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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
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 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
,ASMIRT- MRI Accreditation Actual Exam Test Bank Newest / ASMIRT- MRI Accreditation Exam
Preparation /ASMIRT- MRI Accreditation Practice Exam With Complete 250 Questions And Correct
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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
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
,ASMIRT- MRI Accreditation Actual Exam Test Bank Newest / ASMIRT- MRI Accreditation Exam
Preparation /ASMIRT- MRI Accreditation Practice Exam With Complete 250 Questions And Correct
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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)
• 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)
• 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? - (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? - (ANSWER)Factors which will
reduce SAR if required include:
• reducing the number of slices
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• 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? - (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
• 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 - (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? - (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.
Preparation /ASMIRT- MRI Accreditation Practice Exam With Complete 250 Questions And Correct
Detailed Answers |Already Graded A+(Newest Version!)
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
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 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
,ASMIRT- MRI Accreditation Actual Exam Test Bank Newest / ASMIRT- MRI Accreditation Exam
Preparation /ASMIRT- MRI Accreditation Practice Exam With Complete 250 Questions And Correct
Detailed Answers |Already Graded A+(Newest Version!)
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
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
,ASMIRT- MRI Accreditation Actual Exam Test Bank Newest / ASMIRT- MRI Accreditation Exam
Preparation /ASMIRT- MRI Accreditation Practice Exam With Complete 250 Questions And Correct
Detailed Answers |Already Graded A+(Newest Version!)
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)
• 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)
• 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? - (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? - (ANSWER)Factors which will
reduce SAR if required include:
• reducing the number of slices
, ASMIRT- MRI Accreditation Actual Exam Test Bank Newest / ASMIRT- MRI Accreditation Exam
Preparation /ASMIRT- MRI Accreditation Practice Exam With Complete 250 Questions And Correct
Detailed Answers |Already Graded A+(Newest Version!)
• 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? - (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
• 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 - (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? - (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.
