Magnetic Resonance: Risk and safety

There are many potential risks for workers in Magnetic Resonance (health care professionals and others). It is necessary to provide policies and practices for MR safety.
Keywords: 
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Main Author: 
María Isabel
Marco Galve
Co-authors: 
Ignacio
García Delgado
Francisco José
Gómez Gómez
Antonio Ángel
Chaves Manceras
Sebastián
González Álvarez
Aurora
Villalobos Sánchez

Marco Galve, María Isabel

Facultativo Especialista de Área del Servicio de Radiodiagnóstico / Centro Hospitalario de Alta Resolución de Benalmádena / Benalmádena, Málaga, España+34 657 92 92 53 / isabelmarcogalve@yahoo.es

García Delgado, Ignacio

Unidad de Prevención de Riesgos Laborales / Hospital Regional Universitario de Málaga (Carlos Haya) / Av. Carlos Hayal, s/n / 29010 Málaga, España

+34 95 129 12 76 / ignacio.garcia.sspa@juntadeandalucia.es

Gómez Gómez, Francisco José

Unidad de Prevención de Riesgos Laborales / Hospital Regional Universitario de Málaga (Carlos Haya) / Av. Carlos Hayal, s/n / 29010 Málaga, España

+34 95 129 15 44 / fjose.gomez.sspa@juntadeandalucia.es

Chaves Manceras, Antonio Ángel

Unidad de Prevención de Riesgos Laborales / Hospital Regional Universitario de Málaga (Carlos Haya) / Av. Carlos Hayal, s/n / 29010 Málaga, España

+34 95 129 12 31 / antonioa.chaves.sspa@juntadeandalucia.es

González Álvarez, Sebastián

Unidad de Prevención de Riesgos Laborales / Hospital Regional Universitario de Málaga (Carlos Haya) / Av. Carlos Hayal, s/n / 29010 Málaga, España+34 95 129 12 76 /

sebastian.gonzalez.sspa@juntadeandalucia.es Villalobos Sánchez, Aurora

Facultativo Especialista de Área / Hospital Regional Universitario de Málaga (Carlos Haya) / Av. Carlos Hayal, s/n / 29010 Málaga, España

+34 95 129 12 31 / aurora.villalobos.sanchez@andaluciajunta.es

ABSTRACT

ABSTRACT

There are many potential risks for workers in Magnetic Resonance (health care professionals and others). It is necessary to provide policies and practices for MR safety.

Key words

Key words

Magnetic resonance, safety.

INTRODUCTION

INTRODUCTION

Magnetic resonance imaging has radically changed the diagnosis and treatment of many diseases. Today, magnetic resonance (MR) is the technique of choice for a lot of pathologies, such as central nervous system and musculoskeletal diseases.

The introduction of MR technology as a clinical imaging modality isresponsible for a substantial increase in human exposure to strong static magnetic fields. Most MR systems in use today operate at fields ranging form 0.2 to 3 Tesla.

There are many potential risks in the MR environment, not only for the patient, but also for the accompanying members, family, health care professionals and other workers who can occasionally be in the MR room (clean service, security, firemen…).

MRI employs electromagnetic fields (EMF) in three frequency ranges: the static magnetic field (0 Hz), the time-varying magnetic field generated by the imaging gradients (100–1000 Hz), and the radiofrequency (RF) field (10–100 MHz).

The available information with regard to the effects of static magnetic fields on biological tissues is extensive for short-term exposures. There are investigations on alterations in cell growth, cell reproduction and teratogenicity, DNA structure and gene expression, pre-and post- natal reproduction and development, nerve activity, cardiovascular dynamics, haematological indices, temperature regulation, circadian rhythms, immune responsiveness and other biological processes. The majority of these studies concluded that exposures to static magnetic fields produce no substantial harmful bioeffects. There are injuries attributed to the inadvertent presence of ferromagnetic objects into the MR environment.

There are not controlled studies that demonstrate the absolute safety of chronic exposure to powerful magnetic fields, so there is a need for investigations.

In 2004 the European Union (EU) adopted a Directive limiting occupational exposure to EMF.

It applies to all employment sectors, including medical MR.

These limits are needed to protect workers from known short-term adverse effects on the central nervous system occurring instantaneously on exposure to EMF above a well-defined threshold. EU Directive now postponed until April 2013

Exposure limits and Action values

The directive defines two sets of values.

