Fig. 4.

Comparison of ³¹P B₁ maps (in the axial plane) of the selected human calf muscle (left panel) from one representative subject. (A) shows the schematic placement of 4 uHDC blocks (blue) around the leg. The B₁ maps (the scale bar is in an arbitrary unit, a.u) with the uHDC blocks (B, E) show large enhancement of B₁ efficiency as compared to the case without the uHDC blocks (C, F). The B₁ ratio maps (D, E) represent theB₁ with uHDC over B₁ without uHDC. (H) shows the calibration of the B₁ values of the highlighted voxel (green box in A) using a nonlinear curve fitting algorithm with saturation effect correction.