Research On Techniques Of MR Myelin Water Imaging

MR myelin water imaging(MWI)provides mapping of the myelin content in the white matter,which depicts the integrity or damage of white matter(WM)fibers quanti-tatively,thus is significant for clinical diagnosis and prognosis of demyelinated diseases.The research in this thesis focuses on two technical topics related with MWI that are cru-cial for its potential clinical applications:(1)improving the stability for multi-echo GRE based MWI in high spatial resolution,and(2)enhancing scan efficiency(reducing scan time)for MWI.We proposed a MWI method by using tissue susceptibility induced phase with no additional QSM data acquisition to improve the stability for high resolution multiecho GRE based MWI.Comparing with the direct complex fitting method in low spatial reso-lution,the proposed method showed refined details for WM/GM boundaries and reduced partial volume effects in 4 x higher resolution with sufficient stability.Additionally,we proposed a calibrationless parallel imaging method dubbed "grouped Joint Non-linear Inversion(gJNLINV)",reconstructing the 4× undersampled k-space dataset of multi-echo GRE based MWI.The quality of the accelerated MWI is closed to the fully sampled gold standard.gJNLINV also dramatically accelerated the reconstruction speed,and sig-nificantly alleviated the problem of discontinuities in the estimated coil sensitivity maps.We proposed wave-CAIPI ViSTa,a novel method for highly accelerated direct myelin water imaging,covering the whole brain within a 15-minute scan.A very in-tuitive ZP(Zero Padding)method incorporating wave-CAIPI reconstruction was also proposed and proven to be effective in reducing the artifacts and blurring generated by residual wave PSF,especially for its significant improvements in wave-CAIPI ViSTa.