Saturation transfer ratio in magnetic resonance imaging. A novel physical parameter for evaluation of the hydrophilicity of synthetic copolymer gels

It was first found that there is good correlation between saturation transf er ratio (STR) values in magnetic resonance imaging (MRI) measurement and t he hydrophilicity of various synthetic copolymer gels containing 2-hydroxye thyl methacrylate (HEMA), glycidryl methacrylate (GMA), N-vinyl-2-pyrrolidi none (N-VP), and/or methyl methacrylate (MMA). The hydrophilicity of these copolymer gels was characterized by water contents evaluated by differentia l scanning calorimeter (DSC) and also the solubility parameter in theoretic al sense. The MRI measurement was performed by conventional held-echo imagi ng as well as under the irradiation of an off-resonance saturation pulse ap art by 75, 19, and 4 ppm from a resonance point of water. The STR values of fset at the 75-ppm correlated well with the total water contents in the sam ples. The values offset at the 19-ppm divided the samples into two classes corresponding to hydrophilic and hydrophobic gels. In the case of 4-ppm off set, the hydrophilic gels showed significantly higher STR values than the h ydrophobic ones and the values among the hydrophilic gels were reflective t o the constrained water content in the gel. Moreover the values correlated linearly with the solubility parameter of the samples. Thus the STR values in measurement of MRI could be adopted as a new useful parameter for molecu lar or material characterization of synthetic copolymers without any invasi ve processes.