What happens to protons in a DWI sequence if there is no net movement between gradient pulses?

In a Diffusion Weighted Imaging (DWI) sequence, the behavior of protons is closely linked to their movement in response to applied gradient pulses. When there is no net movement of protons between these gradient pulses, this means that the protons remain essentially in the same position throughout the sequence.

Under these conditions, the protons experience a process known as dephasing due to the diffusion gradients being applied. However, because they do not move significantly, they will rephase effectively after the second gradient pulse. This rephasing leads to a situation where the protons that initially lost coherence due to dephasing regain it, which results in a higher signal intensity.

The crucial aspect here is that the lack of net movement means there is a greater chance for rephasing to occur completely, enhancing the visibility of the signals from the protons, hence producing a high signal intensity on the DWI image. This contrasts with scenarios where movement occurs, leading to different diffusion characteristics and potentially lower signal intensity. Therefore, when considering the behavior of protons in DWI under these circumstances, the outcome is the production of high signal intensity due to effective rephasing.