Effects on medical equipment
The results of the electromagnetic interference testing conducted with a dipole antenna on the 22 pieces of medical equipment (49 components) revealed that 14 main components from 13 pieces of equipment exhibited some kind of electromagnetic interference effect (Table 8). All the affected pieces of equipment that required maintenance were restored to their normal state upon in situ maintenance of the unit. The interference extinction power and distance for the respective equipment were detailed (Supplemental Digital Content, Table 1, http://links.lww.com/HP/A68).
Four occurrences of interference were irreversible (8%), and one case (2%) was of Category 5 or higher with the possibility of exacerbation of the patient’s medical condition. This was confirmed to be Category 7 for “Artificial respirator C2.” For this model, however, an alarm and error display started following the initial electromagnetic interference; actual interruption of the artificial respirator operation occurred only if the transmission source (dipole) continued to be directed toward the C2. Thus, interruption of the artificial respirator operation was avoided when the source of the radiation was promptly removed from the C2's vicinity soon after the alarm and error display started.
In tests using an actual mobile phone, effects from electromagnetic interference were confirmed for six pieces of equipment, but no irreversible effects occurred.
Interference extinction distance for different communications systems
The communication systems were compared at maximum transmission power output using the mobile phones based on the results of inspection of the electromagnetic interference generated by each system. PHS had weaker associated interference (Fig. 3) than any of the other systems, while LTE, HSUPA, and W-CDMA exhibited nearly the same interference. PHS also had a smaller result for the interference extinction distance than any of the other communication systems.
The interference extinction distances for the medical equipment per transmission power were confirmed with the respective interference extinction distances for the four transmission power settings at 10, 80, 200, and 250 mW (Figs. 3 and 4). At the maximum transmission power in the frequency band of 2 GHz, the longest interference extinction distance for all medical equipment tested in this study was measured for LTE to be 28 cm (transmission power: 200 mW; radiation source: dipole antenna; modulation scheme: 64QAM). The 2‐GHz band was commonly used in the LTE, HSUPA, and W-CDMA tests. For HSUPA, the longest interference extinction distance was 38 cm (transmission power: 250 mW; radiation source: dipole antenna; frequency: 2‐GHz band; modulation scheme: QPSK); for W-CDMA, it was 29 cm (transmission power: 250 mW; radiation source: dipole antenna; frequency: 2‐GHz band; modulation scheme: QPSK); and for PHS, it was 6 cm (transmission power: 80 mW; radiation source: dipole antenna; frequency: 1.9‐GHz band; modulation scheme: π/4 DQPSK). At maximum transmission power, the interference extinction distances for HSUPA and W-CDMA at 250 mW and LTE at 200 mW were nearly the same but slightly larger than that for PHS (80 mW). Nagase and colleagues reported that the difference in PAPRs between the LTE, HSUPA, and W-CDMA did not have a significant effect (Nagase et al. 2012).
Similarly, the maximum interference extinction distances at maximum transmission power for actual mobile phones using HSUPA, W-CDMA, and LTE were 10, 10, and 11 cm, respectively. At maximum transmission power, the electric field strength at 10 cm from the mobile phones was almost the same as the strength at 30 cm from the dipole antenna. The lengths also correspond approximately to the longest interference extinction distances for the mobile phones and dipole antenna, respectively. From these results, the relation between the electric field distribution and the interference extinction distance was confirmed.
At the minimum transmission power of 10 mW, the maximum interference extinction distances for HSUPA, W-CDMA, and LTE were 1, 2, and 2 cm, respectively. For PHS (80 mW), however, the result was the same as before at 6 cm, as the transmission power was the same.
At transmission powers of 80 and 10 mW, the interference extinction distances decreased tremendously compared with those at 250 and 200 mW. These results show that a change in transmission power has a large effect on the electromagnetic interference. In addition, it was revealed that when the transmission power of a mobile phone drops below that of PHS, the magnitude of the effect on medical equipment also becomes smaller than that for PHS. The transmission power of a mobile phone is varied according to a control signal from the base station with which it communicates. If the transmission power changes from 10 mW, the interference extinction distance may also change.
IEC 60601‐1‐2 specifies the recommended separation distance between mobile/PHS phone handsets and medical equipment (ECES 2007). Table 9 shows a comparison between the recommended separation distances in the frequency range used in this study and the longest interference extinction distances at each transmission power in this study. All interference extinction distances in this study were shorter than the recommended separation distances.
