SMRT MRI Safety Lvl 1

to generate images the MRI system uses three magnetic fields

1. Static Magnetic Field

2. Radio-Frequency (RF) Magnetic Field

3. The Gradient Magnetic Field

Static Magnetic Field

• produced by a large and powerful magnet

• types of MRI magnets

  • permanent magnets

  • resistive magnets

  • superconductive magnets —

    • most common for clinical MRI systems

    • require power supply of cryogens to maintain static magnetic field

magnetic field strength is measured in

tesla (T) or gauss (G); 1 tesla = 10,000 gauss

Radio-Frequency (RF) magnetic field

• require RF pulses to create MR signal

• RF energy is transmitted from transmit RF coil to the patient & a receive coil is used to detect signal from the patient

Gradient Magnetic Field

• gradient coils of MRI system produce Gradient Magnetic Fields that spatially vary in strength

• localize the signal for image formation

• 3 sets of gradient coils — one set for each direction

safety zones for MRI environment

1. lobby / reception

2. changing rooms & screening area

3. MRI control area

   • RESTRICTED — all persons screened and/or supervised by trained MRI personnel

4. MRI scanner room

   • RESTRICTED — all persons screened & supervised by trained MRI personnel

Fringe Field

refers to the strength of the static magnetic field away from the center of the magnet

• decreases with increasing distance

• measured in T/m or G/cm

5 gauss line

the point in the fringe field beyond which it is considered unsafe for an unscreened person to pass

• dependent on the scanner field strength & system design

safety risk: static magnetic field

is always ON.. even when the scanner is not in operation

RISK: the projectile or missile effect

• translational or attractive forces on ferrous metallic objects when in the MRI field present potential for severe injury

• metallic objects that are ferrous are drawn to the magnet bore and can be easily pulled out of hands, pockets etc

safety risk: RF magnetic field

• conducting materials within RF field can cause excessive heating

• results in severe tissue damage

• most frequently reported issue with MRI

summary of metal in MRI

• projectile or missile effect

  • ferrous metal objects / implants are attracted to magnets and can be strongly drawn towards the magnet bore

• mri related burns

  • all metals conduct electricity and can potentially be associated with heating caused by exposure to the RF magnetic field

safety risk: acoustic noise level

sound in MRI (whilst scanning) is caused by the interaction between the static magnetic field and the gradient magnetic fields

• sound levels in MRI can routinely be >85dB which can potentially cause auditory damage

• auditory protection required

Safety risk: nerve stimulation

During imaging time varying magnetic fields can induce currents that cause peripheral nerve stimulation

• results in patient experiencing sensations of pressure and/or pain

other safety risks

• clothing containing anti-microbial solutions or metal infused material can heat & cause burns

• medication patches and skin patches may have metallic components that can heat & cause burns

safety risk: MRI contrast agents

• gadolinium is a paramagnetic contrast agent often used in MRI to improve the visualization of vascular anatomy, pathological lesions or disease

• administered via an intravenous (IV) injection

key steps to promote safety in MRI

• annual mri safety training

• restricted access & appropriate supervision established for MRI control room & exam room

• appropriate screening prior to persons entering the MRI control room

• establishing MRI safety of implants / devices

• MRI risk assessments for equipment & appropriate use

• established protocols for MRI emergencies

annual mri safety training

• level 1 - basic MRI safety training for ALL staff

• level 2 - advance training for MRI staff

MRI screening procedures for patients

1. screen patient before scan date to identify any surgeries /accidents potentially involving metal

2. review all info regarding implants / devices

3. confirm & document MR conditions of implants

4. MRI tech to re-review all safety screening documents upon patient arrival

3 MRI safety categories

• MR safe

  • items that pose no known hazards in all MRI environments

  • no harm can come to patient or staff

• MR conditional

  • items that do not pose any known hazards in specific MRI environment with specific conditions of use

  • we can use but…

• MR unsafe

  • things should never go into MRI scanner rooms

what to do in event of a quench:

• open scanner door

• evacuate MRI scanner room safely and quickly

• do not close door until MRI scanner room has been evacuated

  notes:

  • mri system is not disconnected from the power supply

  • it may take minutes before the field has dropped to a safe level

  • objects held by the magnet field may fall towards the floor