The optimum number of echoes for fat-corrected R2* mapping is heavily dependent on the underlying R2* value. Plots shows the theoretical noise performance (standard deviation) of fat-corrected R2* mapping as a function of number of TEs, for fixed initial TE (1 ms) and echo spacing (1 ms). Except for low values of R2* (e.g., 40 s−1), there is little benefit to increasing the echo train length beyond 6. Even with 6 echoes, the noise performance of R2* estimation when R2* = 40 s−1, is very good because the signal levels are high compared with tissue with high R2*.