Effects of different transmission modes on medical equipment
An inspection of the prominence of the electromagnetic interference generated for each transmission mode revealed that intermittent transmissions clearly caused more detrimental electromagnetic interference than continuous transmissions. The maximum interference distance during continuous transmission was 20 cm for the dipole antenna and 11 cm for a mobile phone, while the maximum interference distance during intermittent transmission was 38 cm for the dipole antenna and 15 cm for a mobile phone.
Effects on medical equipment under the minimum radio wave conditions
According to the considered characteristics of electromagnetic interference under the reduced transmission power and restricted frequency band, testing proceeded under a frequency of 2 GHz and a power of 10 mW.
Four components from four different pieces of medical equipment experienced interference, or 8% of the total 49 components from the 22 pieces of equipment (Table 10).
The electromagnetic interference became considerably weaker when the conditions were restricted to 10 mW for the 2‐GHz band. Compared to the maximum transmission power across all frequency bands, the number of main components for which electromagnetic interference was confirmed dropped from 14 to 4; the maximum hindrance category dropped from 7 to 3. The maximum interference distance dropped from 38 cm to 2 cm.
Effects of radio wave interference on medical equipment
Testing was conducted using the 2‐GHz frequency band and a power of 10 mW in order to consider the characteristics of electromagnetic interference under reduced transmission power and a restricted frequency band. According to the results, the effects of mobile phones on most daily medical practices are essentially nonexistent unless they are almost in contact with the medical equipment in question. However, in poor radio wave environments, the transmission power from mobile phones tends to increase to establish a sufficient connection with the base tower. One possible way to reduce the transmission power and frequency-band restrictions is to introduce indoor base stations, known as In-building Mobile Communication Systems (IMCSs) to medical centers. These are generally installed in ceilings away from medical equipment and have low radiofrequency emissions. Installation of an IMCS in poor radio wave environments reduces the distance between mobile phones and the communicating counterpart (the IMCS), resulting in a diminished propagation loss. Therefore, it is likely that a lower transmission power will be required in comparison to a scenario where no IMCSs are installed. This is due to a base station system whereby a control is applied that reduces the transmission power output whenever propagation loss is small. As described above, an IMCS may reduce the transmission power of mobile phones. However, if the propagation loss between mobile phones and the IMCS is large, or if there are many mobile phones in the same area, the transmission power required may reach the maximum power. If the distance between the mobile phones and the medical equipment is short, the effects of direct waves from the mobile phones can dominate over those of reflected waves. However, if the distance is longer, the opposite may be true. Future studies are required to clarify the relationship between the distance and the effect of reflected waves.
The current standards in Japan for medical equipment can be found in the “Guidelines on the Use of Radiocommunications Equipment such as Cellular Telephones and Safeguards for Electronic Medical Equipment” (CCAUE 1997) prepared in 1997 at the Electromagnetic Compatibility Conference. Subject equipment includes implanted pacemakers and general electrical medical equipment. The guidelines express in detail the prohibition of mobile phones in the operating room or ICU; the powering down of mobile phones in laboratories, consultation rooms, patient wards, and treatment rooms; and the use of mobile phones elsewhere, including solely in zones authorized by the medical institution. However, operative rules are not necessarily enforced by each medical institution. Moreover, since the establishment of the guidelines, efforts to lower outputs from mobile phones and enhance countermeasures to electromagnetic interference for medical equipment have been made. In 2002, MIC implemented electromagnetic interference testing within hospitals jointly with the Japan Federation of Medical Devices Associations and confirmed the appropriateness of the guidelines established at the Electromagnetic Compatibility Conference (CCAUE 1997). With respect to implanted medical equipment (pacemakers), the first edition of the Guidelines to Prevent Effects of Radio Waves from Types of Radio-using Equipment to Implanted Medical Equipment was presented in 2005. The recommended separation distance was 22 cm, which was reviewed and revised in January 2013 to 15 cm (MIC 2013).
For general medical equipment, however, only a few surveys have been completed since then. The details for general medical equipment should be reviewed in the same manner as those for implanted pacemakers.
As a result of the testing discussed here, it is highly likely that if the radio wave environments inside hospitals could be improved through the installation of IMCSs in locations with poor radio wave environments, the effect on general medical equipment can be significantly reduced. A mobile phone, for instance, must be almost in direct contact with ordinary medical equipment for any effects to occur at minimum transmission levels. In Japan, there have been no reports of electromagnetic interference from mobile phones that caused faults in medical equipment and consequently affected the condition of a patient. Therefore, it may be necessary to review the restrictions on mobile phone use in hospitals and medical facilities, including ICUs and ERs, due to the benefit of using such devices. If well regulated, the professional in charge would have immediate access to the knowledge and opinions of others, resulting in a great improvement in the quality of medical practice.
