Monday, June 08, 2015

Magnetic resonance imaging (MRI): A review of genetic damage investigations

Magnetic resonance imaging (MRI): A review of genetic damage investigations

Vijayalaxmi, Fatahi M, Speck O. Magnetic resonance imaging (MRI): A review of genetic damage investigations. Mutat Res Rev Mutat Res. 2015 Apr-Jun;764:51-63. doi: 10.1016/j.mrrev.2015.02.002. Epub 2015 Feb 21.


Magnetic resonance imaging (MRI) is a powerful, non-invasive diagnostic medical imaging technique widely used to acquire detailed information about anatomy and function of different organs in the body, in both health and disease. It utilizes electromagnetic fields of three different frequency bands: static magnetic field (SMF), time-varying gradient magnetic fields (GMF) in the kHz range and pulsed radiofrequency fields (RF) in the MHz range. There have been some investigations examining the extent of genetic damage following exposure of bacterial and human cells to all three frequency bands of electromagnetic fields, as used during MRI: the rationale for these studies is the well documented evidence of positive correlation between significantly increased genetic damage and carcinogenesis. Overall, the published data were not sufficiently informative and useful because of the small sample size, inappropriate comparison of experimental groups, etc. Besides, when an increased damage was observed in MRI-exposed cells, the fate of such lesions was not further explored from multiple 'down-stream' events. This review provides: (i) information on the basic principles used in MRI technology, (ii) detailed experimental protocols, results and critical comments on the genetic damage investigations thus far conducted using MRI equipment and, (iii) a discussion on several gaps in knowledge in the current scientific literature on MRI. Comprehensive, international, multi-centered collaborative studies, using a common and widely used MRI exposure protocol (cardiac or brain scan) incorporating several genetic/epigenetic damage end-points as well as epidemiological investigations, in large number of individuals/patients are warranted to reduce and perhaps, eliminate uncertainties raised in genetic damage investigations in cells exposed in vitro and in vivo to MRI.

MRI is generally considered as a safe technology with very high clinical impact. It is accepted more readily as a powerful non-invasive diagnostic tool to investigate the anatomical structures and functions in the body, in both health and disease, since it does not involve the use of ionizing radiation which is known to cause deleterious effects directly and indirectly. MRI has been in use in numerous medical practices during the last 3 decades. According to the OECD health data collected from ∼30 countries in 2009 [92], there were >7950 MRI scanners in the USA (ranks #2 in the world, equals to ∼25.9 MRI scanners per million population) and perform ∼91.2 MRI scans per 1000 population (ranks #1 in the world, >50,000 MRI scans/year). Also, since the introduction of MRI in clinics, it is estimated that some 200 million MRI scans have been performed worldwide [16] and no direct ‘adverse biological’ effects have been reported from such subjects/patients. In the past, MRI was contraindicated and not suggested for patients with implantable electronic, ferromagnetic or conducting objects such as cardiac pacemakers, cerebral aneurysm clips and cardio-ventricular defibrillators (ICDs) because of concerns that the powerful magnet and the heat generated from RF might deliver inappropriate shocks and trigger arrhythmia: some such events have been reported. However, advances in technology have paved the way. MRI-safe pacemakers and ICDs have been developed: such devices, along with appropriate exposure protocols, have been tested in patients. In February 2011, one such pacemaker received FDA approval for use in patients in the United States [93]. So far, the observations were that the new devices are safe and allow patients to undergo MRI at 1.5 T. It is likely that in the next several years, MRI-safe pacemakers and ICDs would become standard for their use in patients [94][95][96] and [97]. However, care has to be taken that implants are MR-safe in order to avoid direct patient hazard by ferromagnetic forces or implant heating. Besides, during the past decade, the strength of the static magnetic fields used in MRI systems is increasing due to the technical developments for improved diagnosis/therapy and this leads to increased SMF exposure levels [98][99][100] and [101]. Hence, it is not only imperative but also essential to conduct investigations examining the interaction between the combination of three different types of electromagnetic fields generated by MRI systems and the associated genetic risks, if any, to the patients as well as healthy individuals working in and around the MRI scanner (for few minutes to several hours per day for several years) since there is well documented evidence of positive correlation between increased genetic damage and carcinogenesis. Furthermore, MRI exposure per se may not be genotoxic, but can contribute to the development of cancer by enhancing the damage induced by known genotoxic agents (i.e., epigenetic effect). So far, investigators have used the blood samples collected from patients and/or healthy volunteers for obvious reasons of convenience. The numbers of subjects examined were not large and often did not include comparable groups. Also, when an increased damage was observed, for example, γ-H2AX, the fate of such lesions was not examined using multiple ‘down-stream’ end-points, viz., CA and MN, and the mechanism of the formation of the latter.
MRI technology has very high clinical impact as an extremely powerful and non-invasive technology for use in both health and disease. The reports on genetic damage which are reviewed in this paper not only need attention but also deserve further investigations. Despite its very good safety record comprehensive, international multi-centered collaborative studies, using a common and widely used MRI exposure protocol (cardiac or brain scan) and several genetic/epigenetic damage end-points, in large number of individuals/patients can further reduce uncertainties in genetic damage investigations.


Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley

Electromagnetic Radiation Safety

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