Relaxation Rates vs Times
What is the difference between relaxation rates and relaxation times?
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Relaxation times and relaxation rates are simple inverses of each other. The values specified for T1 and T2 are relaxation times and typically measured in milliseconds (ms). The corresponding relaxation rates are therefore measured in units of [1/ms]. Relaxation rates corresponding to T1 and T2 are typically designated by the symbols R1 and R2, where
R1 = 1/T1 and R2 = 1/T2
Although a simple concept I have found students to sometimes be confused because a larger rate means a shorter time, and vice-versa. For example, if Tissue A has a higher transverse relaxation rate than Tissue B, the T2 value for A will be smaller than the T2 value for B.