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Purpose: Investigation of the feasibility of the R2* mapping techniques byusing latest theoretical models corrected for confounding factors and optimizedfor signal to noise ratio. Theory and Methods: The improvement of theperformance of state of the art MRI relaxometry algorithms is challengingbecause of a non-negligible bias and still unresolved numerical instabilities.Here, R2* mapping reconstructions, including complex-fitting withmulti-spectral fat-correction by using single-decay (1D) and double-decay (2D)formulation, are studied in order to identify optimal configuration parametersand minimize numerical artifacts. The effects of echo number, echo spacing, andfat/water relaxation model are evaluated through simulated and in-vivo data. Wealso explore the stability of such models by analyzing the impact of highpercentage of fat infiltrations and local transverse relaxation differencesamong biological species. Results: The main limits of the MRI relaxometry arethe presence of bias and the occurrence of artifacts which affect its accuracy.Chemical-shift complex reconstructions R2*-corrected with 1D formulationexhibit a large bias in presence of a significant difference in the relaxationrates of fat and water and with fat concentration larger than 30%. We find thatfor fat-dominated tissues or in patients affected by iron overload, MRIreconstructions accounting for multi-exponential relaxation time provideaccurate R2* measurements and are less prone to numerical artifacts.Conclusions: Complex fitting 2D formulation outperforms the conventional 1Dapproximation in various diagnostic scenarios. Although it still lacks ofnumerical stability which requires model enhancement and support fromspectroscopy, it offers promising perspectives for the development ofrelaxometry as a reliable tool to improve tissue characterization andmonitoring of neuromuscular disorders.

On the R2* Relaxometry in Complex Multi-Peak Multi-Echo Chemical Shift-Based Water-Fat Quantification: Applications to the Neuromuscular Diseases