Effects from continuous transmissions and intermittent transmissions
Nojima and Tarusawa (2002) noted that intermittent transmissions are more likely to affect medical equipment, as medical equipment frequently includes control circuits based on biological rhythms such as pulse and respiration. Hence, the present research indicates that the possibility of malfunction emerges when any signal closely aligned to a biological rhythm is applied as noise to the circuit of the medical equipment. Development of methods to prevent the interference between mobile phones and medical equipment is desired such that there are no effects on medical equipment even under intermittent transmissions.
Not all general medical equipment was tested. In fact, verification remains necessary for a variety of medical equipment in future work. Given the rapid advancement in mobile phone technology in recent years, the effects of electromagnetic interference on medical equipment should be examined at least once every 2 y.
Medical institutions are incidentally built with thicker walls than ordinary buildings due to the need for radiation shielding, containment of MRI magnetic fields, and other factors. Thus, many locations may have poor radio wave conditions, and these conditions influence the transmission power of mobile phones (Lonn et al. 2004). Such variations in transmission power can have a substantial effect, so the structure of the hospital building must be considered as a major factor in the issue of radio wave interference.
The maximum radiated power from the antennas of mobile phones is lower than 250 or 200 mW, but varies according to phone type. The electric field distribution around mobile phones also varies with phone type, and it is difficult to extrapolate accurately from the distribution around the mobile phones used in this study. However, a dipole antenna was used preliminarily in all tests. The radiated power from the dipole antenna was in the region of 200 to 250 mW; the conducted test using the dipole antenna is conservative compared to the test using mobile phones.
Telemedicine has been used in emergency departments to treat general patients (Brennan et al. 1998; Benger et al. 2004; Galli et al. 2008), stroke patients (Silva et al. 2012), and trauma patients (Latifi et al. 2007). Traub et al. (2013) used telemedicine to perform telemedical physician triage. The use of mobile phones, particularly videophones, could cut technology costs by an order of magnitude and expedite the setup, connection, and consultation processes (Gonzalez et al. 2011; Anderson et al. 2013).
Improvement and equalization of medical practice quality through the use of telemedicine
Currently, nearly all hospitals in Japan have established a zone in which the use of mobile phones is permitted; however, the rapid reception of large volumes of medical data at any time and at any location could be a life-saving capability. For example, to improve the handling of strokes through earlier diagnosis and faster treatment, telemedicine was implemented in Japan that used a fixed videophone rather than a mobile phone (Saito et al. 2007); however, it has been stated in other reports that an improved survival rate can be achieved with remote imaging diagnosis via a mobile phone (Iguchi et al. 2011; Demaerschalk et al. 2012).
Telemedicine will hopefully overcome the geographical disparity among physicians by allowing the judgment of specialists to be sought easily. If a specialist could obtain medical data regardless of location through the use of a mobile phone, and subsequently administer or aid in healthcare, then standards of healthcare could be elevated worldwide. Therefore, in Japan, the established zonal system in medical centers whereby mobile phone use is prohibited in all but designated areas must be revised. Aziz and colleagues reported that no evidence exists for interference in a real hospital environment and that there are no reasons to prohibit the use of mobile phones within medical facilities (Aziz et al. 2003).
The effects of electromagnetic interference from mobile phones on general medical equipment, even those used in ICUs and ERs, are not absolutely irrelevant; however, they can essentially be considered as such according to the experimental results, except when the mobile phone is near (≤38 cm) or in direct contact with the medical equipment. With ample knowledge at hand with respect to the hindrances to general medical equipment, the use of mobile phones and other mobile communication systems should be increased to a level suitable for the modern information society, with an aim to improve the standards of healthcare.
Depending on the equipment or radio wave conditions (radio wave environment), there is the possibility that mobile phones have an effect on general medical equipment. This research indicates that interference is not relevant if the mobile device is at least 38 cm away from the medical device, even in a bad cellphone network condition. This study also showed that the risk of interference can be further reduced by improving the cellphone network environment, resulting in lower radio transmissions by mobile devices. Thus, the range of mobile phone use should be expanded in medical facilities by establishing very few zones in which the use of mobile phones is prohibited or only restricting mobile phone use to areas more than 38 cm from medical equipment.
We are very grateful to Satoshi Ishihara and Junji Higashiyama at the research laboratories of NTT DOCOMO, INC., for their valuable cooperation in our experiments. All research was conducted in the anechoic chamber at NTT DOCOMO R&D Center. All environment preparation and experiment annotation regarding the medical equipment and mobile phone research was conducted by Ishihara and Higashiyama.
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electromagnetic fields; exposure, radiofrequency; radiation, nonionizing; safety standards
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