ASMIRT - MRI Accreditation Exam Latest
Update Questions & Answers with
Rationales| 100% Correct | Grade.
Mild sensory effects due to static magnetic fields include:
Answ >• Vertigo
• Nausea
• Taste Sensations
Quiz Sensory effects of the static magnetic field increase or decrease with field strength?
Answ >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
Quiz Explain what t-wave artefact is and why it occurs
Answ >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.
,Quiz What risks does the static magnetic field pose in terms of implants and objects?
Answ >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.
Quiz What strategies can be employed to reduce the risks of the static magnetic field impacting on
implants and objects?
Answ >• 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.
Quiz What effect do gradient magnetic fields have on patient safety?
Answ >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;
• 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
Quiz What strategies can be employed to keep gradient effects to a minimum?
Answ >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
Quiz What is the cause of acoustic noise during an MRI scan?
Answ >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.
Quiz What is the greatest concern in terms of MR safety?
Answ >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.
Quiz RF field safety concerns increase or decrease with increasing field strength>
Answ >The amount of energy absorbed will increase with frequency of the RF field delivered and is
therefore greater at higher field strengths
, Quiz What is SAR?
Answ >SAR= Specific Absorption Rate - the term used to describe energy dissipation
Quiz SAR is expressed in:
Answ >Watts / kg
Quiz SAR will depend on factors including:
Answ >• frequency (& therefore the field strength)
• RF pulse - where power deposited is proportional to (flip angle / 90)
• TR
• RF coil - transmit / receive or receive only
• volume of tissue within the coil
• conductivity of the tissue
Quiz What determines the SAR calculation?
Answ >The SAR is calculated for each sequence on the basis of the sequence parameters and the
patient weight
Quiz What are the FDA recommendations regarding SAR?
Answ >• Maximum SAR of 0.4 W/kg (whole body)
Update Questions & Answers with
Rationales| 100% Correct | Grade.
Mild sensory effects due to static magnetic fields include:
Answ >• Vertigo
• Nausea
• Taste Sensations
Quiz Sensory effects of the static magnetic field increase or decrease with field strength?
Answ >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
Quiz Explain what t-wave artefact is and why it occurs
Answ >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.
,Quiz What risks does the static magnetic field pose in terms of implants and objects?
Answ >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.
Quiz What strategies can be employed to reduce the risks of the static magnetic field impacting on
implants and objects?
Answ >• 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.
Quiz What effect do gradient magnetic fields have on patient safety?
Answ >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;
• 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
Quiz What strategies can be employed to keep gradient effects to a minimum?
Answ >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
Quiz What is the cause of acoustic noise during an MRI scan?
Answ >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.
Quiz What is the greatest concern in terms of MR safety?
Answ >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.
Quiz RF field safety concerns increase or decrease with increasing field strength>
Answ >The amount of energy absorbed will increase with frequency of the RF field delivered and is
therefore greater at higher field strengths
, Quiz What is SAR?
Answ >SAR= Specific Absorption Rate - the term used to describe energy dissipation
Quiz SAR is expressed in:
Answ >Watts / kg
Quiz SAR will depend on factors including:
Answ >• frequency (& therefore the field strength)
• RF pulse - where power deposited is proportional to (flip angle / 90)
• TR
• RF coil - transmit / receive or receive only
• volume of tissue within the coil
• conductivity of the tissue
Quiz What determines the SAR calculation?
Answ >The SAR is calculated for each sequence on the basis of the sequence parameters and the
patient weight
Quiz What are the FDA recommendations regarding SAR?
Answ >• Maximum SAR of 0.4 W/kg (whole body)
