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RAD413 > MRI safety > Flashcards

MRI safety Flashcards

1
Q

what are local rules in MRI

A

documents detailing the work practices required in order to maintain safety in MRI environment

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2
Q

what are controlled ares in MRI

A

help maintain control of personnel, equipment and patients

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3
Q

what are 4 main publishers of MRI guidlines

A
  • MHRA
  • British standard
  • IEC
  • ICNIRP
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4
Q

What method of access are used in MRI areas and what is the optimal number of entrances into MRI areas

A
  • swipe cards
  • 1 access only is best
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5
Q

what are 4 forms of MRI hazards

A
  • projectiles
  • heating
  • gradients
  • implants
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6
Q

the magnetic field is ON at all times

A
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7
Q

what does the force of a projectile object/hazard depend on?

A
  • weight of object
  • magnetic field strength
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8
Q

earths magnetic field = 30-70 microT
fridge magnet= 10mT
scrap yard magnet= 0.3T
scanner= 3/1.5 T

A
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9
Q

As you approach the scanner, the magnetic field strength increases

A
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10
Q

what is the main way of minimising risk in terms of objects in MRI

A

never assume any piece of equipment is MRI safe

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11
Q

define MR unsafe, conditional, safe and no label

A

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

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12
Q

how does heating become a hazard in terms of patient positioning in MRI

A
  • skin contact may lead to large surface current loops
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13
Q

how can u avoid heating due to contact in MRI

A
  • 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
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14
Q

what are 3 important precautions to take with cables in MRI

A
  • 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)
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15
Q

give some examples of alternative items that can cause burns on patients during MRI

A
  • patient monitoring equipment e.g ECG pads
  • transdermal patched e.g nicotime
  • tattoos
  • metallic make-up
  • clothes
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16
Q

define SAR (units) + what is it

A

specific absorption rate
- watts per KG
- measure of RF power being deposited into the patient

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17
Q

what is the average SAR across the whole body given in 6 minutes from normal and 1st level controlled mode?

A

normal = less than 2 W/Kg
1st level controlled = less than 4 W/Kg

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18
Q

what is the average body temperature increase in normal and 1st level controlled mode?

A

normal = less than 0.5 degrees celcius
1st = less than 1 degree celcius

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19
Q

what is the link between SAR and magnetic field strength

A

SAR is proportional to magnetic field strength

20
Q

define SED (units) + what it is and how to calculate it

A

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

21
Q

what is B1+rms

A
  • 10 second average of RF magnetic field exposure
  • measured in microtesla
22
Q

what is DWI

A

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

23
Q

what is EPI

A
  • 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.
24
Q

what are the 3 types of magnetic fields and how can they affect implanted devices

A
  • 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)
25
Q

when can you scan a patient with MR conditional devices on them

A
  • when the exact model and Mae has been ascertained
  • documented from recognised MR safety lists or manufacturer to be MR safe
26
Q

active devices shouldn’t be scanned at 3T unless included in manufacturers MR conditions

A
27
Q

implants with weak attraction to 1.5 T may experience substantial attraction at 3T

A
28
Q

What is the relationship of SAR going from a 1.5 to 3T

A

quadruples

29
Q

how can increase Tesla affect elongated implants

A

implants are more susceptible to increased heating

30
Q

why are medical implants grouped to be treated the same

A
  • to allow generic implant policy to be made to avoid checking each patient
  • quality improvement
  • increase workflow
31
Q

give some examples of implants that require outside personnel advice

A
  • shunts
  • deep brain stimulator
  • vagus nerve stimulator
  • pacemaker
  • intrathecal baclofen pumps
32
Q

give some examples of contraindicated implants

A
  • retinal tracks
  • cardiac pacemakers
  • automatic internal defibrilators
33
Q

what 4 teams are involved in the risk assessment of scanning contraindicated devices in MR?

A
  • MR responsible person
  • MR safety expert
  • radiologist
  • specialised clinician/referrer
34
Q

what are some things to consider if one is MR unsafe

A
  • alternate imaging modalities
  • lower field strength systems
  • implant manufacturer adivce
  • MR device parameters
  • SAR considerations
  • professional body reccomendations
35
Q

what is MR non-conditional

A

devices in patients that do not meet all the specified conditions of use

36
Q

what is done prior to ppl with implants from entering MRI room

A

screening/ MR screening form

37
Q

what are the 3 screenings recommended to MRI patient

A
  • acceptance of MR booking (referral etc)
  • patient arriving and filling in screening form
  • prior to entering scan room (mr personnel) interviews
38
Q

patients to be anaesthetised or sedated should complete safety questionnaire before whilst fully conscious

A

when not satisfactorily completed:
- relatives can complete form where applicable
- 2 doctor consent form
- x-ray requested

39
Q

how would you deal with non-english speaking patients

A
  • use trust approved interpreting service provider
  • potentially departmental staff speaking appropriate language
  • family used as last option
40
Q

safe to enter controlled access area and MR environment when pregnant

  • MHRA dont recommend staying in scan room whilst on
  • choice given to staff if they want to stay in scanning room when pregnant
  • no known risk from MRI to foetus or mother
A
41
Q

what mode of gradient is effective in reducing noise of MRI

A

whisper gradient mode

42
Q

contrast is generally contraindicated

A
43
Q

should be scanned in normal mode when possible

  • decision to scan in controlled mode made by referring clinician, radiologist or patient
A
44
Q

how do you become authorised personnel

A
  • complete screening form
  • attend MRI safety lectures
  • read and understand local rules
  • be designated as an authorised person by the nominated lead manager for MR safety
45
Q

what 3 main things do the MRI department keep records of

A
  • list of responsible persons
  • screening forms
  • safety training undertaken
46
Q

what form of protection is crucial for patients to have during scan or person accompanying scan

A

ear protection
- ear plugs and headphones

RAD413 (24 decks)

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