Cross-linked polydimethylsiloxane colloid as novel contrast agent for gastrointestinal magnetic resonance imaging: Transient nuclear Overhauser effect within the interface

Abstract

With good contrast in T₁ and T₂ weighted imaging as well as low toxicity in 3- (4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, this work proposes the cross-linked polydimethylsiloxane colloids as a novel non-ionic contrast agent for gastrointestinal magnetic resonance imaging. The experiments of nuclear magnetic resonance spectra and relaxation show that within the interface of the colloids, there are nuclear Overhauser effect and transient nuclear Overhauser effect (cross-relaxation). Regarding the longitudinal relaxation experiments of CH₂CH₂O segments of Tween 80, a two spins system is found and modeled well by the equation $I_Z-I_0=S_0\left(\left(1-X\right)e^{\frac{-t}{D_1}}-\left(1+X\right)e^{\frac{-t}{T_1}}\right)$ which is deduced based on the transient nuclear Overhauser effect proposed by Solomon. The arbitrary constant X is additionally added with the initial conditions (I_z − I₀) _{t =0} = −2XS₀ and (S_z − S₀) _{t =0} = −2S₀. For the two spins system, D₁ and T₁ are corresponding to longitudinal relaxation times of the bound water and the CH₂CH₂O respectively. Concerning the transverse relaxation experiments of the CH₂CH₂O, they agree with the equation with three exponential decays, defined by three relaxation times, likely corresponding to three mechanisms. These mechanisms possibly are intramolecular and intermolecular dipole–dipole (DD) interactions and scalar coupling. Within the interface, hydrogen bonding causes the positive nuclear Overhauser effect of the CH₂CH₂O’s nuclear magnetic resonance spectra, the transient nuclear Overhauser effect of the CH₂CH₂O’s longitudinal relaxation experiments and the intermolecular dipole–dipole interactions of the CH₂CH₂O’s transverse relaxation experiments.