Figure 9.

Dependence of α̂ on the total number of coil channels included in the combined pixel. Shown are 2D histograms depicting the value of α̂ as a function of the number of coil channels in the combined data from a single representative subject (1×1×3 mm³ images, 3T, 32Ch array coil). Combinations of channels were formed using both: (A) global weights from a birdcage-like combination or (B) weights for the rSoS of those channels. The color scale represents the number of EPI voxels falling within a particular bin. The bin is determined by the number of channels included in the array combination (horizontal axis) and the observed α̂ value (vertical axis). For both combination methods, the value of α̂ increases nonlinearly as the number of channels increases, converging to a value in the range of 2–3 for the rSoS SNR combination and 0.6–1.2 for the birdcage combination.