ASMIRT MRI Accreditation
ASMIRT MRI ACCREDITATION | EXAM QUESTIONS AND
CORRECT ANSWERS | LATEST VERSION 2026/2027
AUSTRALIAN SOCIETY OF MEDICAL IMAGING AND RADIATION THERAPY
MRI ACCREDITATION
1. What is the approximate Larmor frequency of hydrogen protons in a
1.5 T magnetic field?
A. 63.86 MHz
B. 42.58 MHz
C. 127.7 MHz
D. 21.29 MHz
ANSWER : A. 63.86 MHz
The precessional frequency equals the gyromagnetic ratio (42.58 MHz/T)
multiplied by field strength, so 42.58 x 1.5 = 63.86 MHz.
2. At 3.0 T, hydrogen protons precess at approximately:
A. 255.4 MHz
B. 63.86 MHz
C. 127.7 MHz
D. 85.2 MHz
ANSWER : C. 127.7 MHz
Doubling the field from 1.5 T to 3.0 T doubles the Larmor frequency to
roughly 127.7 MHz.
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, ASMIRT MRI Accreditation
3. The gyromagnetic ratio of hydrogen is:
A. 40.05 MHz/T
B. 10.71 MHz/T
C. 42.58 MHz/T
D. 17.24 MHz/T
ANSWER : C. 42.58 MHz/T
Hydrogen has a gyromagnetic ratio of 42.58 MHz/T; 10.71 belongs to
carbon-13 and 40.05 to fluorine-19.
4. At thermal equilibrium, the net magnetisation vector (NMV) lies:
A. Parallel to B0 along the longitudinal (z) axis
B. At 90 degrees to the receiver coil axis
C. Anti-parallel to B0 along the z axis
D. In the transverse (xy) plane
ANSWER : A. Parallel to B0 along the longitudinal (z) axis
Slightly more spins sit in the low-energy parallel state, so the NMV points
along B0 in the longitudinal direction.
5. Precession is best described as:
A. The wobbling rotation of a magnetic moment around the axis of B0
B. The transfer of energy from spins to the surrounding lattice
C. The loss of phase coherence between neighbouring spins
D. The flipping of spins into the high-energy state
ANSWER : A. The wobbling rotation of a magnetic moment around
the axis of B0
Each proton's magnetic moment spins around the external field axis at
the Larmor frequency.
6. For resonance to occur, the RF excitation pulse must be applied at:
A. The frequency of the gradient switching
B. Twice the Larmor frequency
C. The Larmor frequency of the nuclei being imaged
D. Any frequency within the audio range
ANSWER : C. The Larmor frequency of the nuclei being imaged
Energy is absorbed efficiently only when the RF frequency matches the
precessional frequency of the target nuclei.
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, ASMIRT MRI Accreditation
7. Immediately after a 90 degree RF pulse, the NMV is located:
A. Anti-parallel to B0
B. Entirely in the transverse plane
C. Parallel to B0
D. At 45 degrees to B0
ANSWER : B. Entirely in the transverse plane
A 90 degree pulse tips all longitudinal magnetisation into the transverse
plane where it can induce signal.
8. The signal induced in the receiver coil immediately after an RF
excitation pulse is called:
A. Spin echo
B. Free induction decay
C. Stimulated echo
D. Gradient echo
ANSWER : B. Free induction decay
FID is the decaying signal produced as transverse magnetisation
precesses freely and dephases after excitation.
9. Hydrogen is the nucleus of choice for clinical MRI mainly because it:
A. Is only present in fat
B. Is highly abundant in the body and has a relatively large magnetic
moment
C. Has no magnetic moment
D. Has an even mass number
ANSWER : B. Is highly abundant in the body and has a relatively
large magnetic moment
Hydrogen's abundance in water and fat plus its strong magnetic moment
produce the most usable signal.
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, ASMIRT MRI Accreditation
10. At 1.5 T, the excess of spins aligned with the field compared with
those against it is approximately:
A. Exactly equal numbers
B. A few per million
C. Half of all spins
D. About one in ten
ANSWER : B. A few per million
The population difference is tiny, only a few parts per million, which is
why MRI is an inherently low-signal technique.
11. As the static field strength increases, the SNR in MRI:
A. Decreases
B. Remains unchanged
C. Increases approximately linearly
D. Increases with the fourth power of field strength
ANSWER : C. Increases approximately linearly
A stronger B0 increases the population difference and therefore the
available signal roughly in proportion to field strength.
12. Signal reception in MRI is based on which physical principle?
A. Faraday's law of electromagnetic induction
B. The inverse square law
C. Compton scattering
D. The photoelectric effect
ANSWER : A. Faraday's law of electromagnetic induction
A changing magnetic flux from precessing magnetisation induces a voltage
in the receiver coil.
13. Phase coherence refers to:
A. Spins that have fully recovered longitudinal magnetisation
B. Spins located within the same voxel
C. Spins precessing in step at the same position on their precessional path
D. Spins aligned anti-parallel to B0
ANSWER : C. Spins precessing in step at the same position on their
precessional path
When magnetic moments precess together in phase, their transverse
components add to produce a measurable signal.
