Magnetic Resonance Imaging (MRI) Practice Test

Which of the following parameter adjustments will shorten can time in an MR pulse sequence?

1. Decrease TR

2. Increase NEX

3. Enable half fourier

4. Decrease the parallel imaging factor

The correct answer is: Decrease TR

Shortening the repetition time (TR) in an MR pulse sequence directly affects the cycle time of the imaging process. TR is the time between successive pulse sequences applied to the same slice. By decreasing TR, you can reduce the overall scan time because the system has less time between each pulse sequence. This allows for more rapid collection of data, thus speeding up the imaging process. In contrast, increasing the number of excitations (NEX) would actually lengthen scan time, as it involves acquiring multiple signal averages for better signal-to-noise ratio. Enabling half Fourier will also generally help in reducing scan time, but it does so through different mechanisms, and is not applicable under all imaging conditions. Lastly, decreasing the parallel imaging factor would also lengthen scan time since parallel imaging is used to acquire data more quickly, thus mitigating the effects of longer scan times that would normally occur due to other sequence parameters.