FIG. 4.

(a) A group-averaged ³¹P MR spectral series acquired from the resting human brain at 7T using band inversion module-II at constant TR 4 sec and varying inversion delay time t_d = 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 t_d series. The inset displays the time course of Pi signals with respect to inversion delay t_d. Note the MT effect at Pi manifested as a “fall-rise” biphasic change. (b) Plots of normalized ³¹P magnetizations at different inversion delay t_d and the fitted curves according to the 5-spin exchange model illustrated in Figure 1b. For clarity, only Pi, PCr and γ-ATP datasets are shown.