Pregnant women models analyzed for RF exposure and temperature increase in 3TRF shimmed birdcages

Abstract

Purpose-MRI is increasingly used to scan pregnant patients. We investigated the effect of 3 Tesla (T) two-port radiofrequency (RF) shimming in anatomical pregnant women models. Theory and Methods-RF shimming improves B 1+ uniformity, but may at the same time significantly alter the induced current distribution and result in large changes in both the level and location of the absorbed RF energy. In this study, we evaluated the electrothermal exposure of pregnant women in the third, seventh, and ninth month of gestation at various imaging landmarks in RF body coils, including modes with RF shimming.Results-Although RF shimmed configurations may lower the local RF exposure for the mother, they can increase the thermal load on the fetus. In worst-case configurations, whole-body exposure and local peak temperatures-up to 40.8°C-are equal in fetus and mother.Conclusions-Two-port RF shimming can significantly increase the fetal exposure in pregnant women, requiring further research to derive a very robust safety management. For the time being, restriction to the CP mode, which reduces fetal SAR exposure compared with linear-horizontal polarization modes, may be advisable. Results from this study do not support scanning pregnant patients above the normal operating mode.

Sensitivity analysis of neurodynamic and electromagnetic simulation parameters for robust prediction of peripheral nerve stimulation

“…This is a significant simplification which does not accurately represent anatomical variability. Applying morphing operations (Murbach et al 2017) to the same body model is an improvement over this, but does not sufficiently explore anatomical variability, as it does not introduce new tissue features or changes in the relationship between neighboring tissues. Realistic anatomical variations can likely only be modeled by using additional different body models that have been generated independently based on different underlying anatomical data.…”

A numerical and experimental study of RF shimming in the presence of hip prostheses using adaptive SAR at 3 T

“…Different thermoregulation models exist, and as described by Laakso et al, can result in different temperature distributions. In this study, the thermoregulation model previously described in Destruel et al was used.…”

“…The absolute temperature distribution was calculated in Sim4Life using the Pennes Bioheat Equation . A Dirichlet thermal boundary condition was imposed on the skin, with a heat transfer coefficient of 6 W/m 2 /K, corresponding to normal clothing and no sweating . The core temperature was assumed to be constant, the initial body temperature was set to 37°C, the ambient temperature was set to 25°C, and the temperature distribution was allowed to reach a steady state for 40 minutes …”

A numerical investigation on the effect of RF coil feed variability on global and local electromagnetic field exposure in human body models at 64 MHz

“…Conversely, EM field propagation for the S2 coil model was numerically computed following two different approaches, one for the case without lead and one for the case with the lead. For simulations without the lead, each feeding source of the pair was excited by a broadband signal from 0 to 140 MHz, with the peak at 64 MHz. For field extraction, results were postprocessed and combined, imposing the same signal amplitude and a phase shift of 90° at the two feeds.…”