ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH ACCURATE ANSWERS LATEST
UPDATED| GET IT CORRECT!!
Mild sensory effects due to static magnetic fields include: - correct answer • Vertigo
• Nausea
• Taste Sensations
Sensory effects of the static magnetic field increase or decrease with field strength? - correct
answer Sensory effects are related to the strength of the magnetic field with few symptoms at
1.5T and more appearing approaching a 4T field strength
Explain what t-wave artefact is and why it occurs - correct answer Any charged particle moving
through a magnetic field will have a current induced via this interaction. As blood, a conductive
fluid flows through a magnetic field it induces an electrical biopotential. This electrical
biopotential can be seen on the ECG waveform of patients in MRI. It is demonstrated by an
increase in the T-wave amplitude on ECG. This change in T-wave amplitude is directly
proportional to the strength of the Static Filed. It is important that MR radiographers are aware
of this as elevated T-waves are also associated with ischemia and myocardial infarction.
What risks does the static magnetic field pose in terms of implants and objects? - correct
answer Static Fields also pose hazards through the displacement of ferro-magnetic implants
and objects. The static field imparts both a translation (attractive force) and a torque (twisting
force). The strong nature of the Static Field also has the potential to disrupt the function of
Cardiac Pacemakers. Anyone entering beyond the 5G line should be screened for
contraindications to strong Magnetic Fields. Also be aware of what is being taken over the 5G
line.
What strategies can be employed to reduce the risks of the static magnetic field impacting on
implants and objects? - correct answer • Ferromagnetic objects may become airborne - 40
km/hr terminal velocity possible at 1.5T
• Test any metal objects with a hand held magnet before allowing them to enter the room.
• Keep the general public behind the 5G line. •
Possible contra-indications include pacemakers, aneurysm clips, intra-vascular coils and stents,
heart valves, penile implants, cochlear implants, ocular implants (Fatio eyelid springs), neuro
stimulators, bone growth stimulators, drug infusion pumps.
What effect do gradient magnetic fields have on patient safety? - correct answer Faraday's Law
dictates that changing magnetic fields will generate a voltage and a current in a conductor. The
switching of the gradients induces electrical currents in conductive tissues. Voltage generation
will occur during the rise and fall times - ie. while the field is changing. The largest voltages will
be generated at the periphery where the gradient amplitudes are highest. The most common
result of these voltages is Peripheral Nerve Stimulation (PNS). Other side-effects are listed
below;
,ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH ACCURATE ANSWERS LATEST
UPDATED| GET IT CORRECT!!
• magnetophosphenes - electromagnetically induced flashes of light
• seizures
• tissue heating
• peripheral nerve stimulation
• muscle contractions
• cardiac arrhythmias
• some degree of patient heating has been shown to be a result of Gradient Magnetic effects.
However, this has been shown to be so low as to be negligible
What strategies can be employed to keep gradient effects to a minimum? - correct answer In
order to keep these effects to a minimum the following is recommended.
• keep dB/dT less than those required to produce peripheral nerve stimulation.
• max limit for dB/dT of 6 Tesla / sec
What is the cause of acoustic noise during an MRI scan? - correct answer The characteristic
noise that is heard during an MRI scan is the result of the interaction of Lorentz forces
generated by the Gradient Coil when a current is pulsed through them in the presence of a
Static Magnetic Field. The noise results as these forces are so strong as to twist the coils on
their mounts. In some cases this can be in excess of 100dB particularly when running EPI
sequences. Thus all patients need to be provided hearing protection.
What is the greatest concern in terms of MR safety? - correct answer RF effects are of the
greatest concern in terms of MR safety. The main effect is the deposition of energy resulting in
tissue heating. Of particular concern are heat sensitive organs such as the eyes and testes. One
of the major concerns is where a patient has a metallic implant which results in greater heating.
RF field safety concerns increase or decrease with increasing field strength> - correct answer
The amount of energy absorbed will increase with frequency of the RF field delivered and is
therefore greater at higher field strengths
What is SAR? - correct answer SAR= Specific Absorption Rate - the term used to describe energy
dissipation
SAR is expressed in: - correct answer Watts / kg
SAR will depend on factors including: - correct answer • frequency (& therefore the field
strength)
• RF pulse - where power deposited is proportional to (flip angle / 90)
• TR
,ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH ACCURATE ANSWERS LATEST
UPDATED| GET IT CORRECT!!
