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MRSO PRACTICE EXAM (ACTUAL / )
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 1 / 3
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=
- 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...
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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....
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