Basic studies on the equivalent cross-relaxation rate imaging (equivalent CRI)-phantom studies

We have studied saturation transfer in hydrophilic, cross‐linked copolymer gels from irradiated polymer protons to observed water protons, using f2 (ppm) profiles of [1 − (I∞/I0)], [(I0/I∞) − 1] or 1/TIS(H2O), where I0 and I∞ are the longitudinal magnetization of the observed water protons before and after long‐time­f2‐irradiation on polymer protons, respectively, and 1/TIS(H2O) is the cross‐relaxation rate. (A) [1 − (I∞/I0)] (magnetization transfer ratio, MTR) was used in magnetic resonance imaging (MRI) as the MTR imaging. 1/TIS(H2O) (cross‐relaxation rate) was used in the imaging of the magnetization transfer rate constant. This method was quite time‐consuming compared with MTR imaging. However, f2 (ppm) profiles of [(I0/I∞) − 1] correlated well with corresponding profiles of 1/TIS(H2O), because [(I0/I∞) − 1] is equal to 1/[TIS(H2O)/T1(H2O)]. These results lead us to the conclusion that [(I0/I∞) − 1] might be applicable to cross‐relaxation rate (CR)‐like imaging, i.e. equivalent CRI. (B) W (%) (dry weight) profiles of [(I0/I∞) − 1] and 1/TIS(H2O), obtained by near‐resonance f2‐irradiation, seem to indicate participation of molecular rigidity and an amount of bound water. However, those values, monitored with off‐resonance f2‐irradiation, seem to be independent of monomer composition and to indicate mainly participation of rigidity, i.e. W (%) of copolymer gels. Copyright © 2001 John Wiley & Sons, Ltd.