Time Constant Tool: Introduction
Answer: The time constant of an exponential is simply the denominator of the fraction to which e is powered.
A simple exponential decay may be defined in general form as
f(t) = A·e-t/τ
where f is a function of time (t), A is the peak amplitude (a scalar) and τ is the time constant of the exponential. The time constant is the denominator of the fraction to which e is powered.
In MRI, T1, T2 and T2* are time constants.
Navigate below to the first equation in the list: exp (x/400).
Further reading on this topic:
Books: Q&A in MRI p29-30
Remember, T1, T2 and T2* are time constants.