Power deposition inside a phantom for testing of MRI heating

A patient in MRI is exposed to the time varying gradient and radio-frequency (RF) fields. Measurements of RF-induced temperature rise in implant in phantoms are used to predict the in-vivo temperature rise. This paper focuses on the numerical computation of power deposition inside such a phantom. The finite-difference time domain (FDTD) was used for the calculations. The phantom was placed inside a whole body bird cage coil. For landmarks in the torso of the phantom, the power deposition is concentrated near the edges. The whole phantom average specific absorption rate (SAR) for a mean square field intensity of 1(μT)² ranged from 0.032 W/kg for the eyes landmark to 0.151 W/kg for the waist landmark. The SAR increased with increasing conductivity in the range 0.2 to 0.8 S/m. The distribution of the measured temperature rise versus lateral position at the landmark was consistent with the calculation. The electric field is tangential to the phantom edges but has significant elliptical polarization near the corners.