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Safety of magnetic resonance imaging

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Medical MRI scanner

Magnetic resonance imaging (MRI) is in general a safe technique, although injuries may occur as a result of failed safety procedures or human error.[1] During the last 150 years, thousands of papers focusing on the effects or side effects of magnetic or radiofrequency fields have been pub­li­shed. They can be categorized as incidental and physiological.[2] Contraindications to MRI include most cochlear implants and cardiac pacemakers, shrapnel and metallic foreign bodies in the eyes. The safety of MRI during the first trimester of pregnancy is uncertain, but it may be preferable to other options.[3] Since MRI does not use any ionizing radiation, its use generally is favored in preference to CT when either modality could yield the same information.[4] (In certain cases, MRI is not preferred as it may be more expensive, time-consuming and claustrophobia-exacerbating).

Structure and certification

In an effort to standardize the roles and responsibilities of MRI professionals, an international consensus document, written and endorsed by major MRI and medical physics professional societies from around the globe, has been published formally. The document outlines specific responsibilities for the following positions:

  • MR Medical Director / Research Director (MRMD) – This individual is the supervising physician who has oversight responsibility for the safe use of MRI services.
  • MR Safety Officer (MRSO) – Roughly analogous to a radiation safety officer, the MRSO acts on behalf of, and on the instruction of, the MRMD to execute safety procedures and practices at the point of care.
  • MR Safety Expert (MRSE) – This individual serves in a consulting role to both the MRMD and MRSO, assisting in the investigation of safety questions that may include the need for extrapolation, interpolation, or quantification to approximate the risk of a specific study.

The American Board of Magnetic Resonance Safety (ABMRS) provides testing and board certification for each of the three positions, MRMD, MRSO, and MRSE. As most MRI accidents and injuries are directly attributable to decisions at the point of care, testing and certification of MRI professionals seeks to reduce the rates of MRI accidents and improve patient safety through the establishment of safety competency levels for MRI professionals.

Implants

MR-Safe sign
MR-Conditional sign
MR-Unsafe sign

All patients are reviewed for contraindications prior to MRI scanning. Medical devices and implants are categorized as MR Safe, MR Conditional or MR Unsafe:[5]

  • MR-Safe – The device or implant is completely non-magnetic, non-electrically conductive, and non-RF reactive, eliminating all of the primary potential threats during an MRI procedure.
  • MR-Conditional – A device or implant that may contain magnetic, electrically conductive, or RF-reactive components that is safe for operations in proximity to the MRI, provided the conditions for safe operation are defined and observed (such as 'tested safe to 1.5 teslas' or 'safe in magnetic fields below 500 gauss in strength').
  • MR-Unsafe – Objects that are significantly ferromagnetic and pose a clear and direct threat to persons and equipment within the magnet room.

The MRI environment may cause harm in patients with MR-Unsafe devices such as cochlear implants, aneurysm clips, and many permanent pacemakers. In November 1992, a patient with an undisclosed cerebral aneurysm clip was reported to have died shortly after an MRI exam.[6] Several deaths have been reported in patients with pacemakers who have undergone MRI scanning without appropriate precautions.[7] Increasingly, MR-conditional pacemakers are available for selected patients.[8]

Ferromagnetic foreign bodies such as shell fragments, or metallic implants such as surgical prostheses and ferromagnetic aneurysm clips also are potential risks. Interaction of the magnetic and radio frequency fields with such objects may lead to heating or torque of the object during an MRI.[9]

Titanium and its alloys are safe from attraction and torque forces produced by the magnetic field, although there may be some risks associated with Lenz effect forces acting on titanium implants in sensitive areas within the subject, such as stapes implants in the inner ear.

