Figure 3.

Performance of B ₀ shimming. (a) The mean and standard deviation of the B ₀ maps for 1^st–2^nd and 1^st–4^th+ degree shims are displayed in Talairach space (n = 8 subjects). The scale is truncated at ±80 Hz to show detail (note that the dynamic ranges for 1^st–2^nd and 1^st–4^th+ degree shimming are 423 ± 47 Hz and 390 ± 54 Hz, respectively). (b) Histogram analysis for the distribution of B ₀ values for whole brain and gray‐matter area (left: whole brain, right: gray matter) averaged from n = 8 subjects and truncated for display at ±90 Hz with 1^st–4^th+ degree shimming, the center of B ₀ distribution (excluding the 0‐Hz peak) is closer to carrier frequency and narrower than with 1^st–2^nd degree shimming. The peak of 1^st–2^nd degree shimming at the 0‐Hz carrier is marked with blue symbols for visualization from the overlapped peak. It should be noted that the histogram analysis was directly obtained from each subject without transformation into Talairach space.