Analytical Evaluation of Radio-Frequency Energy-Induced Heating in a Hot Spot without perfusion

The specific absorption rate (SAR) averaged over the mass of 10 gram human tissue and over a 6 minute time (SAR10g) is the primary safety limit for 7T MRI scanners [1]. SAR10g is also the safety limit for multi modal study, i.e., a combination of MRI with another technique, for example transcranial electric stimulation (tES) or electroencephalography (EEG), if additional equipment is entered into the effective exposure volume of the MRI radio-frequency (RF) coil. Especially in the latter case, locations with the highest RF power deposition, i.e., hot spots, in a human body can be substantially separated in space. The dimension of volume that consists of 10 gram human tissue is 21.55 mm as cube edge or 13.365 mm as sphere radius for most human tissues. Radius of a hot spot of substantial amount of active and passive implants is in a range from 1 mm till 15 mm. Radio-frequency energy-induced heating in human tissues is a very complex process with large influence of blood perfusion that in most cases decrease the level of heating. Thus heating estimation without blood perfusion res