MRI MRI Image Quality and Optimization 2 — Questions and Answers
Question 1: Which coil type generally provides the highest SNR for imaging a small superficial structure?
- Surface coil (Correct answer)
- Volume coil
- Body coil
- Quadrature head coil
Correct answer: Surface coil
Surface coils placed close to the target anatomy have superior SNR for small or superficial structures because they detect signal from a limited volume with less noise.
Question 2: What is the effect of increasing receiver bandwidth on MRI image quality?
- SNR decreases but chemical shift artifact is reduced (Correct answer)
- SNR increases and scan time decreases
- Image contrast improves significantly
- Spatial resolution decreases
Correct answer: SNR decreases but chemical shift artifact is reduced
Increasing bandwidth reduces chemical shift artifact and allows shorter TE/TR, but more noise is accepted per unit time, lowering SNR.
Question 3: In MRI, what does the term 'k-space' represent?
- The raw frequency-domain data before Fourier transformation into an image (Correct answer)
- The final reconstructed image space
- The physical space inside the MRI bore
- A map of gradient field inhomogeneities
Correct answer: The raw frequency-domain data before Fourier transformation into an image
K-space is the mathematical frequency domain where raw MRI data is stored; a Fourier transform converts k-space data into the final spatial image.
Question 4: Which portion of k-space primarily determines image contrast?
- The center (low spatial frequencies) (Correct answer)
- The periphery (high spatial frequencies)
- The edges equally with the center
- The corners of k-space only
Correct answer: The center (low spatial frequencies)
The center of k-space contains low spatial frequency data, which encodes the bulk signal intensity and contrast of the image.
Question 5: A technologist increases slice thickness from 3 mm to 6 mm. What is the expected change in image quality?
- SNR improves but through-plane resolution decreases (Correct answer)
- Both SNR and spatial resolution improve
- SNR decreases and spatial resolution improves
- No change occurs because FOV is unchanged
Correct answer: SNR improves but through-plane resolution decreases
Thicker slices contain more protons and generate more signal, improving SNR, but fine anatomical detail in the through-plane direction is reduced.
Question 6: What is the purpose of applying a saturation band in MRI?
- To suppress signal from specified tissue or flowing blood to reduce artifacts (Correct answer)
- To increase SNR from the target anatomy
- To improve spatial resolution in the phase direction
- To shorten the overall scan time
Correct answer: To suppress signal from specified tissue or flowing blood to reduce artifacts
Saturation bands apply an RF pulse to a defined region, nulling its magnetization so it contributes no signal, which suppresses motion or flow-related artifacts.
Question 7: Which of the following best describes the concept of signal-to-noise ratio (SNR) in MRI?
- The ratio of mean signal intensity in a region of interest to the standard deviation of background noise (Correct answer)
- The number of signal averages divided by scan time
- The difference in signal between two adjacent tissues
- The ratio of TE to TR
Correct answer: The ratio of mean signal intensity in a region of interest to the standard deviation of background noise
SNR is quantitatively defined as the mean signal from a region of interest divided by the standard deviation of noise measured in a background air region.
MRI MRI Image Quality and Optimization 2
Which coil type generally provides the highest SNR for imaging a small superficial structure?