Aqueous paramagnetic solutions for MRI phantoms at 3 T:A detailed study on relaxivities

Phantoms with known T₁ and T₂ values that are prepared using solutions of easily accessible paramagnetic agents are commonly used in MRI imaging centers, especially with the goal of validating the accuracy of quantitative imaging protocols. The relaxivity parameters of several agents were comprehensively examined at lower B₀ field strengths, but studies at 3 T remain limited. The main goal of this study is to measure r₁ and r₂ relaxivities of three common paramagnetic agents (CuSO₄, MnCl₂, and NiCl₂) at room temperature at 3 T. Separate phantoms were prepared at various concentrations of 0. 05-0. 5 mM for MnCl₂ and 1-6 mM for CuSO₄ and NiCl₂. For assessment of T₁ relaxation times, inversion recovery turbo spin echo images were acquired at 15 inversion times ranging between 24 and 2500 ms. For assessment of T₂ relaxation times, spin-echo images were acquired at 15 echo times ranging between 8. 5 and 255 ms. Voxel-wise T₁ and T₂ relaxation times at each concentration were separately determined from the respective signal recovery curves (inversion recovery for T₁ and spin echo decay for T₂). Relaxivities r₁ and r₂ for all three agents that were derived from these relaxation time measurements are reported: r₁ = 0. 602 mM^-1 s^-1 and r₂ = 0. 730 mM^-1 s^-1 for CuSO₄, r₁ = 6. 397 mM^-1 s^-1 and r₂ = 108. 266 mM^-1 s^-1 for MnCl₂, r₁ = 0. 620 mM^-1 s^-1 and r₂ = 0. 848 mM^-1 s^-1 for NiCl₂. These results will serve as a practical reference to design phantoms of target T₁ and T₂ values at 3 T, in particular phantoms with relaxation times equivalent to specific human tissues.