Intrauterine devices with copper are generally safe in MRI, but may become dislodged or even expelled, and it is therefore recommended to check the location of the IUD both before and after MRI.[10]

Projectile risk

The very high strength of the magnetic field may cause projectile effect (or "missile-effect") accidents, where ferromagnetic objects are attracted to the center of the magnet. Pennsylvania reported 27 cases of objects becoming projectiles in the MRI environment between 2004 and 2008.[11] There have been incidents of injury and death.[12][13] In one case, a six-year-old boy died in July 2001, during an MRI exam at the Westchester Medical Center, New York, after a metal oxygen tank was pulled across the room and crushed the child's head.[14][15] To reduce the risk of projectile accidents, ferromagnetic objects and devices typically, are prohibited near the MRI scanner, and patients undergoing MRI examinations must remove all metallic objects, often by changing into a gown or scrubs. Some radiology departments use ferromagnetic detection devices to ensure that no ferromagnetic objects enter the scanner room.[16][17]

MRI-EEG

In research settings, structural MRI or functional MRI (fMRI) may be combined with EEG (electroencephalography) under the condition that the EEG equipment is MR-compatible. Although EEG equipment (electrodes, amplifiers, and peripherals) are either approved for research or clinical use, the same MR Safe, MR Conditional and MR Unsafe terminology applies. With the growth of the use of MR technology, the U.S. Food & Drug Administration [FDA] recognized the need for a consensus on standards of practice, and the FDA sought out ASTM International [ASTM] to achieve them. Committee F04 [18] of ASTM developed F2503, Standard Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment.[19]

Genotoxic effects

There is no proven risk of biological harm from any aspect of a MRI scan, including very powerful static magnetic fields, gradient magnetic fields, or radio frequency waves.[20][21] Some studies have suggested possible genotoxic (i.e., potentially carcinogenic) effects of MRI scanning through micronuclei induction and DNA double strand breaks in vivo and in vitro,[22][23][24] however, in most, if not all cases, others have been unable to repeat or validate the results of these studies,[20][21] and the majority of research shows no genotoxic, or otherwise harmful, effects caused by any part of MRI.[20] A recent study confirmed that MRI using some of the most potentially-risky parameters tested to date (7-tesla static magnetic field, 70 mT/m gradient magnetic field, and maximum strength radio frequency waves) did not cause any DNA damage in vitro.[25]

Peripheral nerve stimulation

The rapid switching on and off of the magnetic field gradients is capable of causing nerve stimulation. Volunteers report a twitching sensation when exposed to rapidly switched fields, particularly in their extremities.[26][27] The reason the peripheral nerves are stimulated is that the changing field increases with distance from the center of the gradient coils (which more or less coincides with the center of the magnet).[28] Although PNS was not a problem for the slow, weak gradients used in the early days of MRI, the strong, rapidly switched gradients used in techniques such as EPI, fMRI, diffusion MRI, etc. are capable of inducing PNS. American and European regulatory agencies insist that manufacturers stay below specified dB/dt limits (dB/dt is the change in magnetic field strength per unit time), or else prove that no PNS is induced for any imaging sequence. As a result of dB/dt limitation, commercial MRI systems cannot use the full rated power of their gradient amplifiers.

Heating caused by absorption of radio waves

Every MRI scanner has a powerful radio transmitter that generates the electromagnetic field that excites the spins. If the body absorbs the energy, heating occurs. For this reason, the transmitter rate at which energy is absorbed by the body must be limited (see Specific absorption rate). It has been claimed that tattoos made with iron-containing dyes may lead to burns on the subject's body.[29][30] Cosmetics are very unlikely to undergo heating, as well as body lotions, since the outcome of the reactions between those with the radio waves is unknown. The best option for clothing is 100% cotton.

There are several positions strictly forbidden during measurement such as crossing arms and legs, and the patient's body may not create loops of any kind for the RF during the measurement.

