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