变延迟进动定制激发(DANTE)序列在工程中的优化设计
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摘要
变延迟进动定制激发(Delays Alternating with Nutation for Tailored Excitation,DANTE)序列作为一种黑血预脉冲序列,通过连续施加小角度激发脉冲,以及结合散相梯度,使得流动物质和静态物质达到不同的稳态,从而抑制流动的血液.对于静态物质而言,施加DANTE序列后在图像等间隔的位置会出现暗条纹,暗条纹的宽度与梯度幅值和小单元持续时间乘积相关:乘积越大,暗纹宽度越小.对于动态物质而言,为达到较好的抑制效果,需要增加整个DANTE序列模块的准备时间,并且增大梯度幅值和小单元持续时间的乘积.因此,该方法对于梯度系统的要求较高,而实际梯度放大器(Gradient Amplifier,GPA)有一定的限额.在有限的GPA条件下,为使得DANTE序列具有更好抑制流动信号效果,本文在读出方向以及片层旋转两个方面进行了梯度优化,实现了更好的黑血效果.
Delays alternating with nutation for tailored excitation(DANTE) is often used as the preparation sequence in black blood imaging. After applying trains of small angle DANTE excitation pulse along with a gradient, the protons in blood flow and static tissues reach different steady states and thus have differente signal intensity. The static tissues shows dark strips, whose width is related to the product of the gradient amplitude and the duration of the DANTE sequence block.The larger the product is, the narrower the stripes are. A better suppression of flowing spins also require larger gradient amplitude ? DANTE sequence block duration product and longer preparation time of the entire DANTE sequence module.As such, a high-performance gradient system is often required for this method. However, gradient amplifier(GPA) has limitations in reality. To solve this problem, we proposed here an optimized gradient for DANTE sequence in both the readout direction and slice rotation. The results demonstrated that a better black blood effect could be obtained by using the optimized method.
Delays alternating with nutation for tailored excitation(DANTE) is often used as the preparation sequence in black blood imaging. After applying trains of small angle DANTE excitation pulse along with a gradient, the protons in blood flow and static tissues reach different steady states and thus have differente signal intensity. The static tissues shows dark strips, whose width is related to the product of the gradient amplitude and the duration of the DANTE sequence block.The larger the product is, the narrower the stripes are. A better suppression of flowing spins also require larger gradient amplitude ? DANTE sequence block duration product and longer preparation time of the entire DANTE sequence module.As such, a high-performance gradient system is often required for this method. However, gradient amplifier(GPA) has limitations in reality. To solve this problem, we proposed here an optimized gradient for DANTE sequence in both the readout direction and slice rotation. The results demonstrated that a better black blood effect could be obtained by using the optimized method.
引文
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[9]ZUR Y,WOOD M L,NEURINGER L J.Spoiling of transverse magnetization in steady-state sequences[J].Magn Reson Med,1991,21(2):251-263
[10]CARR H Y.Steady-state free precession in nuclear magnetic resonance[J].Phys Rev,1958,112(5):1693-1701.
[11]STOREY P,ATANASOVA I P,LIM R P,et al.Tailoring the flow sensitivity of fast spin-echo sequences for noncontrast peripheral MRangiography[J].Magn Reson Med,2010,64(4):1098-1108.
[12]BUSSE R F.Flow sensitivity of CPMG sequences with variable flip refocusing and implications for CSF signal uniformity in 3D-FSEimaging[C].Proceedings of the 14th Annual Meeting of ISMRM.2006:2430.
[2]KOKTZOGLOU I,LI D.Diffusion-prepared segmented steady-state free precession:application to 3D black-blood cardiovascular magnetic resonance of the thoracic aorta and carotid artery walls[J].J Cardiovasc Magn Reson,2007,9(1):33-42.
[3]WANG J N,YARNYKH V L,HATSUKAMI T,et al.Improved suppression of plaque-mimicking artifacts in black-blood carotid atherosclerosis imaging using a multislice motion-sensitized driven-equilibrium(MSDE)turbo spin-echo(TSE)sequence[J].Magn Reson Med,2007,58(5):973-981.
[4]LI L Q,MILLER K L,JEZZARD P.DANTE-prepared pulse trains:a novel approach to motion-sensitized and motion-suppressed quantitative magnetic resonance imaging[J].Magn Reson Med,2012,68(5):1423-1438.
[5]LI L,ZHOU Y C,YUAN C,et al.Imaging lenticulostriate arteries at 3 tesla using optimized flow-sensitive black-blood technique[J].Chinese JMagn Reson,2016,33(4):528-538.李律,周赜辰,苑纯,等.基于优化后流动敏感黑血序列的豆纹动脉3 T磁共振成像[J].波谱学杂志,2016,33(4):528-538.
[6]LI L Q,MILLER K L,JEZZARD P.DANTE-prepared pulse trains:a novel approach to motion-sensitized and motion-suppressed quantitative magnetic resonance imaging[J].Magn Reson Med,2012,68(5):1423-1438.
[7]WANG J N,HELLE M,ZHOU Z C,et al.Joint blood and cerebrospinal fluid suppression for intracranial vessel wall MRI[J].Magn Reson Med,2016,75(2):831-838.
[8]LI L Q,KONG Y Z,ZAITSU Y,et al.Structural imaging of the cervical spinal cord with suppressed CSF signal using DANTE pulse trains[J].Magn Reson Med,2015,74(4):971-977.
[9]ZUR Y,WOOD M L,NEURINGER L J.Spoiling of transverse magnetization in steady-state sequences[J].Magn Reson Med,1991,21(2):251-263
[10]CARR H Y.Steady-state free precession in nuclear magnetic resonance[J].Phys Rev,1958,112(5):1693-1701.
[11]STOREY P,ATANASOVA I P,LIM R P,et al.Tailoring the flow sensitivity of fast spin-echo sequences for noncontrast peripheral MRangiography[J].Magn Reson Med,2010,64(4):1098-1108.
[12]BUSSE R F.Flow sensitivity of CPMG sequences with variable flip refocusing and implications for CSF signal uniformity in 3D-FSEimaging[C].Proceedings of the 14th Annual Meeting of ISMRM.2006:2430.