Specific absorption rate in neonates undergoing magnetic resonance procedures at 1.5 T and 3 T

Abstract

MRI is finding increased clinical use in neonatal populations; the extent to which electromagnetic models used for quantification of specific absorption rate (SAR) by commercial MRI scanners accurately reflect this alternative scenario is unclear. This study investigates how SAR predictions relating to adults can be related to neonates under differing conditions when imaged using 1.5 T and 3 T MRI scanners. Electromagnetic simulations were produced in neonatal subjects of different sizes and positions within a generic MRI body transmit device operating at both 64 MHz and 128 MHz, corresponding to 1.5 T and 3 T MRI scanners, respectively. An adult model was also simulated, as was a spherical salt‐water phantom, which was also used in a calorimetry experiment. The SAR in neonatal subjects was found to be less than that experienced in an adult in all scenarios; however, the overestimation factor was variable. For example a 3 T body scan resulting in local 10 g SAR of 10.1 W kg−1 in an adult would deposit 2.6 W kg−1 in a neonate: an approximately fourfold difference. The SAR experienced by neonatal subjects undergoing MRI is lower than that in adults in equivalent situations. If the safety of such procedures is assessed using adult‐appropriate models then the result is a conservative estimate. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.

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

“…The psSAR10g values for the neonate (infant without the mother) did not exceed 12.7 W/kg for a wbSAR of 2 W/kg (normal OM) in any excitation regime (not depicted). Compared with adult patients this is approximately 4 times less, because of the small body dimensions, and in good agreement with the estimation in .…”

“…Exposure to the full allowance of the first level controlled OM may cause local temperatures of up to 43.1°C in neonates (infant without the mother). Thus, it may be advisable to limit exposures to the normal OM for neonates, especially as this would not change clinical practice, in which wbSAR levels typically remain below 1 W/kg .…”

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

“…Exposure to the full allowance of the first level controlled OM may cause local temperatures of up to 43.1° C in neonates (infant without the mother). Thus, it may be advisable to limit exposures to the normal OM for neonates, especially as this would not change clinical practice, in which wbSAR levels typically remain below 1 W/kg (23).…”

How Can Pelvic MRI with Diffusion-Weighted Imaging Help My Pregnant Patient?

“…There are also no known safety concerns to the fetus regarding the specific absorption rate. [12][13][14] DWI relies on the Brownian motion of water molecules described by Albert Einstein in 1905. 15 The movement of water molecules, or protons, is restricted by cellular membranes in living tissues.…”