Magnetic Resonance Imaging (MRI) Practice Test

Which of the following adjustments will reduce the overall SNR in an MR image?

1. Decrease TR, Increase pixel size, Increase FOV

2. Increase TR, Decrease pixel size, Decrease NEX

3. Decrease TR, Reduce pixel size, Decrease FOV, Increase rBW

4. Decrease TR, Reduce pixel size, Decrease FOV, Increase rBW, Decrease NEX, Increase ETL

The correct answer is: Decrease TR, Reduce pixel size, Decrease FOV, Increase rBW, Decrease NEX, Increase ETL

To understand why the choice that mentions decreasing TR (Repetition Time), reducing pixel size, decreasing FOV (Field of View), increasing rBW (Receiver Bandwidth), decreasing NEX (Number of Excitations), and increasing ETL (Echo Train Length) would lead to a reduction in the overall Signal-to-Noise Ratio (SNR) in an MR image, it is essential to break down each component's impact on SNR. Decreasing TR will limit the time available for signal acquisition, making it less likely to collect sufficient signal relative to the noise. This will generally lead to a diminished SNR because the noise floor will not change significantly while the signal decreases due to reduced time for relaxation. Reducing pixel size is another factor that negatively impacts SNR. Smaller pixels collect less signal from the area of interest because the voxel (volume element) itself is reduced in size. Consequently, with less signal available, the SNR will drop. Decreasing FOV also plays a significant role. By decreasing the FOV, the number of signals captured over a given area decreases, which can lead to a lower SNR since the system gains less signal from a smaller volume of tissue. Increasing rBW results in a higher bandwidth, which captures a