Figure 1.

Simulation and CRLB results for 4 (crosses), 8 (squares), 12 (triangles), and 16 (circles) echoes. This simulation used 20 000 trials. Estimates for chemical shift achieved an uncertainty at the CRLB for SNR≥5 for each ETL (4–16 echoes) (a). The uncertainties in $T_2^{*}$ for ETL=16 achieved the CRLB for all SNRs≥5 (b). As the ETL decreases, the uncertainty diverges from the CRLB. For instance, at ETL=8, the uncertainty is higher than the CRLB at SNR<10.Compared with the chemical shift (a) and $T_2^{*}$ (b), the uncertainties of the amplitudes in the simulation and their CRLBs are less dependent on the number of echoes (c).