MRI Safety Lecture 1 Fall
what is the measurement of SAR
watts per kilogram (W/KG)
when does NSF happen
when patient has abnormal kidney function and are not able to excrete the GD
when should a manual quench be performed
when there is clear danger of life/limb
What is the Kaiser Burn
- 2001 - Kaiser Sunnyside Medical Center in Oregon - patients arm caught fire stated it was smoking for 20 mins and bursted into flames
What is the Colombini Tragedy
- 6 year old child - Westchester medical center - happened from poor planning, lack of safety training, and improper material screening - vitals drops, techs left and nurse brought it O2 that was not MRI safe and it flew to the center of the magnet
What are the old safety terminology
- MR compatible - MR incompatible
What does a Quench involve
- Solenoidal electromagnetis super-cooled with cryogens - Used with liquid helium generally 4K or -269 celsius - 748 liters of gas = 1 liter of liquid
Whats a security zone
- avoid collision with ferromagnetic objects - suitable screening occurs hear - area prior to entrance of scan room is considered the shield room
what is MR operator caution
- bc its safe at 1 level that's higher does not mean it is safe at a lower level
RF Antennae effects with RF fields
- burn hazards due to electrical currents produced in the conductive loops
What are some accidents that are always a potential
- burns - projectiles - device failures - contrast reactions - death
Pregnant employees should and can
- can safely enter scan room - should leave while RF and gradient fields employed - some restrict entrance during 1st trimester
what are changing magnetic fields caused by and what do they concern with
- caused by induced currents - concern with nerves, blood vessels, and muscles
What is acoustic noise from
- generated by gradient coils, significant noise is generated
what are the Bio effects of RF irradiation
- heating of tissues - RF antennae effects - thermal injuries
What are the brands of Gad
- magnevist, prohance, omniscan, dotarem, eovist, prohance, multihance
What is the magnet and what is it responsible for
- main magnetic field - potential for biological effects - responsible for alignment of nuclei - no respect for confines of walls floors or ceilings
What does EPI cause
- mild cutaneous sensations - involuntary muscle contractions
pregnant patient conditions
- no known biological effects on fetus - avoid GD administration - case-by-case basis
Longterm exposure to magnetic field what happens
- pathological changes in humans - below the threshold of significance with respect to long term adverse bioeffects
what can gradient magnetic fields do to the body
- peripheral nerve stimulation like tingling or tapping - discomfort or pain - cardiac stimulation
what is torque and heating
- potentially move unpredictably within the body - type of metal determines the force exerted on them in magnetic fields - can cause significant heating
What can happen with ECG leads and surface coils and what must you prevent
- prevent looping upon itself, prevent cords from touching patient - tissue or clothing can be ignited by noninsulated cables - coupling of a transmitting coil to receive coil may also cause sever thermal injury
Who is allowed in the MRI scan room
- properly screened and trained personnel
if helium is not properly vented to outside what happens
- replaces oxygen in the room - oxygen motior will sound alarm if below a certain level - immediate evacuation of patient and personnel
Above 2.0 T produces
- reversible biological effects including fatique, headaches, hypotension and irritability - effect on magnetic interaction energy and cell orientation
what happens during visual disturbances
- stars in eyes - light flashes
What are the 3 fields used in the creation of an MR image
- static - radiofrequency - gradient
what are transient magnetic fields dependent on
- stimulates nerves or muscles field freq max flux density avg flux density presence of harmonic freq waveform characteristics of signal polarity of the signal current distribution electrical properties sensitivity of the cell membrane
What is a fringe field
- stray magnetic field outside magnets bore - secondary concern but can be fatal effect of main field
what is zone 3
- strictly resitricted - area where there is potential for serious injury or death from ferromagnetic objects - strictly controlled by MR personnel
What are Thermal injuries that can happen
- tattoo heating - 2nd and 3rd degree burns - localized injuries where no wire was in proximity
In the case of a fire what has to happen with fire fighters
