This presentation is based on mri safety and precautions

1. MRI SAFETY

2. INTRODUCTION
• There have been no known long - term adverse biological effects associated
with extended exposure to the magnetic fields used in MR imaging.
• On review of the individual components of the magnetic resonance imaging
process several reversible effects of magnetic field, gradient and radio
frequency fields can be observed.

3. THREE MAIN FACTORS
1. The main magnetic field
2. Time varying magnetic fields (Magnetic field gradients)
3. Radio frequency fields

4. THE MAIN MAGNETIC FIELD
Ranges of magnetic field strength is 0.01T-7T.
MR scanners used for clinical imaging worldwide
are 1.5 T-3T imaging systems.
 American Society for Testing and Materials
(ASTM) and FDA (Food and Drug Administration)
recommended MR scanners used for clinical imaging
is 0.5T-3T imaging systems.

5. BIOLOGICAL EFFECTS
Magneto-hydrodynamic effect <2T
Fatigue, Headache, Hypotension >2T
 SAR ULTRA HIGH FIELD IMAGING

6. STATIC MAGNETIC FIELD
Field strength Related disadvantage
<2T • No biological effects.
• Reversible effect on ECG due to magnetic hemodynamic
effect.
>2T • Reversible biological effect.
• Effects of magnetic interaction energy & cell orientation.
Ultra high field imaging • SAR.
• Lack of clinical safety , only for research.

7. FRINGE FIELD
Stray magnetic field outside the bore of the magnet.
FDA recommended that general public who have not been screened, limit
exposed of magnetic field strength of 5G or below.

8. PROJECTILES
Ferromagnetic substance - as projectiles in the presence of strong magnetic field
Small object Velocity -40miles/hr into a 1.5T scan room
1. Loose projectiles
2. Implants

9. LOOSE PROJECTILES

10. INCIDENT IN MUMBAI TATA MEMORIAL
HOSPITAL

12. QUENCHING
Sudden loss of absolute zero of temperature in the magnet
coils
It will terminate the superconducting and become resistive
Helium will escape from the cryogen bath
May happen accidentally or manually in case of
emergency

13. GRADIENT MAGNETIC FIELDS
 Gradients are used to spatially encode signal. In some sequences they
are also used to generate echoes. Gradients create at time- varying
magnetic field (TVMF) that result in unique safety considerations
different from those associated with the RF and static field. TVMF
effects include:
• Peripheral Nerve Stimulation
• Magneto- Phosphenes
• Acoustic Noise

14. PERIPHERAL NERVE STIMULATION
 TVMF effects vary with the strength, speed and duration of the gradient pulses.
 Biological effects that vary with current amplitude include reversible alterations in vision,
irreversible effects of cardiac fibrillation, alterations in the biochemistry of cells and
fracture union.
 Examinations using echo planar techniques include mild cutaneous sensations and
involuntary muscle contractions. This phenomenon is known as peripheral nerve
stimulation.

15. MAGNETO- PHOSPHENES
• Patients will note unusual visual disturbances during MR scanning.
• Visual effects may occur when retinal phosphates are stimulated by induction
from TVMF.
• This phenomenon is known as magneto - phosphenes and is described as ‘ stars
in one ’s eyes ’ or presents as light flashes. It is thought to be due to stimulation
of the retina by an external magnetic field.

16. ACOUSTIC NOISE
Noise tends to be enhanced by decreases in:
1. Section thickness,
2. Field of view,
3. Repetition time,
4. Echo time.
The gradient magnetic field is the main source of acoustic noise – Created due to
current passing through gradient coils during image acquisition

17. ACOUSTIC NOISE AND PERMISSIBLE LIMIT
The U.S. FDA released guidelines for acoustic noise levels:
• In the united kingdom, guidelines issued by the department of health recommend
hearing protection be worn by staff exposed to an average of 85-db over an eight
hour day.

18.  MR systems effects : communication interference patient annoyance
Temporary(99db),permanent hearing loss(140db).
 Solution : ear plugs /head phones
Silent MRI

19. RADIOFREQUENCY FIELD
• Non ionising radiation.
• Exposure to radiofrequency occurs during the MR examination –
hydrogen nuclei are subjected to an oscillating magnetic field.
• The source of this Electro-Magnetic Radiation is the radio
frequency coil that surrounds the patients inside the magnet bore.
• As the RF pulse is doubled – four times the power is used.

20. RF COIL EFFECT
RF ANTENNAE :
Cause significant burn hazards due to electric current .
Insulated cables should be used .
Surface coils should be well placed to avoid a conductive loop
formed by its own cable .
RF IRRADIATION
Heating due to absorbed energy increase which increase with
frequency.

21. SAR
Power absorbed per unit mass of the tissue on exposure of RF is called Specific
absorption rate (SAR) and it is measured in watt per kilogram.
Concern of temperature rise increases in patient with implant, pregnancy, obesity, who
are unable to sense heat or unable to communicate heat sensations, with excessive tattoos.

