Equivalent cross-relaxation rate in magnetic resonance imaging. A novel physical parameter for evaluation of conditions of water in synthetic copolymer gels

Being similar to values of saturation transfer ratio (STR) in magnetic reso nance imaging (MRI) described in our previous paper, values of equivalent c ross-relaxation rate (ECR) correlated well with conditions of water in vari ous copolymer gels composed of any two or three monomers among a-hydroxyeth yl methacrylate (HEMA), glycidyl methacrylate (GMA), N-vinyl-2-pyrrolidinon e (N-VP), methyl methacrylate (MMA), and benzyl methacrylate (BMA). The wat er conditions in these copolymer gels were characterized in terms of not on ly total also free and constrained water contents in the matrix. The MRI me asurement was performed by using an off-resonance saturation pulse under co nventional field-echo imaging at frequency apart within +/- 75 ppm from the water resonance frequency. The ECR values were readily to determine and no n-time consuming parameter for cross relaxation rate. Both the STR and ECR values at the frequency offset by 4-ppm were divided the sample gels two cl asses, which must correspond to hydrophilic or hydrophobic ones. In the cas e of 4-ppm offset. the ECR values were more sensitive parameters than the S TR values for evaluation of water condition in the gels and the sensitivity was nearly equivalent to cross-relaxation rate itself. Moreover the ECR va lues showed excellent correlation with the HEMA as well as constrained wate r contents in the series of copolymers. Thus the ECR values in the MRI meas urement would be adopted as a novel parameter helpful for molecular/materia l characterization of synthetic copolymers without invasive process to the samples.