Magnetization transfer explains most variablity of T1-estimates in the MRI literature

Motivation: T1-estimates vary substantially throughout the literature. Goal(s): To provide evidence that magnetization transfer (MT) explains most of this variability. Approach: We simulated 16 literature T1-mapping approaches with an MT model and fitted a T1-value to each simulated dataset. We then modified a global set of MT parameters to best explain the T1-variability. Results: We found that MT explains 71% of the literature's T1-variability. The largest reduction and minimal Bayesian and Akaike information criteria were achieved when incorporating two recent advances in MT modeling: describing the semi-solid pool's spin dynamics with the generalized Bloch model and removing commonly-used constraints on the semi-solid pool's T1. Impact: Our results suggest that T1 should be considered a semi-quantitative metric in biological tissue, meaning comparisons between different T1-mapping methods and validations in doped-water phantoms are of limited value.