Possible temperature effects computed for acoustic microscopy used for living cells

Area of Science:

• Biophysics
• Acoustic Microscopy
• Cellular Imaging

Background:

• High-frequency ultrasound microscopy (GHz) enables advanced biological applications.
• Potential temperature increases from focused ultrasonic beams pose a risk to living cells.
• Limited data exists on local temperature rises due to nonlinear propagation effects at GHz frequencies.

Purpose of the Study:

• To numerically compute temperature distributions in a water medium simulating living cells at 1 GHz.
• To investigate the influence of nonlinear propagation effects and transducer power on temperature increases.
• To assess the impact of water absorption and repetition frequency on thermal effects.

Main Methods:

• Numerical solution of temperature distributions at 1 GHz using water as a model for acoustic parameters.
• Simulation of high (0.32 W) and low (0.002 W) transducer powers.
• Calculation of pressure distributions and effective focal radius for fundamental and harmonic frequencies.

Main Results:

• Focal temperature increase reached 14°C at 10 MHz repetition frequency and 0.32 W transducer power.
• Maximum temperature increase of 20°C occurred at the sapphire lens-water boundary.
• Water's high absorption significantly suppressed focal temperature peaks; temperature increases are proportional to repetition frequency.

Conclusions:

• At practical repetition frequencies (e.g., 0.1 MHz), temperature increases are substantially lower.
• Lower transducer power (0.002 W) resulted in approximately 140 times lower temperature increases compared to high power.
• Effective focal radius was 1.1 µm at 1 GHz and 0.7 µm for the second harmonic, independent of transducer power.