Acoustic noise

Switching of field gradients causes a change in the Lorentz force experienced by the gradient coils, producing minute expansions and contractions of the coil. As the switching typically is in the audible frequency range, the resulting vibration produces loud noises (clicking, banging or beeping). This behaviour, of sound being generated by the vibration of the conducting components, is described as a coupled acousto-magneto-mechanical system, solutions to which provide useful insight to the behaviour of the scanners.[31] This is most marked with high-field machines,[32] and rapid-imaging techniques in which sound pressure levels may reach 120 dB(A) (equivalent to a jet engine at take-off),[33] and therefore, appropriate ear protection is essential for anyone inside the MRI scanner room during the examination.[34]

Radio frequency in itself does not cause audible noises (at least for human beings), since modern systems are using frequencies of 8.5 MHz (0.2 T system) or higher.[35]

Cryogens

As described in the Physics of magnetic resonance imaging article, many MRI scanners rely on cryogenic liquids to enable the superconducting capabilities of the electromagnetic coils within. Although the cryogenic liquids used are non-toxic, their physical properties present specific hazards.[36]

An unintentional shut-down of a superconducting electromagnet, an event known as "quench", involves the rapid boiling of liquid helium from the device. If the rapidly expanding helium cannot be dissipated through an external vent, sometimes referred to as a 'quench pipe', it may be released into the scanner room where it may cause displacement of the oxygen and present a risk of asphyxiation.[37]

Oxygen deficiency monitors usually are used as a safety precaution. Liquid helium, the most commonly used cryogen in MRI, undergoes near explosive expansion as it changes from a liquid to gaseous state. The use of an oxygen monitor is important to ensure that oxygen levels are safe for patients and physicians. Rooms built for superconducting MRI equipment should be equipped with pressure relief mechanisms [38] and an exhaust fan, in addition to the required quench pipe.

Because a quench results in rapid loss of cryogens from the magnet, recommissioning the magnet is expensive and time-consuming. Spontaneous quenches are uncommon, but a quench also may be triggered by an equipment malfunction, an improper cryogen fill technique, contaminants inside the cryostat, or extreme magnetic or vibrational disturbances.[39][40]

Pregnancy

Main article: Magnetic resonance imaging in pregnancy

No effects of MRI on the fetus have been demonstrated.[41] As opposed to many other forms of medical imaging in pregnancy, MRI avoids the use of ionizing radiation, to which the fetus is particularly sensitive. As a precaution, however, many guidelines recommend pregnant women only undergo MRI when essential, especially during the first trimester.[42]

The concerns in pregnancy are the same as for MRI in general, but the fetus may be more sensitive to the effects—particularly to heating and to noise. The use of gadolinium-based contrast media in pregnancy is an off-label indication and may be administered only in the lowest dose required to provide essential diagnostic information.[43]

Despite these concerns, MRI is rapidly growing in importance as a way of diagnosing and monitoring congenital defects of the fetus because it is able to provide more diagnostic information than ultrasound and it lacks the ionizing radiation of CT. MRI without contrast agents is the imaging mode of choice for pre-surgical, in-utero diagnosis and evaluation of fetal tumors, primarily teratomas, facilitating open fetal surgery, other fetal interventions, and planning for procedures (such as the EXIT procedure) to safely deliver and treat babies whose defects would otherwise be fatal.[44][45]

Claustrophobia and discomfort

Although painless, MRI scans may be unpleasant for those who are claustrophobic or otherwise uncomfortable with the imaging device surrounding them. Older closed bore MRI systems have a fairly long tube or tunnel. The part of the body being imaged must lie at the center of the magnet, which is at the absolute center of the tunnel. Because scan times on these older scanners may be long (occasionally up to 40 minutes for the entire procedure), people with even mild claustrophobia are sometimes unable to tolerate an MRI scan without management. Some modern scanners have larger bores (up to 70 cm) and scan times are shorter. A 1.5 T wide short bore scanner increases the examination success rate in patients with claustrophobia and substantially reduces the need for anesthesia-assisted MRI examinations even when claustrophobia is severe.[46]

Alternative scanner designs, such as open or upright systems, may be helpful where these are available. Although open scanners have increased in popularity, they produce inferior scan quality because they operate at lower magnetic fields than closed scanners. Commercial 1.5-tesla open systems have become available recently, however, providing much better image quality than previous lower field strength open models.[47]

Mirror glasses may be used to help create the illusion of openness. The mirrors are angled at 45 degrees, allowing the patient to look down their body and out the end of the imaging area. The appearance is of an open tube pointing upward (as seen when lying in the imaging area). Even though one is able to see around the glasses and the proximity of the device is very evident, this illusion is quite persuasive and relieves the claustrophobic feeling.

