Figure 3. Unconstrained Cramér-Rao bounds as coefficients of variation.

Three methods are presented using five sets of intrinsic parameter values (1–5 in Table 1). This study was performed at σ_SPGR = 1×10⁻³ M₀, which corresponds to a clinically-feasible SNR for gradient echo sequences, and it should be noted that coefficients of variation scale with image SNR. The dotted lines on each plot are a reference goal for quantitative precision. In all cases, estimates of all parameters except M₀ have impractically high variance. There is a surprising improvement in precision when multiple phase cycling patterns are utilized in SSFP acquisitions, despite the addition of an eighth free parameter.