Relaxometry to get the right values, or getting the right data for the patient: a false dilemma

Motivation: Quantitative MRI claims to give reproducible values, but different systems, techniques and settings influence the results. Goal(s): To find how the accuracies of different relaxometry sequences compare to each other, and determine the implications for the future of quantitative MRI. Approach: T1 and T2 were determined in a NIST-calibrated phantom using the variable TE, variable TI, multi-delay multi-echo, 3D-QALAS, MR fingerprinting, and MP2RAGE techniques. Results: Variable TI and MP2RAGE perform very similar, and estimate T1 within 6%. MRF estimates T1 and T2 within 10%, while MDME and 3D-QALAS have lower accuracy and precision. However, MDME and 3D-QALAS see more use in the clinic. Impact: Currently no simultaneous T1-T2-relaxometry technique exists which is both accurate in phantoms and integrated in the clinic. Clinical usefulness, advanced physical system models, and high-quality phantoms should all be integrated into the development of quantitative relaxometry techniques to achieve this.