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