The electromagnetic environment of Magnetic Resonance Imaging systems. Occupational exposure assessment reveals RF harmonics

Abstract

Abstract. Magnetic Resonance Imaging (MRI) systems played a crucial role in the postponement of the former occupational electromagnetic fields (EMF) European Directive (2004/40/EC) and in the formation of the latest exposure limits adopted in the new one (2013/35/EU). Moreover, the complex MRI environment will be finally excluded from the implementation of the new occupational limits, leading to an increased demand for Occupational Health and Safety (OHS) surveillance. The gradient function of MRI systems and the application of the RF excitation frequency result in low and high frequency exposures, respectively. This electromagnetic field exposure, in combination with the increased static magnetic field exposure, makes the MRI environment a unique case of combined EMF exposure. The electromagnetic field levels in close proximity of different MRI systems have been assessed at various frequencies. Quality Assurance (QA) & safety issues were also faced. Preliminary results show initial compliance with the forthcoming limits in each different frequency band, but also revealed peculiar RF harmonic components, of no safety concern, to the whole range detected (20-1000MHz). Further work is needed in order to clarify their origin and characteristics.

Αξιολόγηση Της Επαγγελματικής Έκθεσης Σε Ηλεκτρομαγνητικά Πεδία

“…Measurements of the RF EF and the ELF MF were performed next to the examination bed, during the MRI scans for 1.5T and 3T systems, during occupational exposure assessment (Figure 4.3.4) (13). Apart from the 'main' safety SRM-3006 Narda equipment, the use of Narda IDA-3106 Interference and Direction Analyzer revealed low amplitude RF harmonic components (187); three different directional antennas were used.…”

“…The RF safety issues are linked to the 63.5 MHz of no safety concern, examination whether or the main 63.5 MHz frequency are the half of the main frequency. This RF harmonic components (spectrogram) between 200 and 500 MHz for a 1.5T MRI system (187).…”

“…Measurements of all the fields have been also reported indicating the ELF overexposures (222,223) and even the WPM (weighted peak method) has . The European Commission has launched a big survey concerning occupational MRI exposure that has also indicated overexposures (225) since the clinical and research use off MRI was pending concerns the protection of the MRI workers is of great importance ( RF harmonic components (spectrogram) between 400 and 1,000 MHz for a 1.5T the background RF mall shielding discontinuities can be that is the check of the MRI room RF shielding FM radio interference next to Faulty RF shielding (FM radio interference), due to some copper lamina missing (187).…”