MRI screening and safety Flashcards
family members and ancillary personnel accompanying the patient into the scan room
should be screened as if they are going through the procedure themselves
in preparatoin for the MRI examination patients should be encourage to
change into a hostpital gown or scrub suit provided by the imaging center and known to be MR safe
MRs jones has just been sent to the MRI department from the mergency room followoing a severe motor vehichle accident. She ahs suffered a fracture of C3 and her physicians are concerned about a cervical spinal cord compression at that level
select the best method for proceeding with this case
ask her and her family about the possibility of her having metal fragments in her body
persons should be educated about the effects of the static magnetic field especially in high field superconducting magnets include
nursing staff and code team
housekeeping
members of fire department
anesthesiologist and respiratory therapists
technologist and radiologist
accodring to the White Paper on MRI safety persons are identified into levels where by level 2 personnel include
persons with extensive training in MRI safety to include the broader aspects of MRI
according to the White Paper on MRI safety imaging centers should be separated into zones including all of the following
zone 1 freely accessible to any level MR personnel
Zone 2 interface between 1 and 3
zone 3 warm zone, generally console area and last stop before scan room
zone 4 the hot zone, scan room itself
a screening questionaire for patients about to undergo MRI should include information about
prior injuries
prior surgery and implants
pregnancy
the terminology for devices and implants in MRI was modified a few years ago, whereby the term MR compatible has been replace with all of the following
MR safe
MR unsafe
MR conditional
absolute contraindications to MRI include
intracranial vascular clips, unless they are KNOWN to be safe
cardia pacemakers, unless they are KNOWN to be safe
intraocular ferrous foreign bodies
the accepted standard of care for the detection of intraocular ferrous foreign bodies is
plain film
a method that is more accurate in the detection of small inraocular ferrous foreign bodies is
CT
before a patient enters the MRI environment they should be screened for
prior injuries
prior surgical implants
pregnancy
of the following implants which would be considered acceptable to scan my MRI
heart valves
if monitoring is to be achieved by electrical and or mechanical devices it is important that compatibility with the MR system be demonstrated by
manufacturer declaration
the following items are usually allowed to enter the scan room in high magnetic field systems
copper tools
when used for MRI cables from RF coils and ECG leads should be
braided and placed straight though the imager
surface soil cables can potentially cause damage to the patient when
they are slightly touching the patient and frayed
a quench can be used to
rapidly remove superconductivity and the magnetic field
during a quench patients and operators should be evacuatied from the room to avoid
asphyxiation and frostbite
ruptured tympanic membranes
what is regulated by the FDA
accoustic noise
for optimum operation of MRI systems the ambient temperature and relative humidity should remain between
65-75 F and 70%
the acceptable safe level for exposure to magnetic fringe fields with respect to patients with cardiac pacemakers has been reported to be
below 5g
magnetic field shielding can be achieved wither actively or passively passive shielding can be achieved by lining the MRI room with
steel
RF shielding can be achieved by lining the MRI room with
copper
it is acceptable for the general population to be exposed to a field strength of
5.0 guass
the unit of measure of RF absorption is
watts per kilogram
MR imagers are magnetic field shielded such that
the fringe field is confined to/within the scan room
firnge fields are less of a concern for
low field
vertical field permanent magnet imagers
in July of 2003 the FDA center for devices and radiologic health (CDRH) modified the limit on RF absorption (dose) to ______for the HEAD
4.0W/kg absorption for 15 min
the FDA limits the allowable RF absorption to
4.0 W/kg averaged over the body
the term used to describe RF absorption is
specific absorption rate (SAR)
the predominant biologic effect of RF fields is
tissue heating
RF antenna effects can cause
RF interference artifacts
thermal injury and flames
the FDA limits the effect of RF absorption to an increase in core body temperature of
1 C
the increse in body temperature as the result of RF absorption is
greatest on the outside becoming less at the center
RF energy used in MRI is classified as
low energy, nonionizing radiation
as the flip angle is double RF deposition increases by a factor of
four
RF hearing is more of a concern in imaging sequences usch as
fast spin echo
areas of the body that are most sensitive to the heat from SAR are
globes of the eyes and testicles
for adult imaging in MRI the FDA guidellines limit the field strength of clinical imagers to
8.0 T
a magnetic field strength of 1 T is equal to
10,000 g
all of the following are regulated by the FDA
field strangth of the main magnet for clinical imaging
RF absorption (SAR)
acoustic noise
no biologic effects have been reported in humans as the result of exposure for
static magnetic fields below 2 T
the field strength at isocenter is measured in units of
tesla
magnetic field strength outside the imager is usually measured in
gauss
the attractive force that an object will experience at a distance of 6 feet from isocenter is dependent on
ferromagnetic properties of the opbject
mass of the object
field strength of the system
as a conductive medium (blood) moves across a magnetic field, an effect knows as the magnetic hemodynamic effec occurs resulting in
elevated T-wave
it is _____for all patients to be provided with hearing protection in the form of________
recommened
headphones or earplugs
the gradient magnetic fields
produce heat in the gradient coils during the scan
can produce noise to cause temporary hearing loss
change rapidly during the scanning process
when a patien is placed within the bore of a magnetic resonance imager an effect can be noted on the ECG whereby there is an elevated T wave. This effect is known as
magnetohydrodynamic effect
magnet-hydrodynamic effect
magnet hemodynamic effect
the effect whereby the patient experiences a visual impression of seeing stars in their eyes is known as
magnetophosphenes
the FDA lmit on time varying magnetic fields is
until a patient experiences peripheral nerve stimulation
time carying magnetic field (TVMF) effects include all of the followoing
acoustic damage and hearing loss
peripheral nerve stimulation and tingling
magnetophosphenes and stars in the eyes
TVMF effects are of greater concern for which type of scanner
EPI
the strength of gradient magnetic fields is measured in
Milli Tesla per meter
Gauss per centimeter
gradient magnetic fields are a safety concern because they
induce current in conductors
time varying magnetic fields have been reported to have caused
mild cutaneous sensations and images of flashing lights in patients
involuntary muscle contractions and cardiac arrhythmias in patients
the FDA limit for the static magnetic field for clinial imaging for patients over 1 month of age is
4.0 T
the FDA limit for the static magnetic field for clinical imaging for ALL patients is
4.0 T
the imaging sequence that is of the most concern for time varying magnetic field effects is
echo planar
gradient rise time is
the time it takes for a gradient to get full amplitude
the duty cycle is
the time gradients are on during a TR period
to avoid auditory damage during MRI all patients should be offered
headphones
earplugs
antinoise devices
