Apr 1, 2016

An HF exposure system for mice with improved efficiency

Myles Capstick, Yijian Gong, Boris Pasche, and Niels Kuster, Bioelectromagnetics, Volume 37, Issue 4, pp. 223–233, May 2016, online March 31, 2016

An exposure system that addresses the difficulties that arise during exposure of small animals at low frequencies with high exposure levels is presented. The system, operating at 27 MHz and consisting of two identical transverse electromagnetic (TEM) cells for exposure and sham exposure of groups of 16 free-running mice housed in pairs within standard cages, is capable of exposure over extended daily periods with provision of food and water. The inclusion of theTEM cell in half-wavelength resonator increases the exposure by >50-fold compared to traditional TEM cell configurations. The system described allows both daily and weekly exposure schedules and supports blinded protocols with continuous wave (CW) and amplitude modulation (AM) signals with programmable modulation depths and frequencies. Electric field homogeneity across the TEM cell along a vertical plane orthogonal to the axis of the TEM line was within 3.3%, and within 3.1% along the horizontal plane. Accurate and comprehensive dosimetric assessments based on whole-body and organ-specific specific absorption rates (SAR) essential for in vivo bioelectromagnetic experiments that take into account various factors, e.g., mouse activities, close proximity, and field homogeneity, are presented. Average SAR levels are controllable in the range of 1 mW/kg – 2 W/kg, with expanded uncertainty (k = 2) of 1 dB and instantaneous variation (k = 1) of 4 dB.

The scientific and technical impact of the study can be summarized as:

  • The development of an exposure system with the novel inclusion of the TEM cell in a λ/2 resonator inceased the exposure by 19 dB with a field homogeneity of 0.45 dB
  • The identical TEM cells of the system enable tests of radiofrequency (RF) and sham exposure of mice housed pairwise and unconstrained in standard cages, with water and food provided during exposure, and with well-controlled and accurately defined SAR distributions.
  • Organ-specific dosimetry is provided to enable assessment of RF EMF dosage delivered in key organs, which is an important asset for biomedical and risk assessment research