9.3 MRI Flashcards
You are asked to transfer an intubated intensive care patient for a magnetic resonance imaging (MRI) scan.
a) What is meant by the terms magnetic resonance (MR) safe
in relation to equipment
used in the MRI scanner room? (1 marks)
MR Safe:
these devices pose no MR-related hazards
to patients or staff when used
according to instructions and
can therefore be used in any MR setting.
What is meant by the terms magnetic resonance MR conditional, in relation to equipment
used in the MRI scanner room? (1 marks)
MR Conditional:
this equipment poses no MR-related hazard
in a specified MR environment
under specific conditions of use,
e.g. static field strength,
rate of change of magnetic field.
b) What precautions can be taken to prevent burns caused by monitoring equipment used in an MRI
scanner? (6 marks)
> > Use only MR safe
monitoring equipment
or MR conditional that has been
deemed appropriate to use in that scanner.
> > Check all equipment
prior to use,
that it is intact, that there is no breach
in any insulating surfaces that might risk
metal touching skin.
> > Fibreoptic cables
for ECG and pulse oximeter
eliminate use of electrical current,
which may result in induction currents
and burns to underlying skin.
> > Telemetric monitor
to eliminate the risk of induction
currents in connecting leads.
> > ECG leads should be high impedance,
braided and short to minimise risk
of induction currents.
> > ECG electrodes must be MR safe.
> > Do not allow any cables
to coil or cross each other as induction of
current can result from capacitance coupling.
> > Ensure leads are positioned
to exit the scanner down the centre rather
than at the side of the patient, close to the radiofrequency (RF) coils.
> > Separate leads from patient’s skin with
e.g. foam insulating padding.
c) List other precautions you would take to minimise the risks associated with MRI. (7 marks)
> > Equipment check:
ensure all equipment to be used
is MR safe or MR conditional
and has been checked as safe t
o use on that scanner.
> > Checklist:
all staff and patients to complete checklist
to ensure no
contraindications to entering MRI scanner
(see answer to d for more detail).
> > Ferromagnetic objects:
• Staff and patient to remove all
ferromagnetic objects from clothes/
pockets to avoid the possibility of them becoming projectiles.
• Ensure all equipment,
e.g. trolley, is non-ferromagnetic,
remove oxygen cylinders etc.
• Some clothes,
e.g. sportswear, contain silver fibres –
cotton hospital gown to be worn.
• Drug delivery patches may contain metal – remove due to risk of burns.
> > Padding over RF coils:
ensure padding intact to prevent direct contact
between patient and coils.
> > Ear protection:
for all patients, anaesthetised or not,
due to high noise levels in scanner.
> > Monitoring equipment and breathing circuit:
check that there is sufficient
length by checking planned
range of movement of
MRI stretcher before
leaving the scanning room.
> > Inaccessibility of airway:
meticulous securing of airway to ensure it does
not become dislodged as difficult to access once in scanner.
> > Monitoring:
telemetric monitoring to
facilitate the presence of monitoring
screen in control room,
reduces risk of failing to notice abnormalities.
> > Remote site anaesthesia:
ensure senior support available,
ensure orientation with equipment/location/emergency kit prior to commencement, especially as some equipment will be unfamiliar as
it is MR safe and therefore different to that used elsewhere.
Ensure identical monitoring standards to those used elsewhere can be achieved;
awareness of low light
levels often used in radiology.
> > Risks of gadolinium-based contrast agents:
• Avoid contrast if eGFR is less than 30 ml/min – risk of nephrogenic systemic fibrosis.
• Do not repeat contrast within seven days.
• Avoid in pregnancy unless absolutely necessary.
• Drugs to manage anaphylaxis to be readily available.
d) What are the contraindications to an MRI scan? (5 marks)
> > Recent surgery involving ferromagnetic
clips or implants.
> > Ferromagnetic material in eye.
> > Ferromagnetic cochlear implants.
> > Ferromagnetic neurosurgical clips.
> > Intra-aortic balloon pumps,
ventricular assist devices.
> > Ferromagnetic cardiac occluder
devices within six weeks of implantation.
> > Neurostimulators:
some are safe for use in MRI.
> > Programmable shunts/drug pumps:
check for compatibility and check
that exposure to MRI will not reprogram it.
> > Pacemaker or ICD:
risks of device failure,
dislodgement and burns.
However, some newer devices are MRI-compatible.
> > Some aortic stent grafts.
