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Frankel, J. (2021). Characterization of the MRI patient exposure environment and exposure assessment methods for magnetic fields in MRI scanners. (Doctoral dissertation). Umeå: Umeå universitet
Open this publication in new window or tab >>Characterization of the MRI patient exposure environment and exposure assessment methods for magnetic fields in MRI scanners
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetic resonance imaging (MRI) has become one of the most common imaging modalities available in modern medicine, and it is an indispensable diagnostic tool thanks to the unparalleled soft-tissue contrast and high image resolution. It is also a unique exposure environment consisting of a complex mix of magnetic fields. During an MRI scan, the patient is simultaneously exposed to a strong static magnetic field, a fast-switching gradient magnetic field, and a pulsed radiofrequency (RF) magnetic field. Transient acute effects, such as nerve excitation and tissue heating, are well known and limited by universal safety guidelines. Long-term health effects related to MRI exposure have, however, not been scientifically established, and no interaction mechanisms have been verified, despite a growing body of research on electromagnetic field exposure. Further epidemiological and experimental research on MRI exposure has been recommended but the lack of a common definition of dose or exposure metric makes evaluation of past research and the design of future experiments difficult.

The objectives of this thesis were to characterize the MRI patient exposure environment in terms of the magnetic fields involved, suggest relevant exposure metrics, and introduce exposure assessment methods suitable for epidemiological and experimental research on MRI and long-term health effects.

In Paper I, we discussed the MRI exposure environment and its complexity and gave an overview of the current scientific situation. In Paper II, we investigated the exposure variability between different MRI sequences and suggested patient-independent exposure metrics that describe different characteristics of the magnetic field exposure, including mean, peak, and threshold values. In Paper III, we presented three exposure assessment methods, specifically suited to the complex MRI exposure environment: a measurement-based method, a calculation-based method, and a proxy method.

Papers I and II showed that MRI exams are not homogenous in terms of exposure, and exposure variability exists between the individual sequences that comprise an exam. Differences in mean exposure between sequences were several-fold, peak exposure differences up to 30-fold, and differences in threshold exposure were in some cases more than 100-fold. Furthermore, within-sequence exposure variability, related to the parameter adjustments that can be made at the scanner console before the start of a scan, gave rise to 5-to-8-fold exposure increases. Paper III showed that magnetic field models could be used to approximate the exposure at arbitrary locations inside the scanner, with slight underestimation of gradient field metrics and large variability in some RF field metrics. With improvements in accuracy and efficiency, the method could become a useful exposure assessment tool for in vitro and in vivo research as well as clinical work on medical implant safety. Our search for suitable exposure metric proxies resulted in a limited selection with low correlation between proxies and their counterpart metrics, but, with further development, the proxy method has the potential to allow for much needed exposure classification relevant to large-scale epidemiological research.

The work in this thesis has contributed to increased awareness of the unique MRI exposure environment, the characteristics of the magnetic fields involved, and the inherent exposure variability in MRI exams. The metrics and methods presented are specifically suited to exposure assessment of the unique MRI environment, and may contribute to improved research quality by allowing for meaningful comparisons between study results and for experimental conditions to be easily replicated in future studies.

Abstract [sv]

Magnetisk resonanstomografi (MR), som är en av de vanligaste medicinska avbildningsmetoderna idag, är ett oumbärligt diagnostiskt verktyg tack vare den oöverträffade mjukvävnadskontrasten och höga bildupplösningen. MR-kameran är också en unik exponeringsmiljö bestående av en komplex blandning av magnetfält med olika frekvenser och fältstyrkor. Under en vanlig MR-undersökning exponeras patienten för ett starkt statiskt magnetfält på 1,5 eller 3 Tesla, ett snabbt växlande gradientmagnetfält och ett pulsat radiofrekvent (RF) magnetfält. Gradientfältet kan ibland generera en pirrande känsla i huden på armarna och benen och RF-fältet kan orsaka vävnadsuppvärmning. Dessa övergående effekter är välkända och begränsas av allmänna säkerhetsriktlinjer. 