• RF coil - transmit / receive or receive only
• volume of tissue within the coil
• conductivity of the tissue
What determines the SAR calculation? - correct answer The SAR is calculated for each sequence
on the basis of the sequence parameters and the patient weight
What are the FDA recommendations regarding SAR? - correct answer • Maximum SAR of 0.4
W/kg (whole body)
• 3.2 W/kg (head)
• 8.0 W/kg (in any one gram of tissue)
• RF exposure should be insufficient to produce a core temperature increase of 1 degree C
Why is patient heating a concern in MRI? - correct answer • Heating will also vary with the
state of the patient's thermo-regulatory system, the ambient temperature, the humidity and
the air flow around the patient.
• The eye and the testes are particularly sensitive organs due to a low capacity for heat
dissipation.
• Excessive RF exposure and temperature increase can lead to an increase in blood pressure
and heart rate.
A SAR warning appears during a scan preventing you from continuing with an examination
unless factors are altered to a safe level, what can be changed in order to achieve this? - correct
answer Factors which will reduce SAR if required include:
• reducing the number of slices
• reducing the ETL
• increasing the TR
• GE rather than SE
• Use quadrature coils rather than linear coils for transmission
• Change to low SAR sequence design
How can patient burns be avoided? - correct answer • use only equipment tested to be MR
compatible
• allow only MR trained staff to use the equipment
• check the integrity of the electrical insulation of all cables
, ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH ACCURATE ANSWERS LATEST
UPDATED| GET IT CORRECT!!
• remove all unnecessary electrically conductive equipment from the bore
• keep electrically conductive equipment from directly contacting the patient
• keep electrically conductive equipment from forming large diameter conductive loops
• position cables to avoid cross points
• position ECG cables to exit down the centre of the bore
• do not allow contact between the patient's skin and the magnet bore
Explain the deleterious effects of MRI on pregnant patients - correct answer There are no
known biological effects of MRI on foetuses. MR imaging may be used in pregnant women if
other non-ionizing forms of diagnostic imaging are inadequate or if the examination provides
important information that would otherwise require exposure to ionizing radiation (e.g.,
fluoroscopy, CT, etc.). Pregnant patients should be informed that, to date, there has been no
indication that the use of clinical MR imaging during pregnancy has produced deleterious
effects." This policy has been adopted by the American College of Radiology and is considered
to be the "standard of care" with respect to the use of MRI procedures in pregnant patients.
Importantly, this information applies to MR systems operating up to and including 3-Tesla. (MR
Imaging Safety and Patient Management issued by the Safety Committee of the Society for
Magnetic Resonance Imaging) Pregnant patients should be reviewed on a case by case basis to
assess whether the risks outweigh the potential benefits.
Can pregnant staff enter the MRI environment? - correct answer No increased incidence of
spontaneous abortion has been demonstrated among MR radiographers or nurses. The most
common policy seems to be that pregnant staff are allowed exposure to the static field (ie. to
set patients up) but leave the room during image acquisition to avoid exposure to RF and
gradient fields.
Is contrast recommended in pregnant patients? - correct answer Contrast is not recommended
during pregnancy. It has been shown to cross the placenta.
What is a quench? - correct answer Quenching the magnet results in a large amount of helium
gas boil off from liquid helium inside the magnet. One litre of liquid helium expands to 760
litres of helium gas. During a quench, the liquid helium is heated causing it to boil off. The
quench pipe vents the resultant gas outside. If the vapour pressure exceeds a predetermined
value, the vent-bursting disk on the vent pipe ruptures and ventilates the excess vapour. Some
may enter the scan room reducing oxygen levels. Helium gas displaces oxygen and is hard to
detect until it is too late. Asphyxia is possible due to low oxygen levels. Another concern is the
increase in pressure due to helium flooding the scan room. It may become impossible to open
an inward opening door due to the pressure differential. In this case kick out panels should be
used to reduce the pressure differential and allow opening of the door. In the absence of these
panels the scan room window should be broken to allow access to the patient if necessary.
