| Three major tasks were completed in this thesis. Firstly, the FDTD method was adopted to model the design of birdcage and TEM coils, and to improve the accuracy of their representation. Secondly, the specific absorption rate (SAR) and temperature distributions inside human-head models loading the MRI coils were computationally simulated. Thirdly, the evaluation of a novel biological response, i.e., the auditory effect from MRI pulse induced elastic pressure waves inside the human head was investigated.; Several approaches were proposed to overcome previous shortcoming in modeling coil designs. Besides more realistic modeling of the MRI coils, a direct approach was used to determine the capacitance, which avoided the computationally intensive FFT for obtaining frequency responses.; The bio-heat equation was employed for computation of temperature increases in canonical head models (9- and 5-cm radius spheres for adults and children, respectively). Results for the different sized, homogeneous spherical models could serve as references for comparison of difference in sources and frequencies. The bio-heat equation also was applied to evaluate temperature increases for an anatomically accurate human head in both high-pass and low-pass birdcage coils at 7T (300 MHz). Computed results showed that the spatial correlation of SAR and temperature distributions was poor due to the heterogeneous configuration and electrical and thermal properties of the human head. Incorporating the thermoregulatory mechanism, the bio-heat equation was used to investigate the temperature rise at frequencies from 64 MHz to 400 MHz for the TEM coil. The thermoregulatory system strongly limits the temperature elevation and prevents the possibility of thermally induced brain tissue damage from MRI.; Considerable effort was devoted to investigating the amplitude and power spectra of thermoelastic pressure waves generated by RF pulses absorbed by subjects inside a MRI coil. We found that RF-induced thermoelastic pressure waves depend on model size, pulse width and SAR. The fundamental elastic pressure frequency varied from 8 kHz to 16 kHz for sphere radii of 9 cm and 5 cm, as theory had predicted. For the human head model, the computed fundamental thermoelastic pressure frequency was about 8 kHz at the center of human head. |
