Development of a tissue water fraction analysis method using quantitative parameter mapping for magnetic resonance imaging.

The myelin sheath is a multilayered structure that surrounds the axons of nerve cells. It acts as an insulator to ensure rapid and accurate transmission of electrical signals in the nervous system. Myelin water fraction (MWF) serves as a biomarker for the myelin sheath. Several methods for determining the MWF have been proposed; however, the inconsistency of MWF values is a challenge. In this study, we attempted to derive the MWF using quantitative parameter mapping (QPM). QPM ensures reproducibility by maintaining consistent imaging conditions across different scanners, enabling stable acquisition of quantitative parameters. This is expected to improve the reliability of the MWF measurements. Additionally, a significant correlation between QPM-derived parameters and the MWF has been reported. Five healthy volunteers were included in this study. QPM-MRI was performed using a 3-Tesla MR scanner with a three-dimensional radio frequency-spoiled steady-state gradient-echo (3D-RSSG) method. Using the derived quantitative values, pseudo-intensity images were generated for arbitrary continuous echo time values. Subsequently, a model equation for the brain tissue was defined. The generated signals were fitted with triexponential curve to estimate the amplitudes of each tissue component. Finally, the MWF was calculated using the amplitude ratio of each tissue. The mean MWF values for white matter and gray matter were 8.20 ± 4.97% and 7.99 ± 3.45%, respectively. This method using QPM allows for 3D data collection within a scan time applicable to standard clinical examinations and provides high accuracy in relaxation time estimation, thereby enabling stable quantification of MWF and suggesting its potential for clinical implementation.