Magnetic Resonance Imaging (MRI) Practice Test

In an inversion recovery sequence, the selected inversion time (TI) should be what percentage of the T1 relaxation time for tissue nulling?

1. 50%

2. 69%

3. 80%

4. 90%

The correct answer is: 69%

In an inversion recovery sequence, the goal is often to nullify the signal from specific tissues by selecting an appropriate inversion time (TI). The selected TI should be a particular percentage of the T1 relaxation time of the tissue being targeted for nulling. The correct choice corresponds to approximately 69% of the T1 relaxation time. This percentage reflects the time at which a tissue’s longitudinal magnetization recovers to a point where it effectively cancels out the signal in the imaging process. Specifically, using around 69% of T1 ensures that the magnetization of the tissue of interest is at zero when the readout is performed. At this time, the longitudinal magnetization of the specified tissue will have recovered sufficiently to reach a null point due to its T1 properties, while other tissues with different T1 values will continue to provide a detectable signal. This principle is foundational in MRI for achieving contrast by selectively suppressing signals from certain tissues. Other percentages such as 50%, 80%, and 90% do not provide the same effective nulling for this purpose, as they do not align with the optimal point in the recovery curve of the longitudinal magnetization of the tissue being nullified. This misalignment would result in residual signals