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Parametric dependence of SAR on permittivity values in a man model
P Gajsek1, W D Hurt, J M Ziriax
1Air Force Research Laboratory, Directed Energy Bioeffects Division, Brooks AFB, TX 78235, USA.
IEEE Transactions on Bio-Medical Engineering
|October 5, 2001
Summary
Variations in dielectric properties of human tissues significantly impact localized specific absorption rate (SAR) values, but not whole-body SAR. Conductivity is a more critical factor than dielectric value for energy absorption in tissues.
Area of Science:
- Electromagnetics and Computational Biology
- Bioelectrics and Dosimetry
Background:
- Advanced 3D digital anatomical models are crucial for calculating specific absorption rate (SAR) values.
- Understanding the influence of model parameters, such as permittivity, on SAR is essential for accurate dosimetry.
Purpose of the Study:
- To investigate how variations in permittivity (dielectric value and conductivity) affect predicted whole-body and localized SAR values in a 3D human model.
- To determine the sensitivity of SAR values to changes in tissue permittivity across various frequencies and orientations.
Main Methods:
- Utilized a 3-mm-resolution 3D human model with 39 tissue types.
- Adjusted permittivity values for all tissues simultaneously and independently for key tissues (muscle, fat, skin, bone marrow).
- Employed finite-difference time-domain (FDTD) code to calculate normalized SAR values under far-field conditions at multiple frequencies (70-2060 MHz) and orientations (E, K, H).
Main Results:
- Variability in permittivity did not substantially influence whole-body SAR values.
- Localized SAR values were significantly affected by changes in permittivity, especially in tissues with large mass like muscle.
- Conductivity was found to be a more substantial factor than dielectric value in tissue energy absorption across most exposure conditions.
Conclusions:
- Permittivity variations have a limited impact on whole-body SAR but a significant effect on localized SAR.
- Accurate tissue conductivity values are critical for precise localized SAR predictions in electromagnetic dosimetry.
- The study provides insights into the sensitivity of SAR calculations to material property uncertainties in digital human models.
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