Subjective symptoms and their evolution in a small group of magnetic resonance imaging (MRI) operators recently engaged

Health effects related to exposure of static magnetic fields and acoustic noise-comparison between MR and CT radiographers

OBJECTIVES

We explored the prevalence of health complaints subjectively associated with static magnetic field (SMF) and acoustic noise exposure among MR radiographers in Sweden, using CT radiographers as a control group. Additionally, we explored radiographers' use of strategies to mitigate adverse health effects.

METHODS

A cross-sectional survey was sent to all hospitals with MR units in Sweden. MR and/or CT personnel reported prevalence and attribution of symptoms (vertigo/dizziness, nausea, metallic taste, illusion of movement, ringing sensations/tinnitus, headache, unusual drowsiness/tiredness, forgetfulness, difficulties concentrating, and difficulties sleeping) within the last year. We used logistic regression to test associations between sex, age, stress, SMF strength, working hours, and symptom prevalence. Data regarding hearing function, work-environmental noise, and strategies to mitigate adverse symptoms were also analysed.

RESULTS

In total, 529 out of 546 respondents from 86 hospitals were eligible for participation. A ≥ 20 working hours/week/modality cut-off rendered 342 participants grouped into CT (n = 75), MR (n = 121), or mixed personnel (n = 146). No significant differences in symptom prevalence were seen between groups. Working at ≥ 3T increased SMF-associated symptoms as compared with working at ≤ 1.5T (OR: 2.03, CI₉₅: 1.05-3.93). Stress was a significant confounder. Work-related noise was rated as more troublesome by CT than MR personnel (p < 0.01). MR personnel tended to use more strategies to mitigate adverse symptoms.

CONCLUSION

No significant differences in symptom prevalence were seen between MR and CT radiographers. However, working at 3T increased the risk of SMF symptoms, and stress increased adverse health effects. Noise nuisance was considered more problematic by CT than MR personnel.

KEY POINTS

• No significant differences in symptom prevalence were seen between MR and CT radiographers. • Working at ≥ 3 T doubled the odds of experiencing SMF symptoms (vertigo/dizziness, nausea, metallic taste, and/or illusion of movement) as compared to working exclusively at ≤ 1.5 T. • Work-related acoustic noise was less well mitigated and was rated as more troublesome by CT personnel than by MR personnel.

Electromagnetic Exposure of Personnel Involved in Cardiac MRI Examinations in 1.5T, 3T and 7T Scanners

(1) Background: It has been hypothesised that a significant increase in the use of cardiac magnetic resonance (CMR), for example, when examining COVID-19 convalescents using magnetic resonance imaging (MRI), has an influence the exposure profiles of medical personnel to static magnetic fields (STmf). (2) Methods: Static exposure to STmf (SEmf) was recorded during activities that modelled performing CMR by radiographers. The motion-induced time variability of that exposure (TVEmf) was calculated from SEmf samples. The results were compared with: (i) labour law requirements; (ii) the distribution of vertigo perception probability near MRI magnets; and (iii) the exposure profile when actually performing a head MRI. (3) Results: The exposure profiles of personnel managing 42 CMR scans (modelled using medium (1.5T), high (3T) and ultrahigh (7T) field scanners) were significantly different than when managing a head MRI. The majority of SEmf and TVEmf samples (up to the 95th percentile) were at low vertigo perception probability (SEmf < 500 mT, TVEmf < 600 mT/s), but a small fraction were at medium/high levels; (4) Conclusion: Even under the “normal working conditions” defined for SEmf (STmf < 2T) by labour legislation (Directive 2013/35/EC), increased CMR usage increases vertigo-related hazards experienced by MRI personnel (a re-evaluation of electromagnetic safety hazards is suggested in the case of these or similar changes in work organisation).

Issues in the Implementation of Directive 2013/35/EU Regarding the Protection of Workers against Electromagnetic Fields

In 2016 the Directive 2013/35/EU regarding the protection of health and safety of workers exposed to electromagnetic fields was transposed in Italy. Since then, the authors of this paper have been faced with several issues related to the implementation of the provisions of the Directive, which pose some interpretative and operative concerns. A primary critical feature of the Directive is that, in some circumstances, conditions of "overexposure", i.e., of exceeding the exposure limits, are allowed. In the case of transient effects, the "flexibility" concerning the compliance with exposure limits is based on the approach introduced by ICNIRP in its guidelines on static magnetic fields and on time-varying electric and magnetic fields. On the contrary, the possibility of exceeding the exposure limits for health effects, formally recognized in the article of the Directive dealing with derogations, is not included in the ICNIRP guidelines. This paper analyzes the main concerns in interpreting and managing some provisions of the Directive with particular reference to the issue of how the employer can manage the situations of overexposure.

