Abstract
Radiation from cell phones and cellular devices is ubiquitous and, in the microwave frequency bands used, human tissue is a highly absorbing complex electromagnetic material. Safety guidelines are currently based on heating and specific absorption rate using limited measurement and modeling techniques. Here, we present a method to image microwave electromagnetic fields from cellular device radiation in tissue mimics using hyperpolarized low-field magnetic resonance imaging (MRI). Resonant absorption of microwave radiation in free radicals added to the tissue mimics, transfers polarization to the water proton system and, at cell phone power levels, can not only be detected, but can increase the signal over the native low-field MRI signal. Electromagnetic field imaging can be done before substantial heating of the material. Imaging and quantification provide a better understanding of how cellular radiation penetrates and is absorbed in complex materials, such as tissues, and may allow validation of numerical models. We further demonstrate the use of this technique to image microwave field distortion and reradiation around implants and foreign objects, including from a millimeter-sized biopsy marker. We present initial steps at quantifying the hyperpolarized low-field images to allow extraction of electromagnetic field values. The concurrent use of quantitative MRI allows critical tissue parameters to be monitored before, during, and after microwave exposure.