CAMRT Practice Exam
Is SNR proportional or inversely proportional to voxel volume - ANS-Proportional
3 fields used in MRI - ANS--static magnetic field
-TVMF (gradient field)
-RF field
3 main types of magnets used - ANS--Superconducting (most common_
-Resistive
-Permanent
FDA limits for the 3 fields in MRI - ANS-Static field: 2T
TVMF: 3T/s
RF field:
- does not cause an increase in temperature of more than .5 deg C or any body part of 1
deg C
-SAR does not exceed 1W/kg avg over 25% of whole body for longer than 15mins
-SAR does not exceed 2W/kg avg over 25% of whole body for durations of 15mins or
less
Eddy currents are caused by - ANS-TVMF (gradients)
What are Eddy Currents - ANS-Small currents induced in the body via the TVMF
Biological effects of the TVMF - ANS--Fibrillation
-Electroshock
-Visual phosphenes
-Peripheral nerve stimulation
SAR meaning and units - ANS-Specific Absorption Rate
W/kg- Watts/kilogram
Which field is responsible for tissue heating and temperature increase - ANS-The RF
field
How are cardiac pacemakers affected in MRI - ANS-Affected by all 3 fields
-Static field affects the operation and also exerts torque
,-TVMF and RF field can interfere with circuitry
3 types of ferromagnetic materials? - ANS-iron, cobalt, nickel
Level 2 MR Personnel - ANS-Those more extensively trained and educated in MRI
safety
How many times should a non emergent patient be screened - ANS-Twice, once
verbally with a level 2 MR Tech
How should emergent patients and their non MR personnel be screened - ANS-Once
How should unconscious/ unresponsive patients be screened - ANS-- A family member
should fill out the screening form
-If no reliable history can be obtained and MR exam cannot wait they must undergo
plain film radiography of head/neck, chest, abdomen/pelvis, upper arms and thighs
How should children and teens be screened - ANS-Twice, once in front of parents and
once without
MRI and pregnant patients - ANS-No known harmful effects but risk vs benefit
assessment should be made
MRI contrast and pregnant patients - ANS-Should not be routinely given to pregnant
patients but risk vs benefit assessment needed
What is the spatial field gradient - ANS-The variance in the fixed static field surrounding
the scanner, the manufacturerer supplies a SFG map
Lenz forces - ANS-Faradays law states that a changing magnetic field will induce a
current in a conductor, Lenzs law states that the induced current will generate a
secondary field that opposes the original field
Normal respiratory ranges - ANS-Adult: 15-20 breaths per minute
Infant: 30-60 breaths per minute
Normal pulse oximetry - ANS-95%-100%
Tachycardia - ANS-Fast heart rate over 100 bpm
Bradycardia - ANS-Slow heart rate less than 60 bpm
Spots to get a pulse reading - ANS--Radial (wrist)
-Carotid (neck)
-Popliteal (knee)
-Temporal (head)
-Brachial (elbow)
-Dorsalis pedis (foot)
-Femoral(leg)
Most accurate spot for pulse rate in infants - ANS-Apical over apex of the heart
Normal BP ranges - ANS-Adult: 80-120mmHg/60-80mmHg
Child: 90-120mmHg/50-70mmHg
Infant: 85-130mmHg/45-85mmHg
3 types of motion in an atom - ANS-(1) Electron on its axis (2) Electron around the
nucleus (3) Nucleus on its axis
Isotope of hydrogen - ANS-protium (MR active nuclei)
True or false: Hydrogen nuclei only align themselves to the field in 2 directions -
ANS-True
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