Subjective Symptoms in Magnetic Resonance Imaging Personnel: A Multi-Center Study in Italy

Introduction: Magnetic Resonance Imaging (MRI) personnel have significant exposure to static and low-frequency time-varying magnetic fields. In these workers an increased prevalence of different subjective symptoms has been observed. The aim of our study was to investigate the prevalence of non-specific subjective symptoms and of "core symptoms" in a group of MRI personnel working in different centers in Italy, and of possible relationships with personal and occupational characteristics. Methods: The occurrence of 11 subjective symptoms was evaluated using a specific questionnaire with 240 subjects working in 6 different Italian hospitals and research centers, 177 MRI health care and research personnel and 63 unexposed subjects employed in the same departments. Exposure was subjectively investigated according to the type of MRI scanner (≤1.5 vs. ≥3 T) and to the number of MRI procedures attended and/or performed by the personnel, even if no information on how frequently the personnel entered the scanner room was collected. The possible associations among symptoms and estimated EMF exposure, the main characteristics of the population, and job stress perception were analyzed. Results: Eighty-six percent of the personnel reported at least one symptom; drowsiness, headache, and sleep disorders were the most frequent. The total number of symptoms did not differ between exposed persons and controls. Considering the total number of annual MRI procedures reported by the personnel, no significant associations were found nor with the total number of symptoms, nor with "core symptoms." Only subjects complaining of drowsiness also reported a significantly higher mean annual number of MRI procedures with ≤ 1.5 T scanners when compared with exposed subjects without drowsiness. In a multivariate model, subjects with a high level of perceived stress complained of more symptoms (p = 0.0002). Conclusions: Our study did not show any association between the occurrence of reversible subjective symptoms, including the more specific "core symptoms," and the occupational exposure of MRI personnel to static and low-frequency time-varying magnetic fields. On the other hand, the role played by occupational stress appears to be not negligible. In further research in this field, measurements of EMF exposure should be considered.

Occupational exposure to electromagnetic fields in magnetic resonance environment: an update on regulation, exposure assessment techniques, health risk evaluation, and surveillance

Magnetic resonance imaging (MRI) is one of the most-used diagnostic imaging methods worldwide. There are ∼50,000 MRI scanners worldwide each of which involves a minimum of five workers from different disciplines who spend their working days around MRI scanners. This review analyzes the state of the art of literature about the several aspects of the occupational exposure to electromagnetic fields (EMF) in MRI: regulations, literature studies on biological effects, and health surveillance are addressed here in detail, along with a summary of the main approaches for exposure assessment. The original research papers published from 2013 to 2021 in international peer-reviewed journals, in the English language, are analyzed, together with documents published by legislative bodies. The key points for each topic are identified and described together with useful tips for precise safeguarding of MRI operators, in terms of exposure assessment, studies on biological effects, and health surveillance.

Exposure levels of radiofrequency magnetic fields and static magnetic fields in 1.5 and 3.0 T MRI units

Magnetic resonance imaging (MRI) staff is exposed to a complex mixture of electromagnetic fields from MRI units. Exposure to these fields results in the development of transient exposure-related symptoms. This study aimed to investigate the exposure levels of radiofrequency (RF) magnetic fields and static magnetic fields (SMFs) from 1.5 and 3.0 T MRI scanners in two public hospitals in the Mangaung Metropolitan region, South Africa. The exposure levels of SMFs and RF magnetic fields were measured using the THM1176 3-Axis hall magnetometer and TM-196 3 Axis RF field strength meter, respectively. Measurements were collected at a distance of 1 m (m) and 2 m from the gantry for SMFs when the brain, cervical spine and extremities were scanned. Measurements for RF magnetic fields were collected at a distance of 1 m with an average scan duration of six minutes. Friedman’s test was used to compared exposure mean values from two 1.5 T scanners, and Wilcoxon test with Bonferroni adjustment was used to identify where the difference between exist. The Shapiro–Wilk test was also used to test for normality between exposure levels in 1.5 and 3.0 T scanners. The measured peak values for SMFs from the 3.0 T scanner at hospital A were 1300 milliTesla (mT) and 726 mT from 1.5 T scanner in hospital B. The difference in terms of SMFs exposure levels was observed between two 1.5 T scanners at a distance of 2 m. The difference between 1.5 T scanners at 1 m was also observed during repeated measurements when brain, cervical spine and extremities scans were performed. Scanners’ configurations, magnet type, clinical setting and location were identified as factors that could influence different propagation of SMFs between scanners of the same nominal B0. The RF pulse design, sequence setting flip-angle and scans performed influenced the measured RF magnetic fields. Three scanners were complaint with occupational exposure guidelines stipulated by the ICNIRP; however, peak levels that exist at 1 m could be managed through adoption of occupational health and safety programs.

