Are mono-exponential fits to a few echoes sufficient to determine T2 relaxation for in vivo human brain?

T2 relaxation decay curves from in vivo human brain tissue are rarely mono‐exponential. Partial volume averaging further reduces the chance of mono‐exponential decay. Moreover, the parameters derived from few‐echo mono‐exponential fits change with the measurement echo times and have the largest possible variance. In this note, multi‐exponential fits to 32‐echo relaxation decay curves from in vivo human brain are used to design simulations (where the truth is known) to demonstrate the pitfalls of few‐echo mono‐exponential interpretations. Magn Reson Med 41:1255–1257, 1999. © 1999 Wiley‐Liss, Inc.