MRI Knowledge 2 — Questions and Answers
Question 1: What does the term 'repetition time' (TR) refer to in MRI pulse sequences?
- The time between the RF pulse and the echo
- The time between successive RF excitation pulses applied to the same slice (Correct answer)
- The total scan duration
- The time for magnetization to return to equilibrium after T2 decay
Correct answer: The time between successive RF excitation pulses applied to the same slice
TR is the interval between the beginning of one RF excitation pulse and the beginning of the next for the same slice, controlling T1 contrast.
Question 2: Which MRI artifact is caused by periodic patient motion such as cardiac or respiratory movement?
- Chemical shift artifact
- Gibbs ringing artifact
- Ghosting (motion) artifact (Correct answer)
- Magnetic susceptibility artifact
Correct answer: Ghosting (motion) artifact
Ghosting artifacts appear as repeated copies of moving structures along the phase-encoding direction due to periodic physiologic motion.
Question 3: The flip angle in an MRI sequence refers to which of the following?
- The angle of the main magnetic field relative to the bore
- The degree to which the net magnetization vector is rotated from B0 by the RF pulse (Correct answer)
- The angular velocity of proton precession
- The tilt of the gradient coil axis
Correct answer: The degree to which the net magnetization vector is rotated from B0 by the RF pulse
The flip angle is how far the net magnetization vector is tipped away from the longitudinal axis by the RF pulse.
Question 4: Which type of MRI coil surrounds the entire body and is used to transmit RF energy uniformly?
- Surface coil
- Phased-array coil
- Body (volume) coil (Correct answer)
- Gradient coil
Correct answer: Body (volume) coil
The body (volume) coil is built into the bore and provides uniform RF transmission across the entire patient.
Question 5: In MRI, what is k-space?
- The physical space inside the magnet bore
- The raw data space containing spatial frequency information used to reconstruct images (Correct answer)
- The region of the brain studied in neuroimaging
- A unit of measurement for gradient strength
Correct answer: The raw data space containing spatial frequency information used to reconstruct images
K-space is the mathematical domain that stores the raw MRI signal as spatial frequencies; a Fourier transform converts it into an image.
Question 6: What is the primary purpose of fat saturation techniques in MRI?
- To increase the signal from fat-containing tissues
- To suppress the fat signal so adjacent structures are more conspicuous (Correct answer)
- To reduce T1 relaxation time of fat
- To eliminate chemical shift artifact entirely
Correct answer: To suppress the fat signal so adjacent structures are more conspicuous
Fat saturation applies a frequency-selective RF pulse to null the fat signal, improving visibility of adjacent enhancing or edematous tissue.
Question 7: Which safety zone in an MRI facility is defined as the area that requires screening and controlled access due to the fringe magnetic field?
- Zone I
- Zone II
- Zone III (Correct answer)
- Zone IV
Correct answer: Zone III
Zone III is the area where the fringe field poses risk and requires restricted access; only screened individuals may enter.
MRI Knowledge 2
What does the term 'repetition time' (TR) refer to in MRI pulse sequences?