For young children who cannot hold still or would be frightened during the examination, chemical sedation or general anesthesia are the norm. Some hospitals encourage children to pretend the MRI machine is a spaceship or other adventure.[48] Certain hospitals with Children's wards have decorated scanners for this purpose, such as that at the Boston Children's Hospital, which operates a scanner with a special casing designed to resemble a sandcastle.[49]

Obese patients and pregnant women may find the MRI machine a tight fit. Pregnant women in the third trimester also may have difficulty lying on their backs for an hour or more without moving.

MRI versus CT

MRI and computed tomography (CT) are complementary imaging technologies and each has advantages and limitations for particular applications. CT is more widely used than MRI in OECD countries with a mean of 132 vs. 46 exams per 1000 population performed respectively.[50] A concern is the potential for CT to contribute to radiation-induced cancer and in 2007 it was estimated that 0.4% of current cancers in the United States were due to CTs performed in the past, and that in the future this figure may rise to 1.5–2% based on historical rates of CT usage.[51] An Australian study found that one in every 1800 CT scans was associated with an excess cancer.[52] An advantage of MRI is that no ionizing radiation is used and so it is recommended over CT when either approach could yield the same diagnostic information.[4] Although the cost of MRI has fallen, making it more competitive with CT, there are not many common imaging scenarios in which MRI can simply replace CT, however, this substitution has been suggested for the imaging of liver disease.[53] The effect of low doses of radiation on carcinogenesis also are disputed.[54] Although MRI is associated with biological effects, these have not been proven to cause measurable harm.[55]

Iodinated contrast medium is routinely used in CT and the main adverse events are anaphylactoid reactions and nephrotoxicity.[56] Commonly used MRI contrast agents have a good safety profile, but linear non-ionic agents in particular have been implicated in nephrogenic systemic fibrosis in patients with severely impaired renal function.[57]

MRI is contraindicated in the presence of MR-unsafe implants, and although these patients may be imaged with CT, beam hardening artefact from metallic devices, such as pacemakers and implantable cardioverter-defibrillators, also may affect image quality.[58] MRI is a longer investigation than CT and an exam may take between 20 and 40 minutes depending on complexity.[59]

Guidance

Safety issues, including the potential for biostimulation device interference, movement of ferromagnetic bodies, and incidental localized heating, have been addressed in the American College of Radiology's White Paper on MR Safety, which originally was published in 2002 and expanded in 2004. The ACR White Paper on MR Safety has been rewritten and was released early in 2007 under the new title ACR Guidance Document for Safe MR Practices.

In December 2007, the Medicines and Healthcare Products Regulatory Agency (MHRA), a UK healthcare regulatory body, issued their Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use. In February 2008, the Joint Commission, a U.S. healthcare accrediting organization, issued a Sentinel Event Alert #38, their highest patient safety advisory, on MRI safety issues. In July 2008, the United States Veterans Administration, a federal governmental agency serving the healthcare needs of former military personnel, issued a substantial revision to their MRI Design Guide,[60] that includes physical and facility safety considerations.

The European Directive on electromagnetic fields

This Directive (2013/35/EU – electromagnetic fields) [61] covers all known direct biophysical effects and indirect effects caused by electromagnetic fields within the EU and repealed the 2004/40/EC directive. The deadline for implementation of the new directive was 1 July 2016. Article 10 of the directive sets out the scope of the derogation for MRI, stating that the exposure limits may be exceeded during "the installation, testing, use, development, maintenance of or research related to magnetic resonance imaging (MRI) equipment for patients in the health sector, provided that certain conditions are met." Uncertainties remain regarding the scope and conditions of this derogation.[62]

