Reduction Of Scan Time And Echo Time In 3D Time-of-flight(TOF) MR Angiography,using Reverse Elliptical Centric Dual-echo Acquisition

Recently,with the development of the magnetic resonance imaging in scientific research and clinical application,more and more novel methods were proposed to solve the problems like the long scan time and low SNR of images existing in the conventional methods.And the work of this paper is to propose an improved sequence based on the conventional single-echo three dimension(3D)time-of-flight(TOF)magnetic resonance angiography(MRA)sequence.In the conventional single-echo three dimension(3D)time-of-flight(TOF)magnetic resonance angiography(MRA),it always takes long scan time to obtain the good images.In addition,high-resolution MRA with flow compensation requires long echo time(TE).Here,a reverse elliptical centric dual-echo 3D TOF MRA pulse sequence was developed to reduce the scan time and minimize the effective TE.Dual-echo and reverse elliptical centric acquisition in the phase encoding and slice phase encoding direction were used to reduce the scan time by 61%.Furthermore,the effective echo time(TE)was also minimized from 4.8ms to 4.1ms.In order to evaluate the advantages and disadvantages of this met hod more accurately,three different sequences were used to acquire the data in vivo.The main work include:(1)The design of the conventional dual-echo three dimension(3D)time-of-flight(TOF)magnetic resonance angiography(MRA)sequenceThe conventional single-echo three dimension(3D)time-of-flight(TOF)magnetic resonance angiography(MRA)sequence has been realized on the UIH-1.5T platform,using asymmetric RF,minimum gradient,and partial echo acquisition.So based on it,the design of the conventional dual-echo three dimension(3D)time-of-flight(TOF)magnetic resonance angiography(MRA)sequence was developed to acquire the second echo in one repetition time(TR).(2)The design of the reverse elliptical centric dual-echo 3D TOF MRA pulse sequenceBased on the conventional single-echo three dimension(3D)time-of-flight(TOF)magnetic resonance angiography(MRA)sequence,the reverse elliptical centric dual-echo 3D TOF MRA pulse sequence was developed by redesigning the trajectory of k-space.(3)Comparison of three sequencesTo compare the three sequences,visual observation of the final MRA and the quantitative measurement of the CNR were made.The results show that the CNR only decrea se by 2.5% with the scan time reduced to 39% when compared with the conventional single-echo 3D TOF.Compared with the conventional dual-echo 3D TOF acquisition,the developed pulse sequence brings advantages in three aspects:(1)reduce scan time by 22%;(2)increase CNR by 10.9%;(3)reduce the artifacts induced by dual-echo effects.In addition,while keeping the similar scan time as the conventional single-echo 3D TOF acquisition,the results shows that reverse elliptical centric dual-echo 3D TOF acquisition increase CNR by 54.3%.