ASMIRT - MRI Accreditation MOSTLY TESTED QUESTIONS WITH
ACCURATE ANSWERS 2024-2025 LATEST UPDATED| GET IT
CORRECT!!
Mild sensory effects due to static magnetic fields include: - (answer)• Vertigo
• Nausea
• Taste Sensations
Sensory effects of the static magnetic field increase or decrease with field strength? -
(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
眼睛是人类最重要
Explain what t-wave artefact is and why it occurs - (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? -
(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? - (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
眼睛是人类最重要
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? - (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;
• 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? - (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
眼睛是人类最重要
What is the cause of acoustic noise during an MRI scan? - (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? - (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> - (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? - (answer)SAR= Specific Absorption Rate - the term used to describe energy
dissipation
SAR is expressed in: - (answer)Watts / kg
SAR will depend on factors including: - (answer)• frequency (& therefore the field strength)
眼睛是人类最重要
• 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
What determines the SAR calculation? - (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? - (answer)• Maximum SAR of 0.4
W/kg (whole body)
• 3.2 W/kg (head)
ACCURATE ANSWERS 2024-2025 LATEST UPDATED| GET IT
CORRECT!!
Mild sensory effects due to static magnetic fields include: - (answer)• Vertigo
• Nausea
• Taste Sensations
Sensory effects of the static magnetic field increase or decrease with field strength? -
(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
眼睛是人类最重要
Explain what t-wave artefact is and why it occurs - (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? -
(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? - (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
眼睛是人类最重要
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? - (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;
• 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? - (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
眼睛是人类最重要
What is the cause of acoustic noise during an MRI scan? - (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? - (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> - (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? - (answer)SAR= Specific Absorption Rate - the term used to describe energy
dissipation
SAR is expressed in: - (answer)Watts / kg
SAR will depend on factors including: - (answer)• frequency (& therefore the field strength)
眼睛是人类最重要
• 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
What determines the SAR calculation? - (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? - (answer)• Maximum SAR of 0.4
W/kg (whole body)
• 3.2 W/kg (head)