References

  1. ^ Watson, Robert E. (2015-10-01). "Lessons Learned from MRI Safety Events". Current Radiology Reports. 3 (10): 37. doi:10.1007/s40134-015-0122-z. ISSN 2167-4825.
  2. ^ "Rinck, PA. Magnetic Resonance Imaging: Safety of Patients and Personnel. Free Offprint from Rinck PA. Magnetic Resonance in Medicine - A Critical Introduction. The Basic Textbook of the European Magnetic Resonance Forum. 12th edition, 2018/2020. BoD. ISBN 978-3-7460-9518-9".
  3. ^ Wang PI; Chong ST; Kielar AZ; Kelly AM; Knoepp UD; Mazza MB; Goodsitt MM (2012). "Imaging of pregnant and lactating patients: part 1, evidence-based review and recommendations". AJR Am J Roentgenol. 198 (4): 778–84. doi:10.2214/AJR.11.7405. PMID 22451541.
  4. ^ a b "iRefer". Royal College of Radiologists. Retrieved 10 November 2013.
  5. ^ ASTM International (2005). "American Society for Testing and Materials (ASTM) International, Designation: F2503-05. Standard Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment". {{cite journal}}: Cite journal requires |journal= (help)
  6. ^ "MRI-Related Death of Patient With Aneurysm Clip". Food and Drug Administration. 25 November 1992. Retrieved 19 October 2016. FDA has learned of a fatal injury sustained by a patient with a cerebral aneurysm clip while she was being prepared for an MRI procedure. It was reported that upon exposure to the magnetic field in the room, the clip moved and lacerated the patient's middle cerebral artery. Subsequently, the explanted device was shown to be magnetically active. This particular style or clip, which was implanted in 1978, was listed in several articles and recent medical texts as non-deflecting in a magnetic field.
  7. ^ "Physics of magnetic resonance imaging". My-MS.org. Retrieved 27 April 2012.
  8. ^ Colletti, P.M.; Shinbane, J; S, Shellock; F. G. (2011). "MR-conditional" pacemakers: the radiologist's role in multidisciplinary management". AJR Am J Roentgenol. 197 (4): W457–9. doi:10.2214/AJR.11.7120. PMID 21862773.
  9. ^ "Magnetic resonance safety policy of ucsf". University of California, San Francisco. Retrieved 28 April 2012.
  10. ^ Berger-Kulemann, Vanessa; Einspieler, Henrik; Hachemian, Nilouparak; Prayer, Daniela; Trattnig, Siegfried; Weber, Michael; Ba-Ssalamah, Ahmed (2013). "Magnetic Field Interactions of Copper-Containing Intrauterine Devices in 3.0-Tesla Magnetic Resonance Imaging: In Vivo Study". Korean Journal of Radiology. 14 (3): 416–22. doi:10.3348/kjr.2013.14.3.416. ISSN 1229-6929. PMC 3655294. PMID 23690707.
  11. ^ "Safety in the MR Environment: Ferromagnetic Projectile Objects in the MRI Scanner Room". Pa Patient Saf Advis. 6 (2): 56–62. June 2009. Archived from the original on 4 February 2015. Retrieved 4 February 2015.
  12. ^ Randal C. Archibold, "Hospital Details Failures Leading to M.R.I. Fatality, The New York Times, August 22, 2001
  13. ^ Donald G. McNeil Jr, "M.R.I.'s Strong Magnets Cited in Accidents," The New York Times, August 19, 2005.
  14. ^ Hartwig, Valentina; Giovannetti, Giulio; Vanello, Nicola; Lombardi, Massimo; Landini, Luigi; Simi, Silvana (2009). "Biological Effects and Safety in Magnetic Resonance Imaging: A Review". International Journal of Environmental Research and Public Health. 6 (6): 1778–1798. doi:10.3390/ijerph6061778. ISSN 1660-4601. PMC 2705217. PMID 19578460.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  15. ^ Chen, David W. (31 July 2001). "Boy, 6, Dies Of Skull Injury During M.R.I." The New York Times. Retrieved 24 October 2019.