Långsiktiga hälsoeffekter relaterade till MR-exponering är dock inte vetenskapligt fastställda och det finns inga vedertagna interaktionsmekanismer. Det finns en hel del forskning på magnetfältsexponering och biologiska effekter, men resultaten är blandade och svåra att tyda. Till skillnad från joniserande strålning (används i bl.a. röntgenundersökningar), som vi vet kan skada DNA-molekylerna i våra celler och som medför en ökad risk att utveckla cancer vid alltför höga doser, så har vi inga etablerade mått på dos och exponering när det gäller låg- och radiofrekventa magnetfält. Därför kan kvaliteten på exponerings-bedömningarna skilja betydligt mellan olika forskningsstudier, vilket innebär att det är svårt att jämföra resultat från olika studier och ofta omöjligt att reproducera och verifiera tidigare forskningsresultat. Ytterligare epidemiologisk och experimentell forskning om MR-exponering behövs, men för att kunna genomföra den på ett meningsfullt sätt behövs tydliga exponeringsmått och metoder för exponeringsbedömning som är anpassade till den komplexa blandning av magnetfält som finns i MR-kameran.

Syftet med denna avhandling var att karakterisera MR-patientens exponerings-miljö med avseende på de tidsvarierande magnetfälten, föreslå lämpliga exponeringsmått och presentera exponeringsbedömningsmetoder som är relevanta för epidemiologisk och experimentell forskning om MR och långsiktiga hälsoeffekter.

I artikel I diskuterade vi MR-kamerans exponeringsmiljö och dess komplexitet och gav en översikt av det nuvarande vetenskapliga läget gällande MR och exponering. I artikel II undersökte vi hur exponeringen kan variera mellan de olika bildtagningssekvenserna som ingår i en MR-undersökning, och föreslog patient-oberoende exponeringsmått (olika typer av medelvärden, maxvärden och tröskelvärden) för att beskriva magnetfältens egenskaper. I artikel III presenterade vi tre metoder för att bedöma exponering, särskilt lämpade för den komplexa MR-exponeringsmiljön: en metod för mätningar av magnetfälten inne i kameran, en metod som simulerar kamerans magnetfält, och en metod för att identifiera mer lättillgängliga magnetfältsrelaterade parametrar som korrelerar starkt med de egentliga exponeringsmåtten.

I artiklar I och II visade vi att MR-undersökningar inte är homogena med avseende på exponering, så det går inte att enkelt klassificera en undersökning baserat på hur länge den pågår eller vilken kroppsdel som avbildas. Exponeringen kan variera betydligt mellan de olika sekvenserna som ingår ett undersöknings-protokoll. För vissa exponeringsmått är det bara några procents skillnad mellan olika sekvenser, medan det i andra fall kan vara mer än 100-faldig skillnad i exponering. Dessutom fann vi att exponeringen för en enskild sekvens kan varieras genom att MR-kamerans inställningar justeras inför en bildtagning. Detta innebär att det finns väldig många variabler som påverkar exponeringen i en MR-undersökning, och en medvetenhet om detta är viktigt om vi ska kunna genomföra meningsfulla exponeringsbedömningar. 

I artikel III visade vi hur simulerade magnetfält kan användas för att beräkna exponeringen på godtyckliga platser inuti MR-kameran. Modellen av gradient-fältet var stabil och fungerade bra för olika exponeringsmått, trots en liten underskattning av exponeringen. RF-fältets exponering visade sig vara svårare att simulera och resultaten varierade mer i jämförelsen med uppmätta värden. Med förbättringar i noggrannhet och effektivitet kan metoden bli ett användbart verktyg för exponeringsbedömning i framtida in vitro- och in vivo-studier samt i kliniska säkerhetsbedömningar, till exempel vid utvärdering av medicinska implantat. Jakten på lämpliga ersättningsparametrar för magnetfältens exponeringsmått resulterade i ett begränsat urval med relativt låg korrelation mellan parametrar och motsvarande mätvärden, så sökandet fortsätter. Med fortsatt utveckling har den här metoden potential att möjliggöra välbehövlig exponeringsklassificering som är relevant för storskalig epidemiologisk forskning.

