Relaxivity comparison of Gadoteric acid and Gadopiclenol using clinical and reference MRI sequences at 1.5 T.

INTRODUCTION: Gadolinium-based contrast agents (GBCAs) exhibit variable relaxivity, and accurate relaxivity assessment is essential both for technical characterization and for optimizing clinical protocols. While reference relaxometry sequences are considered the gold standard for T1 and T2 quantification, clinical T1/T2 mapping techniques are used in routine MRI despite known limitations. This study aimed to compare relaxivity measurements obtained with reference relaxometry and clinically available T1/T2 mapping sequences at 1.5 T, using Gadoteric acid and Gadopiclenol as test agents. METHODS: A phantom containing multiple dilutions of Gadoteric acid (0.1-3.0 mM) and Gadopiclenol (0.05-1.5 mM) was scanned on a routine 1.5 T MRI system. T1 relaxivity was assessed with spin-echo, inversion recovery, and clinical mapping techniques, while T2 relaxivity was measured with multi-echo spin echo and clinical mapping protocols. Relaxivity constants were derived from linear fitting. Water and oil vials were included as reference samples to verify signal stability and fitting consistency. RESULTS: Clinical mapping sequences yielded relaxivity values broadly consistent with reference methods, although their performance varied depending on the T1/T2 range. MP2RAGE showed non-physiological behavior at high gadolinium concentrations (very short T1 values), MOLLI exhibited reduced precision for the shortest T1 values, and the cardiac T2 mapping sequence had to be excluded due to inconsistent measurements in vials with very short T2 values. As expected, Gadopiclenol demonstrated higher r₁ and r₂ relaxivity than Gadoteric acid across all techniques. CONCLUSION: Clinical T1/T2 mapping sequences can provide reliable relaxivity estimates over most of the relevant range but show predictable limitations at extreme relaxation times. Reference relaxometry remains the most accurate approach. Using two contrast agents with different relaxivity profiles allowed a robust comparison of the strengths and limitations of clinical versus reference relaxometry techniques. Gadopiclenol exhibited higher relaxivity than Gadoteric acid under phantom conditions, consistent with its potential for dose-efficient protocols, although any clinical dose reduction requires dedicated in vivo validation.