Reevaluation and improved design of the TEM cell in vitro exposure unit for replication studies.

The transverse electromagnetic (TEM) cell system developed by Litovitz et al. and utilized by Penafiel et al. for the exposure of cells in T25 flasks at 835 MHz has been reevaluated for the purpose of replicating the studies published by Penafiel. The original setup has been reconstructed as closely as possible, with improvements enabling blinded exposures, forced cooling and better repeatable positioning of the flasks, as well as tight exposure and environmental parameter control. The signal unit can simulate the original signal but also enables various other exposure schemes. The setup has been evaluated for four T25 flasks filled with 5 and 10 ml of cell medium by experimental and numerical means. Comparing E field, SAR and temperature measurements resulted in good agreement: <0.4 dB (4.5%) for E field and 0.48 dB (10.5%) for SAR. The overall average SAR within the medium is 6.0 W/kg at 1 W input power with a standard deviation of less than 52%. The temperature increase was determined to be 0.13 degrees C/(W/kg). This can be reduced to 0.045 degrees C/(W/kg) by applying active air flow cooling. The comparison of SAR values from temperature measurements with the corresponding simulated values resulted in excellent agreement. These results do not correspond to the previous study reporting an average SAR within the medium of 2.5 W/kg at an input power of 0.96 W.