- they cannot enter until MF has been quenched - tanks can be ferromagnetic
what is Magnetophosphenes
- unusual visual disturbances
What are the 3 types of effects of TVMF
-Reversible alterations in vision -irreversible effects of cardiac fibrillation -alterations in biochemistry
What are the operating levels of SAR
0 - normal 1 - first level controlled operating mode 2 - second level controlled operating mode
spontaneous boil off results in
1,000,000 Liters of gas
What are the safety rules
1. access to magnet room strictly controlled 2. caution signs are place prominently at the entrance as well as in control booth 3. Don't ignor signs 4. magnet always on and cannot be turned off 5. no metal allowed in room unless shows to be safe
how many liters in scanner
1500
what do small objects have a terminal velocity of
40mph when pulled into 1.5T
what is the decibel related
95 - between a football game and Hard Rock Café
What are the contrast products available
Chelate of Gadolinium, a paramagnetic element
what does EPI stand for
Echo Planar Imaging
what are the 4 new terms or MR safety
MR safe MR unsafe MR conditional MR operator caution
what is zone 4
MRI room - clearly marked with warning signs - visible to MR personnel at all times - properly trained MR personnel will stabilize patient in such emergencies of cardiac arrest and remove person to zone 2
What does the Quanity of SAR depend on
RF pulse Characterisitcs (WATTS) Patient Characteristics
What is SAR
Specific Absorption Rate. The FDA limit for RF exposure is either an increase in body temperature or RF absorption and can be expressed in watts per kilogram (W/kg).
what is rate of change measured in
Tesla per second
What are some patient characteristics
Tissue Density, conductivity, and patient size
What happened February 1982
US FDA issued guidelines for clinical trials in NMR - followed up with an eval of potential risks and hazards
what do gradient magnetic fields depend on
activation of X,Y,Z gradient
what are contraindications of GD
allergies and pregnancy
What does ultra high field imaging cause
an increase in RF power at higher field strengths
what is zone 1
areas freely accessible by public, all personnel are permitted
Where do changing magnetic fields exist
around power transformers and high voltage lines
what can a quench cause
asphyxiation
where does the majority of heating occur
at the periphery of the patient -easily dissipated
what are some occupational hazards
automechanics welders machinists h/o intraorbital metal
what should we avoid with ultra high field
avoid imaging in pregnancy or implants
short term exposure does what to the body
bbb permeability circadian rhythms visual and auditory info by the brain immune responsiveness
what should all people who have access to the MRI scan room do
be screened and complete safety training annually
where are peripheral nerve stimulation sites
bony prominences
what can the 2nd and 3rd degree burns be caused by
cables from coils and contact with patient skin
What are 4 reversible or irreversible effects of acoustic noise
communication interference patient annoyance transient hearing loss permanent hearing loss
level 1 MR personnel
completed minimal MR safety training - allows them to work safely within zone 3
What temp is effected from SAR
core body temp and peripheral body temp
what are some personal affects that should be removed before entering
credit cards, watches, tape recorders, calculators, jewlery, shoes with metal supports, wigs, hairpins, dentures
what is the rates of change
dB/dT rate of change of magnetic field over time
what can happen to unconscious, sedated or patients with limited feelings
danger of burns
when do RF fields occur
during excitation phase of a sequence
What is used to allow escape of helium/ what is the danger of someone on the roof
emergency helium gas vent / danger of frostbite or choking
non-MR personnel
essentially no MR safety training - not allowed beyond zone 2
What are the 4 things that the ACR do
establish, implement and maintain current MR safety policies and procedures - static magnetic field issues (site access restriction) - MRI techs - pregnancy related issues
level 2 MR personnel
extensive MR safety and training - unrestricted access to zones 3 and 4
what is the missile affect
ferromagnetic metal objects can become airborne as projectiles as the presence of strong magnetic field
What is translational force responsible for
ferromagnetic objects being violently attracted to scanner - increases as object approaches isocenter
What should the public be limited to
field strengths of 5G and below
Why are there visual disturbances
