Radiofrequency (RF). Is it Safe?

26 June 2015

Issues on RF in MRI & Others

What follows is from an interview, conducted online with Prof C-K Chou, PhD, a multiple award-winning scientist and currently Motorola Chief EME Scientist, and the Director of Corporate EME Research Laboratory, responsible for RF product safety.

Dr Chou was in Kuala Lumpur in June 2007 to speak on the topic of “RF heating of Metallic Implants during Magnetic Resonance Imaging (MRI)” during the International EMF (Electromagnetic Field) Conference from 4-6 June 2007. The EMF conference was focussed on Electromagnetic Fields, Bioeffects Research, Medical Applications, and Standards Harmonisation.

Recorded lectures from the conference are available online at


RM: Dr Chou, you spoke on RF Heating of Metallic Implants during MRI in the above conference? How significant is this problem in clinical practice?

Dr Chou: The RF heating studies I presented on June 5, 2007 were carried out while I was working at my previous institution, City of Hope National Medical Centre in Duarte, California (east of Los Angles). It is well known that metals in RF fields can cause problems. This is the reason why gold rim glasses or metallic plates cannot be used for heating food in a microwave oven. Cochlear Corporation first approached me in early 1990s to study possible heating in patients with cochlear implants during MRI. Our study showed no problem for this device. They then asked us to evaluate a new product which was to be implanted at the brainstem to help totally deaf patients.

The FDA did not accept their data and the product was not approved until a proper testing was done. We tested the implant on a full size phantom and showed no adverse temperature rise with the implant. The FDA approved the device one month after we turned in the report.

After this project, Electrobiology Company requested for an evaluation of their spinal cord fusion stimulator. The results showed less than 2 degree Celsius heating on the stimulator, but up to 14 degrees Celsius at the broken leads which could cause injury. We made the suggestion to examine the patients with X-ray before MRI to ensure the leads are not broken (this happens in some patients).

The third study was for a cervical brace company to find out why some patients jump off the MRI table, and how to resolve the problem. Our study verified that there was up to 50 degrees temperature rise at the head pins, which explained the clinical observations. Insulated pins solved the excessive heating. All phenomena are consistent with RF dosimetry principles. The above three studies indicate that evaluation of individual devices is necessary.

RM: The third study pre-empted my question if there had been adverse effects reported. The MRI operators must have wondered why the patients literally “jumped off” the MRI table. Well that is one puzzle solved by your research. Do you think there may be under-reporting of adverse effects in MRI?

Dr Chou: I cannot speak on this subject, because I am not a radiologist.

RM: Would this become an issue as more and more centres get a higher tesla machine (eg from 1T, to 1.5T and now 3T MRI units) or is it just unrecognised?

Dr Chou:
We only tested with the 1.5 T machine at 64 MHz. Interactions of RF energy with tissue or metallic implants are very complicated. It is difficult to predict from one condition to the next. As stated above, each size or type of metallic devices need to be evaluated individually. With the advancements in computational electromagnetics, it is possible to evaluate with numeric methods now.

RM: Issues of MRI safety for the health workers (the radiology technologist, the radiologist and other staff working in an MRI unit):
What are your comments on the 2007 launch of an European Society of Radiology-Alliance for MRI to lobby against the implementation of the EU Physical Agents 2004/40/EC (EMF) Directive to reduce adverse health effects on workers (such as dizziness) linked to short term exposure to electromagnetic fields.

Dr Chou:
Certainly MRI procedures have to continue for medical purpose. To protect workers from adverse effects is also part of the safety implementation. This should be a manageable issue. Expert groups need to come up with recommendations how to deal with this.

RM: Why the apparent delayed-reaction to the 2004 directive?

Dr Chou: The delayed reaction is because the MRI community realized the static fields per se would be a problem for them, and lobbied successfully to have static field limits removed at the time that the Directive was negotiated. They forgot, though, about motion through static fields and switched-gradient fields and only realized about a year ago when implementation was almost upon us.

RM: Do you know the USA stand on this and how strong is the ICNIRP influence on this matter?

Dr Chou:
In the United States, NIOSH is the national research institute that focuses on workplace safety and health hazards and provides information to workers and managers related to various occupational health issues. However, the FDA is the regulator on MRI. To date, I have been told that the FDA is developing a response to the ICNIRP report.

RF and Mobile Phones

RM: Since you now work with Motorola, I cannot help but ask you about mobile phones and RF! The RF issue has caused a hoo-hah amongst the public with regard safety and causation of brain cancer amongst other nebulous ill health effects. Are the newer versions of mobile phones higher or lower in intensity of RF emissions? What determines how intense the RF emission is?

Dr Chou: Mobile phones are limited in maximum power emission. Under compliance test, they are required to use maximum power and tested on human phantoms. The maximum SAR (Specific Absorption Rate) found in the phantoms must be within the regulatory limits. During real use, the power is under adaptive power control, i.e., 1% power would be enough to function when the signals from base stations are strong. Therefore during normal use, people are exposed to SAR much lower than that tested in the laboratory. Computational studies show the maximum temperature at one small location in the brain is about 0.1 oC at the compliance limit. This is small compared to the 3-4 oC increase in the pinna due to the blocking of air circulation.