Page 4 of 56
ASMIRT MRI ACCREDITATION | EXAM QUESTIONS AND
CORRECT ANSWERS | LATEST VERSION 2026/2027
AUSTRALIAN SOCIETY OF MEDICAL IMAGING AND RADIATION THERAPY
MRI ACCREDITATION
1. What is the approximate Larmor frequency of hydrogen protons in a
1.5 T magnetic field?
A. 63.86 MHz
B. 42.58 MHz
C. 127.7 MHz
D. 21.29 MHz
ANSWER : A. 63.86 MHz
The precessional frequency equals the gyromagnetic ratio (42.58 MHz/T)
multiplied by field strength, so 42.58 x 1.5 = 63.86 MHz.
2. At 3.0 T, hydrogen protons precess at approximately:
A. 255.4 MHz
B. 63.86 MHz
C. 127.7 MHz
D. 85.2 MHz
ANSWER : C. 127.7 MHz
Doubling the field from 1.5 T to 3.0 T doubles the Larmor frequency to
roughly 127.7 MHz.
Page 1 of 56
, ASMIRT MRI Accreditation
3. The gyromagnetic ratio of hydrogen is:
A. 40.05 MHz/T
B. 10.71 MHz/T
C. 42.58 MHz/T
D. 17.24 MHz/T
ANSWER : C. 42.58 MHz/T
Hydrogen has a gyromagnetic ratio of 42.58 MHz/T; 10.71 belongs to
carbon-13 and 40.05 to fluorine-19.
4. At thermal equilibrium, the net magnetisation vector (NMV) lies:
A. Parallel to B0 along the longitudinal (z) axis
B. At 90 degrees to the receiver coil axis
C. Anti-parallel to B0 along the z axis
D. In the transverse (xy) plane
ANSWER : A. Parallel to B0 along the longitudinal (z) axis
Slightly more spins sit in the low-energy parallel state, so the NMV points
along B0 in the longitudinal direction.
5. Precession is best described as:
A. The wobbling rotation of a magnetic moment around the axis of B0
B. The transfer of energy from spins to the surrounding lattice
C. The loss of phase coherence between neighbouring spins
D. The flipping of spins into the high-energy state
ANSWER : A. The wobbling rotation of a magnetic moment around
the axis of B0
Each proton's magnetic moment spins around the external field axis at
the Larmor frequency.
6. For resonance to occur, the RF excitation pulse must be applied at:
A. The frequency of the gradient switching
B. Twice the Larmor frequency
C. The Larmor frequency of the nuclei being imaged
D. Any frequency within the audio range
ANSWER : C. The Larmor frequency of the nuclei being imaged
Energy is absorbed efficiently only when the RF frequency matches the
precessional frequency of the target nuclei.
Page 2 of 56
, ASMIRT MRI Accreditation
7. Immediately after a 90 degree RF pulse, the NMV is located:
A. Anti-parallel to B0
B. Entirely in the transverse plane
C. Parallel to B0
D. At 45 degrees to B0
ANSWER : B. Entirely in the transverse plane
A 90 degree pulse tips all longitudinal magnetisation into the transverse
plane where it can induce signal.
8. The signal induced in the receiver coil immediately after an RF
excitation pulse is called:
A. Spin echo
B. Free induction decay
C. Stimulated echo
D. Gradient echo
ANSWER : B. Free induction decay
FID is the decaying signal produced as transverse magnetisation
precesses freely and dephases after excitation.
9. Hydrogen is the nucleus of choice for clinical MRI mainly because it:
A. Is only present in fat
B. Is highly abundant in the body and has a relatively large magnetic
moment
C. Has no magnetic moment
D. Has an even mass number
ANSWER : B. Is highly abundant in the body and has a relatively
large magnetic moment
Hydrogen's abundance in water and fat plus its strong magnetic moment
produce the most usable signal.
Page 3 of 56
, ASMIRT MRI Accreditation
10. At 1.5 T, the excess of spins aligned with the field compared with
those against it is approximately:
A. Exactly equal numbers
B. A few per million
C. Half of all spins
D. About one in ten
ANSWER : B. A few per million
The population difference is tiny, only a few parts per million, which is
why MRI is an inherently low-signal technique.
11. As the static field strength increases, the SNR in MRI:
A. Decreases
B. Remains unchanged
C. Increases approximately linearly
D. Increases with the fourth power of field strength
ANSWER : C. Increases approximately linearly
A stronger B0 increases the population difference and therefore the
available signal roughly in proportion to field strength.
12. Signal reception in MRI is based on which physical principle?
A. Faraday's law of electromagnetic induction
B. The inverse square law
C. Compton scattering
D. The photoelectric effect
ANSWER : A. Faraday's law of electromagnetic induction
A changing magnetic flux from precessing magnetisation induces a voltage
in the receiver coil.
13. Phase coherence refers to:
A. Spins that have fully recovered longitudinal magnetisation
B. Spins located within the same voxel
C. Spins precessing in step at the same position on their precessional path
D. Spins aligned anti-parallel to B0
ANSWER : C. Spins precessing in step at the same position on their
precessional path
When magnetic moments precess together in phase, their transverse
components add to produce a measurable signal.
Page 4 of 56
