Magnetic Resonance Imaging (MRI) Practice Test

Why is less T1 information obtained when the flip angle is decreased?

1. It reduces the energy supplied to protons

2. It decreases proton alignment

3. It alters the relaxation times

4. It minimizes the effect of contrast agents

The correct answer is: It reduces the energy supplied to protons

The correct choice indicates that less T1 information is obtained when the flip angle is decreased because it reduces the energy supplied to protons. In MRI, the flip angle refers to the angle at which the external radiofrequency pulse tips the net magnetization of the protons away from the longitudinal (z) axis into the transverse (xy) plane. A decreased flip angle means that less energy is being imparted to the protons. When the flip angle is reduced, there is less tipping of the proton spins, leading to less longitudinal magnetization recovery before the next imaging sequence. Thus, the protons do not have as much time to return to their equilibrium state, which limits the information related to T1 relaxation. T1 relaxation is heavily reliant on the extent of proton alignment and energy state, determining the time it takes for protons to relax back to their original state after being excited. Therefore, when the flip angle is smaller, there is insufficient energy supplied to fully capture the T1 characteristics of the tissue, resulting in suboptimal T1 weighting in the images. In contrast, alterations in proton alignment and relaxation times as suggested by the other options do not directly explain the relationship between flip angle and T1 information. The role of contrast agents primarily