Currently, there is a 13 country study coordinated by the International Agency for Research on Cancer looking into the question whether mobile phone use can cause cancer. While most published reports show no effect, the question on acoustic neuroma is still waiting for the final pooled analysis of the entire study. More than 50 years of research and exhaustive analysis of possible low-level non-thermal mechanisms cannot identify any testable hypothesis for non-thermal effects. Although RF power emission from mobile phone is kept below a set maximum power (0.125 to 0.25 W average power), the RF absorption in head is a complex function of form factor, and antenna location. In any case, all phone models must be tested to meet compliance before shipping. As long as the SAR is below the limit, there is no need for concern of safety.

Dr Chou and his passion in RF research

RM: Why the passion in RF research? How did you get involved in this field?

Dr Chou:
It is like a mother loves her baby because the baby came out of her and she spent a lot of time on the baby. I have been doing this RF research since I was a graduate student in the early 70s. I had a great mentor and we worked together for 14 years and have published a lot of interesting papers. After I left the University of Washington, I had the fortune to continually engage in RF research at the City of Hope and Motorola. We created and are part of the history of RF research. I am glad that our research results contribute to the understanding of RF bioeffects and medical applications. The most important is that I enjoy what I do.

RM: How do you keep yourself “safe” from RF fields while working with it on a regular basis?

Dr Chou: In the studies at the University of Washington and City of Hope, high power RF devices were involved. At Motorola, the total energy outputs from the communication devices are usually small. In either case, we make sure our workers not exposed above the safety limits of IEEE standard or ICNIRP guidelines.

RM: What’s the future for RF?

Dr Chou: As I said in my d’Arsonval Award paper in 2006 (Bioelectromagnetics 28:1-15, 2007), after more than 50 years of studies looking for EMF bioeffects , we found that electrostimulation (below 100 kHz) and heating (above 100 kHz) are the only proven adverse effects. It is time for the Bioelectromagnetics research community to clarify the identified gaps in knowledge on EMF bioeffects as listed in the WHO research agenda. We need to move on to study what EMF can do for people, instead of continued efforts to look for what EMF can do to people.

Basically, there is no mechanism for low intensity RF exposure to cause adverse effects. It is not possible to prove a null hypothesis. Proving something is dangerous is easy, but it is not possible to prove absolute safety of anything, especially if the risks are very low or absent.
Biography of Chung-Kwang Chou

CKDr. C-K. (Chung-Kwang) Chou received the B.S.E.E. degree from National Taiwan University, Taipei, in 1968, the M.S. degree from Washington University, St. Louis, MO, in 1971, and the Ph.D. degree from the University of Washington, Seattle, in 1975. He served as Assistant Professor from 1977 to 1981 and Research Associate Professor from 1981 to 1985 in the Department of Rehabilitation Medicine and Center for Bioengineering of the University of Washington. During 1985 -1998, he was a Research Scientist and the Director of the Department of Radiation Research at the City of Hope National Medical Center in Duarte, CA. In April 1998, he joined Motorola Florida Research Labs, Fort Lauderdale, FL. His research has been on Radiofrequency (RF) biological effects, RF dosimetry and exposure systems, hyperthermia and electrochemical treatment of cancer. His current position is Motorola Chief EME Scientist, and the Director of Corporate EME Research Laboratory, responsible for RF product safety.

In 1981, Dr. Chou received the first special award for the decade (1970-1979) from the International Microwave Power Institute, in 1985, the outstanding paper award from the Journal of Microwave Power, in 1995, the Curtis Carl Johnson Memorial Award for Preceptor of Best Student Poster from the Bioelectromagnetics Society, in 2005, IEEE Standards Medallion Award, and in 2006, the highest honor d’Arsonval Medal from the Bioelectromagnetics Society, and Motorola Standards Award.

His professional service include Chairman of IEEE/EMBS Committee on Man and Radiation (1996-1997), Co-Chairman of IEEE Scientific Coordinating Committee 28, Subcommittee 4 on RF Safety Standard (1997- 2005), Board of Directors of the Bioelectromagnetics Society (1981-1984), Associate Editor of the Journal of Bioelectromagnetics (1987-2003) responsible for editing papers on high frequency RF fields, Electromagnetics Academy (1990- ), Distinguished Lecturer of IEEE Engineering in Medicine and Biology Society (1991-1992), Vice Chairman of Committee 89-5 on “Biological effects and exposure criteria for radio frequency electromagnetic fields” of the National Council on Radiation Protection and Measurements (1996-1999), Council Member of NCRP (1998-2004). He is an Associate Member of the Motorola Science Advisory Board (2005- ) and the Science Adviser of Mobile Manufacturers Forum (2001 – ). Dr. Chou has published about 190 peer-reviewed papers and book chapters, and additional 260 conference papers. He is a Fellow of IEEE (1989), the American Institute for Medical and Biological Engineering (1996), and Electromagnetics Academy (2007). He is chaired the IEEE International Committee on Electromagnetic Safety Technical Committee 95 responsible for Electromagnetic Field (EMF) exposure standards.