UPDATED| GET IT CORRECT!!
Mild sensory effects due to static magnetic fields include: - correct answer • Vertigo
• Nausea
• Taste Sensations
Sensory effects of the static magnetic field increase or decrease with field strength? - correct
answer Sensory effects are related to the strength of the magnetic field with few symptoms at
1.5T and more appearing approaching a 4T field strength
Explain what t-wave artefact is and why it occurs - correct answer Any charged particle moving
through a magnetic field will have a current induced via this interaction. As blood, a conductive
fluid flows through a magnetic field it induces an electrical biopotential. This electrical
biopotential can be seen on the ECG waveform of patients in MRI. It is demonstrated by an
increase in the T-wave amplitude on ECG. This change in T-wave amplitude is directly
proportional to the strength of the Static Filed. It is important that MR radiographers are aware
of this as elevated T-waves are also associated with ischemia and myocardial infarction.
What risks does the static magnetic field pose in terms of implants and objects? - correct
answer Static Fields also pose hazards through the displacement of ferro-magnetic implants
and objects. The static field imparts both a translation (attractive force) and a torque (twisting
force). The strong nature of the Static Field also has the potential to disrupt the function of
Cardiac Pacemakers. Anyone entering beyond the 5G line should be screened for
contraindications to strong Magnetic Fields. Also be aware of what is being taken over the 5G
line.
What strategies can be employed to reduce the risks of the static magnetic field impacting on
implants and objects? - correct answer • Ferromagnetic objects may become airborne - 40
km/hr terminal velocity possible at 1.5T
• Test any metal objects with a hand held magnet before allowing them to enter the room.
• Keep the general public behind the 5G line. •
Possible contra-indications include pacemakers, aneurysm clips, intra-vascular coils and stents,
heart valves, penile implants, cochlear implants, ocular implants (Fatio eyelid springs), neuro
stimulators, bone growth stimulators, drug infusion pumps.
What effect do gradient magnetic fields have on patient safety? - correct answer Faraday's Law
dictates that changing magnetic fields will generate a voltage and a current in a conductor. The
switching of the gradients induces electrical currents in conductive tissues. Voltage generation
will occur during the rise and fall times - ie. while the field is changing. The largest voltages will
be generated at the periphery where the gradient amplitudes are highest. The most common
result of these voltages is Peripheral Nerve Stimulation (PNS). Other side-effects are listed
below;
,ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH ACCURATE ANSWERS LATEST
UPDATED| GET IT CORRECT!!
• magnetophosphenes - electromagnetically induced flashes of light
• seizures
• tissue heating
• peripheral nerve stimulation
• muscle contractions
• cardiac arrhythmias
• some degree of patient heating has been shown to be a result of Gradient Magnetic effects.
However, this has been shown to be so low as to be negligible
What strategies can be employed to keep gradient effects to a minimum? - correct answer In
order to keep these effects to a minimum the following is recommended.
• keep dB/dT less than those required to produce peripheral nerve stimulation.
• max limit for dB/dT of 6 Tesla / sec
What is the cause of acoustic noise during an MRI scan? - correct answer The characteristic
noise that is heard during an MRI scan is the result of the interaction of Lorentz forces
generated by the Gradient Coil when a current is pulsed through them in the presence of a
Static Magnetic Field. The noise results as these forces are so strong as to twist the coils on
their mounts. In some cases this can be in excess of 100dB particularly when running EPI
sequences. Thus all patients need to be provided hearing protection.
What is the greatest concern in terms of MR safety? - correct answer RF effects are of the
greatest concern in terms of MR safety. The main effect is the deposition of energy resulting in
tissue heating. Of particular concern are heat sensitive organs such as the eyes and testes. One
of the major concerns is where a patient has a metallic implant which results in greater heating.
RF field safety concerns increase or decrease with increasing field strength> - correct answer
The amount of energy absorbed will increase with frequency of the RF field delivered and is
therefore greater at higher field strengths
What is SAR? - correct answer SAR= Specific Absorption Rate - the term used to describe energy
dissipation
SAR is expressed in: - correct answer Watts / kg
SAR will depend on factors including: - correct answer • frequency (& therefore the field
strength)
• RF pulse - where power deposited is proportional to (flip angle / 90)
• TR
,ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH ACCURATE ANSWERS LATEST
UPDATED| GET IT CORRECT!!
