MRI - Lets ease ourselves in Flashcards
2 reasons why MRI is a relatively safe imaging technique (2 points)
no ionising radiation
no significant biological effects
Name the 3 principle safety considerations
magnetic projectile effect
acoustic noise
bio-effects
Describe the magnet projectile effect
when a ferromagnetic object is brought close to the magnet, it will experience a force which can turn an object into a high-velocity projectile that could be dangerous
Bigger the object ….
the stronger the forces involved
Describe the MRI fringe field (2 points)
decreases rapidly with distance
controlled area should be defined within the vicintiy of the magnet
What could happen with patients with metallic foreign bodies
could move and rupture a blood vessel during the scan
What could happen to the function of metallic medical devices, such as pacemakers or cochlear implants
could become severely impaired by the static magnetic field
Describe the problems that arise with acoustic noise
in some MR sequences, the noise level exceeds safety guidelines, therefore, recommend all patients and any other people in the room should be given ear defenders for protection
Which 3 types of fields are patients exposed to
main static field
gradient fields
radiofrequency fields
What is the main effect of RF fields
heating of patient tissue
How can the main effect of RF fields be prevented
make sure the Specific Absorption Rate (SAR) is kept to a minimum
What is the SAR
the potential for heating of the patients tissue due to the application of RF energy necessary to produce a MR signal
What is one factor in SAR
Field Strength - if it doubles then it leads to quadrupling f the SAR
Why should it be ensured the cables should not be in a loop
It will cause conduction of electrical currents causing heat and therefore burns
uses pads to separate patient from coming into contact with the bore of the magnet
Who can come into contact with the ultra cold liquids that maintain the superconducting magnet
Restricted to fully trained MR engineering staff
