Research On Gradient Echo Based Standardized Fast Quantitative MRI Techniques In Brain Imaging

Gradient recalled echo(GRE)is one of important magnetic resonance imaging(MRI)sequences which has been widely used in clinical MRI.Especially for brain imaging studies in stroke and neurodegenerative disease,people usually use GRE based sequences to provide whole brain T1 weighted imaging(T1W),spin density weighted imaging(PDW),MR angiography(MRA),susceptibility weighted imaging(SWI).It also can be used to provide brain tissue property and cerebral vasculature system quantifications such as T1 mapping(T1MAP),spin density mapping(PDMAP)and quantitative susceptibility mapping(QSM).However,in clinical usage,these various qualitative images and quantitative data usually are acquired separately which leads a very long scanning time and inefficient use of the scanner.In addition,long scanning time introduces more motion artifacts and less tolerance by patients,especially in acute stroke and Parkinson’s diseases.Furthermore,a T1W image with better grey matter(GM)and white matter(WM)contrast is essential for all these studies.However,the T1W from a conventional GRE scan has limited GM to WM contrast due to the intrinsic T1 value of them.On the other hand,Time-of-flight MRA(TOF-MRA),which depends on the transmit slab thickness,repetition time and blood flow velocity,usually cannot provide sufficient depiction of small arteries.Therefore,contrast enhanced MRA(CE-MRA)is usually used for depicting small arteries,which has known limitations and disadvantages.To solve these problems,this thesis introduces a strategically acquired gradient echo(STAGE)imaging technique.With a few fully flow compensated multi-echo GRE acquisitions,STAGE provides whole brain qualitative images and quantitative data including T1WE,T1W,PDW,T1MAP,PDMAP,SWI,tSWI,QSM,R2*MAP,MRAV and MRA.STAGE has following creative conceptions:1)STAGE takes much less scanning time than conventional technique to provide all these information;2)STAGE has unique algorithm to correct RF transmit(Bit)and RF receiver(B ir)filed variations.It provides homogeneous T1W,PDW images and T1MAP,PDMAP data;3)STAGE introduces a homogenous T1W with enhanced GM to WM contrast(T1WE);4)STAGE uses multi-echo phase images to improve the SNR of QSM;5)One scan generates naturally co-registered MRA,SWI and QSM;6)The interleaved MRA(iMRA)which uses flow compensated echoes and a flow dephased echo to provide an MRA image with better visualization for small arteries and with a clear background;7)STAGE introduces a rapid and robust multi-echo phase unwrapping method for QSM reconstruction which has more than ten folds acceleration than conventional phase unwrapping method.STAGE related research tasks,MR pulse sequence developments,image processing software development have been completed.Through University-Industry Cooperation,it has been converted to a product by a famous medical company integrated into their MR products.