Irradiation-induced modulation of T2 relaxation times in sucrose solutions: a novel externally controlled design strategy for quantitative magnetic resonance imaging phantoms.

This study investigated whether irradiation-induced chemical changes in sucrose solutions could be utilized to control magnetic resonance imaging (MRI) relaxation properties and to propose a novel design strategy for quantitative MRI phantoms. Aqueous sucrose solutions at concentrations of 5-40% (w/w) containing 3.6 g/L NaCl were irradiated with 6 MV photons at doses of 0-20,000 monitor units. T1 and T2 relaxation times were measured at 1.5 T. Hydrogen peroxide (H₂O₂) and glucose concentrations were quantified to assess the radiolytic products. Linear regression and Type III ANOVA were used to evaluate the effects of sucrose concentration and irradiation dose. The T2 relaxation times increased with increasing irradiation dose (p < 0.001), with a significant interaction between sucrose concentration and dose (p < 0.001). The slope of T2 monotonically decreased with increasing sucrose concentration. R2 (defined as 1/T2) showed a significant linear dose-dependence at all concentrations, with the absolute magnitude of the negative regression coefficients increasing at higher sucrose concentrations, which was consistent with the reciprocal relationship between T2 and R2. In contrast, both T1 and R1 (defined as 1/T1) exhibited minimal dose-dependence. The H₂O₂ concentration increased stepwise with the dose and demonstrated a strong positive correlation with T2 (Spearman's ρ = 1.00), whereas glucose showed no consistent dose-dependence. Irradiation enabled concentration-dependent modulation of T2 relaxation in sucrose solutions without altering the initial composition. This externally controllable approach provides a simple and flexible framework for designing quantitative MRI phantoms with tunable relaxation properties and offers a new paradigm beyond conventional composition-based phantom fabrication.