Combining CW and pulsed saturation allows in vivo quantitation of magnetization transfer observed for total creatine by H-1-NMR-spectroscopy of rat brain

Selective saturation of bound nuclei attenuates the MR visible CH2 and the CH3 signal of total creatine (tCr) in rat brain in vivo. The low contrast t o noise ratio achieved during the limited experiment time makes it difficul t to quantify the effect. It is shown that by combining data from continuou s-wave and pulsed saturation experiments, quantitation is possible using th e standard magnetization transfer model. The model parameters obtained are the transverse relaxation time of the bound spin fraction B, T-2(R) = 31 +/ - 8 mu s, the exchange rate r(x) = 0.36 +/- 0.04 s(-1), and the concentrati on ratio of bound nuclei taking part in the exchange to free tCr magnetizat ion, f = M-0(B)/M-0(A) = 0.04 +/- 0.01. The phenomenon can be explained by either an intermolecular exchange of free and bound creatine molecules or b y through-space interaction with bound nuclei showing not necessarily the s ame chemical shift. Magn Reson Med 42:222-227, 1999. (C) 1999 Wiley-Liss, I nc.