Denna avhandling har belyst MR-kamerans unika exponeringsmiljö med fokus på de tidsvarierande magnetfältens egenskaper, och de många variabler som påverkar exponeringen under en MR-undersökning. De exponeringsmått och bedömningsmetoder som presenterats i detta arbete är särskilt lämpade för den unika exponeringsmiljö som finns i MR-kameror, och kan bidra till förbättrad forskningskvalitet genom att möjliggöra meningsfulla jämförelser mellan olika studiers resultat och upprepning av experimentella förhållanden i framtida studier.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2021. p. 49
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 2125
Keywords
electromagnetic fields, exposure assessment, magnetic resonance imaging, switched gradient fields, radiofrequency fields, exposure metrics
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
radiation physics
Identifiers
urn:nbn:se:umu:diva-182597 (URN)978-91-7855-502-4 (ISBN)978-91-7855-501-7 (ISBN)
Public defence
2021-05-21, Triple Helix, Samverkanshuset, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2021-04-30 Created: 2021-04-26 Last updated: 2023-09-14Bibliographically approved
Wilén, J., Olsrud, J., Frankel, J. & Hansson Mild, K. (2020). Valid Exposure Protocols Needed in Magnetic Resonance Imaging Genotoxic Research [Letter to the editor]. Bioelectromagnetics, 41(3), 247-257
Open this publication in new window or tab >>Valid Exposure Protocols Needed in Magnetic Resonance Imaging Genotoxic Research
2020 (English)In: Bioelectromagnetics, ISSN 0197-8462, E-ISSN 1521-186X, Vol. 41, no 3, p. 247-257Article in journal, Letter (Refereed) Published
Abstract [en]

Several in vitro and in vivo studies have investigated if a magnetic resonance imaging (MRI) examination can cause DNA damage in human blood cells. However, the electromagnetic field (EMF) exposure that the cells received in the MR scanner was not sufficiently described. The first studies looking into this could be regarded as hypothesis-generating studies. However, for further exploration into the role of MRI exposure on DNA integrity, the exposure itself cannot be ignored. The lack of sufficient method descriptions makes the early experiments difficult, if not impossible, to repeat. The golden rule in all experimental work is that a study should be repeatable by someone with the right knowledge and equipment, and this is simply not the case with many of the recent studies on MRI and genotoxicity. Here we discuss what is lacking in previous studies, and how we think the next generation of in vitro and in vivo studies on MRI and genotoxicity should be performed. Bioelectromagnetics.

Place, publisher, year, edition, pages
WILEY, 2020
Keywords
DNA, magnetic field, pulse sequence, isocenter, genotoxicity
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:umu:diva-169358 (URN)10.1002/bem.22257 (DOI)000519338000008 ()32157722 (PubMedID)2-s2.0-85081679643 (Scopus ID)
Available from: 2020-04-07 Created: 2020-04-07 Last updated: 2023-03-24Bibliographically approved
Frankel, J., Hansson Mild, K., Olsrud, J. & Wilén, J. (2019). EMF exposure variation among MRI sequences from pediatric examination protocols. Bioelectromagnetics, 40(1), 3-15
Open this publication in new window or tab >>EMF exposure variation among MRI sequences from pediatric examination protocols
2019 (English)In: Bioelectromagnetics, ISSN 0197-8462, E-ISSN 1521-186X, Vol. 40, no 1, p. 3-15Article in journal (Refereed) Published
Abstract [en]

The magnetic resonance imaging (MRI) exposure environment is unique due to the mixture and intensity of magnetic fields involved. Current safety regulations are based on well-known acute effects of heating and neuroexcitation while the scientific grounds for possible long-term effects from MRI exposure are lacking. Epidemiological research requires careful exposure characterization, and as a first step toward improved exposure assessment we set out to characterize the MRI-patient exposure environment. Seven MRI sequences were run on a 3-Tesla scanner while the radiofrequency and gradient magnetic fields were measured inside the scanner bore. The sequences were compared in terms of 14 different exposure parameters. To study within-sequence variability, we varied sequence settings such as flip angle and slice thickness one at a time, to determine if they had any impact on exposure endpoints. There were significant differences between two or more sequences for all fourteen exposure parameters. Within-sequence differences were up to 60% of the corresponding between-sequence differences, and a 5-8 fold exposure increase was caused by variations in flip angle, slice spacing, and field of view. MRI exposure is therefore not only sequence-specific but also patient- and examination occurrence-specific, a complexity that requires careful consideration for an MRI exposure assessment in epidemiological studies to be meaningful. 

