Are mono-exponential fits to a few echoes sufficient to determine T-2 relaxation for in vivo human brain?

T-2 relaxation decay curves from in vivo human brain tissue are rarely mono -exponential. Partial volume averaging further reduces the chance of mono-e xponential decay. Moreover, the parameters derived from few-echo mono-expon ential fits change with the measurement echo times and have the largest pos sible 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-exponenti al interpretations. (C) 1999 Wiley-Liss, Inc.