Evaluation of local B1 field as dosimeter of RF heating for implant in MRI

Radio frequency (RF) heating is a serious risk for a patient with an elongated implant during MRI scan. The conventional dosimeter of specific absorption rate (SAR) and the recently proposed B1+rms may not accurately indicate the implant heating. The local B1 field around the tip of a lead and its relationship with the RF heating were studied by numerical simulations. It was found that regardless of the route of the lead, the angle or position of placement, there was a strong linear correlation between the averaged square of local B1 field and the rise in temperature. The evaluation range had an effect on the linearity. Generally, the local B1 field performed better as a dosimeter of RF heating than SAR or B1+rms at the isocentre.