Place, publisher, year, edition, pages
Wiley-Blackwell, 2019
Keywords
children, electromagnetic field, epidemiology, exposure assessment, radiofrequency
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:umu:diva-155086 (URN)10.1002/bem.22159 (DOI)000453860500001 ()30500987 (PubMedID)2-s2.0-85057846232 (Scopus ID)
Funder
Swedish Research Council, 521-2013-2702
Available from: 2019-01-10 Created: 2019-01-10 Last updated: 2023-03-24Bibliographically approved
Frankel, J., Wilén, J. & Hansson Mild, K. (2018). 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. Frontiers In Public Health, 6, Article ID 66.
Open this publication in new window or tab >>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
2018 (English)In: Frontiers In Public Health, ISSN 2296-2565, Vol. 6, article id 66Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2018
Keywords
electromagnetic field, occupational exposure, switched gradient field, diagnostic imaging, asurement
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:umu:diva-147347 (URN)10.3389/fpubh.2018.00066 (DOI)000429555100001 ()29594090 (PubMedID)2-s2.0-85057822404 (Scopus ID)
Available from: 2018-05-11 Created: 2018-05-11 Last updated: 2023-03-24Bibliographically approved
Mild, K. H., Friberg, S., Frankel, J. & Wilen, J. (2017). Exposure to the magnetic field from an induction loop pad for a hearing aid system. International Journal of Occupational Safety and Ergonomics, 23(1), 143-145
Open this publication in new window or tab >>Exposure to the magnetic field from an induction loop pad for a hearing aid system
2017 (English)In: International Journal of Occupational Safety and Ergonomics, ISSN 1080-3548, E-ISSN 2376-9130, Vol. 23, no 1, p. 143-145Article in journal (Refereed) Published
Abstract [en]

As a case study we have measured the magnetic field from an induction loop pad designed for hearing aid assistance. The magnitude of the field was high, although well below international guidelines. We recorded values up to 70% of the recommended standard in some instances. However, in view of the many reports indicating health effects of low-level exposure, we recommend that the precautionary principle is applied when such pads are given to people who might be especially vulnerable, such as children, pregnant women and women on breast cancer medication.

Keywords
hearing aid, cancer, reproduction, tamoxifen
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:umu:diva-132622 (URN)10.1080/10803548.2016.1226597 (DOI)000393712900016 ()2-s2.0-84988360798 (Scopus ID)
Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2023-03-24Bibliographically approved
Bäcklund, T., Frankel, J., Israelsson, H., Malm, J. & Sundström, N. (2017). Trunk sway in idiopathic normal pressure hydrocephalus: quantitative assessment in clinical practice. Gait & Posture, 62-70, Article ID 54.
Open this publication in new window or tab >>Trunk sway in idiopathic normal pressure hydrocephalus: quantitative assessment in clinical practice
Show others...
2017 (English)In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, p. 62-70, article id 54Article in journal (Refereed) Published
Abstract [en]

Background: In diagnosis and treatment of patients with idiopathic normal pressure hydrocephalus (iNPH), there is need for clinically applicable, quantitative assessment of balance and gait. Using a body worn gyroscopic system, the aim of this study was to assess postural stability of iNPH patients in standing, walking and during sensory deprivation before and after cerebrospinal fluid (CSF) drainage and surgery. A comparison was performed between healthy elderly (HE) and patients with various types of hydrocephalus (ventriculomegaly (VM)).

Methods: Trunk sway was measured in 31 iNPH patients, 22 VM patients and 58 HE. Measurements were performed at baseline in all subjects, after CSF drainage in both patient groups and after shunt surgery in the iNPH group.

Results: Preoperatively, the iNPH patients had significantly higher trunk sway compared to HE, specifically for the standing tasks (p < 0.001). Compared to VM, iNPH patients had significantly lower sway velocity during gait in three of four cases on firm support (p < 0.05). Sway velocity improved after CSF drainage and in forward-backward direction after surgery (p < 0.01). Compared to HE both patient groups demonstrated less reliance on visual input to maintain stable posture.

Conclusions: INPH patients had reduced postural stability compared to HE, particularly during standing, and for differentiation between iNPH and VM patients sway velocity during gait is a promising parameter. A reversible reduction of visual incorporation during standing was also seen. Thus, the gyroscopic system quantitatively assessed postural deficits in iNPH, making it a potentially useful tool for aiding in future diagnoses, choices of treatment and clinical follow-up. 

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Idiopathic normal pressure hydrocephalus, Trunk sway, Balance, Gait, Gyroscope
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:umu:diva-138239 (URN)10.1016/j.gaitpost.2017.02.017 (DOI)000405044400011 ()28259041 (PubMedID)2-s2.0-85014113899 (Scopus ID)
Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2023-03-23Bibliographically approved
Frankel, J., Hansson Mild, K., Olsrud, J., Garpebring, A. & Wilén, J.Exposure assessment methods for magnetic fields in MRI.
Open this publication in new window or tab >>Exposure assessment methods for magnetic fields in MRI
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
radiation physics
Identifiers
urn:nbn:se:umu:diva-182596 (URN)
Available from: 2021-04-26 Created: 2021-04-26 Last updated: 2023-09-14
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4084-6652

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