MRI Gradient-Induced Nerve
Stimulation Exam Practice Questions
and Correct Answers (Verified Answers)
Plus Rationales 2027 Q&A | Instant
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1. What is the primary mechanism by which rapidly switching MRI gradients can
produce peripheral nerve stimulation?
A. Direct absorption of RF energy by nerves
B. Heating of neural tissue by the static magnetic field
C. Induction of electric fields in conductive body tissues
D. Mechanical vibration of the gradient coils
Rationale: Rapidly changing magnetic fields produced by gradient coils induce
electric fields within conductive tissues according to electromagnetic induction. If
the induced electric field is sufficiently strong and appropriately distributed, it can
depolarize excitable nerves and produce PNS.
2. Which gradient parameter most directly describes how rapidly a gradient
magnetic field changes?
A. Gradient amplitude
B. Slew rate
C. Static field strength
D. RF frequency
Rationale: Slew rate describes the rate at which the gradient changes with time,
commonly expressed in T/m/s. Faster changes in gradient fields generally produce
greater induced electric fields and therefore increase the potential for PNS.
,3. Which unit is commonly used to express gradient slew rate?
A. mT/m
B. Hz
C. W/kg
D. T/m/s
Rationale: Gradient amplitude is commonly expressed in mT/m, while gradient
slew rate is expressed in tesla per meter per second (T/m/s). Slew rate represents
the rate of change of gradient strength with time.
4. Which patient sensation is most characteristic of mild peripheral nerve
stimulation during MRI?
A. Complete loss of sensation
B. Tingling or tapping sensations
C. Permanent numbness
D. Visual loss
Rationale: PNS commonly begins as sensations such as tingling, tapping, buzzing,
or brief muscle twitching. The ACR describes gradient-induced PNS as potentially
producing sensations ranging from tingling to muscle contractions.
5. Which MRI system component is primarily responsible for gradient-induced
PNS?
A. Main static magnet
B. RF transmit coil
C. Gradient coil system
D. Patient table motor
Rationale: The gradient coils generate rapidly changing magnetic fields during
image acquisition. These time-varying fields can induce electric fields and currents
in the patient's tissues, potentially stimulating peripheral nerves.
,6. What happens to the induced electric field when the magnetic field changes
more rapidly?
A. It necessarily decreases
B. It remains completely unchanged
C. It becomes independent of gradient switching
D. It generally increases
Rationale: Faraday's law indicates that a changing magnetic field produces an
induced electric field. A greater rate of change of magnetic flux generally produces
a greater induced electric field, increasing the potential for neural stimulation.
7. Which imaging sequence is particularly associated with higher PNS potential
because of rapid, repetitive gradient switching?
A. Conventional spin echo with very low gradient activity
B. Echo-planar imaging (EPI)
C. Basic inversion recovery without rapid gradients
D. Static field shimming alone
Rationale: EPI uses rapid, repetitive gradient switching to acquire large amounts
of spatial information quickly. This gradient activity can produce substantial
induced electric fields and is therefore particularly relevant to PNS considerations.
8. What is the primary physiological event responsible for a nerve being
stimulated by an induced electric field?
A. Increased tissue temperature
B. Suppression of sodium channels
C. Depolarization of the nerve membrane
D. Conversion of RF energy into sound
Rationale: An induced electric field can alter the transmembrane potential of
excitable nerve fibers. When the membrane is sufficiently depolarized, an action
potential can be initiated, producing a sensory or motor response.
, 9. Which term describes the minimum stimulus needed to produce a detectable
nerve response?
A. Resonance frequency
B. Duty cycle
C. Stimulation threshold
D. Gradient offset
Rationale: The stimulation threshold is the minimum effective exposure or
stimulus required to produce a measurable or perceptible neural response. PNS
safety limits are designed to keep gradient exposure below relevant stimulation
thresholds.
10. Which statement best describes gradient-induced PNS in routine MRI?
A. It is caused primarily by the static B0 field.
B. It occurs only when RF power is high.
C. It results from electric fields induced by time-varying gradient magnetic fields.
D. It is caused exclusively by acoustic noise.
Rationale: PNS is a consequence of time-varying magnetic fields from the
gradients. These changing fields induce electric fields in the body that can
stimulate peripheral nerves.
11. What does gradient amplitude describe?
A. How quickly a gradient changes
B. The strength of the gradient magnetic field per unit distance
C. The frequency of RF transmission
D. The patient's nerve conduction velocity
Rationale: Gradient amplitude describes the spatial variation of magnetic field
strength and is commonly expressed in mT/m. It is distinct from slew rate, which
describes the temporal rate of gradient change.
