Is SNR proportional or inversely proportional to voxel volume - ACCURATE ANSWER-Proportional
3 fields used in MRI - ACCURATE ANSWER--static magnetic field
-TVMF (gradient field)
-RF field
3 main types of magnets used - ACCURATE ANSWER--Superconducting (most common_
-Resistive
-Permanent
...
is snr proportional or inversely proportional to v
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MRI CAMRT Exam Questions With Highest Ratings
Is SNR proportional or inversely proportional to voxel volume - ACCURATE ANSWER-
Proportional
3 fields used in MRI - ACCURATE ANSWER--static magnetic field
-TVMF (gradient field)
-RF field
3 main types of magnets used - ACCURATE ANSWER--Superconducting (most common_
-Resistive
-Permanent
FDA limits for the 3 fields in MRI - ACCURATE ANSWER-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 - ACCURATE ANSWER-TVMF (gradients)
What are Eddy Currents - ACCURATE ANSWER-Small currents induced in the body via the TVMF
Biological effects of the TVMF - ACCURATE ANSWER--Fibrillation -Electroshock
-Visual phosphenes
-Peripheral nerve stimulation
SAR meaning and units - ACCURATE ANSWER-Specific Absorption Rate W/kg- Watts/kilogram
Which field is responsible for tissue heating and temperature increase - ACCURATE ANSWER-The RF field
How are cardiac pacemakers affected in MRI - ACCURATE ANSWER-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? - ACCURATE ANSWER-iron, cobalt, nickel
Level 1 MR Personnel - ACCURATE ANSWER-Passed MR safety education requirements
Level 2 MR Personnel - ACCURATE ANSWER-Those more extensively trained and educated in MRI safety
How many times should a non emergent patient be screened - ACCURATE ANSWER-
Twice, once verbally with a level 2 MR Tech
How should emergent patients and their non MR personnel be screened - ACCURATE ANSWER-Once How should unconscious/ unresponsive patients be screened - ACCURATE ANSWER--
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 - ACCURATE ANSWER-Twice, once in front of parents and once without
MRI and pregnant patients - ACCURATE ANSWER-No known harmful effects but risk vs benefit assessment should be made
MRI contrast and pregnant patients - ACCURATE ANSWER-Should not be routinely given to pregnant patients but risk vs benefit assessment needed
What is the spatial field gradient - ACCURATE ANSWER-The variance in the fixed static field surrounding the scanner, the manufacturerer supplies a SFG map
Lenz forces - ACCURATE ANSWER-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
TVMF (gradient) effects - ACCURATE ANSWER--Induced voltages
-Auditory considerations
Normal temperature ranges - ACCURATE ANSWER-Adult: 36.7-37.4 C
Child (4-13): 36.7-37 C
Infant (3mo-3yrs): 37.2-37.7 C
Normal pulse ranges - ACCURATE ANSWER-Adult: 60-90 bpm
Child (4-10): 90-100 bpm
Infant: 120 bpm
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