(a) A group-averaged 31P MR spectral series acquired from the resting human brain at 7T using band inversion module-III at constant TR 4 sec and varying inversion delay time td = 25, 197, 405, 668, 1026, 1589, and 3000 msec (n = 6 subjects). For comparison, the last trace of the spectral series represents a brain 31P MR reference spectrum acquired at TR 4 sec without applying the inversion pre-pulse. The magnetizations measured in the reference spectrum were used for normalizing the magnetizations of the td series. The inset displays the time course of β-ATP signal with respect to inversion delay td. Note the MT effect at β-ATP manifested as a “fall-rise” biphasic change. (b) Plots of normalized 31P magnetizations at different inversion delay td and the fitted curves according to the 5-spin exchange model illustrated in Figure 1b. For clarity, only α-, β- and γ-ATP datasets are shown.