  16. ^ "ACR Guidance Document for Safe MR Practices: 2007". Retrieved 2 August 2010.
  17. ^ "MRI Design Guide" (PDF). Archived from the original (PDF) on 14 July 2011. Retrieved 2 August 2010.
  18. ^ "Committee F04 on Medical and Surgical Materials and Devices." Committee F04
  19. ^ ASTM Standard F2503 – 13, 2013, "Standard Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment," ASTM International, West Conshohocken, PA, 2003, doi:10.1520/C0033-03, Standards F2503.
  20. ^ a b c Formica D; Silvestri S (April 2004). "Biological effects of exposure to magnetic resonance imaging: an overview". Biomed Eng Online. 3: 11. doi:10.1186/1475-925X-3-11. PMC 419710. PMID 15104797.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  21. ^ a b Hartwig, V.; Giovannetti, G.; Vanello, N.; Lombardi, M.; Landini, L.; Simi, S. (2009). "Biological Effects and Safety in Magnetic Resonance Imaging: A Review". Int. J. Environ. Res. Public Health. 6 (6): 1778–1798. doi:10.3390/ijerph6061778. PMC 2705217. PMID 19578460. {{cite journal}}: Unknown parameter |last-author-amp= ignored (|name-list-style= suggested) (help)CS1 maint: unflagged free DOI (link)
  22. ^ Lee JW; Kim MS; Kim YJ; Choi YJ; Lee Y; Chung HW (2011). "Genotoxic effects of 3 T magnetic resonance imaging in cultured human lymphocytes". Bioelectromagnetics. 32 (7): 535–42. doi:10.1002/bem.20664. PMID 21412810.
  23. ^ Simi S; Ballardin M; Casella M; De Marchi D; Hartwig V; Giovannetti G; Vanello N; Gabbriellini S; Landini L; Lombardi M (2008). "Is the genotoxic effect of magnetic resonance negligible? Low persistence of micronucleus frequency in lymphocytes of individuals after cardiac scan". Mutat. Res. 645 (1–2): 39–43. doi:10.1016/j.mrfmmm.2008.08.011. PMID 18804118.
  24. ^ Suzuki Y; Ikehata M; Nakamura K; Nishioka M; Asanuma K; Koana T; Shimizu H (2001). "Induction of micronuclei in mice exposed to static magnetic fields" (PDF). Mutagenesis. 16 (6): 499–501. doi:10.1093/mutage/16.6.499. PMID 11682641.
  25. ^ Fatahi M; Reddig A; Vijayalaxmi, Friebe B; Hartig R; Prihoda TJ; Ricke J; Roggenbuck D; Reinhold D; Speck O (March 16, 2016). "DNA double-strand breaks and micronuclei in human blood lymphocytes after repeated whole body exposures to 7T Magnetic Resonance Imaging". NeuroImage. 133: 288–293. doi:10.1016/j.neuroimage.2016.03.023. PMID 26994830.
  26. ^ Cohen MS; Weisskoff RM; Rzedzian RR; Kantor HL (May 1990). "Sensory stimulation by time-varying magnetic fields". Magn Reson Med. 14 (2): 409–14. doi:10.1002/mrm.1910140226. PMID 2345521.
  27. ^ Budinger TF; Fischer H; Hentschel D; Reinfelder HE; Schmitt F (1991). "Physiological effects of fast oscillating magnetic field gradients". J Comput Assist Tomogr. 15 (6): 909–14. doi:10.1097/00004728-199111000-00001. PMID 1939767.
  28. ^ Reilly JP (March 1989). "Peripheral nerve stimulation by induced electric currents: exposure to time-varying magnetic fields". Med Biol Eng Comput. 27 (2): 101–10. doi:10.1007/BF02446217. PMID 2689806.
  29. ^ James R. Ross, MD; Matthew J. Matava, MD (2011). "Tattoo-Induced Skin "Burn" During Magnetic Resonance Imaging in a Professional Football Player". Sports Health. 3 (5): 431–434. doi:10.1177/1941738111411698. PMC 3445217. PMID 23016039.
