Physicochemical Stability and Crystallization Tendency of the ACR MRI Phantom Solution

Abstract

         The American College of Radiology (ACR) MRI Phantom is an essential standard device for the calibration and quality control of Magnetic Resonance Imaging (MRI) systems, and its performance depends significantly on the stability of the internal solution. This study aimed to evaluate the stability of the Nickel (II) chloride (NiCl₂) and Sodium chloride (NaCl) solution after one year of use by examining its physicochemical properties, including pH, temperature, UV-Visible spectroscopy, and crystallization behavior using X-ray Diffraction (XRD). The results showed that the solution had an average pH of 5.29±0.02 and an average temperature of 24.0±0.12°C. UV-Visible spectroscopic analysis revealed an average absorbance of 0.027 at λmax 394 nm, indicating that the dissolved Ni²⁺ ion concentration remained chemically stable near the expected 10 mM level. XRD analysis of the crystallized residues identified mixed crystals consisting of NaCl, NiCl₂·6H₂O, and NiCl₂·4H₂O, suggesting that solution evaporation induced physical changes in both NiCl₂ and NaCl. In conclusion, although the dissolved Ni²⁺ ions retained chemical stability, the structural transformation observed after evaporation and crystallization indicates sensitivity to environmental conditions. Improper storage may affect the long-term homogeneity and stability of the ACR MRI Phantom solution, potentially leading to inaccuracies in MRI quality assessment. Therefore, the findings of this study provide important insights for establishing quality control guidelines and support future development of in-house standard solutions to reduce costs and enhance the sustainability of MRI quality control in Thailand.