Fig. 7
B 0 and B 1 field homogeneity. a B 0 field homogeneity across the nine phantom compartments as a measure of off-resonance in Hz at 3 T (single E-model phantom results). These are extremely small shifts in frequency (30 Hz = 0.25 ppm) at 3 T and should not be regarded as significantly different between the tubes. b Diagonal profile of the B 1 field (as per green discontinuous line in the inset) comparing relative flip angles on a Siemens 3 T system. Variance of B 1 was smallest across the 9 compartments with CoV 1.54 % for HDPE beads consisting of smooth, semi-translucent, colourless compact discs (as colouring in plastics has the potential to distort the B 0 magnetic field [12], see Fig. 2h) with a melt index >60 °C. We choose pellets that had not been regrinded, reblended or composite for this purpose. Highly monosized microbeads measured 6 μm and were composed of crosslinked PMMA polymer. Neither microbeads, sucrose nor NaCl were comparably effective in flattening the B 1 field. PMMA = poly methyl methacrylate. Other abbreviation as in Fig. 4