Magnetization transfer explains most of the <i>T</i> ₁ variability in the MRI literature

Abstract

Abstract Purpose To identify the predominant source of the variability described in the literature, which ranges from 0.6–1.1 s for brain white matter at 3 T. Methods 25 ‐mapping methods from the literature were simulated with a mono‐exponential and various magnetization‐transfer (MT) models, each followed by mono‐exponential fitting. A single set of model parameters was assumed for the simulation of all methods, and these parameters were estimated by fitting the simulation‐based to the corresponding literature values of white matter at 3 T. We acquired in vivo data with a quantitative magnetization transfer and three ‐mapping techniques. The former was used to synthesize MR images that correspond to the three ‐mapping methods. A mono‐exponential model was fitted to the experimental and corresponding synthesized MR images. Results Mono‐exponential simulations suggest good inter‐method reproducibility and fail to explain the highly variable estimates in the literature. In contrast, MT simulations suggest that a mono‐exponential fit results in a variable and explain up to 62% of the literature's variability. In our own in vivo experiments, MT explains 70% of the observed variability. Conclusion The results suggest that a mono‐exponential model does not adequately describe longitudinal relaxation in biological tissue. Therefore, in biological tissue should be considered only a semi‐quantitative metric that is inherently contingent upon the imaging methodology, and comparisons between different ‐mapping methods and the use of simplistic spin systems—such as doped‐water phantoms—for validation should be viewed with caution.

Topics & Concepts