Analysis of proton-density bias corrections based on T₁ measurement for robust quantification of water content in the brain at 3 Tesla

Purpose: Estimating tissue water content using high field MRI, such as 3 Tesla (T), is challenging due to the difficulty in dissociating the radio frequency inhomogeneity pattern from the signal arising from tissue intrinsic proton density (PD) variations. To overcome this problem the longitudinal relaxation time T₁ can be combined with an initial guess of the PD to yield the desired PD bias correction. However, it is necessary to know whether T₁ effects, i.e., any effect contributing to T₁ while being independent of tissue hydration, influence the estimated correction.

Methods: Twenty-five healthy subjects underwent a quantitative 3T MRI protocol enabling acquisition of 64 slices with 1 mm in-plane resolution and 2 mm slice thickness in 14 min. Influence of T₁effects on the estimated water content map is evaluated using a dedicated method including T₁ and T₂ ^∗ information and region of interest-based water content values are compared with the literature.

Results: Our analysis indicates that the PD bias correction based on T₁ is largely insensitive to T₁ effects. Besides, water content results are in good agreement with literature values obtained at 1.5T.

Conclusion: This study demonstrates the applicability of a PD bias correction based on T₁ to yield tissue water content at 3T.