Unit 3 Flashcards
What is SAR?
Specific Absorption Rate
measure of energy (RF) dissipation in the body
What are time varying magnetic fields?
magnetic fields caused by the gradient magnetic coils
What is exclusion zone?
area where fringe field is 5G or more;
area should not be allowed to public access
Types of EM fields in MR
static, gradient, RF
Max static magnetic field strength allowed in patients >1mo
8T
Primary safety hazard associated w/ static fields
projectile
Primary safety hazard associated w/ gradient fields
Induced electrical currents in conductors
Reversible biological effects associated w/ rapid switching of gradient field
altered vision, involuntary muscle contractions, skin sensations
Unit of measure of SAR
W/kg
Max SAR for whole body imaging
4 W/kg
Max SAR for head imaging
3.2 W/kg
Primary biological response to RF in MR
absorption => tissue heating
Primary hazard associated w/ RF in MR
burns
Patient info directly affecting SAR calculation
weight, age
Objects that have wires that can form a conductive loop in MR
monitoring equipment, coil cables
Hazards of metallic implants
torque, heating, artifacts
Fringe field strength that determines the exclusion zone
5G
Primary hazard assoccaiated w/ quenching
suffocation
Safety issues w/ noise generation of MR
communication issues, hearing loss (permanent vs temp)
Guidelines for scanning pregnant patients
FDA - MR is allowed if equal info would be more invasive
SMRI - case by case, try to avoid 1st trimester
avoid gadolinium
Where is the most reliable source of MR safety info on specific implants?
inplant manufacturer
Irreversible biological effects of static magnetic fields <2T
no known effects
Dangers of cardiac pacemakers in MR
deflection of pacemaker generator, reed switch malfunction, reprogramming, induced electrical current in leads