Occupational exposure to MRI-related magnetic stray fields and sleep quality among MRI - Technicians - A cross-sectional study in the Netherlands

We investigated the association between occupational exposure to MRI-related magnetic stray fields with sleep quality in a cross-sectional study among 490 imaging technicians in the Netherlands. Imaging technicians filled in questionnaires about MRI exposure, lifestyle, work practices and sleep quality and quantity (Medical Outcomes Study sleep scale). Of six sleep domains, exposure to MRI-related magnetic stray fields appeared to be associated with increased sleep disturbance (OR 1.93, 95% CI 1.00-3.70) and non-optimal sleep duration (OR 1.95, 95% CI 1.11-3.44). Given earlier findings of possible increased accident risks among exposed imaging technicians, these findings merit follow-up.

Assessing Exposures to Magnetic Resonance Imaging's Complex Mixture of Magnetic Fields for In Vivo, In Vitro, and Epidemiologic Studies of Health Effects for Staff and Patients

A complex mixture of electromagnetic fields is used in magnetic resonance imaging (MRI): static, low-frequency, and radio frequency magnetic fields. Commonly, the static magnetic field ranges from one to three Tesla. The low-frequency field can reach several millitesla and with a time derivative of the order of some Tesla per second. The radiofrequency (RF) field has a magnitude in the microtesla range giving rise to specific absorption rate values of a few Watts per kilogram. Very little attention has been paid to the case where there is a combined exposure to several different fields at the same time. Some studies have shown genotoxic effects in cells after exposure to an MRI scan while others have not demonstrated any effects. A typical MRI exam includes muliple imaging sequences of varying length and intensity, to produce different types of images. Each sequence is designed with a particular purpose in mind, so one sequence can, for example, be optimized for clearly showing fat water contrast, while another is optimized for high-resolution detail. It is of the utmost importance that future experimental studies give a thorough description of the exposure they are using, and not just a statement such as “An ordinary MRI sequence was used.” Even if the sequence is specified, it can differ substantially between manufacturers on, e.g., RF pulse height, width, and duty cycle. In the latest SCENIHR opinion, it is stated that there is very little information regarding the health effects of occupational exposure to MRI fields, and long-term prospective or retrospective cohort studies on workers are recommended as a high priority. They also state that MRI is increasingly used in pediatric diagnostic imaging, and a cohort study into the effects of MRI exposure on children is recommended as a high priority. For the exposure assessment in epidemiological studies, there is a clear difference between patients and staff and further work is needed on this. Studies that explore the possible differences between MRI scan sequences and compare them in terms of exposure level are warranted.

OCCUPATIONAL EXPOSURE OF NMR SPECTROMETRISTS TO STATIC AND RADIOFREQUENCY FIELDS

Occupational exposure to static and radiofrequency fields emitted by nuclear magnetic resonance spectrometers was assessed through systematic field metering during operation of 19 devices in nine research centers. Whereas no measurable levels of radiofrequency radiation were registered outside the spectrometers, significant exposure to static field was detected, with maximum values recorded at the user's hand (B = 683.00 mT) and head-thorax (B = 135.70 mT) during spectrometer manipulation. All values were well below the exposure limits set by the European standard for workers protection against the effects of acute field exposure only. As for potential effects of chronic exposure, waiting for more complete knowledge, adoption of technical and operational strategies for exposure minimizing is advisable. In this respect, the data revealed that compared with standard magnetic shielding, ultrashield technology allows a 20-65-fold reduction of the field strength received by the operator.