Stimulation Exam Practice Questions
and Correct Answers (Verified Answers)
Plus Rationales 2027 Q&A | Instant
Download Pdf
1. What is the primary mechanism by which rapidly switching MRI gradients can
produce peripheral nerve stimulation?
A. Direct absorption of RF energy by nerves
B. Heating of neural tissue by the static magnetic field
C. Induction of electric fields in conductive body tissues
D. Mechanical vibration of the gradient coils
Rationale: Rapidly changing magnetic fields produced by gradient coils induce
electric fields within conductive tissues according to electromagnetic induction. If
the induced electric field is sufficiently strong and appropriately distributed, it can
depolarize excitable nerves and produce PNS.
2. Which gradient parameter most directly describes how rapidly a gradient
magnetic field changes?
A. Gradient amplitude
B. Slew rate
C. Static field strength
D. RF frequency
Rationale: Slew rate describes the rate at which the gradient changes with time,
commonly expressed in T/m/s. Faster changes in gradient fields generally produce
greater induced electric fields and therefore increase the potential for PNS.
,3. Which unit is commonly used to express gradient slew rate?
A. mT/m
B. Hz
C. W/kg
D. T/m/s
Rationale: Gradient amplitude is commonly expressed in mT/m, while gradient
slew rate is expressed in tesla per meter per second (T/m/s). Slew rate represents
the rate of change of gradient strength with time.
4. Which patient sensation is most characteristic of mild peripheral nerve
stimulation during MRI?
A. Complete loss of sensation
B. Tingling or tapping sensations
C. Permanent numbness
D. Visual loss
Rationale: PNS commonly begins as sensations such as tingling, tapping, buzzing,
or brief muscle twitching. The ACR describes gradient-induced PNS as potentially
producing sensations ranging from tingling to muscle contractions.
5. Which MRI system component is primarily responsible for gradient-induced
PNS?
A. Main static magnet
B. RF transmit coil
C. Gradient coil system
D. Patient table motor
Rationale: The gradient coils generate rapidly changing magnetic fields during
image acquisition. These time-varying fields can induce electric fields and currents
in the patient's tissues, potentially stimulating peripheral nerves.
,6. What happens to the induced electric field when the magnetic field changes
more rapidly?
A. It necessarily decreases
B. It remains completely unchanged
C. It becomes independent of gradient switching
D. It generally increases
Rationale: Faraday's law indicates that a changing magnetic field produces an
induced electric field. A greater rate of change of magnetic flux generally produces
a greater induced electric field, increasing the potential for neural stimulation.
7. Which imaging sequence is particularly associated with higher PNS potential
because of rapid, repetitive gradient switching?
A. Conventional spin echo with very low gradient activity
B. Echo-planar imaging (EPI)
C. Basic inversion recovery without rapid gradients
D. Static field shimming alone
Rationale: EPI uses rapid, repetitive gradient switching to acquire large amounts
of spatial information quickly. This gradient activity can produce substantial
induced electric fields and is therefore particularly relevant to PNS considerations.
8. What is the primary physiological event responsible for a nerve being
stimulated by an induced electric field?
A. Increased tissue temperature
B. Suppression of sodium channels
C. Depolarization of the nerve membrane
D. Conversion of RF energy into sound
Rationale: An induced electric field can alter the transmembrane potential of
excitable nerve fibers. When the membrane is sufficiently depolarized, an action
potential can be initiated, producing a sensory or motor response.
, 9. Which term describes the minimum stimulus needed to produce a detectable
nerve response?
A. Resonance frequency
B. Duty cycle
C. Stimulation threshold
D. Gradient offset
Rationale: The stimulation threshold is the minimum effective exposure or
stimulus required to produce a measurable or perceptible neural response. PNS
safety limits are designed to keep gradient exposure below relevant stimulation
thresholds.
10. Which statement best describes gradient-induced PNS in routine MRI?
A. It is caused primarily by the static B0 field.
B. It occurs only when RF power is high.
C. It results from electric fields induced by time-varying gradient magnetic fields.
D. It is caused exclusively by acoustic noise.
Rationale: PNS is a consequence of time-varying magnetic fields from the
gradients. These changing fields induce electric fields in the body that can
stimulate peripheral nerves.
11. What does gradient amplitude describe?
A. How quickly a gradient changes
B. The strength of the gradient magnetic field per unit distance
C. The frequency of RF transmission
D. The patient's nerve conduction velocity
Rationale: Gradient amplitude describes the spatial variation of magnetic field
strength and is commonly expressed in mT/m. It is distinct from slew rate, which
describes the temporal rate of gradient change.