• RF coil - transmit / receive or receive only
• volume of tissue within the coil
• conductivity of the tissue
What determines the SAR calculation? - correct answer The SAR is calculated for each sequence
on the basis of the sequence parameters and the patient weight
What are the FDA recommendations regarding SAR? - correct answer • Maximum SAR of 0.4
W/kg (whole body)
• 3.2 W/kg (head)
• 8.0 W/kg (in any one gram of tissue)
• RF exposure should be insufficient to produce a core temperature increase of 1 degree C
Why is patient heating a concern in MRI? - correct answer • Heating will also vary with the
state of the patient's thermo-regulatory system, the ambient temperature, the humidity and
the air flow around the patient.
• The eye and the testes are particularly sensitive organs due to a low capacity for heat
dissipation.
• Excessive RF exposure and temperature increase can lead to an increase in blood pressure
and heart rate.
A SAR warning appears during a scan preventing you from continuing with an examination
unless factors are altered to a safe level, what can be changed in order to achieve this? - correct
answer Factors which will reduce SAR if required include:
• reducing the number of slices
• reducing the ETL
• increasing the TR
• GE rather than SE
• Use quadrature coils rather than linear coils for transmission
• Change to low SAR sequence design
How can patient burns be avoided? - correct answer • use only equipment tested to be MR
compatible
• allow only MR trained staff to use the equipment
• check the integrity of the electrical insulation of all cables
, ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH ACCURATE ANSWERS LATEST
UPDATED| GET IT CORRECT!!
• remove all unnecessary electrically conductive equipment from the bore
• keep electrically conductive equipment from directly contacting the patient
• keep electrically conductive equipment from forming large diameter conductive loops
• position cables to avoid cross points
• position ECG cables to exit down the centre of the bore
• do not allow contact between the patient's skin and the magnet bore
Explain the deleterious effects of MRI on pregnant patients - correct answer There are no
known biological effects of MRI on foetuses. MR imaging may be used in pregnant women if
other non-ionizing forms of diagnostic imaging are inadequate or if the examination provides
important information that would otherwise require exposure to ionizing radiation (e.g.,
fluoroscopy, CT, etc.). Pregnant patients should be informed that, to date, there has been no
indication that the use of clinical MR imaging during pregnancy has produced deleterious
effects." This policy has been adopted by the American College of Radiology and is considered
to be the "standard of care" with respect to the use of MRI procedures in pregnant patients.
Importantly, this information applies to MR systems operating up to and including 3-Tesla. (MR
Imaging Safety and Patient Management issued by the Safety Committee of the Society for
Magnetic Resonance Imaging) Pregnant patients should be reviewed on a case by case basis to
assess whether the risks outweigh the potential benefits.
Can pregnant staff enter the MRI environment? - correct answer No increased incidence of
spontaneous abortion has been demonstrated among MR radiographers or nurses. The most
common policy seems to be that pregnant staff are allowed exposure to the static field (ie. to
set patients up) but leave the room during image acquisition to avoid exposure to RF and
gradient fields.
Is contrast recommended in pregnant patients? - correct answer Contrast is not recommended
during pregnancy. It has been shown to cross the placenta.
What is a quench? - correct answer Quenching the magnet results in a large amount of helium
gas boil off from liquid helium inside the magnet. One litre of liquid helium expands to 760
litres of helium gas. During a quench, the liquid helium is heated causing it to boil off. The
quench pipe vents the resultant gas outside. If the vapour pressure exceeds a predetermined
value, the vent-bursting disk on the vent pipe ruptures and ventilates the excess vapour. Some
may enter the scan room reducing oxygen levels. Helium gas displaces oxygen and is hard to
detect until it is too late. Asphyxia is possible due to low oxygen levels. Another concern is the
increase in pressure due to helium flooding the scan room. It may become impossible to open
an inward opening door due to the pressure differential. In this case kick out panels should be
used to reduce the pressure differential and allow opening of the door. In the absence of these
panels the scan room window should be broken to allow access to the patient if necessary.
