Electromagnetic and modeling analyses of an implanted device at 3 and 7 Tesla

AbstractPurposeTo study the specific absorption rates (SAR) associated with implantable devices at 3T and 7T.Materials and MethodsStudies were carried out utilizing a finite difference time domain (FDTD) model that treats the radio frequency (RF) coil and an anatomically detailed human head mesh as a single system. Analyses were performed at 3T and 7T for different orientations and positions of an implanted (in the brain) aneurysm clip. Studies were also performed for two different types of FDTD mesh of the same aneurysm clip.ResultsThe results showed that: 1) the electromagnetic effects of implanting the aneurysm clip (in the brain) is mostly local on SARs; and 2) orientations of the implanted aneurysm clip have considerable effect on the local SARs near the implanted clip; the level of such an effect can also vary significantly between 3T and 7T.ConclusionIn general, the presented study shows that the local SARs (in 1 g and in 10 g of tissue) near the implanted aneurysm clip are lower than the peak SARs (due to the standard RF coil operation) in other regions of the human head mesh/brain. For specific orientations, however, if the aneurysm clip is implanted in a region in which the brain peak‐SAR occurs due the standard RF coil operation, the brain peak SAR increases further. This is more prevalent at 7T compared to 3T. Additionally, it was also found that basic structured and Cartesian FDTD modeling produces relatively higher local SARs than that obtained with simple non‐Cartesian FDTD modeling. J. Magn. Reson. Imaging 2007;26:1362–1367. © 2007 Wiley‐Liss, Inc.