E. I don’t know. I’m here to learn some fMRI analysis so just show me the answer

There is nothing wrong about the signal phase generated by the tissues. However, when we sampled the signal, the phase values are constrained to the range $-\pi \leq phase < \pi$ . When the true phase is outside of this range, a $\pi$ will be added or subtracted to the true phase such that the apparent phase we observed from the data will still be inside the range.

Figure 1: An illustration of phase wrapping. The actual phase developed outside the range $-\pi \leq phase < \pi$ over time but our measurement will only show the apparent phase.

Note

Think of an analogue clock with one hand only representing the hour. Every 12 hours the hand starts a new cycle again. If you look at the clock 13 hours after the first watch, it apparently advanced 1 hour only but the actual time difference between the two observations is 13 hours.

Back to Exercise 1.