Exposure limit values: Limits to exposure to EMFs which are based on established health effects and biological considerations. Compliance with these limites will ensure the workers are protected against known adverse health effects.

Action values: The magnitude of directly measurable parameters (E,H,B etc)at which one or more specified measures in the Directive must be undertaken. Compliance with these values will ensure compliance with the exposure limits.

Frequenc y range (Hz)

rms Current density for head and trunk (mA/m^2)

Whole body averag e SAR(W/kg)

Localise d SAR(head and trunk) (W/kg)

Localise d SAR(limbs) (W/kg)

Maximu m contact current (mA)

Power density (W/m^ 2)

Magnetic flux density B (T)

0

-

-

-

-

-

-

2 (5 forlimbs) Time weighted average: 0.2T

>0-1

40

-

-

-

8.0

-

-

1-4

40/f

-

-

-

8.0

-

-

4-1000

10

-

-

-

8.0

-

-

1-2.5k

f/100

-

-

-

8.0

-

-

2.5-100k

f/100

-

-

-

5x10^- 4f

-

-

100k-10M

f/100

0.4

10

20

50

-

-

10-110M

-

0.4

10

20

50

-

-

110M-10G

-

0.4

10

20

-

-

-

10-200G

-

-

-

-

-

50

-

Action Values

Frequency range (Hz)

E(V/m)

H (A/m)

B (10^-6T)

S(W/m^2)

Contact current (m/A)

>0-1

-

1.63 x10^5

2x10^5

-

1.0

1-8

20000

1.63x10^5/f^2

2x10^5/f

-

1.0

8-25

20000

2x10^4/f

2.5x10^4/f

-

1.0

0.25-0.82 k

500/f

20/f

25/f

-

1.0

0.82-65 k

610

24.4

30.7

-

4x10^-4f

0.065-1M

610

1.6/f

2.0/f

-

40

1-10 M

610/f

1.6/f

2.0/f

-

40

10-400 M

61

0.16

0.2

10

40

400-2000 M

3f^(1/2)

0.008f^(1/2)

0.01f^(1/2)

f/40

-

2-300 G

137

0.36

0.45

50

-

Ferrous objects should be restricted from entering the area close to the MR scanner, in order to prevent “missile effect “ accidents.

MR SAFETY POLICIES

MR safety policies

The powerful magnetic field makes necessary to divide the MR site into four zones and the workers into “MR personnel” and “non-MR personnel”(3)

Personnel definitions

Non-MR personnel: patients, visitors and facility staff who do not meet the criteria of level 1 or level 2 MR personnel.

Level 1 MR personnel: people who have passed safety educational efforts toensure their own safety.

Level 2 MR personnel: people who have been more extensively trained in thebroader aspects of MR safety issues ( MRI technologists, radiologists and radiology department nursing staff).

Zone definitions

Zone I: area that is freely accessible to the general public. This area is typically outside the MR environment and is the zone through which patients, health care personnel and other employees of the MR site access the MR environment.

Zone II: this one is the interface between the zone I and the controlled zone. The patients are not free to move throughout zone II. In this zone, the personnel make the screening questions and patient histories.

Zone III: all access to zone III is to be strictly restricted in order to avoid interactions between the individuals or equipment and the environment of MR scanner. So, zone III is controlled and under supervision of MR personnel.

Zone IV: this area is the MR scanner room itself. By definition is located within zone III as it is the MR magnet and is associated magnetic field which generates the existence of zone III.

MR AND PREGNANT WORKERS

Pregnant MR workers are allowed to work in the MR environment throughout all stages of pregnancy. They can enter to the MR room, position patients, scan,inject contrast material, but no must remain within the MR room during the acquisition of images.

This policy is caused by a conservative point of view, due to the insufficientknowledge about this.

There are no statistically differences between MR pregnant workers y the others in miscarriage percentage, infertility, number of fetus, low weigth at born.

REFERENCES

  • 1. Electromagnetic field exposure limitation and the future of MRI. BJR 78 (2005), 973–975
  • 2. MRIsafety.com. MRI safety, bioeffects and patient management.
  • 3. ACR Guidance Document for Safe MR practice: 2007. AJR 2007, 188: 1447 1474
  • 4. http://www.ismrm.org/safety/EU_Safety.htm (available on February 2008)

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