0.9961 at a depth of 1 cm, demonstrating its potential as a reference for precise temperature calibration.Clinical Relevance-no clinical relevance needs to be declared.