Experimental validation of predicted temperature rises in tissue-mimicking materials

Area of Science:

• Medical Physics
• Biomedical Engineering
• Acoustics

Background:

• Diagnostic ultrasound can induce significant tissue temperature rises, potentially causing thermal damage.
• Existing thermal prediction models often oversimplify in vivo conditions and acoustic physics.
• Experimental verification of ultrasound-induced heating, especially for focused beams, is limited.

Purpose of the Study:

• To develop and utilize a measurement system for directly quantifying temperature increases in tissue-mimicking materials exposed to diagnostic ultrasound.
• To validate existing theoretical models and safety guidelines for ultrasound thermal effects.
• To investigate the accuracy of the National Council on Radiation Protection and Measurements (NCRP) and American Institute of Ultrasound in Medicine/National Electrical Manufacturers Association (AIUM/NEMA) soft-tissue models.

Main Methods:

• Development of a measurement system using thin-film thermocouples for non-invasive temperature monitoring.
• Acquisition of temperature rise data in tissue-mimicking materials using transducers (2-10 MHz frequency, 1-3 mm focal beam-widths).
• Comparison of experimental measurements with theoretical predictions and established safety models (NCRP, AIUM/NEMA).

Main Results:

• Measurements closely align with theoretical predictions utilizing measured or simplified Gaussian beam profiles.
• The NCRP formula predictions were, on average, 15% higher than measured values, supporting its role as a conservative safety model.
• The AIUM/NEMA formula predictions were, on average, 30% lower than measured values, indicating potential underestimation of thermal effects.

Conclusions:

• The developed measurement system provides a reliable method for assessing ultrasound-induced heating in tissue.
• Experimental data validates theoretical models and highlights discrepancies in current safety guidelines.
• Findings suggest a need to review and potentially revise the AIUM/NEMA model for more accurate thermal risk assessment in diagnostic ultrasound.