Theory: MR Phase

As mentioned in the Introduction, water protons resonate at different frequencies in the brain because of the tissue magnetic susceptibility. The frequency difference in brain tissues, $f$ , can be detected as the difference in phase accumulation, $\theta$ , over time, $t$ ( $\theta(t) = f \times t$ ). Therefore, the phase measurement of the MRI signal allows us to directly map the effect of the magnetic susceptibility of brain tissues.

It should be noted that the phase can only be measured in the range of [-180, 180] degrees (or [ $-\pi, \pi$ ] in radian).

Back to Exercise 1.