  30. ^ Rose Eveleth (March 6, 2014). "Some Tattoo Inks Can Burn You During an MRI".
  31. ^ S. Bagwell, P.D. Ledger, A.J. Gil, M. Mallett, M. Kruip, A linearised hp–finite element framework for acousto-magneto-mechanical coupling in axisymmetric MRI scanners, DOI: 10.1002/nme.5559
  32. ^ "The Evolution of Magnetic Resonance Imaging: 3T MRI in Clinical Applications" Archived 2013-06-15 at the Wayback Machine, Terry Duggan-Jahns, www.eradimaging.com
  33. ^ Price DL; De Wilde JP; Papadaki AM; Curran JS; Kitney RI (February 2001). "Investigation of acoustic noise on 15 MRI scanners from 0.2 T to 3 T". J Magn Reson Imaging. 13 (2): 288–93. doi:10.1002/1522-2586(200102)13:2<288::AID-JMRI1041>3.0.CO;2-P. PMID 11169836.
  34. ^ The Open University 2007: Understanding Cardiovascular Diseases, course book for the lesson SK121 Understanding cardiovascular diseases, printed by Cambridge University Press, ISBN 978-0-7492-2677-0 (can be found at OUW), pages 220 and 224.
  35. ^ "Introduction to MRI Physics, Page 4". www.simplyphysics.com. Retrieved 2017-06-09.
  36. ^ "Safety data sheet Nitrogen, refrigerated, liquid" (PDF). BOC. Archived from the original (PDF) on 2013-10-19. Retrieved 2014-09-11.
  37. ^ Kanal E; Barkovich AJ; Bell C; Borgstede JP; Bradley WG; Froelich JW; Gilk T; Gimbel JR; Gosbee J; et al. (2007). "ACR guidance document for safe MR practices: 2007". AJR Am J Roentgenol. 188 (6): 1447–74. doi:10.2214/AJR.06.1616. PMID 17515363.
  38. ^ International Electrotechnical Commission 2008: Medical Electrical Equipment – Part 2-33: Particular requirements for basic safety and essential performance of magnetic resonance equipment for medical diagnosis, manufacturers' trade standards [1], published by International Electrotechnical Commission, ISBN 2-8318-9626-6 (can be found for purchase at [2]).
  39. ^ "Cryogen Awareness Quenching and MRI Safety Training". Falck Productions. Retrieved 10 July 2012.
  40. ^ "GE Health Care" (PDF). GE. Archived from the original (PDF) on 15 January 2013. Retrieved 10 July 2012.
  41. ^ Alorainy IA; Albadr FB; Abujamea AH (2006). "Attitude towards MRI safety during pregnancy". Ann Saudi Med. 26 (4): 306–9. doi:10.5144/0256-4947.2006.306. PMC 6074503. PMID 16885635.
  42. ^ Coakley, F; Glenn, O; Qayyum, A; Barkovich, A; Goldstein, R; Filly, R (2004). "Fetal MRI: A Developing Technique for the Developing Patient". American Journal of Roentgenology. 182 (1): 243–252. doi:10.2214/ajr.182.1.1820243. PMID 14684546.
  43. ^ Webb JA; Thomsen HS (2013). "Gadolinium contrast media during pregnancy and lactation". Acta Radiol. 54 (6): 599–600. doi:10.1177/0284185113484894. PMID 23966544.
  44. ^ Kathary, N; Bulas, D; Newman, K; Schonberg, R (October 2001). "MRI imaging of fetal neck masses with airway compromise: utility in delivery planning". Pediatric Radiology. 31 (10): 727–731. doi:10.1007/s002470100527. PMID 11685443.
  45. ^ Mota, Raquel; Ramalho, Carla; Monteiro, Joaquim; Correia-Pinto, Jorge; Rodrigues, Manuela; Guimarães, Hercília; Spratley, Jorge; Macedo, Filipe; Matias, Alexandra; Montenegro, Nuno (27 November 2006). "Evolving Indications for the EXIT Procedure: The Usefulness of Combining Ultrasound and Fetal MRI". Fetal Diagnosis and Therapy. 22 (2): 107–111. doi:10.1159/000097106. PMID 17135754. Our two cases stress once more the importance of combining fetal ultrasound and magnetic resonance imaging in the characterization of cervical masses and its usefulness in programming the procedure with a multidisciplinary team.
