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 f 2 (ppm) profiles of [1 − ( I ∞ / I 0 )], [( I 0 / I ∞ ) − 1] or 1/ T IS (H 2 O), where I 0 and I ∞ are the longitudinal magnetization of the observed water protons before and after long‐time f 2 ‐irradiation on polymer protons, respectively, and 1/ T IS (H 2 O) is the cross‐relaxation rate. (A) [1 − ( I ∞ / I 0 )] (magnetization transfer ratio, MTR) was used in magnetic resonance imaging (MRI) as the MTR imaging. 1/ T IS (H 2 O) (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, f 2 (ppm) profiles of [( I 0 / I ∞ ) − 1] correlated well with corresponding profiles of 1/ T IS (H 2 O), because [( I 0 / I ∞ ) − 1] is equal to 1/[ T IS (H 2 O)/ T 1 (H 2 O)]. These results lead us to the conclusion that [( I 0 / I ∞ ) − 1] might be applicable to cross‐relaxation rate (CR)‐like imaging, i.e. equivalent CRI. (B) W (%) (dry weight) profiles of [( I 0 / I ∞ ) − 1] and 1/ T IS (H 2 O), obtained by near‐resonance f 2 ‐irradiation, seem to indicate participation of molecular rigidity and an amount of bound water. However, those values, monitored with off‐resonance f 2 ‐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.