2. OUTLINE
Introduction to MRI
The mri system
The mri environment
Safety concern of mri
Ensuring safe practice
Mri screening procedure
Summary of safety issues
3. OBJECTIVES
At the end of the presentation all staff accessing
the mri environment will be able to describe:
the mri system and the mri environment
Key mri issues
The impartance of mri screening
The mri safety screening process
Emergency situation that could be potentially
arise in the mri environment.
4. MAGNETIC RESONANCE IMAGING(MRI)
mri uses a strong magnetic field to produce
detailed images of the body.
Mri does not involve ionizing
radiation eg. X-rays
5. THE MRI SYSTEM
The mri system is operated by trained staff
The mri system is housed in a dedicated unit
All mri equipment &accessories need to
approved for use in mri scan room
6. BASIC CONCEPTS:MAGENTIC FEILDS
To generate images the mri system uses three
magnetic fields:
1. The static magnetic field
2. Radiofreqency (RF)magnetic field
3. The gradient magnetic field
7. THE STATIC MAGNETIC FIELD
The static magnetic field is produced by a large and
powerful magnet.
Types of magnetic :
1. Permant magnets
2. Resistive magnet
3. Superconducting magnets
-Superconducting mri system may use very cold gases
(cryogens)to maintain the static magnetic field.
-such mri system need a power supply to keep the
cryogens at the low temperature required for
superconduction.
9. TERMINOLOGY
Magnetic field strength is measured in tesla
(T) or gauss(G) 1tesla=10000 gauses.
The spatial gradient of a magnetic field is
measuued in tesla/metre (t/m) or
gause/centimetre(G/cm).
10. RADIOFREQENCY (RF)MAGNETIC FIELD
Mr system require RF pulses to create the MR
signal
RF energy is transmitted from the transmit coil
to the patient and a receive coil used to
detect signal from the patient
12. THE GRADIENT MAGNETIC FIELD
The gradient magnetic field of the mri system
produce gradient magnetic field that spatial
very in strength.
The spatial varying gradient localize the signal
for image formation.
There are 3 sets of gradient coil-one set for
each direction (x,y,z).
17. THE FRINGE FIELD
• The Fringe Field refers to the strength of the static magnetic field away from the centre of the magnet (in 3
Diemention)
• Field strength decrese with increasing distance.
• Spatial gradient of the fringe field id measured in T/M or G/cm.
18. SAFETY RISK:STATIC MAGNETIC FEILD
• static magnetic field is always on…even when the
scanner is not 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 object that are ferrous are drawn to the
magnet bore and can be easily pulled out
hand,pocket.etc
Such incident have caused injury and death.
24. SAFETY RISK:RF MAGNETIC FEILD
when conduction material are placed within
the RF a concentration of electrical current
can cause excessive heating.
Even under normal scanning condition some
patients may feel warm.
Excessive heating can result in severe tissue
damage
Tissue burns are the most frequently reported
adverse incident associated with MRI.
26. SAFETY RISK:ACOUSTIC NOISE LEVEL
The sound in MRI is caused by the interaction
between the static magnetic field and the
gradient magnetic field.
Sound levels in mri can routinely be >85db
which can potentially cause auditory damage
Hearing protect is mandatory for all persons
remaining in scanner room.
28. SAFETY RISK:nerve stimulation
During imaging time varying magnetic field (e.g. the gradient magnetic
field)can induce current that cause peripheral nerve stimulation.
This can results in the patient experiencing sensation of pressure and pain
Severity is depending on the pulse sequences the patient position & the
sensitivity of patient.
29. SAFETY RISK:others
Clothing containing anti –microbial solution or
metal infused material can heat and cause
burns.
SAFETY RISK:mr contrast
.renal non- function
Pregency patients
Allergy to gadolium contrast