  46. ^ Hunt CH; Wood CP; Lane JI; Bolster BD; Bernstein MA; Witte RJ (2011). "Wide, short bore magnetic resonance at 1.5 t: reducing the failure rate in claustrophobic patients". Clin Neuroradiol. 21 (3): 141–4. doi:10.1007/s00062-011-0075-4. PMID 21598040.
  47. ^ "Siemens Introduces First 1.5 Tesla Open Bore MRI". Medical.siemens.com. 2004-07-29. Retrieved 2010-08-02.
  48. ^ Tom Kelley; David Kelley (18 October 2013). "Kids Were Terrified of Getting MRIs. Then One Man Figured Out a Better Way". Slate.com. {{cite news}}: Unknown parameter |last-author-amp= ignored (|name-list-style= suggested) (help)
  49. ^ "Magnetic Resonance Imaging (MRI)". Boston Children's Hospital. Retrieved 12 September 2018.
  50. ^ Oecd (2011). Health at a Glance 2011. doi:10.1787/health_glance-2011-en. ISBN 9789264111530. ISSN 1995-3992. {{cite book}}: |journal= ignored (help)
  51. ^ Brenner DJ; Hall EJ (November 2007). "Computed tomography—an increasing source of radiation exposure". N. Engl. J. Med. 357 (22): 2277–84. doi:10.1056/NEJMra072149. PMID 18046031.
  52. ^ Mathews JD; Forsythe AV; Brady Z; Butler MW; Goergen SK; Byrnes GB; Giles GG; Wallace AB; Anderson PR; et al. (2013). "Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians". BMJ. 346: f2360. doi:10.1136/bmj.f2360. PMC 3660619. PMID 23694687.
  53. ^ Semelka RC; Armao DM; Elias J; Huda W (2007). "Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI". J Magn Reson Imaging. 25 (5): 900–9. doi:10.1002/jmri.20895. PMID 17457809.
  54. ^ Health risks from exposure to low levels of ionizing radiation : BEIR VII Phase. Washington, D.C.: National Academies Press. 2006. ISBN 978-0-309-09156-5.
  55. ^ Formica D; Silvestri S (2004). "Biological effects of exposure to magnetic resonance imaging: an overview". Biomed Eng Online. 3: 11. doi:10.1186/1475-925X-3-11. PMC 419710. PMID 15104797.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  56. ^ Bettmann MA (2004). "Frequently asked questions: iodinated contrast agents". Radiographics. 24 (Suppl 1): S3–10. doi:10.1148/rg.24si045519. PMID 15486247.
  57. ^ "Nephrogenic Systemic Fibrosis" (PDF). ACR Manual on Contrast Material. American College of Radiology. Retrieved 13 October 2012.
  58. ^ Mak GS; Truong QA (2012). "Cardiac CT: Imaging of and Through Cardiac Devices". Curr Cardiovasc Imaging Rep. 5 (5): 328–336. doi:10.1007/s12410-012-9150-8. PMC 3636997. PMID 23626865.
  59. ^ "MRI procedure". Royal College of Radiologists. Archived from the original on 24 July 2003. Retrieved 17 November 2013.
  60. ^ "MRI Design Guide". United States Department of Veterans Affairs. April 2008. Retrieved 12 October 2012.
  61. ^ "Directive 2013/35/EU of the European Parliament and of the Council. Official Journal of the European Union 2004 L179/1".
  62. ^ Keevil SF; Lomas DJ (2013). "The European Union physical agents (electromagnetic fields) directive: an update for the MRI community". Br J Radiol. 86 (1032): 20130492. doi:10.1259/bjr.20130492. PMC 3856543. PMID 24096591.
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