Fully Flow Compensated Multi-Echo Gradient Recalled Echo Sequence

Imaging the vasculature of the human brain is important in diagnosing many diseases.The two dominant non-contrast enhanced methods in use today include Time-Of-Flight(TOF)magnetic resonance angiography(MRA)for visualizing arteries through the in-flow enhancement effect,and Susceptibility Weighted Imaging(SWI)for MR venography(MRV)by utilizing the susceptibility difference between paramagnetic deoxyhemoglobin and normal parenchyma.Today,these two scans are run separately using different imaging sequences hence requiring extra time and having potential misregistration between the two vasculature networks.To overcome the above problems,we propose to combine TOF with SWI into a single-scan to image arteries and veins simultaneously.The key issue involved is how to design the imaging gradients to meet the flow compensation requirement for multiple echoes.We develop a new fully flow-compensated multi-echo(ME)gradient echo sequence,in which each echo is flow compensated independently,and the data acquired from short TE is used for imaging MRA and the data from long TE is used for MRV.The experimental results show that this new sequence(ME-GRE)can provide:1)full flow compensation for each echo independently hence making it possible to collect MRA and MRV simultaneously without flow artifacts(making the sequence highly efficient);2)ME-SWI to help differentiate thrombus from vein and also for tissues within a wide range of susceptibility values because of the use of short and long echo times;3)good image quality for quantitative susceptibility mapping(QSM)processing;4)reasonable T2*estimation free of flow artifacts;5)arterial information in the right location to allow vessel wall imaging;6)avoiding regions of false enhancement from arteries that are not fully flow compensated because of air/tissue interface inhomogeneities in Multi-Echo SWI and QSM reconstructions to suppress false enhancement and streaking artifacts;and 7)background field gradient and flow acceleration estimates.This new sequence offers the ability to better image diseases such as stroke and traumatic brain injury where vascular damage is often prevalent.