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. Author manuscript; available in PMC: 2016 Mar 16.
Published in final edited form as: Concepts Magn Reson Part A Bridg Educ Res. 2013 Aug 10;42(4):116–129. doi: 10.1002/cmr.a.21269

Figure 2.

Figure 2

The Stejskal-Tanner pulse sequence (A) and its two effective gradient pulse sequences (B) and (C). In (A), the top diagram is the spin echo pulse sequence with the initial 90 degrees radiofrequency pulse along the x-axis, and after some time TE/2, the 180 degrees radiofrequency pulse along the x-axis. In the middle diagram of panel (A) the application of gradient pulses are shown. The effective gradient pulse sequences, (B) and (C), are equivalent to (A) when there is no motion (i.e., r1 = r2 in Section 3). When translational motion exists, (B) remains consistent with (A) but (C) has a sign difference. The sign difference in (B) resulted in the normalized q-space signal as the inverse Fourier transform of the average propagator while (C), which is inconsistent with (A), resulted in the forward Fourier transform.