relationship between molecular tumbling rate and T2 relaxation time

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the image is here

who can explain the relationship between molecular tumbling rate and T2 relaxation time. Why it is the relationship like this as the image said above.

PS:The movement, or tumbling is rotation, vibration and translation of the molecule in which the hydrogen proton resides. Water molecules, which are the source of most of the signal in MRI, can be found in three states which affect their movement or tumbling.