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Steady state temperature rise in multilayered tissue due to arbitrary periodic SAR using finite difference FFT and
Gregory B Gajda1, Jonathan Paradis1, Eric Lemay1
1Non-ionizing Radiation Physical Sciences Division, Consumer and Clinical Radiation Protection Bureau, Health Canada, 775 Brookfield Rd., Ottawa, Ontario, K1A 1C1, Canada.
Biomedical Physics & Engineering Express
|June 2, 2021
Summary
This study presents an efficient method to calculate tissue temperature rise from pulsed radiofrequency exposure. The technique uses the Fast Fourier Transform (FFT) to analyze complex specific absorption rate (SAR) waveforms, crucial for safety guidelines.
Area of Science:
- Biophysics
- Electromagnetic dosimetry
- Thermal modeling
Background:
- International exposure guidelines for radiofrequency (RF) rely on understanding steady-state (SS) and transient tissue temperature rise.
- Periodically pulsed exposures present unique challenges due to oscillating temperature profiles.
- Accurate thermal modeling is essential for setting safe RF exposure limits.
Purpose of the Study:
- To develop an efficient computational method for determining tissue temperature rise under periodic specific absorption rate (SAR) modulation with arbitrary waveforms.
- To provide a versatile tool for analyzing thermal effects of pulsed RF exposure relevant to international safety standards.
Main Methods:
- Utilized a finite difference solution of the Pennes Bioheat Transfer Equation (BHTE).
- Employed the transfer function concept combined with the Fast Fourier Transform (FFT) to convert the time-dependent BHTE into a steady-state harmonic version.
- Calculated temperature response by taking the inverse FFT of the product of the transfer function and the FFT of the SAR waveform.
Main Results:
- The developed method efficiently computes tissue temperature rise for various periodic SAR modulation waveforms (rectangular, triangular, cosine).
- Demonstrated the method's versatility by calculating temperature-rise crest factor as a function of pulse duty factor and repetition frequency.
- The transfer function's slow variation with harmonic number allows for computational efficiency through interpolation and extrapolation.
Conclusions:
- This FFT-based transfer function approach provides a highly efficient and versatile method for calculating tissue temperature rise from pulsed RF exposure.
- The technique is particularly advantageous for scenarios requiring repeated temperature-rise calculations with parameter variations in the SAR waveform.
- The findings support the refinement of exposure guidelines by offering a robust tool for thermal effect assessment.
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