MRI safety Flashcards
what are local rules in MRI
documents detailing the work practices required in order to maintain safety in MRI environment
what are controlled ares in MRI
help maintain control of personnel, equipment and patients
what are 4 main publishers of MRI guidlines
- MHRA
- British standard
- IEC
- ICNIRP
What method of access are used in MRI areas and what is the optimal number of entrances into MRI areas
- swipe cards
- 1 access only is best
what are 4 forms of MRI hazards
- projectiles
- heating
- gradients
- implants
the magnetic field is ON at all times
what does the force of a projectile object/hazard depend on?
- weight of object
- magnetic field strength
earths magnetic field = 30-70 microT
fridge magnet= 10mT
scrap yard magnet= 0.3T
scanner= 3/1.5 T
As you approach the scanner, the magnetic field strength increases
what is the main way of minimising risk in terms of objects in MRI
never assume any piece of equipment is MRI safe
define MR unsafe, conditional, safe and no label
unsafe= not same in MRI room
conditional= only safe within conditions described on notice fixed to the equipment
safe= safe in magnet room, non-metallic, non-magnetic and non-conducting
no label= assume unsafe unless found otherwise
how does heating become a hazard in terms of patient positioning in MRI
- skin contact may lead to large surface current loops
how can u avoid heating due to contact in MRI
- ensure patient clothes aren’t wet + sufficient ventilation
- avoid direct contact between skin and tunnel ocvers
- ensure arms and legs aren’t touching
- use patient positioning aids e.g pads
what are 3 important precautions to take with cables in MRI
- never used damaged RF coils
- always handle coils with care
(store safe from mechanical damage, dont compress or stretch coils) - cable and coil heating
(avoid cable loops, use pads/blankets to avoid skin contact with cables and coils, ensure coils/accessories are correctly connected to scanner)
give some examples of alternative items that can cause burns on patients during MRI
- patient monitoring equipment e.g ECG pads
- transdermal patched e.g nicotime
- tattoos
- metallic make-up
- clothes
define SAR (units) + what is it
specific absorption rate
- watts per KG
- measure of RF power being deposited into the patient
what is the average SAR across the whole body given in 6 minutes from normal and 1st level controlled mode?
normal = less than 2 W/Kg
1st level controlled = less than 4 W/Kg
what is the average body temperature increase in normal and 1st level controlled mode?
normal = less than 0.5 degrees celcius
1st = less than 1 degree celcius
what is the link between SAR and magnetic field strength
SAR is proportional to magnetic field strength
define SED (units) + what it is and how to calculate it
specific energy dose
- total accumulated amount of energy calculated to have beed deposited int the patient
- J/KG
- SED = SAR X time RF energy applied
- also known as specific absorbed energy
what is B1+rms
- 10 second average of RF magnetic field exposure
- measured in microtesla
what is DWI
diffusion weighted imagine
- a method of signal contrast generation based on the differences in Brownian motion
- Brownian motion= any of various physical phenomena in which some quantity is constantly undergoing small, random fluctuations
what is EPI
- Echo planar imaging
- pulse sequence in which multiple echoes of different phase steps are acquired using rephasing gradients instead of repeated 180-degree radiofrequency pulses following the 90°/180° in a spin echo sequence.
what are the 3 types of magnetic fields and how can they affect implanted devices
- static magnetic field (constant horizontally)
(exert substantial force, affects operation) - time-varying magnetic field ( crosses diagonally through cylindrical bore)
( affects operation) - radio frequency field (random fires of radio frequency from any chosen angle)
( localised heating and burns)
