Impacts of RF shimming on local SAR caused by MRI 3T birdcage coil near femoral plate implants

Abstract

Numerical studies of local specific absorption rate (SAR) were conducted for femoral plate implants in MRI 3T birdcage coil. Both the quadrature excitation and RF shimming conditions were evaluated in anatomical models of human body. All the results were normalized to 2W/kg average whole body SAR and Q-Matrices formalism method was used to improve the SAR calculation efficiency. The RF shimming procedure homogenize the magnitude of B 1+ field in femur region. Under RF shimming condition both the value and location of the worst local SAR point were changed. The maximum local SAR is 573 W/kg under quadrature excitation condition and 154 under RF shimming condition. As the results suggested, significant impacts on local SAR near femoral plate implants due to RF shimming were observed.