NMR imaging of cell phone radiation absorption in brain tissue

Abstract

A method is described for measuring absorbed electromagnetic energy radiated from cell phone antennae into ex vivo brain tissue. NMR images the 3D thermal dynamics inside ex vivo bovine brain tissue and equivalent gel under exposure to power and irradiation time-varying radio frequency (RF) fields. The absorbed RF energy in brain tissue converts into Joule heat and affects the nuclear magnetic shielding and the Larmor precession. The resultant temperature increase is measured by the resonance frequency shift of hydrogen protons in brain tissue. This proposed application of NMR thermometry offers sufficient spatial and temporal resolution to characterize the hot spots from absorbed cell phone radiation in aqueous media and biological tissues. Specific absorption rate measurements averaged over 1 mg and 10 s in the brain tissue cover the total absorption volume. Reference measurements with fiber optic temperature sensors confirm the accuracy of the NMR thermometry.nuclear shielding | dipole antenna | mobile communications | SAR | RF safety H umans are exposed to an increasing amount of nonionizing electromagnetic radiation emitted from sources such as cell phones, power transmission lines, radars, and medical equipment (1), causing public health concerns (2). Safety standards defining upper limits for the specific absorption rates (SARs) were thus established to serve as guidelines for equipment manufacturers in various fields (3-5). Extensive cell phone use is known to present the highest radio frequency (RF) exposure to the general public, prompting this study.The 6 billion current global cellular phone subscriptions (6, 7) indicate an average airtime of about 30 min/d and an average call length of about 3 min/user (8). Tremendous research efforts starting in the early 1980s to assess the health effects from cell phone radiation have focused on the significant absorption of radiation by those parts of the human brain that are located in close proximity to antennae (9).In general, the effects of nonionizing radiation have been divided into thermal and nonthermal and have been extensively investigated through cell and animal studies (10-13), neurological studies (14, 15), thermographic measurements (16), computer model-based simulations (17, 18), metabolic human studies (19), and large epidemiological data (20). Among those, researchers have focused on a possible link between cell phone radiation and cancer (21). The International Agency for Research on Cancer (IARC), the cancer research institute of the World Health Organization (WHO), has recently classified RF emission from cell phones as possibly carcinogenic to humans (group 2B) and concluded the aforementioned studies cannot reliably serve to exclude harmful radiation effects, prompting further research (22). This uncertainty can be attributed to limitations of epidemiological data unsuitable for assessing long-term effects and incomplete knowledge of the impact of physical radiation effects on the brain tissue (23)(24)(25). Whereas the predominant scientifi...

Heat equation inversion framework for average SAR calculation from magnetic resonance thermal imaging

“…Temperature errors of the same magnitude have been demonstrated in various phantom studies [Gultekin and Moeller, 2013; Alon et al, 2015] with slightly higher errors for in vivo studies [Kickhefel et al, 2010]. At the reported standard deviation of the temperature measured here, proper reconstruction was conducted; however, average SAR reconstruction depends on the signal-to-noise of the measurement.…”

“…Okano and Shimoji have shown that RF energy exposure quantification can be conducted by measuring temperature increase due to RF exposure using highly sensitive temperature probes [Okano and Shimoji, 2012]. Gultekin and Moeller [2013] have shown that magnetic resonance (MR) methods can be used to measure temperature increase due to RF energy absorption, where the magnitude of temperature increase was a function of RF power and exposure time in brain equivalent gels and brain tissue [Gultekin and Moeller, 2013]. Recently, high-resolution MR thermal mapping has been utilized for assessment of RF energy absorption from handheld wireless devices [Alon et al, 2015] that output less than 1W of power.…”

A method for safety testing of radiofrequency/microwave‐emitting devices using MRI

“…Recently, it has been shown that MRI temperature mapping has been used to quantify RF energy deposition induced by MRI coils (operating at the Larmor frequency) and other antennas , where both RF heating and temperature mapping were conducted inside the bore of the MRI scanner. However, many wireless devices are not MRI‐compatible and therefore cannot be inserted inside the bore of the magnet while maintaining standard operation of the device.…”

Easy Determination of Radiation Absorption in Brain Tissue from Mobile Phones Using Finite Element Method

“…The Federal Communications Commission (FCC) in the United States has set an SAR limit of 1.6 W/kg averaged over 1 g of tissue for partial-body exposure, whereas the Council of the European Union allows a limit of 2.0 W/kg averaged over 10 g of tissue [9] [10]. Extensive cell phone use is known to present the highest radio frequency (RF) exposure to the general public [11].…”