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

Abstract

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 T1 effects 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.

Keywords: cerebral oedema; parametric mapping; proton density; quantitative imaging; water content.