from stimulation of retina by external magnetic field
what are two reversible effects from magnetic fields
gradient and radiofrequency
what does the American College of Radiology offer
guidelines for safe and effective operation of the MR imaging facility
how to decide if something is safe
handheld magnet of at least 100millitesla strength can evaluate and screen suspicous objects
inner ear hazards require use of what
hearing protection
What is ultra high field imaging considered
higher than 1.5T
What do RF pulse characteristics include
induced electrical field, and pulse duty cycle
Gradient magnetic field causes what
induces stimulation - peripheral nerve stimulation as tingling or tapping sensations - discomfort or pain - cardiac stimulation
what does the contrast do
injecting a heavy metal agent, allows us to slow down what we are looking at to visualize it on imaging
what is zone 2
interface between publicly accessible uncontrolled zone 1 and strictly controlled zone 3 - - waiting room , lock and warning signs between zone 2 or 3 - area where persons supervised by MR personnel
what is MR conditional
item has been demonstrate to pose no harm in a specific environment 8 conditions asscociated with it
what is MR unsafe
item is known to pose hazard in all mr environments Unsafe level 1: result of movement or dislodgement of object Unsafe level 2: only minor intereactions in consideration to invo of object and unlikely to pose a hazard or risk with movement or dislodgement
what is MR safe
item poses no harm in all MR environments
what lacks or is limited of Ultra high field imaging
lack of research and testing - limited clinical experience - limited experience in protocol optimization
other safety guidlines
look at page 5 of notes
what are the energy level of frequencies in clinical MRI
low non ionizing potential heating of tissue
if there is a quench pipe failure what can happen if there is an inwardly opening magnet room door
may get sealed shut by sudden pressure differential between magnet and control room
What is SAR
measures BIO effects of radiation - Specific absorption rate
what can localized injuries be from
med patches, and metallic foil
what are some adverse effects of GD
nausea, headache, metallic taste, parasthesia, nephrogenic systemic fibrosis
Below 2.0T produces
no biological effects - reversible effects on ECG's
what must be accurate for SAR
patients weight
what are considered some contraindications
patients with electrically, magnetically, or mechanically activated implants - cardiac pacemakers, implantable nerve stimulators or csf drain tubes - intracranial aneurysm clips - adhesive skin patches with conductive metallic substances
what is the most concern with TVMF increase
peripheral nerve stimulation - effects perfusion, diffusion, and blood oxygen level
what are the 3 people who should not be allowed within exclusion area
persons with pacemakers persons with intracranial aneurysm slips persons subject to uncontrollable seizures
what are stimulated by induction from TVMF
retinal phosphates
What are 4 issues associated with MRI safety
risk of malfunction of implanted devices - increased heating and potential for burns - projectile effects -allergic reactions
when should you evaluate and warn?
risks related to - implanted clips or metal implants - fetuses and infants - patients with cardiac pacemakers or other implanted electronic devices - patients with cardiac diseases or greater potential for Cardiac arrest
what do metallic implants pose as
serious damaging effects that include torque and heating
What could a quench cause
severe and irreparable damage to the super conducting coils
what are the 2 primary effects
static - associated with devices, implants, and projectiles gradient - switching on/off (time-varying) are oscillating and alternating
transient magnetic fields do what
stimulate nerves or muscles
What does EPI sequences possess
strong gradients that switch rapidly during acquisition
when is imaging used in pregnant patients
suspected abnormalities of fetus or mother when US is not feasible
also carefully warn patients with
tattoos, permanent eyeliner or makeup - patients with possible embedded conductive or ferromagnetic fragments in or near eye - patients with colored or decorative contact lenses - patients at risk for seizures
what is rotational force responsible for
the aneurysm clip moving or twisting when entering the bore of the magnet - torque of clip can result in devastating circumstances, hemorrhage or death
where are the vents
through ducts outside building
what is TVMF
time varying magnetic field