Occupational Exposure To Radiofrequency Energy And Static Magnetic Fields In Mri Units In The Public Sector Within Mangaung Metropolitan Region

Abstract

The healthcare workers (HCWs) working with magnetic resonance imaging (MRI) units are constantly exposed to MRI-related electromagnetic fields, and epidemiological studies have confirmed association between exposure to emitted static magnetic fields (SMFs) and development of transient exposure-related health effects. The thermal effects associated with induced tissue heating from radiofrequency (RF) energy have also been confirmed, however, there is still controversy on non-thermal effects. The development of health effects among workers is dependent on the performance of activities in close proximity to MRI scanner in zone IV. The aim of this study was i) to assess the exposure levels of SMFs and RF magnetic fields, including the health effects resulting from exposure to MRI-related EMFs among MR staff as well as MR safety risks. ii) the second aim was to develop a health and safety model that will reduce MR safety risks and exposure of MR staff to SMFs and RF magnetic fields emitted by 1.5 and 3.0 T MRI scanners. Transient health effects reported in others studies were assessed among radiographers, nurses, cleaners, medical physicists, radiologists, porters, medical doctors and maintenance engineers. The exposure levels of SMFs and RF magnetic fields were also measured in zone IV, in the MRI rooms using distance as an exposure surrogate. Different distance points were considered, particularly one and two meter; when patient examinations were performed. Furthermore, a health and safety model focussing on administrative controls as well as recommendations on the use of personal protective equipment (PPE) has been developed to guide the MRI facilities to reduce exposure, health effects and existing MR safety risks. This study was conducted in two public hospitals located in Bloemfontein, Free State Province of South Africa. The SMFs and RFmagnetic fields exposure levels from two 1.5 and one 3.0 T MRI scanners in Pelonomi and Universitas hospitals. The exposure levels were measured through spotmonitoring when patients underwent brain, cervical spine and extremities scans. The measurements for SMFs were collected at 1 meter (m) and 2 meters away from the right, left and front side of the scanner gantry, in zone IV. The RF magnetic fields’ measurements were collected at 1 m away from the scanner on the right and left side of the scanner gantry. A questionnaire survey based on transient health effects and safety perception of MR staff around MRI scanners was also administered. Additionally, interviews on MR safety risks were conducted with four staff members from Pelonomi and Universitas hospital. The existing health and safety measures in zone III and IV were reviewed through the use of baseline risk assessment and image quality control test results were benchmarked against the relevant ACR guidelines. The results of chapter 3 demonstrated that the three scanners from two hospitals respect ICNIRP guidelines in terms of occupational exposure to both SMFs and RF magnetic fields. Configurations of scanners such as clinical setting, magnetic field shielding and magnet type influence propagation of stray static fields in zone IV. The emission of RF magnetic fields is influenced by scans performed, RF pulse design and sequence settings-lip angle. In chapter 4, a significant difference between job titles and safety around the scanners (p< 0.0023), as well as the number of years working in the MRI units (p< 0.0002) was observed. Headache was significantly associated with perceived MRI safety (p< 0.014). MR staff were more likely (OR 39.15, 95% CI: 4.91- 312.02) to experience transient health effects compared to the control group (p <0.0001), with radiographers being affected the most (OR 60.75, 95% Cl: 5.99- 616.67). SMFs exposure effects such as vertigo, feeling of instability and metallic taste were significantly associated with shift duration and movement of head/upper body in the scanner bore. However, RF exposure effects were mainly associated with job title and presence in the scanner room for longer durations of time. MRI safety policies, safety training of MR staff, demarcation of safety zones and absence of ferromagnetic detectors were identified as shortfalls in both hospitals. As reported in chapter 5, the results of risk assessment suggested that both hospitals scored a moderate risk score of 12.3 for hospital A and 13.1 for hospital B. Similar risks were observed; however, lack of demarcation of four MRI safety zones, ferromagnetic detectors, 5-gauss line and access control increased the risk rating in both facilities. Defective air-cooling systems influenced the ACD measurements performed from 1.5 T Siemens. Low contrast object detectability had 29 spokes for ACR T2, while the PIU for image intensity uniformity was 78.2% on a 3.0 T Philips. The model designed in chapter 6 addresses exposure levels of SMFs and RF magnetic fields reported in Chapter 3, and transient health effects reported by MR staff and MR safety risks identified in Chapter 4. The model also provides solutions (once a re-test is performed) to health risks and safety hazards reported, using the baseline risk assessment discussed in Chapter 5. The major shortfalls identified in both MR facilities studied include insufficient MR safety training, performance of activities in close proximity to the scanner bore, and failure to follow relevant ACR guidelines appropriately.