22. Increase in field strength, radio frequency power, duty cycle, RF coil type and body
size increases SAR. Lowering flip angle and time of repetition (TR) reduces the SAR.
Patient information such as weight and age are important inputs to the system for
selection of RF power.
Selection of pulse sequences and scan parameters are also important factors to
optimize SAR. Pulse sequence such as spin echo needs more RF pulse than gradient
echo.

23. Whole body Head Torso Extremities
FDA 4W/kg-15min
exposure averaged
3W/kg-10 minute
exposure averaged
8W/kg-5minute exposure
per gram of tissue
12W/kg-5 minute exposure per
gram of tissue
IEC (Level 0)
Normal operating
mode
2W/kg 3.2W/kg 10W/kg 20W/kg
IEC (Level I)
1st level controlled
Operating Mode
4W/kg 3.2W/kg 10W/kg 20W/kg
IEC (Level II)
1st level controlled
Over level I values
MRI scanner estimates SAR before scan is initiated for every pulse sequence on the basis of technical
parameters and patient weight. FDA, USA and International electro-technical commission recommend
the limit of SAR as under:
Any pulse sequence must not raise the temperature by more than
1º Celsius and no greater than 38º Celsius in the head.

25. To ensure patient safety, completion of the MRI screening form is required
prior to every MRI scan.
The MRI screening form is used to help identify any potential dangers for
patients.
The form consists of a series of questions intended to identify any metallic
objects within patient body that could be affected by the magnetic field.
2 screening are required:
- During the consent process
- Before the MRI (TECHNOLOGIST)
MRI SCREENING

26. IMPLANTS
Identify any previous done procedure - Metallic implants pose serious damaging effects.
Effects : Torque - seen by some metallic implants.
Heating – due to inability to dissipate heat causing by RF absorption.
Artifacts - causing misinterpretation.

27. PATIENT MONITORING
ISMRM safety committee : all patient be monitored verbally and visually.
In case of un-responsive, comatose, unconscious sedated ,hearing impaired
patients : pulse dosimeter monitoring can be use.

28. SAFETY EDUCATION
• All patients and accompanying personal should
complete a screening questionnaire prior to the exam
to ensure a controlled environment and reduce
potential risk of hazard.

29. PREGNANT PATIENTS
MRI is not considered to be hazardous to the fetus.
Cells undergoing division in first trimester of pregnancy are more susceptible to
adverse effect.
FDA : If the information to be gained by MR would have required more invasive
testing , MRI is acceptable.
 Pregnant patients or suspected should be identified before undergoing MRI to assess
the relative risk vs. The benefits of the examination.
Ultra high field strength should be avoid .

30. ZONE I
• All areas that are freely accessible to the general public
• Generally includes the parking lot, the general hallway, etc.
• All personnel are permitted in zone I.

31. ZONE II
• Is the interface between the publicly accessible uncontrolled Zone I and the strictly
controlled Zone III.
• Here should be a lock and warning signs between zone II and zone III
• Generally pertains to the patient waiting room.
• All personnel are permitted in zone II; however, there should be a MR trained ‘ gate-
keeper’ to keep patients (non- M R personnel) from inadvertently wandering into zone
III and zone IV.

32. ZONE III
– All access to at least zone III is to be strictly restricted, with
limited access.
– Is the region in which free access by unscreened non - MR
personnel and/or ferromagnetic objects and equipment can result
in serious injury or death.
– Generally pertains to the dressing room and/or the console area;
this area should be strictly monitored as it is the interface to zone
IV.
– Only level 2 personnel can escort level 1 personnel into this
zone. Level 2 personnel should also keep visual and/or verbal
contact with level 1 personnel at all times while in zone III and IV.

33. ZONE IV
• Is only suitable for screened patients under
direct constant supervision of MRI staff as
there is a risk of patient heating, RF antenna
effects, missile effects and anoxia due to
quench pipe failure.
• Only level 2 personnel can escort level 1
personnel into this zone. Level 2 personnel
should also keep visual and/or verbal contact
with all level 1 personnel at all times while in
zone III and IV.

34. LEVELS OF PERSONNEL
 NON- MR PERSONNEL – essentially no MRI training (includes patients,
visitors or facility staff who do not meet the criteria of level 1 or level 2 MR
personnel).
 LEVEL 1 – individuals who have passed minimal safety educational efforts to
ensure their own safety as they work within zone III regions (e.g. MRI
department office staff , patient aides).
 LEVEL 2 – individuals who have been more extensively trained and educated
in the broader aspects of MR safety issues.

35. MEDICAL EMERGENCIES
The MR suite should be equipped with
medical supplies on a crash cart
If there is a patient emergency in MRI
Get the patient out of the room

36. DETERMINING IF A MEDICAL DEVICE IS
SAFE IN THE MRI ENVIRONMENT
MR Safe
MR Conditional
MR Unsafe

37. REFERENCES
• MRI IN PRACTICE FOURTH EDITION -
CATHERINE WESTBROOK