变延迟进动定制激发(DANTE)序列在工程中的优化设计

Optimization of Delays Alternating with Nutation for Tailored Excitation(DANTE) Sequence in Engineering

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 inblack blood imaging. After applying trains of small angle DANTE excitation pulse along with a gradient, the protons inblood flow and static tissues reach different steady states and thus have differente signal intensity. The static tissues showsdark 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 gradientamplitude？ 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） haslimitations in reality. To solve this problem, we proposed here an optimized gradient for DANTE sequence in both thereadout direction and slice rotation. The results demonstrated that a better black blood effect could be obtained by using theoptimized method.