MRSO PRACTICE EXAM (ACTUAL 2025/2026)
QUESTIONS AND VERIFIED ANSWERS
physical effects of STATIC FIELDS
translation
rotation
lenz
physical effects of TIME-VARYING FIELDS
motion
noise
induced currents (on object/in person)
lenz
translation
rotation
SAR
Specific Absorption Rate
= time rate at which RF electromagnetic energy is imparted to
an element of mass of a biological body
,REMAINS SAME no matter what frequencies / field
strengths are-- just easier to reach SAR with higher static
magnetic field (7T easier than 3T, etc.)
THRESHOLD for irreversible effects due to thermal damage=
4 Watts/kilogram
SAR thresholds...
whole body: 4w/kg (15 min)
head: 3.2w/kg (10min)
Ways to reduce SAR
reduce flip angle (ex. use gradient echo)
increase TR
decrease # slices
decrease # phase encoding steps
use less energy...
, SAR normal more
whole body SAR ≤2
head SAR ≤3.2
no physiolog. stress expected
SAR first-lev controlled
whole body SAR between 2 and 4
head SAR ≤ 3.2
some ppl who can't tolerate a thermal challenge might
experience physiolog. stress (eg obese, diabetic, etc)
Same for 1.5,3,7T
SAR second-lev controlled
SAR may exceed 4 for body
B1+rms
mag field composed of frequency wave ..??? unit is
Tesla/microTesla....
QUESTIONS AND VERIFIED ANSWERS
physical effects of STATIC FIELDS
translation
rotation
lenz
physical effects of TIME-VARYING FIELDS
motion
noise
induced currents (on object/in person)
lenz
translation
rotation
SAR
Specific Absorption Rate
= time rate at which RF electromagnetic energy is imparted to
an element of mass of a biological body
,REMAINS SAME no matter what frequencies / field
strengths are-- just easier to reach SAR with higher static
magnetic field (7T easier than 3T, etc.)
THRESHOLD for irreversible effects due to thermal damage=
4 Watts/kilogram
SAR thresholds...
whole body: 4w/kg (15 min)
head: 3.2w/kg (10min)
Ways to reduce SAR
reduce flip angle (ex. use gradient echo)
increase TR
decrease # slices
decrease # phase encoding steps
use less energy...
, SAR normal more
whole body SAR ≤2
head SAR ≤3.2
no physiolog. stress expected
SAR first-lev controlled
whole body SAR between 2 and 4
head SAR ≤ 3.2
some ppl who can't tolerate a thermal challenge might
experience physiolog. stress (eg obese, diabetic, etc)
Same for 1.5,3,7T
SAR second-lev controlled
SAR may exceed 4 for body
B1+rms
mag field composed of frequency wave ..??? unit is
Tesla/microTesla....
